A full analytic potential energy curve for the a 3Σ+ state of KLi from a limited vibrational data set

Fourier transform spectra of near-infrared laser-induced fluorescence in (KLi)-K-39-Li-6 show transitions to high vibrational levels of both the X (1)Sigma(+) and a (3)Sigma(+) electronic states. These include 147 transitions into six vibrational levels of the a (3)Sigma(+) state, which lie between 7 and 88 cm(-1) below the dissociation asymptote. Unfortunately, their energies span less than 30% of the well depth. However, fitting those data to eigenvalues of analytical model potential functions whose outer limbs incorporate the theoretically predicted long-range form, V(R)similar or equal to D-C-6/R-6-C-8/R-8, yields complete, plausible potential curves for this state. The best fits converge to remarkably similar solutions which indicate that D-e=287(+/- 4) cm(-1) and R-e=4.99(+/- 0.09) A for the a (3)Sigma(+) state of KLi, with omega(e)=47.3(+/- 1.4) and 44.2(+/- 1.5) cm(-1) for (KLi)-K-39-Li-6 and (KLi)-K-39-Li-7, respectively. Properties of the resulting potential are similar to those of a published ab initio potential and are consistent with those of the analogous states of Li-2, K-2, Na-2, and NaK.(C) 2007 American Institute of Physics.