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