Energy and radiative properties of the (3)1Π and (5)1Σ+ states of RbCs: Experiment and theory
We combined high-resolution Fourier-transform spectroscopy and large-scale electronic structure calculation to study energy and radiative properties of the high-lying (3)1Π and (5)1Σ+ states of the RbCs molecule. The laser-induced (5)1Σ+(4)1Σ+(3)1Π-A(2)1Σ+ b(1)3Π fluorescence (LIF) spectra were recorded by the Bruker IFS-125(HR) spectrometer in the frequency range ν 5500 to 10000cm-1 with the instrumental resolution of 0.03 cm-1. The rotational assignment of the observed LIF progressions, which exhibit irregular vibrational-rotational spacing due to strong spin-orbit interaction between A1Σ+ and b3(Π) states was based on the coincidences between observed and calculated energy differences. The required rovibronic term values of the strongly perturbed A-b complex have been calculated by a coupled-channels approach for both 85Rb133Cs and 87Rb133Cs isotopologs with accuracy of about 0.01 cm-1, as demonstrated in A. Kruzins et al. [J. Chem. Phys. 141, 184309 (2014)]. The experimental energies of the upper (3)1(Π) and (5)1Σ+ states were involved in a direct-potential-fit analysis performed in the framework of inverted perturbation approach. Quasirelativistic ab initio calculations of the spin-allowed (3)1Π,(5)1Σ+- (1-4)1Σ+(1-3)1Π transition dipole moments were performed. Radiative lifetimes and vibronic branching ratios of radiative transitions from the (3)1Π and (5)1Σ+ states were evaluated. To elucidate the origin of the Λ-doubling effect in the (3)1Π state, the angular coupling (3)1Π-(1-5)1Σ+ electronic matrix elements were calculated and applied for the relevant q-factors estimate. The intensity distributions simulated for the particular (5)1Σ+(3)1Π-A-b LIF progressions have been found to be remarkably close to their experimental counterparts.