Streuung von Ionen I. Regenbogeneffekt bei der elastischen Streuung von Protonen an Argon

Abstract

A crossed beam apparatus for scattering experiments with ions on atoms or molecules is described. The results for the elastic scattering of H+ on Ar are reported. Both the structure of the secondary rainbows and the superimposed fine structure were resolved. In order to fit the experimental curves, differential cross sections were calculated in WKB approximation using the following reduced potentials: n, m, g1, g2 , g3 , L, G1 and G2 are form parameters for adjusting the width of the potential well. The fitting procedure and the influence of the chosen potentials on the resulting potential depth E and the equilibrium distance rm are described. Further, the information which can generally be obtained from the observed rainbows and the superimposed fine structure are discussed. No combination of n, m, rm and ε yielded a differential cross section in agreement with the experiments, if the Lennard-Jones potential ULJ or the modifications of Mason and Vanderslice or Schlier and coworkers are used, but excellent agreement can be obtained with the above expressions for U1 and U2 using suitable parameters. For the system H+-Ar we obtain ε = (4.04+0.1) eV, rm = (1.31±0.07) Å. These values are in good agreement with recent ab-initio calculations of Roach and Kuntz. They are considerably different from those obtained by Champion et al. 8, who did not observe the fine structure and used a too narrow potential in the evaluation of the scattering data.