Observation and modelling of bound-free transitions to the $X^1\Sigma^+$ and $a^3\Sigma^+$ states of KCs

TL;DR

This study records and models the bound-free transitions in KCs molecules using Fourier-transform spectroscopy, reconstructs interatomic potentials with improved accuracy, and compares empirical potentials' effectiveness in reproducing observed spectra.

Contribution

It introduces a new analytical potential model for KCs states based on combined experimental and ab initio data, improving the accuracy of the repulsive potential.

Findings

The derived $a^3\Sigma^+$ potential better reproduces experimental data.

All tested potentials accurately model the $X^1\Sigma^+$ state spectrum.

The model enhances understanding of KCs molecular transitions.

Abstract

The oscillation continuum in laser-induced fluorescence spectra of bound-free $c^3\Sigma^+ \to a^3\Sigma^+$ and (4)$^1\Sigma^+ \to X^1\Sigma^+$ transitions of the KCs molecule were recorded by Fourier-transform spectrometer and modelled under the adiabatic approximation. The required interatomic potentials for ground $a^3\Sigma^+$ and $X^1\Sigma^+$ 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 $a^3\Sigma^+$ 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 $X^1\Sigma^+$ state reproduce the bound-free (4)$^1\Sigma^+ \to X^1\Sigma^+$ spectrum with equal quality in the range of observations.