Knowledge Bank

We report a. high resolution study of the $A2\Pi \leftarrow X2\Sigma$ transition in the van der $Waals1$ molecule NaAr by fluorescence excitation spectroscopy. The NaAr was formed by supersonic expansion of a mixture of 5% argon in helium passed through a heated oven containing sodium vapor. The fluorescence excitation spectrum of NaAr in the region 5935-5996 {\AA} was measured using the output of a cw tuneable dye laser as an excitation source. Nine vibronic bands, arising from the ground vibrational level of the $X2\Sigma$ state, were observed. The rotational structure of those bands has been resolved and assigned. On the basis of these assignments, molecular constants for the ground and excited states have been determined.