B3Π +u—X1∑ +g system of 127I2: rotational analysis and long-range potential in the B3Π +u state

Abstract

The results of detailed rotational and term-value analyses involving some 7000 lines with 58 levels in B³Π_0⁺u(4 ⩽v⩽ 77) and 6 levels in X¹∑⁺_g(0 ⩽v⩽ 5) are given. For the B³Π_0⁺u state the rotational constants B_v can be represented by B_v= [graphic omitted]c_n(v+½)ⁿ, but neither the vibrational levels nor the centrifugal stretching constants follow simple polynomials in (v+½). At high v, ([graphic omitted])^10/7 is linear in E_v and a short extrapolation leads to a value of the limit, 20 043.208 ± 0.033 cm^–1, relative to X¹∑⁺_g(v= 0, J= 0). The highest bound vibrational level has v= 87. An RKR potential energy curve has been calculated for the B³Π_0⁺u state, and a consistent value of the limit, 20 043.220 ± 0.015 cm^–1, is obtained from a fit to an attractive part of the curve near the limit, assuming a potential V(r)=–C₅/r⁵–C₆/r⁶–C₈/r⁸. Values of the long-range interaction constants have been obtained: the term in r^–6 is not negligible even at internuclear distances as large as 20 Å. The ground-state dissociation energy, D₀(I₂) is found to be 12 440.1 cm^–1, corresponding to 35.568 kcal mol^–1 or 148.81₅ kJ mol^–1.