Spin–orbit effects in chemical reactions. Investigation of ground-state products from reactions of Ba(3D)

Abstract

The dependence of the cross-sections for production of ground-state barium halide products on incident spin–orbit state has been determined by means of optical-pumping state selection for the reaction of metastable Ba(6s5d³D) with HCl, CH₃Cl, HBr and CH₃Br. In addition, cross-sections for the metastable ¹D level were related to those of the ³D_J multiplet by optical pumping on an intercombination line. For alkyl halide (RX) reactants, the spin–orbit dependence of the reactivity for the ground-state channel was substantial with an ordering J= 1 > J= 2 > J= 3. This is an opposite ordering to that previously observed for the chemiluminescence channels in analogous reactions. The hydrogen halide reactions exhibited a varying spin–orbit dependence with vibrational level. For the most highly populated vibrational levels v, the spin–orbit dependence was comparable in sign and magnitude to that for RX reactants, while a significantly diminished variation of reactivity with incident J was observed for lower v. The variation of spin–orbit effect with product vibrational level is believed to be due to the dependence of the reaction dynamics on incident impact parameter.