Associative detachment in low-energy collisionsbetween hydrogen atoms and atomic halogen anions

Abstract

Using an improved nonlocal resonance theory, total crosssections, rovibrational final state distributions and electronspectra for low-energy (<2 eV) associative detachment (AD)collisions between hydrogen atoms and negative halogen ionsX- (X = F, Cl, Br) as well as deuterium atoms and F- ions have been calculated. The model involves realisticlong-range interactions for the H + X- systems andtakes into account the dependence of the dipole-modifiedthreshold exponent on internuclear distance. Good agreement isfound between experimental data for the total AD cross sectionsand the theoretical results. In the calculated electron energyspectra nonlocal effects are manifest through step structurewhich is (almost) independent of collision energy; thisstructure should therefore be observable in experiments withrather modest collision energy resolution. For illustration,electron spectra are presented which correspond to realisticexperimental conditions with regard to the energy widths of theelectron spectrometer and the collision energy distribution. Therovibrational final-state distributions in the HX(v, J)molecules formed are reported for a thermal kinetic energy distributionat T ≈ 300 K; for HF, DF and HCl the rotational-summedvibrational populations pv are compared with previoustheoretical and experimental results.