Construction of analytic functions for the potential energy curves, dipole moments, and transition dipole moments of RbBe and CsBe molecules

- The potential energy curves of RbBe and CsBe molecules are obtained.
- There vibrational energy levels and spectroscopic parameters are determined.
- The decrease trend of the ωes for the ground states of BeAlm is found.
- The curves and analytical functions of the DMs and TDMs are obtained.

BeAlm (Alm=Li-Cs) molecules have attracted research interests on cold molecules. To date, RbBe and CsBe molecules have not been reported. In this paper, potential energy curves (PECs), as well as curves of dipole moments (DMs) and transition dipole moments (TDMs), for 12Σ+, 22Σ+, 12Π, and 22Π states of RbBe and CsBe are obtained using a multireference configuration interaction method. The effective basis sets ECP28MDF and ECP46MDF are used for Rb and Cs, respectively, as well as an all-electron basis set Aug-cc-pwCV5Z for Be. Small-core approximation is used to obtain the correlation effect of the inner-shell electrons. Analytical potential energy functions (APEFs) are fitted according to the obtained PECs by using Morse long-range potential energy function with damping function and nonlinear least-square method. Rotational and vibrational energy levels of states are determined by solving Schrödinger equation of nuclear movement based on the obtained APEFs. Spectroscopic parameters are also determined. Spin-orbit coupling for the four 2Π states is calculated and analyzed. We propose new analytical functions for the DMs and TDMs of the states on the basis of the obtained curves. The results of this study are beneficial for investigating the photoassociation of the title molecules.