Observation of the Ou−(3P1) ion-pair state of Cl2 by perturbation-facilitated optical-optical double resonance

Perturbation-facilitated optical-optical double resonance spectroscopy was used to study the Ou−(3P1) ion-pair state of Cl2 correlating to Cl−(1S) + Cl+(3P1). The Ou−(3P1) state was combined with the X1Σg+ ground state in a (1 + 2) photoexcitation sequence through A3Π(1u) ∼ B′3Π(Ou−) mixed intermediate levels. The spectra were analyzed by including the heterogeneous interaction with a new 1u(3P1) state, and the Dunham coefficients were derived for the Ou−(3P1) state.