A modified additivity rule for the calculation of electron impact ionization cross-section of molecules ABn

This paper describes a modified additivity rule for the calculation of electron impact ionization cross-sections of molecules and radicals of the form AB(n) (n = 1-6). This additivity rule incorporates weighting factors for the contributions to the molecular ionization cross-sections from the ionization cross-sections of the constituent atoms, which depend explicitly on the atomic radii and the effective number of atomic electrons. In a few special cases (hydrides where the other constituent atom has a radius smaller than the radius of the H atom and species where both constituent atoms have radii smaller than the radius of the H atom), the weighting factors can be simplified, so that they depend only on the atomic radii, i.e. on geometric effects. A comprehensive comparison of the predictions of this new modified additivity rule with available experimental data and with other theoretical predictions is presented. (C) 1997 Elsevier Science B.V.