Molecular states of HeH+. Energies and dynamical couplings

We complete the molecular results reported in a previous paper by presenting additional energies (for ${}_{}{}^{1,3}{}_{}{}^{}\Sigma$ states) and radial couplings (between ${}_{}{}^1{}_{}{}^{}\Sigma$ states) of the He${\mathrm{H}}^{+}$ system. These results are needed to treat elastic and inelastic charge-exchange processes when full account is taken of momentum-transfer problems. We also present a formalism to calculate radial couplings between wave functions computed with the use of different variational methods and basis sets. The detailed form of the radial couplings is discussed and related to the Barat-Lichten correlation diagram. The effect of using finite basis sets in calculating degenerate molecular energies is also discussed.