Parity Mixing in the Valence States of I2 Probed by Optical-Optical Double-Resonance Excitation of Ion-Pair: Characterization of a New Ion-Pair State, H1u(3P1), and a Valence State, c1g

Abstract

Two new electronic states of molecular iodine are reported: the ion-pair H1u(3P1) state is characterized by its fluorescence excitation spectrum and dispersed fluorescence to the known a1g state, and a shallow bound valence state, the c1g state correlating with I(2P3/2) + I(2P1/2) is identified from the dispersed fluorescence spectrum, γIu → clg. Between 3.5 and 3.8 Å the independently derived H and c state potentials successfully reproduce the observed H (v′ = 0) → c dispersed fluorescence. The two ungerade ion-pair states H and γ are populated using the optical-optical double-resonance technique through a hyperfine coupled intermediate [BO+u (v = 59) ∼ clg (v = 14)]. The u/g coupling mechanism and the magnitude of the matrix element are deduced from the J-dependence of the mixing in the intermediate state, as monitored by the overall efficiency of two-photon production of an ungerade ion-pair state from the ground state.