15min:

MARJAN MOHAMMADI AND ROBERT J. LE ROY, Guelph-Waterloo Centre for Graduate Work in Chemistry and Biochemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.

Some years ago we reported an analysis of a high resolution absorption spectrum for the A ³ _1u-X ¹ _g⁺ system of I₂ consisting of approximately 9700 lines from 79 bands spanning the vibrational range v'\!=\!0-35 and v''\!=\!3-17.\footnote D.R.T. Appadoo, R.J. Le Roy, P.F. Bernath, S. Gerstenkorn, P. Luc, J. Vergès J. Sinzelle, J. Chevillard and Y. D'Aignaux, J. Chem. Phys. 104, 903--913 (1996).~ 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_\mathcalD\!=\!55.57(\pm 0.01)). Shortly thereafter, Yukiya et al. reported additional high resolution absorption data spanning the range v'(A)\!=\! 16-45, and showed that the Appadoo et al. ^a NDE expression for B_v did not, in fact, extrapolate reliably. However, they analyzed their results only in terms of a set of band constants for levels v'(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.