Anion Photoelectron Spectroscopy

byDjango H. Andrews

B.A., University of Oregon, 1999

A thesis submitted to the
Faculty of the Graduate School of the
University of Colorado in partial fulfillmentof the requirements for the degree ofDoctor of Philosophy
Physical Chemistry
2006

ii

This thesis entitled:Anion Photoelectron Spectroscopy
Written by Django H. Andrews
has been approved for the Physical Chemistry program by___________________________
W. Carl Lineberger___________________________
Veronica M. Bierbaum

Date: ______________

The final copy of this thesis has been examined by both the signatories, and we find that boththe content and the form meet acceptable presentation standards of scholarly work in theabove mentioned discipline.

iii
Andrews, Django H. (Ph.D. Physical Chemistry)
Anion Photoelectron Spectroscopy
Thesis directed by Professor W. Carl Lineberger

This thesis presents the results of anion photoelectron spectroscopy experiments
conducted on three classes of anions. One class is that of heteronuclear coinage metal
diatomic molecules. These include AgO−, AuO−, AuS−, CuH−, and CuD−. The photoelectron
spectra of these molecules are characterized by short vibrational progressions in transitions to
the ground electronic states and confident assignments of the electronic state origins andelectron affinities. The photoelectron spectra of these molecules measured for the first timethe electron affinities of the corresponding neutral molecules. Frank-Condon simulation of
the observed ground state vibrational structure coupled with observation of a wellcharacterized excited state allowed for the assignment of the anion equilibrium bond lengths
for AgO−, CuH−, and CuD−. Because no excited electronic states were observed in thephotoelectron spectra of AuO− and AuS−, only the magnitude of the bond length change
between the anion and the neutral molecules was assigned. Observation of hot-bands in thephotoelectron spectra allowed for the first assignment of anion harmonic vibrationalfrequencies for AgO− and AuS−. In addition, a predicted, yet previously unobserved, 3Σ+
excited electronic state of CuD and CuH was observed in the photoelectron spectra of CuD−
and CuH−.
The second class of molecules studied was that of copper anion complexes. These
included Cu− CD3OD, CuCD3O−, CuH2−, and CuD2−. The photoelectron spectra of thesecomplexes are characterized by extended vibrational progressions in the transitions to nearly
all observed electronic states. These extended vibrational progressions are the product oflarge geometry changes between the anion and neutral complexes. The geometry change

iv
between the anion and neutral of CuH2 and CuD2 is also very severe, as the anions are linear
and the neutrals are bent. The spectra are dominated by a short vibrational progression in thesymmetric stretch mode which allows determination of the electron affinities of CuH2 andCuD2.
The photoelectron spectra of two related organic compounds were also taken.
Photoelectron spectra of the 1,2,3-triazolide anion were recorded and show signatures ofstrong vibronic coupling of the low lying electronic states of the neutral. Still, the vibrational
origin of transitions to the ground electronic state of the neutral allowed for easy assignmentof the neutral electron affinity. Combination of the measured electron affinity with the gas
phase acidity measured elsewhere allowed for determination of the N-H bond dissociationenergy of the parent molecule 1H-1,2,3-triazolide. In addition, the heat of formation of the
1,2,3-trizolyl radical was also determined. It was also found that, under the experimental
source conditions used in these experiments, about 40% of the 1,2,3-triazolide anions ring
open to form the E-iminodiazomethide anion, the structure of which was assigned on thebasis of a simulation of the measured photoelectron spectrum. The simulation also allowedassignment of several normal mode frequencies of the anion and neutral.

v
Contents

Introduction to Anion Photoelectron Spectroscopy..................................................................................1
1.1

Anion Photoelectron Spectroscopy Overview........................................................................1

1.2

Selection Rules.......................................................................................................................3

1.5

Thesis Overview.....................................................................................................................5

References for Chapter I ......................................................................................................................7
Chapter II. Hemispherical Analyzer and Velocity Map Imaging Methods.............................................8
2.1

Anion Photoelectron Spectrometers Overview ......................................................................8

2.2

Hemispherical Analyzer Photoelectron Spectrometer Overview ...........................................9

2.3

Hemispherical Analyzer Instrument Ion Sources .................................................................10

2.4

Hemispherical Analyzer Instrument Ion Beam Formation and Mass Selection...................13

2.5

Hemispherical Analyzer Instrument Photoelectron Detection .............................................16

2.6

Hemispherical Analyzer Instrument Laser System ..............................................................19

2.7

Hemispherical Analyzer Methodology and Data Analysis...................................................20

2.8

Velocity Map Imaging Photoelectron Spectrometer Overview............................................21

2.9

Velocity Map Imaging Instrument Ion Sources ...................................................................22

2.10

Velocity Map Imaging Instrument Ion Beam Formation and Mass Selection .....................24

2.11

Velocity Map Imaging Instrument Photoelectron Detection................................................26

2.12

Velocity Map Imaging Instrument Tunable Nanosecond Laser System ..............................33

2.13

Velocity Map Imaging Instrument Data Analysis ................................................................38

2.14

Theoretical Geometry and Frequency Calculations and Photoelectron Spectral Simulation
Methods................................................................................................................................41

References for Chapter II ...................................................................................................................45
Photoelectron Imaging Spectroscopy of 1,2,3-Triazolide ......................................................................48
3.1

Introduction ..........................................................................................................................48

3.2

Experimental Methods .........................................................................................................50

vi
3.3

Results ..................................................................................................................................50

3.4

Discussion ............................................................................................................................56

References for Chapter III..................................................................................................................59
Hemispherical Analyzer Photoelectron Spectroscopy of Iminodiazomethide .......................................62
4.1

Introduction ..........................................................................................................................62

4.2

Experimental Methods .........................................................................................................64

4.3

Results ..................................................................................................................................66

4.4

Discussion ............................................................................................................................72

References for Chapter IV..................................................................................................................75

Hemispherical Analyzer Photoelectron Spectroscopy of AgO−, AuO−, and AuS− .................................77
5.1

Introduction ..........................................................................................................................77

5.2

Experimental Methods .........................................................................................................78

5.3.1

AgO− Results........................................................................................................................78

5.3.2

AuO− Results........................................................................................................................82

5.3.3

AuS− Results.........................................................................................................................84

5.4

Discussion ............................................................................................................................86

References for Chapter V...................................................................................................................88
Photoelectron Velocity Map Imaging of CuH− and CuH2− ....................................................................92
6.1

Introduction ..........................................................................................................................92

6.2

Experimental Methods .........................................................................................................94

6.3

CuH− and CuD− Photoelectron Imaging Results ..................................................................97

6.4

CuH2− and CuD2− Photoelectron Imaging Results..............................................................108

6.5

Discussion ..........................................................................................................................117

References for Chapter VI................................................................................................................120
Photoelectron Velocity Map Imaging of CuCD3O− and CuCD3OD− ...................................................125

vii
7.1

Introduction ........................................................................................................................125

7.2

Experimental Methods .......................................................................................................130

7.3

Results ................................................................................................................................131

7.4

Discussion ..........................................................................................................................141

References for Chapter VII ..............................................................................................................144
Conclusions and Future Directions ......................................................................................................145
Bibliography...........................................................................................................................................92
Appendix A. Detector Chamber Vacuum Interlock System ...............................................................161
A.1

Detection region interlock flowchart..................................................................................163

viii
FiguresFigure 1.1 Schematic diagram depicting processes and energies present in photoelectron
spectra. ................................................................................................................... 2
Figure 1.2 Simulated diatomic photoelectron spectra showing the effect of bond lengthchange between the anion and neutral on the spectral profile ............................... 4
Figure 2.1 Hemispherical energy analyzer photoelectron spectrometer. .............................. 10
Figure 2.3 Microwave discharge ion source for the hemispherical energy analyzer
instrument. ........................................................................................................... 13
Figure 2.4 Hemispherical analyzer instrument ion optics, mass selection, and laserinteraction regions................................................................................................ 15
Figure 2.5 Hemispherical photoelectron kinetic energy analyzer. ........................................ 18
Figure 2.6 Hemispherical analyzer instrument ultraviolet continuous wave laser system.... 20
Figure 2.7 Photoelectron velocity map imaging spectrometer.............................................. 22
Figure 2.8 Potential field lines for the electron photodetachment region with typical imaging
voltages ................................................................................................................ 29
Figure 2.9 Photoelectron velocity map imaging instrument ion, laser, and detection timing
scheme. ................................................................................................................ 31
Figure 2.10 Atomic copper and fluoride anion photoelectron images showing effect of ion
velocity on image quality and resolution. ............................................................ 33
Figure 2.11 Infinity XPO energy per pulse as a function of wavelength measured at 250 mJ
IR pump. .............................................................................................................. 35
Figure 2.12 Doubled Infinity XPO energy per pulse as a function of wavelength measured at
200 mJ IR............................................................................................................. 36
Figure 2.13 Measured Infinity XPO linewidth as a function of wavelength........................... 37
Figure 2.14 CuH− 355 nm photoelectron velocity map imaging spectrum showing difference
in resolution using different spectral features to center the image....................... 40

ix
Figure 4.1 Structures of 1H-1,2,3-triazole, C4 deprotonated 1H-1,2,3-triazolide, and Eiminodiazomethide............................................................................................... 64
Figure 4.2 351.1 nm photoelectron spectrum of iminodiazomethide anion.......................... 68
Figure 4.3 320 nm photoelectron velocity map images of 1,2,3-triazolide and Eiminodiazomethide............................................................................................... 71
Figure 4.4 320 nm velocity map imaging photoelectron spectrum of 1,2,3-triazolide andiminodiazomethide............................................................................................... 72
Figure 4.5 Reaction energetics for production of E-iminodiazomethane from 1H-1,2,3triazole ................................................................................................................. 74
Figure 5.1 364 nm photoelectron spectra of AgO− with Franck-Condon simulation............ 81
Figure 5.2 363.8 nm photoelectron spectrum of AuO− ........................................................ 84
Figure 5.3 AuS− 363.8 nm photoelectron spectrum. ............................................................. 86
Figure 6.1 Atomic copper anion 355 nm photoelectron spectrum. ....................................... 94
Figure 6.2 Time-of-flight mass spectrum obtained with the dc sputter ion source and d4methanol. ............................................................................................................. 95
Figure 6.3 CuH− 355 nm full scale raw photoelectron image, reconstructed photoelectron
image, and photoelectron spectrum. .................................................................... 99
Figure 6.4 CuD− 355 nm full scale raw photoelectron image, reconstructed photoelectron
image, and photoelectron spectrum. .................................................................. 100
Figure 6.5 CuH− 600 nm raw photoelectron image, reconstructed photoelectron image, andphotoelectron spectrum...................................................................................... 102
Figure 6.6 CuH− 600 nm photoelectron spectrum with Franck-Condon spectral simulation ...
......................................................................................................................... 104
Figure 6.7 CuD− 600 nm raw photoelectron image, reconstructed photoelectron image, andphotoelectron spectrum...................................................................................... 106

xFigure 6.8 CuD− 600 nm photoelectron spectrum with Franck-Condon spectral simulation ...
......................................................................................................................... 107
Figure 6.9 CuH2− 355 nm full scale raw photoelectron image, reconstructed photoelectron
image, and photoelectron spectrum ................................................................... 109
Figure 6.10 CuH2− 355 nm 0 – 1 eV eKE raw photoelectron image, reconstructed
photoelectron image, and photoelectron spectrum ............................................ 111
Figure 6.11 CuH2− 355 nm 0 − 1 eV photoelectron spectrum showing low intensity structure..
..................................................................................................................... 112
Figure 6.12 CuD2− 355 nm full scale raw photoelectron image, reconstructed photoelectron
image, and photoelectron spectrum ................................................................... 114
Figure 6.13 CuD2− 355 nm expanded photoelectron raw image, reconstructed image, andphotoelectron spectrum...................................................................................... 116
Figure 6.14 CuD2− 355 nm 0 – 1 eV scale photoelectron spectrum showing low intensity
structure ............................................................................................................. 117
Figure 7.1 Atomic copper anion 355 nm photoelectron spectrum ...................................... 126
Figure 7.2 Cu− H2O 355 nm photoelectron spectrum.......................................................... 127
Figure 7.3 Calculated anion and neutral structures for copper d4-methanol ...................... 128
Figure 7.4 Time-of-flight mass spectrum obtained with the dc sputter ion source with
relevant species labeled ..................................................................................... 130
Figure 7.5 CuCD3OD− 355 nm full scale raw photoelectron image, reconstructed
photoelectron image, and photoelectron spectrum ............................................ 133
Figure 7.6 CuCD3OD− 600 nm raw photoelectron image, reconstructed photoelectron image,and photoelectron spectrum ............................................................................... 136
Figure 7.7 CuCD3O− 355 nm raw photoelectron image, reconstructed photoelectron image,and photoelectron spectrum ............................................................................... 138

xiFigure 7.8 CuCD3O− 500 nm raw photoelectron image, reconstructed photoelectron image,and photoelectron spectrum ............................................................................... 140
TablesTable 2.1

Atomic copper photodetachment transitions used to focus and calibrate thevelocity map imaging photoelectron spectrometer............................................ 29

Table 2.2

Recommended configurations, maximum pulse energies, and maximum
linewidths for production of 210 – 750 nm nanosecond laser pulses. ............... 38

Table 4.2

Peak positions and assignments for E-iminodiazomethide photoelectron
spectrum. ....................................................................................................... 70

Table 5.1

Spectroscopic constants for AgO− and AgO...................................................... 82

Table 5.2

Spectroscopic constants for AuO− and AuO...................................................... 83

Table 5.3

Spectroscopic constants for AuS− and AuS........................................................ 85

Table 5.4

Comparison of spectroscopic constants for CuO, AgO, and AuO. ................... 88

Table 6.1

Spectroscopic constants for CuH and CuH−. ................................................... 104

Table 6.2

Spectroscopic constants for CuD and CuD−. ................................................... 107

Table 6.3

Electron binding energies, angular anisotropy parameters, and peak spacings in
the CuH2− and CuD2− photoelectron spectra. ................................................... 115

Table 6.4

Electron affinities and symmetric stretch frequencies for CuH2 and CuD2..... 120

Table 7.1

Measured electron affinities and anion electron binding energies forphotodetachment of Cu−, Cu− H2O, and Cu−CD3OD to the neutral states whichcorrelate to the 2D5/2 and 2D3/2 electronic states of copper atom. ..................... 142

Table 7.2

Measured anion electron binding energies for detachment to the three lowest
lying neutral electronic states of CuOH and CuCD3O..................................... 143

________________
Introduction to Anion Photoelectron Spectroscopy________________
1.1

Anion Photoelectron Spectroscopy Overview
Anion photoelectron spectroscopy is a powerful tool to study the geometries,

vibrational modes, thermochemistry, and electronic structure of anions and neutrals.1
Through the use of different ion sources, laser souces, and electron kinetic energy
measurement techniques anion photoelectron spectroscopy has been applied to a wide rangeof systems.1 These include atoms,2 organic molecules,3 metal-ligand systems,4 and a wide
variety of clustered systems.5-8

As explained below, the electron affinity, vibrationalfrequencies, and electronic term energies of the photodetached neutral are readily measured
in an anion photoelectron experiment. Often vibrational (and occasionally electronic) levelsof the anion may be measured as well. Theoretical geometry and frequency calculations areoften employed to simulate9 a photoelectron spectrum in order to make spectral assignments
and to identify the photoelectron signal carrier.
In an anion photoelectron spectroscopic experiment, a beam of molecular or atomic
anions is prepared and laser light is used to photodetach electrons from the anion beam. The
kinetic energy of the photodetached electrons is measured and, when combined with thephoton energy of the photodetachement laser, the binding energy of the electrons to the anion
is obtained. The process is simply defined for a molecular anion in equation 1.1 below.

AB − + hν = AB + e − (eKE )(1.1)

Here AB− is the molecular anion energy, hν is the photon energy, AB is the energy of thephotodetached neutral, and e− (eKE) is the photodetached electron kinetic energy (eKE). It isclear from equation 1.1 that, given a well defined molecular anion energy state and a narrow

2
bandwidth photon source, measuring the electron kinetic energies directly gives thedifference in energy between the initial anion state(s) and the final neutral state(s). This
energy is the electron binding energy (eBE) of the anion and is found by subtracting theelectron kinetic energy from the photon energy. Given sufficient photon energy, transitions
to excited vibrational and electronic energy levels of the neutral may be accessed. The
process is diagrammed in Figure 1.1 below. While the process is a direct photodetachment, it
may be thought of as absorption of the photon by the anion followed by concurrent molecularelectron Binding Energy (eBE)relaxation and photoejection.

hν

β*

~
AB* A

~
X

AB

−

Te

β

EA

AB
Figure 1.1

Schematic diagram depicting processes and energies present in photoelectron
spectra.

In Figure 1.1 the electronic and vibrational features of the anion are represented by
the potential labeled AB−. The “absorption” process is depicted by the large upward pointing
arrow, while relaxation to various vibronic energy levels and photoejection (as well as theeKE) is represented by the downward pointing arrows. The electron affinity of the neutral is3the energy of the 0 − 0 transition between the anion and neutral and is labeled as “EA” in
Figure 1.1. If energetically accessible, term energies for excited neutral electronic states may
be directly measured and are represented by “Te” in Figure 1.1.
1.2

Selection Rules
Since the electronic states of the neutral are accessed by removal of an electron, theonly electronic selection rule is that the spin quantum number must change by ½ (i.e.,removal of an electron from a doublet spin state will produce either a singlet or triplet spinstate).

The transition moment (Μ) for photodetachement, within the Frank-Condon

approximation, is given by equation 1.2 below.1

Μ = C × Ψ" (Q" ) Ψ ' (Q' )

2
(1.2)

Here ψ”(Q”) is the vibrational wavefunction of the initial anion state and ψ’(Q’) is thevibrational wavefunction of the final neutral state, both as a function of the normal vibrational
coordinates Q. Note that only transitions to and from totally symmetric vibrational modes (oreven quanta of non-totally symmetric modes) are allowed.
1.3Frank-Condon Profiles
The transition moment is extremely sensitive to differences between vibrational

normal coordinates between the anion and neutral and determines the profile for vibrational
progressions observed in photoelectron spectra.

This effect is demonstrated for ahomonuclear diatomic molecule in Figure 1.2 below. For a homonuclear diatomic molecule,the normal vibrational coordinate is the bond length of the anion or neutral. Figure 1.2
displays the results of simulated9 photoelectron transitions with increasing change in normal
vibrational coordinates (bond length) between the anion and neutral.

1.2

1.2

1.0

1.0

0.8

0.8

intensity

intensity

4

0.6
0.4

0.4

0.2

0.2

0.0

0.0

1.0

1.1

1.2

1.3

(a)

1.4

1.5

1.6

1.7

1.8

1.9

2.0

1.0

1.1

1.2

1.3

(b)

eKE (eV)

2.5

10

2.0

8

1.5

6

1.0

0.5

1.4

1.5

1.6

1.7

1.8

1.9

2.0

1.7

1.8

1.9

2.0

eKE (eV)intensity

intensity

0.6

4

2

0.0

0
1.0

(c)

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2.0

eKE (eV)Figure 1.2

1.0

(d)

1.1

1.2

1.3

1.4

1.5

1.6

eKE (eV)

Simulated diatomic photoelectron spectra showing the effect of bond lengthchange between the anion and neutral on the spectral profile. The spectrapresented were simulated with a (a) 5%, (b) 10%, (c) 15%, and (d) 20%
change in bond length between the anion and the neutral.

Notice that the vibrational progression increases with the change in bond length, as
does the most likely final vibrational state of the neutral. By simulating the photoelectron
spectrum the change in the normal vibrational coordinates between the anion and the neutral
can be inferred. Matching the vibrational profiles and identifying transitions to different
electronic states by examination of the β parameters10 leads to accurate vibrational andelectronic state assignments in the spectrum.

5
1.4

Anisotropy (β) Parameters
Electrons photodetached from orbitals of different symmetry (hence leading todifferent electronic states of the neutral) have different angular distributions defined10 byequation 1.3 below.

I (θ ) =σo(1 + β P2 ( cosθ ) )
4π

(1.3)

Here I(θ) is the photoelectron intensity as a function of the angle between the electric field of
the laser and the electron collection direction. σ0 is the total photodetachment cross-section,
P2 is the second Legendre polynomial, and β is the anisotropy parameter.

For atomic

photodetachment, β = 2 for detachment from an s orbital, β=0 for near threshold detachmentfrom a p orbital, and negative β values result from photodetachment from p and d orbitals notnear threshold, with a minimum value of −1. For molecular photodetachment, β is not aswell defined. However, electrons photodetached from Σ orbitals will have positive β values
and electrons photodetached from Π and Δ orbitals will have negative β values. Thus
measurement of the anisotropy parameters for features in a photoelectron spectrum will help
to assign transitions to different electronic states of the neutral.
1.5

Thesis Overview
This thesis contains photoelectron spectra of several different types of molecules

taken with two different photoelectron spectrometer systems. The first system is cw, contains
a flowing afterglow ion source, and employs a hemispherical electron kinetic energy
analyzer. The second system is pulsed, employs a supersonic expansion ion source, and uses
the velocity map imaging technique to measure the electron kinetic energies. Both of thesesystems are described in detail in chapter 2, along with theoretical methods for photoelectron
spectral simulations.

6
As part of a research program conducted by the Lineberger and Bierbaum groups tolearn about the thermodynamics of the azoles (five-membered nitrogen-containing rings), thepulsed photoelectron imaging spectrometer was used to study the 1,2,3-triazolide anion.
These results are presented in chapter 3. Iminodiazomethide, a concurrently produced ringopened isomer of 1,2,3-triazolide, was studied using both photoelectron spectrometers. These
results are presented in chapter 4.
As part of a research program conducted with undergraduate physical chemistry
students, the hemispherical analyzer photoelectron spectrometer was used to record thephotoelectron spectra of AgO−, AuO−, and AuS−. The results of the metal oxide and sulfide
experiments are presented in chapter 5.
Photoelectron spectra of CuH− and CuH2− recorded with the photoelectron imaging
spectrometer are presented in chapter 6. The electronic structure and vibrational frequenciesof the CuH molecule are compared frequently with high level theoretical calculations tobetter treat relativistic effects and transition metals in general. The electron affinity of thismolecule has not been reported previously, as well as a low lying triplet state which is dark to
traditional absorption or emission spectroscopies. Both are reported here for the first time.
In order to better understand time resolved photodetachment-photoionization (PDPI)
studies of the Cu− CD3OD system, photoelectron spectra of Cu− CD3OD and CuCD3O− wererecorded using the photoelectron imaging spectrometer.

The results of this study arepresented in chapter 7. A summary of the experimental results is given in chapter 8.
In order to protect the low pressure detection region of the photoelectron imaging
spectrometer, a smart power backup vacuum interlock system was designed and built. The
details of the design, interlock flow chart, and interlock program code are presented inappendix A.

7References for Chapter I

1

K. M. Ervin and W. C. Lineberger, in Advances in Gas Phase Ion Chemistry, editedby N. G. Adams and L. M. Babcock (JAI Press, Greenwich, 1992), Vol. 1, pp. 121.

2

T. Andersen, H. K. Haugen, and H. Hotop, Journal of Physical and Chemical
Reference Data 28 (6), 1511 (1999).

3

S. J. Blanksby and G. B. Ellison, Accounts of Chemical Research 36 (4), 255 (2003).

4

G. J. Rathbone, T. Sanford, D. Andrews, and W. C. Lineberger, Chemical Physics
Letters 401 (4-6), 570 (2005).

5

J. Ho, K. M. Ervin, and W. C. Lineberger, Journal of Chemical Physics 93 (10), 6987
(1990).

6

F. Misaizu, K. Tsukamoto, M. Sanekata, and K. Fuke, Surface Review and Letters 3(1), 405 (1996).

7

A. Nakajima, T. Taguwa, K. Nakao, K. Hoshino, S. Iwata, and K. Kaya, Surface
Review and Letters 3 (1), 417 (1996).

8

D. Radisic, S. J. Xu, and K. H. Bowen, Chemical Physics Letters 354 (1-2), 9 (2002).

9K. M. Ervin, T. M. Ramond, G. E. Davico, R. L. Schwartz, S. M. Casey, and W. C.
Lineberger, Journal of Physical Chemistry A 105 (48), 10822 (2001).

10

J. Cooper and R. N. Zare, Journal of Chemical Physics 48, 942 (1968).

8________________
Hemispherical Analyzer and Velocity Map Imaging Methods________________
2.1

Anion Photoelectron Spectrometers Overview
Two types of photoelectron spectrometers were used in the course of the experiments

conducted here. The main difference between the two is the method used to measure thekinetic energy of photodetached electrons. One instrument employs a hemispherical analyzer
while the other uses a velocity map imaging system. Because the hemispherical analyzer
system detects only a small fraction (1/1000) of the photodetached electrons, the anion source
and laser system must produce large amounts of anions and photons, respectively. The
velocity map imaging system, in contrast, detects nearly all photodetached electrons, and thus
requires only a moderate amount of anions and photons. The resolution of the velocity map
imaging detector is approximately 2% of the electron kinetic energy, while the resolution of
the hemispherical analyzer is about 10 meV for all electron kinetic energies.
Historically the two instruments were designed to study very different systems. The
hemispherical analyzer instrument was initially designed to photodetach electrons fromatomic negative ions. It has been used in recent years to study many small organic anions,through the use of rational gas phase reaction anion synthesis, as well as metal based anions.
The velocity map imaging instrument was originally designed for time resolved photofragmentation studies of cluster anions, with the velocity map imaging capabilities only
recently added. The hemispherical analyzer instrument uses a laser system with a maximum
photon energy of 3.531 eV, while the velocity map imaging laser system can currently
produce photon energies up to 5.904 eV. The resolution of the mass spectrometers used to
select an anion mass are greatly different as well: the hemispherical analyzer can separate
masses with a 1 amu difference up to 35 amu, while the velocity map imaging instrument can

9separate masses with 1 amu difference up to several hundred amu. The anion temperatures
are also very different between the two systems. The velocity map imaging instrument uses apulsed supersonic expansion source which can produce cluster anions with temperatures as
low as tens of Kelvin.

Conversely, the hemispherical analyzer instrument uses a highpressure (~ 500 mtorr) source which produces anions with typical temperatures between 200
K and 400 K.
The advantages of the velocity map imaging instrument, then, are superior mass
resolution, higher photon energies, and production of large anion clusters. The advantages of
the hemispherical analyzer instrument are constant energy resolution, thermalized anions, andrational anion synthesis.

The remainder of this chapter is devoted to description andmethodology of both instruments. The hemispherical analyzer instrument is described in
sections 2.2 – 2.7, while the velocity map imaging instrument is described in sections 2.8 –2.13. Theoretical calculations and spectral simulation methods used to aid the interpretationof the photoelectron spectra are presented in section 2.14.
2.2

Hemispherical Analyzer Photoelectron Spectrometer Overview
The hemispherical analyzer photoelectron spectrometer and methodology used in theexperiments presented here have been described in great detail previously,1-4 thus a moderate
description is given here. The apparatus is diagrammed in Figure 2.1. The spectrometerconsists of an anion source coupled to a high pressure reaction flow tube to create anions via
rational gas phase ion reactions. This region is described in section 2.3. Anions are extracted
into a low pressure beam formation and mass selection region, which is presented in section
2.4. The mass-selected anion beam is crossed with a fixed frequency laser beam producing
photoelectrons. The kinetic energy of the photoelectrons is measured by a hemisphericalenergy analyzer which is described in section 2.5. Section 2.6 describes the continuous wave

10external build-up cavity laser system.

Data manipulation and analysis are presented in

section 2.7.

Figure 2.1

2.3

Hemispherical energy analyzer photoelectron spectrometer.

Hemispherical Analyzer Instrument Ion Sources
Two anion sources were used in the hemispherical analyzer photoelectron

spectrometer experiments presented here. A cold cathode dc sputter source was used to
produce AuS−, AgO− and AuO−, while a microwave discharge source was used to produce
1,2,3-triazolide and its ring-opened isomer iminodiazomethide.
The cold cathode dc sputter source is described first and diagrammed in Figure 2.2.
The source consists of a high purity metal rod which is biased up to –3,000 volts with respect
to chamber ground in a helium and argon atmosphere of ~ 500 mtorr. The rod is biased by anelectrically ballasted dc power supply, with the ballast consisting of a 100 kΩ resistor and 4
H inductor in series. High purity helium seeded with 10% − 15% argon is introduced justabove the metal rod, the flow of which is regulated by a Tylan flow controller with a flow of

11
6-7 standard liters per minute. The strong electric field between the metal rod and thechamber walls ionizes the argon atoms creating Ar+. The Ar+ ions are then accelerated into
the metal rod, sputtering off metal atoms and clusters. The rod holder is cooled by a flow ofwater through the stainless steel tube to which the holder is attached (see Figure 2.2). In
addition, the sputter source region is externally wrapped with a copper cooling water line. A
glass cylinder around the rod holder prevents arcing between the holder and the chamber
walls. Metal oxide (sulfide) anions are formed by adding a trace amount of O2 (CS2) to the
He/Ar mixture.

Chamber
Cooling Water
Coils

He, ArSampleCooling
Water In

Sample Rod

SampleCooling
Water OutElectrical Ballast
3 kV

100 kΩ

Figure 2.2+

4H

DC sputter ion source for the hemispherical analyzer instrument.

12
The microwave discharge ion source used to produce 1,2,3-triazolide and its ringopened isomer iminodiazomethide is diagrammed in Figure 2.3. Atomic oxygen anion isformed by passing a trace of oxygen in 500 mtorr of helium through a resonant microwave
cavity which is tuned with a ceramic tuning rod. A flow rate of 6 -7 standard liters per
minute is maintained by a Tylan flow controller. The discharge is created by ignition with aTesla coil and maintained by a 2.45 GHz microwave generator. Electrons from the Tesla coil
are accelerated in the microwave field and create a plasma containing high energy He+
metastable ions and O− ions, as well as other neutrals and ions. The O− anion is created via
slow electron dissociative attachment to molecular oxygen.
Upon exiting the microwave discharge region the plasma enters a flowing afterglow
ion reaction region. The ions may be reacted with neutral reagents introduced into the flow
tube via two moveable neutral ring inlets. To create 1,2,3-triazolide and iminodiazomethide
anions, O− was first reacted with methane introduced via the first ring inlet to form HO−.
Gaseous 1H-1,2,3-triazole is introduced through the second ring inlet by flowing helium overa liquid sample of 1H-1,2,3-triazole (97%, Aldrich). The HO− abstracts a proton from 1H1,2,3,-triazole to form both 1,2,3,-triazolide and iminodiazomethide.

