Photodissociation spectroscopy and dynamics of CH3O and CD3O

The photodissociation spectroscopy and dynamics of the methoxy radical Ã(A1) r X̃(2E) transition have been investigated using fast radical beam photofragment translational spectroscopy. The à state of both CH3O and CD3O is observed to predissociate via curve crossings with one or more repulsive electronic states. The photofragment yield spectrum consists of the C-O stretch progression and combination bands based on this mode. The major product channel is CH3 (CD3) + O, with a threshold 3775 cm-1 above the zero-point level of the à state. The product translational energy distributions reveal ν2 umbrella excitation in CH3 (CD3), yielding considerable insight into the dissociation dynamics for this channel. CD3O shows a modespecific dynamical effect in which energy deposited in parent umbrella motion preferentially populates umbrella motion in the fragment. The product channels CH2 + OH (CD2 + OD) and D + CD2O are also observed, with evidence that the methylene fragment is predominantly in the excited ã(A1) state.