Selected Chemical Actinometers

The requirements for chemical actinometers, listed in the previous sections [such as sensitivity, reproducibility, (thermal) stability, ease of analytical procedure, etc.], reduce the seemingly unlimited number of actinometers reported over the years (9) to a short list of well-established and highly recommended chemical actinometers. In this section, we first present a selected list of such reliable actinometers, which all operate in the liquid phase. After that, a few controversial systems are described and their potential error sources discussed. Finally, actinometric procedures suitable for solid-state applications, polychromatic sources, and laser irradiation will be introduced in section Special Applications.  

The potassium ferrioxalate actinometer developed by Hatchard et al. (10,11) in the 1950s is probably the most widely used and most thoroughly investigated solution-phase actinometer [Ref. (9) and references therein]. Irradiation of an aqueous solution (0.006-0.15M) of K3Fe(C20 )j-3H20 with radiation between 250 and 470run (vide infra) results in a two-step photoreduction of iron (III) to iron (11) with quantum yields higher than unity, i.e.. 

The reversible E/Z photoisomerization of azobenzene upon UV/VIS irradiation, in methanolic solution, has been utilized to develop the first reusable chemical 

Owing to the different absorption spectra of the E- and the Z-isomer of azobenzene (Fig. 1), the irradiation and evaluation procedures depend on the irradiation wavelength as follows  

In the 275-340 nm wavelength range, the concentrated solution of E-azobenzene absorbs the incident radiation completely (100% absorption). Thus the E Z isomerization, with a quantum yield of b=0.14 (13,15), can be monitored spectroscopically by measuring the decrease in absorbance at 358 nm as a func- 

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The determination of photochemical quantum yields is not a simple task, and, in some cases, approximations are required. Nevertheless, according to the parameters chosen, various well-known photochemical reactions can be used to measure irradiance, which is an essential quantity in the field of photokinetics. Finally, some selected chemical actinometers will be discussed with respect to their pros and cons and their best areas of application. At the end, special applications of actinometry such as measurements of polychromatic light and high-intensity light sources (lasers) will be described. The overall aim of this chapter is to help the reader to choose the best actinometers out of the numerous examples in the literature and avoid technical mistakes. 

The actinometers described in the section "Selected Chemical Actinometers" are mostly used to measure the intensity of monochromatic radiation emitted by conventional sources, such as mercury or xenon arc lamps, metal halide lamps, etc. In this section, special applications of chemical actinometer will be reviewed, including the measurement of intensities of lasers and polychromatic light sources. In addition. 

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