HIGH-RESOLUTION LASER SPECTROSCOPY UP TO THE DISSOCIATION LIMIT OF THE NAK B1-PI STATE, AND PREDISSOCIATION NEAR THE DISSOCIATION LIMIT

Doppler-free high resolution spectrum of the B 1-PI(upsilon',J')-X 1-SIGMA+ (upsilon",J") transitions of (NaK)-Na-23-K-39 was measured by the optical-optical double resonance (OODR) polarization spectroscopy. The transition lines up to the upsilon' = 43 level, which was estimated to be 1.8 cm-1 below the dissociation limit, were observed. The potential energy curve for internuclear distance from 3.25 to 15.6 angstrom was calculated by the RKR method, and the inverse-power coefficient was determined by analyzing the long-range RKR turning points. The B PI-1 state dissociates to Na(3s2S1/2) + K(4p2P3/2) atoms without a potential hill near the dissociation limit. The dissociation energy was determined to be 1324.3 +/- 0.3 cm-1 from the LeRoy-Bernstein plots. Remarkable line broadenings were observed for transitions higher than the dissociation energy to Na(3s2S1/2) + K(4p2P1/2) atoms. This is identified as originating from the predissociation to Na(3s2S1/2) + K(4p2P1/2) atoms. The predissociation is shown to be caused by a spin-orbit interaction between the B PI-1 and (2) 3-SIGMA+ states, and the potential curves are expected to cross around the inner turning point of the B PI-1 (upsilon' = 34) level.