AbstractThe infrared spectra of 1,1‐dimethyl‐1‐silacyclopentane in the vapor and solid phases have been recorded from 4000 to 20 cm−1. The Raman spectra (3500‐0 cm−1) of all phases have been measured and depolarization data have been obtained for both the gaseous and liquid phases. An assignment for the 57 normal modes is presented. The vibrational data are consistent with a twisted ring with molecular symmetryC2. The two low frequency bending modes were observed at 260 cm−1(radial motion) and 63 cm−1(puckering motion) but distinct ‘hot band’ transitions were not observed. Thus, the potential functions and the dynamics of the low frequency ring‐bending motions co