PHOTOCHEMISTRY AND DYNAMICS OF C6H6-O-2 CLUSTERS AT 226 NM

摘要

The photochemistry and dynamics of small C6H6-O-2 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(P-3(2)) 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 O-2 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(P-3(2)) 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-3(j)) was also examined and the resultant branching fractions, P-2,P-1,P-0 = 0.68 +/- 0.03, 0.26+/-0.06, 0.06+/-0.01, are similar to those obtained for photodissociation of isolated O-2 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-O-2 charge-transfer state, or localized excitation of a perturbed transition in O-2. 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-I-2 complex. (C) 1997 American Institute of Physics. [References: 62]