  We combined high-resolution Fourier-transform spectroscopy and large-scale
electronic structure calculation to study energy and radiative properties of
the high-lying (3)1{\Pi} and (5)1{\Sigma}+ states of the RbCs molecule. The
laser-induced (5)1{\Sigma}+(4)1{\Sigma}+(3)1{\Pi}-A(2)1{\Sigma}+ b(1)3{\Pi}
fluorescence (LIF) spectra were recorded by the Bruker IFS-125(HR) spectrometer
in the frequency range {\nu} 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 A1{\Sigma}+ and b3(\Pi) 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(\Pi) and (5)1{\Sigma}+ 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)1{\Pi},(5)1{\Sigma}+- (1-4)1{\Sigma}+(1-3)1{\Pi} transition dipole moments
were performed. Radiative lifetimes and vibronic branching ratios of radiative
transitions from the (3)1{\Pi} and (5)1{\Sigma}+ states were evaluated. To
elucidate the origin of the {\Lambda}-doubling effect in the (3)1{\Pi} state,
the angular coupling (3)1{\Pi}-(1-5)1{\Sigma}+ electronic matrix elements were
calculated and applied for the relevant q-factors estimate. The intensity
distributions simulated for the particular (5)1{\Sigma}+(3)1{\Pi}-A-b LIF
progressions have been found to be remarkably close to their experimental
counterparts.
