An ab initio study of the structures and heats of formation of fluorosilanes cations (SiHmFn+, m + n = 1-4)

Abstract

The equilibrium geometries of SiH{sub m}F{sub n}{sup +} (m + n = 1-4) were determined at the Hartree-Fock level by using the 3-21G and 6-31G* basis sets. The structures of SiH, SiF, and SiH{sub 2{minus}n}F{sub n}{sup +} resemble the neutral molecules; the tricoordinate cations are planar, whereas the neutral radicals are pyramidal. The SiH{sub 4{minus}n}F{sub n}{sup +} distort to form a complex between a silicon-containing cation and a neutral atom or diatom: SiH{sub 2}{sup +}-H{sub 2}, SiHF{sup +}-HF, SiHF{sup +}-HF, SiF{sub 2}{sup +}-HF, and SiF{sub 3}{sup +}-F are the lowest energy structures. Adiabatic ionization potentials and proton affinities were calculated at the MP4SDTQ/6-31G** level. Heats of formation were computed by the bond additivity correction method and from the ionization potentials and proton affinities.