Sunlight photodestruction of CO₃⁻, CO₃⁻·H₂O, and O₃⁻: The importance of photodissociation to theDregion electron densities at sunrise

Experimental studies at photon energies between 1.8 and 2.7 eV have recently shown that photodissociation occurs well below the photodetachment threshold for CO3− and CO3−·H2O and dominates the photodestruction of O3− at visible wavelengths. Experimental cross sections have been averaged over the solar flux spectrum to yield zero optical depth rates. Production of O− by dissociation of CO3− and CO3−·H2O and its subsequent photodetachment can probably account for the rapid increase of electron density in the D region of the ionosphere at sunrise. Photodissociation is also an important daytime loss mechanism for CO3− and its hydrate in the 50- to 80-km region.