title: Collision-energy-resolved penning ionization electron spectroscopy of phenylacetylene and diphenylacetylene by collision with He*(2(3)s) 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.
authors.affiliation: Department of Chemistry, Graduate School of Science, Tohoku University, Aramaki, Sendai 980-8578, Japan.
authors.forename: Andriy
authors.initials: A
authors.lastname: Borodin
authors.forename: Masakazu
authors.initials: M
authors.lastname: Yamazaki
authors.forename: Naoki
authors.initials: N
authors.lastname: Kishimoto
authors.forename: Koichi
authors.initials: K
authors.lastname: Ohno