The vacuum ultraviolet laser excitation spectra for free ion-pair (X+ + Y−) formation from jet-cooled I2 and ICl

Abstract

The energy difference between the threshold for free ion-pair formation (X⁺ + Y⁻) and the molecular ionization energy (XY⁺) is relatively large in I₂ and ICl. Photodissociation to free ion-pairs in this energy region has been probed by vacuum ultraviolet laser radiation generated by four-wave mixing. The negative ion excitation spectra are highly structured and closely follow the one-photon absorption cross-sections. Several Rydberg series are identified, the f series being particularly prominent. Direct absorption to the free ion-pair continuum is negligible in this region and all of the Rydberg states that are accessed act as efficient doorway states to ion-pair production.