DIRECT MEASUREMENT OF THE GROUND-STATE DISSOCIATION-ENERGY OF NA-2

We report a direct measurement of the Na-2 X(1) Sigma(g)(+) ground-sta te dissociation energy. Three spectroscopic measurements are combined to directly yield the energy of the lowest (upsilon=O) vibrational lev el relative to the free-atom limit. The X(1) Sigma(g)(+) (upsilon=0--> 31) splitting is measured by double-resonance spectroscopy; X(1) Sigma (g)(+)(upsilon=31)-->A(1) Sigma(u)(+)(upsilon'=165) by laser-induced f luorescence; and free atoms-->A1 Sigma(u)(+)(upsilon'=165) by photoass ociation of ultracold atoms. The result is D-0=5942.6880(49) cm(-1). T he uncertainty is a factor of 6 improvement over a previous (indirect) determination.