Interaction Energies and Scattering Cross Sections of Hydrogen Ions in Helium

Abstract

The interaction energies for the H+–He and H2+–He system have been calculated for a range of internuclear distances and, in the H2+–He case, for two different configurations. The results are used to analyze the ion-scattering measurements of Simons and co-workers. It has been found that the predicted scattering cross sections are in remarkable agreement with the measured ones, provided allowance is made for a finite width of the ion beam, as suggested by Amdur and Harkness. This agreement implies that the method of interpreting measured cross sections in terms of molecular forces is correct, and that specific apparatus effects have been correctly analyzed. The present calculations suggest, in contrast to previous assumptions, that the important forces are ones of repulsion rather than attraction, with the exception of those cases where chemical binding is clearly involved. As expected, to obtain precise force information of physical significance from such scattering measurements, it is again necessary to make allowance for the finite width of the ion beam. This has been illustrated for the scattering of H3+ ions in helium. Finally, the cross-section equations have been integrated for the case of scattering by an exponential potential and by a Lennard-Jones (8–4) potential.