C-Cl bond fission dynamics and angular momentum recoupling in the 235 nm photodissociation of allyl chloride

Abstract

The photodissociation dynamics of allyl chloride at 235 nm producing atomic Cl( 2P j ;J = 1/2,3/2) fragments is investigated using a two-dimensional photofragment velocity ion imaging technique. Detection of the Cl( 2P 1/2) and Cl( 2P 3/2) products by [2+1] resonance enhanced multiphoton ionization shows that primary C-Cl bond fission of allyl chloride generates 66.8% Cl( 2P 3/2) and 33.2% Cl( 2P 3/2). The Cl( 2P 3/2) fragments evidenced a bimodal translational energy distribution with a relative weight of low kinetic energy Cl( 2P 3/2)/high kinetic energy Cl( 2P 3/2) of 0.097/0.903. The minor dissociation channel for C-Cl bond fission, producing low kinetic energy chlorine atoms, formed only chlorine atoms in the Cl( 2P 3/2) spin-orbit state. The dominant C-Cl bond fission channel, attributed to an electronic predissociation that results in high kinetic energy Cl atoms, produced both Cl( 2P 1/2) and Cl( 2P 3/2) atomic fragments. The relative branching for this dissociation channel is Cl( 2P 1/2)/[Cl( 2P 3/2) + Cl( 2P 3/2)] = 35.5%. The average fraction of available energy imparted into product recoil for the high kinetic energy products was found to be 59%, in qualitative agreement with that predicted by a rigid radical impulsive model. Both the spin-orbit ground and excited chlorine atom angular distributions were close to isotropic. We compare the observed Cl( 2P 1/2)/[Cl( 2P 1/2)+Cl(2P 3/2)] ratio produced in the electronic predissociation channel of allyl chloride with a prior study of the chlorine atom spin-orbit states produced from HCl photodissociation, concluding that angular momentum recoupling in the exit channel at long interatomic distance determines the chlorine atom spin-orbit branching. © 2004 American Institute of Physics.