D-atom products in predissociation of CD2CD2OH from the 202-215 nm photodissociation of 2-bromoethanol.

Experimental observations of D fragments from the predissociation of rovibrationally excited partially deuterated 2-hydroxyethyl radicals, CD(2)CD(2)OH, are reported, and possible dissociation channels are analyzed by theory. The radicals are produced by photolysis of 2-bromoethanol at 202-215 nm, and some of them have sufficient internal energy to predissociate. D fragments are detected by 1 + 1' REMPI and their TOF distributions are determined. They can be associated with vinyl alcohol and/or acetaldehyde cofragments. From analysis of the maximum velocities and kinetic energies of the observed D fragments it is concluded that they originate from the decomposition of CD(2)CD(2)OH, but the experimental resolution is insufficient to distinguish between the two possible channels leading to D products. Theoretical analysis and RRKM calculations of microcanonical dissociation rates and branching ratios for the range of available excess energies (up to 5000-8000 cm(-1) above the OH + C(2)D(4) threshold) indicate that the D-producing channels are minor (about 1%) compared to the predominant OH + C(2)D(4) channel, and the branching ratio for D production is more favorable when the reactant radicals have low rotational energy. The vinyl alcohol channel is strongly favored over the acetaldehyde channel at all excess energies, except near the threshold of these channels.