Ionization cross-sections of molecules due to electron impact

Abstract

Recently, Mayol and Salvat have employed a semi-phenomenological approximation along with the first Born approximation to calculate K-shell ionization cross-sections of atoms. Their method requires optical oscillator strengths (OOS) as input instead of the generalised oscillator strengths (GOS). As the generation of the GOS for molecules is a difficult task, in the present paper we have extended the semi-phenomenological approximation of Mayol and Salvat to investigate molecular ionisation because of the availability of OOS for a large number of molecules. Cross-sections for the total ionisation and for the formation of the parent ions of H 2, N 2,O 2, NH 3, H 2O and CO 2 by electron impact are calculated in a modified first Born approximation for the incident energy E varying from the threshold of ionisation to 1 keV. The contribution of the exchange is included through the Ochkur approximation. Dissociative ionisation cross-sections of NH 3, H 2O and CO 2 giving rise to NH 2 +, OH + and O + ions, respectively, have also been evaluated. The calculated cross-sections are, in general, in good agreement with the experimental data over a wide energy range ( E ⪖ 50 eV) and the same holds for ratios of the partial to the total ionisation cross-sections.