Laser spectroscopic investigation of the X 2Σ1/2 state of the van der Waals molecule NaAr

The laser-excitation spectrum of the transition X ²Σ⁺ → A ²Π of NaAr has been investigated using a supersonic expansion of a mixture of sodium vapor and argon gas for production of the molecules. In comparison to preyous investigations the rotational constants of the vibrational levels ν″ = 2, 3 and 4 of the X ²Σ⁺ state could in addition be determined. From our results we deduce a value of R_e = 5.008(5) × 10^?10 m for the equilibrium internuclear distance and of D_e = 41.7(δ) cm^?1 for the well depth of the X ²Σ⁺ state.