Roaming Dissociation of Ethyl Radicals

Previous studies on the photodissociation of C2H5 reported rate constants for H-atom formation several orders of magnitude smaller than that predicted by Rice-Ramsperger-Kassel-Marcus (RRKM) theory. This Letter provides a potential explanation for this anomaly, based on direct trajectory calculations of C2H5 dissociation. The trajectories reveal the existence of a roaming dissociation channel that leads to the formation of C2H3 and H2. This channel is found to proceed over the ridge between the transition state of H-atom elimination and that of bimolecular H-abstraction. The formed C2H3 radical can subsequently dissociate to C2H2 and a H atom; this secondary dissociation is suggested to be a potential reason for the unexpectedly slow H-atom formation observed in the photodissociation experiments.