A MODIFIED ADDITIVITY RULE FOR THE CALCULATION OF ELECTRON-IMPACT IONIZATION CROSS-SECTION OF MOLECULES AB(N)

This paper describes a modified additivity rule for the calculation of electron impact ionization cross-sections of molecules and radicals o f the form AB(n) (n = 1-6). This additivity rule incorporates weightin g factors for the contributions to the molecular ionization cross-sect ions from the ionization cross-sections of the constituent atoms, whic h depend explicitly on the atomic radii and the effective number of at omic electrons. In a few special cases (hydrides where the other const ituent atom has a radius smaller than the radius of the H atom and spe cies where both constituent atoms have radii smaller than the radius o f the H atom), the weighting factors can be simplified, so that they d epend only on the atomic radii, i.e. on geometric effects. A comprehen sive comparison of the predictions of this new modified additivity rul e with available experimental data and with other theoretical predicti ons is presented. (C) 1997 Elsevier Science B.V.