Fourier-transform spectroscopy and deperturbation analysis of the spin-orbit coupled A ¹Σ⁺ and b ³Π states of KRb

Fourier-transform A¹Σ⁺ - b³Π → X¹Σ⁺ laser-induced fluorescence spectra were recorded for the natural mixture of ^39,41K^85,87Rb isotopologues produced in a heatpipe oven. Overall 4200 rovibronic term values of the spin-orbit coupled A¹Σ⁺ and b³Π states were determined with an uncertainty of about 0.01 cm^-1 in the energy range [10 850, 14 200] cm^-1 covering rotational quantum numbers J' ∈ [3, 280]. Direct deperturbation analysis of the A ∼ b complex performed within the framework of the A¹Σ⁺ ∼ b³Π_Ω=0,1,2 coupled-channel approach reproduced experimental data with a standard deviation of 0.004 cm^-1. Initial parameters of the internuclear potentials and spin-orbit coupling functions along with the relevant transition dipole moments were obtained by performing the quasi-relativistic electronic structure calculations. The mass-invariant molecular parameters obtained from the fit were used to predict energy and radiative properties of the A ∼ b complex for low J levels of ³⁹K⁸⁵Rb as well as for ⁴¹K⁸⁷Rb isotopologues, allowing us to identify the most reasonable candidates for the stimulated Raman transitions between the initial uppermost vibrational levels of the a³Σ⁺ and X¹Σ⁺ states, the intermediate levels of the A ∼ b complex, and the lowest absolute ground X¹Σ⁺(v = 0, J = 0) state.