The crystal structure of deuteroammonia between 2 and 180 K by neutron powder profile refinement

The structure of ND₃ has been refined by neutron powder profile analysis at 2, 77 and 180 K to a resolution of sin θ/λ = 0.85 Å^-1. No orientational phase transition was found in this range. However, even at 2 K, a strong librational motion exists. The N--D bond length, after correction for libration, is constant with temperature (1.06 Å), as are the D-N-D angles (107.5 ± 0.2°). This bond length is 5% longer than that found in the free molecule, because of hydrogen bonding, but the bond angles are virtually identical.