EVALUATION OF PRIMARY PHOTOPRODUCT QUANTUM YIELDS IN FULVIC-ACID

Time-resolved photoacoustic spectroscopy in conjunction with magnetic circular dichroism (MCD) spectroscopy has been applied to determine energies and quantum yields for the formation of triplet states in aqueous solutions of two well-characterized (Laurentian and Armadale) fulvic acids. For the Laurentian sample, intersystem, crossing quantum yields range from 0.79 to 0.28 for the pH range 2.0-9.5. The average triplet energy is estimated as 1.8 X 10(2) kJ mol-1 from MCD spectra. For the Armadale sample, intersystem crossing quantum yields range from 0.82 to 0.35 for the pH range 2.0-9.5. The triplet energy is estimated as 1.7 X 10(2) kJ mol-1. With the primary photoproduct quantum yields, the overall photophysics and primary photochemistry of the fulvic acid may be described. The donor-acceptor model of humic spectra is also reinforced. Observed initial yields greatly exceed reported steady-state yields which appear to emphasize quenching and scavaging by humics themselves.