Conversion of sulfur dioxide to sulfur trioxide facilitated by in situ UV photolysis of formaldehyde and sulfur dioxide in an oxygen matrix at 12 K

The photooxidation product distributions observed in photolyses of H/sub 2/CO and H/sub 2/CO x SO/sub 2/ molecular complexes in O/sub 2/ matrices at lambda = 270-420 nm are compared. Photodissociation of H/sub 2/CO produces RO/sub 2/ species, i.e., HO/sub 2/ and HC(O)OO radicals, which then efficiently oxidize SO/sub 2/ to SO/sub 3/ (and H/sub 2/SO/sub 4/). This process occurs with an efficiency of approx. 0.7 +/- 0.3 per H/sub 2/CO x SO/sub 2/ molecular complex photodissociated. Various photooxidation mechanisms are considered. Implications of the low-temperature/matrix photooxidation results on atmospheric photooxidation of SO/sub 2/ by RO/sub 2/ species are discussed.