Photodissociation dynamics of the ethyl radical via the Ã2A′(3s) state: H-atom product channels and ethylene product vibrational state distribution.

The photodissociation dynamics of jet-cooled ethyl radical (C2H5) via the A ̃ 2A′(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 ̃ 1Ag) product channel is characterized by a repulsive translational energy release, anisotropic product angular distribution, and partially resolved vibrational state distribution of the C2H4( X ̃ 1Ag) product. This fast dissociation is initiated from the 3s Rydberg state and proceeds via a H-bridged configuration directly to the H + C2H4( X ̃ 1Ag) products. A statistical-like H + C2H4( X ̃ 1Ag) product channel via unimolecular dissociation of the hot electronic ground-state ethyl ( X ̃ 2A′) 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(ã3B1u) 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(ã3B1u) 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 ̃ 1Ag) 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 ̃ 1Ag) product channel is <5 ns. [ABSTRACT FROM AUTHOR]