Low energy electron collisions with He₂ ⁺ molecules

The R-matrix method is used in an ab initio study of low energy elastic scattering by He₂ ⁺ molecular ions. SCF and correlated CI wavefunctions have been used in a two state approximation, which retains the lowest two states, ²∑_u ⁺ and ²∑_g ⁺, of the He₂ ⁺ molecular ion in the scattering basis. Cross section calculations have been performed at two fixed internuclear separations, 1.8 and 2.0625 a₀. At the equilibrium bond separation we have detected and fitted the lowest lying npσ ³Σ_u ⁺ resonances in the ³Σ⁺ _u scattering symmetry. In addition, bound state calculations have also been carried out for the He₂ (1σ_g ⁺1σ_u2s a³Σ_u ⁺) state at these two internuclear separations and are seen to compare favorably with MCSCF and SOCI results.