HOUSSAM SALAMI, AMANDA J. ROSS, PATRICK CROZET, Université Lyon 1; CNRS; LASIM UMR 5579, 43 Bd du 11 novembre 1918, F-69622 Villeurbanne, France; ROBERT J. LE ROY, Guelph-Waterloo Centre for Graduate Work in Chemistry and Biochemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada; PAWEL KOWALCZYK, Institute of Experimental Physics, Warsaw University, ul. Hoza 69, 00681 Warsaw, Poland; WLODZIMIERZ JASTRZEBSKI, Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02668 Warsaw, Poland.
Fourier transform resolved fluorescence spectra of the 39K6Li molecule have been recorded in the near-infrared, following laser excitation (Coumarin 6 dye) to high vibrational levels of the B 1 state. The FT spectra show transitions to high vibrational levels of both the X 1 + and a 3 + electronic states. These include 147 transitions into six vibrational levels of the a 3 + state, which lie between 7 and 88 cm-1 below the dissociation asymptote. Unfortunately, their energies span less than 30% of the total ground-triplet-state well depth, and even vibrational assignment is not immediately obvious. However, fitting those data to eigenvalues of analytical model potential functions whose outer limbs incorporate the theoretically predicted long-range form, V(R) eq D - C6/R6 - C8/R8 , yields complete, plausible potential curves for this state. The best fits converge to remarkably similar solutions which strongly suggest that the lowest observed level is v=5. Equilibrium parameters from these fits indicate De =287(\pm 4)~ cm-1 and Re= 4.99(\pm 0.09) Å for the a 3 + state of KLi, with e= 47.3(\pm 1.5) and 44.2(\pm 1.5)~ cm-1 for 39K6Li and 39K7Li, respectively. Properties of the resulting potential are compared with those of an ab initio potential and with those of the analogous states of Li2, K2, Na2 and NaK. The optimized potential curve predicts that the last bound level of both isotopologues lies less than 0.002~ cm-1 below the atomic asymptote, but since these binding energies are much smaller than the current uncertainty in the ground state dissociation energy (\pm 0.07~ cm-1), they remain subject to caution.