Vibronic transitions in the alkali-metal (Li, Na, K, Rb) – alkaline-earth-metal (Ca, Sr) series: A systematic analysis of de-excitation mechanisms based on the graphical mapping of Frank-Condon integrals

Abstract

Research on ultracold molecules has seen a growing interest recently in the context of high-resolution spectroscopy and quantum computation. After forming weakly bound molecules from atoms in cold collisions, the preparation of molecules in low vibrational levels of the ground state is experimentally challenging, and typically achieved by population transfer using excited electronic states. Accurate potential energy surfaces are needed for a correct description of processes such as the coherent de-excitation from the highest and therefore weakly bound vibrational levels in the electronic ground state via couplings to electronically excited states. This paper is dedicated to the vibrational analysis of potentially relevant electronically excited states in the alkali-metal (Li, Na, K, Rb)-alkaline-earth metal (Ca,Sr) diatomic series. Graphical maps of Frank-Condon overlap integrals are presented for all molecules of the group. By comparison to overlap graphics produced for idealized potential surfaces, we judge the usability of the selected states for future experiments on laser-enhanced molecular formation from mixtures of quantum degenerate gases.

The RbSr2Σ+ground state investigatedviaspectroscopy of hot and ultracold molecules

“…As a next step, we plan to further refine the PECs derived in this work via new LIF experiments with rotational resolution, and to characterize the effects induced by hyperfine and spin-rotation couplings via additional two-color PA. We will also use the results of this work to determine an efficient STIRAP Table VI. Comparison of spectroscopic constants and dispersion coefficients for the X(1) 2 Σ + and B(2) 2 Σ + states of the 85 Rb 88 Sr molecule, between the present experiment-based work, the ab-initio calculations used here [32,33], and other relevant works labelled as in their respective publication. Units of energy and length are cm −1 and Å, respectively, while Φ 0 W KB is dimensionless.…”

“…In this section, we first describe the experimental setup we use to record the fluorescence from RbSr molecules in a heat-pipe oven. We then explain how we simulate theoretical spectra using three published sets of potential energy curves produced by independent abinitio methods [32,33]. By comparing these spectra with our experimental data, we identify a few band heads, from which we extract Dunham coefficients describing the deepest parts of the B(2) 2 Σ + and X(1) 2 Σ + states.…”

“…In order to interpret the experimental spectra, we first simulate fluorescence spectra using PECs and transition dipole moments computed theoretically, and compare theory and experiment. The simulations start from three sets of PECs, obtained independently with FCI-ECP+CPP [32], RCCSD(T) [32], and MRCI [33] methods. We calculate the energies of rovibrational levels of the B(2) 2 Σ + and X(1) 2 Σ + states by solving the radial Schrödinger equation with each of the three sets of PECs.…”

“…Figure 9. Simulated thermoluminescence spectra based on the three sets of theoretical PECs for the X(1) 2 Σ + and B(2) 2 Σ + states, calculated with (a) RCCSD [32], (b) FCI-ECP+CPP [32], and (c) MRCI [33], compared with the experimental data (d). The positions of identified band heads are marked with dashed lines and labelled with their vibrational quantum numbers ν − ν (where primed and double primed symbols refer to B(2) 2 Σ + and X(1) 2 Σ + , respectively).…”

“…Units of energy and length are cm −1 and Å, respectively. The number of digits in the presented values of parameters is necessary to reproduce band-head positions and weakly-bound energy levels with the experimental uncertainty MRCI [33] FCI-ECP+CPP [32] RCCSD(T) […”