Abstract
The far-infrared spectra of silacyclopentane and its 1-d1 and 1,1-d2 isotopomers have been recorded and analyzed. Spectral series corresponding to the bending and twisting transitions were observed. Bend-twist combination bands and bending overtone spectra were also detected. Kinetic energy (reciprocal reduced mass) expansions were calculated for the bending and twisting motions. These were used along with a five-term two-dimensional potential energy surface in the vibrational Hamiltonian in order to calculate the energy states. The basis sets were carefully generated to ensure that these levels were accurately calculated. The potential energy surface calculation does an excellent job of reproducing the 103 observed transition frequencies. The potential surface has energy minima at twist angles of 30°. The barrier to planarity is 2110±200 cm−1. The bent structure, which corresponds to a saddle point on the surface, has an energy about 1500 cm−1 above the twisted conformation.
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