Ab-initio study of the ground and low-lying excited states including the spin-orbit effect of RbBa molecule and laser cooling feasibility

Abstract

In this work, we present a thorough theoretical structure and spectroscopic study of the ground and low lying excited states of RbBa molecule. High-level ab-initio calculations are performed, using MCSCF/MRCI+Q level of method, based on the effective core potential (ECP) and core-polarization potential (CPP) approach. The potential energy curves, spectroscopic parameters, vibrationnel energy levels of the 16(2,4Σ+,2,4Π,2,4Δ) first electronic states, with respect to the lowest five dissociation limits were calculated. The comparison of the spectroscopic constants of the ground state X2Σ+ with the available theoretical work, are in good agreement. The study of all the excited states is performed in this work for the first time. Afterwards, the spin-orbit operator is incorporated in valence MRCI calculation using optimized relativistic spin-orbit pseudo-potentials and 33 Ω states are generated and split into Λ-S states. In addition, both relativistic and non relativistic calculations of permanent and transition dipole moments are presented and discussed. Stimulated black body (T= 300 K) and spontaneous transition rates of vibrational states of X2Σ+ state were evaluated. The related vibrational lifetimes for RbBa are found to be in order of 103 s which is sufficiently large for ultracold experiments. Moreover, the vibrational life-time for the A2Σ+(v’) and A2П (v”) states are measured and the possibility of Laser Cooling for the RbBa molecule is discussed based on Franck–Condon factors calculation of A2Σ+ (v’)→ X2Σ+(v) and A2П(v”) → X2Σ+(v) transition. This work represents a significant contribution for experimentalists as it provides efficient information in order to form cold alkali and alkaline-earth RbBa molecules.