Penning ionization of substituted benzenes (aniline, phenol and thiophenol) by collision with He*(23S) metastable atoms

Abstract

Penning ionization electron spectra of substituted benzenes (aniline, phenol and thiophenol) upon collision with He*(23S) metastable atoms were observed, and a collision energy dependence of partial ionization cross-sections (CEDPICS) of the sample molecules was studied using collision-energy-resolved Penning ionization electron spectroscopy. CEDPICS indicates that the interaction potential between He* and the target molecule was anisotropic in the studied collision energy range (90–300 meV). The interaction potential around the hetero atoms and the out-of-plane direction of the phenyl ring is attractive, while a repulsive interaction around the hydrogen atoms was derived from the small negative slope of CEDPICS for ionization from π orbitals and model potential calculations. An attractive interaction around the nitrogen atom of aniline indicates the ‘lone pair’ character of the nonbonding molecular orbital. For thiophenol, the interaction potential for the out-of-plane direction around the sulfur atom is attractive in contrast to the in-plane direction. In contrast, the interaction potential for the in-plane direction around the oxygen atom is attractive in the case of phenol. Assignments of photoelectron spectra for ionization from π and nonbonding orbitals were confirmed utilizing large-band intensity in the Penning ionization electron spectra reflecting extending molecular orbitals and an attractive interaction.