Chemical actinometers

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... 

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. 

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. 

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

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. ... 

Drew, H. D., Brower, J. F., Juhl, W. E., and Thornton, L. K. (1998), Quinine photochemistry A proposed chemical actinometer system to monitor UV exposure in photostability studies of pharmaceutical drug substances and drug products, Pharmacopeial Forum, 24(3), 6334. 

The photodecomposition of ferrioxalate in 0.1N H2S04 (reaction (i)) is a Very useful chemical actinometer for the near uv and the visible region upto 400 nm ( 1.12)— ferrioxalate actinometer. In some low-valence hydrated cations, such transition may bring about photo-oxidation ... 

The accurate determination of incident light intensity is of pivotal importance in any quantitative photochemical experiment. While various physical devices are available for making absolute intensity measurements,168 these devices can be difficult to calibrate and usually are rather expensive. A much simpler approach involves the use of a chemical actinometer. This type of system is based upon a photochemical reaction for which product quantum yields are reasonably insensitive to variations in reactant concentration, temperature, light intensity and excitation wavelength. Once the quantum yield is calibrated by an absolute method, a chemical actinometer becomes a rapid, inexpensive and highly accurate secondary standard for light intensity measurements. 

A chemical actinometer especially designed for intensity measurements on high power lasers in the 330—520 nm range has been described.179 It consists of a closed 02-filled system containing methanolic [Ru(bipy)3]2+ and tetramethylethylene (TME). Photoexcited [Ru(bipy)3]2+ is quenched efficiently by dissolved Oz to generate singlet oxygen which then reacts with TME to form a nonvolatile hydroperoxide. The laser intensity is determined from the rate of 02 consumption monitored on a gas buret. 

The measurement of quantum yield is a more complicated process. Before these measurements can be made, the instrument must be calibrated. A thermopile or chemical actinometer may be used to measure the absolute intensity of incident light on the sample. Alternatively, quantum yields may be measured relative to some accepted standard. Two commonly used fluorescence standards are quinine sulfate in 0.5 M H2S04 (jQ = 0.70) and fluorescein in 0.1 M NaOH (f9 = 0.93). The quantum yield of the unknown, Q, is then calculated by Equation 5.7. 

The (chemical) actinometer A (Figure 7.40), is a photo reactive sample of known quantum yield a. For the determination of the quantum yield of the unknown sample S, this sample and the actinometer are irradiated simultaneously through the beam splitter B, which divides the incoming beam in a ratio rA, which is independent of time and of light intensity. The change of concentration, Ac(A), of the actinometer gives the number of photons absorbed, so that the quantum yield of the unknown reaction is obtained as the ratio of the concentration changes... 

Kelly P., Dickerson R.R, Luke W. and Kok G, Chemical actinometer for measuring nitogen dioxide photolysis rates, Geophys. Res. Lett,22,2621-2632, 1995. 

Bovina E, De Filippis P, Cavrini V, Ballardini R. Trans-2-nitrocinnamalde-hyde as chemical actinometer for the UV-A range in photostability testing of pharmaceuticals. In Albini A, Fasani E. Drugs Photochemistry and Photostability. Cambridge The Royal Society of Chemistry, 1998 305-316. 

Allen JM, Allen SK, Baertschi SW. 2-Nitrobenzaldehyde a convenient UV-A and UV-B chemical actinometer for drug photostability testing. J Pharm Biomed Anal 2000 24 167-178. 

III 4.2 Chemical Actinometers in the Ultraviolet Region. 127 111—5 Determination of the Elementary Reaction Rates, 128... 

The author showed, that only UV light was active and that a polar solvent was required and described the reaction as a benzylic heterolysis. This and related photochemical reactions with the leuco derivatives of crystal violet and malachite green were later studied in detail in their mechanism [3-9] and were among the first compounds proposed as chemical actinometers [10-12], although in the event these were found to be less suited than other derivatives, since the high sensitivity was counterbalanced by the high absorption of the photoproducts in the UV. 

H. G. Heller and J. R. Langan, Photochromic heterocyclic fulgides. Part 3. The use of (E)-a-(2,5-dimethyl-3-furylethylidene) (isopropylidene) succinic anhydride as a simple convenient chemical actinometer, J. Chem. Soc., Perkin. Trans. 2, 1981, 341. 

Oxalic acid forms complexes with Fe(III) that absorb strongly from 254 to 442 nm. The absorption corresponds to a LMCT band, with smax values around 103-104 M 1 cm x. Photolysis of trisoxalatoferrate(III) (ferrioxalate, FeOx) constitutes the most used chemical actinometer the quantum yield of Fe2+ formation is high (

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Photocells may be used in place of thermopiles. Still other devices are chemical actinometers, which are merely gas mixtures or solutions sensitive to light. When radiation impinges upon these, a chemical reaction ensures whose extent is determined by the amount of energy absorbed. The most common of these is the uranyl oxalate actinometer, consisting of 0.05 molar oxalic acid and 0.01 molar uranyl sulphate (U02 S04) in water. Under the action of light following reaction take place ... 

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