Photodissociation dynamics of the ethyl radical via the A²A(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 Ag-1) 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-likeH+ C2H4((X) over tilde Ag-1) 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 Ag-1) 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>Ag-1) product channel is < 5 ns. Published under an exclusive license by AIP Publishing.