A considerable difference of iodine emission spectra after optical-optical double resonance excitation of the E0+g, vE ≤ 19, JE ≈ 55 and JE ≈ 85 rovibronic levels is observed. The latter include strong transitions from the γ1u ion-pair state to valence ones. This feature is interpreted as a result of hyperfine coupling of near-resonant E0+g, vE ≤ 19, JE ≤ 81 and γ1u, vγ ≤ 18, Jγ ≤ 80 states. The hyperfine matrix element and dipole moment functions of transitions from the γ state are estimated. The hyperfine g/u mixing of the iodine ion-pair states is observed for the first time. © 2007 IOP Publishing Ltd.