Investigation of the D 1Î state of NaK by polarisation labelling spectroscopy

Two-colour polarisation labelling experiments measuring the D-X system of NaK have furnished observations of the D 1Π state of NaK up to v″ = 42. The last observed level is located 7 cm−1 below the Na(3p 2P3/2) + K(4s) atomic asymptote, 22247.15 cm−1 above the minimum of the electronic ground state, clearly indicating the dissociation products of this state. The vibrational progressions all exhibit irregular intervals, predominantly because of strong interactions with the nearby d 3Π state, which also dissociates to Na(3p) + K(4s) atoms. The polarisation data have been combined with some resolved fluorescence D-X transitions, and analysed by fitting to spectroscopic parameters and to an analytical potential curve. A full deperturbation treatment has not been attempted, but a 'robust' weighting scheme has been used to reduce the influence of levels that cannot be properly represented by a single channel model. Parameters determined in a fit to a potential curve include Te = 20090.18 ± 0.02 cm−1, well depth 2157.0 ± 0.3 cm−1, Re = 4.1547 ± 0.0002 Å, with an unweighted root mean square error of 0.12 cm−1 for 959 data.