Permanent electric dipoles and Λ-doubling constants in the lowest ¹Π states of RbCs

The article presents first experimental data on the Stark induced e-f mixing in the (4) ¹Π state of the ⁸⁵Rb¹³³Cs molecule, as well as the ab initio calculations of permanent electric dipole moments (d) in the (1,2,3,4) ¹Π states and q factors in the (2,4) ¹Π states. The appearance of the “forbidden” lines in the laser-induced (4) ¹Π→X ¹Π⁺ fluorescence spectrum in the presence of an electric field allowed us to obtain, for the rovibronic v^′(J^′)=2(82) level of the (4) ¹Π state correlating to the Rb(4d)+Cs(6s) atomic limit, the ratio q∕d=0.9×10⁻⁷ cm⁻¹∕D with 20% experimental error. Electronic structure calculations on the ground and excited states of the RbCs molecule were performed in the framework of the Hund’s a-coupling scheme by means of the many-body multipartitioning perturbation theory. The ab initio d(R) estimates revealed large values of about d≈−7 D for the (4) ¹Π state. The calculated q factor value for the (2) ¹Π state is in excellent agreement with the literature data. The theoretical estimate of the q∕d ratio for the v^′(J^′)=2(82) level of the (4) ¹Π state agrees satisfactory well with the present experimental value.