DIRECT-POTENTIAL-FIT ANALYSIS FOR Li$_2(a\,^3\Sigma_u^+)$ AND EXTENSIONS OF THE `MLR' POTENTIAL FUNCTION MODEL
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Date
2008
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Ohio State University
Abstract
While a number of studies of the weakly bound $a\,^3\Sigma_u^+$ state of $^{6,6}$Li$_2$ and $^{7,7}$Li$_2$ have been reported, the only potential functions obtained for these systems were based on point-wise semiclassical RKR curves generated from Dunham or near-dissociation expansions for the vibrational energies and $B_v$ constants.} {\bf 44A}, 1369 (1988); (b) C.\ Linton {\em et al., J.\ Chem.\ Phys.}\ {\bf 91}, 6036 (1989); (c) W.T.\ Zemke and W.C.\ Stwalley, {\em J.\ Phys.\ Chem.}\ {\bf 97}, 2053 (1993); (d) A.J.\ Moerdijk {\em et al., Phys.\ Rev.\ Lett.}\ {\bf 72}, 40 (1994); (e) C.\ Linton {\em et al., J.\ Mol.\ Spectrosc.}\ {\bf 196}, 20 (1999).}~ Moreover, to date the data for $^{6,6}$Li$_2$ and $^{7,7}$Li$_2$ have always been treated independently, so the effect of Born-Oppenheimer breakdown in this system is unknown. The present work reports a combined-isotopologue direct-potential-fit analysis of all available fluorescence and PAS data for the $1\,^3\Sigma_g^+ -a\,^3\Sigma_u^+$ and $2\,^3\Pi_g -a\,^3\Sigma_u^+$ systems of $^{6,6}$Li$_2$ and $^{7,7}$Li$_2$. The analytic potential energy functions used to characterize the $a\,^3\Sigma_u^+$ and $1\,^3\Sigma_g^+$ states are extended versions of the `Morse-Long-Range' (MLR) potential model which explicitly incorporates the theoretically-known inverse-power long-range behaviour within a unified potential function form.}\ {\bf 125}, 164310 (2006);\, R.J.\ Le Roy and R.D.E.\ Henderson, {\em Mol.\ Phys.}\ {\bf 105}, 663 (2007).}~ `Adiabatic' Born-Oppenheimer breakdown functions are required to yield a consistent analysis of the data for the two isotopologues, and they yield isotopologue-dependent well depths for these two states. The $-C_3/r^3$ limiting long-range behaviour of the $1\,^3\Sigma_g^+$-state potential presented a challenge to the use of the MLR potential function form with two or more long-range terms, and this led to better understanding and a significant extension of the MLR model.
Description
(a) F. Martin et al., Spectrochim. ActaR.J. Le Roy, Y. Huang and C. Jary, J. Chem. Phys.
Author Institution: Guelph-Waterloo Centre for Graduate Work in Chemistry and; Biochemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada; Universite Lyon 1; CNRS; LASIM UMR 5579, 43 Bd du 11 novembre; 1918, F-69622 Villeurbanne, France; Physics Department, University of New Brunswick, Fredericton, NB; E3B 5A3, Canada
Author Institution: Guelph-Waterloo Centre for Graduate Work in Chemistry and; Biochemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada; Universite Lyon 1; CNRS; LASIM UMR 5579, 43 Bd du 11 novembre; 1918, F-69622 Villeurbanne, France; Physics Department, University of New Brunswick, Fredericton, NB; E3B 5A3, Canada