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Study of Electron Distributions of Molecular Orbitals by Penning Ionization
Penning ionization electron spectroscopy (PIES) has been used to study spatial
electron distributions of individual molecular orbitals. On the basis of
comparison of observed band intensities with electron densities of ab initio
molecular orbitals, a simple principle for orbital activities in Penning
ionization has been established; the outer orbital which is exposed outside
the van der Waals surface is active and the inner orbital which is localized
inside the van der Waals surface is inactive.
Penning ionization can be considered as an electrophilic reactions of rare
gas atoms in metastable states with sample molecules. It is concluded that
PIES is a sensitive metohd for probing orbital electron densities at the very
frontier of the molecule where the molecule is attacked by the reagent.
A Scaled Hypersphere Search Method for the Topography of Reaction Pathways on the
Potential Energy Surface
An algorithm for finding pathways to transition states (TS) or dissociation channels
(DC) from equilibrium structures (EQ) on the potnetial energy surface (PES) is
presented. The pathways around an EQ can be discovered at minima on the scaled
hypersphere which would have a constant energy when the potnetials are harmonic.
Topographic maps including all TS, DC, and EQ were obtained for ab initio PES of
H2O and HCHO in the MP2/3-21G level. The present scaled hypersphere search technique
in conbination with a downhill-walk algorithm enables us to make a topographic
analysis of the PES for a given chemical composition.
State-Resolved Collision Energy Dependence of Penning Ionization Cross
Sections for N2 and CO2 by He*23S
The state-resolved collision-energy dependence of Penning ionization cross
sections were measured in an energy range (60 < E < 400 meV) for N2 and
CO2 with He*23S by using a very high-intensity He* beam and
detecting energy analyzed electrons as functions of time-of-flight of He*.
The partial ionization cross sections for Π states were observed to increase
more rapidly with the increase of the collision energy than those for Σ states.
In the studied energy range, the repulsive walls for end-on collisions were
indicated to be harder than those for side-on collisions. The directional
peculiarity of the potential surfaces was related to the anisotropy in the
hybridization of He* orbitals interacting with the target molecules.
Kinetic Energy Dependence of Partial Cross Sections for the Collisional
Ionization of H2O, H2S, and Ar with He*23S Metastable Atoms
Exterior Electron Model for Penning Ionization. Unsaturate Hydrocarbonds
A simple theoretical model is described for Pening ionization (M + A* -
M++A+e- in which a metastable-state rare gas atom (A*) extracts
an electron from a target molecule (M) and ejects another elecron into a
continuum state. One of the most importnat factors governing Penning
ionization is electron distributions of molecular orbitals which are directly
connected with the electronic transition probabilities.
Another key factor is the repulsive molecular surafce which divides the
unreactive electron densities in the interior region from the reactive electron
densities in the exterior region, because the metastable atom A* cannot penetrate
into the interior region. In the present model, exterior electron densities (EED)
for individual molecular orbitals are considered to be proportional to Penning
ionization branching ratios.
Good agreements between ab initio MO calculations of EED's and experimental
branching ratios of Penning ionization were obtained for various unsaturated
Penning Ionization Electron Spectroscopy of CO and Fe(CO)5. Study
of Electronic Structure of Fe(CO)5 from Electron Distribution of
Individual Molecular Orbitals
Penning Ionization of (CH3)4C and (CH3)sCCl
by Collision with He*(23S) Metastable Atom
Normal Coordinate Calculations of Benzenoid Hydrocarbons. Classification
and Characterization of Aromatic Planar Vibrations in Polyacenes
Collision Energy-Resolved Penning Ionization Electron Spectra of Unsaturated
Hydrocarbons with He*(23S) Metasatble Atoms
Selective Observation of Outermost Surface Layer during Epitaxial Growth by
Penning Ionization Electron Spectroscopy: Pentancene on Graphite.
Application of Penning Ionization Electron spectroscopy to the Study of
the Outermost Layer of the Solid Surface
Penning Ionization Electron Spectroscopy of Nitriles
Collision-Eenergy/Electron-Energy Resolved Two-Dimensional Study of Penning
Ionization of Ar by He metastable atoms 23S and 21S
Collision-Energy-Resolved Penning Ionization Electron Spectroscopy of Nitriles:
Conjugation Effects on Interactions with He*(23S) Metastable Atoms
Normal Coordinate Calculations of Benzenoid Hydrocarbons.
Theoretical Models of Simplified Valence Force Fields