BL2B

Velocity Map Imaging of Fragment Mixtures from Fullerenes
H. Katayanagi1, 2 and K. Mitsuke3
1

Department of Photo-Molecular Science, Institute for Molecular Science, Okazaki 444-8585, Japan
School of Physical Sciences, The Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585,
Japan
3
Faculty of Science, Josai University, Sakado 350-0295, Japan2

We have developed a photofragment imaging
spectrometer suitable for synchrotron radiation
excitation of gaseous molecules of refractorymaterials such as fullerenes [1, 2]. Using this imaging
spectrometer we have measured “yt images” in whichfragment masses are shown in t axis andone-dimensional velocity distributions of thefragments are shown in y axis. Translationaltemperatures (Ttrans) of the fragments were obtained
from the y distributions of the fragments. Values of
average kinetic energy release were obtained from
Ttrans.
So far the velocity map images (xy images) havebeen used to elucidate photodissociation mechanismsof small molecules [3]. Prodhan et al. have expectedthat velocity map images of fullerene fragments
would reveal details of photodissociation mechanismof the fullerenes [4]. Thus we tried to obtain xy
images of fragments from the fullerenes in the present
study.
The experiments were performed at BL2B in
UVSOR. Fullerene powder was loaded in a quartz
tube and heated up by an electric heater in vacuum.
The fullerene vapor passed through two apertures andreached the ionization region. The fullerene
molecular beam thus generated along x axis
intersected the monochromatized synchrotron
radiation (y axis) at the ionization region. Ions
produced there were extracted by a velocity map
imaging electrode assembly and projected along z
axis on to a position sensitive detector (PSD). Hencethe xy images were obtained on the PSD.
Figure 1(a) shows the experimental xy image ofparent ions (C702+) in the molecular beam of C70 and
1(b) shows the xy image of a fragment mixture of
C682+ - C582+ from C70 at the photon energy of 105 eV.
Scattering velocity distributions of the fragments are
expected to be isotropic [1], so that the fragment
images should be circular. However Fig. 1(b) has anoval shape. This shape can be explained as the
convolution of the isotropic velocity distribution of
the fragments and the anisotropic velocity distributionof the parent molecular beam. These xy images havealready been reported in Ref. 2.
Figure 2(a) shows the mixture of C582+ - C482+
fragments produced from C60 at the photon energy of
102 eV. The oval shape was observed. Figure 2(b)shows a result of computer simulation for C582+
fragments. In this simulation we assumed that the
fragments were emitted isotropically with Ttrans of 100

K from the anisotropic parent molecular beam of 685
K. Figure 2(b) is similar to 2(a), although 2(a) is a
mixture of the fragments. This similarity suggests that
the C582+ is the most abundant fragment and that all
the fragments have velocity distributions following
the Maxwell-Boltzmann distribution. These are inaccord with the results in Refs. 1 and 2. However wecannot distinguish singularities of the velocity
distributions for production of magic number
fragments (C502+ from C60 [1] and C602+ from C70 [2])on these xy images, because abundance of thesemagic number fragments are very small in the
mixtures.
We are trying to obtain the xy images of suchscarce fragments with improvement of our imaging
spectrometer. Observing such xy images will allow us
to examine finer details of the production
mechanisms of the magic number fragments. This
will lead to the understanding of the formation
mechanism of the fullerenes.

Fig. 1. Velocity map (xy) images of (a) parent
molecular beam and (b) fragment mixtures from C70.

Fig. 2. Velocity map (xy) images of (a) fragment
mixtures from C60 and (b) simulated image of C582+
fragments.
[1] H. Katayanagi and K. Mitsuke, J. Chem. Phys.
133 (2010) 081101.
[2] H. Katayanagi and K. Mitsuke, J. Chem. Phys.
135 (2011) 144307.
[3] A. T. J. B. Eppink and D. H. Parker, Rev. Sci.
Instrum. 68 (1997) 3477.
[4] Md. S. I. Prodhan et al., Chem. Phys. Lett. 469(2009) 19.

51

BL3U

Electrochemical Reaction Studied by Soft X-Ray Absorption Spectroscopy
I. Development of Liquid Cell for Electrochemistry
M. Nagasaka1, H. Yuzawa1, T. Horigome1, A. P. Hitchcock2 and N. Kosugi1
1

Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan
Department of Chemistry, McMaster University, Hamilton, ON L8S 4M1, Canada

2

To better understanding electrochemistry, it isnecessary to investigate the structures of electrolytes
including electric double layers at different potentials.
The structures of electric double layers were mainly
studied by vibrational spectroscopies as reviewed byAshley and Pons [1], in which the structures ofsolvent water molecules were determined from the
OH stretching mode. It is difficult to investigate thestructures of electrolytic solutes in dilute electrolyte
solutions. Soft X-ray absorption spectroscopy (XAS)
is a powerful tool to study local electronic structure ofliquids. The structures of solutes are observed
element-selectively even in dilute solutions. Recently,
we have developed a liquid cell for the measurement
of XAS in transmission mode [2]. In this work, wehave developed an in-situ XAS measurement system
for studying electrochemical reactions of electrolytes
by using the liquid cell with built-in electrodes.
The experiments were performed at BL3U. Figure1(a) shows schematics of the liquid cell. It consists offour regions I, II, III, and IV, separated by 100
nm-thick Si3N4 membranes (NTT AT Co.). Region I
is connected to the beam line under vacuum. Regions
II and IV are at atmospheric pressure of helium gas.
The flow rate of helium gas is controlled by a mass
flow controller, and the helium pressure is adjusted
by a needle valve set in the gas outlet. The thin liquid
layer (region III) is sandwiched between two Si3N4
membranes with spacers. Liquid samples aresubstituted by other samples in combination with atubing pumping system. The thickness of the liquid
layer can be varied from 20 to 2000 nm by changing
the He backpressure in regions II and IV [2]. Soft
X-rays, which pass through region II and the liquid
layer III, are detected by a photodiode (IRD
AXUV100) in region IV.
For the investigation of electrochemical reactions,
three electrodes are included in the liquid layer III, as
shown in Fig. 1(b). The working electrode (WE) is a
Au deposited Si3N4 membrane, which is one side ofthe liquid layer III. This membrane is connected witha Au tab for electric conduction. At the opposite sideof the Au contact is a teflonTM spacer. The counterelectrode (CE) is a Pt mesh. The reference electrode(RE) is a Ag/AgCl electrode with saturated KClsolution, which is isolated from liquid samples by ateflonTM cover. The potential is controlled using a
potentiostat (Solartron 1287).
In the present configuration, XAS spectra ofelectrolytes can be measured at different potentials byusing this system. The XAS spectra of solutes indilute electrolyte solutions are obtained by adjusting
the thickness of the liquid layer. We have investigatedthe change in valence of Fe ions in aqueous ironsulfate solutions by measuring Fe L-edge XAS at
different potentials. These results are discussed
elsewhere in this volume [3].

