REFLECTION-ABSORPTION IR SPECTROSCOPIC INVESTIGATION OF THE PHOTOLYSIS OF THIN-FILMS OF DICHLORINE MONOXIDE AND CHLORINE DIOXIDE

Reflection-absorption infrared (RAIR) spectroscopy and mass spectromet ry have been employed in order to investigate the low-temperature phot ochemistry of thin films of chlorine dioxide, OClO, and dichlorine mon oxide, Cl2O, grown on a gold foil in an ultra-high vacuum system. Phot olysis of a neat him of OClO (1 > 300 nm, 90-110 K) produces chloryl c hloride, ClClO2. Irradiation of a co-deposited OClO/H2O film also prod uces chlorine superoxide, ClOO, which suggests that OClO isomerisation is the first step in the reaction producing ClClO2. Photolysis of Cl2 O (300 < lambda < 515 nm, 90-110 K) is shown to produce OClO, initiall y, which is subsequently converted to ClClO2. Analysis of the observed IR band intensities and consideration of the metal surface selection (MSS) rule indicates that the photochemically produced OClO intermedia te aligns perpendicular to the gold substrate. Mechanistic details and the atmospheric implications of the chemistry are discussed.