This proposal requests the allocation of six days beamtime on PEARL to collect neutron powder diffraction data suitable for the structure solution of phases II and III of deuterated hydroxylamine. These phases were discovered in two earlier PEARL studies, the last of which was carried out more than six years ago. Phase II has so far eluded all efforts at unit cell indexing, due primarily to its complexity and its narrow range of existence in pressure. High-pressure Raman spectroscopy and PW-DFT/MD computational studies in Edinburgh suggest that the less-complex phase III contains hydroxylamine solely in the form of the elusive long sought-after amine-oxide tautomer. Although the agreement between the best available phase III pattern and that predicted for the tautomer phase is tantalisingly close, it is clear that better quality patterns are required for a definitive structure solution.