Fig. 1. (a) Schematic of the liquid cell for XAS intransmission mode. (b) Schematics of three electrodes
included in the liquid cell.
[1] K. Ashley and S. Pons, Chem. Rev. 88 (1988)
673.
[2] M. Nagasaka et al., J. Electron Spectrosc. Relat.
Phenom. 177 (2010) 130.
[3] M. Nagasaka et al., in this volume.

52

BL3U

Electrochemical Reaction Studied by Soft X-Ray Absorption Spectroscopy
II. Valence Changes of Fe Ions in Aqueous Iron Sulfate Solutions
M. Nagasaka1, H. Yuzawa1, T. Horigome1, A. P. Hitchcock2 and N. Kosugi1
1

Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan
Department of Chemistry, McMaster University, Hamilton, ON L8S 4M1, Canada

2

The redox reactions of Fe ions are one of the mostcommon electrochemical systems because of theirimportance in a variety of fields. Previously, Fe redox
reactions were mainly studied by voltammetricmethods [1], but it is difficult to measure the change invalence of Fe ions in dilute electrolyte solutions. Soft
X-ray absorption spectroscopy (XAS) is a powerfultool to study local electronic structures of liquids.
Recently, we have developed a liquid cell for XAS intransmission mode [2]. We have also developed anin-situ system for electrochemistry by using the liquidcell with built-in electrodes [3]. Here we report Fe
L-edge XAS results for the change in valence of Fe
ions in an aqueous iron sulfate solution induced byvariation of the potential at a gold electrode. The
experiments were performed at BL3U. The details of
the liquid cell are described in this volume [3]. The
electrolyte is 0.5 M aqueous iron sulfate at pH = 2.2.
Figure 1 shows the Fe L-edge XAS spectra of anaqueous iron sulfate solution at different potentials.
Each XAS spectrum is measured at a constantpotential. The XAS L3 spectra have signals from Fe(II)and Fe(III) ions and show an isosbestic point,
indicating only two species are involved. As shown in
Fig. 1(a), a nonlinear oxidation of Fe(II) to Fe(III) ionsis observed when the potential is increased from 0.0 to
0.9 V. On the other hand, the reduction of Fe(III) to
Fe(II) ions varies linearly with the potential when thepotential is decreased from 0.9 to -0.4 V, as shown in
Fig. 1(b).
Figure 2 shows the fraction of Fe(II) ions from total
Fe ions at different potentials, which is determinedfrom the curve fitting procedure of the XAS spectra.
The amount of Fe(II) ions decreases by oxidation of
Fe(II) to Fe(III) with increasing the potential. Twooxidation processes are revealed. One is a simple
oxidation process and the other is a process involving
the sulfate ions, which affect electrode kinetic
parameters and diffusion coefficients [1]. On the other
hand, the formation of Fe(II) from Fe(III) withdecreasing the potential is a simple reduction of
Fe(III) ions. We will investigate these redox processes
by correlating with the XAS results from the cyclic
voltammetry at different scanning rates.

Fig. 1. Fe L-edge XAS spectra of Fe ions in a 0.5 M
aqueous iron sulfate solution at different potentials;(a) increasing from 0.00 to 0.90 V, and (b) decreasingfrom 0.90 to -0.40 V.

Fig. 2. Fractional composition of Fe(II) ions as afunction of potential, obtained from Fe L-edge XAS
spectra measured at different potentials.

[1] A. F. Gil et al., J. Electroanal. Chem. 417 (1996)
129.
[2] M. Nagasaka et al., J. Electron Spectrosc. Relat.
Phenom. 177 (2010) 130.
[3] M. Nagasaka et al., in this volume.

53

BL3U

In-Situ Observation of Solid-Liquid Heterogeneous Catalytic Reaction by
Soft X-ray Absorption Spectroscopy
H. Yuzawa, M. Nagasaka and N. Kosugi
Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan

logarithmic plot for the normalized XAS intensity of
cyanopyrazine, which is obtained from the factor
analysis for Figure 1a (green lines) by using thestandard spectra of cyanopyrazine and pyrazinamide.
This plot shows linear relationship to the reaction
time, indicating that the observed catalytic reaction is
the first-order reaction for the concentration of
cyanopyrazine and the slope of the line is a reaction
rate constant. When the same procedure is applied tothe hydration reaction in other temperatures (325.1,
329.8 and 338.5 K), the linear relationship is also
obtained. The obtained rate constants show linear
relationship in the Arrhenius plot (Ea = 52.4 kJ/mol).
Thus, this analytical procedure would be reasonable.
Through the above experiments, we can conclude
that the transmission soft X-ray XAS approach has apotential for the in-situ observation of the solid-liquid
heterogeneous catalysis. In the future, we willobserve
improve the system to obs
serve reaction intermediates.

Study of catalytic reaction mechanism is important
to obtain some clue to the improvement of activity
and selectivity. In-situ observation of the catalytic
reaction by spectroscopic approaches such as FT-IR,
NMR and XPS, are effective methods to elucidate thereaction mechanism. However, in-situ observation ofsolid-liquid heterogeneous catalytic reaction isdifficult because the photoabsorption of bulk liquids(substrate and/or solvent) hinder the objective change
in the spectrum. The spectroscopic observation of thiskind of system has been generally carried out by
using vapor substrate adsorbed on the catalyst surface
instead of liquid substrate [1] although its condition isdifferent from the real one.
We developed a transmission-type liquid cell,which is able to control easily the liquid thin layer,
for the soft X-ray XAS [2] and demonstrated that thisspectroscopic method was effective to clarify the
local structure of various liquid solutions [3]. Thus, inthis study, we have extended this method to thein-situ observation of solid-liquid heterogeneous
catalytic reaction. As a probe reaction, we haveselected hydration of cyanopyrazine on TiO2 (eq. 1).
N

N

N
C
+

N

H2O

O
i
T

2

O
C

NH2

(a)

(b)

2.1 h

(1)

