Single crystal neutron diffraction study of sodium cyanide

Abstract

The neutron diffraction pattern of a single crystal of cubic NaCN has been measured at 295°K. These data and earlier results for KCN at 180 and 295°K have been analyzed in terms of a model which expands the angular distribution of CN⁻ orientations in symmetry‐adapted spherical harmonics. From this analysis, the distributions of CN⁻ in these crystals have been derived, and these indicate a monotonic trend in the series KCN (295°K) thru KCN (180°K) to NaCN (295°K) involving a shift in preferential orientation from the [111] toward the [100] directions in the crystal. Unusually large translational Debye‐Waller factors have also been derived for NaCN and KCN from the fitting procedure, in agreement with earlier results and analysis on KCN. In addition, an average $\mathrm{C}\equiv \mathrm{N}$ bond distance of 1.18 Å is obtained.