Kinetic energy dependence of partial cross sections for the collisional ionization of H2O, H2S, O2, and Ar with He(2 3S) metastable atoms

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Abstract
The kinetic‐energy dependences of partial cross section σ(E) for the collisional ionization of H2O, H2S, O2, and Ar with He(2 3S) metastable atoms are measured in the energy range of 40–300 meV by collision‐energy‐resolved electron spectroscopy. The σ(E) functions are markedly dependent on the system and, in some cases, on final ionic states because of the anisotropy of incoming interaction potential surfaces or potential surface crossings with other potentials. Negative energy dependences of σ(E) are obtained for H2O+ (X 2B1, A 2A1, B 2B2) and H2S+ (X 2B1, A 2A1, B 2B2), whereas positive energy dependences for O+2 (a 4Πu, b 4Σ−g) and Ar+ (2P3/2). The σ(E) curves for O+2 (X 2Πg, A 2Πu) produced by Penning ionization via the ion‐pair potential of He+(2S)+O−2(2Πg) are almost independent of the collision energy. The results are interpreted in terms of the semiclassical scattering theory of Penning ionization with assuming appropriate function forms to the potential and the transition rate.