Far-Infrared Spectra of Ring Compounds. III. Spectrum, Structure, and Ring-Puckering Potential of Silacyclobutane

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Abstract
The infrared spectra of gaseous silacyclobutane and silacyclobutane-1, 1-d2 have been recorded in the range 24-300 cm−1. Both molecules show the complicated vibrational fine structure expected from a double-minimum potential for the ring-puckering vibration. The absorption maxima of silacyclobutane were fitted to a potential of the form V = a (x4 − bx2), where x is the ring-puckering coordinate. The potential barrier is calculated as 440 ± 3 cm−1, and the dihedral angle of the puckered ring as 35.9 ± 2°. The spectrum of silacyclobutane-1, 1-d2 can be interpreted with the same potential function but the quantitative agreement with observed levels above the barrier is less accurate. The discrepancy is ascribed to interaction between the ring-puckering mode and the SiD2 rocking vibration.