He * (2 3 S) penning ionization of H2S. II. Formation of the SH+(A 3Π) and H2S+(Ã 2A1) ions

Abstract

Emissions in the 200–750 nm region produced by the collision of He*(2 3S) with H2S were studied under single-collision conditions. The hydrogen Balmer lines and the SH+(A 3Π–X 3Σ−) and H2S+(à 2A1–X̃ 2B1) bands were assigned. The total emission cross section (σem) was evaluated to be (1.7±0.3)×10−20 m2 at a collision energy of 150 meV. The σems of the SH+(A–X) and H2S+(ÖX̃) bands decreased with increase in the collision energy in the 115–200 meV range, indicating that attractive forces are effective for the incident channels with regard to the formation of these species. The rotational distribution of SH+(A 3Π,ν′=0) is represented by a Boltzmann temperature of 870±80 K. The H2S+(à 2A1–X̃ 2B1) emission, which was assigned for the first time in the Penning ionization of H2S, primarily consists of the bending progressions. The internal populations of H2S+(Ã) were analyzed using the vibrational energies and Einstein’s A coefficients calculated in this study. The details of the calculation and derived spectroscopic constants are reported in the accompanying paper, Paper I. The populations obtained for the bending vibration (ν2′) of H2S+(Ã) show an inverted distribution with a peak at ν2′=3. This distribution is shifted lower compared that with a peak at ν2′=4–5 observed by He*(2 3S) Penning ionization electron spectroscopy and that with a peak at ν2′=6–7 predicted by the theoretical Franck–Condon factors for the H2S(X̃)–H2S+(Ã) ionization. The origin of the difference is discussed concerning the formation mechanism of H2S+(à 2A1).