Photodissociation of styrene oxide at 193 nm in gas phase generates OH, as detected by laser-induced fluorescence technique. Under similar conditions, OH was not observed from ethylene and propylene oxides, primarily because of their low absorption cross-sections at 193 nm. Mechanism of OH formation involves first opening of the three-membered ring from the ground electronic state via cleavage of either of two C-O bonds, followed by isomerization to enolic forms of phenylacetaldehyde and acetophenone, and finally scission of the C-OH bond of enols. Ab initio molecular orbital calculations support the proposed mechanism. (c) 2006 Elsevier B.V. All rights reserved.