Intramolecular coupling of vibrational modes and the assignments of the partially deuterated dihalogenomethanes, -silanes, and -germanes

The fundamental vibrational wavenumbers of seven molecules of the type MHDX₂ (where M = C, Si, Ge and X = F, Cl, Br) have been calculated from those of the corresponding species MH₂X₂ and MD₂X₂, using the complete isotopic rule of Brodersen and Langseth. These wave-numbers have been used to test the force fields previously computed for the MH₂X₂ and MD₂X₂ molecules. The potential energy distributions calculated for the MHDX₂ species have been employed as aids in clarifying the assignments of their vibrational spectra.