13

QuartzDischarge
CylinderMicrowave
CavityCeramic
Tuning Rod

He,
O

2

Reaction
Flow Tube

Adjustable Reactant
Ring Inlets
Figure 2.3

Microwave discharge ion source for the hemispherical energy analyzer
instrument.

After formation the anions are thermalized by collisions with the helium buffer gas in
the flow tube. The anions have a temperature which is near the temperature of the flow tube
walls, usually around 300 K. The flow tube is surrounded by a jacket which may be filledwith liquid nitrogen to cool the flow tube, reducing the anion temperature to near 200 K.
2.4

Hemispherical Analyzer Instrument Ion Beam Formation and Mass Selection
The flow tube is terminated by a 1 mm orifice in a nosecone which is biased near +1

volt to gently extract negative ions into a lower pressure (0.1 mtorr) region. This region
consists of a series of lenses and deflectors for ion beam formation, acceleration, mass
selection, and deceleration. In addition, apertures allow for differential pumping of thisregion, which is diagrammed in Figure 2.4.

The left side of Figure 2.4 shows the

successively decreasing pressure of this region, while the right side indicates the ion beam

14
potential in each section. Lenses are denoted by L’s, deflectors by D’s, quadrupoles by Q’s,and apertures by A’s.
The first set of lenses (L1 − L3) acts as an einzel lens, which accelerates and focuses
the beam. The ions are accelerated and deflected both horizontally and vertically by a set ofdeflectors labeled D1. They then pass through an aperture (A1) and through another set ofaccelerating lenses (L3, L4) before being steered through deflector set D2. The ions thenpass a second accelerating einzel lens set (L4 – L6), and are steered through a 10° bend in the
instrument by deflector set D3. The purpose of the 10° bend is to remove any neutrals which
may have formed after the ions were extracted through the nosecone. The ion beam potential
after D3 is 735 eV and the beam is focused and deflected through aperture A2 by quadrupolelens Q1. Current induced by ions which impact A2 rather than traveling through the apertureis measured by an electrometer and is minimized to ensure a large portion of the ion beam
passes through A2.

15

Figure 2.4

Hemispherical analyzer instrument ion optics, mass selection, and laserinteraction regions. L = lens, D = deflector, A = aperture, and Q =quadrupole.

Once through A2, the ions pass a deflector set (D4), aperture (A3), and quadrupole(Q2). A gate valve between A3 and Q2 separates the chamber and allows the high pressure
ion formation section of the chamber to be vented without risk to the low pressure detection
region. The ions are separated according to their velocities by a velocity filter. This filter

16
consists of perpendicular electric and magnetic fields, each of which exerts a force on theions. The electric field deflects the ions according to their charge, while the magnetic field
deflects ions according to their velocity in a direction perpendicular to their velocity. Since
all ions have the same energy (735 eV), they are distributed according to their masses byvelocity. The magnetic field strength is tuned such that the electric and magnetic forces
acting upon the anion of interest are equal and opposite, resulting in zero deflection. Anionsof higher or lower velocity (mass) are deflected out of the beam path. The velocity filter has
a mass resolution of m

Δm

≅ 35.

After mass selection, the ion beam is focused and deflected by quadrupole Q3
through aperture A3. Quadruple Q4 and deflector D5 steer the ions into a set of decelerationlenses where the beam energy is reduced to 38 eV, greatly reducing the ion velocity. The ion
beam passes through the laser interaction region after which the beam is terminated by a
Faraday cup. The current on the cup is measured by an electrometer, with typical beam
currents ranging from several picoamps to several nanoamps.
2.5

Hemispherical Analyzer Instrument Photoelectron Detection
The laser-anion interaction region of the chamber also serves as the first lens elementof the photoelectron hemispherical kinetic energy analyzer. Photoelectrons produced in thelaser-ion volume have velocities in all directions. An aperture with 5° half-angle cone
acceptance angle sits below the anion-laser beam plane. The analyzer consists of accelerationand magnification input sets of lenses, a hemispherical analyzer, output acceleration andmagnification lenses, and position sensitive electron detector with are diagrammed in Figure
2.5.
The hemisphere consists of an inner and outer sphere with static electrontransmission energy. Electrons input into the analyzer with this energy will pass through,while those at higher or lower energies will impact either the inner or outer hemisphere. The17function of the input stack is to accelerate the sampled photoelectrons to the transmission
energy and focus the beam onto the entrance of the hemisphere. The elements labeled VIR,
V1, and V2 in Figure 2.5 act as a three element accelerating and focusing lens, while V2, V3,
and VHC act as a three element focusing lens.

The elements labeled VHC are Herzog

correctors which compensate for stray electric fields created by the hemisphere.

Oncethrough the analyzer, the electrons are accelerated (VHC, V4) and focused (V4, V5, V6) onto a
position sensitive detector.
The detector consists of five microchannel plates connected to a position sensitive
resistive anode collector. A 3,400 volt potential is distributed evenly across the plates by an
external voltage divider. A photoelectron spectrum is taken by changing the input stackelectron acceleration voltage and measuring the photoelectron counts on the detector. The
photoelectron counts are integrated for a short time (typically 1 second) per acceleration
voltage and stored as X, Y data. The data for each acceleration voltage segment are added
together using the often measured energy range of a single segment.

18

Position Sensitive
Detector

V6

Acceleration

VIR
V1

V5

Magnification

Photodetachment
VolumeV2

V3
VHC

Hemispherical Energy
Analyzer
Figure 2.5

Hemispherical photoelectron kinetic energy analyzer.

Acceleration

Magnification

V4

19
2.6

Hemispherical Analyzer Instrument Laser System
The ultraviolet laser system used to produce either 363.8 nm or 351.1 nm laser

radiation is presented in Figure 2.6. The system consists of a narrow line argon ion laser andexternal build-up cavity. The laser consists of an argon lasing medium excited by a 6 amp
current. The laser cavity is defined by an ultraviolet high reflecting mirror and output
coupler. An etalon positioned in the laser cavity damps all but one longitudinal lasing mode
below the lasing threshold. The remaining mode has a full width at half maximum in thekilohertz range. The power of the UV light which exits the laser cavity is typically 1 W, far
below the amount needed to effectively conduct photoelectron spectroscopy experiments.
To increase the laser power, the interaction region of the chamber is used as anexternal build-up cavity. Laser light exits the lasing cavity and is relayed through a telescopeby the mirrors labeled “M” in Figure 2.6. The beam then travels through an acousto-opticalmodulator (AOM in Figure 2.6), the first order output of which shifts the laser frequency by
55 – 85 MHz. This first order output of the AOM is then steered through a half wave plate
which allows for rotation of the laser polarization.

The laser beam then enters thephotodetachment and electron detection portion of the vacuum chamber through the mirror
labeled R1 in Figure 2.6. Mirror R1 is 99.6% reflective in the ultraviolet and together withmirror R2 (99.8% reflective) defines the external laser build-up cavity.
The 1 W laser light which enters the build-up cavity is increased to 150 – 200 W
inside the cavity by constructive interference. Build-up only occurs when the same mode
which exits the laser is built-up in the cavity. Because small changes in either cavity length
will change the resonance mode of the cavities, a system of electronics is in place to keep thetwo cavities in resonance. The light reflected from the external build-up cavity input mirror(R1) is monitored by a photodiode. The light reflected is at a minimum when the circulating
power in the build-up cavity is at a maximum, thus decreases in the power measured by the

20photodiode are preferred. There are three adjustments which can be made by the cavity
resonance locking electronics. The first is the laser cavity length and is changed by moving
the high reflecting optic (labeled “back mirror” in Figure 2.6) which is attached to a piezo
electric mount. The input mirror of the external build up cavity (R1) is likewise held by apiezo electric mount in order to adjust the build-up cavity length. In addition, the frequency
shift induced by the AOM can be changed to bring the frequency produced by the laser into
resonance with the build-up cavity length.

Figure 2.6

2.7

Hemispherical analyzer instrument ultraviolet continuous wave laser system.

Hemispherical Analyzer Methodology and Data Analysis
The raw photoelectron data are contained in segments. Each segment contains thenumber of counts in each pixel of the detector array (256 pixels per segment) for the given
input lens voltages. The segments are tagged with the center experimental electron kinetic
energy as derived from the well known5 atomic transitions observed in the tungsten anion
photoelectron spectrum. These segments are added using the PESCON program which

21
outputs the total number of photoelectron counts as a function of the electron kinetic energy.
This energy scale is calibrated using a well known atomic transition observed in the atomic
anion photoelectron spectrum, with atomic oxygen anion6 being the most common. The
width of each segment in eKE is also determined by observation of a known atomic
transition. This width is used when adding the segments together. Also of importance is asmall energy scale compression caused by the hemispherical analyzer. This compression iscorrected for by routinely measuring the positions of the atomic transitions in the tungsten
anion photoelectron spectrum mentioned above.
Spectral assignments of photoelectron spectra and theoretical calculations performed
to aid these assignments are presented in section 2.13.
2.8

Velocity Map Imaging Photoelectron Spectrometer Overview
The photoelectron velocity map imaging apparatus is diagrammed in Figure 2.7. It

has been described in some detail in several publications,7-9 thus a moderate description is
given here, with more attention paid to methodology and data analysis. The apparatus
consists of a pulsed source region, Wiley-McLaren time-of-flight mass spectrometer,10 andvelocity map imaging photoelectron detection system.11,12 Because the resolution of thespectrometer decreases with increasing electron kinetic energy, a nanosecond laser system
tunable between 210 nm and 2,000 nm is used for photodetachment in order to resolve subtle
spectral features. The description of the velocity map imaging photoelectron spectrometer isgiven in the following sections. Pulsed anion sources used in these experiments are describedin section 2.9. Anion beam formation and mass separation are described in section 2.10.
Section 2.11 describes the photoelectron velocity map imaging system and data collection
methodology. The tunable nanosecond laser system is described in section 2.12, and data
analysis procedures are described in section 2.13.

22

CCD Camera
Phosphor Screen

PulsedSourceMicro channel Plates
Ions

Ion Optics

Mass Gate

Figure 2.7

2.9

Neutrals

Ref
le

ctro
n

Ions

La
se
21
r
020
00
nm

Potential Switch

Electron
Gun

Electron
Flight Tube

Photoelectron velocity map imaging spectrometer.

Velocity Map Imaging Instrument Ion Sources
Two ion source configurations were used during the course of the photoelectron

velocity map imaging experiments presented here. The heart of both sources is a mixed-gas
pulsed supersonic expansion. The expansion is formed when a gas mixture with stagnationpressure between 40 psi and 50 psi is expanded through a pulsed valve (General Valve Series
9, 0.8 mm aperture) into a low pressure region (base pressure 1x10−7 torr). The valve isdriven by a General Valve IOTA ONE pulsed valve driver. The valve trigger, repetition rate,
and open time are externally controlled by a high precision delay generator (Stanford
Research Systems model DG535). The full experimental timing scheme is presented in
section 2.11.
In the ion source configuration used to produce 1,2,3-triazolide, a gas mixture
containing 10% O2 and 20% CH4 in argon is passed through a liquid sample of 1H-1,2,3-

23
triazole in a heated (85°C) scintillated glass bubbler. This mixture is brought to the pulsed
valve through heated (75°C) stainless steel tubing with a stagnation pressure of 45 psi. The
gas expansion is met collinearly (see Figure 2.7) by a 1 keV beam of electrons produced by ahome-built electron gun. The electron gun consists of a filament, anode, einzel lens, anddeflectors, and is located 30 cm from the pulsed valve face. Electrons are thermally emitted
by passing a current of 5 to 7 amps through a thoriated iridium filament (Electron
Technology, Inc.). Emitted electrons are extracted from the filament region and moderately
focused by an anode plate which is biased at −80 volts to −120 volts with respect to thefilament. Both the filament and anode plate are floated at 1 kV. The extracted electrons arefocused by an einzel lens, the first and third plates of which are held at ground potential,
while the middle plate is biased between 600 volts and 1100 volts. The electron beam issteered into the gas expansion by a set of horizontal and vertical deflectors located beyond theeinzel lens, each set of plates typically having a potential difference of 0 – 50 volts. The
electron beam is further directed to the center of the gas expansion by a 5 mm thicksamarium-cobalt magnetic annulus mounted to the front of the pulsed valve face.

Agrounding clip attached to the valve face keeps the annulus and pulsed valve at chamber
ground.
The likely synthesic route to 1,2,3-triazolide is as follows. Slow secondary electrons
produced by interaction of the electron beam with argon dissociatively attach to O2 forming
oxygen atom and O−. The O− then abstracts a hydrogen atom from CH4 producing neutral
CH3 and HO−. The HO− abstracts the N-H proton from 1H-1,2,3-triazole producing the 1,2,3triazolide anion.
The second source used in the experiments described here is a dc metal sputtering
source used to produce atomic metal ions with and without ligands. In this source, a large
potential difference is applied between two metal rods. One rod is a stainless steel anode,24
while the other is the metal of interest (copper in these experiments). The stainless steel rod
is connected directly to the chamber and the metal of interest is biased at –1,000 to –3,000
volts. The rods are held in a Macor block approximately 1 cm from the pulsed valve orifice
and are separated by 0.5 to 2.0 mm. The Macor block has a 4 mm orifice in the center toallow the passage of gas from the pulsed valve and is attached to the valve face with stainlesssteel screws. A gas mixture of methanol seeded in argon is produced by passing argon over aliquid sample of neat spectroscopic grade (Aldrich) methanol held in a stainless steel cup.
When this gas mixture passes between the rods a discharge is formed which ionizes the argon
and the resulting Ar+ is accelerated towards and impacts the negatively biased rod with
sufficient force to sputter the metal. The process creates a plasma of neutral and ionic metal
atoms and clusters. Metal-ligand anions are formed by three body reactions of metal anions,
ligands, and a neutral collision partner (argon).
2.10

Velocity Map Imaging Instrument Ion Beam Formation and Mass Selection
Once formed, the plasma drifts 15 cm until the negative ions are transversely repelled

by a pulsed electric field. The negative pulse is generated by a home-built module whichtakes a TTL pulse and dc high voltage as input and outputs a 2 ms (internally adjustable) lessthan 10 ns rise time pulse. The time delay between the pulsed valve opening and thisrepelling plate firing is set by maximizing the anion signal and is typically 300 μs to 800 μs.
Negative ions are accelerated towards a ground aperture plate which defines the beginning of
the second acceleration stage of the Wiley-McLaren time-of-flight mass spectrometer. The
ground plate has a 3 mm aperture which defines the anion beam diameter and is in directelectrical contact with the vacuum chamber.
Once past this aperture plate, the anions enter the region marked “Ion Optics” inFigure 2.7. The first ion optical element is a 10 annuli acceleration region, with each annulus
spaced by 0.43 cm with 2.54 cm diameter apertures. A dc voltage of +2.3 – +2.5 kV is25
applied to the last plate and divided down to ground by 1 MΩ resisters, which accelerates theions to this beam potential. All the elements labeled “Ion Optics” in Figure 2.7 are floated at
this potential, including a three element einzel lens, horizontal deflectors, and verticaldeflectors. The first and last elements of the einzel lens are held at the beam potential, while
the middle element is held between +500 and +1100 volts. The voltage across the deflectors
is 0 V – 135 V.
Beyond the einzel lens is an aperture plate (2.54 cm diameter aperture), also held at
the beam potential, which defines the beginning of a 70 cm long potential switch13 region.
The switch is a cylindrical section which is electrically isolated from the ion optics and thechamber walls. When the anion repelling plate is fired, the potential of the cylindrical regionis switched from ground up to the beam potential by a Directed Energy Inc I PVX-4140 pulse
switcher. When the anion of interest is in the cylindrical region, the potential is rapidly
switched to ground. This allows the chamber and ion optics elements beyond the switch
region to be held at chamber ground and not the beam potential, as was previously the case.
After the potential switch the ions are steered through a 1.5° bend in the chamber and into theentrance of a three element mass gate. The 1.5° bend removes any neutrals which haveformed in the beam, while the mass gate selects the anion (or range of anions) of interest.
The mass gate consists of three pairs of parallel horizontal plates between two aperture plates.
These aperture plates, along with the first and third pairs of plates are held at chamber
ground, while the middle pair of plates is held at a high voltage (typically 1 kV) and pulsed
down to ground when the anion of interest is between the plates. See Figure 2.9 for the fullexperimental timing scheme. A gate valve between the 1.5° bend and the mass gate separates
the ion production region from the ion and electron detection region.
The anions then travel through the photoelectron velocity map imaging region(described in section 2.11), reflectron (not used in the experiments described here), and26horizontal deflector before impinging on the front face of a microchannel plate detector. Thisdetector consists of two impedance matched microchannel plates (Hamamatsu Corp. F461209 and Burle 32733) in a chevron configuration. The plates have a 2.0 cm diameter active
area and the back plate is held at 1,600 volts for detection of anions and 1,800 – 1,950 voltsfor detection of neutral photoproducts. Anions may be deflected from the beam by applying
a voltage of 200 – 1,000 volts on the horizontal deflector mentioned above. A mesh held atchamber ground sits before the front face of the MCPs and provides a field-free region for theanions just before the detector. Electrons emitted from the microchannel plates (typically 107
per particle) are collected by an anode plate biased at 200 volts above the back face of the
MCPs. The anode signal is amplified by a Stanford Research Systems (model SR 240A) 350
MHz fast pre-amplifier which provides a maximum gain of 625. This signal is monitored on
a 200 MHz oscilloscope (Tektronix model 2445B).

A time-of-flight mass spectrum isrecorded on this oscilloscope by monitoring the anion arrival time in reference to the highpulse of the anion repelling plate. These data are transferred from the oscilloscope to a PC
via 3.5” floppy disk.
2.11

Velocity Map Imaging Instrument Photoelectron Detection

The photoelectron imaging spectrometer is based on the velocity map imaging
technique developed by Parker and Eppink11 and the design is a modified version ofthat employed by Sanov and coworkers.12

The electron imaging detector iscomprised of a three element lens consisting of negatively biased repelling (V1),ground (V0), and positively biased extracting (V2) 7.62 cm diameter 0.762 mm thickoxygen-free high-conductivity copper disks spaced by 2.54 cm. These electrodes arecontained in a μ-metal (Magnetic Shielding Corp.) enclosure with 2.54 cm apertures
for entrance and exit of the ion and laser beams, as well as ions directed towards the27

off-axis detector by the reflectron (not used in the experiments reported here). In
addition, there is a 2.54 cm aperture in the bottom of the enclosure to enable efficientpumping of the imaging region. The ground (V0) and extracting plates (V2) have 2.54
cm centered apertures, while the repelling plate has none. The extractor plate (V2) isin electrical contact with, and defines the beginning of, a 15 cm long 7 cm diameter
oxygen-free high-conductivity copper field free flight tube which is mounted on an 8”
conflat flange. The inner surface of the electron flight tube is lined with four layersof 0.5 mm thick μ-metal to shield photoelectrons from the earth’s magnetic field. At
the end of the flight tube is a 4 cm active diameter imaging dual impedance matchedchevron configured microchannel plate detector and P47 type phosphor screen
coupled by a fiber optic bundle to a chamber window (Burle Electro-Optics, Inc.).
This window is monitored by a 1280 x 1074 pixel CCD camera (LaVision 3LS, 6.7
μm x 6.7 μm pixel size) controlled by a desktop PC.
The anion of interest is photodetached approximately halfway between therepelling (V1) and ground plates (V0) of the electron imaging assembly. The repelling
plate is pulsed high by an externally switched power supply (Directed Energy PVM4210) ~ 10 μs prior to the arrival of the photodetachment laser pulse, with a pulse
duration of ~ 50 μs. Since this repelling plate repels anions as well as electrons, it
must be switched on well before the anions are near the plate. This is done to ensurethat there is no dependence of the image size on the repelling plate being switchedhigh. The V2:V1 voltage ratio (~ 3:1 for our configuration) must be optimized (alsoreferred to as focused) for each laser photodetachment wavelength because the laser
beam height changes with changing wavelength (regardless of laser source). Even

28

small changes in the laser height will significantly affect the optimum V2:V1 ratio,
because there is a significant electric field gradient in the photodetachment region. A
SIMION plot of the laser-ion interaction region is presented in Figure 2.8. The plotshows a high density of field lines in this region, confirming that a slight change inthe laser position will significantly change the optimum V2:V1 voltage ratio. The
ratio is optimized by monitoring the full-width-at-half-maximum of one, or more,well known electronic transitions in the photoelectron spectrum of an atomic anion.
For the 1,2,3-triazolide spectra reported here, the 3P3/2 ← 1S0 transition in the wellknown14 photoelectron spectrum of F− was used to determine the optimum V2:V1
ratio. For photoelectron imaging of copper based anions reported here, the transitionsin the well known15 photoelectron spectrum of atomic copper anion were used to findthe optimum ratio. These transitions along with the corresponding electron binding
energies are listed in Table 2.1. These atomic transitions are also used to calibrate theelectron binding and electron kinetic energy scales (see section 2.13 for a thoroughprocedure). An atomic photoelectron spectrum is focused and recorded whenever theimage size (V1 and V2) or laser (height or wavelength) is changed.

29+86.9 volts
extraction plate

0.0 volts
ground plate-20.0 volts
repelling plate

Figure 2.8

Potential field lines spaced at 0.5 volt computed using SIMION for theelectron photodetachment region with typical imaging voltages. The black
dot is the approximate laser-anion interaction region.

Table 2.1

Atomic copper photodetachment transitions used to focus and calibrate thevelocity map imaging photoelectron spectrometer during copper based anion
studies.

anion electronic state
and tem symbol[Ar] 4s2 3d10, 1S0

neutral electronic
configuration and term
symbolelectron binding energy
and photodetachment
threshold[Ar] 3d10 4s1, 2S1/2

1.235 eV / 1004 nm[Ar] 3d9 4s2, 2D5/2

2.624 eV / 472.5 nm[Ar] 3d9 4s2, 2D3/2

2.677 eV / 463.2 nm

To decrease the background from non-photodetached electrons, the front face of theimaging detector is held at the flight tube voltage, while the back plate is pulsed from

30

1600 volts to 2000 volts above the front face by an externally switched high voltage
pulse generator (Directed Energy PVM-4140). The high and low voltages for thispulse generator are externally provided. Switching of such a large voltage causes thevoltage on the front face of the microchannel plates to ring, causing subtle potential
differences between the MCP front face and the flight tube. These small differencesin potential create in effect a transient electron lens which causes the image size tochange with the MCP switch high time for a short duration (0 – 1 μs) after the MCPs
are brought high.

To allow for this ringing to subside, while still significantly

reducing the background, the imaging MCPs are pulsed high for 2 μs beginning 1 μs
before the arrival of the photodetachment laser pulse. The phosphor screen is held ~3,000 volts above the high voltage of the rear micro channel plate to increase theelectron detection efficiency of the phosphor and is not pulsed. See Figure 2.9 for theexperimental timing scheme.
The CCD camera is operated in a digital event counting mode. In this mode,
the CCD is exposed for 50 – 1000 ms, after which the 2D peak position of each event
over 25 analog counts is recorded. A typical data set contains 5,000 – 100,000 ofthese images which represent 125,000 to 5,000,000 laser shots and are summed. The
CCD exposure time is set such that individual events do not overlap in a single
image; otherwise the event counting macro may count these two events as a single
event, effectively reducing the number of events counted per second.

31

A
Pulsed Valve [A = T0 + (100 – 200) μs]
B

Ion Repelling Plate [B = T0 + (400 – 900) μs]

Potential Switch (comes on with Ion Repelling Plate)C

Mass Gate [C = B + (10 – 50) μs]

D

Electron Repeller (D ≈ B + 10 μs)
Laser Flash Lamp (E = F – 301.1 μs)

E

Laser Q-Switch (F ≈ ½ C +½ Anion Inline Arrival Time)F

G

Imaging MCP (G = F – 1 μs)

T0Figure 2.9

Photoelectron velocity map imaging instrument ion, laser, and detection
timing scheme.

32

The resolution of the spectrometer is approximately 2% of the electron kinetic
energy with the narrowest feature measured to date the above mentioned F− transition
with a full-width-at-half-maximum of 4 meV, as measured in the 355 nm
photoelectron spectrum.

It should be mentioned that due to the perpendicularorientation of the velocity map imaging detector relative to the ion propagation
direction, the photoelectron images are subject to a Doppler shift due to the ion
velocity. Figure 2.10 shows the effect of anion velocity on the ultimate resolution of
the spectrometer. The top panel shows raw and BASEX reconstructed (see section
2.13 for a description of the image reconstruction method) images of Cu− and thebottom panel contains similar images for F−. Notice that the ΔeKE/eKE of the copper
image is significantly smaller than that of the fluorine image. Also notice that thecopper image is much more symmetric than the fluorine image. Because of thiseffect, one should always choose the heaviest calibration anion available.

33

(a)

Cu− 600 nm (eKE = 0.831 eV, ΔeKE/eKE = 1.7)(b)

F− 325 nm (eKE = 0.413 eV, ΔeKE/eKE = 2.5)

Figure 2.10

2.12(a) Atomic copper and (b) fluoride anion raw (left) and reconstructed (right)
photoelectron images showing effect of ion velocity on image quality andresolution.

Velocity Map Imaging Instrument Tunable Nanosecond Laser System
Fundamental laser radiation at 1064 nm with 0.1 – 100 Hz repetition rate andcharacteristic pulse duration of 3 ns is produced by a Coherent Infinity laser system which
has been described in detail previously,16 thus only a moderate description is given here.
Initial 1064 nm pulses are created in a diode-pumped Nd:YAG prism in a ring resonator.
These pulses are amplified by passing twice through each of two flashlamp-pumped Nd:YAG

34rods, with the amount of amplification user defined. After amplification the 1064 nm pulses
have pulse energies up to 600 mJ. These pulses undergo frequency doubling in an angletuned BBO crystal to produce 532 nm pulses with over 50% efficiency. These 532 nm pulses
are combined with the residual 1064 nm pulses in another angle-tuned BBO crystal toproduce 355 nm pulses, again with over 50% efficiency.

At this point the Infinity is

producing intense 1064 nm, 532 nm, and 355 nm laser pulses, which can be separated by useof appropriate laser mirrors. The residual 1064 nm pulses have not been used to date and aresteered into an internal beam dump. The 355 nm pulses can be used for photodetachment, or
to pump an optical parametric oscillator (OPO), the Coherent Infinity option is called “XPO”.
The 355 nm pulses undergo difference frequency mixing in a BBO crystal to produce signal
and idler beams. The idler beam is tunable from 710 nm to 2,000 nm, while the signal beamis tunable between 410 nm and 710 nm.

Wavelength tuning is accomplished throughchanging the angle of the BBO crystal used to produce both beams. A measured tuning
efficiency curve for the signal beam is presented in Figure 2.11. Selection of signal or idler
beam is done through selection of different sets of optics. Either signal or idler radiation may
be doubled in an angle-tuned BBO crystal and compensator assembly, called the “SHG”
package by Coherent. The doubled signal efficiency curve is presented in Figure 2.12. At
710 nm the OPO is producing both signal and idler beams; this condition is called the“degeneracy” of the OPO. As the BBO crystal angle is tuned away from degeneracy, it isstill producing both signal and idler beams, both of which have large linewidths neardegeneracy. The signal beam measured linewidth as a function of wavelength is presented in
Figure 2.13.

35

20

Pulse Engergy (mJ)

18

16

14

12

10
400

450

500

550

600

650

700

750

Wavelength (nm)Figure 2.11

Infinity XPO energy per pulse as a function of wavelength measured at 250
mJ IR pump.

36

700
600

Energy (μJ/pulse)

500
400
300
200
100
0

200

220

240

260

280

300

320

340

360

Wavelength (nm)Figure 2.12

Doubled Infinity XPO energy per pulse as a function of wavelength
measured at 200 mJ IR.

37

6

5

FWHM (meV)

4

3

2

1

0
400

450

500

550

600

650

700

Wavelength (nm)Figure 2.13

Measured Infinity XPO linewidth as a function of wavelength.

Because the linewidth near degeneracy is large enough to significantly compromise
the resolution of the photoelectron velocity map imaging spectrometer, another laser sourcewith narrower linewidth must be used. Therefore the 532 nm output of the Infinity is used topump a Quanta-Ray PDL-1 dye laser, which has linewidth less than 1 meV between 600 nm
and 800 nm. Two dyes have been used for the experiments described here. One is Exciton
DCM dye which produces 610 – 690 nm pulses, and the other is Exciton LDS-698 which
produces 650 – 750 nm pulses.

Both dyes were dissolved in spectral grade methanol(Aldrich), and were frequency doubled in broad angle-tuned BBO. Attainable UV-Vis pulse
wavelengths along with their production methods, maximum pulse energies, and linewidths
are presented in Table 2.2.

