Differential cross section for the H + D 2 → H D ( v ′ = 1 , j ′ = 2 , 6 , 10 ) + D reaction as a function of collision energy

We have measured differential cross sections (DCSs) for the HD ( v ′ = 1 , j ′ = 2 , 6 , 10 ) products of the H + D 2 exchange reaction at five different collision energies in the range 1.48 ⩽ E coll ⩽ 1.94 eV . The contribution from the less energetic H atoms formed upon spin-orbit excitation of Br in the photolysis of the HBr precursor is taken into account for two collision energies, E coll = 1.84 and 1.94 eV , allowing us to disentangle the two different channels. The measured DCSs agree well with new time-dependent quantum-mechanical calculations. As the product rotational excitation increases, the DCSs shift from backward to sideward scattering, as expected. We also find that the shapes of the DCSs show only a small overall dependence on the collision energy, with a notable exception occurring for HD ( v ′ = 1 , j ′ = 2 ) , which appears bimodal at high collision energies. We suggest that this feature results from both direct recoil and indirect scattering from the conical intersection.