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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 Rb2 molecule up to 5s+5d dissociation limit of about 26,000 cm-1. In order to correctly predict the spectroscopic behaviour of Rb2, 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 X¹ Σg+ electronic ground state and the A¹Σu+ and b³πu 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 109 W/cm², 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. [ABSTRACT FROM AUTHOR]

A symmetry-adapted perturbation theory (SAPT) is formulated for interaction-induced electrical properties of weakly bound complexes. Asymptotic (large R) expressions are reported for the contributions to the collision-induced dipole moments and polarizabilities up to and including second order in the intermolecular potential. These long-range expressions require knowledge only of the multipole moments and (hyper)polarizabilities of the isolated monomers. Numerical results are given for the dipole moment of He-H2 and the polarizability of He2 and the accuracy of the SAPT approach is examined by comparison with full configuration interaction results. The role of various physical contributions to the dipole moment of He-H2 and the polarizability of He2 is investigated. The validity of the long-range approximation and the importance of charge penetration (damping) effects are discussed. [ABSTRACT FROM AUTHOR]