High resolution laser spectroscopy up to the dissociation limit of the NaK B 1Π state, and predissociation near the dissociation limit

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Abstract
Doppler‐free high resolution spectrum of the B 1Π(v’,J’)–X 1Σ+(v‘,J‘) transitions of 23Na39K was measured by the optical–optical double resonance (OODR) polarization spectroscopy. The transition lines up to the v’=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 Å was calculated by the RKR method, and the inverse‐power coefficient was determined by analyzing the long‐range RKR turning points. The B 1Π 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 1Π and (2)3Σ+ states, and the potential curves are expected to cross around the inner turning point of the B 1Π (v’=34) level.