38
Table 2.2

Recommended configurations, maximum pulse energies, and maximum
linewidths for production of 210 – 750 nm nanosecond laser pulses.

wavelength (nm)production method

maximum energy
per pulse

FWHM not morethan (meV)

210 – 300

OPO + BBO

1.5 mJ2266

355 nm + 532 nm

10 mJ

0.001

305 – 345

DCM + BBO

1.5 mJ

2.5

355

Infinity 3rd Harmonic

100 mJ

0.001

325 – 375

LDS 698 + BBO

1.5 mJ

2.5

420 – 625

OPO

20 mJ

2

532

Infinity 2nd Harmonic

200 mJ

0.001

610 – 690

DCM

20 mJ

1.25

650 – 750

LDS 698

20 mJ

1.25

2.13

Velocity Map Imaging Instrument Data Analysis

The center of the summed image for each data set is found by fitting a circle
to a distinct feature in the photoelectron image. This is usually done using the“overlay” option in the DaVis program. This subroutine allows one to choose theradius and the center of the image in pixels. In general it is best to choose a radius
which is 1 or 2 pixels larger than the radius of the feature to be fit. The center of theimage is found by adjusting the center of the circle to fit the experimental image byeye. While other methods exist for finding the image center, fitting a circle to the39image by eye has proven to be the most accurate and reliable method to date. Thiscenter is then used to reconstruct the full 3D distribution using the BASEX program
developed by Dribinski and co-workers,17 which outputs a 2D slice through the centerof the 3D distribution, a radial integration of this 2D slice, and angular anisotropy
parameters (β1, β2, and β3) at each radial pixel position. The photoelectron featureused to find the image center should be chosen with care as different features haveslightly different centers. The greater the difference in energy between the featureused to find the image center and the feature of interest, the worse the resolution for
the feature of interest. Figure 2.14 shows the difference in resolution caused by using
different features in a photoelectron image to find the image center. The bottom
panel contains the photoelectron spectrum attained using the feature near 2.85 eV tocenter the image, while the top panel shows the spectrum attained using the feature at
0.45 eV to find the image center. Note that the resolution in the bottom panel isbetter for high eBE features compared to the top panel. Also notice that the features
at low eBE in the bottom panel have superior resolution when compared to the samefeatures in the top panel. Thus when all features of a spectrum spanning a large
electron binding energy range are to be resolved, the center of several different
features must be used in order to attain the best resolution possible for the entire
image.

40

16000
14000

integrated counts

12000
10000
8000
6000
4000
2000
0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.0

eBE (eV)Figure 2.14

CuH− 355 nm photoelectron velocity map imaging spectrum showing
difference in resolution using different spectral features to center the image.
The arrows indicate the feature used to center the image for each trace.

The BASEX program outputs a text file with pixel in the first column andintegrated counts in the second, referred to in BASEX as a speed plot. The next stepin the data analysis is to transform the pixel axis into electron kinetic energy (eKE)and electron binding energy (eBE).

This is done by finding the constant ofproportionality in the equationeKE ∝ C × P 2(2.1)

where C is the proportionality constant and P is the distance in pixel from the image
center. The proportionality constant is unique for each image size, laser beam height,

41

and laser wavelength combination. The constant is found by making a plot of eKE
versus P2 for known atomic transitions measured in an atomic photoelectron image.
A linear function is then fit to this plot, the slope of which is the constant ofproportionality. The linear function is forced through the origin for cases when only
one atomic transition is available at the image size and laser wavelength used. The
pixel position(s) for the atomic transition(s) are found by fitting a gaussian to theatomic peak(s) in a plot of counts as a function of pixel from the image center (the“speed plot” mentioned above). Once the proportionality constant is found, the pixel
scale can be converted to eKE using equation 2.1. The scale is converted to binding
energy by subtracting the eKE from the photon energy.
Since the photodetachment cross-section varies as eKE(ℓ + ½) near threshold for
detachment from an atomic anion,18 where ℓ is the angular momentum of thephotodetached electron (ℓ = 0 for the case of detachment from a p orbital nearthreshold),19 the experimental intensities for features close to threshold (within ~ 750meV) are often scaled by this function to approximate the true relative intensities ofthe features in the spectrum.

2.14

Theoretical Geometry and Frequency Calculations and Photoelectron Spectral
Simulation Methods
Often photoelectron spectra are complex enough that theoretical calculations areneeded to aid in the spectral assignments. This may be the case because it is not clear whichanion is being photodetached (due to structural isomers, anions with the same mass or poor
mass resolution) or to understand the nature of the vibrational or electronic features present in

42
the photoelectron spectrum. Two methods for geometry and frequency calculations andspectral simulation have been used to study the systems presented here. In one, the program
ACES II20 was used to calculate the geometries and frequencies of 1,2,3-triazolide and 1,2,3triazolyl molecules, with the spectral simulation carried out using the method pioneered by
Stanton and coworkers.21 These calculations and corresponding spectral simulations were not
performed by the author, so only the results are presented here.
The method used to study all other anion systems, and that performed by the author,
is presented in detail in this section. First, the geometries and frequencies of the anion,
resulting neutral, and anion precursor parent neutral are calculated using the Gaussian suite ofprograms.22 Careful attention is paid to the starting geometry to insure the correct isomer andsymmetry is calculated.

Much information is gained by calculating the geometry andfrequencies of a particular system. From the results of the anion, radical, and anion precursor
parent calculations one can extract the electron affinity of the radical, the gas phase acidity ofthe parent, the bond dissociation energy of the parent, as well as the relative stabilities ofdifferent structural and conformational isomers.
For the purposes of anion photoelectron spectral simulations, however, thegeometries and frequencies of the anion and neutral are most important. Specifics of themethod and basis set used in the Gaussian calculations are given along with the results for
specific anions (i.e., in the chapters in which they are discussed). Once the geometries andfrequencies are calculated, the outputs are converted for input into the FCFGAUS03 programby running what is referred to as an “FCF” Gaussian job. This job essentially requests highprecision vectors and masses from Gaussian03. A generic Gaussian03 input file for this job
is presented below. For use, text in quotes should be replaced by actual files names or
methods / basis sets where appropriate.
------------------------------------------------------------------------------------------------------%chk= “check point file name of original geometry/frequency job”
# “method”/”basis set” freq=(readfc,readiso) iop(7/33=1) geom.=check guess=check43

title card info on this line
“charge” “multiplicity”
298.15 1.0 1.0“isotope data listed one per line in the order in which they are listed in the original
geometry/frequency job”------------------------------------------------------------------------------------------------------An example set of an original geometry/frequency job and corresponding FCF job is given
below.
Original Gaussian03 Job input file:------------------------------------------------------------------------------------------------------%chk=HNCHCNN-cis2-anion.chk# opt=verytight freq ub3lyp/6-311++g(d,p)
HNCHCNN cis2 anion
-1 1
N
N
C
C
H
N
H

1
2
3
4
4
6

B1
B2 1
B3 2
B4 3
B5 3
B6 4

A1
A2 1
A3 2
A4 2
A5 3

D1
D2
D3
D4

B1=1.15924647
B2=1.27271276
B3=1.41988792
B4=1.1021695
B5=1.31273286
B6=1.02223365
A1=171.7841783
A2=122.28371912
A3=112.89185454
A4=127.95431811
A5=108.59511052
D1=180.
D2=180.
D3=0.
D4=180.
-------------------------------------------------------------------------------------------------------

44
Corresponding FCF job input file:------------------------------------------------------------------------------------------------------%chk=HNCHCNN-cis2-anion.chk# ub3lyp/6-311++g(d,p) freq=(readfc,readiso) iop(7/33=1) geom=check guess=check
HNCHCNN cis2 anion FCF-1 1
298.15 1.0 1.0
14
14
12
12
1
14
1
------------------------------------------------------------------------------------------------------Once the FCF Gaussian job has been run, the output files are input into the FCFGaus03
program which reads the normal coordinates and frequencies and calculates the Dushinsky
rotation matrix J and the displacement vector K. J and K are then transformed to the Sharp &Rosenstock arrays A, B, C, D, and E. The frequencies may be scaled. In addition the atomordering and Cartesian axis of one file may be changed to match those of the other (this isessential). The outputs of the FCFGaus03 program are matrices which may be read into the
PESCAL23 program for spectral simulation.
As stated above, the PESCAL program can be used to simulate photoelectron spectra.
If using FCFGaus03 output files, the Dushinsky rotation option should be used. For thesimulation, the intensity and eKE position of the photoelectron band origin are adjustableparameters. Other adjustable parameters include the anion temperature for each normalmode, the type and full-width-at-half-maximum of a spectral convolution, and the option to
apply the hemispherical analyzer instrument sensitivity function.

Additionally, an

experimental photoelectron spectrum in .eke format may be loaded for direct comparison to
the spectral simulation.

It should be noted that the program only simulates a vertical

45
transition and does not treat vibronic coupling. Transitions to/from excited electronic states
are able to be simulated, given that their geometries and frequencies may be calculated using
Gaussian03.
Once a satisfactory simulation is complete, the transition positions and intensities(the “stick” spectrum) as well as the convolution may be saved as x, y data. Comparison of
the main features in the stick spectrum to the calculated anion and neutral frequencies allows
assignment of the modes active in the photoelectron spectrum.
References for Chapter II

1

K. M. Ervin, J. Ho, and W. C. Lineberger, Journal of Chemical Physics 91, 5974
(1989).

2

K. M. Ervin and W. C. Lineberger, in Advances in Gas Phase Ion Chemistry, editedby N. G. Adams and L. M. Babcock (JAI Press, Greenwich, 1992), Vol. 1, pp. 121.

3

D. G. Leopold, K. K. Murray, A. E. Stevens-Miller, and W. C. Lineberger, Journal ofChemical Physics 83, 4849 (1985).

4T. M. Ramond, PhD, University of Colorado, 2001.

5

C. E. Moore, Atomic Energy Levels. (US GPO Circular No. 467, Washington, 1952).

6

D. M. Neumark, K. R. Lykke, T. Andersen, and W. C. Lineberger, Physical Review A
32 (3), 1890 (1985).

7

D. H. Andrews, T. Ichino, R. M. D. Calvi, A. J. Gianola, S. Kato, J. R. Rathbone, F.
Misaizu, V. M. Bierbaum, and W. C. Lineberger, (In Press) (2006).

8

M. E. Nadal, P. D. Kleiber, and W. C. Lineberger, The Journal of Chemical Physics
105 (2), 504 (1996).

9

A. Sanov, T. Sanford, S. Nandi, and W. C. Lineberger, The Journal of Chemical
Physics 111 (2), 664 (1999).

46
10

W. C. Wiley and I. H. McLaren, Journal of Mass Spectrometry 32 (1), 4 (1997).

11

A. T. J. B. Eppink and D. H. Parker, Review of Scientific Instruments 68 (9), 3477
(1997).

12

E. Surber, R. Mabbs, and A. Sanov, Journal of Physical Chemistry A 107 (40), 8215
(2003).

13

L. A. Posey, M. J. DeLuca, and M. A. Johnson, Chemical Physics Letters 131 (3),170 (1986).

14

C. Blondel, P. Cacciani, C. Delsart, and R. Trainham, Physical Review A 40 (7), 3698
(1989).

15

R. C. Bilodeau, M. Scheer, and H. K. Haugen, Journal of Physics B-Atomic
Molecular and Optical Physics 31 (17), 3885 (1998).

16

T. J. Sanford, PhD, Colorado, 2004.

17

V. Dribinski, A. Ossadtchi, V. A. Mandelshtam, and H. Reisler, Review of Scientific
Instruments 73 (7), 2634 (2002).

18

E. P. Wigner, Physical Review 73, 1002 (1948).

19

J. Cooper and R. N. Zare, Journal of Chemical Physics 48, 942 (1968).

20

J. F. Stanton, J. Gauss, J. D. Watts, M. Nooijen, N. Oliphant, S. A. Perera, P. G.
Szalay, W. J. Lauderdale, S. A. Kucharski, S. R. Gwaltney, S. Beck, A. Balková, D.
E. Bernholdt, K. K. Baeck, P. Rozyczko, H. Sekino, C. Hober, and R. J. Bartlett,
ACES II (Quantum Theory Project, University of Florida, 2006).

21

J. F. Stanton, T. Ichino, A. J. Gianola, and W. C. Lineberger, (2006).

22

M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R.
Cheeseman, J. A. Montgomery, Jr. , T. Vreven, K. N. Kudin, J. C. Burant, J. M.
Millam, S. S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N.
Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J.
Hasegama, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li,

47
J. E. Knox, H. P. Hratchian, J. B. Cross, C. Adamo, J. Jaramillo, R. Gomperts, R. E.
Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, P. Y.
Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzewski,
S. Dapprich, A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K.
Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J.
Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L.
Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, M.
Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, C. Gonzalez, and J.
A. Pople, Gaussian 03, Revision B.05 (Gaussian, Inc., Pittsburgh, PA, 2003).
23

K. M. Ervin, PESCAL, Fortran program (2003).

48________________
Photoelectron Imaging Spectroscopy of 1,2,3-Triazolide________________
3.1

Introduction

The 1,2,3-triazoles have been the subject of many theoretical andexperimental investigations over the years. While most of the investigations wereconcerned with structural and spectroscopic properties, some have concentrated on
the biological activity,1-6 electrochemical properties,7-11 and usefulness in fuels andexplosives12,13 of 1H-1,2,3-triazole and 2H-1,2,3-triazole. The N-H deprotonated
1,2,3-triazolide anion has been the subject of only a few investigations (see Figure 3.1
for the structures of the above mentioned species).14-17 Because of the broad
importance of the azoles, recent investigations by Gianola and co-workers havemeasured the N-H bond dissociation energies of pyrrole,18 imidazole,19 and pyrazole25
via photoelectron spectroscopy of the N-H deprotonated anions and gas phase protontransfer kinetic measurements of the parent azoles. These investigations revealed thatboth the N-H and C-H sites of imidazole and pyrazole are acidic enough to be
deprotonated by hydroxide in the gas phase.

These investigations also reveal

significant vibronic coupling in the photoelectron spectra due to the presence of lowlying electronic states of the neutral radicals formed via photodetachment.

Theexperiments in this chapter are a continuation of this previous work from one and two
nitrogen-containing to three nitrogen containing azoles in an attempt to better
understand the effect of nitrogen substitution on the geometries, energetics, andthermodynamics of the azoles.

49

H

N2

N2
H
N1

C5

(a)

N1

N3

N3

C5

C4

H

H

C4

(b) H

H

N2

N2
H
N3

N1

C5

(c)

H

Figure 3.1.

N3

N1

C4

C5

H

(d)

C4

H

Molecular structures of 1H-1,2,3-triazole (a), 2H-1,2,3triazolde (b), 1,2,3-triazolide (c), and C4-1,2,3-triazolide (d).
Stuctures taken from Gaussian03 output.

50

3.2

Experimental Methods
The 1,2,3-triazolide anion was formed by deprotonation of 1H-1,2,3-triazole as

described in chapter 2. Typical anion intensities of 700 – 800 mV were detected from thepost-MCP preamp with a voltage of 1600 volts across the MCP inline detector.
Photoelectron spectra were recorded using ultraviolet photodetachment wavelengths of 320
nm, 335 nm, and 355 nm. Doubled dye laser output was used to create the 320 nm and 335
nm pulses, while the 355 nm pulses were produced by the Infinity laser system (see chapter2). The photoelectron imaging optics were set to maximize the 1,2,3-triazolide photoelectron
image size. The well known21 electron affinity of F atom observed in the photoelectron
spectrum of F− was used to both focus the photoelectron images and to calibrate the electronenergy scale.

Images were taken in the event counting mode with one second CCD

exposures and very moderate laser pulse energies of less than 200 μJ for 320 nm and 335 nm
pulses, and less than 2 mJ for 355 nm pulses.
3.3

Results

Representative 320 nm, 335 nm, and 355 nm raw and BASEX inverted
photoelectron images of 1,2,3-triazolide anion are presented in Figure 3.2.

The

320 nm images show several distinct photoelectron features at high electron velocities(outer rings), with less distinct photodetachment occurring at lower electron velocities(inner features). These images also show a large amount of detachment near the very
center of the image which is slightly off center. Most of this detachment is caused byionization of background gas by the laser pulse and is not signal from 1,2,3-triazolide.
The 335 nm photoelectron images contain all but the inner most features of the 320

51

nm images, but they are much more distinct. The greater distinctiveness of thesefeatures is mostly due to much less laser photoionization background, but also due toenhanced resolution, as the electron kinetic energies are ~ 175 meV less than in the
320 nm images. The 355 nm images contain only the outermost ring of the 320 nm
and 335 nm images. However, this wavelength has the best resolution and near zerolaser photoionization background, which allows a very accurate determination of theelectron binding energy of the main photoelectron feature, as well as the electron
affinity of the 1,2,3-triazolyl radical.
The 335 nm photoelectron spectrum is presented in Figure 3.3. The spectrum
shows transitions from the anion ground electronic and vibrational state to several
electronic and vibrational states of the 1,2,3-triazolyl neutral radical. A constantbackground of 0.1 counts has been subtracted due to the 1,2,3-triazolide spectrum
sitting atop a background of photoelectrons detached from the concurrently produced
C-H deprotonated and ring-opened isomer iminodiazomethide, which has a lower
electron binding energy (the photoelectron spectrum of iminodiazomethide ispresented in chapter 4). The intense peak labeled “a” in Figure 3.3 is assigned as theelectron affinity of the 1,2,3-triazolyl neutral radical with a value of 3.447 (4) eV,
reported to a 2σ level of uncertainty. The electron affinity of 1,2,3-triazolyl has also
been calculated at the (U)B3LYP/6-311++G(d,p) level of theory22 as 3.478 eV, ingood agreement with the experimental value.

52

(a)

------------------------------------------------------------------------------(b)------------------------------------------------------------------------------(c)Figure 3.2. 1,2,3-triazolide raw photoelectron images (left panel) and BASEX
reconstructed images (right panel) taken at (a) 320 nm, (b) 335 nm,
and (c) 355 nm.

53

1.0

a
c

normalized counts

0.8

f
0.6

h

g

d

0.4

b

e
0.2

0.0
3.70

3.65

3.60

3.55

3.50

3.45

3.40

electron binding energy (eV)Figure 3.3.

1,2,3-triazolide 335 nm photoelectron imaging spectrum (points) withconvoluted (line) transition positions and intensities (sticks).

To aid in the spectral assignments, the photoelectron spectrum of 1,2,3triazolide was simulated using the method developed by Stanton and co-workers.23
This simulation was not performed by the author, thus the details are not given here,
as they will be presented elsewhere.24 It should be mentioned, however, that thesimulation is not complete, thus only a small amount of the observed structure in thephotoelectron spectrum is assigned at this time. A full assignment of the spectrum
will be given in a future publication.24 The experimental peak positions and spectral
assignments derived from this simulation are presented in Table 3.1.

54

Table 3.1.

aPeak positions and assignments for 1,2,3-triazolide 335 nm
photoelectron spectrum.

peak labela

peak position (eV)cm−1 from origina3.447 (4)0b3.534 (4)696 (26)2c3.552 (2)846 (34)2d3.570 (3)988 (50)2e3.598 (10)1214 (108)f

3.634 (3)1497 (28)g3.657 (20)1684 (62)h3.674 (30)1825 (74)assignment
2

B1 origin

B1 , 1 quantum b2
B1 , 1 quantum a1

B1 , 2 quantum b2

See Figure 3.3.
The 320 nm and 355 nm 1,2,3-triazolide spectra, along with the 335 nm

spectrum, are presented in Figure 3.4 for comparison. Figure 3.4 illustrates thedependence of the resolution on the electron kinetic energy.

In this figure theelectron kinetic energy is increasing from left to right (high eBE to low eBE), while
the resolution is degrading in the same direction. This effect is also shown in the
resolution of the origin peak (“a” in Figure 3.3). In the 320 nm photoelectron
spectrum in Figure 3.4 the origin is a wide peak with several shoulders, in the 335 nm
spectrum the peak is narrower with one resolved peak to higher electron binding
energy. In the 355 nm spectrum, the origin is quite narrow and several features whichwere shoulders in the other spectra are there clearly resolved.

55

photoelectron counts

2.0

1.5

1.0

0.5

0.0

3.8

3.7

3.6

3.5

3.4

electron binding energy, eV

Figure 3.4.

3.3

1,2,3-triazolide photoelectron imaging spectra taken at 320 nm (toptrace), 335 nm (middle trace), and 355 nm (bottom trace).

All spectra in Figure 3.4 were taken at velocity imaging magnifications whichplaced the electron affinity feature of the 1,2,3-triazolide spectrum very near thedetector edge. In order to determine the relative amount of the iminodiazomethide
anion produced, 320 nm images were taken (see chapter 4) at a magnification which
included the photoelectron features arising from this isomer. The 1,2,3-triazolide andiminodiazomethide photoelectron features of this spectrum were integrated and aring-to-linear ratio of approximately 2.5-to-1 was found. This ratio is similar to thering-to-fragmented ratio of 2-to-1 measured in flowing afterglow-selected ion flow
tube experiments.24

56

3.4

Discussion

As mentioned in the introduction, study of the thermodynamic properties of
the azoles is one aim of the research conducted on 1,2,3-triazolide in this chapter. It
should be mentioned that the thermodynamic properties extracted from themeasurements here are all for 2H-1,2,3-triazole. This is because 1,2,3-triazolide
protonates to the more stable 2H-1,2,3-triazole neutral in the FA-SIFT experiments
used to measure the deprotonation enthalpy, and thus the derived acidity (as well as
the thermochemical cycle) corresponds to that for 2H-1,2,3-triazole. The gas phase
acidity (ΔacidG298) of 2H-1,2,3-triazole, N-H bond dissociation energy of 2H-1,2,3triazole, and radical heat of formation for 1,2,3-triazolyl were calculated as follows.
The measured24 gas phase acidity (ΔacidG298) of 2H-1,2,3-triazole was converted to thegas phase enthalpy of deprotonation (ΔacidH298) using the change in entropy between
2H-1,2,3-triazole and 1,2,3-triazolide calculated at the UB3LYP/6-311++G(d,p) levelof theory.22 The N-H bond dissociation energy was calculated by adding the electron
affinity of 1,2,3-triazolyl to the enthalpy of deprotonation of 2H-1,2,3-triazolide andsubtracting the ionization potential of the hydrogen atom. The enthalpy of formation
for the 1,2,3-triazolyl radical was evaluated by adding the enthalpy of formation andthe bond dissociation enthalpies of 2H-1,2,3-triazole and subtracting the enthalpy offormation of the hydrogen atom. Thermodynamic properties of the azoles as studied
by photoelectron spectroscopy and gas phase acidity measurements are summarizedin Table 3.2.

57

As is clear from Table 3.2, the addition of nitrogen atoms to the ringincreases the electron binding energy of the N-H deprotonated anions. As discussed
elsewhere,25 the increase in electron binding energy of the azole anions is due to thestabilization of the anion HOMO which has significant nitrogen p-orbital character.
The table also shows that the anion HOMO is also stabilized by having nitrogenatoms adjacent: the measured electron binding energy of pyrazolide is greater thanthat of imidazolide, just as the measured electron binding energy of 1,2,3,-triazolide isgreater than the calculated electron binding energy of 1,2,4-triazolide. Note that theelectron affinity of 1,2,3-triazolide calculated at B3LYP/6-311++G(d,p)22 is 3.477
eV. The ΔacidG298 values for the azoles show a very modest dependence on thearrangement of nitrogen atoms in the ring with a mild decrease with increasing
number of nitrogen atoms. Accordingly, the N-H bond dissociation energy increases
with the number of nitrogen atoms and is higher for azoles with a high number ofadjacent nitrogen atoms.

58

Table 3.2.

Thermodynamic trends in the azoles.

parent molecule
RN-H
NH

radicalelectronaffinity RN•(eV)ΔacidG298 RN-H
(kcal•mol−1)

D0 RN-H(kcal•mol−1)

radical ΔfH0
RN• (kcal•mol−1)

2.145 (10)a351.9 (4)a93.92 (11)a72.16 (2)a2.613 (6)b342.6 (4)b95.1 (5)b79.7 (6)b2.937 (6)c346.4 (3)c101.5 (5)c102.1 (5)c

3.426d337.7d110.3d108.4d340.7 (20)e114.9 (45)137.4 (93)pyrroleHN
N
imidazoleNHN
pyrazoleNNH
N

1,2,4-triazoleNNHN

3.447 (4)f

2H-1,2,3-triazole

3.477

d

a

From Reference 18b

From Reference 19

cFrom Reference 25dCalculated Using UB3LYP/6-311++G(d,p)22e

From Reference 26

fExperimentally determined in this study

59

References for Chapter III

1

C. W. Tornoe, S. J. Sanderson, J. C. Mottram, G. H. Coombs, and M. Meldal,
Journal of Combinatorial Chemistry 6 (3), 312 (2004).

2

Y. Ding, S. A. Hofstadler, E. E. Swayze, L. Risen, and R. H. Griffey, Angewandte
Chemie, International Edition 42 (29), 3409 (2003).

3

M. M. Balkis, S. D. Leidich, P. K. Mukherjee, and M. A. Ghannoum, Drugs 62 (7),1025 (2002).

4

H. M. Guardiola-Diaz, L. A. Foster, D. Mushrush, and A. D. N. Vaz, Biochemical
Pharmacology 61 (12), 1463 (2001).

5

T. Joseph-Horne and D. W. Hollomon, Fems Microbiology Letters 149 (2), 141(1997).

6

E. Stenz, G. Menzel, and G. Schuster, Mikrobiologicheskii Zhurnal (1978-1993) 43(2), 239 (1980).

7

Z. Zhou, R. Liu, J. Wang, S. Li, M. Liu, and J.-L. Bredas, Journal of Physical
Chemistry A 110 (7), 2322 (2006).

8

H. Kusama, M. Kurashige, and H. Arakawa, Journal of Photochemistry andPhotobiology, A: Chemistry 169 (2), 169 (2005).

9

K. Babic-Samardzija and N. Hackerman, Journal of Solid State Electrochemistry 9(7), 483 (2005).

10

G. Rauhut, Physical Chemistry Chemical Physics 5 (5), 791 (2003).

11

S. A. Kaluzhina and G. V. Shatalov, 1975.

12

Z. X. Chen and H. M. Xiao, Propellants Explosives Pyrotechnics 24 (5), 319 (1999).

60
13

M. Arai, T. Tsukahara, and M. Tamura, Proceedings of the International
Pyrotechnics Seminar 26th, 7 (1999).

14

R. Vianello and Z. B. Maksic, Molecular Physics 103 (2-3), 209 (2005).

15

A. A. El-Azhary, H. U. Suter, and J. Kubelka, Journal of Physical Chemistry A 102(3), 620 (1998).

16

C. Toernkvist, J. Bergman, and B. Liedberg, Journal of Physical Chemistry 95 (8),3119 (1991).

17

S. B. Bulgarevich, V. S. Bolotnikov, V. N. Sheinker, O. A. Osipov, and A. D.
Garnovskii, Zhurnal Obshchei Khimii 45 (8), 1821 (1975).

18

A. J. Gianola, T. Ichino, R. L. Hoenigman, S. Kato, V. M. Bierbaum, and W. C.
Lineberger, J. Phys. Chem. A. 108 (46), 10326 (2004).

19

A. J. Gianola, T. Ichino, R. L. Hoenigman, S. Kato, V. M. Bierbaum, and W. C.
Lineberger, J. Phys. Chem. A. 109 (50), 11504 (2005).

20

A. J. Gianola, PhD, University of Colorado, 2006.

21

C. Blondel, P. Cacciani, C. Delsart, and R. Trainham, Physical Review A 40 (7), 3698
(1989).

22

M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R.
Cheeseman, J. A. Montgomery, Jr. , T. Vreven, K. N. Kudin, J. C. Burant, J. M.
Millam, S. S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N.
Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J.
Hasegama, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li,
J. E. Knox, H. P. Hratchian, J. B. Cross, C. Adamo, J. Jaramillo, R. Gomperts, R. E.
Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, P. Y.
Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzewski,
S. Dapprich, A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K.
Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J.

61
Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L.
Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, M.
Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, C. Gonzalez, and J.
A. Pople, Gaussian 03, Revision B.05 (Gaussian, Inc., Pittsburgh, PA, 2003).
23

J. F. Stanton, T. Ichino, A. J. Gianola, and W. C. Lineberger, (2006).

24

D. H. Andrews, T. Ichino, R. M. D. Calvi, A. J. Gianola, S. Kato, G. J. Rathbone, F.
Misaizu, V. M. Bierbaum, and W. C. Lineberger, (In Preparation) (2006).

25

A. J. Gianola, T. Ichino, S. Kato, V. M. Bierbaum, and W. C. Lineberger, J. Phys.
Chem. A., (in press) (2006).

26

J. Catalán, R. M. Claramunt, J. Elguero, J. Laynez, M. Menéndez, F. Anvia, J. H.
Quian, M. Taagepera, and R. W. Taft, J. Am. Chem. Soc. 110 (13), 4105 (1988).

________________
Hemispherical Analyzer Photoelectron Spectroscopy of Iminodiazomethide________________
4.1

Introduction
This chapter presents photoelectron spectroscopy results of iminodiazomethide, a C-

H deprotonated ring-opened isomer of 1,2,3-triazole. iminodiazomethide is concurrently
produced along with 1,2,3-triazolide in the pulsed supersonic expansion source used in thephotoelectron imaging studies.

While a few photoelectron imaging spectra of

iminodiazomethide were recorded, the majority of the results reported here were obtainedusing the hemispherical analyzer photoelectron spectrometer. From the results of a spectral
simulation (see results, section 4.3, for details), the structure is E-iminodiazomethide and ispresented in Figure 4.1 along with the structures of1H-1,2,3-triazole and C5 deprotonated
1H-1,2,3-triazole. This structure is very similar to that of E-vinyldiazomethide, which is a CH deprotonated ring-opened isomer of pyrazole. Vinyldiazomethide was synthesized byreaction of the allyl anion and nitrous oxide, and its photoelectron spectrum and analysis havebeen presented elsewhere.1 Interestingly, vinyldiazomethide was not concurrently producedwith pyrazolide in the hemispherical analyzer microwave discharge source.
Fabian and coworkers have modeled the cyclization of iminodiazomethanes as apossible synthetic route to 1H-1,2,3-triazole.2

They found that the cyclization of E-

iminodiazomethane to form 1H-1,2,3-triazole was exothermic by 15 kcal mol−1, with areaction barrier of ~ 9 kcal mol−1. Trifonov and coworkers3 have modeled the ring-openingof 1,2,3-triazolide at the N-N position and found it to be highly endothermic by ~ 65 kcal
mol−1. To date, no theoretical or experimental results on the ring-opening of C4 1H-1,2,3triazolide or the ring closing of iminodiazomethide have been reported. Likewise, there have

63
been no theoretical or experimental reports in the literature on the structure or energetics ofiminodiazomethide anion or iminodiazomethyl radical. The photoelectron spectra as well as
the calculated geometries and frequencies presented here, then, are the first investigations of
the iminodiazomethide anion and the iminodiazomethyl radical.

