Bound–free 1 3Π→1 3Σ+ emission from the NaK molecule: Determination of the 1 3Σ+ repulsive wall above the dissociation limit

We report the observation of bound–free emission on the 1 3Π→1 3Σ+ band of the NaK molecule. The spectra, which consist of oscillating continua in the near-infrared, have been analyzed to determine parameters describing the repulsive wall of the 1 3Σ+ state above the dissociation limit. Spectra calculated using a potential of the form Ae−BR +C for the 1 3Σ+ state were compared to experimental spectra to yield the following values: A=5.94×105 cm−1, B=1.605 Å−1, C=−220.520 cm−1. This potential, which is referenced to the bottom of the RKR 1 3Σ+ well (De =209.1 cm−1), is valid over the range R=3.4–4.5 Å (R=6.4–8.5 a.u.). The relative transition dipole moment of the 1 3Π→1 3Σ+ band has also been determined over a limited range in R (7.5<R<8.9 a.u.) through the study of relative intensities of various maxima within each oscillating spectrum. In the simulated spectra, the dipole moment was represented by a functional form D(R)=m(R−R0)+D0 where D0 was used to normalize the results to a recent theoretical calculation (D0=1.07 a.u. R0=8.034 a.u.). The best fit for the parameter m was determined to be 0.121±0.029 in atomic units.