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Abstract

A five parameter semiempirical Tang–Toennies type model is used to describe the potential curves of the a3Σ+-state of the heteronuclear
polar molecules NaCs, KCs, and RbCs. These molecules are of current interest in experiments at ultra-cold conditions to explore the effects
of the strong dipole–dipole forces on the collective many-body quantum behavior. New quantum phenomena are also anticipated in systems
consisting of atomic species with different fermion/boson statistics. The model parameters are obtained by simultaneously fitting all five of
the parameters to the extensive LIF-Fourier transform spectroscopy published by Tiemann and collaborators [e.g., Docenko et al. J. Phys. B:
At., Mol. Opt. Phys. 39, S929–S943 (2006)], who also report best fit potential curves. Although the new potentials are in good agreement with
the earlier potentials, they have the advantage that they are continuous over the entire range of internuclear distances and have the correct
long-range behavior. The scattering lengths for all isotope combinations show good agreement with dedicated experiments where available.
The new potentials are also in excellent agreement with combining rules based on the potentials of the homonuclear systems.