Observation and modelling of bound-free transitions to the $X^1Σ^+$ and $a^3Σ^+$ states of KCs
The oscillation continuum in laser-induced fluorescence spectra of bound-free $c^3Σ^+ \to a^3Σ^+$ and (4)$^1Σ^+ \to X^1Σ^+$ transitions of the KCs molecule were recorded by Fourier-transform spectrometer and modelled under the adiabatic approximation. The required interatomic potentials for ground $a^3Σ^+$ and $X^1Σ^+$ states were reconstructed in an analytical Chebishev-polynomial-expansion form in the framework of the regularization direct-potential-fit procedure based on the simultaneous consideration of experimental line positions from [R. Ferber et al, Phys. Rev. A, \textbf{80}, 062501 (2009)] and the present \emph{ab initio} calculation of short-range repulsive potential data. It was proved that the repulsive part over dissociation limit of the derived $a^3Σ^+$ potential reproduces the experiment better than the potentials reported in literature. It is also shown that all empirical and semi-empirical potentials available for the $X^1Σ^+$ state reproduce the bound-free (4)$^1Σ^+ \to X^1Σ^+$ spectrum with equal quality in the range of observations.