The sulfur-ammonia (SNH3) cycle uses the entire solar radiation spectrum to split water. It uses the UV radiation to promote the photolytic oxidation of ammonium sulfite to produce hydrogen and ammonium sulfate. Here, Raman and inelastic neutron scattering spectra of (NH4)2SO3·H2O at 20 K are discussed, supported by density functional theory (DFT) calculations. The feasibility of photolytic oxidation of this monohydrate to produce hydrogen at room temperature was also demonstrated. Synopsis: Raman and inelastic neutron scattering spectra of (NH4)2SO3·H2O were discussed, DFT calculations were carried to support vibrational modes assignments. Feasibility to produce hydrogen through photolytic oxidation of such monohydrate was also demonstrated. Display omitted •Photolytic oxidation of ammonium sulfite monohydrate in solid state was proven.•Vibrational modes of (NH4)2SO3, (NH4)2SO4, Na2SO3 were assigned.•INS spectrum of Na2SO3 was accurately reproduced by density functional theory.