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. Spectroscopic constants were determined to summarize data belonging to inner well, outer well, and above the barrier regions of the electronic state. The Rydberg-Klein-Rees and inverted perturbation approach methods were used to construct a potential which reproduces the experimental rovibrational energies within a root-mean-square deviation of 2.33 cm. An alternative to the pointwise potential approach was also used to determine the potential energy curve by directly fitting an expanded Morse oscillator functional form. Advantages between the two approaches as they apply to double minimum wells are discussed.