Photoreactions providing sources

Zepp, R. G., and L. F. Ritmiller, Photoreactions providing sinks and sources of halocarbons in aquatic environments . In Aquatic Chemistry - Inerfacial and Interspecies Processes, C. P. Huang, C. R. O Melia and J. J. Morgan, Eds., American Chemical Society, Washington, DC, 1995, pp. 253-278. 

Photoreactions Providing Sinks and Sources of Halocarbons in Aquatic Environments... 

Photochemical reductions and oxidations in aquatic environments provide sinks or sources for halocarbons. Such photoreactions are an important process in the dissipation of low-volatility halocarbons, such as halogenated agrochemicals, in aquatic environments (reference 9 contains lead references). For example, field studies of Crossland and Wolff (10) demonstrated the rapid dissipation of pentachlorophenol residues by its photoreaction in English ponds. Evidence emerged that volatile halocarbons such as 1,1,1-trichloroethane (methylchloroform) may have significant sinks in the aquatic environment... 

These discussions indicate that aquatic photochemical processes play an im portant role as sinks for halogenated pollutants and as a source of certai natural halocarbons, including volatile halocarbons that escape from the se to the atmosphere. Those photoreactions that provide sinks often result i dehalogenation. Direct photoreactions such as photohydrolysis are likely to b the dominant photoreactions of aromatic halocarbons that strongly absorb sc lar radiation. 

To obtain IR spectra on a time scale of nanoseconds, the sample cell in conventional spectrometers is usually excited by an Nd YAG laser. Flow cells with a pathlength of at least 0.1 mm must be used for photoreactive samples and the pulse repetition frequency is then limited to 1 Hz. In step scan FTIR spectroscopy,211 the time evolution is collected at single points of the interferogram, which is then reconstructed point-by-point and subsequently transformed to time-resolved IR spectra. Alternatively, dispersive instruments equipped with a strong IR source can be used.212 The time resolution of both methods is about 50 ns. FTIR instruments provide a triggerable fast-scan mode to collect a complete spectrum within a few milliseconds.213... 

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