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 SiY 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 .

Negative ion formation through dissociative electron attachment to the group IV tetrachlorides: Carbon tetrachloride, silicon tetrachloride and germanium tetrachloride

“…With respect to the resonance positions, their agreement [83] with the experimental TCS of Wan et al [80] and Mozejko et al [81] is also good. Furthermore, in conjunction with the sharp rise in the s-wave cross section observed in their calculations at low energies and the dominant SiCl4 − threshold contribution observed by Moelly et al [74], Bettega et al [83] have explored the potential presence of a virtual state enabling s-wave attachment at threshold. In fact, from their calculations of the s-wave eigenphase at very low energies, they derive large negative numbers for the scattering length, i.e., values that support the presence of a virtual state at threshold.…”

“…This assertion is substantiated through converged coupled-channel calculations by Bettega et al [83]. All fragments formed upon DEA to SiCl4 are observed through features peaking in the energy range from 6.9-7.7 eV and Cl − and SiCl3 − are also observed through appreciable contributions peaking close to 2 eV.…”

“…Further, in their ion yield they observe a dominant formation of SiCl4 − at threshold (0 eV incident electron energy), which they also associate with a single electron occupation of the a1 LUMO mediated by the rapid increase of the capture cross section near 0 eV. In a more recent study, Bettega et al [83] report SMC results on the elastic…”

“…Elastic integral and differential scattering cross sections in the energy range from 20 to 2000 eV have also been calculated by Mozejko et al [82], using the independent atom method (IAM) with a static-polarization model potential. More recently, Bettega et al [83] extended their SMC calculations to compute elastic integral, differential and momentum transfer cross sections that cover the energy range from about 0 to 10 eV and the full 180° scattered electron angular range. Finally, Verma et al [84] calculated total inelastic and ionization cross sections for silicon tetrachloride in the energy range from the ionization threshold up to 5000 eV, using a spherical complex optical potential formalism for the total inelastic cross sections.…”