The proton affinity and the structure of protonated species of methylsilane

An ab initio LCAO‐MO‐SCF calculation was made on the proton affinity ( PA ) of methylsilane (CH 3 SiH 3 ) by using STO ‐3G, MIDI ‐1, and MIDI ‐1* basis sets. Three types of protonated methylsilane are taken into account, and their geometrical parameters are optimized. The calculated PA of CH 3 SiH 3 is 160.5 kcal/mol, which exceeds that of SiH 4 by 11.5 kcal/mol. The protonated species (I) which refers to Si—C bond protonation is shown to be most favorable, and to be a weak σ‐complex between CH 4 and SiH   + 3 . Other two species are also σ‐complexes between H 2 molecule and SiH 3 CH   + 2or CH 3 SiH   + 2 , and similar to CH   + 5 , SiH   + 5 , GeH   + 5 , and C 2 H   + 7 .