Optical-optical double resonance spectroscopy and quantum scattering calculations are used to obtain total rate constants, electronic branching ratios, and vibrational product state distributions for non-adiabatic transitions among the first-tier ion-pair states of the I2 molecule excited to the E 0g+, vE = 8, 19, JE ≈ 55 rovibronic levels in collisions with I2, He, Ar, Kr and Xe. Theoretical predictions agree well with the experiment and reveal that the near-resonant E 0g+ → D0u+ transition dominates for collisions with He, while somewhat more statistical distributions are typical of collisions with heavier rare gas atoms. This trend is correlated to the dipole polarizability of the collision partner that determines the strength of intermolecular interactions. © 2006 Elsevier B.V. All rights reserved.