N

The experiments were carried out in BL3U.
Suspension of catalyst was prepared by mixing of
cyanopyrazine (3 ml, 0.78 M), ethanol (5 ml), water(35 ml) and TiO2 (JRC-TIO-4, 0.15 g). Then, thesuspension of thin layer (< 1 Pm thickness) was
sandwiched between two 100 nm-thick Si3N4
membranes, and the C K-edge XAS was measured at
323.8í338.5 K. The photon energy was calibrated by
the C 1sí3pt2 Rydberg peak (297.99 eV) of the CH4
gas mixture in He [4].
Figure 1a shows the C K-edge XAS spectra of
cyanopyrazine, pyrazinamide at 298K and hydrationof cyanopyrazine at 331.5 K. Three absorption peaks(285.4, 286.0 and 286.6 eV) are observed incyanopyrazine (red line) and one absorption peak(285.3 eV) is observed in pyrazinamide (blue line).
All these peaks are assigned to the 1síS* excitation.
Other absorption peaks could not be observed in thehigher photon energy than 287 eV because of overlap
with the C K-edge absorption of ethanol. In the
spectra of cyanopyrazine hydration (green lines), theintensity of the absorption peak at 285.4 eV decreases
slightly, while the other two peaks decrease
conspicuously with the reaction time, corresponding
to the production of pyrazinamide. Figure 1b shows a0Fig. 1. (a) C K-edge XAS spectra for the
cyanopyrazine (0.78 M)íethanolíwater solution (redline), pyrazinamide (0.20 M)íethanolíwater solution(blue line) at 298 K and catalytic hydration of
cyanopyrazine on TiO2 (10 scans (0í2.1 h), green
lines) at 331.5 K. (b) A logarithmic plot of thenormalized XAS intensity of cyanopyrazine obtained
from the factor analysis of green lines in (a).
[1] A. Vimont et al., Chem. Soc. Rev. 39 (2010) 4928.
[2] M. Nagasaka et al., J. Electron Spectrosc. Relat.
Phenom. 177 (2010) 130.
[3] For example, M. Nagasaka et al., UVSOR
Activity Report 37 (2010) 57.
[4] K. Ueda et al., Chem. Phys. Lett. 236 (1995) 311.

54

BL4B

Development of a High-Resolution Magnetic Bottle Electron Spectrometer
M. Sawa1, Y. Konosu1, K. Soejima1, E. Shigemasa2 and Y. Hikosaka1
1

Department of Environmental Science, Niigata University, Niigata 950-2181, Japan
2
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan

Observing kinetic energy correlation for all theemitted electrons is very useful to understandmultiple ionization process of molecules. Suchmulti-electron coincidence measurements can beachieved with an electron spectrometer using
magnetic bottle technique. However, it is difficult fora magnetic bottle electron spectrometer to observehigh energy electrons with sufficient energy
resolutions, because of their short time-of-flights(TOFs). We have introduced retarding electrodes into
our magnetic bottle electron spectrometer, in order toimprove energy resolution for high energy electrons.
The electron retarding system consists of an inner
drift tube and three metal meshes, as schematicallyillustrated in Fig. 1. Electrons collected by aninhomogeneous magnetic field in the ionization
region are retarded between first and second meshes,
when we apply a negative voltage to the second meshand the inside drift tube. This retardation expands
electron TOFs, and higher energy resolution can beachieved.
We have carried out photoelectron-Auger electron
coincidence measurements with the electron retarding
system to evaluate the kinetic energy resolution anddetection efficiency. The results are shown in Fig. 2.
Compared to the original energy resolution of E/ǻE =35 (black dots), the energy resolution is improved up
to E/ǻE > 200 by applying retardation voltages. Here,
while we cannot observe electrons with lower
energies than the retardation voltages, and we has toadjust the retardation voltage to a value lower thanthe energies of the concerned electrons. The bottom
panel of Fig. 2 shows detection efficiencies
determined by the ratios between all photoelectron
yields and the photoelectron yields measured incoincidence with Auger electron. The detection
efficiencies are fairly constant against electron energy,
even when the retarding voltage of -180 or -320 V isapplied. The detection efficiencies around 50% arereasonable considering the transmission efficienciesof the three meshes and the detection efficiency of the
microchannel detector.
We have applied the developed system to theobservation of the OCS S2p photoionization and thesubsequent Auger decay. Figure 3 displays a
two-dimensional map of the coincidence yields
between the S2p photoelectron and Auger electrons.
The spin-orbit splitting of the S2p-1 state is resolved(see the right panel), and the Auger spectrum
associated with each core-hole state is derived (thetop panel). From these coincidence spectra, the Augertransition probabilities from the two core-hole states
can be evaluated.

Fig. 1. Schematic of the electron retarding system.

Fig. 2. Energy resolutions (a) and Detection
efficiencies (b) observed with/without retarding
voltages.

Fig. 3. Energy correlation between OCS S2p
photoelectrons and Auger electrons.

55

BL5B

Development of a Novel Pulsed Nozzle
for Probing Large Molecules in Vacuum Chamber
T. Tajiri, K. Sakamoto, T. Gejo and K. Honma
Univ. of Hyogo, Koto 3-2-1, Kamigori-cho, Hyogo 678-1205, Japanand operated with a repetition rate in the 1–2 Hz
range.
The time profile shows the large molecular are
generated relatively slowly after opening the nozzle.
Main signal due to mist arises 5 ms after the opening.
Since the fluorescence excitation spectra of water
clusters strongly depend on its cluster size [1], we canestimate the mean size of droplet in vacuum chamberby these spectra. Simple analysis shows that the size
is more than 1000.

The liquid water has been regarded as fundamental
material and has been investigated for many years.
Particularly interest is the hydrogen network in liquidwater, which were investigated by many
spectroscopic studies. Since then, many models havebeen proposed. Recently, in order to investigate theelectronic states of liquid water with hydrogen
networks, photoelectron spectroscopy and soft x-ray
emission spectra have been investigated. To obtain
those spectra, liquid phase in vacuum chamber isnecessary. Therefore, liquid water beam technique has
been employed.
For this liquid phase experiments, we havedeveloped the device that utilizes ultrasonicatomization to produce a dense aerosol microdropletof water. The ultrasonic atomization technique has
been used for generate the microdroplets in mist: The
size of liquid droplets was distributed around themicrometer scale. Therefore one can achieve micro
droplet of liquid water in vacuum chamber by the
injecting them directly.
Last year we have utilized a nozzle with a apertureof 500 ȝm diameter. Although we have tried tomeasure photoelectron spectra with this nozzle, lowintensity did not allow any significant measurement.
This time, we modified the nozzle, in which pulsed
valve with high conductance is used.
The experiments were carried out on the bending
beamline BL5B at the UVSOR facility in IMS. As
figure 1 shows, the experimental set-up consists ofthree parts: a mist generation part, a transportation
part and a nozzle. The microdroplets are generated
via ultrasonic atomization. Ultrasonic oscillators(HM2412, Honda Electronics Co., Ltd) operating at
2.4 MHz were installed at the bottom of the waterbath. The microdroplet were carried by He andpumped out to obtain a stable stream. A pulsed valve
has been placed just before pumping system and thegenerated microdroplet going into the vacuum
chamber. After 10 mm down stream, 10 - 15 eV VUVphotons have been radiated to the microdroplets andthe excitation UV fluorescence spectra has beenmeasuredbyphotomultipliertube(R928,
HAMAMATSU) installed.
Figure 2 shows the cross section of the pulsed
nozzle for microdoloplet. We have modified
commercially available General Valve Series 9 withits magnetically activated plunger, which is widelyused in the field of atomic and molecular beams.
These types produce pulses with a typical width of afew hundreds of microseconds. The 45-mm long, 1.5
mm in diameter plunger was attached to the armature

