500 nm system of RbCs: assignments and intensity anomalies

We have investigated the RbCs 500 nm system by mass-resolved resonance enhanced two-photon ionization in a cold molecular beam. The 4 3Pi0 v' = 10-39, 4 3Pi1 v' = 14-28, and 6 1Sigma+ v' = 12-28 <-- X 1Sigma+ v'' = 0 transitions have been observed and assigned for the first time. The 4 3Pi0 v' <-- X 1Sigma+ v'' = 0 transitions abnormally show double maxima of the vibronic-band intensity distribution around v' = 22 and 38. The intensities of the transitions to the lower vibrational levels (4 3Pi0 v' = 10-32) are explained well by the direct transitions from the X 1Sigma+ v'' = 0 level following the Franck-Condon principle. The transitions to the higher vibrational levels (4 3Pi0 v' > or = 33) borrow intensities through the interaction with nearby 6 1Sigma+ perturber levels.