Yr. Lee et al., Photodissociation of 1,2-C2H2Br2 at 248 nm: Competition between three-bodyformation Br+Br+C2H2 and molecular Br-2 elimination, J CHEM PHYS, 115(7), 2001, pp. 3195-3200
The photodissociation of 1,2-C2H2Br2 at 248 nm has been studied by product
translational spectroscopy. The results show that the molecule dissociates
exclusively into the products (1) Br-2+C2H2 and (2) Br (fast)+Br (slow)+C2H
2 with a branching ratio similar to0.2:0.8. While the cleavages of the C-Br
bonds are not symmetric, producing the Br atoms at unequal velocities, the
anisotropy of the products indicates that both reactions occur in a fracti
on of a rotational period. Following an asynchronous concerted reaction, th
e triple products were simulated with the P(E-t) distributions coupled by a
symmetric angular distributions. A mechanism consistent with the measured r
esults is proposed that the Br-2 elimination is a result of a fast intersys
tem crossing from the pi pi* pumped state while the triple products occur v
ia a simultaneous asymmetric scission of the C-Br bonds along the n sigma*
state. (C) 2001 American Institute of Physics.