Calculation of electron-impact ionization cross sections of perfluoroketone (PFK) molecules CxF2xO (x=1-5) based on Binary-Encounter-Bethe (BEB) and Deutsch-Mark (DM) methods

Perfluoroketone (PFK) gases are widely used in industry, e.g. as an insulating medium in high-voltage apparatus and as a cleaning agent in chemical vapor deposition (CVD) chambers. A great deal of attention has been paid to them recently because of their low global warming potential (GWP). In order to describe the ionization processes in various plasmas resulting from PFK gases, the electron-impact ionization cross sections (Q(ion)) of PFK molecules CxF2xO (x = 1-5) were calculated by the Binary-Encounter Bethe (BEB) and the Deutsch-Mark (DM) methods. The chemical structures of PFK molecules were optimized by the hybrid Density Functional Theory (DFT) method with the Austin-Petersson-Frisch functional including dispersion (APF-D). The binding and kinetic energies of electrons in molecular orbitals were also determined with the APF-D hybrid DFT method. The binding energies of valence electrons were then improved by the electron propagator theory (EPT) method. The ionization potentials of PFK molecules were calculated as the difference between the energy of a molecule and its cation using the complete basis set (CBS) method. The molecular orbital compositions were obtained by the natural atomic orbital (NAO) analysis. The results show that Q(ion) determined by the BEB method are always larger than those by the DM method. The difference is reduced with the EPT corrections considered. The comparison between the theoretical and experimental Q(ion) demonstrates that the EPT correction improves Q(ion) considerably.