R-matrix calculations of triplet gerade states of molecular hydrogen and their use for high-resolution spectroscopy

A variational R-matrix approach combined with multichannel quantum defect theory is used for a computational study of triplet gerade states of H-2. Electron-ion reaction (quantum defect) matrices are calculated as functions of internuclear distance and energy for the bound and continuum ranges including singly and doubly excited configurations built on the 1 sigma(g) (X+2 Sigma(+)(g)) and 1 sigma(u) (A(+2)Sigma(+)(u)) core states of the H-2(+) ion. It is shown how these matrices can be reduced to effective quantum defect functions adapted to the analysis of high-resolution spectra in the bound range. These R-matrix effective quantum defects are finally adjusted to the available experimental data [Sprecher et al., J. Phys. Chem. A 117, 9462 (2013)], producing agreement with experiment to within 0.5 cm(-1), nearly as good as obtained by Sprecher et al. In addition, the R-matrix calculations predict the evolution of the quantum defects for higher energies, in a range extending far into the electronic continuum.