Vacuum-ultraviolet absorption and fluoresence excitation spectra of iodine chloride

Absorption and fluorescence excitation spectra for ICl in the vacuum-ultraviolet (125-195 nm) have been recorded using tunable synchrotron radiation. Fluorescence occurs mainly from the E(0{sup +}) ion-pair state, and pronounced resonance structure is observed. These resonances result from an unusual three-state interaction. Both homogeneous and heterogeneous coupling between the E(0{sup +}) ion-pair state and degenerate Rydberg states takes place. Pronounced broadening of the Rydberg levels occurs through heavy predissociation by a repulsive valence state or states.