C-Br bond fission dynamics in ultraviolet photodissociation of propargyl bromide

The photodissociation dynamics of propargyl bromide has been investigated at 234 and 267 nm using ion velocity imaging technique coupled with a [2+1] resonance-enhanced multiphoton ionization scheme. The translational energy and angular distributions of Br(P-2(3/2)) and Br*(P-2(1/2)) fragments were obtained. The energy distributions for Br and Br* fragments were found to consist of two Gaussian components, which corresponding to two reaction paths on the excited potential energy surface. The high kinetic energy component was produced via an electronic dissociation from the repulsive n sigma* state, while the low kinetic energy component stem from intersystem crossing from pi pi* state to pi sigma* state. The average fraction of available energy imparted into product recoil for the high kinetic energy products was found to be nearly 0.46, in qualitative agreement with that predicted by a soft radical impulsive model. The angular distributions of Br and Br* fragments show a mostly isotropic, which exhibited an admixture of pi(C C) character with sigma*(C-Br) character in the Frank-Condon region upon electronic excitation. (C) 2008 Elsevier B.V. All rights reserved.