The ground state Χ1Σ+ of NaK revisited

Laser-induced fluorescence (LIF) optical spectra of the D (II)-I-1-X(1)Sigma(+) system of the NaK molecule have been reinvestigated. In this new analysis, quantum numbers have been assigned to 3000 selected fluorescence lines for a wide range of vibrational and rotational levels (J less than or equal to 149, upsilon' less than or equal to 23, upsilon " less than or equal to 47). A new set of constants of the X(1)Sigma state (Dunham type coefficients) and term values of the D-1 II state have been determined by a weighted least-squares fit of the LIF optical lines of the D-X system, some lines of the C-X system, and microwave spectral data reported recently. Constants for X (1)Sigma (in cm(-1)) are as follows: omega(e) = 123.993, omega(e)x(c) = 0.3045, B-e = 0.095229, and alpha(e), = 4.48 x 10(-4). The equilibrium internuclear distance is r(c) = 3.49903 Angstrom, very little changed from the microwave value. (C) 1998 Academic Press.