Close collision cross sections for ions and symmetric top molecules

Abstract

Close collision cross sections have been calculated for ions with symmetric top molecules by an extension of a previously described procedure for ions with linear molecules. Excitation functions for individual collisions were found to be markedly dependent on the rotational state of the molecule. For dipolar molecules, the bulk excitation function is of somewhat steeper slope than a simple “Langevin” function, implying that the rate constants for such collisions will be weakly dependent on collision energy. The limitations on the usefulness of close collision treatments are discussed in the light of these results and other considerations.