Spectrum of potential-energy curves for the He2+ system

Low-energy, collisional excitation of neutral helium in He-He+ collisions is investigated using the potential-energy curves for the molecular ions. Ground and excited states of the 2Σ/sub g/+, 2Σ/sub u/+, 2Pi/sub g/, and 2Pi/sub u/ states are calculated using an ab initio configuration-interaction method for the n = 2 neutral excitations of helium. A threshold of 23.5 eV is determined for the 1S-2 3S excitation. Thresholds for the 1S-2 1S, -2 3P, and -2 1P states are also estimated from the potential-energy curves. Σ-Pi interactions are also considered to explain the photon polarization reported in the 2 1P excitation cross section. The 2Σ/sub g/+ spectrum of potential-energy curves appears to dominate the Σ-Σ radial interactions, while the 2Σ/sub u/+ and 2Pi/sub u/ states are apparently necessary to explain the 2 1P cross section