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 K39Li6 show transitions to high vibrational levels of both the XΣ+1 and aΣ+3 electronic states. These include 147 transitions into six vibrational levels of the aΣ+3 state, which lie between 7 and 88cm-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 )≃D-C6/R6-C8/R8, yields complete, plausible potential curves for this state. The best fits converge to remarkably similar solutions which indicate that De=287(±4)cm-1 and Re=4.99(±0.09)Å for the aΣ+3 state of KLi, with ωe=47.3(±1.4) and 44.2(±1.5)cm-1 for K39Li6 and K39Li7, 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 Li2, K2, Na2, and NaK.