Nonadiabatic coupling between the E F+G K+H 1Σ+g, I 1Πg, and J 1Δg states of the hydrogen molecule. Calculation of rovibronic structures in H2, HD, and D2

Publisher Website
Google Scholar
Abstract
The Born–Oppenheimer potential curves of the first two excited 1Σ+g states of H2, EF and GK, exhibit double minima which arise from avoided crossings between the electronic energy curves of the doubly excited 1σ2u configuration and of the 1Σ+g Rydberg states of the 1σg2sσg and 1σg3dσg configurations. The vibrational structures of the adiabatic electronic states are mutually coupled via strongly R‐dependent off‐diagonal electronic matrix elements of the d/dR and d2/dR2 operators. Furthermore the rotational structures are characterized by strong angular coupling within the complex of 3d‐singlet‐gerade states G 1Σ+g, I 1Πg, and J 1Δg. We have evaluated the nonadiabatic coupling functions involving the first three excited 1Σ+g states EF, GK, and H, and the I 1Πg and J 1Δg states, and have calculated their nonadiabatic rovibronic structures for the J=0–5 levels of H2, HD, and D2 up to the H(1s)+H(2s,2p) dissociation limit. The simultaneous radial and angular couplings within these five electronic states have been treated using ab initio potential curves, adiabatic corrections, and nonadiabatic coupling functions. The coupled equations have been transformed into a diabatic electronic basis and solved numerically, and the resulting eigenfunctions have been transformed back into the adiabatic basis. Energy eigenvalues, nonadiabatic energy shifts, B values, Landé g factors, band transition moments, Einstein coefficients, and radiative lifetimes have been evaluated and compared with spectroscopic results where possible. The discrepancies between observed and calculated rovibronic term values depend systematically on electronic state, vibrational energy, and isotopic mass, and their magnitudes indicate that the absolute energy errors of the ab initio potential curves amount to less than 1 cm−1 near the minima of the EF 1Σ+g and I 1Πg states, approximately 2 cm−1 in the J 1Δg state, and 5 cm−1 in the H 1Σ+g state. The nonadiabatic ab initio results have already aided spectroscopic identifications of new energy levels and they indicate that several old assignments must be discarded.