The $a^3{\Sigma }^{+}$ state of KCs revisited: hyperfine structure analysis and potential refinement

Abstract

Laser-induced fluorescence spectra of the $c^3{\Sigma }^{+}(v_c,J_c=N_c)\to a^3{\Sigma }^{+}(v_a,N_a=J_c\pm 1)$ transitions excited from the ground $X^1{\Sigma }^{+}$ state of ${}^{39}$K${}^{133}$Cs molecule were recorded with Fourier-transform spectrometer IFS125-HR (Bruker) at the highest achievable spectral resolution of 0.0063 cm${}^{-1}$. Systematic study of the hyperfine structure (HFS) of the $a^3{\Sigma }^{+}$ state for levels with $v_a\in [0,27]$ and $N_a\in [24,90]$ shows that the splitting monotonically increases with $v_a$. The spectroscopic study was supported by ab initio calculations of the magnetic hyperfine interaction in $X^1{\Sigma }^{+}$ and $a^3{\Sigma }^{+}$ states. The discovered variation of the electronic matrix elements with the internuclear distance $R$ is in a good agreement with the observed $v_a$-dependencies of the HFS. Overall set of available experimental data on the $a^3{\Sigma }^{+}$ state was used to improve the potential energy curve particularly near a bottom, providing the refined dissociation energy $D_e$=267.21(1) cm${}^{-1}$. The ab initio HFS matrix elements, combined with the empirical $X^1{\Sigma }^{+}$ and $a^3{\Sigma }^{+}$ PECs in the framework of the invented coupled-channel deperturbation model, reproduce the experimental term values of both ground states within 0.003 cm${}^{-1}$ accuracy up to their common dissociation limit.

References in corpus (8)

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• Feshbach resonances, molecular bound states and prospects of ultracold molecule formation in mixtures of ultracold K and Cs
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Cited by in corpus (2)

• Diatomic molecules of alkali-metal and alkaline-earth-metal atoms: interaction potentials, dipole moments, and polarizabilities
• Intensities of KCs $E(4{)}^1{\Sigma }^{+}\to (a^3{\Sigma }^{+},X^1{\Sigma }^{+})$ band system up to dissociation threshold: an interplay between spin-orbit, hyperfine and rovibronic coupling effects