Aqueous solutions of isolated humic substances were investigated by laser flash photolysis. Kinetics of the decay of excited states were measured in emission and absorption. From the absorption data at least two transients with different lifetimes (order of 10-5 and 10-4 s) could be deduced. Quenching effects were determined for oxygen and Ni(II), Co(II), and Cd(II). The quenching efficiency of oxygen is similar to the efficiency of the paramagnetic metal ions. The quantum yield of the singlet oxygen production sensitized by humics was determined to be 1-3% with the furfuryl alcohol method. The results are discussed with respect to the photochemistry of aquatic ecosystems. � 1987 American Chemical Society.
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