Observation and modeling of bound-free transitions to the X 1 Σ + and a 3 Σ + states of KCs.

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