We report the results of a study of biacetyl and biacetyl-d6 with water and water- d2 trapped in inert gas matrices. In solution, irradiation has been shown to produce an enol (3-hydroxy-3-butene-2-one), although no indication of this compound is observed in the gas phase or for matrix-isolated biacetyl. DFT calculations predict the existence of three stable enol conformers, as well as several biacetyl*water and enol*water complexes. The calculations also predict that biacetyl*water complexes should have lower barriers to enolization than the uncomplexed biacetyl. The pre-irradiation infrared spectra contain features attributed to two different biacetyl*water complexes. Irradiation using an unfiltered UV output yields various isotopomers of ketene, as well as both cis and trans forms of 3-hydroxy-3-butene-2-one and enol*water complexes. Several photoproducts found to be present in a water free matrix, but absent once water is introduced include gamma butyrolactone (GBL), one vibration of ketene, and cis methyl hydroxy carbene (HMC).

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