On the Additivity Rule in the Ionization Cross Section of Molecules

Validity of the additivity rule in the ionization cross section of molecules is investigated. So far as the present calculation is concerned, we have concluded that the rule is considered to be approximately valid within the allowance of 20% under the condition where electrons are impacted with incident energies more than 80 eV and the internuclear distance between every couple of atoms in a molecule is more than 2.5a 0 . If the internuclear distance is less than 2.5a 0 , one must take account of the diffraction effects due to the interference of waves scattered by the neighbour atoms. Numerical computation was carried out to the cases of C n H 2 n +2 and C n F 2 n +2 . The results for C n H 2 n +2 were found in plausible agreement with mass spectroscopic data but those for C n F 2 n +2 were found in small disagreement with data.