Primary Photochemical Processes in Photolysis Mediated by Humic Substances

Natural water samples and humic substance solutions were probed for their phototransient behavior. Laser flash kinetic spectroscopy was used to study two transients common to most samples. One transient with a maximum around 720 nm was quenched by decreasing pH and nitrous oxide. It was present in all waters with DOC and had a spectrum which resembled that of a solvated electron. The signal was linear with laser power. The quantum yield for this transient was measured. Samples with higher ground state absorbance yielded a transient with a maximum at 475 nm that was quenched by oxygen. This transient seemed to be a photophysical hybrid with triplet and radical cation character. Additional work done to characterize these transients and predict their environmental fates is discussed.