Photochemistry and dynamics of C6H6–O2 clusters at 226 nm

The photochemistry and dynamics of small C6H6–O2 clusters were studied in a supersonic expansion using 226 nm laser excitation and multiphoton ionization probes. We were able to detect a strong signal due to O(P2) when mixed clusters were present in the expansion but no O atom fragments could be observed in the absence of benzene in the expansion mixture. Photofragmentation of O2 in the unique environment of the cluster is enhanced by at least three orders of magnitude compared to the isolated oxygen molecule. The kinetic energy release of the O(P2) was determined with a time-of-flight method and found to be relatively small and characterized by a completely isotropic spatial distribution. The fine structure population of the O(P j) was also examined and the resultant branching fractions, P2,1,0 5 0.68 6 0.03, 0.2660.06, 0.0660.01, are similar to those obtained for photodissociation of isolated O2 by other workers. We also find that photochemical production of oxygen containing products, such as C6H6O, becomes feasible in larger cluster species due to solvent cage effects which trap the recoiling O atom fragments. The observed dynamics can be attributed to either excitation of the supramolecular C6H6–O2 charge-transfer state, or localized excitation of a perturbed transition in O2. The net effect of cluster absorption is to greatly enhance a chemical pathway that is only weakly observed in the separated molecules, similar to the behavior that has recently been described for the C6H6–I2 complex. © 1997 American Institute of Physics. @S0021-9606~97!01113-6#