Vibrational-torsional coupling. High-resolution stimulated Raman spectrum of the ν3 band of ethane (12C2H6)

Abstract

We report a stimulated Raman spectrum of the Q branch of the ν3 band of ethane recorded with a resolution of about 0.0055 cm-1 and an absolute wave-number accuracy of the order of 0.001 cm-1. This spectrum is analyzed in terms of a vibrational-torsional coupling Hamiltonian that allows for the calculation of the observed wave numbers within the experimental uncertainty. The following spectroscopic parameters (in cm-1) have been obtained: ν30=994.1108(10), B3A1s-B0=-0.006 165(3), B3E3d-B0=-0.006 170(2), B 3E3s-B0 =-0.006 184(2), B3A3d-B0=-0.006 257(2), A3A1s-A 0=-0.003 037(15), A3E3d-A0 =-0.003 040(12), A3E3s-A0=-0.003 054(12), and A 3A3d-A0=-0.003 065(12). A strong dependence of the threefold torsional potential barrier with respect to the q3 normal mode, ∂V3/∂q3=-275.9±1.4 cm -1, is deduced from the present analysis. © 1992 American Institute of Physics.