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

Abstract

The Raman spectra (10–3500 cm−1) of gaseous and solid disiloxane and disiloxane‐d 6 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 q 4−21.9±0.3 q 2 for the ’light’ compound and V (cm−1) =0.973±0.015 q 2−19.2±0.4 q 4 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 † 36molecular 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.