Fitting an experimental potential energy curve for the 10(0)[4Π] electronic state of NaCs.

We present experimentally determined potential energy curves for the 10(0)[4Π] electronic state of NaCs. The 10(0)[4Π] state exhibits a double-minimum structure, resulting in a distinctive bound-free fluorescence signature. The perturbation facilitated optical-optical double resonance method was used to obtain Doppler-free excitation spectra corresponding to rovibrational transitions to the 10(0)[4Π] state.