Interatomic potentials, electric properties and spectroscopy of the ground and excited states of the Rb2 molecule: ab initio calculations and effect of a non-resonant field

We formulate the theory for a diatomic molecule in a spatially degenerate electronic state interacting with a non-resonant laser field and investigate its rovibrational structure in the presence of the field. We report on ab initio calculations employing the double electron attachment intermediate Hamiltonian Fock space coupled cluster method restricted to single and double excitations for all electronic states of the Rb-2 molecule up to 5s+5d dissociation limit of about 26,000cm(-1). In order to correctly predict the spectroscopic behaviour of Rb-2, we have also calculated the electric transition dipole moments, non-adiabatic coupling and spin-orbit coupling matrix elements, and static dipole polarisabilities, using the multireference configuration interaction method. When a molecule is exposed to strong non-resonant light, its rovibrational levels get hybridised. We study the spectroscopic signatures of this effect for transitions between the X-1 sigma(+) (g) electronic ground state and the A(1)sigma(+) (u) and b(u)(3) excited state manifold. The latter is characterised by strong perturbations due to the spin-orbit interaction. We find that for non-resonant field strengths of the order 10(9) W/cm(2), the spin-orbit interaction and coupling to the non-resonant field become comparable. The non-resonant field can then be used to control the singlet-triplet character of a rovibrational level.