EXTERIOR CHARACTERISTICS OF
MOLECULAR ORBITALS AND
MOLECULAR SURFACESAS STUDIED BY ATOMIC PROBES

Koichi Ohno
Graduate School of ScienceTohoku UniversityJAPANhνe

EXTERIOR

CHARACTERISTICS AtomicProbe

OF

MOLECULAR

ORBITALS

MOLECULAR& SURFACES

are important, because molecules and atoms interact witheach other at exterior parts, not via interior parts.
Photons and electrons go through molecules, but atoms do not.
Thus, atomic probes are most suitable.

An Excited Atom He* can be used toProbe Outer Properties of Molecules

K. Ohno,H. Mutoh, &Y. Harada

J.Am.Chem.Soc.
105, 4555, (1983)

Outerorbital

PIES

Innerorbital

MOLECULAR SURFACE

K. Ohno,H. Mutoh, &Y. Harada

J.Am.Chem.Soc.
105, 4555, (1983)

EXTEIOR
INTERIOR

MOLECULAR
SURFACE

Molecular Surface is important,because it divides chemically active
exterior parts from inactive interiorparts.

Development of
2D-PIES
Simultaneous
Analyses ofReactants &Products result in
5 orders of Signal
Reduction !
1D-PIES

2D-PIES

3 hrs → 34 years !

Improvementsof Experimental
Techniquesmade it possible
to do 2D-PIES
experiments
without waiting34 years !

He*limited collection

4allcollectionHe*2D-PIES Apparatus

He*ca. 1015 atoms s-1sr-1

Crossed Molecular Beam 2D-PIES

All electron collectionHe*2D-PIES made it possible to observe

Collision Energy Dependence ofPartial Ionization Cross Sections (CEDPICS)
Ionic States-Unresolved
Total Ionization Cross Section :Illenberger & Niehaus (1975)

Ionic States-Resolved
Partial Ionization Cross Sections :Ohno et al. J.Chem.Phys.94,2675 (1991)

2D-PIES made it possible to observe

Collision Energy Resolved Penning
Ionization Electron Spectra (CERPIES)
Collision-Energy Unresolved PIES :Ohno et al. (1983)

Collision-Energy Resolved PIES :Takami & Ohno (1992)
J.Chem.Phys.96,6523(1992)

2D-PIES of N2/He*(23S)
In order to elucidate
collisional ionization
dynamics,
we have developed
a new method fortheoretical constructionof 2D-PIES bytrajectory calculations.

TheoreticalConstructionof2D-PIES
requires
Entrance andExit Potentials
together withTransition Rates

Entrance Potential for Reactants
can be obtained as
ab initio model
potentials using a Li
atom in place of an
excited He* atom,
based on the wellknown similarity
between He* and Li.
Both of them show
very similar welldepths.

Interaction
Potentials
Trajectory
calculations
are Trajectory Calculationsfor
then performed for various
initial conditions more thanby M
10,000, based on calculated
potential energy surfaces andtransition rates.
Here, it is important to notethat transition rates arerelated with MO functions.
MOComparison of Observed and Calculated
2D-PIES of N2/He*(23S)

Optimization of Theoretical Simulations
to Observed CEDPICS leads toDetermination of Interaction Potentials
Interaction Potentials
Ionization Rates
Molecular Orbitals

Calculated
CEDPICS

Observed
CEDPICS

Interaction Potentials for N2 , C2H2 /Li, He*Ab
Optimized
initio Li Model
He* Potentials
Potentials-50 meVInteraction Potential for OCS /Li, He*

Interaction Potential for C6H6 /He*

Determination of Molecular Orbitals
via Optimization of Theoretical Simulations
to Observed CEDPICS
Interaction Potentials
Ionization Rates
Molecular Orbitals

Calculated
CEDPICS

Observed
CEDPICSDetermination of Molecular Orbitals
 Input Data Experimental 2D-PIES / CEDPICS DATA Entrance Potential for Reactants

 Molecular Orbitals
 Initial guess : SCF-LCAO-MOs in a Minimal Basis Optimization : MO Coefficients & Exponents

Crude MO

Optimized MO

ζ（N) ＝ 1.95

ζ（N) ＝ 1.63

Crude MO

Optimized MO

ζ（C） ＝ 1.72
ζ（O） ＝ 2.25

ζ（C）＝ 1.42
ζ（O）＝ 1.92

Summary & Conclusions
 1010 times of improvements were made forconstructing a crossed-beam 2D-PIES apparatus.
 Ionic-state resolved CEDPICS became observable.
 Collision-energy resolved PIES became observable.

 A theoretical simulation method was established.
 Anisotropic interaction potentials between He* andmolecules could be determined.
 Spatial distributions of molecular orbitals could beobtained based on the observed CEDPICS.

Collaborators
1D-PIES ( Univ. Tokyo )Y. Harada, T. Munakata, K. Kuchitsu,
S. Fujisawa, H. Mutoh, K. Imai,
S Matsumoto, T. Veszpremi, S. Masuda

2D-PIES ( Univ. Tokyo : Tohoku Univ. )K. Mitsuke, T. Takami, T. Ishida, H. Yamakado,
N. Kishimoto, S. Hoshino, T. Ogawa, T. Yamata,T. Pasinszki, F. Misaizu, Y. Yamakita, H. Tanaka,
M. Yamazaki, S. Maeda, R. Maruyama, T. HorioJAPANSENDAI