Photodissociation of 1, 2-C_2H_2Br_2 at 248 nm: Competition between three-body formation Br+Br+C_2H_2 and molecular Br_2 elimination

摘要

The photodissociation of 1, 2-C_2H_2Br_2 at 248 nm has been studied by product translational spectroscopy. The results show that the molecule dissociates exclusively into the products (1) Br_2+C_2H_2 and (2) Br (fast)+Br(slow)+C_2H_2 with a branching ratio (approx) 0.2:0.8. While the cleavages of the products indicates that both reactions occur in a fraction of a rotational period. Following an asynchronous concerted reaction, the triple products were simulated with the P(E_t) distributions coupled by asymmetric angular distributions. A mechanism consistent with the measured results is proposed that the Br_2 elimination is result of fast intersystem crossing from the (#pi##pi#)~* pumped state while the triple products occur via a simultaneous asymmetric scission of the C-Br bonds along the n #sigma#~* state.