UV photodissociation dynamics of ethyl radical via the (A)over-tilde 2A′(3s) state

H-atom channels in the photodissociation of jet-cooled ethyl radical (C2H5) via the (A) over tilde (2)A'(3s) state are studied near 245 nm by using the high-n Rydberg-atom time-of-flight technique. Bimodal product translational energy release and energy-dependent angular distribution suggest two dissociation pathways. A slow ([f(T)]similar to0.35) and isotropic channel corresponds to unimolecular dissociation of the radical, presumably after internal conversion. A previously unobserved fast ([f(T)]similar to0.78) and anisotropic (beta =0.5 +/-0.1) channel is consistent with direct H-atom scission via a nonclassical H-bridged transition state from the 3s state to yield H+C2H4((X) over tilde (1)A(g)). The fast/slow branching ratio is similar to0.2. Site-selective loss of the beta hydrogen atom is confirmed by using the partially-deuterated CH3CD2 radical. (C) 2001 American Institute of Physics.