Configuration interaction studies of HeH+ molecular ion. II. Dipole and radial coupling matrix elements for the singlet sigma states

Configuration interaction calculations of the dipole, gradient, and radial coupling matrix elements among the lowest 10–12 1Σ states of HeH+ are reported for internuclear separations in the range 0≤R≤50 a.u. The forms 〈n|∂/∂R|m〉 and (Em − En)−1 〈n|∂V/∂R|m〉 of the radial coupling element are compared. The results are compared with those of other investigators. The accurate evaluation of these matrix elements in the present work demonstrates the feasibility of a quantitative ab initio treatment of low-energy collisions between light atoms.