Elastic collisions of low-energy electrons with SiY4(Y=Cl, Br, I) molecules

Abstract

We employed the Schwinger multichannel method to compute elastic integral, differential, and momentum transfer cross sections for low-energy electron collisions with Si$Y$${}_{4}$ ($Y$ $=$ Cl, Br, I) molecules. The calculations were carried out in the static-exchange and static-exchange plus polarization approximations for energies up to 10 eV. The elastic integral cross section for SiCl${}_{4}$ and SiBr${}_{4}$, computed in the static-exchange plus polarization approximation, shows two shape resonances belonging to the ${T}_{2}$ and $E$ symmetries of the ${T}_{d}$ group, and for SiI${}_{4}$ shows one shape resonance belonging to the $E$ symmetry of the ${T}_{d}$ group. The present results agree well in shape with experimental total cross sections. The positions of the resonances observed in the calculated integral cross sections are also in agreement with the experimental positions. We have found the presence of a virtual state for SiCl${}_{4}$ and a Ramsauer-Townsend minimum for SiI${}_{4}$ at 0.5 eV. The present results show that the proper inclusion of polarization effects is crucial in order to correctly describe the resonance spectra of these molecules and also to identify a Ramsauer-Townsend minimum for SiI${}_{4}$ and a virtual state for SiCl${}_{4}$.