Photodesorption of O2 (X3∑g -) and O2 (a Δ1g) from amorphous solid water at 90 K has been studied following photoexcitation within the first absorption band at 157 nm. Time-of-flight and rotational spectra of O2 reveal the translational and internal energy distributions, from which production mechanisms are deduced. Exothermic and endothermic reactions of OH+O (3P) are proposed as plausible formation mechanisms for O 2 (X 3∑g- and a 1Δ g). To examine the contribution of the O ( 3P) +O (3P) recombination reaction to the O2 formation following 157 nm photolysis of amorphous solid water, O2 products following 193 nm photodissociation of SO2 adsorbed on amorphous solid water were also investigated.
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