64
N2

N2

H

H
N1

N3

C5

(a)

N1

C4

N3

C5

H

H

(b)

C4

H

H6
H7

A2

B3

A1

B1

C5

A3

N1

B4

B2

C4
A4
B5

N3

A5

B6

(c)

N2

Figure 4.1

4.2

Structures of (a) 1H-1,2,3-triazole, (b) C4 deprotonated 1H-1,2,3-triazolide,and (c) E-iminodiazomethide. Geometries calculated at the b3lyp/6311++g(d,p) level of theory.4 Structures taken directly from Gaussian03
output files.

Experimental Methods

Ultraviolet negative ion photoelectron spectra of E-iminodiazomethide havebeen obtained with the hemispherical analyzer and photoelectron velocity map
imaging spectrometers described in chapter 2.

For the hemispherical analyzer

studies, atomic oxygen anion (O⎯) was formed by microwave discharge of helium

65buffer gas (~0.5 Torr) in the presence of a trace amount of oxygen in a flowing
afterglow source. The O⎯ reacted with methane to produce hydroxide anion (HO⎯).
Then 1H-1,2,3-triazole (Sigma, 97 %) was introduced downstream via a stream ofhelium flowing over a liquid sample. HO⎯ deprotonation of 1H-1,2,3-triazole at theN-H position produced the 1,2,3-triazolide anion, while deprotonation at the C4
position (along with ring opening) produced E-iminodiazomethide (see Figure 4.1 forthe relevant molecular structures). In order to better understand the structure of
iminodiazomethide, spectra were taken using both HO− and O− to abstract a proton
from 1H-1,2,3-triazole. Because O− is a weaker base5 than HO−, it is more likely to
abstract the more acidic N-H proton than one of the less acidic C-H protons.
Photoelectron spectra were taken of the m/z = 68 ion produced with HO− (1,2,3triazolide and iminodiazomethide) and O− (1,2,3-triazolide only), and were recordedat laser electric field polarizations of 0°, 90°, and 54.7° (magic angle) with respect tothe photoelectron collection direction.
For the photoelectron velocity map imaging studies, iminodiazomethide wasproduced by passing a mixture of 10% molecular oxygen and 20% methane in argon
through a scintillated glass bubbler containing liquid 1H-1,2,3-triazole heated to
85°C. This mixture was expanded through a pulsed valve with a stagnation pressureof 45 psi. The expansion was met collinearly by a 1 keV beam of electrons, with
1,2,3-triazolide and iminodiazomethide produced via the reactions above. The 320
nm photoelectron images were recorded with imaging voltages which allowed thesimultaneous detection of photoelectrons detached from both 1,2,3-triazolide and66

iminodiazomethide. The electron energy scale was calibrated using the well-known6
electron affinity of F atom observed in the photoelectron spectrum of F−.
4.3

Results

Photoelectron spectra were measured at 351.1 nm for the anion at m/z 68
formed both in the presence of HO− and in the presence of O−. Both spectra contain afeature at high electron binding energy which is assigned to detachment from 1,2,3triazolide anion. In addition, the mass 68 anion formed in the presence of HO− also
contains a lower electron binding energy feature which is assigned to the C4
deprotonated 1,2,3-triazolide ring-opened isomer E-iminodiazomethide.

The

ΔacidH298 for deprotonation of 1H-1,2,3-triazolide was calculated at the (U)B3LYP/6311++G(d,p) level of theory4 as 390.6 kcal mol−1 for deprotonation at the C4 position
and 372.2 kcal mol−1 at the C5 position. Since the deprotonation enthalpy at the C4
position is greater than both H2O (390.3 kcal mol−1)7 and HO (382.6 kcal mol−1)5,
deprotonation at the C4 position of 1H-1,2,3,-triazole most likely does not occur inthe isolated system, nor does it effectively compete with deprotonation at the much
more acidic C1 and C5 positions. In addition, no photodetachment was observed
from C4 or C5 triazolide anion, and only ring opened C4 anion photodetachment wasobserved.

This strongly suggests that when deprotonation occurs at the carbon

positions, it either leads to fragmentation (C5) or to ring-opening (C4). Calculations
with the same basis set and method show that the E-iminodiazomethide anion is morestable than the C4 deprotonated 1H-1,2,3-triazolide anion by ~ 16 kcal mol−1, and atransition state of Cs symmetry for ring opening to form E-iminodiazomethide was

67

found ~ 19 kcal mol−1 above C4 deprotonated 1H-1,2,3-triazolide.

A probable

pathway for production of E-iminodiazomethide from 1H-1,2,3-triazolide is presented
in the discussion, section 4.4.
The

351.1

nm

hemisphericalanalyzer

photoelectron

spectrumofiminodiazomethide formed in the presence of HO− is presented in Figure 4.2. The
intense peak at 2.484 (5) eV electron binding energy is assigned as the electron
affinity of the iminodiazomethyl neutral radical. The peaks to lower electron binding
energies are transitions from excited vibrational states of the anion, while the peaks tohigher electron binding energy are transitions to excited vibrational states of theneutral radical. To aid the spectral assignments, the geometry and frequencies ofseveral geometric isomers of the iminodiazomethane anion and neutral were
calculated at the (U)B3LYP/6-311++G(d,p) level of theory.4

The 351.1 nm

photoelectron spectrum was simulated for all isomers in order to confirm which
iminodiazomethide isomer is the signal carrier for the photoelectron spectrum. It was
found that the E form of iminodiazomethide gave the most accurate spectral
simulation, thus the signal carrier is identified as E-iminodiazomethide.

Theadiabatic electron affinity extracted from these calculations is 2.339 eV, in good
agreement with the experimental value.

The general structure of E-

iminodiazomethane is presented in Figure 4.1, with the optimized anion and neutral
radical geometries presented in Table 4.1.

68

Photoelectron Counts

800

C

700
600

D
E

500
400

B

F

300

G

200

A

100
0
2.9

2.8

2.7

2.6

2.5

2.4

2.3

electron binding energy (eV)Figure 4.2

351.1 nm photoelectron spectrum of iminodiazomethide anion. The points
are the experimental data. Transition energies and intensities from a FrankCondon calculation (sticks) which are convoluted by the instrument
resolution function (line) are also presented.

69
Table 4.1

E-iminodiazomethane anion and neutral radical calculateda structures. See
Figure 4.1 for bond length and angle definitions.
Anion

Neutral Radicalbond lengths (Å)

bond angles (deg.)bond lengths (Å)

bond angles (deg.)

B1 = 1.02

A1 = 108.6

B1 = 1.02

A1 = 110.5

B2 = 1.31

A2 = 119.1

B2 = 1.29

A2 = 123.0

B3 = 1.10

A3 = 112.9

B3 = 1.09

A3 = 114.7

B4 = 1.42

A4 = 122.2

B4 = 1.44

A4 = 119.8

B5 = 1.27

A5 = 171.8

B5 = 1.29

A5 = 170.0

B6 = 1.16a

B6 = 1.14

Calculated at (U)B3LYP/6-311++G(d,p)4

The optimized geometries and normal mode frequencies of the anion andneutral were used to perform an initial Franck-Condon simulation using the PESCAL
program.8,9 The position and intensity of the electron affinity peak in this simulation
were set to match the experimental values. While this simulation (not shown) is inqualitative agreement with the measured spectrum, the transition positions were insignificant error (~ 10%). Rather than use this simulation to directly make thespectral assignments, the simulation was used to identify the normal modes active in

70

the observed spectrum. In a second simulation the frequencies of the main spectralfeatures were set to the values observed in the experimental spectrum (found bymeasuring the spectral distance from the origin). These new line positions andintensities were convoluted by a Lorenzian function with a 15 meV full-width-at-halfmaximum. This second simulation is in excellent agreement with the experimental
spectrum, allowing for confident spectral assignments.

The peak positions andassignments are presented in Table 4.2, while the simulated spectrum is presented
along with the experimental spectrum in Figure 4.2.

Table 4.2

aPeak positions and assignments for E-iminodiazomethide photoelectron
spectrum.

peak labela

peak position(eV)

cm−1 from origin

assignment

excited motion

A

2.428

-452 (12)310

C-N-N bend

B

2.461

-184 (7)110

C-C-N bend

C

2.484

0

0 00

−

D

2.510

213 (5)210

C-C-N bend

E

2.538

441 (5)410

C-N-N bend

F

2.574

730 (12)610 and 210 410

ν6 = C-C-N bend

G

2.712

1837 (14)1310

N-N stretch

See Figure 4.2.

71

The polarization measurements reveal an anisotropy parameter of ~ −0.36 forall features in the spectrum. This suggests that the photodetached electrons originate
from the same molecular orbital in the anion, further confirming the assignments(which simulated photodetachment producing a single electronic state in the neutral
radical).
The 320 nm photoelectron velocity map raw and BASEX reconstructed
images are presented in Figure 4.3. The corresponding photoelectron spectrum ispresented in Figure 4.4, with the inner (low eKE, high eBE) features assigned tophotodetachment from 1,2,3-triazolide and the outer (high eKE, low eBE) features
assigned to photodetachment from E-iminodiazomethide. The 1,2,3-triazolide and Eiminodiazomethide photoelectron features of this spectrum were integrated and aring-to-linear ratio of approximately 2.5-to-1 was found. This ratio is similar to thering-to-fragmented ratio of 2-to-1 measured in a flowing afterglow-selected ion flow
tube experiment.10

Figure 4.3

320 nm photoelectron velocity map imaging raw (left) and BASEX
reconstructed (right) images containing features arising from 1,2,3-triazolide(inner) and E-iminodiazomethide (outer) photodetachment.

72

Threshold Corrected Integrated Counts

6000

1,2,3-triazolide
5000

4000

3000

Iminodiazomethide
2000

1000

0
3.5

3.0

2.5

2.0

eBE (eV)Figure 4.4

4.4

320 nm velocity map imaging photoelectron spectrum containing features
arising from photodetachment of 1,2,3-triazolide (high eBE) andiminodiazomethide (low eBE).

Discussion

The electron binding energy of E-iminodiazomethide, 2.461 (8) eV, isconsiderably less than the electron binding energy of 1,2,3-triazolide, 3.447 (4) eV.
This is most likely due to the aromaticity of the 1,2,3-triazolide ring whichsignificantly stabilizes the anion, and is absent in the E-iminodiazomethide structure.
The observed photoelectron spectrum and the calculated geometry of Eiminodiazomethide are very similar to that of E-vinyldiazomethide,1 while the73electron binding energy is approximately 630 meV higher, due to the electron
stabilization caused by the presence of an additional nitrogen atom.
As mentioned in section 4.3, the ring opening of C4 deprotonated 1H-1,2,3triazole to form E-iminodiazomethide does not occur in the isolated system.
However, deprotonation at the C4 position to form an ion-dipole complex of C4-1H1,2,3-triazolide and water was calculated4 at the UB3LYP/6-311++G(d,p) level oftheory to be exothermic by ~ 24 kcal mol−1. Since deprotonation to form theseparated products was calculated to be slightly endothermic, the exothermicity of the
deprotonated ion-dipole complex is due entirely to the ion-dipole complexationenergy. It is reasonable to assume that the barrier to ring-opening is not significantly
higher in the ion-dipole complex than in the isolated anion, thus the complex has
enough energy to overcome this barrier. Likewise, the transition state for dissociationof the ring-opened anion water complex must lie below the energy of the isolated
reactants (1H-1,2,3-triazolide and hydroxide). This reaction scheme is consistent
with the experimental observation that E-iminodiazomethide is produced while C4
deprotonated 1H-1,2,3-triazolide is not.

The energetics of the ring-opening arepresented in Figure 4.5.
This is opposite of the experimental observations in pyrazole11 and imidizole12
where the C4 deprotonated ions were observed without ring-opening. Deprotonation
at the C4 site of these azoles was calculated to be exothermic by several kcal mol−1.
The transition state for dissociation of the lower azole C4 deprotonated ion-dipole
complex to remove water is significantly loose compared to the transition state for74

ring-opening of the C4 deprotonated anion, thus dissociation of the ion-dipole
complex is much more likely than ring-opening of the anion.
C− + H2O

CH + HO−RO− + H2OTS

C− • H2O
RO− • H2O

Figure 4.5

Reaction energetics for production of E-iminodiazomethane from 1H-1,2,3triazole. CH represents 1H-1,2,3-triazole, C− represents C4 deprotonated 1H1,2,3-triazole, TS is the ring-opening transition state, and RO− represents Eiminodiazomethide.

75
References for Chapter IV

1

A. J. Gianola, PhD, University of Colorado, 2006.

2

W. M. F. Fabian, V. A. Bakulev, and C. O. Kappe, Journal of Organic Chemistry 63(17), 5801 (1998).

3

R. E. Trifonov, I. Alkorta, V. A. Ostrovskii, and J. Elguero, Heterocycles 52 (1), 291(2000).

4

M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R.
Cheeseman, J. A. Montgomery, Jr. , T. Vreven, K. N. Kudin, J. C. Burant, J. M.
Millam, S. S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N.
Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J.
Hasegama, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li,
J. E. Knox, H. P. Hratchian, J. B. Cross, C. Adamo, J. Jaramillo, R. Gomperts, R. E.
Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, P. Y.
Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzewski,
S. Dapprich, A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K.
Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J.
Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L.
Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, M.
Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, C. Gonzalez, and J.
A. Pople, Gaussian 03, Revision B.05 (Gaussian, Inc., Pittsburgh, PA, 2003).

5

E. P. Hunter and S. G. Lias, in NIST Chemistry WebBook, NIST Standard Reference
Database Number 69, edited by P. J. Linstrom and W. G. Mallard (National Instituteof Standards and Technology, Gaithersburg MD, 20899, 2005).

76
6

C. Blondel, P. Cacciani, C. Delsart, and R. Trainham, Physical Review A 40 (7), 3698
(1989).

7

J. R. Smith, J. B. Kim, and W. C. Lineberger, Physical Review A 55, 2036 (1997).

8

K. M. Ervin, PESCAL, Fortran program (2003).

9K. M. Ervin, T. M. Ramond, G. E. Davico, R. L. Schwartz, S. M. Casey, and W. C.
Lineberger, Journal of Physical Chemistry A 105 (48), 10822 (2001).

10

D. H. Andrews, T. Ichino, R. M. D. Calvi, A. J. Gianola, S. Kato, G. J. Rathbone, F.
Misaizu, V. M. Bierbaum, and W. C. Lineberger, (In Press) (2006).

11

A. J. Gianola, T. Ichino, S. Kato, V. M. Bierbaum, and W. C. Lineberger, J. Phys.
Chem. A., (in press) (2006).

12

A. J. Gianola, T. Ichino, R. L. Hoenigman, S. Kato, V. M. Bierbaum, and W. C.
Lineberger, J. Phys. Chem. A. 109 (50), 11504 (2005).

77________________
Hemispherical Analyzer Photoelectron Spectroscopy of AgO−, AuO−, and AuS−________________
5.1

Introduction
Silver and gold metal oxides have been the subject of both experimental andtheoretical investigations because of their usefulness in catalysis,1-8 as electrodes in powercells,9 and as thin film substrate materials for surface-enhanced Raman spectroscopy(SERS).10 Several experimental11-18 and theoretical19-23 investigations have reported bondlengths, vibrational frequencies, spin-orbit splittings, and term energies for the neutral groundstate and several electronic excited states of AgO.

Likewise there have been few

experimental24-27 and theoretical28,29 investigations of AuO properties. To date the only
investigations of gold or silver oxide anions are those reported here.30,31 In addition, very
little experimental26,32,33 and theoretical34-36 attention has been paid to the AuS molecule.
Most recently O’Brien14 has measured the harmonic frequencies, bond lengths, andelectronic term energies for the ground 2Πi and excited 2Σ+ states of AgO.

The bond

dissociation energy of AgO has been measured by Smoes and coworkers.26 O’Brien27 has
also recently reported the bond lengths, vibrational frequencies, and spin-orbit splittings forthe 2Πi ground states of AuO. A moderate resolution photoelectron spectrum of AuS− hasbeen reported by Nakajima,32 with only the electron affinity and ground state spin-orbit
splitting reported.
This chapter presents the results of hemispherical energy analyzer phototelectron
studies of AgO−, AuO−, and AuS−. The experimental conditions are briefly explained in
section 5.2, the photoelectron spectroscopy and spectral simulations are presented in section

78
5.3, comparison of transition metal oxide photoelectron results are presented in section 5.4,
and some brief conclusions are made in section 5.5
5.2

Experimental Methods
Photoelectron spectra were taken using the hemispherical analyzer photoelectron

spectrometer described in Chapter 2. Briefly, AgO− was produced by sputtering a silver rod(Goodrich) in 500 mtorr of He/Ar and reacting the resulting plasma with oxygen. AuO− wasproduced in a similar manor using a gold rod (Goodrich). AuS− was produced by reacting agold plasma with CS2 (Aldrich, 97%). After production the ions were mass selected by aWein velocity filter resulting in typical anion beams of a few picoamps of current.
Photoelectron spectra were recorded using 363.8 nm radiation to photodetach the anions.
Spectra were taken with the angle between the laser electric field vector and thephotoelectron collection axis at 54.7° (magic angle), 0°, and 90°.
5.3.1

AgO− Results
A survey of the photoelectron spectrum of AgO− shows photodetachment in theregion between 1.5 eV and 2.8 eV electron binding energy. The features in this range areplotted in Figures 5.1(a) and 5.1(b). The single peak in Figure 5.1(a) at 2.70 eV binding
energy is the transition to the ν = 0 level in the A 2Σ+ state of AgO. Peaks C, E, and G in
Figure 5.1(b) are transitions from the anion ground state to the ν = 0, 1, and 2 levels, in the X2

Π3/2 state of AgO, respectively. Peaks D, F, and H are transitions from the anion groundstate to the ν = 0, 1, and 2 levels, in the X 2Π1/2 state of AgO, respectively. Peaks A and B
are vibrational hotband transitions from the anion ν = 1 state to the ground vibrational level inthe X 2Π3/2 and X 2Π1/2 states of AgO, respectively. The position of peak C defines theelectron affinity of AgO as 1.655(4) eV. Many of the experimental investigations11,17,18,24

79
report a 2Π state lying about 24,400 cm−1 above the ground state, which was not accessible by
the photon energy used here.
The peak assignments were confirmed by simulating the vibrational progression in
Figure 5.1(b). A Franck-Condon simulation of the data in Figure 5.1(b) using the program
PESCAL37,38 was carried out as follows. The anion and neutral electronic ground states weremodeled as Morse oscillators. The neutral parameters (re, ωe, ωexe) were fixed to known
literature values.12,16 The lack of a vibrational progression for transitions to the A state showsthat the anion bond length and the neutral A state bond lengths are essentially identical. Thus
the anion equilibrium bond length was fixed at the 1.935 Å neutral A 2Σ+ state literature
value,14and only the anion harmonic vibrational frequency ωe was allowed to vary,effectively determining the hot band position. Franck-Condon factors were determined bynumerical integration of the Laguerre wave function solutions39 to the Morse potentials. The
instrumental lineshape was modeled as a Gaussian with 15 meV full width at half maximum.
Other parameters input into the simulation were the 0-0 transition position and height and theanion temperature (~300 K). The simulated spectrum is plotted in Figure 5.1(b) as a solidline.

Molecular constants and electronic state splittings derived from the transition

assignments and the Franck-Condon simulation are summarized in Table 5.1, along withrecent literature values for comparison. The electronic ground state of AgO− is found to havea vibrational frequency of 497 (15) cm−1 and an equilibrium bond length of 1.935 (2) Å. The
neutral A state term energy and the X state spin-orbit splitting and vibrational frequency
reported here are in good agreement with the known literature values.14
The adiabatic dissociation energy of AgO− to Ag + O− can be obtained from athermodynamic cycle:
D0 (AgO−) = D0 (AgO) – EA (O−) + EA (AgO)

(5.1)

80
The dissociation energy of AgO has been determined to be 2.29(15) eV from a mass
spectrometric Knudsen cell measurement,26 while the electron affinity of O−[1.461 122(3)eV] is well known.40 Using the EA (AgO) measured in this work, the D0(AgO−) obtained is2.48(15) eV [57.2(3.5) kcal mol−1]. The accuracy of this dissociation energy is limited by themass spectrometric Knudsen cell measurement. A quantity measured with greater accuracy isthe difference in bond strengths:
D0 (AgO−) − D0 (AgO) = 0.193(2) eV [4.45(5) kcal mol−1](5.2)

This difference in dissociation energies clearly shows that AgO− is more strongly bound than
AgO.

Photoelectron Counts

5000

(a)

81

4000
3000
2000
1000
0
3.0

2.9

2.8

2.7

2.6

2.5

Electron Binding Energy (eV)
800

(b)

Photoelectron Counts

D C

600

400

F E

200

H G

B A

0
2.0

1.9

1.8

1.7

1.6

1.5

Electron Binding Engery (eV)Figure 5.1

364 nm photoelectron spectra of AgO− showing transitions to the (a) 2Σ+
excited state and (b) 2Πi spin-orbit split ground states of AgO. The points are
the data and the solid line is a Franck-Condon simulation.

82
Spectroscopic constants for AgO− and AgO.

Table 5.1

ωe (cm−1)

Te (eV)
State

−

1 +

AgO (X Σ )2

AgO (X Π3/2)

2

AgO (X Π1/2)

2 +

AgO (A Σ )aFrom reference 14bThis workc

Best value

5.3.2

This work

Literaturea

This work

Literaturea

re (Å)−1.655 (4) c−

497 (20) c−

1.935 (2) b,c

0−481 (15)485 c

2.005 a,c

0.033 (5)0.033 c481 (15)485 c

2.005 a,c

1.045 (8)1.045 c−−1.935 a,c

AuO− Results
Unlike the AgO− photoelectron spectrum, only transitions from the anion groundelectronic state to the 2Πi states of AuO are observed in the 363.8 nm photoelectron spectrumof AuO−. The 363.8 nm photoelectron spectrum is presented in Figure 5.2. The spectrum
contains a strong transition to the neutral ν = 0 vibrational level of the X 2Π3/2 electronic state(peak A), which is assigned as the electron affinity with a value of 2.374(7) eV. A very weaktransition to the ν = 1 vibrational level of this state is also observed (peak B). In contrast, thetransition to the ν = 1 level in the 2Π1/2 state (peak D) has a much higher intensity, though it
remains less intense than the transition to the ν = 0 (peak C). The vibrational frequency ofthe 2Π3/2 state is 620 (15) cm−1, while the vibrational frequency for the 2Π1/2 state is 570 (15)cm−1. The spin-orbit splitting of the ground state is the splitting of peaks A and C and is83
found to be 0.179 (10) eV. The anisotropy parameters for peaks A and C were found to be –0.25 and 0.50, respectively. The large difference in anisotropy parameters suggests that thesetwo peaks arise from different electronic states, strengthening the electronic origin
assignments.
To further confirm the spectral assignments, and to determine the difference in bondlength between the anion and neutral AuO, Franck-Condon simulations were performed as
described above. In these simulations the neutral 2Π3/2 state bond length was set at thecurrent literature value (1.912 Å)27 and hot band transitions were not considered.

The

simulated spectrum is presented in Figure 5.2 as the solid line. The change in bond length
between the anion X 1Σ+ electronic state and the neutral X 2Π3/2 state is found to be 0.010 (2)Å and 0.020 (2) Å for detachment to the 2Π1/2 state. The spectroscopic constants derived
from the spectral simulations are presented in Table 5.2.

From equation 1 above, thecalculated difference in bond dissociation energies (D0) between AuO− and AuO is:
D0(AuO−) – D0(AuO) = EA (AuO) – EA(Au) = 0.065 (7) eV

Table 5.2

(5.3)

Spectroscopic constants for AuO− and AuO.

State

Te (eV)ωe (cm−1)

Δre (Å)AuO− (X 1Σ+)

−2.374 (7)not observed0

AuO (X 2Π3/2)

0620 (15)0.010 (2)AuO (X 2Π1/2)

0.179 (10)570 (15)0.020 (2)

84

7000

C

photoelectron counts

6000
5000
4000

A

3000
2000
1000
0
2.80

D
2.75

2.70

2.65

2.60

B
2.55

2.50

2.45

2.40

2.35

2.30

electron binding energy (eV)Figure 5.2

5.3.3

363.8 nm photoelectron spectrum of AuO− showing transitions to the 2Πiground states of AuO.

AuS− Results
Much like the AuO− photoelectron spectrum, the AuS− 363.8 nm photoelectron

spectrum contains transitions from the anion ground electronic ν = 0 state to the neutral 2Πispin-orbit split states, with no higher lying electronic states accessible. The spectrum ispresented in Figure 5.3. The AuS− spectrum contains a transition to the ν = 1 vibrational
level of both the 2Π3/2 state (peak C) and the 2Π1/2 state (peak E), though the magnitude ofpeak E is much less than that of peak C. In addition, the AuS− photoelectron spectrum
contains a hot band transition (peak A) which is built off of the origin peak. The measured
angular anisotropy parameters of 0.15 for peak B and 0.30 for peak D confirm that thesetransitions involve different electronic states. Thus peak B is assigned as the electron affinityof AuS with a value of 2.469 (6) eV, while the spin-orbit splitting of the 2Πi states is found to85
be 0.159 (7) eV from the splitting of peaks B and D. Spacings between peaks B and C (aswell as peaks D and E) define the neutral vibrational frequency of the 2Πi states as 400 (15)cm−1. Similarly, the spacing between peaks A and B defines the anion ground 1Σ+ statevibrational frequency as 380 (15) cm−1.
The extremely small magnitude of the vibrational progression of the transition to the2Π1/2 state of AuS strongly suggests that the equilibrium bond length change between thisstate and the anion ground state is very small.

In contrast, the moderate vibrational

progression of the 2Π3/2 state suggests a modest bond length change between that state and theanion ground state.

Unfortunately there are no reports of an experimentally obtained

equilibrium bond length for AuS or AuS−, thus only the relative bond lengths can beobtained. To do this, and to confirm the spectral assignments above, the AuS− photoelectron
spectrum was simulated. The simulation for transitions to both the 2Πi states is presented in
Figure 5.3 as the solid line. The difference in bond length between the anion and the 2Π3/2
state was found to be 0.030 (2) Å, while the bond length change between the anion and the2

Π1/2 state was found to be 0.011 (2) Å. The difference in bond dissociation energies between

the anion and neutral is found as above to be
D0(AuS−) – D0(AuS) = EA (AuS) – EA (Au) = 0.160(6) eV(5.4)

The derived spectroscopic constants for AuS− and AuS are summarized in Table 5.3.
Table 5.3

Spectroscopic constants for AuS− and AuS.

State

Te (eV)ωe (cm−1)

Δre (Å)AuS− (X 1Σ+)−2.469 (6)380 (15)

0

AuS (X 2Π3/2)

0400 (15)0.030 (2)AuS (X 2Π1/2)

0.159 (7)400 (20)0.011 (2)

86

1800

D

photoelectron counts

1600
1400

B

1200
1000
800
600
400

C
E

200
0
2.85

2.80

2.75

2.70

A
2.65

2.60

2.55

2.50

2.45

2.40

2.35

electron binding energy (eV)Figure 5.3

5.4

AuS− 363.8 nm photoelectron spectrum showing transitions to the spin-orbit
split 2Πi states of AuS.

Discussion
The negative ion photoelectron spectra of copper,41 silver, and gold oxides areamazingly simple, especially when compared to the photoelectron spectra of the nickel,
platinum, and palladium oxides.42 The relative simplicity is due in most part to the small
number of accessible low lying atomic electronic states of the coinage metal (group 11)
oxides (two or three) as compared to the group 10 oxides (minimum four). The difference ofcourse is the s1 d10 valence electronic configuration of the group 11 metals as compared to thes2 d8 valence electronic configuration of the group 10 metals. The coinage metal oxide
neutrals (AgO, AuO, CuO) are well described23 by an ionic M+(s1d10) O−(2s22p5)

87
configuration. This configuration leads to pσ2pπ3 2Πi ground states and pσ1pπ4 2Σ+ low lying
excited states (not observed in the AuO− photoelectron spectrum). Assuming a one photon
process for photodetachment, the anions then have pσ2pπ4 1Σ+ ground states.
Insight into the bonding character of the π and σ molecular orbitals of the group 11
metal oxide (sulfide) anions may be gained by examining the bond length change between theanion and neutral derived from the Franck-Condon spectral simulations. These bond lengthchanges along with the electron affinities, and electronic term energies are presented in Table
5.4. The equilibrium bond length change between the anion the neutral for removal of the anelectron from the anion π orbital to produce the neutral 2Πi states is moderate for CuO andAgO, and less for AuO and AuS. This suggests that these electrons are mildly bonding in
CuO− and AgO−, and weakly bonding in AuS− and AuO−. Furthermore, removal of a σelectron to produce the 2Σ+ state produces a mild bond length change for CuO, and no bondlength change for AgO (this state was not spectroscopically accessible in the AuO− and AuS−
photoelectron experiments). Therefore, the σ electrons are slightly bonding in CuO− and nonbonding in AgO−.
Examination of the other spectroscopic constants in Table 5.4 reveals very little
difference in the electron affinities, spin-orbit splittings, and 1Σ+ state term energies of CuO
and AgO. There is significant difference between CuO/AgO and AuO/AuS, however. Thisdifference is attributed to the significant relativistic effects of Au.43-45 The larger electron
affinity of AuO/AuS (and Au) is caused by the contraction of the Au 6s orbital. The spinorbit splitting of the 2Πi states, while nearly identical for CuO and AgO, is much larger for
AuO and AuS, due to these relativistic effects.

