The reactions of dimethylsulfide (DMS) with molecular iodine (I₂) and iodine monochloride (ICl) have been studied by infrared matrix isolation spectroscopy by co-condensation of the reagents in an inert gas matrix. Molecular adducts of DMS + I₂ and DMS + ICl have also been prepared using standard synthetic methods. The vapour above each of these adducts trapped in an inert gas matrix gave the same infrared spectrum as that recorded for the corresponding co-condensation reaction. In each case, the infrared spectrum has been interpreted in terms of a van der Waals adduct, DMS : I₂ and DMS : ICl, with the aid of infrared spectra computed for their minimum energy structures at the MP2 level. Computed relative energies of minima and transition states on the potential energy surfaces of these reactions were used to understand why they do not proceed further than the reactant complexes DMS : I₂ and DMS : ICl. The main findings of this research are compared with results obtained earlier for the DMS + Cl₂ and DMS + Br₂ reactions, and the atmospheric implications of the conclusions are also considered.