IMPROVED POTENTIAL ENERGY CURVE AND MOLECULAR CONSTANTS FOR THE $A^{3}\Pi_{1u}$ STATE OF $I_{2}$

$^{a}$D.R.T. Appadoo, R.J. Le Roy, P.F. Bernath, S. Gerstenkorn, P. Luc, J. Verg\'{e}s J. Sinzelle, J. Chevillard and V. D'Aignaux, J. Chem. Phys. 104, 903-913 (1996).$^{b}$ T. Yukiya, N. Nishimiya and M. Suzuki, J. Mol. Spectrosc. 182, 271-279 (1997).Author Institution: Guelph-Waterloo Centre for Graduate Work in Chemistry and Biochemistry, University of WaterlooSome years ago we reported an analysis of a high resolution absorption spectrum for the $A_{3}\Pi_{1u} - X^{1}\Sigma^{+}_{g}$ system of $I_{2}$ consisting of approximately 9700 lines from 79 bands spanning the vibrational range $\nu^{\prime} = 0 - 35$ and $\nu^{\prime\prime} = 3 - 17.^{a}$ Results were presented in the forms both of empirical Dunham-type expansions and of near-dissociation expansion (NDE) expressions for the band constants of the A-state. Because of the use of NDE's, the resulting expressions were expected to be fairly reliable for extrapolation to dissociation $(v_{\mathcal{D}} = 55.57(\pm0.01))$. Shortly thereafter, $Yukiya et al.^{b}$ reported additional high resolution absorption data spanning the range $\nu^{\prime} (A) = 16 - 45$, and showed that the Appadoo et al.$^{a}$ NDE expression for $B_{\nu}$ did not, in fact, extrapolate reliably. However, they analyzed their results only in terms of a set of band constants for levels $\nu^{\prime} (A) = 16 - 45$. The present paper describes a comprehensive analysis of both data sets (which together span 99.2% of the potential well) which critically compares the utility of Dunham expansions vs. NDE expressions vs. direct-potential-fit techniques, and yields an optimum description of this system