Variational R-matrix calculations for singly and doubly excited singlet gerade channels in H2 -: art. no. 012713

Variational ab initio R-matrix theory is combined with generalized multichannel quantum defect theory, implemented in spheroidal coordinates, to calculate clamped-nuclei (1)Sigma(g)(+), (1)Pi(g), and (1)Delta(g)(+) electron-ion scattering phase shift matrices for H-2. The calculations cover the bound state region below H-2(+) 1sigma(g), the resonance region between H-2(+) 1sigma(g) and H-2(+) 1sigma(u), and they extend beyond the H-2(+) 1sigma(u) threshold. They span the range of internuclear distances 1less than or equal toRless than or equal to5 a.u. The use of spheroidal instead of spherical coordinates allows a restricted partial wave expansion to be used, thus yielding a compact set of interaction parameters pertaining to the electron-ion scattering dynamics in H-2. The accuracy of our fixed-nuclei quantum defects is generally of the order of about 0.02. At the same time the quantum defect matrices obtained here exhibit a smooth behavior across the ionization thresholds and their elements also vary rather smoothly with internuclear distance. These results represent a step toward the goal of constructing a unfied theoretical description of ionization and dissociation fragmentation dynamics of H-2.