Electron detachment in H-(D-) collisions with rare gas atoms: angular distributions of the neutral H(D) atoms

Abstract

The angular distribution of neutral H(D) atoms produced in detachment collisions of H-(D-) ions with rare gas atoms (He, Ne, Ar, Kr, Xe) has been measured in the energy range Elab=50-250 eV and the angular range theta lab=0.15 degrees . A pronounced structure is observed: a sharp peak around 0 degrees and a second broad maximum at a finite angle which scales with the energy according to E theta =constant. For He, Ne and Ar, the experimental data have been normalised to absolute units. By using a simplified model, an angle-dependent detachment probability Pdet( theta cm) has been derived from the measured differential detachment cross sections. The detachment probabilities Pdet are plotted as a function of the relative collision velocity nu for constant values of the parameter tau =Ecm theta cm. At small tau (large impact parameters), Pdet( nu ) increases with the velocity indicating a dynamical coupling mechanism. At large tau (small impact parameters), Pdet( nu ) is nearly constant for Ar and slightly decreasing for He and Ne. The experimental results are discussed in terms of different theoretical models for the detachment process.