The title compound, crystallized with a few percent of deuterium, contains some NH3D+ and HOD. At low temperatures, five N-D stretch bands are observed. These belong to two ammonium sites with apparent C-s symmetry in the low-temperature phase. The N-D bands can be hole-burned with an infrared laser. Burning bands belonging to the A-sites transforms some of them to the higher-energy B sites. The A-and B-sites probably differ from each other by the arrangement of water and sulfate about the ammonium.