The dispersed fluorescence spectrum of NaAr: Ground and excited state potential curves

The van der Waals molecule NaAr has been prepared by supersonic free jet expansion of a mixture of sodium, argon, and helium. The A ²Π←X ²Σ⁺ electronic transition has been excited by a tunable dye laser and the resulting A→X fluorescence has been studied. The dispersed fluorescence spectra display both discrete and diffuse features, corresponding to transitions from excited vibrational levels of the A state to bound and unbound levels of the X state. The characteristic reflection structure in the bound-free spectra permits an unambiguous assignment of the vibrational numbering in the A state. This assignment and the previously measured spectroscopic constants are used to calculate the potential curve of the A state. The discrete structure in the fluorescence spectra is analyzed and, together with the previous measurements, is used to determine the potential curve of the X state in the well region. The repulsive part of the X curve is then deduced through trial-and-error simulation of the biund-free spectra. The potential curves derived in this work are compared critically with results of several previous experimental and theoretical studies of NaAr.