Ab initio calculations of the electronic states of Li-Rare gas molecules and alkali dimers

Abstract

The $X^2\Sigma^+$, $A^2\Pi$, $B^2\Sigma^+$ and $C^2\Sigma^+$ states of LiAr and the ground state of $LiAr^+$ are calculated by configuration interaction methods. The existence of a double potential well is found for the $C^2\Sigma^+$ state. The origin of the double well is surmised to lie in the existence of a nodal plane separating two radial regions of the electron density in the Rydberg atomic orbital. The spectroscopic constants and the transition properties between the calculated states are also reported. The molecular spin-orbit splittings of the $A^2\Pi$ state of LiRg (Rg=Ar, Kr and Xe) complexes, $A^{SO}$, are obtained from the configuration interaction method using two-component spinors based on relativistic effective core potentials (RECP). Calculated $A_{SO}$ strongly depends on internuclear distance and shows a dramatic increasing at short distance. The heavy element effect in LiRg complex is investigated with the emphasis on the role of the rare gas atom. The rare gas atom lends its large spin- orbit splitting to the lithium atom and increases the molecular spin-orbit splitting. It is understood that valence np orbitals of the rare gas atom work on the heavy element effect. The ground state $X^2\Sigma^+$ and the excited states $A^2\Pi_{1/2}$ and $A^2\Pi_{3/2}$ of LiRg complex are also calculated. Molecular spectroscopic constants are determined and compared with a feasible experiments. A large-scale configuration interaction calculations for the electronic states of KRb dissociating into 4s+5s, 4s+5p, 4p+5s, 4s+4d, 4s+6s, 5s+5s, 3d+5s, 5s+6p and 5s+5d are performed using the averaged relativistic effective core potential. The core-valence correlation effect is included through a use of the core-polarization potential. The core-core repulsion is explicitly included by using small-core potential. Comparison with previous calculations without this term shows significant changes of the spectroscopic constants. The spin-orbit effect is calculated ...