Spectroscopic constants and potential energy curve of the iodine weakly bound 1u state correlating with the I(2P1/2) + I(2P1/2) dissociation limit

The stepwise three-step three-color laser population of the I2(β1g, νβ, Jβ) rovibronic states via the B0u+, νB, JB rovibronic states and rovibronic levels of the 1u(bb) and 0g+(bb) states mixed by hyperfine interaction is used for determination of rovibronic level energies of the weakly bound I2(1u(bb)) state. Dunham coefficients of the state, Yi0 (i = 0–3), Yi1 (i = 0–2), Y02 and Y12 for the v1u = 1–5, 8, 10, 15 and J1u ≈ 9–87 ranges, the dissociation energy of the state, De, and equilibrium I–I distance, Re, as well as the potential energy curve are determined. There are aperiodicities in the excitation spectrum corresponding to the β, νβ = 23, Jβ ← 1u(bb), ν1u = 4, 5, J1u progressions in the I2 + Rg = He, Ar mixture, namely, a great number of lines which do not coincide with the R or P line progressions. Their positions conflict with the ΔJ-even selection rule. Furthermore, they do not correspond to the ΔJ-odd progression. (paper)