Direct observation of phototransients in natural waters

Nanosecond laser spectroscopic measurements were made on a variety of natural waters containing humic substances. Both short-lived (nanosecond) and long-lived (microsecond) transient absorptions were observed. The long-lived transients exhibited maxima at 475 and 720 nm. The former is tentatively assigned to a triplet state transition while the latter is due to solvated electrons formed on laser excitation. Water samples from widely diverse sources showed similar transient absorption properties as well as fluorescence properties. All transients were shown to depend linearly on laser intensity, indicating that the photoproducts observed are likely to be formed in water sources illuminated by solar radiation having much lower intensities than used here.