Photochemistry light sources

Use of coherent light sources in industrial appHcations has led to the field of photodynamic therapy as a photochemically based medical technology (9—11). The apphcation of photochemistry to information storage and communication processes is expected (12) (see Information storage materials Resist materials). 

Conventional, incoherent light sources suitable for industrial-scale photochemistry and the reactors exploiting them have been reviewed in depth (2). Subsequent improvements in traditional light sources have been incremental. 

Generally the first thing to be done in preparation for the photochemical study of a compound is to determine the visible and ultraviolet absorption spectrum of the compound. Besides furnishing information concerning the nature of the excited state potentially involved in the photochemistry (see Section 1.4), the absorption spectrum furnishes information of a more applied nature as to the wavelength range in which the material absorbs and its molar absorptivity e. From this information it is possible to decide what type of light source to use for the irradiation, what solvents can be used to... 

The mercury lamp has been the conventional light source used in photochemistry. The ground-state mercury atom, Hg, has two electrons in its highest occupied orbital, the 6s atomic orbital. Excited mercury... 

In the introduction to Volume 1 of this series, the founding editors, J. N. Pitts, G. S. Hammond and W. A. Noyes, Jr. noted developments in a brief span of prior years that were important for progress in photochemistry flash photolysis, nuclear magnetic resonance, and electron spin resonance. A quarter of a century later, in Volume 14 (1988), the editors noted that since then two developments had been of prime significance the emergence of the laser from an esoteric possibility to an important light source, and the evolution of computers to microcomputers in common laboratory use of data acquisition. These developments strongly influenced research on the dynamic behavior of the excited state and other transients. 

Since in industrial photochemistry mostly polychromatic light sources are used, photon quantities are relatively difficult to calculate and require knowledge of the spectral distribution of the radiometric quantity measured. Assuming on the other hand that the radiometric measurements do not need to be corrected for the spectral response of the probe, the photon irradiance at a given point within the reactor volume would then be given by Eqs. (39) and (40), respectively. 

Besides the valuable information obtained from the companies cited in Refs. 2 and 3, cooperation with Atochem Elf-Aquitaine (Paris and Pierre-Benite, France), E. I. DuPont de Nemours Company (Wilmington, Delaware, USA) and Ems-Dottikon AG (Dottikon, Switzerland) in the domain of industrial photochemistry, as well as with Asea Brown Boveri AG (Baden, Switzerland) for the technical application of excimer light sources in photochemistry, provided many interesting discussions, new insights in problems of industrial chemistry, and valuable new tools for their solution. 

Finally, enrichment of isotopic species has been achieved for a number of atoms and molecules using an appropriate monochromatic light source that preferentially excites an isotopic species of interest in mixtures of other isotopic species. The photochemistry associated with isotopic enrichment is briefly described in Chapter VIII. Great efforts have been made recently to obtain information on the detailed photochemical processes involving smog formation, stratospheric pollution, and atmospheres of other planets, and brief discussions of these subjects are also presented in the chapter. 

---