Thesis & Dissertations

Ab-initio based configuration interaction (MRCI) studies on alkali (Li, Na, K, Rb, Cs) – helium van der Waals systems have revealed unexplored excited states. For NaHe system, we seek for a larger number of excited states through ab-initio Rayleigh Schrödinger perturbation theory RSPT-RS2. Neglecting spin-orbit interaction, we present potential energy curves and permanent dipole moment for all investigated states. The binding energy De, equilibrium bond length, Re, and transition energies, Te of potential energy curves are presented and compared with other works. In contrast to all systems, a potential barrier of height 6.59 cm-1 at 5.37 Å is evidenced for the first excited state, (1)2Π, of RbHe. Dipole moment curves of all states of Na-Cs/He systems report dissociation into neutral fragments through a zero asymptotic behavior. For the case of LiHe, ionic character is reflected. Transition dipole moment curves for (1)2Σ+ → X2Σ+ and (1)2Π → X2Σ+ transitions are presented too, with the values of transition dipole moment, , as R tends to infinity. We report undulations of Σ, Π and Δ states unrelated to avoided crossings. Their potential well positions Rmin, barrier positions Rmax, and their minimum and maximum energies, Emin and Emax, with respect to the dissociation asymptote are also indicated. Moreover, we predict partial atomic charges of all systems in their ground states. An overall comparison among Li-Cs/He systems shows specific trends in Re, De and Te. By using the canonical functions approach and the cubic spline interpolation, the eigen values Eυ, The rotational constants Bυ, the centrifugal distortion constants Dυ, and the abscissa of the turning points rmin and rmax were calculated for the first time for the (4)2Π, (1)4Σ+ and (2)2Δ electronic states of the LiHe molecule.