Collision-Energy-Resolved Penning Ionization Electron Spectroscopy of Phenylacetylene and Diphenylacetylene by Collision with He*(2³S) Metastable Atoms

Abstract

Penning ionization of phenylacetylene and diphenylacetylene upon collision with metastable He*(2(3)S) atoms was studied by collision-energy-/electron-energy-resolved two-dimensional Penning ionization electron spectroscopy (2D-PIES). On the basis of the collision energy dependence of partial ionization cross-sections (CEDPICS) obtained from 2D-PIES as well as ab initio molecular orbital calculations for the approach of a metastable atom to the target molecule, anisotropy of interaction between the target molecule and He*(2(3)S) was investigated. For the calculations of interaction potential, a Li(2(2)S) atom was used in place of He*(2(3)S) metastable atom because of its well-known interaction behavior with various targets. The results indicate that attractive potentials localize in the pi regions of the phenyl groups as well as in the pi-conjugated regions of the acetylene group. Although similar attractive interactions were also found by the observation of CEDPICS for ionization of all pi MOs localized at the C[triple bond]C bond, the in-plane regions have repulsive potentials. Rotation of the phenyl groups about the C[triple bond]C bond can be observed for diphenylacetylene because of a low torsion barrier. So the examination of measured PIES was performed taking into consideration the change of ionization energies for conjugated molecular orbitals.

Benchmark Dyson Orbital Study of the Ionization Spectrum and Electron Momentum Distributions of Ethanol in Conformational Equilibrium

“…The determination of the influence of the molecular conformation on the underlying electronic structure and wave function has been over the last two decades a topic of growing interest, both from a fundamental viewpoint and with regard to the structural and chemical characterization of industrially important polymer surfaces and organic thin films. Various ionization techniques have been used to this end, including photoelectron spectroscopy [XPS, ultraviolet photoelectron spectroscopy (UPS), and synchrotron PES], electron momentum spectroscopy (EMS), or Penning electron ionization spectroscopy . Among these techniques, EMS is probably the most attractive, as it combines the principles of scattering and ionization experiments for experimentally reconstructing in momentum space one-electron transition densities that are associated to specific ionization channels and which can be assimilated to orbital momentum densities if a one-electron picture of ionization prevails.…”

“…A recent carbon 1s photoelectron study on ethanol indicates that detailed pieces of information on the molecular conformation are also experimentally amenable from an analysis of the core ionization bands. Most studies − of the interplay between the molecular conformation and the electronic structure have so far focused on rather large systems (from n -butane, 1,3-butadiene, glycine, dimethoxymethane, and stilbene to a variety of organic polymers), and it is exceedingly interesting therefore to learn from the latter study that the simple rotation of one O−H bond in an excessively small molecule can apparently induce highly significant changes in the 1s photoelectron spectrum, in an energy region that is usually regarded as bearing very limited information onto chemical bonds and details of the molecular structure. In line with the latter study, we wish to evaluate on theoretical grounds the potential of EMS in probing the influence of the molecular conformation of ethanol on the shape, topology, and spread of the valence orbitals of this compound.…”

Conformation-Specific Raman Bands and Electronic Conjugation in Substituted Thioanisoles

“…1,2 When a molecule undergoes the large-amplitude vibration, a sizable change in its electron distribution is expected. 3 In particular, the vibrational motion induces modulations of electronic interactions between vertically pointing π electrons of aromatic rings and other contacting electrons. Such electronic redistribution will manifest itself as the probability or intensity of optical transitions.…”

“…In general, low-frequency vibrations including torsional modes give rise to large-amplitude vibrations. They can change the global structure of large molecular systems and will determine the functionality of the system. , When a molecule undergoes the large-amplitude vibration, a sizable change in its electron distribution is expected . In particular, the vibrational motion induces modulations of electronic interactions between vertically pointing π electrons of aromatic rings and other contacting electrons.…”