Excitation of NaK molecules in a collimated molecular beam by a single mode tunable argon laser with subhyphen;Doppler resolution allows selective population of definite vibrational rotational levels (vprime;,Jprime;) in theDthinsp;1Pgr;hyphen;state. The resultant fluorescence consists of a singlet spectrum in the 470ndash;570 nm range and a triplet spectrum in the 625ndash;715 nm range. The analysis of the triplet fluorescence, which consists of discrete lines and of a modulated continuum, allows the determination of theathinsp;3Sgr;+potential and yields very precise values for the dissociation energies in theathinsp;3Sgr;+andXthinsp;1Sgr;+states, which are measured asDe(3Sgr;+) =204plusmn;4 cmminus;1andDe(1Sgr;+) =5269plusmn;6 cmminus;1. For some excitation wavelengths a fluorescence spectrum with discrete lines and with a doublehyphen;modulated continuum is observed which is assigned to rsquo;rsquo; Condon internal diffractionrsquo;rsquo; bands terminating close below and above the dissociation limit of theXthinsp;1Sgr;+state. Its relevance for the determination of the upper and lower potential curves is discussed.
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