Br(2Pj) and Cl(2Pj) atom formation dynamics of allyl bromide and chloride at 234 nm

The photodissociation dynamics of allyl bromide and chloride have been investigated at 234 nm using a two-dimensional photofragment ion imaging technique coupled with a [2+1] resonance-enhanced multiphoton ionization scheme. After absorbing a photon, allyl bromide dissociates into C3H5+Br(P-2(j);j = 1/2,3/2) exclusively via the repulsive surfaces. The enhanced contribution of the singlet state-to the initial transition is' attributed to intensity borrowing from the nearby (1)(pi,pi*) state. Trimodal translational energy distributions of Cl(P-2(j);j = 1/2,3/2) have been observed after the photolysis of allyl chloride. Low-velocity components with Boltzmann shapes are produced vis internal conversion between the initially pumped 1(pi, pi*) state and the vibrationally excited ground state. Middle-velocity components,with Gaussian shapes originated from curve crossing between the bound (1)(pi,pi*) state and the dissociative (1)(pi,pi*) state. High-velocity components are produced via curve crossing from the (1)(pi,pi*) state to the (1)(n,sigma*) state. The enhanced curve crossings in exit channels are attributed to the non-planar geometry of the parent molecule and torsional torque induced by the initial (1)(pi, pi*) transition. The location of the curve crossing between the (1)(pi, pi*) state and the (1)(n,sigma*) state has been estimated to be approximate to 40 000 cm(-1) based on the localized available energy. (C) 2001 American Institute of Physics.