Actinometer

Actinometers are chemical systems or physical devices that determine the number of photons in a beam either integrally or per unit time. In a chemical actinometer, the photochemical change can be directly related to the number of photons absorbed, while the physical device gives a reading correlated to the number of photons detected.  

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Strahlen-gang, n. path of rays beam, -glimmer, m. striated mica, -hitrte, /. hardness of radiation, -kegel, m. cone of rays, -kunde, /. radiology, -kupfer, n. clinoclasite. -mes-ser, m. radiometer actinometer. -optik, /. geometrical optics. 

Chromium, bis(l,2-ethanediamine)difluoro-photochemistry, 1,393 Chromium, bis(l, 2-ethanediamine)oxalato-coordination isomerism, 1, 183 Chromium, diamminetetrakis(isothiocyanato)-photoaquation chemical actinometer. 1,409 photochemistry reactivity, 1, 398... 

Iron, tris(hexafluoroacetylacetone)-structure, 1,65 Iron, tris(oxalato)-chemical actinometer, 1,409 photoreduction, 1,471 relief-image-forming systems, 6,125 Iron, tris(l,10-phenanthroline)-absorptiometry, 1,549 racemization, 1,466 solid state, 1,467 structure, 1, 64 lron(III) chloride amino acid formation prebiotic systems, 6,871 Iron complexes acetonitrile. 4,1210 acetylacetone, 2,371 amidines... 

Product quantum yields are much easier to measure. The number of quanta absorbed can be determined by an instrument called an actinometer, which is actually a standard photochemical system whose quantum yield is known. An example of the information that can be learned from quantum yields is the following. If the quantum yield of a product is finite and invariant with changes in experimental conditions, it is likely that the product is formed in a primary rate-determining process. Another example In some reactions, the product quantum yields are found to be well over 1 (perhaps as high as 1000). Such a finding indicates a chain reaction (see p. 895 for a discussion of chain reactions). 

I>A 0.52) and histidine as actinometer, since this aminoacid reacts completely with O2 with = 4 xlQ7 M-is-i, (Bisby et al., 1999). 

Strongly) from a high intensity source. Uranyl oxalate, which has similar absorption characteristics to the complex (Sn2Cl o), was used for the actinometer. Quantum yields for the process were found to be 0.2. It was concluded that exchange occurs via an activated complex which is unsymmetrical. 

Matsushima, R. Mizuno, H. Kajiura, A. Convenient chemical actinometer with 2-hydroxy-4 -methoxychalcone. Bull. Chem. Soc. Jpn. 1994, 67, 1762. 

A3B2 twb=.25we >Matsushima, R. Suzuki, N. Murakami, T. Morioka, M. Chemical actinometer with 2-hydroxy-4 -dimethylaminochalcone. J. Photochem. Photobiol. A Chem. 1997, 109, 91-94. 

With this actinometer reasonable exposure periods and solution volumes result with total absorbed intensities on the order of 1017 photons. 

The most accurate solution actinometer currently available is the potassium ferrioxalate actinometer. Potassium ferrioxalate solutions absorb light in the range 250-509 nm. This broad range is both an advantage and a disadvantage since the solutions are sensitive to room light and must be carefully shielded from light until the intensity determination is made ... 

If the products of an actinometer solution do interfere by competitive light absorption, one is limited to low conversion such that the concentration of product is much less than that of the initial reactant. 

The quantum yield for the potassium ferrioxalate actinometer as a function of wavelength is shown in Table 2.8. 

Lee and Sdiger 4 have estimated the error involved in the determination of the quantum yield for the ferrioxalate actinometer (at 365 nm) to be 2.5%. This then constitutes the minimum limit of error involved in the... 

The free thiocyanate ions produced are determined spectroscopically by addition of Fe3+ and measurement of the absorbance at 450 nm. The quantum yield for this actinometer as a function of wavelength is given in Table 2.10. 

Many other actinometer systems have been developed, although those described here cover a sufficiently wide region of the spectrum to meet most needs. 

Quantum yield based on the value of = 0.33 for the 2-hexanone actinometer used in this study.<84>... 

Measurement of the light intensity under conditions identical to those used in the photolysis of the compound of interest is essential for the determination of a quantum yield. Although a number of instrumental methods for measuring light intensities are available, unless these are carefully calibrated, the most accurate means is to use a chemical actinometer. This can be any photochemical reaction for which the quantum yield at the wavelength of interest is accurately known. The following photochemical systems are most commonly used for solution actinometry. 

The quantum yield of an actinometer may be affected by temperature. For potassium ferrioxalate this temperature effect is very small, as indicated in Table 2.9. 

A chemical actinometer suitable for use at 254 nm is found in aqueous solutions of monochloroacetic acid,... 

The photoaquation of a transition metal coordination compound (Reinecke s Salt) has recently been developed as an actinometer for the... 

Rates of photodegradation of copolymer films were measured in air using a filtered medium pressure Hg arc as the source of radiation and o-nitrobenzaldehyde as the actinometer. Table 1 gives the dosage levels incident on these films. 

A ferrioxalate actinometer was used to determine the lamp light intensity (12). The quantum yield of loss (4>d) and of product formation ( p) were then calculated by standard methods (12). 

The furyl fulgide 172 has found use as a stable, recyclable actinometer for conventional photochemical experiments in the 313-366 mn wavelength range, where 173 = 0.20 and is independent of temperature and concentration245. It has also been developed as an actinometer in one- and two-laser flash photolysis experiments246. The colored form 173 can be converted back to 172 by simple exposure to visible light (equation 65). 

QUANTUM MECHANICAL TUNNELING CHEMICAL KINETICS HYDROGEN TUNNELING KINETIC ISOTOPE EFFECTS QUANTUM REQUIREMENT QUANTUM YIELD QUANTUM YIELD FLUQRESCENCE ACTINOMETER Quasi-axial,... 

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