Distorted atomic-orbital expansion for slow ion-atom collisions

The distorted atomic-orbital method, proposed by Kobayashi, Ishihara, and Toshima [Muon Catalyzed Fusion 2, 191 (1988)], is applied to low-energy ion-atomic collisions. This method is free from the difficulty of spurious couplings. The basic idea of the method is discussed in detail. An iterative method for the numerical calculation is developed and, as an example, a quantum-mechanical calculation of ${\mathrm{He}}^{2+}$+H collisions for incident energy ${\mathit{E}}_{\mathit{i}}$≤200 eV is carried out. The calculated cross section connects naturally to those obtained from a corresponding semiclassical calculation for ${\mathit{E}}_{\mathit{i}}$≥200 eV [T. G. Winter and G. J. Hatton, Phys. Rev. A 21, 793 (1980)].