Knowledge Bank

The far infrared spectrum of crystalline cyanamide ($NH2CN$) and cyanamide-$d2$ have been recorded from 33--500 $cm-1$ The spectra were recorded on polyethlene and silicon sample support plates. No evidence was found for the inversion doubling and resultant low frequency components of the $NH2$ and $ND2$ wagging frequencies previously proposed. All bands were interpreted on the basis of the fifteen infrared active intermolecular fundamentals allowed by the $D2n15$-Pbea space group with eight molecules per unit cell. These fifteen infrared active bands were distributed as six translational and nine librational species. The group theory of Bhagavantam and Venkatarayudu and that of Horning and Halford were used to describe the intermolecular irreducible representation of the system. Both methods gave identical results. The advantages and disadvantages of the two methods will be discussed.