Heats of Formation and Bond Dissociation Energies of the Halosilanes, Methylhalosilanes, and Halomethylsilanes

Atomization energies at 0 K and heats of formation at 0 and 298 K are predicted for SiH3X, SiH2XCH3, and SiH3CH2X with X = F, Cl, Br, and I from coupled cluster theory (CCSD(T)) calculations with effective core potential correlation-consistent basis sets for Br and I. To achieve near chemical accuracy (+/-1 kcal/mol), three corrections were added to the complete basis set binding energies based on frozen core coupled cluster theory energies: a correction for core-valence effects, a correction for scalar relativistic effects, and a correction for first order atomic spin-orbit effects. Vibrational zero point energies were computed at the CCSD(T) level of theory and the C-H and Si-H stretches scaled to experiment. The C-H, Si-H, Si-C, C-X, and Si-X (X = F, Cl, Br, and 1) bond dissociation energies (BDEs) in the halosilanes, halomethysilanes, and methylhalosilanes were predicted. Except for methyliodosilane, methyl substitution leads to an increase in Si-X BDE when compared to the Si-X BDE in the halosilanes. Except for methyliodosilane, halide substitution leads to an increase in the Si-C BDE in comparison to the Si-C BDE in methylsilane of 86.9 kcal/mol at 0 K. Unlike the methylhalosilanes, the halomethylsilanes all show a decrease in the Si-C BDE when compared to the Si-C BDE in methylsilane. The trends correlate with the electronegativity of the substituent.