The 'approach-induced' I-2(E0(g)(+)(I-2(X))under-left-right-arrow-D0(u)(+)) transition

The dependences of the I-2(E, v(E) <(I2X))under left right arrow> D, v(D)) collision-induced transition rate constant on the vibrational v(E), v(D), r otational J(D) numbers, energy gaps, and Franck-Condon factors (FCF) of the combined levels have been studied. Selected rovibrational levels of the E state have been produced by optical-optical double resonance (OODR) excitat ion via the B0(u)(+) state. Rovibronic levels of the D state populated in c ollision-induced intramolecular transitions (CIIT) in the nearly single-col lision conditions have been identified. Rate constants of CIIT derived from the E --> B and D --> X emission spectra simulation have been determined. It has been shown that the u <-> g, Delta Omega = 0 and Delta J less than o r equal to 3 propensity rules are valid in the I-2(E) + I-2(X) --> I-2(ion- pair states) + I-2(X) process. Its cross-sections are giant ((1.1-3.3) X 10 (3)Angstrom(2)), and there is distinct correlation between them and energy gaps Delta E = f(Delta v, Delta J) of the combined rovibronic levels. The t ransitions between isoenergetic rovibronic levels are the most probable. Th ere is no correlation between the cross-sections of transitions and FCF of the levels. An applicability of some models of CIIT to the processes under study has been discussed. It has been shown that they cannot explain the ob served experimental data. It would be better to call the processes similar to the observed one as 'approach-induced' to emphasize their extremely long -range character. (C) 1999 Elsevier Science B.V. All rights reserved.