Gas-phase reactions of SiH_n⁺ (n = 1,2) with NF₃: A computational investigation on the detailed mechanistic aspects

Abstract

The mechanism of the gas-phase reactions of SiH_n⁺ (n = 1,2) with NF₃ were investigated by ab initio calculations at the MP2 and CAS-MCSCF level of theory. In the reaction of SiH⁺, the kinetically relevant intermediates are the two isomeric forms of fluorine-coordinated intermediate HSi-F-NF₂⁺. These species arise from the exoergic attack of SiH⁺ to one of the F atoms of NF₃ and undergo two competitive processes, namely an isomerization and subsequent dissociation into SiF⁺ + HNF₂, and a singlet-triplet crossing so to form the spin-forbidden products HSiF⁺ + NF₂. The reaction of SiH₂⁺ with NF₃ involves instead the concomitant formation of the nitrogen-coordinated complex H₂Si-NF₃⁺ and of the fluorine-coordinated complex H₂Si-F-NF₂⁺. The latter isomer directly dissociates into NF₂⁺ + H₂SiF, whereas the former species preferably undergoes the passage through a conical intersection point so to form a H₂SiF-NF₂⁺ isomer, which eventually dissociates into H₂SiF⁺ and NF₂. © 2012 Wiley Periodicals, Inc.