Laser spectroscopic measurement of weakly attractive interatomic potentials: The Na+Ar interaction

Abstract

The van der Waals molecule NaAr has been prepared in a supersonic expansion of sodium vapor plus a few percent argon in a helium carrier gas. The fluorescence excitation spectrum of the X2Σ+→A2Π optical transition has been analyzed and the vibrational and rotational spectroscopic constants have been derived from this analysis. The ground state interatomic potential implied by these parameters is consistent with that measured or calculated by other workers. The observed Λ-doubling of the A2Π state suggests that the coupling between the A2Π and B2Σ states may be stronger than would be expected from previous calculations. The magnitude and sign of the dependence of the fine-structure splitting of the A2Π state on vibrational quantum number suggests that the van der Waals bond produces an observable perturbation of the core electrons of the sodium atom.