Аннотация:We perform a high-resolution Fourier-transform spectroscopic study of the (4)1Pi state of the RbCs molecule by applying two-step (4)1Pi← A1Sig+ ∼ b3Pi ← X1Sig+ optical excitation followed by observation of the (4)1Pi → X1Sig+ laser-induced fluorescence (LIF) spectra. In many LIF progressions the collision-induced satellite rotational lines are observed, thus increasing the amount of term values and allowing us to estimate the Lambda-doubling effect in the (4)1Pi state. The direct potential fit (DPF) of experimental term values of 777 rovibronic levels of both 85RbCs and 87RbCs isotopologues is performed by means of the robust weighted nonlinear least-squares method. The DPF analysis based on the adiabatic approximation and analytical expanded Morse oscillator potential reveals numerous regular shifts in the measured level positions. The spectroscopic studies of the (4)1Pi state are supported by the electronic structure calculations including the potential energy
curves of the singlet- and triplet-state manifold and spin-allowed transition dipole moments. The subsequent estimates of radiative lifetimes and corresponding vibronic branching ratios elucidate a dominant contribution of the (4)1PI → A ∼ b channel into the total radiative decay of the (4)1Pi state. The relative intensity distributions simulated for (4)1Pi → X1Sig+ LIF progressions agree well with their observed counterparts even for the profoundly shifted levels of the entirely perturbed (4)1Pi state. To get insight into the origin of the intramolecular perturbations, the relevant spin-orbit- and L-uncoupling electronic matrix elements are evaluated.