㪧㪤㪫㩷

㪼
㪟㪼㩷

㪙㪸㪺㫂㩷㪧㫉㪼㫊㫊㫌㫉㪼㩷㪤㪼㪸㫊㫌㫉㪼㫄㪼㫅㫋㩷㪧㪸㫉㫋㩷㪟㪼㩷㪟㪼㩷㪂㩷㫄㫀㫊㫋㩷㪧㫌㫃㫊㪼㪻㩷㪥㫆㫑㫑㫃㪼㩷㪪㫐㫅㪺㪿㫉㫆㫋㫉㫆㫅㩷㪩㪸㪻㫀㪸㫋㫀㫆㫅㩷㩷㪮㪸㫋㪼㫉㩷
㪤㫀㫊㫋㩷㪞㪼㫅㪼㫉㪸㫋㫆㫉㩷㪈㪅㪇㩷 㬍㩷 㪈㪇㪌㩷㪧㪸㩷㪊㪅㪇㩷 㬍㩷 㪈㪇㪄㪉㩷㪧㪸㩷㪛㫀㪸㫇㪿㫉㪸㪾㫄㩷㪧㫌㫄㫇㩷

Fig. 1. The experimental set-up for the microdroplet
generation in vacuum chamber.
㪤㫀㫊㫋㩷㪂㩷㪟㪼㩷㪞㪼㫅㪼㫉㪸㫃㩷㪭㪸㫃㫍㪼㩷㪤㫀㫊㫋㩷㪂㩷㪟㪼㩷㪣㫆㫅㪾㩷㪧㫆㫇㫇㪼㫋㩷
㪛㫀㪸㫇㪿㫉㪸㪾㫄㩷㪧㫌㫄㫇㩷

Fig. 2. The cross section view of the pulsed nozzle formicrodroplet.
[1] M. Ahmed et al., J. Phys. Chem. A 98 (1994)
12530.

56

BL5B, BL7B

Applicability of Database Values of Atomic Mass Absorption Coefficients on
Absorption Spectra of L-alanyl-L-alanine Film from 3 to 250 eV
Y. Tanigawa1, Y. Momoki1, K. Ishiyama2, S. Takenaka2 and K. Nakagawa1, 2

Graguate school of Human Development and Environment, Kobe University, Kobe 657-8501, Japan
2
Faculty of Human Development, Kobe University, Kobe 657-8501, Japan

Absorption spectra of thin films of L-alanylL-alanine C6H12N2O3 were measured at the photon[3];df(eV-1 ) 1.80 u
F q P aq (Mb) ,dE
q¦energy from 3 eV to 250 eV in an attempt to discusswith which energy of radiation is responsible forchemical evolution in space where molecules interact
with electromagnetic radiation with wide energy
range [1].
Powder of L-alanyl-L-alanine was purchased from
SIGMA Pharmacy Company. We prepared thin filmsof L-alanyl-L-alanine with the vacuum evaporation
technique in which heater temperature was set at
about 370 K. Collodion films or SiO2 plates wereused as substrate. Prepared thin films were transferredto the measurement system without any contact withair.
Spectral measurement was carried out at thebeamlines 5B and 7B. Photon energy region used formeasurements were 3.5 to 37 eV at BL7B and 30 to
250 eV at BL5B. Optical density OD(E) was obtained
as a function of photon energy E for various samples
with different thickness because magnitude of OD(E)around 20 eV was one order larger than that around
90 eV or at higher energies. Here OD(E) was
determined to be OD( E) log( I 0 ( E) / I ( E)) , whereI( E)

0I ( E)eV ( E
) nl

,

(1)

1

A

0.1

B

0.01

and

nSl NH P L .

In the equation 3, Fq is the number of atom q in thatmolecule and Paq is the atomic absorption coefficientof atom q in the unit of Mb.
In Fig. 1, the curve A is df/dE spectrum obtained inthis work and the curve B shows the calculated result
by eq. (3) using the atomic absorption coefficient by
Henke et al. [4].
As seen from the figure, curve B can reasonably
reproduce the experimental result (curve A). In orderto check the applicability in detail of the Henke’s
atomic absorption coefficient to our L-alanylL-alanine data, we extrapolated 250-280 eV part to
the region of E >280 eV to obtain the curve C.
Making the integration of spectrum from 5 eV to10000 eV along with the curve C, we obtained valueof 62.7 which is very close to 64, the number of 2s
and 2p electrons in L-alanyl-L-alanine molecule. Thus
we concluded that the Henke’s atomic absorption
coefficient can reproduce the absorption spectrum
within the region from 30eV
‒ to 200eV.

df / dE (eV -1)

I0(E) and I(E) are transmitted light intensity of(substrate) and that of (substrate+sample). Different
spectra obtained for different sample were connected.
Finally we obtained a smooth spectrum. Similar result
was already reported by our group [2].
Translation from OD(E) to absorption cross section
V(E) was carried out using following equations;

(3)

‒

1

C

(2)

Equation (1) is the Lambert-Beer law, where n thenumber density of sample and l the pass length. The
left side of equation (2) shows the total number of
L-alanyl-L-alanine molecules in a film of which area
is S and the right side shows the total number of
L-alanyl-L-alanine molecules in a film analyzed by ahigh performance liquid chromatography (HPLC).
The first step of our translation from OD(E) to
V(E) was carried out around 7 eV for films
evaporated on SiO2 substrate. We cannot use thistechnique for the films on the collodion substratebecause collodion might damage the HPLC system.
Figure 1 shows the absolute values of absorption
spectra of L-alanyl-L-alanine film. Vertical axis of the
figure was again translated into the optical oscillator
strength distribution df/dE determined by the relation

10
100
Photon energy E / eV

Fig. 1. Absorption spectrum of L-alanyl-l-alanine film.
Curve A: Result in this Work. Curve B: Calculated
result with Henke [4]. Curve c: See text.
[1]K. Nakagawa, Viva Origino, 37 (2009) 24, inJapanese.
[2] M. Kamohara et al., Rad. Phys. Chem. 77 (2008)
1153.
[3] Y. Hatano, In: Sham, T.K. (Ed.), Chemical
Applications of Synchrotron Radiation Part I. World
Scientific, Singapore, (2002) 55.
[4] B. L. Henke et al., Atomic Data and Nuclear Data
Tables, 54(1993)181.

