Electron-impact ionization of fluoromethanes – Review of experiments and binary-encounter models

Abstract

Experiments and recommended data on electron-impact ionization of methane and fluoromethanes (CH3F, CH2F2, CHF3, CF4) are reviewed and compared with binary-encounter models (Gryziński's, Deutsch and Märk's, and Kim and Rudd's). A good agreement between recent experiments and the two latter classical-like models is shown. Kim and Rudd's model (calculated presently in the restricted Hartree-Fock 6-31**G orbital basis) predicts well total ionization cross sections for all five molecules considered. However, counting-ionization cross sections have to be extracted from experimental data to show this agreement. The additivity model of Deutsch and Märk performs equally well, once all molecular orbitals are taken into account. The maxima of total (counting) ionization cross sections calculated presently in Kim and Rudd's binary-encounter approximation correlate linearly with the molecular polarizability.