Low Frequency Vibrations of Molecular Crystals, XIV Raman and Far-infrared Spectra of HNCS and DNCS

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Abstract
The infrared and Raman spectra of polycrystalline HNCS and DNCS have been recorded from 33 to 4000 cm−1. The data have been treated in detail and a vibrational assignment of the six internal fundamentals is suggested. The vibrational data imply a very short N-H[sbnd]N distance of 2.9Å. The subsequent structural implications of such a strong H-bond are considered. Evidence was found that HNCS has two distinct crystalline phases and spectra have been recorded for each form. Factor group splitting of the N[sbnd]H bending fundamental suggests that the crystal has at least four or possibly eight molecules per unit cell depending upon whether or not the crystal is centrosymmetric. Suggested assignments are given for some of the lattice modes.