Forward scattering in the H+D2→HD+D reaction:: Comparison between experiment and theoretical predictions

We investigate the sensitivity of photoinitiated experiments to forward-scattering features by direct comparison of experimental angular distributions with quantum-mechanical calculations as well as by forward-convolution of theoretical and model center-of-mass differential cross sections. We find that the experimental sensitivity to forward-scattering angles depends on the instrumental velocity resolution as well as on the kinematics of the detected product channel. Explicit comparison is made between experimental HD(v(')=1,2;j(')) center-of-mass angular distributions at collision energies approximate to1.6 eV (deduced from time-of-flight profiles using a single-laser, photolysis-probe approach) and quantum-mechanical calculations on the BKMP2 potential energy surface. The comparison takes into account the contributions from both slow and fast H atoms from the photolysis of HBr. We find that the contribution of the slow H atoms, which is the major source of experimental uncertainty, does not greatly affect the extraction of the angular distribution from the experimental time-of-flight profile for a specific HD(v('),j(')) state. Except for HD(v(')=1, j(')=8) and HD(v(')=2, j(')=0), for which either slow H atoms or the presence of a narrow forward-scattering peak make the analysis more uncertain, the agreement between experiment and theoretical predictions is excellent. (C) 2001 American Institute of Physics.