The “approach-induced” and collision-induced transitions from low, vE=8–23, vibronic levels of the I2(E) state

Abstract The dependences of the I 2 ( E0 g + ,v E ,J E → I 2 ( X ) D0 u + ,v D ,J D ) transition rate constants on the vibrational v E , v D , rotational J E , J D quantum numbers, energy gaps, and Franck–Condon factors of the combined levels have been studied in the range v E =8–23. The extremely long-range near-resonance I 2 ( E ,v E → I 2 ( X ) D ,v D ) process as well as nonresonant transitions, corresponding to the energy loss up to ΔE=240 cm −1 (approximately three quanta of vibrational energy), have been observed. Total cross-section of the latter is up to 12 times less than the maximum one of the extremely long-range transition. It has been shown that cross-sections of the processes are independent of initial J E number. The u↔g and ΔΩ=0 propensity rules are valid in the I 2 ( E ) → I 2 ( X ) I 2 (ion-pair states) transitions. The vibrational and rotational populations of the D state levels depend on v E and ΔE . Mechanism of the processes under study has been discussed. It has been shown that essentially nonresonant transitions occur after a mutual I 2 (E) and I 2 (X) capture in orbiting-controlled collision complex. Maybe, one has to take into account relativistic (magnetic) interactions for description of the extremely long-range transitions.