``1-Silavinylidene: The First Unsaturated Silylene,'' C. D. Sherrill and H. F. Schaefer, J. Phys. Chem. 99, 1949 (1995).

Recent photoelectron spectroscopy studies of 1-silavinylidene by Leopold and Bengali have yielded the first experimental values for the vibrational frequencies of this unsaturated silylene prototype. Comparison of the fundamental frequencies with double-zeta plus d function (DZ+d) self-consistent-field (SCF) harmonic frequencies shows that the theoretical methylene rocking frequency (omega6) is 89% larger than the experimentally deduced fundamental, a much larger difference than the expected ~10%. Here we report high-quality theoretical rotational constants and harmonic vibrational frequencies, obtained with a triple-zeta plus double polarization plus f functions basis set (TZ2Pf) in conjunction with the coupled-cluster singles and doubles method with perturbative triples correction [CCSD(T)]. Our results confirm the experimental assignments and bring theory and experiment into satisfactory agreement.