Lattice Vibrations of Molecular Crystals. II. Cyanamide and Cyanamide-d2

The far‐infrared spectra (33–500 cm⁻¹) of crystalline cyanamide (NH₂CN) and cyanamide‐$d_2$ have been recorded with polyethylene and silicon sample support plates. The laser Raman spectra have also been recorded from 40–1600 cm⁻¹ for both molecules. No evidence was found for the inversion doubling and resultant low‐frequency components of the NH₂ and ND₂ wagging frequencies previously proposed. While 14 of the predicted 15 infrared‐active lattice modes were identified, only four of the predicted 24 Raman‐active lattice modes were observed. Force constants were estimated from the observed infrared frequencies by use of modified Born–von Karman valence force field and Wilson‐$\mathrm{FG}$ technique. Lastly, the distortion moment and effective charges were calculated using the method of Szigeti and Kurosawa. These results semiquantitatively reflect the difference in band intensities between the intra‐ and intermolecular vibrations.