Low-temperature IR spectroscopy of sulfurous compounds (thiourea, N-methyl-thiourea, and thioacetamide), either isolated in inert matrices or deposited as thin films (both in amorphous and crystalline forms). Irradiating the matrix-isolated compound and neat ices with UV light or exposing them to H atoms, inducing photodecomposition or tautomerization in the sample. Redeposition studies of the processed neat ices and ice mixtures upon their temperature programmed desorption (TPD) and collecting their IR spectra.