Fourier transform spectroscopy and coupled-channel deperturbation treatment of the A1Sigma+ ~ b3Pi complex of KCs molecule

TL;DR

This study used Fourier transform spectroscopy and coupled-channel deperturbation analysis to investigate the complex interactions between the A1Sigma+ and b3Pi states in KCs molecules, providing detailed potential energy curves and spin-orbit couplings.

Contribution

It presents a novel combined experimental and theoretical approach to analyze the A1Sigma+ ~ b3Pi complex in KCs, including the discovery of weak perturbations and accurate modeling of the energy states.

Findings

Over 3400 rovibronic term values assigned with high precision.

Identified and analyzed weak A1Sigma+ ~ b3Pi Omega=1 perturbations.

Achieved 95% reproduction of experimental data with a standard deviation of 0.004 cm-1.

Abstract

The laser induced fluorescence (LIF) spectra A1Sigma ~ b3Pi --> X1Sigma+ of KCs dimer were recorded in near infrared region by Fourier Transform Spectrometer with a resolution of 0.03 cm-1. Overall more than 200 LIF spectra were rotationally assigned to 39K133Cs and 41K133Cs isotopomers yielding with the uncertainty of 0.003-0.01 cm-1 more than 3400 rovibronic term values of the strongly mixed singlet A1Sigma+ and triplet b3Pi states. Experimental data massive starts from the lowest vibrational level v_A=0 of the singlet and nonuniformly cover the energy range from 10040 to 13250 cm-1 with rotational quantum numbers J from 7 to 225. Besides of the dominating regular A1Sigma+ ~ b3P Omega=0 interactions the weak and local heterogenous A1S+ ~ b3P Omega=1 perturbations have been discovered and analyzed. Coupled-channel deperturbation analysis of the experimental 39K133Cs e-parity termvalues of the A1S+ ~ b3P complex was accomplished in the framework of the phenomenological 4 x 4 Hamiltonian accounting implicitly for regular interactions with the remote states manifold. The resulting diabatic potential energy curves of the interacting states and relevant spin-orbit coupling matrix elements defined analytically by Expanded Morse Oscillators model reproduce 95% of experimental data field of the 39K133Cs isotopomer with a standard deviation of 0.004 cm-1 which is consistent with the uncertainty of the experiment. Reliability of the derived parameters was additionally confirmed by a good agreement between the predicted and experimental termvalues of 41K133Cs isotopomer. Calculated intensity distributions in the A ~ b --> X LIF progressions are also consistent with their experimental counterparts.