The 4 3 S ¿ state of NaK : Potential energy curve and hyperfine structure

High-resolution spectra, including hyperfine structure, have been observed for numerous vibrational-rotational levels (v ,N) of the 4 S Rydberg state of the NaK molecule. The data have been used to construct a Rydberg–Klein–Rees potential curve, and this molecular potential has been further refined using the inverse perturbation approximation method. Bound-free emission from the 4 S electronic state to the repulsive a(1) S state has also been measured and used to determine both the absolute vibrational numbering and the transition dipole moment function M (R). The experimentally derived potential curve and M (R) are compared with recent theoretical calculations of Magnier et al.; the agreement is very good. Each of the levels (v ,N) is typically split into three sets of sublevels by the Fermi contact interaction bI"S. Further splitting ~of order 0.004 cm) has been attributed to the spin-rotation interaction gN"S. The patterns observed exhibit a clear transition from Hund’s case bbS for small N toward Hund’s case bbJ for large N . The data can be fitted very well using a theoretical model based on setting up and diagonalizing a 12312 Hamiltonian matrix with two adjustable parameters (b and g!. The values of b that fit the data best are ;(0.99 60.04)310 cm, with a weak dependence on v . The best fit values of g are in the range 1 – 6310 cm and depend strongly on v . The values of g appear to exhibit anomalous structure for (v ,N) levels perturbed by nearby levels of the 3 P state. © 2003 American Institute of Physics. @DOI: 10.1063/1.1590638#