88Table 5.4

Comparison of spectroscopic constants for CuO, AgO, and AuO.
2 +

Σ state2anion-neutral Δre (Å)

2

oxide

electronaffinity (eV)

Π3/2 – Π1/2
splitting (eV)Te (eV)

CuO

1.777

0.035

AgO

1.655

AuO
AuS

Πi

2 +

0.977

0.054

0.034

0.033

1.045

0.070

0

2.374

0.179

not observed a

0.020

−

2.469

0.159

not observed a

0.030

−

2

Σ

The term energy for this electronic state was too high to be accessed with the photon energy
used in this studyaReferences for Chapter V

1

J. D. Grunwaldt and A. Baiker, Journal of Physical Chemistry B 103, 1002 (1999).

2

J. D. Grunwaldt, M. Maciejewski, O. S. Becker, P. Fabrizioli, and A. Baiker, Journalof Catalysis 186 (2), 458 (1999).

3

M. Haruta, Catalysis Today 36 (1), 153 (1997).

4

M. Haruta, N. Yamada, T. Kobayashi, and S. Iijima, Journal of Catalysis 115 (2),301 (1989).

5

Z. P. Liu, P. Hu, and A. Alavi, Journal of the American Chemical Society 124 (49),14770 (2002).

89
6

N. Lopez and J. K. Norskov, Journal of the American Chemical Society 124 (38),11262 (2002).

7

M. Valden, X. Lai, and D. W. Goodman, Science 281 (5383), 1647 (1998).

8

C. Yang and Z. Y. Meng, Applied Catalysis 71 (1), 45 (1991).

9D. F. Smith, G. R. Graybill, R. K. Grubbs, and J. A. Gucinski, Journal of Power
Sources 65 (1-2), 47 (1997).

10

D. Buchel, C. Mihalcea, T. Fukaya, N. Atoda, J. Tominaga, T. Kikukawa, and H.
Fuji, Applied Physics Letters 79 (5), 620 (2001).

11

V. Bojovic, A. Antic-Jovanovic, M. M. Stoiljkovic, M. Miletic, and D. S. Pesic,
Spectroscopy Letters 32 (5), 875 (1999).

12

L. C. O'Brien, S. J. Wall, and G. L. Henry, Journal of Molecular Spectroscopy 191(1), 218 (1998).

13

T. Steimle, M. Tanimoto, K. Namiki, and S. Saito, Journal of Chemical Physics 108(18), 7616 (1998).

14

L. C. O'Brien, S. J. Wall, and M. K. Sieber, Journal of Molecular Spectroscopy 183(1), 57 (1997).

15

B. R. Vujisic, J. J. Savovic, V. Bojovic, and D. S. Pesic, Spectroscopy Letters 26 (8),1529 (1993).

16

M. J. Griffiths and R. F. Barrow, Journal of Physics B 10 (5), 925 (1977).

17

U. Uhler, Arkiv For Fysik 7 (12), 125 (1953).

18

F. W. Loomis and T. F. Watson, Physical Review 48, 280 (1935).

19

G. Igel, U. Wedig, M. Dolg, P. Fuentealba, H. Preuss, H. Stoll, and R. Frey, Journalof Chemical Physics 81 (6), 2737 (1984).

20

C. W. Bauschlicher, C. J. Nelin, and P. S. Bagus, Journal of Chemical Physics 82 (7),3265 (1985).

21

P. J. Hay and R. L. Martin, Journal of Chemical Physics 83 (10), 5174 (1985).

90
22

J. Andzelm, E. Radzio, and D. R. Salahub, Journal of Chemical Physics 83 (9), 4573
(1985).

23

C. W. Bauschlicher, H. Partridge, and S. R. Langhoff, Chemical Physics 148 (1), 57(1990).

24

M. J. Griffiths and R. F. Barrow, Journal of the Chemical Society-Faraday
Transactions II 73, 943 (1977).

25

A. Hecq, M. Vandy, and M. Hecq, Journal of Chemical Physics 72 (4), 2876 (1980).

26

S. Smoes, F. Mandy, A. Vander Auwera-Mahieu, and J. Drowart, Bulletin desSocietes Chimiques Belges 81 (1-2), 45 (1972).

27

L. C. O'Brien, S. C. Hardimon, and J. J. O'Brien, Journal of Physical Chemistry A
108 (51), 11302 (2004).

28

P. Schwerdtfeger, M. Dolg, W. H. E. Schwarz, G. A. Bowmaker, and P. D. W. Boyd,
Journal of Chemical Physics 91 (3), 1762 (1989).

29

J. M. Seminario, A. G. Zacarias, and J. M. Tour, Journal of the American Chemical
Society 121, 411 (1999).

30

D. H. Andrews, A. J. Gianola, and W. C. Lineberger, Journal of Chemical Physics
117 (8), 4074 (2002).

31

T. Ichino, A. J. Gianola, D. H. Andrews, and W. C. Lineberger, Journal of Physical
Chemistry A 108 (51), 11307 (2004).

32

A. Nakajima, T. Taguwa, K. Nakao, K. Hoshino, S. Iwata, and K. Kaya, Surface
Review and Letters 3 (1), 417 (1996).

33

K. A. Gingerich, Journal of the Chemical Society [Section] D: Chemical
Communications (10), 580 (1970).

34

Z. J. Wu, Journal of Physical Chemistry A 109 (26), 5951 (2005).

35

G. Bravo-Perez and I. L. Garzon, Theochem 619, 79 (2002).

91
36

P. J. Renders and T. M. Seward, Geochimica et Cosmochimica Acta 53 (2), 245(1989).

37

K. M. Ervin, T. M. Ramond, G. E. Davico, R. L. Schwartz, S. M. Casey, and W. C.
Lineberger, Journal of Physical Chemistry A 105 (48), 10822 (2001).

38

K. M. Ervin, Fortran PESCAL (Reno, NV, 2001).

39

K. Cashion, Journal of Molecular Spectroscopy 10, 182 (1963).

40

D. M. Neumark, K. R. Lykke, T. Andersen, and W. C. Lineberger, Physical Review A
32 (3), 1890 (1985).

41

M. L. Polak, M. K. Gilles, J. Ho, and W. C. Lineberger, Journal of Physical
Chemistry 95 (9), 3460 (1991).

42

T. M. Ramond, G. E. Davico, F. Hellberg, F. Svedberg, P. Salen, P. Soderqvist, andW. C. Lineberger, Journal of Molecular Spectroscopy 216 (1), 1 (2002).

43

P. Pyykko, Chemical Reviews 88 (3), 563 (1988).

44

K. S. Pitzer, Accounts of Chemical Research 12 (8), 272 (1979).

45

P. Pyykko and J. P. Desclaux, Accounts of Chemical Research 12 (8), 276 (1979).

92________________
Photoelectron Velocity Map Imaging of CuH− and CuH2−________________
6.1

Introduction
Interest in the copper hydride anions CuH− and CuH2− arose during the studies of thecopper-methanol and copper-methoxy anion complexes reported in Chapter 7. In an effort tolocate copper anion in the spectrum, photoelectron images of CuH− and CuH2− were taken. It
was assumed that photoelectron spectra had previously been taken of these very basic
molecules, but following a rigorous literature search, it was found that they had not. CuH2
and CuH2− have been studied in a series of publications by the Andrews group.1-3 In theseexperiments, laser ablated copper atoms were co-deposited either with pure H2 or H2 and arare gas (Ar or Ne) onto a cold window forming a rare gas or H2 matrix. Infrared spectra
were then taken and the spectral lines assigned with the aid of DFT calculations of thefundamental vibrational frequencies. These studies identified the ground electronic state of
CuH2− to be linear (1Σ+) with a CuH bond length of 1.456 Å and CuH2 to be bent (2B2) withbond length of 1.527 Å and bond angle of 122.6°. The calculations also predict that groundstate CuH2 is higher in energy than Cu and H2, and was only observed by trapping in cold
matrices.
In the case of CuH, some experimental investigators have reported the production,4,5dissociation energy,5-8 and thermodynamic properties.9,10

However, most experimental

investigators have reported the ultraviolet-visible,11-13 infrared,2,3,14-16 and microwave17 spectraof neutral copper hydride and copper deuteride.

Likewise, copper hydride has been

extensively studied theoretically as a benchmark for the treatment of transition metals,18-39 as
well as to test the treatment of relativistic effects.40-50 Both Hliwa24 and Marian28 have

93
reported results which are in good agreement with current experimental data on the
spectroscopic constants of the low lying 1Σ+ states of CuH. They also predict spectroscopic
constants for a low lying 3Σ+ state which was first identified experimentally in thephotoelectron spectra reported here.
The electronic binding energies of the CuH low lying electronic states are similar to
the electron binding energies observed in the copper anion 355 nm photoelectron spectrum
presented in Figure 6.1. Also presented in Figure 6.1 is an energy level diagram showing thetransition energies and term symbols for transitions from the copper anion ground state to thethree lowest lying electronic states of neutral copper atom.
The remainder of this Chapter is partitioned as follows. Experimental methods arepresented in Section 6.2. Results on CuH− and CuD− are presented in Section 6.3, while
those on CuH2− and CuD2− are presented in Section 6.4. Non-trivial spectral assignments arepresented in Section 6.5.

94

8000

Cu 2D3/2
2.878 eVCu 2D5/2

Counts6000

2.623 eV4000

Cu 2S01.236 eV2000

Cu− 1S00.000 eV

0
3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.0

eBE (eV)Figure 6.1

6.2

Atomic copper anion 355 nm photoelectron spectrum showing transitions
from the anion ground state to the three lowest lying electronic states ofatomic copper neutral. Transition energies and electronic term symbols areincluded for reference.

Experimental Methods
The photoelectron images were obtained using the photoelectron imaging

spectrometer with dc discharge copper sputtering source as described in Chapter 2. Copper
hydride anions were produced in the dc sputter discharge source by passing argon over aliquid sample of neat methanol before the pulsed valve. Copper deuteride anions were
produced by passing argon over a liquid sample of neat d4-methanol. Anion signals of
several hundred mV were measured from the inline MCP ion detector for both CuH(D)− andCuH2(D2)− with 1600 volts across the detector. The time-of-flight mass spectrum measured

95with introduction of d4-methanol in the discharge is presented in Figure 6.2 and labeled withanions of interest. Spectra of the copper-methanol and copper-methoxy anion complexes andanalysis are presented in Chapter 7. Because Cu has two naturally occurring isotopes, ~ 70%
63

Cu and ~ 30% 65Cu, most spectra of the copper-hydrides contain photoelectron featuresfrom Cu−. Only the spectra of 65CuD2− and 65CuH2− are uncontaminated. However, thesefeatures can be used to calibrate the spectra, which was the case for all but the above
mentioned species.
55

60

65

70

75

80

85

90

95

100

105

110

100

105

110

-0.5
65CuD −
2
63CuD −
2

-0.4

65CuD−

Intensity-0.3

65CuCD OD−
3

63CuD−
63CuCD O−
3

65Cu−

-0.2

63Cu−

-0.1

0.0
55

60

65

70

75

80

85

90

95

Mass (amu)
Figure 6.2

Time-of-flight mass spectrum obtained with the dc sputter ion source and d4methanol with relevant species labeled. Photoelectron imaging spectra of thecopper-methanol and copper-methoxy complexes are presented in Chapter 7.

The tripled light (355 nm) from the Infinity laser system was used to take survey
scans of CuH(D)− and CuH2(D2)− photoelectron spectra by setting the electron imaging optics
such that 3.5 eV photoelectrons filled the detector area. The laser power used at 355 nm was

96
1 – 2 mJ per pulse at a repetition rate of 50 Hz. In order to better resolve the low electron
binding energy portions of the photoelectron imaging spectra of CuH(D)−, images were takenusing 600 nm laser pulses at 50 Hz produced by the Infinity OPO laser system. Typical pulse
energies used were around 1 mJ. In these experiments the electron imaging optics were set
such that 2.066 eV (600 nm) photoelectrons filled the detector. The photoelectron images
presented here were averaged over 50,000 – 100,000 laser shots. For images taken at
355 nm, observation of transitions to the three lowest lying electronic states51 of copper
neutral were used to calibrate the electron energy scale and to find the optimum electron
imaging optics voltage ratio at each magnification. Images taken at 600 nm were calibrated
and focused using the transition to the ground state of copper neutral.
The 600 nm spectra of CuH− and CuD− contain short vibrational progressions, thefitting of which was used to confirm the spectral assignments. A Franck-Condon simulationof the data using the program PESCAL52,53 was carried out as follows. The anion and neutralelectronic ground states were modeled as Morse oscillators. The neutral parameters (re, ωe,ωexe) were fixed to known literature values.54 Franck-Condon factors were determined bynumerical integration of the Laguerre wave function solutions55 to the Morse potentials. The
instrumental lineshape was modeled as a Gaussian with 45 meV full width at half maximum.
Other parameters input into the simulation were the 0-0 transition position and height and theanion temperature (0 K). The only parameter which was allowed to vary was the equilibrium
bond length; however the simulation is only sensitive to the change in bond length between
the anion and neutral. Thus the change in equilibrium bond lengths between the anion andneutral for the ground states of CuD− and CuH− were determined.

97
6.3

CuH− and CuD− Photoelectron Imaging Results
The 355 nm raw photoelectron image, BASEX reconstructed image, andphotoelectron spectrum of 63CuH− are presented in Figure 6.3. The images clearly show five
sharp features, two at high electron velocities (outer rings) and three at low electron velocities(inner rings). The two high electron velocity features have angular anisotropies which arealigned with the electric field of the laser (vertical in the images), while the angular
distribution of the inner features is more isotropic. Since 63CuH− is 1 amu from both 63Cu−
and 65Cu−, and the photodetachment cross section is so large for copper anion, the spectrum
contains photoelectron features from Cu− photodetachment. However, the photoelectron
spectrum of Cu− is well known,56 thus peaks b and c are assigned as the 2S0 ← 1S0 and2

D5/2 ← 1S0 copper transitions, respectively. Peak d has the correct binding energy for thecopper 2D3/2 ← 1S0 transition, but the intensity is much too large in comparison to theintensity of peak c (the intensity should be slightly less) for this feature to be assigned purely
as the copper 2D3/2 ← 1S0 transition. The top trace in Figure 6.3 is the spectrum which resultsfrom the subtraction of the measured 355 nm 63Cu− from the bottom spectrum. This spectrum
contains photoelectron features only from 63CuH− photodetachment.
The features labeled “a” are assigned as transitions to the ground X 1Σ+ state of CuH
and are discussed in the presentation of the more resolved 600 nm photoelectron spectrum of
CuH− below. Peak e has an electron binding energy of 3.334 (4) eV and is assigned astransitions to the well known57 excited 2nd 1Σ+ state of CuH (refered to as the A 1Σ+ in theliterature).

Peak d has an electron binding energy of 2.862 (7) eV and is assigned astransitions to the predicted,24,58 but as yet unobserved, 1st 3Σ+ state of CuH (given here thestate label of a 3Σ+). No vibrational progression is observed for transitions to this electronic
state, thus the equilibrium bond length of the a 3Σ+ state is essentially equal to the equilibrium

98bond length of the anion, which is reported below as 1.560 (1) Å. Spectroscopic constantsfrom the literature and this study for CuH− are reported in Table 6.1.
To confirm that peaks d and e are purely electronic transitions, and that the images
and spectra reported above do arise from 63CuH− photodetachment, the photoelectron imagesof 63CuD− were taken at 355 nm under the same experimental conditions as the CuH− images.
Figure 6.4 contains the raw photoelectron image, BASEX reconstruction, and photoelectron
spectrum of CuD−. The images and photoelectron spectrum are very similar to CuH−, withthe expected exception of the larger contribution from 65Cu− photodetachment, which has thesame mass. The peak assignments are the same as for CuH−, with slightly different values forthe binding and term energies. The differences, however, are well within the experimental
uncertainties, thus the results are presented in Table 6.2 without discussion of theassignments. The negligible difference does, however, confirm that the only vibrational
structure in the spectrum is found in the lowest binding energy features. These features are
examined in greater detail in the 600 nm spectra reported below.

99

14
13

d

12
11
10
9

counts

a

e

8
7
6

d

5

b

4
3

e

2

a

c

1
0
3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.0

electron binding energy (eV)Figure 6.3

CuH− 355 nm full scale raw photoelectron image (top left), BASEX
reconstructed photoelectron image (top right), and photoelectron spectrum(bottom). The bottom trace contains features from both 63CuH− andCu− photodetachment, while the Cu− photodetachment features have been
removed in the top trace.
63

100

14000

d

12000

a

Integrated Counts

10000

e
8000

d

6000

b

4000

c

e

2000

a

0
3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.0

eBE (eV)Figure 6.4

CuD− 355 nm full scale raw photoelectron image (top left), BASEX
reconstructed photoelectron image (top right), and photoelectron spectrum(bottom). The bottom trace contains features from both 63CuD− and65
Cu− photodetachment, while the 65Cu− photodetachment features have been
removed in the top trace.
63

101
The 600 nm raw photoelectron image, BASEX reconstructed image, andphotoelectron spectrum of CuH− are presented in Figure 6.5.

The low binding energy

features in the 355 nm spectra are much more resolved at this photodetachment energy(2.066 eV). As in the 355 nm spectrum, the 2S0 ← 1S0 copper atom photoelectron transition
is observed (peak c), but a vibrational progression in the ground X 1Σ+ state of copper hydride
is now clearly resolved. Peak a is assigned as the ν = 0 to ν = 0 transition, while peak b is
assigned as the ν = 0 to ν = 1 transition. No hot band transitions are observed in thisspectrum, due to the large anion vibrational frequency, which has negligible thermal
population at the anion temperature.

102

7000

a

6000

c

counts

5000

4000

3000

2000

b

1000

0
2.0

1.5

1.0

0.5

0.0

electron binding energy (eV)Figure 6.5

CuH− 600 nm raw photoelectron image (top left), BASEX reconstructed
photoelectron image (top right), and photoelectron spectrum (bottom). The
inner feature in the images and the high binding energy feature in the
spectrum is detachment from 63Cu−.

63

103
As mentioned in the experimental section, the CuH− 600 nm photoelectron spectrum
was fit using the known spectroscopic constants for the CuH X 1Σ+ electronic ground state
listed in Table 6.1. The only adjustable parameters were the change in equilibrium bondlength between the anion and neutral, and 0 − 0 transition position and intensity. These
parameters were adjusted manually, and the resulting fit is presented in Figure 6.6 over thedata points. The optimized change in bond length from this fit is 0.007 (1) Å. The bondlength for the CuH− anion is found to be 1.560 (1) Å, the assignment of which is presented in
the discussion section. Since the transition to the a 3Σ+ state has no measurable vibrational
progression, the bond length of this state is assigned as the bond length of the anion,
1.560 (2) Å, which is in good agreement with the calculated literature58 value of 1.540 Å.
The spectroscopic constants for all the electronic states mentioned in this section arepresented in Table 6.1.

104

7000

a
6000

counts

5000
4000
3000

b

2000
1000
0
1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

electron binding energy (eV)CuH− 600 nm photoelectron spectrum (points) with calculated FranckCondon transition positions (sticks) and 45 meV Gaussian convolution (line).
The X 1Σ+ state ωe, ωeχe, and re used in the fit are presented in Table 6.1.

Figure 6.663

Table 6.1

Spectroscopic constants for CuH and CuH−.

this worklitωe(cm−1)

CuH− X 2Σ+−0.430 (5)

−

−

−

1.560 (1)−

CuH X 1Σ+CuH a 3Σ+CuH A 1Σ+02.436 (5)2.879 (10)
02.292b
2.905d

1941a
1762§
1698a

37.51a−44.0a−1.560 (1) c

1.463a1.540b
1.572aTe (eV)

State

from reference 54acalculated in reference 28bcestimated from lack of vibrational progression, see textdfrom reference 57

ωeχe(cm−1)

this worklit.

re (Å)

−

105

The

63

CuD− 600 nm photoelectron raw image, BASEX reconstruction, andphotoelectron spectrum are presented in Figure 6.7. The spectrum is very similar to the
600 nm 63CuH− spectrum in that it contains a prominent copper 2S0 ← 1S0 transition (peak c),
but this feature is more intense because the mass of 63CuD− and 65Cu− are equal, and thus theamount of copper anion photodetached is much greater than in the copper hydride spectrum.
The short vibrational progression was fit, as above, extremely well using the known spectral
constants of the ground X 1Σ+ electronic state of CuD listed in Table 6.2. The fit, plotted overthe experimental data, is presented in Figure 6.8. The bond length of CuD− was found to be
the same as that of CuH−, 1.560 (1) Å. Similarly, the lack of a vibrational progression intransitions to the a 3Σ+ state of CuD sets the bond length of this state as that of the anion. The
known spectral constants for the electronic states of CuD and CuD− mentioned in this section
are presented in Table 6.2.

106

10000

c

8000

counts

6000

4000

a
2000

b
0
2.0

1.5

1.0

0.5

0.0

electron binding energy (eV)Figure 6.7

CuD− 600 nm raw photoelectron image (top left), BASEX reconstructed
photoelectron image (top right), and photoelectron spectrum (bottom). The
inner feature in the images and the high binding energy feature in the
spectrum is detachment from 65Cu−.

63

107

a

2000

counts

1500

1000

b
500

1.0

0.8

0.6

0.4

0.2

0.0

electron binding energy (eV)CuD− 600 nm photoelectron spectrum with calculated Franck-Condon
transition positions (sticks) and 45 meV Gaussian convolution (line). The
X 1Σ+ state ωe, ωeχe, and re used in the fit are presented in Table 6.2.

Figure 6.8

63

Table 6.2

Spectroscopic constants for CuD and CuD−.
ωeχe(cm−1)

this work

lit.

this worklitωe(cm−1)

CuD− X 2Σ

−0.427 (5)

−

−

−

1.560 (1)−CuD X 1Σ+CuD a 3Σ+CuD A 1Σ+02.437 (5)2.877 (10)02.417b
2.892d

1384a
1174b
1210d

18.97a−1.560 (2) c

1.463a−1.566dState

Te (eV)a

From reference 54bCalculated in reference 28

cEstimated from lack of vibrational progression, see textd

From reference 57

1210

d

re (Å)

−

108

6.4

CuH2− and CuD2− Photoelectron Imaging Results
The 355 nm full scale CuH2− raw photoelectron image, BASEX reconstruction, andphotoelectron spectrum are presented in Figure 6.9. The images contain two noticeablefeatures at low electron velocity (center of the image) and no other photoelectron features.
The photoelectron spectrum confirms this finding, as the only features in the spectrum are athigh electron binding energies (low electron velocities). This is markedly different from thecopper hydride anion photoelectron spectra above which contain features at low electron
binding energies. The photoelectron spectrum also clearly shows low intensity photoelectronfeatures between peak a and the photon energy (3.493 eV). In order to better utilize thephotoelectron detector, the electron optics were adjusted such that the CuH2−
photodetachment features nearly filled the detector.

109

16000

a

14000
12000

Counts

10000
8000
6000
4000

b

2000
0
3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.0

electron binding energy (eV)Figure 6.9

CuH2− 355 nm full scale raw photoelectron image (top left), BASEX
reconstructed photoelectron image (top right), and photoelectron spectrum(bottom).

65

The magnified CuH2− 355 nm raw photoelectron image, BASEX reconstruction, andphotoelectron spectrum are presented in Figure 6.10.

The images show low intensity

photoelectron features, as well as the two significant photoelectron features mentioned above.

110
The photoelectron spectrum confirms the low intensity photoelectron features which start at
the most intense feature (peak a) and continue to the photon energy (3.493 eV). Peak a has
an electron binding energy of 2.852 (2) eV and peak b has an electron binding energy of
3.086 (2) eV. The splitting between the peaks is 0.234 (2) eV or 1879 (57) cm−1. The
angular anisotropy parameters of peaks a and b have been measured as β = 1.8 (1) for peak aand β = 1.9 (1) for peak b.

111

50000

a

40000

counts

30000

20000

10000

b
0
3.5

3.4

3.3

3.2

3.1

3.0

2.9

2.8

2.7

2.6

2.5

electron binding energy (eV)Figure 6.10

CuH2− 355 nm 0 – 1 eV eKE raw photoelectron image (top left), BASEX
reconstructed photoelectron image (top right), and photoelectron spectrum(bottom).

65

112
Figure 6.11 shows the same portion of the CuH2− photoelectron spectrum as above
with the intensity scale reduced by a factor of 10. In addition the measured intensities havebeen scaled by (eKE) ℓ+1/2 where ℓ = 1 is the angular momentum of an outgoing p-wave. Thisscaling assumes that the electron is detached from an orbital of predominantly d characternear threshold, a reasonable assumption given the high electron binding energy of thefeatures and the low electron kinetic energy (less than 1 eV). This procedure reveals aspectrum with a large amount of structure. There appear to be groups of multiplet peaks,
with the spacing between the groups ranging from 440 cm−1 to 190 cm−1.

16000

a

14000
12000

b

Counts

10000
8000
6000
4000
2000
0
3.4

3.3

3.2

3.1

3.0

2.9

2.8

2.7

2.6

electron Binding Energy (eV)Figure 6.11

CuH2− 355 nm 0 − 1 eV photoelectron spectrum with the photoelectron
intensity scaled to show the low intensity structure.
65

113
The 355 nm CuD2− raw photoelectron image, BASEX reconstructed image, andphotoelectron spectrum are presented in Figure 6.12. As expected, the images show the same
basic structure of the CuH2− images, with photoelectrons observed at low electron velocities(inner rings) and not at high electron velocities (no outer rings). As in CuH2−, low intensity
photoelectron structure extends from the lowest binding energy peak (a) to the highest
binding energy measurable at this photon energy (3.493 eV). Unlike the CuH2− photoelectron
spectrum, however, the spacing of peaks a and b is significantly smaller in the CuD2−
spectrum. As was done with CuH2−, the electron optics were adjusted such that the largest
photoelectron kinetic energy measured was 1 eV.

114

a

10000

Integrated Counts

8000

6000

4000

2000

b

0
3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.0

eBE (eV)Figure 6.12

CuD2− 355 nm full scale raw photoelectron image (top left), BASEX
reconstructed photoelectron image (top right), and photoelectron spectrum(bottom).

65

The CuD2− 355 nm 0 – 1 eV electron kinetic energy raw photoelectron image,
BASEX reconstruction, and photoelectron spectrum are presented in Figure 6.13.

The

images show that the main features (peaks a and b) have very similar angular anisotropies.

115
The measured angular anisotropies are β = 1.8 (1) for peak a and β = 1.8 (1) for peak b,
suggesting that these features are detachment to the same electronic state of the neutral. The
electron binding energies of peaks a and b are 2.841 (5) eV and 3.008 (5) eV, respectively.
The energy splitting of peaks a and b is 1348 (57) cm−1, considerably less than the 1879 (57)
cm−1 of the corresponding features in the CuH2− 355 nm photoelectron spectrum.

Thesignificant lowering of this energy upon deuteration strongly suggests that these arevibrational, not electronic, features. The electron binding energy, peak spacing, and angularanisotropy parameters observed in the photoelectron spectra of CuH2− and CuD2− arepresented in Table 6.3.

Table 6.3

Electron binding energies, angular anisotropy parameters, and peak spacingsin the CuH2− and CuD2− photoelectron spectra.

peakeBE (eV)

CuH2
β

a
b

2.851 (5)3.086 (5)

1.8 (1)
1.9 (1)−1b – a (cm )eBE (eV)CuD2β1879 (57)

2.841 (5)3.008 (5)

1.8 (1)
1.8 (1)b – a (cm−1)
1348 (57)116aIntegrated Counts

4e+5

3e+5

2e+5

1e+5

b
0
3.5

3.4

3.3

3.2

3.1

3.0

2.9

2.8

2.7

2.6

eBE (eV)Figure 6.13

CuD2− 355 nm expanded photoelectron raw image (top left), BASEX
reconstructed image (top right), and photoelectron spectrum (bottom).

65

Figure 6.14 shows the same portion of the CuD2− photoelectron spectrum as above
with the intensity scale reduced by a factor of 10. In addition the measured intensities havebeen scaled by (eKE) ℓ+1/2 where ℓ = 1 is the angular momentum of an outgoing p-wave. This

117
scaling assumes that the electron is detached from an orbital of predominantly d characternear threshold, a reasonable assumption given the high electron binding energy of thefeatures and the low electron kinetic energy (less than 1 eV). This procedure reveals aspectrum with a large amount of structure. There appear to be groups of multiplet peaks,
with the spacing between the groups ranging from 350 cm−1 to 550 cm−1.

1.4e+5ab

Threshold Corrected Counts

1.2e+51.0e+58.0e+46.0e+44.0e+42.0e+4

0.0
3.4

3.3

3.2

3.1

3.0

2.9

2.8

2.7

2.6

eBE (eV)Figure 6.14

6.5

CuD2− 355 nm 0 – 1 eV scale photoelectron spectrum. The counts havebeen threshold corrected as explained in the text and the photoelectron
intensity has been increased by a factor of 10.

65

Discussion
As mentioned in the CuH− and CuD− results section, the equilibrium bond length ofthe copper hydride anion is assigned to be longer than the equilibrium bond length of the118
neutral molecule. There are both theoretical and experimental reasons why this should betrue. Theoretically, the ground state molecular orbital configuration for copper hydride arises
from a combination of Cu 3d104s1 and H 1s1. These atomic orbitals combine to give abonding (Cu3d104s1 H1s1) σ orbital and an anti-bonding (Cu3d104s1 H1s1) σ* orbital. The
neutral ground state has a σ2 configuration, while the ground state of the anion has a σ2σ*1
configuration. The addition of the extra electron in the anion into an anti-bonding orbital
should cause an increase in the equilibrium bond length.
The experimental evidence gives additional weight to this argument. Only transitions
from the anion to the ground vibrational level in the 2nd 1Σ+ (literature A) state of CuH and
CuD are observed. In the case of the CuH− photoelectron spectrum, the photodetachment
energy (3.493 eV) is just below the binding energy of the first vibrationally excited state in
the 2nd 1Σ+ manifold (3.545 eV). However, the binding energy of the first vibrationallyexcited state of the 2nd 1Σ+ state of CuD is within our photodetachment energy at 3.481 eVbinding energy. There is no significant photoelectron intensity at this binding energy in the
355 nm spectra, thus the equilibrium bond length of the anion and the 2nd 1Σ+ state must be
essentially equal.

