Penning ionization electron spectrometry of hydrogen chloride

Abstract

An electron spectrometric study has been performed on HCl using metastable helium and neon atoms as well as neon resonance photons. High resolution electron spectra were obtained with two different beam apparatuses for a mixed He(21 S, 23 S) beam, a pure He(23 S) beam, and, for the first time, state-selected pure Ne(3s 3 P 2) and pure Ne(3s 3 P 0) beams, and for NeI resonance photons. For the system He(23 S)+HCl the vibrational populationsP(υ′) of the formed HCl+ (X 2∏ i , υ′) and HCl+ (A 2Ω+, υ′) ions are found to differ from the Franck-Condon factors for unperturbed potentials, indicating slight bond stretching in HCl upon He(23 S) approach. For He(21 S)+HCl the vibrational peak shapes and vibrational populations are substantially different from the He(23 S) case, pointing to an additional, charge exchanged interaction (He++HCl−) in the entrance channel of the former system. For the first time, we have detected the electrons in both the He(21 S)+HCl and He(23 S)+HCl spectra associated with the major mechanism for the formation of Cl+ ions: energy transfer to repulsive HCl** Rydberg states, dissociating toH(1s) and autoionizing Cl**(1 D 2 nl) atoms. For both Ne(3 P 2)+HCl and Ne(3 P 0)+HCl, the populationsP(υ′) of both final molecular states HCl+ (X, A) agree closely with the Franck-Condon factors at the average relative collision energyĒ coll=55 meV and, for HCl+ (A 2Ω+), also atĒ coll=130 meV.