Purely theoretical electron-impact ionization cross-sections of silicon hydrides and silicon fluorides obtained from explicitly correlated methods

Electron impact total ionization cross-sections of small silicon hydrides, SiHn(n=1-4), and fluorides, SiFn(n=1-3), have been calculated by the applic ation of a recently developed theoretical model. The binary-encounter-Bethe (BEB) model has a simple structure and requires information from calculati ons on the parent ground-state molecule only (binding energies, orbital kin etic energies, and occupation numbers). Previous applications of the BEB th eory to the silicon hydrides and fluorides have employed a combination of e xperimental and Koopman's theorem binding energies. In the current work bin ding energies have been calculated using the explicitly correlated multicon figurational spin tensor electron propagator (MCSTEP) method which gives hi ghly accurate ionization potentials for closed- and open-shell systems. Cal culations have been performed using cc-pVDZ and cc-pVTZ basis sets with mul ticonfigurational self-consistent field (MCSCF) reference wave functions. C omparisons are made between our MCSCF/MCSTEP and previous Hartree-Fock (HF) /Koopman's theorem results and available experimental data. The use of impr oved theoretical data does not have a significant effect on the resultant c ross-sections; however, our new technique is a viable method for calculatin g electron impact ionization cross-sections for systems where Koopman's the orem is known to be unreliable or no experimental data is available. (C) 20 00 American Institute of Physics. [S0021-9606(00)30525-6].