The bond length of this state is well known as 1.566 Å, thus theequilibrium bond length of the copper hydride anion is set higher than the bond length of theneutral.
The assignments of the CuH2− and CuD2− spectra are more difficult. Foremost, it is
not clear if the photoelectron features arise from the ground electronic state, or from an
excited electronic state. Wang3 has calculated the difference in energy between CuH2− andCuH2 to be 2.34 eV at the BPW91/6-311++G(d,p)/SDD level of theory, though it is not stated
if this difference includes zero-point energy. It is certainly possible that the calculation is inerror by 500 meV, or that the exclusion of zero-point energy would cause a shift of thismagnitude.

The angular anisotropy parameters should give an idea if the observed

119
photoelectron originate from a sigma or delta orbital of the anion. The observed angularanisotropy parameters are near 1.8 for the main features in the spectrum, which suggests thatthe outgoing photoelectron has mostly p-wave character.

However, a p-wave may be

produced upon removal of an electron from a sigma type orbital, or from a delta type orbital
where the outgoing electron is near threshold. The electron kinetic energies of the observed
features are less than 700 meV, making them all “near threshold”, so the anisotropy
parameters also provide little guidence.
Assuming the features are transitions to the electronic ground state, peak a would be
the electron affinity while peak b would be assigned as having one quantum of the symmetricstretch excited in the photoelectron transition (Wang calculates the symmetric stretch of
CuH2 neutral as 1770 cm−1). Wang calculates the anion to be linear and symmetric (1Σg+)with a Cu – H distance of 1.560 Å. Wang calculates the neutral to be bent and symmetric(2B2) with a H – Cu – H bond angle of 122.6° and Cu – H bond lengths of 1.527 Å. If thesecalculations are correct, then both the bend and the symmetric stretch vibrations should be
excited in the photoelectron spectrum. However, since there is such a large geometry change
in the bending coordinate (from linear to highly bent), these transitions would have poor
vibrational overlap in the Franck-Condon approximation in the observed region of thespectrum. The use of a higher energy photon for photodetachment may reveal that the low
intensity peaks are merely the onset of an extended vibrational progression. The bendfrequency calculated by Wang is 637 cm−1 for CuH2, which is larger than the observed low
intensity peak spacings.

The observed peaks may be combination bands of the bend,

symmetric stretch, or even quanta of the symmetric stretch. Unfortunately, the spectrum is
too congested and the calculated frequencies too uncertain to accurately assign each peak in
the observed spectrum in this way. Of course the same arguments could be true for an
excited electronic state of CuH2, though there have been no geometries or frequencies

120
calculated for excited states of CuH2 to date. The most likely conclusion, however, is that theobserved features are transitions to the ground state of CuH2 and CuD2. As stated above, thiswould identify peak a as the electron affinity of CuH2 and CuD2 and peak b as excitation of
one quanta of the symmetric stretch mode.
Table 6.4

Electron affinities and symmetric stretch frequencies for CuH2 and CuD2.
CuD2

CuH2
this work

literaturea

this work

literaturea

electron affinity (eV)2.851 (5)2.34

2.841 (5)2.34

symmetric stretch
frequency (cm−1)aFrom reference 3

1879 (57)1770

1348 (57)−

References for Chapter VI

1

L. Andrews and X. Wang, Journal of the American Chemical Society 125 (38),11751 (2003).

2

X. Wang and L. Andrews, Angewandte Chemie, International Edition 42 (42), 5201
(2003).

3

X. Wang, L. Andrews, L. Manceron, and C. Marsden, Journal of Physical Chemistry
A 107 (41), 8492 (2003).

4

M. Ebben, G. Meijer, and J. J. Ter Meulen, Applied Physics B: Photophysics andLaser Chemistry B50 (1), 35 (1990).

5

R. Georgiadis, E. R. Fisher, and P. B. Armentrout, Journal of the American Chemical
Society 111 (12), 4251 (1989).

6

V. N. Belyaev, N. L. Lebedeva, K. S. Krasnov, and L. V. Gurvich, Izvestiya Vysshikh
Uchebnykh Zavedenii, Khimiya i Khimicheskaya Tekhnologiya 21 (11), 1698 (1978).

121
7

A. Kant and K. A. Moon, High Temperature Science 11 (1), 55 (1979).

8

V. M. Rao, M. L. P. Rao, and P. T. Rao, Journal of Quantitative Spectroscopy &Radiative Transfer 25 (6), 547 (1981).

9

R. Burtovyy, E. Utzig, and M. Tkacz, Thermochimica Acta 363 (1-2), 157 (2000).

10

R. Burtovyy, D. Wlosewicz, A. Czopnik, and M. Tkacz, Thermochimica Acta 400 (12), 121 (2003).

11

A. M. Antic-Jovanovic and D. S. Pesic, Glasnik Hemijskog Drustva Beograd 34 (24), 163 (1969).

12

C. M. Brown and M. L. Ginter, Journal of Molecular Spectroscopy 80 (1), 145(1980).

13

U. Ringstroem, Canadian Journal of Physics 46 (20), 2291 (1968).

14

P. F. Bernath, AIP Conference Proceedings 146 (Adv. Laser Sci. - 1), 443 (1986).

15

T. D. Varberg and K. M. Evenson, Journal of Molecular Spectroscopy 164 (2), 531(1994).

16

R. B. Wright, J. K. Bates, and D. M. Gruen, Inorganic Chemistry 17 (8), 2275
(1978).

17

M. C. McCarthy and R. W. Field, Journal of Chemical Physics 100 (9), 6347 (1994).

18

V. Barone and C. Adamo, International Journal of Quantum Chemistry 61 (3), 443(1997).

19

V. Barone and C. Adamo, Journal of Physical Chemistry 100 (6), 2094 (1996).

20

P. Belohorec, S. M. Rothstein, and J. Vrbik, Journal of Chemical Physics 98 (8),6401 (1993).

21

J. C. A. Boeyens and R. H. Lemmer, Journal of the Chemical Society, Faraday
Transactions 2: Molecular and Chemical Physics 73 (3), 321 (1977).

22

G. Das, Journal of Chemical Physics 74 (10), 5766 (1981).

122
23

P. Fantucci, S. Polezzo, G. Morosi, and V. Valenti, Theoretica Chimica Acta 67 (3),245 (1985).

24

M. Hliwa, J. C. Barthelat, M. Pelissier, and F. Spiegelmann, Chemical Physics
Letters 132 (2), 205 (1986).

25

S. Hoyau and G. Ohanessian, Chemical Physics Letters 280 (3,4), 266 (1997).

26

J. Hrusak, S. Ten-No, and S. Iwata, Journal of Chemical Physics 106 (17), 7185
(1997).

27

V. V. Karasiev, Theochem 493, 21 (1999).

28

C. M. Marian, Journal of Chemical Physics 94 (8), 5574 (1991).

29

M. Merchan, J. P. Daudey, R. Gonzalez-Luque, and I. Nebot-Gil, Chemical Physics
148 (1), 69 (1990).

30

N. Minh Tho, M. A. McGinn, and N. J. Fitzpatrick, Journal of the Chemical Society,
Faraday Transactions 2: Molecular and Chemical Physics 82 (9), 1427 (1986).

31

C. Opitz and H. H. Dunken, Zeitschrift fuer Physikalische Chemie (Leipzig) 249 (34), 154 (1972).

32

M. Pelissier, J. P. Daudey, J. P. Malrieu, and G. H. Jeung, NATO ASI Series, Series
C: Mathematical and Physical Sciences 176 (Quantum Chem.: Challenge Transition
Met. Coord. Chem.), 37 (1986).

33

R. Pou-Amerigo, M. Merchan, I. Nebot-Gil, P. A. Malmqvist, and B. O. Roos,
Journal of Chemical Physics 101 (6), 4893 (1994).

34

K. Raghavachari, K. K. Sunil, and K. D. Jordan, Journal of Chemical Physics 83 (9),4633 (1985).

35

S. M. Rothstein, International Journal of Quantum Chemistry 60 (4), 803 (1996).

36

G. Simons and E. R. Talaty, Journal of Chemical Physics 66 (6), 2457 (1977).

123
37

H. Smithson, C. A. Marianetti, D. Morgan, A. Van der Ven, A. Predith, and G.
Ceder, Physical Review B: Condensed Matter and Materials Physics 66 (14),144107/1 (2002).

38

C. Zhang and A. Alavi, Journal of the American Chemical Society 127 (27), 9808
(2005).

39

T. Ziegler, V. Tschinke, and A. Becke, Journal of the American Chemical Society
109 (5), 1351 (1987).

40

C. L. Collins, K. G. Dyall, and H. F. Schaefer, III, Journal of Chemical Physics 102(5), 2024 (1995).

41

V. Kello and A. J. Sadlej, Theochem 547, 35 (2001).

42

V. Kello and A. J. Sadlej, Theoretica Chimica Acta 92 (4), 253 (1995).

43

V. Kelloe and A. J. Sadlej, Journal of Chemical Physics 95 (11), 8248 (1991).

44

V. Kelloe and A. J. Sadlej, Theoretica Chimica Acta 94 (2), 93 (1996).

45

V. Kelloe, A. J. Sadlej, and B. A. Hess, Journal of Chemical Physics 105 (5), 1995
(1996).

46

J. Micanko and S. Biskupic, ACH - Models in Chemistry 137 (5-6), 753 (2000).

47

J. Onoe, Advances in Quantum Chemistry 37, 311 (2001).

48

J. Onoe, H. Nakamatsu, T. Mukoyama, R. Sekine, H. Adachi, and K. Takeuchi,
Journal of the Physical Society of Japan 65 (8), 2459 (1996).

49

T. Suzumura, T. Nakajima, and K. Hirao, International Journal of Quantum
Chemistry 75 (4/5), 757 (1999).

50

C. van Wullen, Journal of Chemical Physics 109 (2), 392 (1998).

51

J. Sugar and A. Musgrove, Journal of Physical and Chemical Reference Data 19, 527(1990).

52

K. M. Ervin, Fortran PESCAL (Reno, NV, 2001).

124
53

K. M. Ervin, T. M. Ramond, G. E. Davico, R. L. Schwartz, S. M. Casey, and W. C.
Lineberger, Journal of Physical Chemistry A 105 (48), 10822 (2001).

54

K. Huber and G. Herzberg, Molecular Spectra and Molecular Structure, Constants ofDiatomic Molecules. (Van Nostrand-Reinhold, New York, 1979).

55

K. Cashion, Journal of Molecular Spectroscopy 10, 182 (1963).

56

J. Ho, K. M. Ervin, and W. C. Lineberger, Journal of Chemical Physics 93 (10), 6987
(1990).

57

U. Ringstrom, Arkiv For Fysik 32, 211 (1966).

58

C. M. Marian, The Journal of Chemical Physics 94 (8), 5574 (1991).

125________________
Photoelectron Velocity Map Imaging of CuCD3O− and CuCD3OD−________________
7.1

Introduction
This chapter presents results of photoelectron imaging experiments conducted on the

Cu− CD3OD anion.

The experiment was designed to help define the initial state of aphotodetachment-photoionization (PDPI) experiment conducted on the same complex. In the
PDPI experiments, mass-selected 65Cu− CD3OD was photodetached by a femtosecond laser
pulse near 400 nm, allowed to evolve on the gound neutral electronic state surface, thenprobed at different time delays via resonance enhanced multi photon ionization coupled withmass spectral detection of the product cations. Photoelectron spectroscopy coupled with highlevel spectral simulations is employed here to elucidate the geometry and thermodynamics ofthe neutral state formed immediately after electron photodetachment of Cu− CD3OD.
Previously Cu− H2O was studied using the same techniques described above. In thosestudies1-4 it was found that a modest potential well exists in the radial Cu − O coordinate of
the neutral complex at the geometry of the anion on the electronic ground state surface. The
geometry of the anion was found to have the water hydrogen atoms between the copper atom
(which carries much of the excess negative charge) and the oxygen atom, while the hydrogenatoms are located further from the copper atom than the oxygen atom in the neutral complex.
Because of this very large difference in geometry between the lowest energy geometries of
the anion and neutral complexes, transitions from the anion to the lowest energy geometry of
the neutral were not observed in the photoelectron spectra, due to negligible vibrationalFrank-Condon factors. Instead, transitions were observed to the neutral complex at the anion
geometry.

126
The ground electronic state of CuH2O was found2 to result from removal of anelectron localized on copper, correlating to the Cu 4s orbital, based on an angular
photoelectron anisotropy parameter of β = 2. Excited electronic states of CuH2O wereaccessed via removal of electrons from the copper 3d orbital. Electrons photodetached fromthis state had an angular anisotropy parameter of β = 0.2. The electronic binding energies ofthese orbitals is very similar to that of the electron binding energies of the observed in thecopper anion 355 nm photoelectron spectrum presented in Figure 7.1. Also presented in
Figure 7.1 is an energy level diagram showing the transition energies and term symbols fortransitions from the copper anion ground state to the three lowest lying electronic states ofneutral copper.

8000

Cu 2D3/2
2.878 eVCu 2D5/2

Counts6000

2.623 eV4000

Cu 2S01.236 eV2000

Cu− 1S00.000 eV

0
3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.0

eBE (eV)Figure 7.1

Atomic copper anion 355 nm photoelectron spectrum showing transitions
from the anion ground state to the three lowest lying electronic states ofatomic copper neutral. Transition energies and electronic term symbols areincluded for reference.

127
The 355 nm photoelectron imaging spectrum of Cu− H2O is presented in Figure 7.2. The
pattern of the electronic states accessed in this spectrum clearly follows the pattern seen in thecopper anion photoelectron spectrum. The low binding energy feature is a transition to theCu(2S0) H2O complex, while the higher binding energy features are transitions to theCu(2D5/2) H2O and Cu(2D3/2) H2O complexes.

10000

8000

counts

6000

4000

2000

0
3.0

2.5

2.0

1.5

electron binding energy (eV)Figure 7.2

Cu− H2O 355 nm photoelectron spectrum as reported in reference ## (2).

Optimized geometries for the copper d4-methanol anion and neutral complexes havebeen calculated elsewhere,5 and the structures are presented in Figure 7.3 along withsymbolic radial Cu – O potential curves for the anion, neutral at anion geometry, and neutrallowest energy geometry. The calculated radial Cu – O well depth for the copper d4-methanol

128
system at the anion geometry of 650 cm−1 is about twice as deep as the analogous calculated4
copper water well depth of 300 cm−1. One aim of the photoelectron imaging spectra of
Cu− CD3OD reported here is to determine if the photoelectron spectrum simulated using the
calculated well depth compares favorably with the measured photoelectron imaging

Energyspectrum.

Cu − O
Figure 7.3

Calculated anion (lower) and neutral (upper) structures for the copper d4methanol complexes. Symbolic radial Cu – O potential curves for the anion(lower solid curve), neutral at anion geometry (upper solid curve), andneutral lowest energy geometry (upper dotted curve) are also presented. The
arrow shows the vertical photoelectron transition to the neutral groundelectronic state surface.

The CuCD3O− complex was studied, and its spectra included here, for several
reasons.

The first is that the mass of 65CuCD3O− is very close in mass to that of

129
63

Cu− CD3OD, thus initially the spectrum was taken to insure that there was no spectral

contamination of 63Cu− CD3OD by 65CuCD3O−. Once the spectra were taken, however, there
appeared to be a very similar vibrational progression in the excited 2D5/2 portion of the 355
nm spectra of both complexes. A very similar vibrational progression was also observed intransitions to the ground state of CuCD3O−. Since the only difference between the twocomplexes is that of the OD proton, it is assumed that the very similar vibrational
progressions observed in the spectra arise from the same excited vibrational mode. Further
more, it is much easier to simulate the spectra for ground electronic to ground electronic statetransitions that to or from excited electronic state transitions. Therefore, simulation of the
CuCD3O− ground state portion of the photoelectron spectrum using the methods described inchapter 2 should elucidate the nature of the vibrational features in both spectra.
The photoelectron spectrum of a similar system, CuOH−, was measured by Misaizu6.
Due to poor mass resolution, this photoelectron spectrum contains photodetachment featuresfrom both CuOH− and Cu− H2O. The Cu− H2O features were identified in our previous2
Cu− H2O study, thus the CuOH− features can also be identified. These features include peaks
with unresolved structure at 0.98 eV eBE, 2.97 eV eBE, 3.25 eV eBE, and 3.43 eV eBE. The
feature at 0.98 eV eBE is assigned as the transition to ground state CuOH, while the featuresat 3.25 eV eBE and 3.43 eV eBE are assigned as transitions to the well known7 low lying
singlet excited states of CuOH. The feature at 2.97 eV eBE is unassigned, but may be atransition to an unobserved or calculated low lying triplet excited state. [Note: This feature
was assigned to Cu− H2O photodetachment by Misaizu. Photodetachment near 2.7 eV eBE
may be attributed to CuOH− photodetachment.] The electronic structure of CuCD3O isassumed to be very similar to that of CuOH, and thus the electronic structure of CuCD3O iscompared to that of CuOH in the discussion section.

130
7.2

Experimental Methods
The photoelectron images were obtained using the photoelectron imaging

spectrometer described in chapter 2.

Completely deuterated methanol (CD3OD) was

introduced into the dc sputter discharge source by passing argon over a liquid sample(Aldrich, 97%) of neat d4-methanol. An ion signal of several hundred mV was measured
from the inline MCP ion detector for both 65Cu− CD3OD and 63CuCD3O− anions. The timeof-flight mass spectrum labeled with anions of interest is presented in Figure 7.4. Spectra of
the copper hydrides, CuH(D)− and CuH2(D2)−, and analysis are presented in chapter 6.

55

60

65

70

75

80

85

90

95

100

105

110

100

105

110

-0.5
65CuD −
2
63CuD −
2

-0.4

65CuD−

Intensity-0.3

65CuCD OD−
3

63CuD−
63CuCD O−
3

65Cu−

-0.2

63Cu−

-0.1

0.0
55

60

65

70

75

80

85

90

95

Mass (amu)
Figure 7.4

Time-of-flight mass spectrum obtained with the dc sputter ion source with
relevant species labeled. Photoelectron imaging spectra of the copper
hydrides are presented in chapter 6.

131
The tripled light (355 nm) from the Infinity laser system was used to take survey
scans of the Cu− CD3OD and CuCD3O− photoelectron spectra by setting the electron imaging
optics such that 3.5 eV photoelectrons filled the detector area. The laser power used at 355
nm was 1 – 2 mJ per pulse at a repetition rate of 50 Hz. In order to better resolve the low
electron binding energy portions of the photoelectron imaging spectra of Cu− CD3OD and
CuCD3O−, images were taken using the 600 nm (for Cu−CD3OD) and 500 nm (for CuCD3O−)
laser pulses at 50 Hz produced by the Infinity OPO laser system. Typical pulse energies usedwere around 1 mJ. In these experiments the electron imaging optics were set such that 2.5 eV(500 nm) and 2.0 eV (600 nm) photoelectrons filled the detector. The photoelectron images
presented here were averaged over 50,000 – 100,000 laser shots. For images taken at 355
nm, observation of transitions to the three lowest lying electronic states8 of copper neutral
were used to calibrate the electron energy scale and to find the optimum electron imaging
optics values at each magnification. Images taken at 500 nm and 600 nm were calibrated andfocused using the transition to the ground state of copper neutral.
7.3

Results
The 355 nm raw photoelectron image, BASEX reconstructed photoelectron image,and photoelectron spectrum of Cu− CD3OD are presented in Figure 7.5. The images are of
sufficient quality that some qualitative information may be extracted from them.
Examination of the BASEX reconstructed photoelectron image (top right panel, Figure 7.5)
clearly shows a high electron velocity feature (outer ring) and an extended progression at low
electron velocity (inner features). Additionally, the lowest velocity feature has a muchdifferent angular distribution (nearly isotropic) when compared with the angular distributionof the other features (aligned with the electric field of the laser, which is vertical in theimage). In contrast to the 355 nm Cu− H2O photoelectron imaging spectrum presented in

132
Figure 7.2 above, there is a clear vibrational progression in the reconstructed photoelectron
image a low electron kinetic energies.
Examination of the photoelectron spectrum in Figure 7.5 shows the photoelectron
spectrum to be similar to that of the Cu− H2O 355 nm spectrum. Both spectra contain a sharp
feature at low binding energy which is assigned as the vertical detachment energy (VDE) of
the complexes (peak a) which arise from transitions to the neutral complex at the anion
geometry.

Both also include broad features at higher electron binding energies whichcorrelate to the excited 2D states of copper atom.

There are several main differences,

however. One is the partially resolved 519 (15) cm−1 vibrational progression (peaks d – g) in
the Cu− CD3OD spectrum. While there is significant broadening in the high electron binding
energy region of the 355 nm Cu− H2O spectrum, there are no resolved vibrational
progressions. Peaks b and c are assigned as a hot band progression with a vibrationalfrequency of 770 cm−1. A second difference is that the relative intensity of the features near
2.9 eV electron binding (peaks d − h) is much greater than the relative intensity of the VDE
peak in Cu− CD3OD, while the relative intensities of these features in Cu− H2O arecomparable.

133

e
f

3000

d

Counts

g
2000

h

1000

a

i
c
b

0
3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.0

eBE (eV)Figure 7.5

CuCD3OD− 355 nm full scale raw photoelectron image (top left), BASEX
reconstructed photoelectron image (top left), and photoelectron spectrum(bottom).

134
A third major difference is the value of the angular anisotropy parameter for thefeatures in the spectra. For Cu− H2O, β = 2 for the VDE peak, suggesting detachment from anunperturbed copper 4s orbital, and β ≈ 0.2 for both high electron binding energy features,
suggesting that these electrons are photodetached from copper 3d orbitals. For Cu− CD3OD
the case is slightly different. The VDE peak has an angular anisotropy parameter of β = 1.8,
which suggest that the anion orbital is not a pure copper 4s orbital, but rather has some small
contribution from an orbital of different character.

The higher binding energy featurescontaining the vibrational progression (peaks d – h) have angular anisotropy parameters
around β = 1.4, suggesting that the anion orbital from which these electrons are detached isvery different than the corresponding orbital (nearly pure Cu 3d) in Cu− H2O. Furthermore,
the highest binding energy feature in the 355 nm Cu− CD3OD photoelectron spectrum (peak i)
has an angular anisotropy parameter of β = 0.6, suggesting that these electrons originate froman anion orbital much more similar in character to an atomic copper 3d orbital.
It is possible, now, to assign peak d as the vibrational origin of the Cu(2D5/2)CD3OD
electronic state as 2.877 (4) eV, and assign peak i as the vertical detachment energy for theCu(2D3/2)CD3OD state as 3.297 (15) eV. When combined with the electron affinity estimatedbelow, the electronic term energies for these states are 1.422 (30) eV [11,470 (242) cm−1] forthe 2D5/2 state and 1.842 (30) eV [14,857 (242) cm−1] for the 2D3/2 state. The large uncertainty
in these values is due to the uncertainty in the calculated difference between the VDE and the
EA for Cu− CD3OD.
The Cu− CD3OD 600 nm raw photoelectron image, BASEX reconstructed
photoelectron image, and photoelectron spectrum are presented in Figure 7.6, along with thespectral simulation mentioned in the introduction. A cursory look at the images immediately
shows that there is negligible vibrational structure, i.e. a single peak. The spectrum shows
this as well, but it also shows that there is some asymmetry in the peak shape, and some

135
subtle shoulders on the low electron binding energy side of the peak. The shoulders, or
ripples, on the high electron binding energy side of the peak are clearly due to the periodic
center line noise caused by the image reconstruction. This noise is seen as a vertical line ofdots in the reconstructed image, but is most intense on the inside (high binding energy) of themain image feature, and much less intense to the outside (low binding energy) of the feature.
The simulation beautifully reproduces the peak asymmetry and the low electron binding
energy shoulders, confirming that the photodetachment signal carrier is the Cu− CD3OD anion
complex in the geometry presented in Figure 7.3. The vertical detachment energy is assigned
as 1.642 (6) eV. The calculations predict that the difference in energy between the VDE andthe electron affinity approximately 0.187 eV, which sets the electron affinity of CuCD3OD as
1.455 (30) eV. As stated above, the error in the EA is largely due to the uncertainty of thecalculation.

136

5000

4000

a

counts

3000

2000

1000

0
1.8

1.7

1.6

1.5

1.4

electron binding energy (eV)Figure 7.6

CuCD3OD− 600 nm raw photoelectron image (top left), BASEX
reconstructed photoelectron image (top right), and photoelectron spectrum(bottom). The points in the spectrum are the experimental data and the solidline is a simulation as explained in the text.

The CuCD3O− 355 nm raw photoelectron image, BASEX reconstructed image, andphotoelectron spectrum are presented in Figure 7.7. The images are very similar to those of
Cu− CD3OD taken at 355 nm. Like the Cu− CD3OD images, the CuCD3O− images contain ahigh electron velocity feature as well as several complicated low electron velocity features.

137
In contrast to the Cu− CD3OD images, however, the CuCD3O− images contain three distinct
features at low electron kinetic energy. The image reconstruction clearly shows that thelowest and highest electron velocity features of these three have extended vibrational
progressions as well as angular anisotropies aligned with the electric field of the laser(vertical in the images). In contrast, the middle feature appears to have no vibrational
structure and little to no angular anisotropy.
The 355 nm photoelectron spectrum shows some unresolved vibrational features in
the low electron binding region, labeled “a” in Figure 7.7. These features are resolved in the
500 nm photoelectron spectrum presented in Figure 7.8 and discussed below. The highelectron binding energy portion of the spectrum clearly shows what appear to be threeelectronic states. The angular anisotropy parameters for these features support this as β ≈ 1.2
for peaks b – d, β = 0.3 for peak e, and β ≈ 1 for peaks f − h. The angular anisotropy
parameters clearly show that these three low electron binding energy features are produced byremoval of electrons from different orbitals in the anion, thus producing different electronic
states of the neutral.
Peak b is assigned as the vibrational origin of the first excited state of CuCD3O with
an electron binding energy of 2.778 (5) eV. When combined with the electron affinity of
CuCD3O (reported below) the electronic term energy of this state is measured to be 1.701 (2)eV, or 13,720 (16) cm−1. A vibrational progression (peaks b – d) of 520 (50) cm−1 is also
seen in the transitions to this electronic state. Peak e is assigned as the second excitedelectronic state of CuCD3O− with an electron binding energy of 3.133 (6) eV and anelectronic term energy of 2.056 (4) eV, or 16,583 (32) cm−1. Peak f is assigned as thevibrational origin of the third excited electronic state of CuCD3O with an electron binding
energy of 3.271 (6) eV and an electronic term energy of 2.194 (4) eV or 17,696 (32) cm−1.
This electronic state also has a vibrational progression (peaks f – h) of 335 (60) cm−1.

138

5000

a
b

4000

c
d

counts

3000

2000

g

f e

h

1000

0
3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.0

electron binding energy (eV)Figure 7.7

CuCD3O− 355 nm raw photoelectron image (top left), BASEX reconstructed
photoelectron image (top right), and photoelectron spectrum (bottom).

139
The CuCD3O− 500 nm raw photoelectron image, BASEX reconstructed image, andphotoelectron spectrum are presented in Figure 7.8. At this photodetachment wavelength theresolution of the ground state features labeled “a” in Figure 7.7 is much improved. The
reconstructed image shows clear vibrational structure in the outmost (high electron velocity)
portion of the image. The angular anisotropy of the image is again aligned with the electricfield of the laser pulse, which is vertical in the images. In addition, both the raw image andreconstruction show significant detachment at the very center of the image, whichcorresponds to near zero kinetic energy electrons.

The images clearly show electron

detachment up to the energy of the photodetachment laser pulse. The photoelectron spectrum
has a very clear and short vibrational progression (peaks a – d) of 528 (50) cm−1. The originof this vibrational progression is peak “a” and is assigned as the electron affinity of CuCD3O
with a value of 1.077 (4) eV. The angular anisotropy values for peaks a – d are very near β ≈1.2, confirming the assignment that these transitions are to and from the same electronic state.

140

2000

b

a

1500

counts

c
1000

d
500

0
2.0

1.5

1.0

0.5

0.0

eBE (eV)Figure 7.8

CuCD3O− 500 nm raw photoelectron image (top left), BASEX reconstructed
photoelectron image (top right), and photoelectron spectrum (bottom).

141

7.4

Discussion
As mentioned in the introduction, the electronic structure of the neutrals created upon

photodetachment of the copper ligand complexes studied here essentially follows the atomic
copper netural electronic structure (see Figure 7.1). Table 7.1 compares the electron affinities
and electronic term energies for the first two electronic excited states, corresponding toCu(2D5/2, 3/2), of Cu, CuH2O, and CuCD3OD. Immediately noticeable from Table 7.1 is thatthe addition of both water and methanol to copper anion increases the neutral electron affinity
by ~ 230 meV. The binding energies for the first excited state (correlating to 2D5/2 in copper
neutral) of the complexes, however, are all increased by the addition of the different ligands.
The “2D5/2” electron binding energies for CuCD3OD and CuH2O differ by 200 – 300 meV. It
is possible that this is due to this value being the vertical detachment energy (VDE) in thecase of CuH2O, as the origin is certainly lower in energy. This strongly suggests that theCu(2D5/2)H2O origin is the shoulder feature at 2.85 eV electron binding energy in Figure 7.2.
In the case of the “2D3/2” state features, the features in the Cu− H2O and Cu− CD3OD spectra
have no obvious origin and are thus reported as vertical detachment energies.

