UV photolysis Of CCl3COCl has been investigated by infrared spectroscopy in cryogenic Ar and O-2 matrices. In the Ar matrix, CCl4 and CO were found to be dominant products over Cl2C=C=O. The CCl3 and COCl species, observed as intermediates, indicated C-C bond cleavage. The C-C bond cleavage was also evidenced by the formation of ClC(O)OO in the O-2 matrix. The marked difference in the photochemistry of matrix-isolated CCl3COCl from that of CH3COCl, where CH2=C=O is the predominant product, can be attributed to the triplet surface reaction Of CCl3COCl, as supported by the present DFT calculations. (c) 2006 Elsevier B.V. All rights reserved.