Penning Ionization of Thiophene, Furan, and Pyrrole by Collision with He*(23S) Metastable Atoms

Abstract

Penning ionization of thiophene, furan, and pyrrole upon collision with He*(23S) metastable atoms was studied by collision-energy-resolved Penning ionization electron spectroscopy. A strong negative collision energy dependence of the partial ionization cross sections was observed for π bands. This tendency was used to make an assignment for the lowest π orbital in the ultraviolet photoelectron spectrum. In the studied collision energy range, the interaction potentials between He*(23S) and target molecules were found to be anisotropic, which is consistent with calculated interaction potential curves. For the out-of-plane directions, attractive interactions were found around the π orbital region. For the in-plane directions, repulsive interactions were found around the σCH orbital region and the sulfur atom of thiophene, while attractive interactions were found around the oxygen atom of furan. In the Penning ionization electron spectrum of pyrrole and thiophene, a satellite band was found to be associated w...