Optical population of the I-2(delta 2(u)) state by three-step laser excitation from the ground state X0(g)(+)'via the valence BOu+ and O-g(+)(bb) states correlating with the I(P-2(3/2)) +I(P-2(1/2)) and the I(P-2(1/2)) +I(P-2(1/2)) dissociation limits, respectively, has been observed for the first time. It has been shown that luminescence from the I2(delta 2(u)) state becomes observable due to interaction between the rovibronic levels of the D-0(u+) and delta 2(u) states described by the nonadiabatic operator V-n of the heterogeneous interaction taken in the second order of the perturbation theory where the main intermediate state contribution is provided by the gamma 1(u) state. (C) 2015 Elsevier B.V. All rights reserved.