Jahn-teller distortions of SiH 4+ and Si(CH 3) 4+

Abstract

In view of current interest in silane radical cations, the Jahn-Teller distortions of SiH 4 + and Si(CH 3) 4 + to the D 2d, C 3v, C 2v, and C s structures are investigated by means of ab initio calculations with flexible basis sets and electron correlation. The C s structure is found to be the most stable in SiH 4, as suggested in a recent theoretical study. On the other hand, the C 3v structure is the most stable in Si(CH 3) 4 +, unlike the suggestion from the ESR study. This contrasts with the fragile C 3v structure in SiH 4 +. The relative stabilities (kcal/mol) of SiH 4 + and Si(CH 3) 4 + decrease in the order C s(0.0) > C 2v(8.5)> C 3v(13.7) > D 2d(27.2) at the MP4 SDTQ/6-31+G(2df, 2p)//MP2/6-31G(d, p)+ZPC level and C 3v(0.0)>C 2v(6.1)>C s(16.3) at MP2/6-31G(d)//HF/6-31G (d)+ZPC level, respectively. In both SiH 4 + and Si(CH 3) 4 +, the C 2v structures are not energy minima but transition structures for the rearrangement to the most stable structures. An interesting finding is that Si(CH 3) 4 + is much more stable to fragmentation than SiH 4 +.