Photodissociation of 2-bromoethanol and 2-chloroethanol at 193 nm.

2-Bromoethanol and 2-chloroethanol were photodissociated in a molecular beam at 193 nm. Only one primary reaction channel was observed, elimination of the halogen atom, with an average translational energy release of 33 kcal/mol. In the case of 2-bromoethanol, some of the C2 H4 OH partner fragment survived and some underwent secondary dissociation to produce C2 H4 and OH. The surviving C2 H4 OH contained up to 43 kcal/mol of internal energy, far more than the expected C2 H4 -OH bond energy of ∼28 kcal/mol. The initial C–Br recoil occurs with a large exit impact parameter and leaves most of the internal energy in C2 H4 OH rotation, creating rotationally metastable fragments. The angular distributions of the secondary C2 H4 and OH products were strongly forward–backward peaked with respect to the primary (C2 H4 OH) velocity vector, consistent with the decay of a long-lived complex in which the total angular momentum is perpendicular to the velocity vector and mainly carried away as orbital angular momentum. This effect is analogous to that observed in the decay of similar long-lived complexes in crossed molecular beam experiments. [ABSTRACT FROM AUTHOR]