The determination of the potential function governing the low frequency bending mode of disiloxane

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Abstract
The Raman spectra (10–3500 cm−1) of gaseous and solid disiloxane and disiloxane-d6 have been recorded. The infrared spectra of the gas from 4000 to 30 cm−1 and of the solid from 4000 to 450 cm−1 have been investigated. An examination of the low frequency Raman spectrum of the gas under moderately high resolution conditions (1.0 cm−1) revealed a Q-branch series for each molecule attributable to the double jumps of the anharmonic, low-frequency skeletal bending mode. The observed Q-branches were assigned with the help of a potential function of the form V (cm−1) =1.07±0.02 q4−21.9±0.3 q2 for the ’light’ compound and V (cm−1) =0.973±0.015 q2−19.2±0.4 q4 for the deuterated compound, where q is one of the reduced polar coordinates q and φ. These functions lead to barriers to linearity of 112±5 and 95±5 cm−1, with the ground state energy levels at 42.6 and 37.8 cm−1, respectively. Transformation of the potential functions to dimensioned form by using the reduced masses for the bending vibration gives an average equilibrium skeletal angle of 149±2°. The vibrational data have been interpreted in terms of G†36 molecular symmetry for the gaseous state, consistent with the concept of the quasilinear molecule, while the spectra of the solid state indicate a bent skeleton. Resolvable fine structure on two perpendicular bands in the infrared indicate very nearly free internal rotation in disiloxane.

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