Molecular Autoionization Lifetimes and Cross Sections for Penning Ionization: Numerical Results for He* (1s2s 3S) + H(1s 2S)

Abstract

The width Γ (or lifetime ℏ/Γ) for autoionization of ${\mathrm{He}}^{*}{\text{(1s2s}}^3\mathrm{S)\; +}\mathrm{H}{\text{(1s}}^2\mathrm{S)}$ has been calculated as a function of internuclear distance, and cross sections for Penning and associative ionization $({\mathrm{He}}^{*}+\mathrm{H}\to \mathrm{He}+{\mathrm{H}}^{+}{\mathrm{+e}}^{-},{\mathrm{HeH}}^{+}{\mathrm{+e}}^{-})$ have been determined for low collision energies. Associative ionization is 22% of the total ionization cross section in the limit of zero collision energy; this fraction decreases with increasing energy, being ·18% at a collision energy corresponding to 300°K. The distribution in energy of the ionized electron is also calculated, and it is seen that measurement of this quantity should lead to a good estimate of the well depth of the He^*–H potential. Comparison of these results with those obtained by an orbiting model shows that the model (suitably scaled) is adequate in predicting the total ionization cross section, but is less accurate for the more detailed collision properties.