C-H and C-D interbond coupling and Fermi resonance interactions in CHD₂Cl

The infrared absorption spectrum of CHD2Cl up to 16 500 cm-1 has been reanalysed in terms of a local mode model Hamiltonian including C-H/C-D stretching 1:1 harmonic resonance and a C-H stretch/bend 1:2 anharmonic Fermi resonance. Predominant extra structure in the C-H stretching overtone region is attributed to harmonic coupling with C-D stretching while weaker structure is attributed to anharmonic coupling with the overtone of the in-plane C-H bend. The Fermi resonance effects of the overtone of the out-of-plane C-H bend are smaller still in comparison. “x-K relations” have been established for this Cs symmetry CHD2 stretching system.