We present the analysis of the 0(g)(-)(P-3(1))-B ('3)Pi(0(u)(-)) system of I-2. Both of the states are optically forbidden to access from the X (1)Sigma(g)(+) ground state, and the perturbation-facilitated optical-optical double resonance technique is used to access the 0(g)(-)(P-3(1)) ion-pair state in the stepwise excitation. The intermediate states we used are the B (3)Pi(0(u)(+))similar to(3)0(u)(-) states coupled by hyperfine interaction, which are identified in the high vibrational levels of the B (3)Pi(0(u)(+)) state near the dissociation limit. These coupled states have the mixed character of the 0(u)(+) and 0(u)(-) states, and allow to combine the X (1)Sigma(g)(+) ground state with the 0(g)(-)(P-3(1)) state in the (1+1) photon excitation following the optical selection rules for one photon transition: 0(g)(-)(P-3(1))<--(3)0(u)(-)similar toB (3)Pi(0(u)(+))<--X (1)Sigma(g)(+). We elucidate the B (3)Pi(0(u)(+))similar to(3)0(u)(-) coupling scheme in the intermediate states by analyzing the second step of double resonance. The 0(g)(-)(P-3(1)) state is located on the absolute energy axis and its molecular constants are reported. The B ('3)Pi(0(u)(-)) valence state is analyzed by the dispersed fluorescence spectra from the 0(g)(-)(P-3(1)) state in conjunction with the Franck-Condon factor calculations.