Analysis of the g−(3P1)–B ′3 Π(0u−) system of I2 by perturbation-facilitated optical–optical double resonance

Abstract

We present the analysis of the 0g−(3P1)–B ′3Π(0u−) system of I2. Both of the states are optically forbidden to access from the X 1Σg+ ground state, and the perturbation-facilitated optical–optical double resonance technique is used to access the 0g−(3P1) ion-pair state in the stepwise excitation. The intermediate states we used are the B 3Π(0u+)∼(3)0u− states coupled by hyperfine interaction, which are identified in the high vibrational levels of the B 3Π(0u+) state near the dissociation limit. These coupled states have the mixed character of the 0u+ and 0u− states, and allow to combine the X 1Σg+ ground state with the 0g−(3P1) state in the (1+1) photon excitation following the optical selection rules for one photon transition: 0g−(3P1)←(3)0u−∼B 3Π(0u+)←X 1Σg+. We elucidate the B 3Π(0u+)∼(3)0u− coupling scheme in the intermediate states by analyzing the second step of double resonance. The 0g−(3P1) state is located on the absolute energy axis and its molecular constants are reported. The B ′3Π(0u−) valence state is analyzed by the dispersed fluorescence spectra from the 0g−(3P1) state in conjunction with the Franck-Condon factor calculations.