High resolution resonance enhanced two photon ionization spectroscopy of RbCs in a cold molecular beam

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 1Σ+ state by the spectrum analysis and comparison with ab initio calculations. The spectroscopic constants of the 5 1Σ+ state are determined to be Te=18 564.560(76) cm−1, ωe=39.193(25) cm−1, Re=4.951(5) Å. The Rydberg–Klein–Rees potential curve is constructed and compared with theoretical calculations. Avoided crossings between the 5 1Σ+ and 6 1Σ+ states of RbCs are observed.