Photodissociation Dynamics of the i-Methylvinoxy Radical at 308, 248, and 225 nm Using Fast Beam Photofragment Translational Spectroscopy.

The photodissociation dynamics of the i-methylvinoxy (CH3COCH2) radical have been studied by means of fast beam coincidence translational spectroscopy. The radical was produced by photodetachment of the i-methylvinoxide anion at 700 nm, followed by dissociation at 225 nm (5.51 eV), 248 nm (5.00 eV), and 308 nm (4.03 eV). At all three dissociation energies, the major products were found to be CH3 + CH2CO, with a small amount of CO + C2H5 produced at the higher dissociation energies. Photofragment mass distributions and translational energy distributions were recorded for each wavelength. Comparison of the mass distributions with dissociation of fully deuterated i-methylvinoxy aided the assignment of the observed channels. Electronic structure calculations were performed to determine the relative energies of minima and transition states involved in the dissociation and to aid interpretation of the experimental results. The proposed dissociation mechanism involves internal conversion from the initially excited electronic state, followed by dissociation over a barrier on the ground state.