An experimental and density functional theory study of the decomposition reaction of NSCl with water molecule(s) into NH3 and SO2 is described. Experiments involving the decomposition of NSCl in the presence of trace amounts of water showed that the formation of both HNSO and SO2 is faster when the cell and the cell surface are fresh and more likely to be coated in adsorbed water. The density functional theory computational results suggest that the decomposition involves two main steps: reactions 1 NSCl + nH(2)O -> HNSO + (n - 1) H2O + HCl and 2 HNSO + nH(2)O - NH3 + SO2 + (n - 1)H2O. The barrier for reaction 1 in which NSCl decomposes to form HNSO becomes substantially lower when the explicit hydrogen bonding of water molecules is considered. The water assisted decomposition reaction mechanism can help account for the experimentally observed conversion of NSCl to produce HNSO in the presence of water. The calculated barrier of reaction 2 (the decomposition of HNSO into NH3 and SO2) can also explain the experimental observation of SO, bands from the decomposition of NSCl in the presence of water.