Neutron Diffraction Study of Solid Deuteroammonia

Abstract

The crystal structure of the stable cubic modification of solid deuteroammonia has been determined by neutron diffraction. The space group is P213—T4, and at —196°C the positions of the atoms are 4N at (a) with u=0.2127±0.0021 and 12D at (b) with x=0.3740±0.0019, y=0.2632±0.0037, and z=0.1094±0.0016. Each nitrogen atom is hydrogen bonded to the six nearest neighbor nitrogen atoms. There is one deuterium atom per site, in contrast to the ``half-hydrogen'' structure of ice. The N—D bond length of 1.005±0.023 A is indistinguishable from that of the free molecule, while the D—N—D bond angle of 110.4°±2.0° is appreciably larger than the free molecule value.