Calculation of potential energy curves for Rb₂including relativistic effects

All-electron relativistic calculations have been performed on the Rb2 molecule. The molecular orbitals are optimized within a spin-free no-pair Hamiltonian formalism and spin-orbit coupling is treated using quasi-degenerate perturbation theory. Potential curves of the ground state and several excited states are calculated, and the spectroscopic constants T e, D e, R e and ωe are in good agreement with experimental values. The spin-orbit splittings at the 5p and 6p asymptotic limits are found to be underestimated by about 30%. Large perturbations in the spectra from the 11Σ+ u(A) state are predicted due to an avoided crossing with a 1 3Πub state caused by spin-orbit interaction. The predissociation dynamics of the 2 1ΠuC and 3 1ΠuD states is discussed. The calculations support the observation that a (1) 3 Δu state causes the fast predissociation of the 3 1ΠuD state but rule out the (2)3Σ+ u state as causing the slow predissociation at the lower part of the 3 1ΠuD potential energy curve.