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

H-atom channels in the photodissociation of jet-cooled ethyl radical (C2H5) via the à 2A′(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 (〈fT〉∼0.35) and isotropic channel corresponds to unimolecular dissociation of the radical, presumably after internal conversion. A previously unobserved fast (〈fT〉∼0.78) and anisotropic (β=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(X̃ 1Ag). The fast/slow branching ratio is ∼0.2. Site-selective loss of the β hydrogen atom is confirmed by using the partially-deuterated CH3CD2 radical.