57

BL6U

Site-Specific Fragmentation Driven by Particular Auger Processes of
the C K-Shell Excited cis-Hexafluorocyclobutane Molecule
S. Ishikawa1, K. Okada1, H. Iwayama2,3, L. Ishikawa2 and E. Shigemasa2,31

Department of Chemistry, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
2
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan3
School of Physical Sciences, Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8585,
Japan

Inner-shell excited states of molecules relax into
various molecular cationic states through Auger
decays. The resultant cations are in general unstableand dissociate into fragment ions. Information on thecorrelation between the Auger-final states and the
products provides us deeper insight into thefragmentation dynamics of the inner-shell excitedmolecules. We found in our previous study that after
the C1sVCC* and F1sVCC* transitions thecis-1,1,2,2,3,4- hexafluorocyclobutane (cis-c-C4H2F6)
molecule dissociates into the fragment ions with C–Fbond(s) in higher yield. In this study we haveacquired the Auger-electron–photoion coincidence
data of the cis-c-C4H2F6 molecule at the C 1s edge byusing a pair of a double toroidal electron analyzer(DTA) and an ion time-of-flight mass spectrometer toobtain information on the Auger processes correlatingwith such specific fragments.
The experiments have been performed on the soft
X-ray beamline BL6U. The experimental setup has
been described in a previous paper [1]. Synchrotron
radiation was irradiated at right angles to the effusive
beam of the gaseous cis-c-C4H2F6 sample. The
electrons traveling through the DTA tube weredetected with a position sensitive detector (RoentDek,
DLD40). Fragment ions were extracted toward thetime-of-flight spectrometer by a pulsed electric field
applied just after the Auger electron detection acrossthe ionization region. The coincidence data wereobtained as list-mode files, containing a series of a setof the detected electron positions and the ion arrival
times. They were acquired in this study at the photon
energies of 290.3, 292.8, 297.0 and 327.6 eV.
The resonant Auger spectrum obtained at thephoton energy of 297.0 eV has characteristic featuresthat distinguish it from the other spectra acquired inthis study. Figure 1a shows the resonant Auger
spectrum measured at 297.0 eV and the components
coincident with the CH0,1F+, CH0,1F2+ and C2H0,1F3+
fragments. The excitation energy corresponds to the
VCC* ĸ CCF2 1s transition of cis-c-C4H2F6, where
CCF2 means the carbon of a CF2 group. The spectra
taken at 292.8 eV are also displayed in Fig. 1b forcomparison. The intense peak at the final-state energy
around 42 eV is distinctive of the 297.0-eV excitation.
The coincidence spectra reveal that in this peak theCH0,1F+ and CH0,1F2+ ions are produced in abundance,
whereas the spectra of the fragment ions without a

C–F bond give no peak (not shown in Fig. 1). We canconclude that the Auger-final states corresponding tothis energy region are responsible for the productionof the specific fragment ions. This study clearly
demonstrates that the site-specific fragmentation of
the C K-shell excited cis-c-C4H2F6 molecule isstrongly correlated with the particular Auger decays.
The experiments at the F K-edge are eagerly inprogress and the results will be published in the near
future.

Fig. 1. Resonant Auger spectra coincident with theCH0,1F+, CH0,1F2+ and C2H0,1F3+ fragments acquired
at 297.0 eV (panel a) and 292.8 eV (panel b). Total
resonant Auger spectra are also plotted as the thicker
black lines and are scaled by a half. Abscissa has beenobtained as the difference between the photon energy
and the electron kinetic energy.

[1] T. Kaneyasu, Y. Hikosaka and E. Shigemasa, J.
Electron Spectrosc. Relat. Phenom. 156-158 (2007)
279.

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Formation of Metastable Carbon Dioxide Dications Following Core-Hole
CreationY. Shibata1, K. Soejima1, H. Iwayama2, E. Shigemasa2 and Y. Hikosaka1
1

Department of Environmental Science, Niigata University, Niigata 950-2181, Japan
2
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan

The ion yield spectra observed in the inner-shellthreshold ranges of carbon dioxide (CO2) molecules[1] indicate that metastable CO22+ is favorably
produced in the Auger decay of the O 1s core-holestate, compared to the Auger decay of the C1s
core-hole state. In this study, we have used anAuger-electron-ion coincidence method to investigate
the formation mechanism of the metastable dications
following the core-hole creations in CO2.
The experiment was performed at the undulator
beamline BL6U, using an electron-ion coincidence
spectrometer [2]. The electrons were analyzed inenergy by a double toroidal electron analyzer, whileions were extracted from the interaction region into
an ion momentum spectrometer by a pulsed electricfield according to the detection of the electron.
Figure 1(a) shows an O 1s Auger spectrum of CO2,plotted as a function of the kinetic energy and of thebinding energy. The Auger spectrum exhibits several
band structures corresponding to the formation ofdifferent CO22+ states. Figures 1(b), (c) and (d)represent the spectra of Auger electrons observed incoincidences with metastable CO22+, O++CO+ ion
pairs and C++O+ ion pairs, respectively. One findsthat the formation of metastable CO22+ is associatedwith the Auger decay into doubly charged states inthe binding energy range of 35-45eV. A calculation
implies that the doubly charged states have theelectronic configuration of ʌ-2 [3].
Figure 2 compares the Auger spectra observed in
the decays of the O1s and C1s core-holes, where thered curves are obtained in coincidences withmetastable CO22+. While the CO22+ states in the same
binding energy range are relevant to the metastable
CO22+ formation following the different core-holecreations, the intensity of the metastable CO22+
formation is about four times more intense in the O 1s
core-hole decay. The favorable production ofmetastable CO22+ following the O 1s core-holecreation is qualitatively explained by considering the
spatial distribution of the ʌ orbital involved in the
decay processes. Since the ʌ valence orbital is mostly
localized around the O atom in the CO2 molecule, theʌ electron preferentially fills the O 1s core-hole due
to a large overlap between the core and valenceorbitals. Thus the Auger transition involving the ʌelectrons is favored in the decay of the O 1s core-holestates rather than the C core-hole states, resulting in
the favorable formation of metastable CO22+ stateswith the configuration of ʌ-2 in the decay of the O 1s
core-hole states.

Fig. 1. O1s Auger spectrum (a) and Auger spectra
obtained in coincidences with (b) metastable CO22+,(c) O++CO+ ion pairs and (d) C++O+ ion pairs.

Fig. 2. O1s and C1s Auger spectra (solid lines) andAuger spectra (a) and Auger spectra obtained incoincidences with metastable CO22+ (red).
[1] G. Ohrwal et al., J. Phys. B 35 (2002) 4543.
[2] T. Kaneyasu et al., J. Electron Spectrosc. Relat.
Phenom. 156-158 (2007) 279.
[3] J. A. Kelber et al., J. Chem. Phys. 75 (1981) 652.

