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

The photodissociation dynamics of allyl chloride at 235 nm producing atomic Cl(P-2(J);J=1/2,3/2) fragments is investigated using a two-dimensional photofragment velocity ion imaging technique. Detection of the Cl(P-2(1/2)) and Cl(P-2(3/2)) products by [2+1] resonance enhanced multiphoton ionization shows that primary C-Cl bond fission of allyl chloride generates 66.8% Cl(P-2(3/2)) and 33.2% Cl(P-2(1/2)). The Cl(P-2(3/2)) fragments evidenced a bimodal translational energy distribution with a relative weight of low kinetic energy Cl(P-2(3/2))/high kinetic energy Cl(P-2(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(P-2(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(P-2(1/2)) and Cl(P-2(3/2)) atomic fragments. The relative branching for this dissociation channel is Cl(P-2(1/2))/[Cl(P-2(1/2))+Cl(P-2(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(P-2(1/2))/[Cl(P-2(1/2))+Cl(P-2(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. (C) 2004 American Institute of Physics.