Use of bound-free structured spectra in determining RKR potentials:: The 43Πg state of Na2

The RKR potential function of the Na-2 4(3)pi(8), state determined by Y. Liu, H. Chen, J. Li, D. Chen, Li Li, and R. W. Field (J. Mot. Spectrosc. 192, 32 (1998)) is checked for its ability to reproduce the experimental continuum of the Na-2 4(3)pi(g)(nu = 12, N = 23) --> a(3)Sigma (+)(u) bound-free transition observed b G. Lazarov, A.M. Lyyra, Li Li, and J. Huennekens (J. Mol. Spectrose. 196, 259 (1999)). A significant difference between the experimental and simulated bound-free spectra is found even though about 300 rovibrational term values spanning the range of nu = 2-25 vibrational quantum numbers and N = 6-15 rotational quantum numbers were used for the construction of this RKR potential. The new potential curve of the Na-2 4(3)pi(g), state was determined by applying the two-step global fit procedure of V. S. Ivanov, V. B. Sovkov, Li Li, A. M. Lyyra, G, Lazarov, and J. Huennekens (J. Mol. Spectrosc. 194, 147 (1999)) to a set of all the available spectroscopic data on the Na-2 4(3)II(g) state. This 4(3)II(g) state is perturbed by the 6(3)Sigma (+)(g) state through L-uncoupling. The "nonperturbed" RKR potential is constructed from a subset of the nonperturbed rovibrational term values solely. The potential curve constructed from the nonperturbed levels only is very close to the potential curve obtained by the two-step global fit and reproduces the term values and the bound-free continuum with the same accuracy. (C) 2001 Academic Press.