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High-Resolution Electron Spectroscopy for Ethyl Trifluoroacetate
H. Iwayama1, F. Penent2, P. Lablanquie2 and E. Shigemasa1
1

UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, JapanLCPMR, Université Pierre et Marie Curie, 75231 Paris Cedex 05, France

2

Inner-shell photoionization of light elements ismostly relaxed via an Auger decay process, causing
the emission of another electron from an outer-shell.
Auger electron spectroscopy (AES) is thus anelement-sensitive method with various analyticalapplications. Since a core hole can be regarded as
being strongly localized at a particular atom, it can be
expected that the Auger final dicationic state has twovalence holes which are also localized near the
inner-shell ionized atom. According to this simple
atomic picture, the binding energies of the molecular
Auger final states would also show chemical shifts.
Owing to a hole-hole repulsion, the chemical shift inAuger electron spectra reflects any localization
character of the two valence holes.
The interpretation of molecular Auger spectra iscomplex and the difficulties increase with increasing
the number of atoms in a molecule. The Auger spectra
become much more complicated in the case where amolecule is composed of several atoms of the sameelement. While well-defined photoelectron peaks
reflecting the chemical shifts can be observed inphotoelectron spectra, direct observations of thecorresponding chemical shifts in molecular Auger
spectra are practically impossible without using acoincidence technique. In order to stabilize theinterpretation on the site-specific Auger spectra
obtained by such coincidence experiments, however,high-resolution Auger electron spectra as well as
theoretical calculations are indispensable. We havecarried out high-resolution electron spectroscopic
measurements on ethyl trifluoroacetate (C4H5F3O2).
The experiment was performed on the soft X-ray
beamline BL6U at UVSOR. The radiation from an
undulator was monochromatized by a variable
included angle varied line-spacing plane grazing
monochromator. The monochromatized radiation was
introduced into a cell with sample gases. Kinetic
energies of the emitted electrons were measured by ahemispherical electron energy analyzer (MBS-A1)
placed at a right angle with respect to the photon beam
direction. The direction of the electric vector was set
to be parallel to the axis of the electrostatic lens of theanalyzer. The kinetic energy resolution of the analyzer
was set to 20 meV.
Figure 1(a) and 1(b) show the C 1s photoelectron
and Auger electron spectra of C4H5F3O2 at the photon
energy of 330 eV, respectively. The chemical shifts
are clearly observed in Fig. 1(a). The oxygen andfluorine Auger electron spectra are displayed in Fig. 2(a) and (b), respectively. It is seen that the populationsof the Auger final states strongly depend on whichcore electron is ionized. No fine structure is found inevery Auger electron spectrum, in spite of thehigh-resolution.

Fig. 1. (a) Carbon 1s photoelectron and (b) Auger
electron spectra of C4H5F3O2.

Fig. 2. (a) Oxygen and (b) fluorine Auger electron
spectra of C4H5F3O2.

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Deexcitation Processes after S 2p Photoexcitation of OCS Studied byAngle-Resolved Resonant Auger Electron Spectroscopy
L. Ishikawa, H. Iwayama and E. Shigemasa
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan

Soft X-ray absorption spectra of molecules exhibit
rich structures in the region below the ionizationthresholds, which are due to the excitations of a coreelectron to unoccupied valence or Rydberg orbitals.
The core excited states are predominantly relaxed via
Auger electron emission, in the case of the molecules
composed of light elements, and subsequently
fragmentation
follows.
Recentworks
onhigh-resolution resonant Auger electron spectroscopy
have revealed that the nuclear motion of themolecular core-excited states is promoted incompetition with the Auger decay.
In the previous work [1], three satellite structures(as labeled 0, 1, and 2 in Fig. 2) between B (26) and C(26) valence ionized states were observed following
the S 2p3/2 oS* excitation, and they were assigned to43, 23, and 2) shake-up-like states on the basis of abinitio theoretical calculations. Here, we revisit thisfirst observation of spin-forbidden shake-up states.
Angle-resolved two dimensional (2D) electron
spectroscopy has been applied.
The experiments were carried out on the soft X-ray
beamline BL6U. The radiation from an undulator was
monochromatized by a variable included angle variedline-spacing plane grazing monochromator. For the
2D electron spectroscopy, the monochromator
bandwidth was set to E/'E ~1000 at hQ=165eV.
Kinetic energies of the emitted electrons were
measured by a hemispherical electron energy analyzer(MBS-A1) placed at a right angle relative to thephoton beam direction. The direction of the electric
vector was set to be either parallel (horizontal
direction) or perpendicular (vertical direction) to theaxis of the electrostatic lens of the analyzer. The
resonant Auger spectra with kinetic energies ranging
from 135 to 155 eV were recorded as a function of
the photon energy in the S 2p excitation region.
Figure 1 shows the 2D maps of resonant Auger
electron spectra following the S 2p excitation of OCS
measured in horizontal (left) and vertical (right)
directions. The horizontal solid lines in Fig. 1 indicate
the resonance peak positions (S 2p3/2,1/2 oS* and S
2p3/2,1/2oV*). The diagonal lines in Fig. 1 are due tothe valence photoelectrons, while the vertical lines
seen in the lower kinetic energy region are owing to
the atomic Auger lines. The atomic line widths show
clear polarization dependence, which may reflect theanisotropic photoexcitation process. The peak
position for the S 2p3/2 oS* excitation (hQ=164.4 eV)corresponds to the lowest horizontal line in Fig. 1,
where clear island-like structures are detected both in

the horizontal and vertical directions in the kinetic
energy region from 146 to 148 eV.
Figure 2 represents the enlargements of theresonant Auger spectra following the S 2p3/2 oS*
excitation around the satellite region. The structures
observed in the horizontal spectrum are good
agreement with those in the previous work [1].
However, some differences are seen in the vertical
spectrum; the peak position of the 43state as labelled“0” in the horizontal spectrum differs from that in thevertical spectrum, and a peak at 17.8 eV is seen onlyin the vertical spectrum. Resonant Auger spectra withmuch higher resolution may reveal the reason for thediscrepancy.

Fig. 1. 2D maps of resonant Auger electron spectra
following the S 2p excitations of OCS, obtained athorizontal and vertical directions.

Fig. 2. Participator Auger spectra following the S
2p3/2 oS* excitation, measured at horizontal andvertical directions.
[1] S. Masuda, T. Hatsui and N. Kosugi, J. Electron
Spectrosc. Rlat. Phenom. 137-140 (2004) 351.

