Abstract
The potential energy curves of the low-lying electronic states correlating up to the limit K(4p)+Rb(5s) of KRb molecule have been calculated using the multi-reference perturbation theory method at the CASSCF/XMCQDPT2 level of theory without and with spin–orbit coupling. The calculated parameters of the ground X1Σ+ state are in the best agreement among all previously performed ab initio calculations for the KRb molecule. The calculated vibrational intervals of the ground electronic term of the 39K85Rb molecule describe the experiment with the accuracy within ±1cm−1. The calculated intensities of the 21Σ+ (v′=3, J′=26)→X1Σ+ (v″=0…24, J″=25, 27) transitions satisfactory reflect the experimentally observed intensities distribution.
Highlights
The KRb molecule is among the most intensively studied polar alkali diatomics, partially because of its successful usage in production and investigation in cold and ultracold conditions
When the spin–orbit coupling (SOC) is taken into account, the X1R+, 21R+ and 31R+ terms correspond to the (X)0+, (3)0+ and (4)0+ terms, respectively; the 11G and 21G terms correspond to the (4)1 and (5)1 terms, respectively; the 13R+, 23R+ and 33R+ terms split into the (1)0À and (1)1, (3)0À and (3)1 and (5)0À and (7)1 terms, respectively; the 13G and 23G terms split into the (2)0+, (2)0À, (2)1 and (1)2 and (5)0+, (4)0À, (6)1 and (2)2 terms, respectively
The ab initio results (PECs, molecular spectroscopic constants, vibrational energies, vibrational intervals, Franck–Condon factors (FCFs)) obtained without any empirical fitting are in good agreement with the experimental and previous theoretical data
Summary
The KRb molecule is among the most intensively studied polar alkali diatomics, partially because of its successful usage in production and investigation in cold and ultracold conditions (see for instance [1,2,3,4]). Recent efforts are often focused on transferring weakly bound ultracold molecules into their ‘‘absolute” ground state X (v00 = 0, J00 = 0) by additional optical cycles via excited electronic states. The efficiency of these processes depends rather critically on the proper choice of optical paths, which needs reliable information about the potential energy curves (PECs) of the combining electronic states in wide range of energies and internuclear distances. The goal of the present paper is to perform ab initio calculations of PECs of the ground and several excited electronic states of the KRb molecule corresponding to the first three asymtotic limits of separated atoms and to derive molecular constants, vibrationalrotation energies and Franck–Condon factors. The calculation of the electronic structure of molecular systems, which contain a heavy alkali metals atom, is a non-trivial task that requires taking into account the relativistic effects for the core electrons, the static
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