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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.
Global Mapping of Equilibrium and Transition Structures on Potnential Energy Surfaces by
the Scaled Hypersphere Search Method: Applications to ab initio Surfaces of Formaldehyde and
Technical details of a new global mapping technique for finding equilibrium (EQ) and
transition structures (TS) on potential energy surfaces (PES), the scaled hypersphere search
(SHS) method (Ohno, K.; Maeda, S. Chem. Phys. Lett. 2004, 384, 277), are presented. On the
basis of a simple principle that reaction pathways are found as an anharmonic dowward
distortion of PES around an EQ point, the reaction pathways can be obtained as energy minimua
on the scaled hypersphere surface, which would have a constant energy when the potentials are
harmonic. Connections of SHS paths between each EQ are very similar to corresponding intrinsic
reaction coordinate (IRC) connections. The energy maximamum along the SHS path reaches a region
in close proximity to the TS of the reaction pathway, and the subsequent geometry optimization
from the SHS maximum structure easily converges to the TS. The SHS method, using the
one-after-another algorithm connecting EQ and TS, considerably reduces the multidimensional
space to be seaerched to ceartain limited regions around the pathways connecting each EQ with
the neighboring TS. Application of the SHS method have beeen made to ab initio surfaces of
formaldehyde and propyne molecules to obtain systematically five EQ and nine TS for
formaldehyde abd seven EQ and 32 TS for propyene.
Global Reaction Route Mapping on Potnential Energy Surfaces of Formaldehyde, Formic Acid, and
Their Metal-Substituted Analogues
Global reaction route mapping of equlibrium structures, transition structures, and their
connections on potential energy surfaces (PES) have been done for MCHO (M = H, Li, Na, Al, Cu)
and HCO2M (M = H, Li). A one-after-another technique based on the scaled hypersphere search
method has been successively applied to exploring unknown chemical structures, transition
structures, and reaction pathways for organometallic systems. Upon metal substitution,
considerable changes of stable structures, reaction pathways, and relative heights of
transition structures have been discovered, though some features are simlilar, especially
around the structures where the Li atom is not directly connected with the methyl group,
which indicates little effects of alkyl substitution on the reaction route topology.
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.
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