Vibrational overtones of some deuterated propanes: the methylene chromophore

The CH bond stretching spectra of two propane isotopomers CD3CH2CD3 and CD3CHDCD3, have been recorded in the gas phase from 2800 to 16,000 cm−1. They exhibit strong evidence of Fermi resonance couplings with other vibrational modes of the molecule. The spectra have been reconstructed with a model Hamiltonian which takes into account the coupling of the CH stretch vibrations, described by Morse potentials, with isoenergetic combination states involving the angle deformations of the methylene chromophore. Such a modelling reproduces the overall spectral features. Introducing a weak resonance with the CC stretching modes only slightly improves the fit of the experimental spectra.