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Ultrafast Dynamics in C 1s Core-Excited CF4 Studied by Two-Dimensional
Resonant Auger Spectroscopy
M. N. Piancastelli1, R. Guillemin1, M. Simon1, H. Iwayama2 and E. Shigemasa2
1

LCPMR, Université Pierre et Marie Curie, 75231 Paris Cedex 05, France
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan

2

The CF4 molecule, tetrafluoro methane, has been abenchmark for several spectroscopic studies, due to its
high symmetry, same as methane, CH4. One of themost interesting observations deriving from thecomparison between CH4 and CF4 is the relative
intensity of below-threshold photoabsorption
structures around the C 1s ionization thresholdassociated with transitions to empty molecular orbitals
versus Rydberg states. CF4 is a good candidate toinvestigate the dynamical properties of core-excitedstates with an electron in the antibonding
lowest-unoccupied molecular orbital (LUMO) in ahighly symmetric system.
Here an investigation of ultrafast dissociation
following C1s-to-LUMO core excitation in CF4, withhigh-resolution resonant Auger spectroscopy, ispresented. The main novelty of this work is the use of
two-dimensional (2D) maps to record resonant Auger
spectra across the resonance as a function of photon
energy with a small energy step and then tocharacterize ultrafast dynamics. This method allows
one to follow in great detail the evolution of theresonant enhancement of spectral features
corresponding to final ionic states while scanning theenergy across the resonance, and to fully exploit theso-called detuning effects.
The experiment was performed on the soft X-ray
beamline BL6U at UVSOR. The photon energy
resolutions were set to 10000 and 4000 for total-ion
yield and 2D map measurements, respectively. Kinetic
energies of the emitted electrons were measured by ahemispherical electron energy analyzer (MBS-A1).
The direction of the electric vector was set to beparallel to the axis of the electrostatic lens of theanalyzer. The kinetic energy resolution of theanalyzer was set to 60 meV. The 2D maps wereobtained by taking decay spectra at regular photon
energy intervals of 100 meV across the resonance.
Figure 1 represents total ion yield curve measured
in the C 1s excitation region of CF4. The double
feature with maxima at 297.7 and 298.4 eV is assigned
to the Jahn-Teller-split transition to the LUMO (V* oft2 symmetry), followed by the Rydberg series. Figure
2 shows the 2D map after subtraction of the
non-resonant contributions, and with on-top two
pseudo-absorption curves obtained by the CIS(Constant Ionic State) method, and namely plotting the
integrated intensity of the two resonant features, thenon-dispersive one related to the fragment and thedispersive one related to the 3t2 state, as a function ofphoton energy. It is seen that while the intensity of themolecular state closely mimics one of the absorption
curve, the non-dispersive feature related to thefragment decreases in relative intensity across theresonance, and disappears in the photon energy regionof the Rydberg states. Detailed calculations on thepotential curves of the intermediate and final state
would be needed to fully clarify this finding.

Fig. 1. Total ion yield curve measured in the C 1s
excitation region of CF4.

Fig. 2. Top: CIS spectra of the fragment (1) and of the
3t2 (2) final states. Bottom: resonant Auger 2-D map
showing only the resonant contributions: (1) the
non-dispersive state and (2) the 3t2 spectral line.

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Cl-L23VV Normal Auger and Resonant Auger Electron Spectra of CCl4
Molecules
H. Iwayama1, M. N. Piancastelli2, R. Guillemin2, M. Simon2 and E. Shigemasa1
1

UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, JapanLCPMR, Université Pierre et Marie Curie, 75231 Paris Cedex 05, France

2

The chlorofluoromethanes have received attention
due to their potentially destructive effect on theearth’s ozone layer. The inner-shell photoabsorption
spectra of the family of tetrahedral molecules CX4(X=H, F, and Cl) are known to exhibit completely
different below-threshold structures, related totransitions to empty molecular orbitals versus Rydberg
states. The behaviors of the Rydberg state energies
and intensities in these molecules are explained by
the cage model, in which the Rydberg states arestrongly excluded from CCl4 but not from CF4.
CCl4 has been a benchmark for several spectroscopic
studies, due to its high symmetry, same as methane,
CH4, with four chlorine atoms around the carbon
center. CCl4 is one of the good candidates toinvestigate the dynamical properties of core-excitedstates with an electron in the antibonding unoccupied
molecular orbitals in a highly symmetric system. We
have studied the deexcitation processes following the
Cl 2p excitations of CCl4 molecules by using Auger
electron spectroscopy.
The experiment was performed on the soft X-ray
beamline BL6U at UVSOR. The radiation from an
undulator was monochromatized by a variable
included angle varied line-spacing plane grazing
monochromator. The photon bandwidth was set toabout 2000 ('E ~100 meV). Kinetic energies of theemitted electrons were measured by a hemisphericalelectron energy analyzer (MBS-A1). The directionof the electric vector was set to be parallel to the axisof the electrostatic lens of the analyzer. The kinetic
energy resolution of the analyzer was set to 30 meV.

bandwidth was about 30 meV. The broad peakaround 198 eV is assigned to the excitation of the Cl
2p3/2 electron into the lowest unoccupied molecularorbital. The normal Auger electron spectrum andresonant Auger electron spectrum measured on top of
this resonance are shown in Fig. 2. The present
normal Auger spectrum displays clearer peakstructures than that reported in Ref. [2], reflecting
much higher resolution. Three peaks near 188 eV in
the resonant Auger spectrum correspond to thephotoionization of valence electrons. Two relatively
sharp peaks around 180 eV seem to be strongly
enhanced by the resonance. In order to examine theso-called detuning effect, higher photon energy
resolution is required for measuring the resonant
Auger spectrum, since its spectral resolution depends
on the photon energy resolution. It is planned torecord high-resolution resonant Auger spectra acrossthe resonances as a function of photon energy.

Fig. 1. Total ion yield curve in the Cl 2p excitation
region of CCl4.

Fig. 2. Cl-L23VV normal and resonant Auger spectraof CCl4.

Figure 1 shows the total-ion yield curve around the
Cl 2p excitation region of CCl4. The spectralfeatures in Fig. 1 resemble the prevously measured
high-resolution spectrum [1], where the photon[1] M. de Simone et al., J. Phys. B 35 (2002) 61.
[2] P. G. Fournier et al., Phys. Rev. A 40 (1999) 163.

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Ultrafast Molecular Dissociation of Core-Excited HCl Revisited
P. Lablanquie1, F. Penent1, H. Iwayama2, K. Soejima3 and E. Shigemasa2
1

LCPMR, Université Pierre et Marie Curie, 75231 Paris Cedex 05, France
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan3
Department of Enviromental Science, Niigata University, Niigata 950-2181, Japan
2