142
Table 7.1

Measured electron affinities and anion electron binding energies forphotodetachment of Cu−, Cu− H2O, and Cu−CD3OD to the neutral states
which correlate to the 2D5/2 and 2D3/2 electronic states of copper atom.
22

species

electron affinity
(eV)

Cu

1.236a2.623a2.878aCuH2O

1.480b,c

3.050 (VDE) c

3.313 (VDE) c

CuCD3OD

1.455b

2.877 (Origin)

3.297 (VDE)

D5/2 eBE derived from
Origin or VDE (eV)D3/2 eBE derived from
Origin or VDE (eV)a

From reference 7b

Estimated from calculated difference between vertical detachment energy and electron affinityc

From reference 2

As mentioned in the introduction, spectral simulation of the ground state portion of
the CuCD3O− photoelectron spectrum will allow an assignment of the ~ 520 cm−1 vibrational
progression seen in the Cu− CD3OD and CuCD3O− excited state portions of the photoelectron
spectra. The simulation was conducted as described in chapter 2, using the B3LYP methodwith the aug-cc-pvtz basis set for carbon, oxygen, and hydrogen, and the (7s,7p,6d,3f ) basis
set of Wang and coworkers9 for copper. The vibrational mode excited in the simulation is a ~720 cm−1 methyl rock motion which contracts the O – C – H bond angle. No other motions
had any appreciable excitation in the simulation, thus the ~ 520 cm−1 vibrational progression
observed in the photoelectron spectra of Cu− CD3OD and CuCD3O− are assigned to thismotion. The same vibrational excitation is assigned in the photoelectron spectrum of CH3O−
recorded by Ramond and coworkers.10
The electronic structure of CuCD3O is very different from the electronic structure of
CuH2O and CuCD3OD. Both water and methanol are closed shell polar molecules, thus thecomplexes are best described as having dipole-induced dipole interactions. In CuCD3O a143
bonding interaction occurs between the copper 4s electron and the oxygen 2p electron, thus
the CuCD3O electronic structure is compared to that of CuOH. Table 7.2 presents themeasured electron affinities and low-lying electronic state term energies for CuOH andCuCD3O. As mentioned in the introduction, the photoelectron spectrum of CuOH− andCu− H2O measured by Misaizu may have been assigned incorrectly. The electron affinities of
the two species differ by less than 10 meV, and the 2nd and 3rd excited electronic state term
energies are very similar as well.

However, the first excited state of CuOH may beoverlapped by the excited states of CuH2O in the Misaizu spectrum. If there is a low-lying
CuOH excited state it is most likely a triplet state, as the observed electronic transitions11,12
were observed between the singlet ground state and excited singlet states. The low-lying
singlet states have also been calculated recently,13 but no calculations of the low-lying triplet
states have been reported. A high mass and high energy resolution photoelectron spectrum of
CuOH− would certainly detect the presence or absence of a low-lying triplet state, and suchan experiment is certainly possible using the photoelectron imaging apparatus described here.
Table 7.2

Measured anion electron binding energies for detachment to the three lowest
lying neutral electronic states of CuOH and CuCD3O.

species

electronaffinity (eV)

1st excited state
Te (eV)

2nd excited state
Te (eV)

3rd excited state
Te (eV)

CuOH

0.98 asee note b

1.973 c2.282 dCuCD3Oe

1.077 (4)1.701 (2)2.056 (4)2.194 (4)aFrom reference 5bAssumed to be unreported and uncalculated low lying triplet excited state of CuOH, see textc

From reference 11de

From reference 10

This work

144
References for Chapter VII
1
2
3
4
5
6
7
8
9
10
11
12
13

F. Muntean, M. S. Taylor, A. B. McCoy, and W. C. Lineberger, The Journal ofChemical Physics 121, 5676 (2004).
G. J. Rathbone, T. Sanford, D. Andrews, and W. C. Lineberger, Chemical Physics
Letters 401 (4-6), 570 (2005).
M. S. Taylor, J. Barbera, C.-P. Shulz, F. Muntean, A. B. McCoy, and W. C.
Lineberger, The Journal of Chemical Physics 122, 05431 (2005).
M. S. Taylor, F. Muntean, W. C. Lineberger, and A. B. McCoy, The Journal ofChemical Physics 121, 5688 (2004).
J. Barbera, S. Horvath, V. Dribinski, A. B. McCoy, and W. C. Lineberger, (InPreparation).
F. Misaizu, K. Tsukamoto, M. Sanekata, and K. Fuke, Surface Review and Letters 3(1), 405 (1996).
NIST, NIST Chemistry Webbook, NIST Standard Reference Database Number 69,
June 2005 Release.
J. Sugar and A. Musgrove, Journal of Physical and Chemical Reference Data 19, 527(1990).
X.-B. Wang, L.-S. Wang, R. Brown, P. Schwerdtfeger, D. Schroder, and H. Schwarz,
The Journal of Chemical Physics 114 (17), 7388 (2001).
T. M. Ramond, G. E. Davico, R. L. Schwartz, and W. C. Lineberger, The Journal ofChemical Physics 112 (3), 1158 (2000).
C. N. Jarman, W. T. M. L. Fernando, and P. F. Bernath, Journal of Molecular
Spectroscopy 144 (2), 286 (1990).
C. N. Jarman, W. T. M. L. Fernando, and P. F. Bernath, Journal of Molecular
Spectroscopy 145, 151 (1991).
S. Wang, A. Paul, N. J. DeYonder, Y. Yamaguchi, and H. F. Shaefer, The Journal ofChemical Physics 123, 014313 (2005).

145________________

Conclusions________________
This thesis presented the results of anion photoelectron spectroscopy experiments
conducted on three classes of anions. One class is that of heteronuclear coinage metal
diatomic molecules. These include AgO−, AuO−, AuS−, CuH−, and CuD−. The photoelectron
spectra of these molecules are characterized by short vibrational progressions in transitions to
the ground electronic states and confident assignments of the electronic state origins andelectron affinities. The photoelectron spectra of these molecules measured for the first timethe electron affinities of the corresponding neutral molecules. Frank-Condon simulation of
the observed ground state vibrational structure coupled with observation of a wellcharacterized excited state allowed for the assignment of the anion equilibrium bond lengths
for AgO−, CuH−, and CuD−. Because no excited electronic states were observed in thephotoelectron spectra of AuO− and AuS−, only the magnitude of the bond length change
between the anion and the neutral molecules was assigned. Observation of hot-bands in thephotoelectron spectra allowed for the first assignment of anion harmonic vibrationalfrequencies for AgO− and AuS−. In addition, a predicted, yet previously unobserved, 3Σ+
excited electronic state of CuD and CuH was observed in the photoelectron spectra of CuD−
and CuH−.
The second class of molecules studied was that of copper anion complexes. These
included Cu− CD3OD, CuCD3O−, CuH2−, and CuD2−. The photoelectron spectra of thesecomplexes are characterized by extended vibrational progressions in transitions to nearly all
the electronic states observed. These extended vibrational progressions are the product of

146large geometry changes between the anion and neutral complexes.

In the case of

Cu− CD3OD, the geometry change is so significant that ground electronic state
photodetachment is only observed which produces a higher energy, yet stable, conformer of
CuCD3OD. Thus, only the vertical detachment energy was experimentally determined, withthe adiabatic electron affinity assigned on the basis of a high level spectral simulation. The
geometry change for transitions to the excited states electronic states of CuCD3OD is lesssevere, which allowed for the assignment of the excited electronic state origins.

The

geometry difference between the anion and neutral CuCD3O is also small enough such that
all the electronic state origins in the photoelectron spectrum were assigned. A vibrationalmode excited in the ground electronic state of CuCD3O, and in the excited states of CuCD3O
and CuCD3OD was identified. It was found to be very similar to a vibrational mode excitedin the photoelectron spectrum of CH3O−.
The geometry change between the anion and neutral of CuH2 and CuD2 is also very
severe, as the anions are linear and the neutrals are very bent (bond angle of ~ 122°).
However, the geometry change is so great in the bending coordinate that the vibrational
overlap of this mode between the anion and neutral in the energy region studied produced
very weak features in the photoelectron spectrum. The spectra, then, are dominated by ashort vibrational progression in the symmetric stretch mode which allows determination of
the electron affinities of CuH2 and CuD2.
The photoelectron spectra of two related organic compounds were also taken.
Photoelectron spectra of the 1,2,3-triazolide anion were recorded and show signatures ofstrong vibronic coupling of the low lying electronic states of the neutral. Still, the vibrational
origin of transitions to the ground electronic state of the neutral allowed for easy assignmentof the neutral electron affinity. Combination of the measured electron affinity with the gas
phase acidity measured elsewhere allowed for determination of the N-H bond dissociation

147
energy of the parent molecule 1H-1,2,3-triazolide. In addition, the heat of formation of the
1,2,3-trizolyl radical was also determined. It was also found that, under the experimental
source conditions used in these experiments, about 40% of the 1,2,3-triazolide anions ring
open to form the E-iminodiazomethide anion, the structure of which was assigned on thebasis of a simulation of the measured photoelectron spectrum. The simulation also allowedassignment of several normal mode frequencies of the anion and neutral. It is interesting tonote that the lower azole anions (pyrolide, pyrazolide, and imidazolide) were found not toring-open under similar experimental conditions.

________________
Bibliography________________

T. Andersen, H.K. Haugen, and H. Hotop, Binding energies in atomic negative ions: III.
Journal of Physical and Chemical Reference Data, 1999. 28(6): p. 1511-1533.
D.H. Andrews, A.J. Gianola, and W.C. Lineberger, On the photoelectron spectrum of AgO−.
Journal of Chemical Physics, 2002. 117(8): p. 4074 - 4076.
D.H. Andrews, T. Ichino, R.M.D. Calvi, A.J. Gianola, S. Kato, G.J. Rathbone, F. Misaizu,
V.M. Bierbaum, and W.C. Lineberger, Photoelectron Spectroscopy of 1,2,3Triazolide Isomers and Gas Phase Acity Bracketing of 2H-1,2,3-Triazole. 2006(InPreparation).
L. Andrews and X. Wang, Infrared Spectra and Structures of the Stable CuH2−, AgH2−, AuH2−, and AuH4− Anions and the AuH2 Molecule. Journal of the American Chemical
Society, 2003. 125(38): p. 11751-11760.
J. Andzelm, E. Radzio, and D.R. Salahub, Model Potential Calculations For 2nd-Row
Transition-Metal Molecules Within the Local-Spin-Density Method. Journal ofChemical Physics, 1985. 83(9): p. 4573-4580.
A.M. Antic-Jovanovic and D.S. Pesic, Emission spectra of copper(I) hydroxide anddeuterated copper(I) hydroxide in the regions between 5100-5600 Ang. and 61506300 Ang. Glasnik Hemijskog Drustva Beograd, 1969. 34(2-4): p. 163-9.
M. Arai, T. Tsukahara, and M. Tamura, Deflagration properties of triazoles and theircompositions as candidates for new gas generating agent of the air bag system.
Proceedings of the International Pyrotechnics Seminar, 1999. 26th: p. 7-14.
K. Babic-Samardzija and N. Hackerman, Triazole, benzotriazole and substituted
benzotriazoles as corrosion inhibitors of iron in aerated acidic media. Journal of
Solid State Electrochemistry, 2005. 9(7): p. 483-497.
M.M. Balkis, S.D. Leidich, P.K. Mukherjee, and M.A. Ghannoum, Mechanisms of fungal
resistance - An overview. Drugs, 2002. 62(7): p. 1025-1040.
V. Barone and C. Adamo, Validation of Hybrid Density Functional/Hartree-Fock
Approaches for the Study of Homogeneous Catalysis. Journal of Physical Chemistry,
1996. 100(6): p. 2094-9.
V. Barone and C. Adamo, First-row transition-metal hydrides: a challenging playground for
new theoretical approaches. International Journal of Quantum Chemistry, 1997.
61(3): p. 443-451.
C.W. Bauschlicher, C.J. Nelin, and P.S. Bagus, Transition-Metal Oxides - CrO, MoO, NiO,
PdO, AgO. Journal of Chemical Physics, 1985. 82(7): p. 3265-3276.

149

C.W. Bauschlicher, H. Partridge, and S.R. Langhoff, An Abinitio Study of the Low-Lying
Doublet States of AgO and AgS. Chemical Physics, 1990. 148(1): p. 57-68.
P. Belohorec, S.M. Rothstein, and J. Vrbik, Infinitesimal, differential, diffusion-quantumMonte-Carlo study of copper hydride (CuH) spectroscopic constants. Journal ofChemical Physics, 1993. 98(8): p. 6401-5.
V.N. Belyaev, N.L. Lebedeva, K.S. Krasnov, and L.V. Gurvich, Flame spectrophotometricdetermination of the dissociation energy of copper oxide and hydroxide. Izvestiya
Vysshikh Uchebnykh Zavedenii, Khimiya i Khimicheskaya Tekhnologiya, 1978.
21(11): p. 1698-700.
P.F. Bernath, Laser and Fourier transform spectroscopy: diatomics to organometallics. AIP
Conference Proceedings, 1986. 146(Adv. Laser Sci. - 1): p. 443-6.
R.C. Bilodeau, M. Scheer, and H.K. Haugen, Infrared laser photodetachment of transition
metal negative ions: studies on Cr-, Mo-, Cu- and Ag. Journal of Physics B-Atomic
Molecular and Optical Physics, 1998. 31(17): p. 3885-3891.
S.J. Blanksby and G.B. Ellison, Bond dissociation energies of organic molecules. Accountsof Chemical Research, 2003. 36(4): p. 255-263.
C. Blondel, P. Cacciani, C. Delsart, and R. Trainham, HIGH-RESOLUTION
DETERMINATION OF THE ELECTRON-AFFINITY OF FLUORINE AND
BROMINE USING CROSSED ION AND LASER BEAMS. Physical Review A, 1989.
40(7): p. 3698 - 3701.
J.C.A. Boeyens and R.H. Lemmer, Valence bond studies. Part 2. Diatomic compounds ofcopper, silver and gold. Journal of the Chemical Society, Faraday Transactions 2:
Molecular and Chemical Physics, 1977. 73(3): p. 321-6.
V. Bojovic, A. Antic-Jovanovic, M.M. Stoiljkovic, M. Miletic, and D.S. Pesic, Vibrational
structure of the B-X system of isotopic AgO molecules. Spectroscopy Letters, 1999.
32(5): p. 875-882.
G. Bravo-Perez and I.L. Garzon, Ab initio study of small AunS, (n=1-5), and AunS2, (n=1-4),
clusters. Theochem, 2002. 619: p. 79-89.
C.M. Brown and M.L. Ginter, The absorption spectrum of copper(I) hydride in the 2350- to1890 angstrom region. Journal of Molecular Spectroscopy, 1980. 80(1): p. 145-57.
D. Buchel, C. Mihalcea, T. Fukaya, N. Atoda, J. Tominaga, T. Kikukawa, and H. Fuji,
Sputtered silver oxide layers for surface-enhanced Raman spectroscopy. Applied
Physics Letters, 2001. 79(5): p. 620-622.
S.B. Bulgarevich, V.S. Bolotnikov, V.N. Sheinker, O.A. Osipov, and A.D. Garnovskii,
Structure and properties of heterocyclic compounds and their complexes. XIX. Vector
additive system for calculating the dipole moments of azoles. Zhurnal Obshchei
Khimii, 1975. 45(8): p. 1821-6.

150
R. Burtovyy, E. Utzig, and M. Tkacz, Studies of the thermal decomposition of copper
hydride. Thermochimica Acta, 2000. 363(1-2): p. 157-163.
R. Burtovyy, D. Wlosewicz, A. Czopnik, and M. Tkacz, Heat capacity of copper hydride.
Thermochimica Acta, 2003. 400(1-2): p. 121-129.
K. Cashion, Calculating vibrational transition probabilities. Journal of Molecular
Spectroscopy, 1963. 10: p. 182-231.
J. Catalán, R.M. Claramunt, J. Elguero, J. Laynez, M. Menéndez, F. Anvia, J.H. Quian, M.
Taagepera, and R.W. Taft, Basicity and Acidity of Azoles: The Annelation Effect inAzoles. J. Am. Chem. Soc., 1988. 110(13): p. 4105-4111.
Z.X. Chen and H.M. Xiao, Theoretical study on tetrazole and its derivatives: 4. Ab initio
study on hydroxyl derivatives of tetrazole. Propellants Explosives Pyrotechnics, 1999.
24(5): p. 319-324.
C.L. Collins, K.G. Dyall, and H.F. Schaefer, III, Relativistic and correlation effects in CuH,
AgH, and AuH: comparison of various relativistic methods. Journal of Chemical
Physics, 1995. 102(5): p. 2024-31.
J. Cooper and R.N. Zare, Angular distribution of photoelectrons. Journal of Chemical
Physics, 1968. 48: p. 942-943.
G. Das, A pseudopotential study of the iron-series transition metal hydrides. Journal ofChemical Physics, 1981. 74(10): p. 5766-74.
Y. Ding, S.A. Hofstadler, E.E. Swayze, L. Risen, and R.H. Griffey, Design and synthesis ofparomomycin-related heterocycle-substituted amino-glycoside mimetics based on amass spectrometry RNA-binding assay. Angewandte Chemie, International Edition,
2003. 42(29): p. 3409-3412.
V. Dribinski, A. Ossadtchi, V.A. Mandelshtam, and H. Reisler, Reconstruction of Abeltransformable images: The Gaussian basis-set expansion Abel transform method.
Review of Scientific Instruments, 2002. 73(7): p. 2634 - 2642.
M. Ebben, G. Meijer, and J.J. Ter Meulen, Laser evaporation as a source of small free
radicals. Applied Physics B: Photophysics and Laser Chemistry, 1990. B50(1): p. 358.
A.A. El-Azhary, H.U. Suter, and J. Kubelka, Experimental and Theoretical Investigation of
the Geometry and Vibrational Frequencies of 1,2,3-Triazole, 1,2,4-Triazole, andTetrazole Anions. Journal of Physical Chemistry A, 1998. 102(3): p. 620-629.
A.T.J.B. Eppink and D.H. Parker, Velocity map imaging of ions and electrons using
electrostatic lenses: Application in photoelectron and photofragment ion imaging ofmolecular oxygen. Review of Scientific Instruments, 1997. 68(9): p. 3477 - 3484.
K.M. Ervin, J. Ho, and W.C. Lineberger, A study of the singlet and triplet states of vinylideneby photoelectron spectroscopy of H2C=C–, D2C=C–, and HDC=C–. Vinylidene–
acetylene isomerization. Journal of Chemical Physics, 1989. 91: p. 5974.

151

K.M. Ervin and W.C. Lineberger, Photoelectron Spectroscopy of Negative Ions, in Advancesin Gas Phase Ion Chemistry, N.G. Adams and L.M. Babcock, Editors. 1992, JAI
Press: Greenwich. p. 121-166.
K.M. Ervin, PESCAL. 2001: Reno, NV.
K.M. Ervin, T.M. Ramond, G.E. Davico, R.L. Schwartz, S.M. Casey, and W.C. Lineberger,
Naphthyl radical: Negative ion photoelectron spectroscopy, Franck-Condon
simulation, and thermochemistry. Journal of Physical Chemistry A, 2001. 105(48): p.
10822-10831.
K.M. Ervin, PESCAL, Fortran program. 2003.
W.M.F. Fabian, V.A. Bakulev, and C.O. Kappe, Pericyclic versus Pseudopericyclic 1,5Electrocyclization of Iminodiazomethanes. An ab Initio and Density Functional
Theory Study. Journal of Organic Chemistry, 1998. 63(17): p. 5801.
P. Fantucci, S. Polezzo, G. Morosi, and V. Valenti, Valence-Only Model Potential
Calculations on Copper Hydride Molecule. Theoretica Chimica Acta, 1985. 67(3): p.
245-253.
M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, J.A.
Montgomery, Jr. , T. Vreven, K.N. Kudin, J.C. Burant, J.M. Millam, S.S. Iyengar, J.
Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G.A. Petersson,
H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegama, M. Ishida, T.
Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J.E. Knox, H.P.
Hratchian, J.B. Cross, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O.
Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, P.Y. Ayala, K.
Morokuma, G.A. Voth, P. Salvador, J.J. Dannenberg, V.G. Zakrzewski, S. Dapprich,
A.D. Daniels, M.C. Strain, O. Farkas, D.K. Malick, A.D. Rabuck, K. Raghavachari,
J.B. Foresman, J.V. Ortiz, Q. Cui, A.G. Baboul, S. Clifford, J. Cioslowski, B.B.
Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R.L. Martin, D.J. Fox, T.
Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, M. Challacombe, P.M.W. Gill,
B. Johnson, W. Chen, M.W. Wong, C. Gonzalez, and J.A. Pople, Gaussian 03,
Revision B.05. 2003, Gaussian, Inc.: Pittsburgh, PA.
R. Georgiadis, E.R. Fisher, and P.B. Armentrout, Neutral and ionic metal-hydrogen andmetal-carbon bond energies: reactions of cobalt, nickel, and copper with ethane,
propane, methylpropane, and dimethylpropane. Journal of the American Chemical
Society, 1989. 111(12): p. 4251-62.
A.J. Gianola, T. Ichino, R.L. Hoenigman, S. Kato, V.M. Bierbaum, and W.C. Lineberger,
Thermochemistry and Electronic Structure of the Pyrrolyl Radical. J. Phys. Chem.
A., 2004. 108(46): p. 10326-10335.
A.J. Gianola, T. Ichino, R.L. Hoenigman, S. Kato, V.M. Bierbaum, and W.C. Lineberger,
Photoelectron Spectra and Ion Chemistry of Imidazolide. J. Phys. Chem. A., 2005.
109(50): p. 11504-11514.

152
A.J. Gianola, Photoelectron Spectroscopy of Negative Ions, in Department of Chemistry andBiochemistry. 2006, University of Colorado: Boulder.
A.J. Gianola, T. Ichino, S. Kato, V.M. Bierbaum, and W.C. Lineberger, ThermochemicalStudies of Pyrazolide. J. Phys. Chem. A., 2006: p. (in press).
K.A. Gingerich, Mass-spectrometric determination of the bond energies of the molecules
AuS, BS, and BS2. Journal of the Chemical Society [Section] D: Chemical
Communications, 1970(10): p. 580-1.
M.J. Griffiths and R.F. Barrow, Observations On a 2Πi - X 2Πi Transition in Gaseous AgO.
Journal of Physics B, 1977. 10(5): p. 925-930.
M.J. Griffiths and R.F. Barrow, Observations on Electronic-Spectra of CuO AgO and AuO
Isolated in Rare-Gas Matrices. Journal of the Chemical Society-Faraday
Transactions Ii, 1977. 73: p. 943-951.
J.D. Grunwaldt and A. Baiker, Gold/Titania Interfaces and Their Role in Carbon Monoxide
Oxidation. Journal of Physical Chemistry B, 1999. 103: p. 1002 - 1012.
J.D. Grunwaldt, M. Maciejewski, O.S. Becker, P. Fabrizioli, and A. Baiker, Comparative
Study of Au/TiO2 and Au/ZrO2 Catalysts for Low-Temperature CO Oxidation. Journalof Catalysis, 1999. 186(2): p. 458 - 469.
H.M. Guardiola-Diaz, L.A. Foster, D. Mushrush, and A.D.N. Vaz, Azole-antifungal binding
to a novel cytochrome P450 from Mycobacterium tuberculosis: implications fortreatment of tuberculosis. Biochemical Pharmacology, 2001. 61(12): p. 1463-1470.
M. Haruta, N. Yamada, T. Kobayashi, and S. Iijima, Gold catalysis prepared bycoprecipitation for low-temperature oxidation of hydrogen and of carbon monoxide.
Journal of Catalysis, 1989. 115(2): p. 301 - 309.
M. Haruta, Size- and support-dependency in the catalysis of gold. Catalysis Today, 1997.
36(1): p. 153 - 166.
P.J. Hay and R.L. Martin, All-Electron and Valence-Electron Calculations On AgH, Ag2, andAgO. Journal of Chemical Physics, 1985. 83(10): p. 5174-5181.
A. Hecq, M. Vandy, and M. Hecq, Determination of Au−O bond energy by glow discharge
mass spectrometry. Journal of Chemical Physics, 1980. 72(4): p. 2876 - 2878.
M. Hliwa, J.C. Barthelat, M. Pelissier, and F. Spiegelmann, Calculation and Analysis of the
Low-Lying Excited 3,1Σ+ States of Copper Hydride. Chemical Physics Letters, 1986.
132(2): p. 205-208.
J. Ho, K.M. Ervin, and W.C. Lineberger, Photoelectron-Spectroscopy of Metal Cluster
Anions - Cun−, Agn− , and Aun−. Journal of Chemical Physics, 1990. 93(10): p. 69877002.

153
S. Hoyau and G. Ohanessian, Complexation of small organic molecules by Cu+. Chemical
Physics Letters, 1997. 280(3,4): p. 266-272.
J. Hrusak, S. Ten-No, and S. Iwata, Quadratic configuration interaction versus coupledcluster theory: importance of orbital relaxation phenomena in CuH and CuF. Journalof Chemical Physics, 1997. 106(17): p. 7185-7192.
K. Huber and G. Herzberg, Molecular Spectra and Molecular Structure, Constants ofDiatomic Molecules. 1979, New York: Van Nostrand-Reinhold.
E.P. Hunter and S.G. Lias, Proton Affinity Evaluation, in NIST Chemistry WebBook, NIST
Standard Reference Database Number 69, P.J. Linstrom and W.G. Mallard, Editors.
2005, National Institute of Standards and Technology: Gaithersburg MD, 20899.
T. Ichino, A.J. Gianola, D.H. Andrews, and W.C. Lineberger, Photoelectron Spectroscopy of
AuO− and AuS−. Journal of Physical Chemistry A, 2004. 108(51): p. 11307 - 11313.
G. Igel, U. Wedig, M. Dolg, P. Fuentealba, H. Preuss, H. Stoll, and R. Frey, Cu and Ag As
One-Valence-Electron Atoms - Pseudopotential CI Results For CuO and AgO.
Journal of Chemical Physics, 1984. 81(6): p. 2737-2740.
C.N. Jarman, W.T.M.L. Fernando, and P.F. Bernath, Further analysis of the ~B1A''-~X1A'
system of copper hydroxide (CuOH) and copper deuteroxide (CuOD). Journal of
Molecular Spectroscopy, 1990. 144(2): p. 286-303.
C.N. Jarman, W.T.M.L. Fernando, and P.F. Bernath, A to X CuOH system. Journal of
Molecular Spectroscopy, 1991. 145: p. 151.
T. Joseph-Horne and D.W. Hollomon, Molecular mechanisms of azole resistance in fungi.
Fems Microbiology Letters, 1997. 149(2): p. 141-149.
S.A. Kaluzhina and G.V. Shatalov, Triazole derivatives as inhibitors of general andthermogalvanic corrosion of iron in a 0.1N sulfuric acid solution. II. Effect oftriazole derivatives on thermogalvanic corrosion of iron in a 0.1N sulfuric acidsolution. 1975, Voronezh. Gos. Univ.,Voronezh,USSR. p. 9 pp.
A. Kant and K.A. Moon, Dissociation energies of gaseous copper, silver, gold, and nickel
hydrides. High Temperature Science, 1979. 11(1): p. 55-62.
V.V. Karasiev, Parameter-free local exchange and Pade approximation for correlation:
application to diatomic molecules. Theochem, 1999. 493: p. 21-28.
V. Kello and A.J. Sadlej, Electron correlation and relativistic effects in the coinage metalcompounds. I. The coinage metal hydrides. Theoretica Chimica Acta, 1995. 92(4): p.
253-67.
V. Kello and A.J. Sadlej, The change of picture of the Hellmann-Feynman force operator inapproximate relativistic methods. Theochem, 2001. 547: p. 35-53.

154
V. Kelloe and A.J. Sadlej, Quadrupole moments of copper hydride, silver hydride, and gold
hydride (CuH, AgH, and AuH). A study of the electron-correlation and relativistic
effects. Journal of Chemical Physics, 1991. 95(11): p. 8248-53.
V. Kelloe and A.J. Sadlej, Standardized basis sets for high-level correlated relativistic
calculations of atomic and molecular electric properties in the spin-averaged
Douglas-Kroll (no-pair) approximation. Part 1. Groups Ib and IIb. Theoretica
Chimica Acta, 1996. 94(2): p. 93-104.
V. Kelloe, A.J. Sadlej, and B.A. Hess, Relativistic effects on electric properties of manyelectron systems in spin-averaged Douglas-Kroll and Pauli approximations. Journalof Chemical Physics, 1996. 105(5): p. 1995-2003.
H. Kusama, M. Kurashige, and H. Arakawa, Influence of nitrogen-containing heterocyclic
additives in I-/I3- redox electrolytic solution on the performance of Ru-dye-sensitizednanocrystalline TiO2 solar cell. Journal of Photochemistry and Photobiology, A:
Chemistry, 2005. 169(2): p. 169-176.
D.G. Leopold, K.K. Murray, A.E. Stevens-Miller, and W.C. Lineberger, Methylene: A studyof the X 3B1 and a 1A1 states by photoelectron spectroscopy of CH2− and CD2−.
Journal of Chemical Physics, 1985. 83: p. 4849.
Z.P. Liu, P. Hu, and A. Alavi, Catalytic role of gold in gold-based catalysts: A density
functional theory study on the CO oxidation on gold. Journal of the American
Chemical Society, 2002. 124(49): p. 14770-14779.
F.W. Loomis and T.F. Watson, Band Spectra of AgO and CuO. Physical Review, 1935. 48: p.
280-282.
N. Lopez and J.K. Norskov, Catalytic CO oxidation by a gold nanoparticle: A density
functional study. Journal of the American Chemical Society, 2002. 124(38): p.
11262-11263.
C.M. Marian, Theoretical study of the spectra of CuH and CuD. The Journal of Chemical
Physics, 1991. 94(8): p. 5574.
C.M. Marian, Theoretical study of the spectra of copper hydride and copper deuteride (CuH
and CuD). Journal of Chemical Physics, 1991. 94(8): p. 5574-85.
M.C. McCarthy and R.W. Field, Frequency-modulation enhanced magnetic rotation
spectroscopy of PdH, PdD, NiH, and CuH. Journal of Chemical Physics, 1994.
100(9): p. 6347-58.
M. Merchan, J.P. Daudey, R. Gonzalez-Luque, and I. Nebot-Gil, On the dissociation energyof the copper dimer and copper hydride (CuH) using a differential correlation
approach. Chemical Physics, 1990. 148(1): p. 69-76.
J. Micanko and S. Biskupic, Relativistic and correlation study of coinage metal hydrides.
ACH - Models in Chemistry, 2000. 137(5-6): p. 753-766.

