Molecular orbital studies of vibrational frequencies

Molecular orbital techniques for the ab initio computation of harmonic force constants are reviewed. Extensive applications with the split‐valence 3‐21G basis are described and a systematic comparison between theoretical and experimental frequencies is undertaken. The 3‐21G force constants are permanently stored on a disk file and may be used to predict frequencies for isotopically substituted species. Applications are made to some deuterated molecules.