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 (omega(6)) is 89% larger than the experimentally deduced fundamental, a much larger difference than the expected similar to 10%. Here we report high-quality theoretical rotational constants and harmonic vibrational fequencies, 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.