Potential construction of the B(1)1 Π state in KCs based on Fourier-Transform spectroscopy data

Abstract The paper presents an empirical pointwise potential energy curve (PEC) of the extensively perturbed B ( 1 ) 1 Π state of the KCs molecule constructed by applying an Inverted Perturbation Approach routine. The experimental term values in the energy range E ( v ′ , J ′ ) ∈ [ 14071 ; 15502 ] cm − 1 involved in the fit were based on Fourier-Transform spectroscopy data obtained with 0.01 cm −1 accuracy from laser-induced B ( 1 ) 1 Π → X 1 Σ + fluorescence spectra in the present work (654 term values) combined with 520 term values from Birzniece et al. (2012) . The data set included vibrational v ′ ∈ [ 0 , 35 ] and rotational J ′ ∈ [ 7 , 233 ] quantum numbers covering about 85% of the potential well. The present fit reproduces the data included in the fit with a standard deviation 0.94 cm −1 . The empirical PEC contains an inflection at about R =4.1 A that reflects the avoided crossing of two Ω = 1 states corresponding to B ( 1 ) 1 Π and c ( 2 ) 3 Σ + states as predicted by ab initio calculations.