15min:

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 D_e =287(\pm 4)~ cm^-1 and R_e= 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.