The stepwise three-step three-colour I2(D0+u, vD, JD 0+g, v0, J0 B0+u, vB, JB X0+g, vX, JX) laser excitation scheme and rotational as well as rovibrational energy transfer processes in the 0+g state induced by collisions with He and Ar atoms are used for determination of rovibronic level energies of the weakly bound 0+g state correlating with the I(2P1/2) + I(2P1/2) dissociation limit. Dunham coefficients of the state, Yi0 (i = 0–3), Yi1 (i = 0–3) and Y02 for the = 0–16 and ≈ 14–135 ranges as well as the dissociation energy of the state, De, and equilibrium I–I distance of the state, Re, are determined. The potential energy curve of the state constructed using these constants is also reported.

The stepwise two-step two-color and three-step three-color laser excitation schemes are used for selective population of rovibronic levels of the first-tier ion-pair E0(g)(+) and D0(u)(+) states of molecular iodine and studies of non-adiabatic transitions to the D and E states induced by collisions with M = I(2)(X) and H(2)O. Collection and analysis of the luminescence after excitation of the v(E) = 8, 13 and v(D) = 13, 18 vibronic levels of the E and D states in the pure iodine vapor and the gas-phase mixtures with H(2)O provide rate constants for the non-adiabatic transitions to the D and E state induced by collisions with these molecules. Vibrational distributions for the [formula: see text] collision-induced non-adiabatic transitions (CINATs) are obtained. Rather strong λ(lum)(max) ≈ 3400 Å luminescence band is observed in the I(2) + H(2)O mixtures, whereas its intensity is ~100 times less in pure iodine vapor. Radiative lifetimes and quenching rate constants of the I(2)(E,v(E) = 8, 13 and D,v(D) = 13, 18) vibronic state are also determined. Rate constants of the [formula: see text], v(E) = 8-54, CINATs are measured again and compared with those obtained earlier. New data confirm resonance characters of the CINATs found in our laboratory about 10 years ago. Possible reasons of differences between rate constant values obtained in this and earlier works are discussed. It is shown, in particular, that differences in rate constants of non-resonant CINATs are due to admixture of water vapor in iodine.

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