Use of bound-free structured spectra in determining RKR potentials: The 4(3)Pi(g) state of Na-2

The RKR potential function of the Na-2 4(3)II(8), state determined by Y. Li u, 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 contin uum of the Na-2 4(3)II(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 exper imental and simulated bound-free spectra is found even though about 300 rov ibrational term values spanning the range of nu = 2-25 vibrational quantum numbers and N = 6-15 rotational quantum numbers were used for the construct ion of this RKR potential. The new potential curve of the Na-2 4(3)II(g), s tate 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. Mot. Spectrosc. 194, 147 (1999)) to a set of all the available spectroscop ic data on the Na-2 4(3)II(g) state. This 4(3)II(g) state is perturbed by t he 6(3)Sigma (+)(g) state through L-uncoupling. The "nonperturbed" RKR pote ntial is constructed from a subset of the nonperturbed rovibrational term v alues solely. The potential curve constructed from the nonperturbed levels only is very close to the potential curve obtained by the two-step global f it and reproduces the term values and the bound-free continuum with the sam e accuracy. (C) 2001 Academic Press.