ИСТИНА

Nowadays, alkali metal diatomics are the most commonly studied ultracold molecules because alkali metals have an unpaired electron and possess strong laser driven optical transitions. Among the heteronuclear bi-alkalis, ultracold LiRb is especially attractive due to its high photoassociation rate and large permanent electric dipole moments in both ground and low-lying excited states. However, the comprehensive high resolution spectroscopic information required for developing efficient laser cooling and electric field manipulation of LiRb molecule is scanty as of yet. We elucidated an origin of the Λ-doubling and spin-orbit coupling effects in the B(1)1Π and D(2)1Π states of LiRb by means of high-level ab initio electronic structure calculations of both angular and spin-orbit coupling matrix elements between the (1,2)1Π and low-lying singlet (1-5)1Σ+ and triplet (1-3)3Σ+,3Π states manifolds. We proved, quantitatively, the empirical observation1,2 that the B1Π state undergoes strong local L-coupling with the nearby C(3)1Σ+ state and regular spin-orbit perturbations with the remote triplet states. In contrast, the D1Π state is found to be locally perturbed by the embedding d(2)3Π state while its Λ-doubling effect is mainly determined by regular interaction with the C1Σ+ state. The ab initio non-adiabatic matrix elements and relevant potential energy curves of the interacting states were refined during the coupled-channel (CC) deperturbation treatment of the experimental rovibronic term values1,2 available for both B and D states. The CC deperturbation model reproduces the raw termvalues of all observed 6,7Li85,87Rb isotopologues within 0.01 cm-1, that is close to uncertainty of the measurements. The present study of the fine structure of the excited states will help in searching for optimal pathways for two steps laser assembly of ultracold LiRb molecules via the intermediate B and D states down to the absolute ground state X1Σ+(v=0,J=0). The work was partly supported by the RFBR grant N 16-03-00529-a. References [1] S. Dutta, A. Altaf, D. S. Elliott, Y. P. Chen, Chem. Phys. Lett., 511, 7, 2011. [2] M. Ivanova, A. Stein, A. Pashov, H. Knöckel, E. Tiemann, J. Chem. Phys. 138, 094315, 2013.