Photodissociative spectroscopy of the hydroxymethyl radical (CH2OH) in the 3s and 3px states

The absorption spectrum and photodissociation dynamics of the hydroxymethyl radical via its two lowest excited electronic states, 3s and 3p(x), are investigated in a supersonic molecular beam by the depletion, resonance enhanced multiphoton ionization, and photofragment yield spectroscopy methods. The measured origins of the electronic transitions to the 3s and 3p(x) states agree with the most recent ab initio calculations. The vibronic bands of the 2 (2)A(')(3p(x))<--1 (2)A(') transition are much broader than those of the transition terminating in the 2 (2)A(')(3p(z)) state, while the transition to the 1 (2)A(')(3s) state appears structureless. The investigation of the deuterated analog CH2OD shows that near the onset of the transition to the 3s state, only the O-D bond fission pathway is important, while both H and D products are detected following excitation to the 3p(x) state. The progressive broadening of the absorption features from the uppermost 3p(z) to the lowest 3s excited state is explained based on recent calculations of surface couplings to lower electronic states. These couplings also control the photodissociation dynamics and the reaction outcomes. (C) 2002 American Institute of Physics.