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.
Highlights
The formation and trapping of molecules in the submicrokelvin range has become a topical research branch in the past decade [1,2,3,4,5,6]
The length of each vertical line in the figure corresponds to the MRCI dissociation energy of a given electronic state, while its upper position is determined by the known atomic excitation energy
Regarding the dependence of the transition dipole moment on the internuclear distance we find an insensitivity for the 2 2 + ← X 2 + transition in the K/Rb-AKE molecules, which is barely affected by moderate geometry changes, see red solid line in the TDM subplots
Summary
The formation and trapping of molecules in the submicrokelvin range has become a topical research branch in the past decade [1,2,3,4,5,6]. In a previous paper we analyzed the behavior of the lowest + states of the doublet and the quartet multiplicity for different combinations of alkali-metal (AK) and alkaline-earth-metal (AKE) atoms, and studied the trends of molecular properties such as the dipole moment [42]. In the first part of the manuscript we focus on the calculation of potential energy surfaces of the first few electronically excited, experimentally relevant states. We employ various ab initio methods, discuss deviations in the curvatures and the relative energy positions, and analyze their consequences for a quantitative analysis of vibronic spectra This is followed by the calculation of Franck-Condon factors and Einstein A coefficients to study potential mechanisms for the transfer of initially formed, weakly bound molecules to the rovibrational ground state. Keeping in mind the experimentally accessible range, we give a few alternatives based on excitations to other electronically excited states
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