| Experimental spectroscopic studies have revealed many interesting phenomena in the excited triplet states of NaK. For example, the excited 33pi and 43pi electronic states of the NaK molecule exhibit an avoided crossing, leading to anomalous behavior of many features of the ro-vibrational energy levels belonging to each state. The nonadiabatic coupling between these states has been formulated exactly using diabatic potential curves. Using our ab initio calculations of the diabatic curves as a starting point, we used a nonlinear fitting routine to adjust the potential curves and the coupling between them to fit the observed spectra. We accurately fit 358 measured energies of ro-vibrational energy levels, including 74 levels that exhibited clear perturbations, with an rms deviation of 0.23 cm -1.; Another feature of interest is the hyperfine structure of various excited triplet states. Changes in the hyperfine structure can be attributed, in part, to changes in the hyperfine coupling constant bF (the Fermi contact constant), thereby providing a sensitive probe of the electronic wave function. We have developed a model for bF based on using diabatic wave functions and have applied it to the 1 3Delta, 43Sigma+, 53Sigma +, 33pi, and 43pi states. The patterns of the experimentally observed hyperfine levels exhibit considerable variation, which can be interpreted by associating different b F values with different classes of diabatic states. In particular, the data and calculations for the 33pi electronic states confirm that there is a dramatic difference in the hyperfine structure between ro-vibrational levels that are localized in different regions of the internuclear separation R, and that this difference can be attributed to differences in the electronic wave function. |
