Photodissociation dynamics of the ethyl radical via the (A)over-tilde²A(3s) state: H-atom product channels and ethylene product vibrational state distribution

The photodissociation dynamics of jet-cooled ethyl radical (C2H5) via the (A) over tilde (2)A '(3s) states are studied in the wavelength region of 230-260 nm using the high-n Rydberg H-atom time-of-flight (TOF) technique. The H + C2H4 product channels are reexamined using the H-atom TOF spectra and photofragment translational spectroscopy. A prompt H + C2H4((X) over tilde (1)A(g)) product channel is characterized by a repulsive translational energy release, anisotropic product angular distribution, and partially resolved vibrational state distribution of the C2H4((X) over tilde (1)A(g)) product. This fast dissociation is initiated from the 3s Rydberg state and proceeds via a H-bridged configuration directly to the H + C2H4((X) over tilde (1)A(g)) products. A statistical-like H + C2H4((X) over tilde (1)A(g)) product channel via unimolecular dissociation of the hot electronic ground-state ethyl ((X) over tilde (2)A ') after internal conversion from the 3s Rydberg state is also examined, showing a modest translational energy release and isotropic angular distribution. An adiabatic H + excited triplet C2H4((a) over tilde B-3(1u)) product channel (a minor channel) is identified by energy-dependent product angular distribution, showing a small translational energy release, anisotropic angular distribution, and significant internal excitation in the C2H4((a) over tilde B-3(1u)) product. The dissociation times of the different product channels are evaluated using energy-dependent product angular distribution and pump-probe delay measurements. The prompt H + C2H4((X) over tilde (1)A(g)) product channel has a dissociation time scale of <10 ps, and the upper bound of the dissociation time scale of the statistical-like H + C2H4(<(X)over tilde>(1)A(g)) product channel is <5 ns.