H-C-SiH3: direct generation and spectroscopic identification of ethylidene's cousin

Ground-state triplet silaethylidene, generated directly by the reaction of 3P carbon atoms with silane under matrix isolation conditions in solid Ar (10-12 K), has been thoroughly characterized by the EPR and IR spectra of both the parent and perdeuterated isotopologs. A theoretical anharmonic vibrational analysis based on a CCSD(T)/cc-pVTZ complete quartic force field gave remarkable agreement with the experimental IR fundamentals, generally within 10 cm-1 and without any empirical scaling of the ab initio frequencies. Silaethylidene exhibits a Cs minimum with a H-C-Si angle near 153 degrees , but the barrier to H-C-Si linearity (C3v symmetry) is only 0.24 kcal mol-1. This minuscule barrier can be surmounted by zero-point vibrations, as evident from the EPR data. The triplet stabilizing effect of the electropositive SiH3 group amounts to about 15 kcal mol-1.