Knowledge Bank

“Sublimed films of $NH4NCS$ and of $ND4NCS$ have been examined over a range of temperatures with an infrared grating spectrometer through the fundamental regions of the ammonium and the thioicyanate ions; partially deuterated material has also been studied. In the phase which is stable at room temperature and which, once formed, persists down to liquid $N2$ temperatures, details of the spectrum are consistent with the site group splittings expected on the basis of the $C2h5$ tetra-molecular unit cell. An apparently metastable phase has also been observed which yields- a larger number of components for each $NH4+$ and $NCS-$ fundamental. A detailed potential function for the ammonium ion has been evaluated, the results being expressed in terms of the compliance matrix, $C=F-1$, where F is the matrix of the force constants.”