The first rotationally resolved high resolution excitation spectrum of RbCs is obtained near 520 nm by resonance enhanced two photon ionization study. The excited electronic state is assigned to the 5 (1)Sigma (+) state by the spectrum analysis and comparison with ab initio calculations. The spectroscopic constants of the 5 (1)Sigma (+) state are determined to be T-e = 18 564.560(76) cm(-1), omega (e) = 39.193(25) cm(-1), R-e = 4.951(5) Angstrom. The Rydberg-Klein-Rees potential curve is constructed and compared with theoretical calculations. Avoided crossings between the 5 (1)Sigma (+) and 6 (1)Sigma (+) states of RbCs are observed.