Fast beam photodissociation spectroscopy and dynamics of the vinoxy radical

The spectroscopy and photodissociation dynamics of the vinoxy ~CH2CHO! radical B̃( A9) ←X̃(A9) transition have been investigated by fast beam photofragment translational spectroscopy. We show conclusively that excitation to the B̃ state is followed by predissociation, even for the origin transition. Two photodissociation channels are observed: ~1! CH31CO, and ~2! H1CH2CO, with a branching ratio of '1:4. The form of the translational energy distributions imply a significant exit barrier to formation of CH31CO, and a considerably smaller barrier for H1CH2CO formation. Dissociation ultimately proceeds by internal conversion to the ground electronic state; the internal conversion rate appears to be significantly enhanced by a curve crossing with either the Ã(A8) or C̃(A8) states. Ab initio calculations of critical points on the global potential energy surfaces aid in determining the dissociation mechanism. We present a simple model for dissociation over a barrier, the statistical adiabatic impulsive model, which satisfactorily reproduces the translational energy distributions. © 1997 American Institute of Physics. @S0021-9606~97!01607-3#