Excitation of a core electron to the lowest
unoccupied antibonding orbital weakens themolecular bonding and populates generally adissociative state. Morin and Nenner demonstrated
that the 3dĺV excitation in HBr leads to a fastneutral dissociation which can precede the Auger
relaxation; in other words, one can observe ‘atomic’
3d hole decays in the Br fragment [1].
In 2012 we showed that the equipment at UVSOR
allows one to revisit the HBr fast dissociation with anunprecedented resolution, revealing more detailed
atomic Auger peaks. Here we extend our studies andexamine ultrafast dissociation following the Cl 2p
core excitation in HCl.
The experiments were carried out on the soft X-ray
beamline BL6U at UVSOR. The exit slit opening was
set to 50 Pm, which corresponds to a photon energy
resolution 'E of ~50 meV. The monochromatizedradiation was introduced into a gas cell filled withsample gas. Kinetic energies of the emitted electrons
were measured by a hemispherical electron energy
analyzer (MBS-A1) placed at a right angle relative tothe photon beam direction. The axis of theelectrostatic lens of the analyzer was set to be parallelto the polarization direction of the incident light. Theenergy resolution of the analyzer was set to ~12 meV.
Under these experimental conditions, the full width at
half maximum of the vibrational fine structure for the
A state of HCl+ was measured to be ~65 meV.
Figure 1 (a) gives the resonant Auger spectrum
measured on top of the 2p3/2oV* resonance.
Comparison with the off resonance spectrum (b)shows that the molecular X, A and B HCl+ states arelittle affected by the resonance, and reveals new
peaks which are mainly the Atomic transitions:
Cl (2p3/2)-1 3s23p6 ĺ Cl+ 3s23p4 or Cl+ 3s3p5
Broad structures at the foot of these peaks correspondto the ‘molecular’ autoionization during the HCl fastdissociation and amount to ~30% of the decays. The
resonant spectrum can thus be used to retrieve theAuger spectrum associated with the decay of a 2p
hole in a Cl atom. This is done in Fig. 2: (a) shows
the decay of a 2p3/2 hole, as obtained on the
2p3/2oV* resonance, while (b) measured on the
2p1/2oV* resonance gives the decay of a 2p1/2 hole,with some contribution of the 2p3/2 hole decay.
Comparison with the well-known Auger spectrum forthe decay of a 2p hole in Ar in (c) is instructive as one
can in this way compare the decay of a 2p hole inatoms with the same 3s23p6 valence configuration,

but with different nucleus. One observes a richer
satellite structure for Cl (Fig. 2 (a) and (b)) compared
to Ar (Fig. 2 (c)), which is probably linked to thedifference of the 3d orbital in each case. Calculations
are required to test this idea.
HCl

3s3p
1

2p3/2 V

5

P

2

4

1

3

3s 3p
1

3

P

S

D

P

(a)

170

175

X

A

B
180
Kinetic Energy / eV

185

(b)
190

Fig. 1. (a) Resonant Auger spectrum measured on topof the 2p3/2oV* resonance, compared to a shifted
off-resonance spectrum (b). Cl atomic lines areindicated with arrows.
Ar Auger Kinetic Energy / eV
180
190

170

(c)

200

Auger decay of
Ar 2p hole :
-1

2

6

Ar 2p 3s 3px5Auger decay of

(b)

-1

2

6

Cl 2p 3s 3p
x11

(a)

Auger decay of
-1

2

6

Cl 2p3/2 3s 3p
x15

155

160

165
170
175
Cl Auger Kinetic Energy / eV

180

Fig. 2. Resonant Auger decay on 2p oV* resonances
showing the atomic Auger lines for the decay of 2p3/2
and 2p1/2 holes in Cl atoms ((a) and (b)), compared to
the Auger spectrum for the decay of a 2p hole in Ar(from reference [2]).
[1] P. Morin and I. Nenner, Phys. Rev. Lett. 56(1986) 1913.
[2] H. Pulkkinen et al., J. Phys. B 29 (1996) 3033.

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Dissociation Pathways of Core Excited CF4 Molecules Studied by anIon Coincidence Method
Auger-Electron
H. Iwayama, L. Ishikawa and E. Shigemasa
UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan
ions were CFn+(nd3) and Fn+(n=1,2) ions. We didn't
observe CF4+ parent ions within the present detection
time. In the Auger-electronion coincidence map, we
found that Auger electrons with high kinetic energy
correlate with large fragment ions such as CF2+ and
CF3+, while Auger electrons with low kinetic energy
correlate with small fragment ions such as C+ and F+.
This means that the Auger final states with highbinding energy lead to efficient C-F bond breakings.
The detailed data analyses are now in progress.

When a molecule composed of light elements is
irradiated by soft x-rays, an inner-shell electron in themolecule is efficiently promoted into unoccupied
molecular orbitals or continua. The core-hole statethus created is quite unstable, and subsequent Auger
decay process follows in general. The molecular
Auger final state possesses more than one hole in thevalence orbitals, which often dissociates into two or
more fragments. To understand such molecular
photochemistry triggered by the core-hole creation, it
is indispensable to correlate the Auger final stateswith the dissociation pathways. For this purpose, wehave developed an Auger-electron-ion coincidence
apparatus, which consists of a double toroidal
electron analyzer (DTA) [1] and an ion momentum
spectrometer. In the present work, we have studied
dissociation pathways of core-excited CF4 moleculesaround carbon K edge. In particular, we haveinvestigated whether the dissociation processes
following the core-to-Rydberg excitation differ fromthose after the core-to-valence excitation.
The Auger-electron-ion coincidence measurements
for core-excited CF4 molecules were carried out on
the undulator beamline BL6U at UVSOR. The
radiation from an undulator was monochromatized bya variable included angle varied line-spacing planegrazing monochromator. The electrons ejected at
54.7 with respect to the electric vector of theionization light were analyzed in energy by DTA,
while ions were extracted from the interaction region
into the momentum spectrometer by a pulsed electricfield according to the electron detection. Arrival
positions on the detector and time-of-flights of ionswere recorded for every event. The pass energy of the
DTA was set to 200 eV for observing resonant Auger
electrons. The energy resolution was about 1.9 eV. All
signals from electron and ion detectors were recordedwith an 8ch TDC board. We used photon energies of
298.5 and 299.4 eV, which correspond to C
1sĺı2) (valence) and 1sĺ3pt2 (Rydberg)
resonances, respectively [2]. The photon bandwidth
was set to be 0.03 eV.
Figure 1 shows a resonant-Auger-electronion
coincidence map obtained at the C 1sĺı2)resonance excitation. The vertical and horizontal axesof the map correspond to the kinetic energies ofAuger electrons and the mass-to-charge ratios of ions,
respectively. The one-dimensional spectra displayedin the right and top panels, represent the total events
for the Auger electron detection and ion
mass-to-charge rations, respectively. Main fragment

Fig. 1. Two-dimensional map for mass-to-charge
ratios of ions in coincidence with resonant Auger
electrons, obtained at the C 1sĺı2) resonanceexcitation of CF4. The horizontal axis corresponds tomass-to-charge ratios of ions, and the vertical axis is
the kinetic energies of the Auger electrons. The
one-dimensional spectra shown at the right and top
panels represent the total events for the Auger
electron detection and the ion mass-to-charge ratios,
respectively.
[1] C. Miron, M. Simon, N. Leclercq and P. Morin,
Rev. Sci. Instrum. 68 (1997) 3728.
[2] R. Guillemin, W. C. Stolte, M.N. Piancastelli andD. W. Lindle, Phys. Rev. A 82 (2010) 043427.

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