Optical population of gerade and ungerade iodine ion-pair states via MI2 vdW complexes of valence states correlating with the third dissociation limit, M = I2, Xe

Graphical abstract: We study luminescence as well excitation spectra of luminescence observed after three-step, λ1 + λf + λ1, λ1 = 5321–5508.2 A, λf = 10644.0 A, laser excitation of pure iodine vapour and I2 + Xe mixtures at room temperature. We discuss three alternative mechanisms of these processes. In our opinion, the mechanism including the MI2, M = I2, Xe, complexes is the most probable at least in the λ1 ≈ 5321–5480 A, λ1 ≈ 5508 A spectral ranges and for population of the states which luminescence occur at λlum ≈ 3400 A. Highlights: ► We populated gerade and underade ion-pair states in three-step, two-color transitions. ► We measured excitation spectra of luminescence from these states. ► We discussed possible mechanisms of population of the states. ► We conclude that the mechanism including vdW complexes is the most probable. - Abstract: The results of measurements and analysis of excitation spectra of the λlum = 2350 A luminescence corresponding to I2(D0+u → X0+g) transition as well as luminescence at λlum = 3400 A, where I2(D'2g → A'2u and/or β1g → A1u) transitions occur, observed after three-step, λ1 + λf + λ1, λ1 = 5321–5508.2 A, λf = 10644.0 A, laser excitation of pure iodine vapour and I2 + Xe mixtures at room temperature are presented. Luminescence spectra in the λlum = 2200–3500 A spectral range are also analyzed. We discuss three alternative mechanisms of optical population of the IP states. In our opinion, the mechanism including the MI2, M = I2, Xe, complexes is the most probable at least in the λ1 ≈ 5321–5480 A, λ1 ≈ 5508 A spectral ranges and for population of the states which luminescence occur at λlum ≈ 3400 A.