155
N. Minh Tho, M.A. McGinn, and N.J. Fitzpatrick, A theoretical characterization of somediatomic copper species. Journal of the Chemical Society, Faraday Transactions 2:
Molecular and Chemical Physics, 1986. 82(9): p. 1427-43.
F. Misaizu, K. Tsukamoto, M. Sanekata, and K. Fuke, Photoelectron spectroscopy of massselected metal-water cluster negative ions: Cu-(H2O)n and Na-(H2O)n. Surface
Review and Letters, 1996. 3(1): p. 405-410.
C.E. Moore, Atomic Energy Levels. NSRDS-NBS. 1952, Washington: US GPO Circular No.
467.
F. Muntean, M.S. Taylor, A.B. McCoy, and W.C. Lineberger, Femtosecond study of Cu(H2O)
dynamics. The Journal of Chemical Physics, 2004. 121: p. 5676.
M.E. Nadal, P.D. Kleiber, and W.C. Lineberger, Photofragmentation of mass-selected ICl−
(CO2)n cluster ions: Solvation effects on the structure and dynamics of the ionicchromophore. The Journal of Chemical Physics, 1996. 105(2): p. 504 - 514.
A. Nakajima, T. Taguwa, K. Nakao, K. Hoshino, S. Iwata, and K. Kaya, Photoelectron
spectroscopy of binary-metal cluster anions containing sulfur atom. Surface Review
and Letters, 1996. 3(1): p. 417-421.
D.M. Neumark, K.R. Lykke, T. Andersen, and W.C. Lineberger, Laser Photodetachment
Measurement of the Electron Affinity of Atomic Oxygen. Physical Review A, 1985.
32(3): p. 1890-1892.
NIST, NIST Chemistry Webbook, NIST Standard Reference Database Number 69, June 2005
Release.
.
L.C. O'Brien, S.J. Wall, and M.K. Sieber, Fourier transform spectroscopy of the A 2Σ+ − X
2
Πi transition of AgO. Journal of Molecular Spectroscopy, 1997. 183(1): p. 57-60.
L.C. O'Brien, S.J. Wall, and G.L. Henry, The A 2Σ+ − X 2Πi (0, 1) band and reanalyses of theblue and ultraviolet transitions of AgO. Journal of Molecular Spectroscopy, 1998.
191(1): p. 218-220.
L.C. O'Brien, S.C. Hardimon, and J.J. O'Brien, Spectroscopy of AuO: Identification of the2
Π1/2 to X 2Π3/2 Transition. Journal of Physical Chemistry A, 2004. 108(51): p. 11302- 11306.
J. Onoe, H. Nakamatsu, T. Mukoyama, R. Sekine, H. Adachi, and K. Takeuchi, Relativisticchange in bond overlap population for the study of relativistic effect on bond lengthof diatomic molecules. Journal of the Physical Society of Japan, 1996. 65(8): p. 24592462.
J. Onoe, Atomic-number dependence of relativistic effects on chemical bonding. Advances in
Quantum Chemistry, 2001. 37: p. 311-323.

156
C. Opitz and H.H. Dunken, Extended Hueckel calculations for first-period transition-metalhydroxides. Zeitschrift fuer Physikalische Chemie (Leipzig), 1972. 249(3-4): p. 15460.
M. Pelissier, J.P. Daudey, J.P. Malrieu, and G.H. Jeung, The electronic structure of transition
metal atoms and diatoms through pseudopotential approaches. NATO ASI Series,
Series C: Mathematical and Physical Sciences, 1986. 176(Quantum Chem.:
Challenge Transition Met. Coord. Chem.): p. 37-51.
K.S. Pitzer, Relativistic Effects on Chemical Properties. Accounts of Chemical Research,
1979. 12(8): p. 272-276.
M.L. Polak, M.K. Gilles, J. Ho, and W.C. Lineberger, Photoelectron Spectroscopy of CuO−.
Journal of Physical Chemistry, 1991. 95(9): p. 3460-3463.
L.A. Posey, M.J. DeLuca, and M.A. Johnson, DEMONSTRATION OF A PULSEDPHOTOELECTRON SPECTROMETER ON MASS-SELECTED NEGATIVE IONSO−, O2−, AND O4−. Chemical Physics Letters, 1986. 131(3): p. 170 - 174.
R. Pou-Amerigo, M. Merchan, I. Nebot-Gil, P.A. Malmqvist, and B.O. Roos, The chemicalbonds in CuH, Cu2, NiH, and Ni2 studied with multiconfigurational second order
perturbation theory. Journal of Chemical Physics, 1994. 101(6): p. 4893-902.
P. Pyykko and J.P. Desclaux, Relativity and the Periodic System of Elements. Accounts ofChemical Research, 1979. 12(8): p. 276-281.
P. Pyykko, Relativistic Effects in Structural Chemistry. Chemical Reviews, 1988. 88(3): p.
563-594.
D. Radisic, S.J. Xu, and K.H. Bowen, Photoelectron spectroscopy of the anions, CH3NHand (CH3)(2)N- and the anion complexes, H-(CH3NH2) and (CH3)(2)N(CH3)(2)NH). Chemical Physics Letters, 2002. 354(1-2): p. 9-13.
K. Raghavachari, K.K. Sunil, and K.D. Jordan, Theoretical study of the bonding in copper(I)hydride and copper dimer (Cu2). Journal of Chemical Physics, 1985. 83(9): p. 463340.
T.M. Ramond, G.E. Davico, R.L. Schwartz, and W.C. Lineberger, Vibronic structure ofalkoxy radicals via photoelectron spectroscopy. The Journal of Chemical Physics,
2000. 112(3): p. 1158.
T.M. Ramond, Negative Ion Photoelectron Spectroscopy of Alkyl Peroxides, Alkoxides, andGroup VIII Transition Metal Oxides, in Department of Physics. 2001, University ofColorado: Boulder. p. 237.
T.M. Ramond, G.E. Davico, F. Hellberg, F. Svedberg, P. Salen, P. Soderqvist, and W.C.
Lineberger, Photoelectron spectroscopy of nickel, palladium, and platinum oxideanions. Journal of Molecular Spectroscopy, 2002. 216(1): p. 1 - 14.

157
V.M. Rao, M.L.P. Rao, and P.T. Rao, Dissociation energy of the ground state of thecopper(I) hydride molecule. Journal of Quantitative Spectroscopy & Radiative
Transfer, 1981. 25(6): p. 547-9.
G.J. Rathbone, T. Sanford, D. Andrews, and W.C. Lineberger, Photoelectron imaging
spectroscopy of Cu−(H2O)1,2 anion complexes. Chemical Physics Letters, 2005.
401(4-6): p. 570-574.
G. Rauhut, Modulation of reaction barriers by generating reactive intermediates: double
proton transfer reactions. Physical Chemistry Chemical Physics, 2003. 5(5): p. 791800.
P.J. Renders and T.M. Seward, The stability of hydrosulfido- and sulfido-complexes of gold(I)and silver(I) at 25 DegC. Geochimica et Cosmochimica Acta, 1989. 53(2): p. 245-53.
U. Ringstroem, New band system of copper hydride in the far ultraviolet. Canadian Journal of
Physics, 1968. 46(20): p. 2291-300.
U. Ringstrom, On the spectra of copper hydride and copper deuteride. Arkiv For Fysik,
1966. 32: p. 211.
S.M. Rothstein, Valence energy in variational Monte Carlo: CuH dissociation energy.
International Journal of Quantum Chemistry, 1996. 60(4): p. 803-808.
T.J. Sanford, Photodissociation Dynamics and Photoelectron Imaging Spectroscopy ofAnions and Anion Clusters, in Department of Chemistry and Biochemistry. 2004,
Colorado: Boulder. p. 212.
A. Sanov, T. Sanford, S. Nandi, and W.C. Lineberger, Spin-orbit relaxation andrecombination dynamics in I2−(CO2)n and I2−(OCS)n cluster ions: A new type ofphotofragment caging reaction. The Journal of Chemical Physics, 1999. 111(2): p.
664 - 675.
P. Schwerdtfeger, M. Dolg, W.H.E. Schwarz, G.A. Bowmaker, and P.D.W. Boyd,
Relativistic effects in gold chemistry. I. Diatomic gold compounds. Journal ofChemical Physics, 1989. 91(3): p. 1762 - 1774.
J.M. Seminario, A.G. Zacarias, and J.M. Tour, Molecular Alligator Clips for Single MoleculeElectronics. Studies of Group 16 and Isonitriles Interfaced with Au Contacts. Journalof the American Chemical Society, 1999. 121: p. 411 - 416.
G. Simons and E.R. Talaty, FSGO model for core d electrons: Optimized structures for thirdrow hydrides. Journal of Chemical Physics, 1977. 66(6): p. 2457-61.
D.F. Smith, G.R. Graybill, R.K. Grubbs, and J.A. Gucinski, New developments in very highrate silver oxide electrodes. Journal of Power Sources, 1997. 65(1-2): p. 47-52.
J.R. Smith, J.B. Kim, and W.C. Lineberger, High-Resolution Threshold Photodetachment
Spectroscopy of OH−. Physical Review A, 1997. 55: p. 2036.

158
H. Smithson, C.A. Marianetti, D. Morgan, A. Van der Ven, A. Predith, and G. Ceder, Firstprinciples study of the stability and electronic structure of metal hydrides. PhysicalReview B: Condensed Matter and Materials Physics, 2002. 66(14): p. 144107/1144107/10.
S. Smoes, F. Mandy, A. Vander Auwera-Mahieu, and J. Drowart, Determination by the massspectrometric Knudsen cell method of the dissociation energies of the Group IB
chalcogenides. Bulletin Des Societes Chimiques Belges, 1972. 81(1-2): p. 45-56.
J.F. Stanton, J. Gauss, J.D. Watts, M. Nooijen, N. Oliphant, S.A. Perera, P.G. Szalay, W.J.
Lauderdale, S.A. Kucharski, S.R. Gwaltney, S. Beck, A. Balková, D.E. Bernholdt,
K.K. Baeck, P. Rozyczko, H. Sekino, C. Hober, and R.J. Bartlett, ACES II, R.J.
Bartlett, Editor. 2006, Quantum Theory Project, University of Florida.
J.F. Stanton, T. Ichino, A.J. Gianola, and W.C. Lineberger, Nonadiabatic effects in thephotoelectron spectrum of the pyrazolide anion: Three-state interactions of thepyrazolyl radical. 2006.
T. Steimle, M. Tanimoto, K. Namiki, and S. Saito, The millimeter wave spectrum of silvermonoxide, AgO. Journal of Chemical Physics, 1998. 108(18): p. 7616-7622.
E. Stenz, G. Menzel, and G. Schuster, Effect of triazoles on DNA- and RNA-containing
bacteriophages and their hosts. Mikrobiologicheskii Zhurnal (1978-1993), 1980.
43(2): p. 239-42.
J. Sugar and A. Musgrove, Energy Levels of Copper, Cu I through Cu XXIX. Journal of
Physical and Chemical Reference Data, 1990. 19: p. 527.
E. Surber, R. Mabbs, and A. Sanov, Probing the Electronic Structure of Small MolecularAnions by Photoelectron Imaging. Journal of Physical Chemistry A, 2003. 107(40):p. 8215 - 8224.
T. Suzumura, T. Nakajima, and K. Hirao, Ground-state properties of MH, MCl, and M2 (M =Cu, Ag, and Au) calculated by a scalar relativistic density functional theory.
International Journal of Quantum Chemistry, 1999. 75(4/5): p. 757-766.
M.S. Taylor, F. Muntean, W.C. Lineberger, and A.B. McCoy, A theoretical andcomputational study of the anion, neutral, and cation Cu(H2O) complexes. The
Journal of Chemical Physics, 2004. 121: p. 5688.
M.S. Taylor, J. Barbera, C.-P. Shulz, F. Muntean, A.B. McCoy, and W.C. Lineberger,
Femtosecond Dynamics of Cu(H2O)2. The Journal of Chemical Physics, 2005. 122: p.
05431.
C. Toernkvist, J. Bergman, and B. Liedberg, Geometry and vibrations of the 1,2,3-triazole
anion. A theoretical and experimental study. Journal of Physical Chemistry, 1991.
95(8): p. 3119-23.
C.W. Tornoe, S.J. Sanderson, J.C. Mottram, G.H. Coombs, and M. Meldal, Combinatorial
Library of Peptidotriazoles: Identification of [1,2,3]-Triazole Inhibitors against a

159
Recombinant Leishmania mexicana Cysteine Protease. Journal of Combinatorial
Chemistry, 2004. 6(3): p. 312-324.
R.E. Trifonov, I. Alkorta, V.A. Ostrovskii, and J. Elguero, A theoretical study of the 1,2,3triazolo-iminodiazomethane isomerism in the gas phase. Heterocycles, 2000. 52(1):p. 291-302.
U. Uhler, On the Band Spectra of Silver Oxide. Arkiv For Fysik, 1953. 7(12): p. 125-147.
M. Valden, X. Lai, and D.W. Goodman, Onset of Catalytic Activity of Gold Clusters on
Titania with the Appearance of Nonmetallic Properties. Science, 1998. 281(5383): p.
1647 - 1650.
C. van Wullen, Molecular density functional calculations in the regular relativistic
approximation: method, application to coinage metal diatomics, hydrides, fluorides
and chlorides, and comparison with first-order relativistic calculations. Journal ofChemical Physics, 1998. 109(2): p. 392-399.
T.D. Varberg and K.M. Evenson, The pure rotational spectra of CuH and CuD in their
ground states measured by tunable far-infrared spectroscopy. Journal of Molecular
Spectroscopy, 1994. 164(2): p. 531-5.
R. Vianello and Z.B. Maksic, Acidities of azoles in the gas phase and in DMSO: an ab initio
and DFT study. Molecular Physics, 2005. 103(2-3): p. 209-219.
B.R. Vujisic, J.J. Savovic, V. Bojovic, and D.S. Pesic, Blue (a − X) System of AgO (Ag107O18)
Molecule. Spectroscopy Letters, 1993. 26(8): p. 1529-1535.
S. Wang, A. Paul, N.J. DeYonder, Y. Yamaguchi, and H.F. Shaefer, The ground and twolowest-lying singlet excited electronic states of copper hydroxide (CuOH). The
Journal of Chemical Physics, 2005. 123: p. 014313.
X.-B. Wang, L.-S. Wang, R. Brown, P. Schwerdtfeger, D. Schroder, and H. Schwarz, The
electronic structure of CuCl2 and CuBr2 from anion photoelectron spectroscopy andab initio calculations. The Journal of Chemical Physics, 2001. 114(17): p. 7388.
X. Wang and L. Andrews, Gold is noble but gold hydride anions are stable. Angewandte
Chemie, International Edition, 2003. 42(42): p. 5201-5206.
X. Wang, L. Andrews, L. Manceron, and C. Marsden, Infrared Spectra and DFT
Calculations for the Coinage Metal Hydrides MH, (H2)MH, MH2, M2H, M2H−, and(H2)CuHCu in Solid Argon, Neon, and Hydrogen. Journal of Physical Chemistry A,
2003. 107(41): p. 8492-8505.
E.P. Wigner, On the behavior of cross sections near thresholds. Physical Review, 1948. 73:
p. 1002-1009.
W.C. Wiley and I.H. McLaren, Time-of-flight mass spectrometer with improved resolution.
Journal of Mass Spectrometry, 1997. 32(1): p. 4-11.

160
R.B. Wright, J.K. Bates, and D.M. Gruen, Matrix-isolation spectroscopy of aluminum,
copper, and nickel hydrides and deuterides produced in a hollow-cathode discharge.
Inorganic Chemistry, 1978. 17(8): p. 2275-8.
Z.J. Wu, Density Functional Study of AuXq (X = O, S, Se, Te, q = +1, 0, -1) Molecules.
Journal of Physical Chemistry A, 2005. 109(26): p. 5951-5955.
C. Yang and Z.Y. Meng, Side-Chain Alkylation of Para-Xylene With Methanol On Alkali
Cation Zeolites. Applied Catalysis, 1991. 71(1): p. 45-54.
C. Zhang and A. Alavi, First-Principles Study of Superabundant Vacancy Formation in
Metal Hydrides. Journal of the American Chemical Society, 2005. 127(27): p. 98089817.
Z. Zhou, R. Liu, J. Wang, S. Li, M. Liu, and J.-L. Bredas, Intra- and Intermolecular Proton
Transfer in 1H(2H)-1,2,3-Triazole Based Systems. Journal of Physical Chemistry A,
2006. 110(7): p. 2322-2324.
T. Ziegler, V. Tschinke, and A. Becke, Theoretical study on the relative strengths of themetal-hydrogen and metal-methyl bonds in complexes of middle to late transition
metals. Journal of the American Chemical Society, 1987. 109(5): p. 1351-8.

________________
Appendix A. Detector Chamber Vacuum Interlock System________________
After photoelectron velocity map imaging capability was added to the pulsed source
instrument described in chapter 2, it became clear that a smart vacuum interlock was needed.
Because the imaging microchannel plates require two days of conditioning if the pressure
rises above 1x10−6 torr, a vacuum interlock system was designed and built to prevent thedetector region from venting due to short power or cooling water outages, while still venting
in the event of a vacuum accident. The system monitors the turbo roughing pump linepressure, cooling water flow rate, and building AC power. The roughing line pressure ismonitored by set point of a thermocouple gauge, the water flow rate is monitored from a flow
meter in the cooling water line, and the building AC power is monitored via a standard two
pronged plug. The interlock box receives its power from an uninterruptible power supply(UPS) and distributes it to the turbo pump controller, turbo pump rough valve, and the turbo
pump vent valve. The operation of the system is laid out in the flow chart in Figure A.1, with
the interlock code presented at the end. What follows are two procedures. The first is theprocedure to turn off the turbo pump and vent the detection region, while the second is theprocedure to pump the system down and reset the interlock.
The procedure to properly vent the detection chamber is very simple. First, makesure that there is plenty of pressure in the nitrogen vent cylinder and that it is supplying gas tothe vent line. Change the number of minutes the system will run off of the UPS to “1”, thenunplug the AC sensor. The system will close the roughing valve, wait ~ 1 minute, turn off
power to the turbo pump controller, wait ~ 15 minutes for the turbo pump to slow down, thenopen the vent valve. The system should take about 20 minutes to vent. In order to close the162vent valve, remove the vent valve power plug from the interlock socket and insert into
building power outlet.
The procedure for pumping down the detection region is as follows. If the system
has vented due to a fault (bad power, bad pressure, bad cooling water), fix the cause of thefault. Be sure that the vent valve power plug is inserted into the corresponding outlet in theback panel of the interlock box. Also be sure that the power button on the turbo pumpcontroller is in the off position. Enable the “override” switch on the front panel of theinterlock box. Toggle the “reset” switch also found on the front panel. At this point thesystem will close the vent valve, open the turbo rough line valve, and supply power to theturbo pump controller. Wait until the pressure of the turbo pump rough line, as read on thethermocouple gauge controller, is well below the set point (currently 100 mTorr). Note that
this may take as long as 25 minutes. Press and hold the turbo pump controller power button
for 3 – 4 seconds until the pump starts (as evidenced by the RPM meter increasing). The
pressure in the turbo pump roughing line will increase and may briefly go above the set point,
but should decrease in a short amount of time (less than one minute). Once the turbo roughline pressure is well below the set point, disable the override switch. The system is now in its
normal state.

163

A.1

Detection region interlock flowchart“start”
The initial power-on mode of the interlock is to check the turbo backing linepressure (Press), AC power (AC), and water flow (H2O). If any are bad, thecorresponding LED is illuminated and the program will continue toilluminate the LED until it is good. When Press, AC, and H2O are good, theprogram proceeds to “start”. The “start” routine monitors PRESS, AC, andH2O at ~ 1 kHz, and is the normal (everything is fine) state of the interlock.

Bad
Press

Go to “close”

Good

Bad
H2O

Go to “H2O”

Good

Bad
AC

Good

Go to “noAC”

164“close”
Notes:•This sub-routine is todetermine if pressure is highbecause of AC off, or vacuum
accident•If vacuum accident, goes toimmediate shut-down (“PRfail”)

AC

Bad

Good

Go to “PRfail”

Go to “noAC”

165

“H2O”

Notes
Press
Checking pressure and power
while waiting 15 min for water
to come back

Bad

Go to “close”

Good

AC

Bad

Go to “noAC”

Good

NO

15 min?

YES

After 15 min, checks water
again: if it is good, then back tonormal mode. If it is not, thengoes into water fail mode.

H2O

Good

Go to
“start”

Bad

Go to “H2Ofail”

166“noAC”
Close Rough Valve

Notes

Wait 1 min•Checks AC every minute fornumber of minutes read fromfront panel T1•If AC still bad, then shuts
down via “ACfail”

Yes
Bad

# Bad
ACs <
T1?

Bad

Wait T2
min

AC

No

Go to “ACfail”

Good•If AC is back, then waits forturbo rough line to pump down

Wait T2 min

Press

Press

Good
Bad

AC

•Two consecutive goodpressure reads are necessary
to make sure that rough linepressure is well below the TC
gauge set point.

Go to “ACfail”

Wait T2 min

Bad

Go to “PRbad2”

Good

AC

Bad

Good
Open roughvalve

Go to “start”

Go to “PRbad2”

Good

Good

Press

Bad

Go to “ACfail”

AC

Bad

Go to “ACfail”

167“PRfail”

Open Vent Valve

Close Rough
Valve

Turn Off Turbo

Turn On
Pressure LED

Note:•Vacuum accident assumed•No delays

168“ACfail”

Turn Turbo Off

Turn On AC
LED

Wait T3 minOpen Vent
Valve

Note:
•Caused by AC off longer than T1 (on front panel)

169“PRbad2”

Turn Turbo Off

Turn On
Pressure LED

Wait T3 minOpen Vent
Valve

Note:
•Caused by AC outage less than T1, but pressure still high170

“H2Ofail”

Turn Turbo Off

Turn On AC
LED

Wait T3 minOpen Vent
Valve

Note:
•Caused by H2O off longer than 15 min171;===================LC045V2.ASM============12/15/2004;;Configuration Bits;
;Oscillator RC;Watchdog Timer Off;Power Up Timer On;Brown Out Detect Off;Low Voltage Program Disabled;Flash Program Write Write Protection Off;Background Debug Disabled;Data EE Read Protect Off;Code Protect Off;;;LC045;;this programme reads 2 BCD numbers on Port B and C;uses them to set time delays for a turbo pump interlock;;;;------------------------------------------------------list p=16f873a
radix hex;-------------------------------------------------------; cpu equates memory map
optionr equ 0x81
status equ 0x03
rp0 equ 0x05
rp1 equ 0x06
rbpu equ 0x07
adcon1 equ 0x9f
trisa equ 0x85
trisb equ 0x86
trisc equ 0x87
porta equ 0x05
portb equ 0x06

172

portc equ 0x07
lobyte equ 0x20
hibyte equ 0x21
times equ 0x22
t equ 0x23
N equ 0x24
NN equ 0x25
T1 equ 0x26 ;Time on Front Panel in minutes
T2 equ 0x27 ;Time between pressure checks after power outage induced
Pressure fault
T3 equ 0x28 ;Time for Turbo Pump to spin down;-------------------------------------------------------;setup I/O
bsf status, rp0 ;switch to bank 1
bcf optionr,rbpu ;pullups on port B
movlw 0x06 ;configure port A as digital i/o
movwf adcon1
movlw 0x38
movwf trisa ;A0:A2 outputs, A3:A5 inputs
movlw 0xff
movwf trisb ;port B inputs
clrw
movwf trisc ;port C outputs
bcf status,rp0 ;switch back to bank 0;;-------------------------------------------------------;
movlw 0x07
movwf portc ;turn on "fail" LED's
bcf porta,0x02 ;vent valve LO = open
bcf porta,0x01 ;roughing valve LO = closed
bcf porta,0x00 ;Turbo Pump LO = off;;------------T1, T2, T3-------------------;
call READT1 ;get T1 value
movlw 0x01 ;value to be loaded into T2
movwf T2 ;T2 = 1
movlw 0x0f ;value to be loaded into T3
movwf T3 ;T3 = 15173;
;initial checks;
begin movlw 0x03
movwf times ;set times = 3;;check pressure;btfss porta,0x04 ;is bit 4 HI, HI => GOOD
goto badPR ;bcf portc,0x02 ;turn off LED
decf times,1
goto ckH2O
badPR bsf portc,0x02 ;turn on LED;check H2O;
ckH2O btfss porta,0x05 ;is bit 5 HI, HI => GOOD
goto badH2O ;bcf portc,0x00 ;turn off LED
decf times,1
goto ckAC
badH2O bsf portc,0x00 ;turn on LED;;check AC;
ckAC btfss porta,0x03 ;is bit 3 HI
goto badAC ;bcf portc,0x01 ;turn off LED
decfsz times
goto begin
goto GOOD
badAC bsf portc,0x01 ;turn on LED
goto begin
;
;
;
;
;
;
;

174

GOOD bsf porta,0x02 ;vent valve HI = closed
bsf porta,0x01 ;roughing valve HI = open
bsf porta,0x00 ;Turbo Pump HI = on;
;check pressure;
start btfss porta,0x04 ;is bit 4 HI, HI => GOOD
goto close ;close RV;;check H2O;
btfss porta,0x05 ;is bit 5 HI, HI => GOOD
goto H2O ;;;check AC;
btfss porta,0x03 ;is bit 3 HI, HI => GOOD
goto noAC
goto start;;close roughing valve;
close bcf porta,0x01 ;close roughing valve;;check AC line;
btfss porta,0x03 ;is bit 3 HI
goto noAC ;power failure
goto PRfail ;power goodnoAC bcf porta,0x01 ;close roughing valve;start T1 timer
movf T1,0
movwf times;
wait btfsc porta,0x03 ;check AC
goto ACgood ;if AC goodcall MINUTE
decfsz times,1
goto wait
btfss porta,0x03 ;if T1 set to 1

175

goto ACfail;;if power good;
ACgood movf T2,0
movwf times
delay1 call MINUTE ;wait T2 minutes
decfsz times,1
goto delay1;
btfss porta,0x04 ;check pressure
goto PRbad1
btfss porta,0x03 ;check AC
goto ACfail;
PRgood movf T2,0
movwf times
delay2 call MINUTE ;wait T2 minutes
decfsz times,1
goto delay2;
btfss porta,0x04 ;check pressure
goto PRbad2
btfss porta,0x03 ;check AC
goto ACfail;;open roughing valve;
bsf porta,0x01 ;set portA bit 1 HI;
goto start ;go back to normal operation;
PRbad1 call MINUTE ;wait 2 minutes
call MINUTE
btfss porta,0x04 ;check pressure
goto PRbad2
btfss porta,0x03 ;check AC
goto ACfail
goto PRgood;15 minute loop, 900 seconds

176

;
H2O
movlw 0x5b ;5b hex is 91
movwf t ;t = 91
loopA
decfsz t,1
goto tensec ;do it 90 times = 1 mimute
goto ckH20
tensec movlw 0x65 ;65h = 101, 10 second delay
movwf N
loopB ;do it 100 times
decfsz N,1goto tenthgoto loopA
tenth movlw 0x42 ;0.1 sec delay, this value good for 10K, 0.01uF
movwf NNloopC
btfss porta,0x04 ;check pressure
goto close
btfss porta,0x03 ;check AC
goto noACdecfsz NN,1
goto loopC
goto loopB;;
ckH20 btfss porta,0x05
goto H2Ofailgoto start;
H2Ofail bcf porta,0x01 ;close Roughing Valvemovf T3,0
movwf times
bcf porta,0x00 ;PORTA 0 => LO turn off TP
bsf portc,0x00 ;turn on H2O fail LED
loopX call MINUTE ;wait T3 minutes
decfsz times
goto loopX
bcf porta,0x02 ;open Vent Valvegoto H2Ofail177;
ACfail movf T3,0 ;wait time for Vent Valve to colse
movwf times
bcf porta,0x00 ;PORTA 0 => LO turn off TP
bsf portc,0x01 ;turn on AC fail LED
loopY call MINUTE ;wait T3 minutes
decfsz times
goto loopY
bcf porta,0x02 ;open Vent Valvegoto ACfail;
PRfail bcf porta,0x00 ;PORTA 0 => LO
bcf porta,0x02 ;open Vent Valvebsf portc,0x02 ;turn on PRESSURE fail LED
goto PRfail;
PRbad2 movf T3,0 ;wait time for Vent Valve to colse
movwf times
bcf porta,0x00 ;PORTA 0 => LO turn off TP
bsf portc,0x02 ;turn on PRESSURE fail LED
loopZ call MINUTE ;wait T3 minutes
decfsz times
goto loopZ
bcf porta,0x02 ;open Vent Valvegoto PRbad2;SUBROUTINE READT1, reads value on PORT B;
READT1
movf portb,w ;read port B to W
movwf lobyte ;data in lobyte
movwf hibyte ;data in hibyte
swapf hibyte ;swap bits 0-3 for 4-7
comf lobyte ;complement these bits since switches in 02 and 03
comf hibyte ;are the complement to that of 01, see project notes
movlw 0x0f ;load w = 00001111
andwf lobyte ;clear upper 4 bits
andwf hibyte ;clear upper 4 bits
movlw 0x9 ;multiply hi byte by 10
movwf times ;load times with multiplier-1
movf hibyte,w ;load w with hi byte

178

mult1 addwf hibyte ;add hibyte to initial value and store
decfsz times ;is times=0
goto mult1 ;no, do again, hibyte=hibyte*multipliermovf hibyte,w ;hibyte to w
addwf lobyte,w ;add w to lobyte
movwf T1 ;result in T1
return;;;subroutine MINUTE, delays for 60 seconds;
MINUTE
movlw 0x3d ;3d hex is 61
movwf t ;t = 61
loop1
decfsz t,1
goto second ;do it 60 times = 1 mimute
returnsecond movlw 0x0b ;1 second delay
movwf Nloop2 ;do it 10 times
decfsz N,1goto innergoto loop1
inner movlw 0x42 ;0.1 sec delay, this value good for 10K, 0.01uF
movwf NNloop3
decfsz NN,1
goto loop3
goto loop2;;
end