We report the analysis of the 2(g)(D-1) ion-pair state of I-2 by perturbation-facilitated optical-optical double resonance. The present study began with the observation of the 2(g)(D-1)-A' (3)Pi(2(u)) emission at around 230. nm during the analysis of the ultraviolet emissions originating form the 1(u)(D-1) ion-pair state: The identification of this new transition helped us to specify the wavelengths for detecting the 2(g)(D-1) state by emission,. and also to estimate its absolute position. The, intermediate states used to observe the 2(g)(D-1) state were the B (3)Pi(0(u)(+))-b' 2(u) mixed states by the hyperfine interaction,: which allowed us to combine the X(1)Sigma(g)(+) ground state with the 2g(1D) state in the (1+1) photon excitation following the optical selection rules for one-photon,transitions: 2(g)(D-1) <--b' 2(u)-B-3&UPi;(0(u)(+)) <--X-1&USigma;(+)(g). Our analysis covered the 2(g)( D-1) state in the 0less than or equal touless than or equal to12 and 9less than or equal toJless than or equal to40 ranges. The molecular constants and Rydberg-Klein-Rees, (RKR) potential of the 2(g)((1) D) state were reported. We discussed the occurrence of the 2(g)(D-1)-A' (3)Pi(2(u)) emission, when. exciting to, the 1(u)(D-1) v = 0 state; and attributed it to the g/u mixing between the 2(g)(D-1) and 1(u)(D-1) states. by the hyperfine interaction. The effect of, the, perturbation on, measured line intensities ands lifetime's was evident. (C) 2004 American Institute of Physics.