Dimethyl Sulfoxide Complexes Detected at Ambient Conditions.

Dimethyl sulfoxide (DMSO) is an important intermediate in the atmospheric oxidation of dimethyl sulfide (DMS). DMS, emitted from the ocean, is the main natural sulfur source, and its oxidation products are essential in the formation of sulfate aerosols. The high atmospheric concentration of water makes hydrogen bonding with DMS and its oxidation products likely. Through hydrogen bonding, water can potentially catalyze and affect the steps of the oxidation. We investigate binary hydrogen-bound complexes involving DMSO. Both water·DMSO and methanol·DMSO complexes are identified in an Ar matrix, and at room temperature, a Gibbs free energy of 0.7 kJ/mol for the formation of the methanol·DMSO complex is determined. Assuming a similar Gibbs free energy of the hydrate, it would suggest a relatively high abundance of the DMSO hydrate relative to the monomer in the atmosphere. The effect of changing the atom divalently bound to the hydrogen bond accepting oxygen, from S to C (DMSO to acetone), is found to significantly decrease the equilibrium constant of complex formation.