We used the perturbation-facilitated optical–optical double resonance technique to access the ungerade ion-pair states of I2 using the (1 + 1) photo-excitation sequence through the B3Π(0u+)–c1g parity mixing states. By analyzing the second step of the double resonance to the F0u+(3P0), γ1u(3P2), and H1u(3P1) states, the g–u coupling schemes were elucidated in the intermediate B3Π(0u+)–c1g state. We were also able to populate the δ2u(3P2) state through the g–u mixing state, and to improve its molecular constants. The interference effect between the parallel γ1u(3P2)–c1g and perpendicular δ2u(3P2)–c1g transitions was used to derive the ratio of their electronic transition moments, (μ||e/μ⊥e) ∼ 5.5.

Articles you may be interested inCollision-induced nonadiabatic transitions in the second-tier ion-pair states of iodine molecule: Experimental and theoretical study of the I 2 ( f 0 g + ) collisions with rare gas atoms

Perturbation-facilitated optical-optical double resonance spectroscopy has been applied to study the h0u−(3P1) and H1u(3P1) ion-pair states of I2 correlating with I−(1S)+I+(3P1). The intermediate states used were the g/u parity mixed states found in the B 3∏(0u+)−X 1∑g+ absorption spectrum near the dissociation limit. We identified several B 3∏(0u+)∼3∏(0g−) coupled states by hyperfine interactions for the first time. These states had the 0u+ and 0g− double-faced character and facilitated to combine the X 1∑g+ ground state with the h0u−(3P1) state in the (1+1) photon excitation scheme following the optical selection rules for one-photon transition. We also accessed the H1u(3P1) state through the B 3∏(0u+)∼c1g mixed state, and elucidated the heterogeneous coupling between the h0u−(3P1) and H1u(3P1) states. Our analyses covered the region of about 48 200 to 50 300 cm−1, and gave the molecular parameters of the h0u−(3P1) state valid for v=0–17 and those of the H1u(3P1) state for v=0–20. The Π3(0g−) state used as an intermediate state was analyzed through the dispersed h0u−(3P1)−3∏(0g−) emission in conjunction with the Franck–Condon factor calculations, and the principle spectroscopic constants of the Π3(0g−) state were reported.

Optical-optical double-resonance spectroscopy is used to study the 1u(3P2) and 2u(3P2) ion-pair states of I2 correlating to the lowest ionic state, I-(1S) + I+(3P2). In the (1 + 2) photoexcitation sequence, we gain access to the 1u(3P2) ion-pair state through the A3Π(1u) state. The 2u(3P2) state is also identified from the occurrence of extra lines through heterogeneous coupling with the 1u(3P2) state and an apparent energy shift in the 1u(3P2) state. The energy levels of the 1u(3P2) and 2u(3P2) states were analyzed in detail by including the heterogeneous interaction between these states. We have established the vibrational numbering of the 2u(3P2) state in considering the 1u-2u(3P2) interaction terms under a pure precession approximation. Combined with other results, the present study has allowed us to characterize and map out the ion-pair states of I2 in the 5 eV region.

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