The UV light-induced reactions of chloroacetone in a cryogenic Ar matrix were investigated using infrared spectroscopy. The photoinduced isomerisations of gauche-chloroacetone to syn-chloroacetone and hypochlorous acid 1-methylethenyl ester were confirmed by comparing the experimental and calculated spectra. In addition, the photolysis products were found to be CH2=C=O and a cyclopropanone center dot center dot center dot HCl complex. The cyclopropanone center dot center dot center dot HCl complex was further decomposed into CH2=CH2, CO and HCl. The hypochlorous acid 1-methylethenyl ester was further isomerized to 2-chloro-2-methyloxirane. (C) 2014 Elsevier B.V. All rights reserved.