Uranyl oxalate actinometer

Uranyl oxalate actinometer. This actinometer has a range of 208-435 nm with an average quantum yield of about 0.5. Since the UO + ion acts as a photosensitizer for the oxalate decomposition the light absorption remains constant, but rather long exposures. re required for final accurate oxalate titrations. It is now mainly of histo al interest. 

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 ... 

In the absence of chemical quenching, uranyl compounds have long luminescent lifetimes and high luminescent quantum efficiency [21]. Often, however, the excited state reacts chemically. The photochemistry of the ion, the most famous example of which is the uranyl oxalate actinometer, has generated an enormous body of work and been the subject of comprehensive reviews [22,23]. It can occur both in solution and in the solid state. The most common reaction is the oxidation of organic substrates. Both the photochemistry and the remarkable properties of the covalent bond, demand a satisfactory interpretation in terms of the electronic structure. 

The quantitative study of any photochemical process requires the measurement of the number of molecules that have formed or reacted and the number of photons absorbed. Chemical actinometers are commonly used for the determination of the intensity of the incident light on the sample or reaction vessel. Among these the ferrioxalate actinometer is probably the most accurate and widely used. Its useful range extends from 250 nm to 509 nm [17]. The uranyl oxalate actinometer, the Reinecke s salt actinometer, the benzophenone—benzhydrol actinometer and the o-nitrobenzaldehyde actinometer have also been used [4,18]. Obviously any photochemical reaction for which the quantum yield has been determined with reference to any known actinometer can itself be used as a standard. 

The most intensive studies of the photolysis of uranyl complexes of carboxylic acids have been conducted on the uranyl-oxalic acid system, particularly because of its use as a chemical actinometer. The overall photochemistry occuring in the uranyl oxalate actinometer solution is summarized by the following equations ... 

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. 

Example of Application Large-Scale Actinometry. Neural network modelling was applied to large-scale actinometry in a continuous elliptical photochemical reactor with a concentric annular reaction chamber [2, 3,108, 148], Uranyl oxalate was used as an actinometer, which is based on the photosensitized decomposition of oxalate ions (Eq. 89) [2, 3] the experimental data were taken from the literature [108],... 

One of the characteristic features of U02+ compounds is fluorescence, and uranyl oxalate is used as an actinometer. 

Accordingly, we determined the quantum yield of the photohydrate of 1,3-dimethyluracil (DMU) for initial DMU concentrations of 1 X 10-3M, and 1 X 10-4M in unbuffered triple-distilled water. The measurements were made according to the conventional double cell technique (12), using uranyl oxalate as the actinometer. In this method, the total number of incident and transmitted quanta are measured by chemical actinometry. The quantum yield for DMU disappearance was found to be 3.93 X 10-3 at 1 X 10-4M DMU and 3.79 X 10-3 at 1 X 10-3M DMU (single determinations), and is thus independent of concentration in this range. 

Acetone is a convenient actinometer for vapor-phase studies of aldehydes and ketones, since Ico is 1.0 at temperatures above 120° and at wavelengtl from 2500-3200 A. In solution, the photolysis of uranyl oxalate is generally useful, and Malachite green leucocyanide is useful for low intensities of light. ... 

The actinometer reaction in the annular reactor The classic uranyl oxalate reaction was used (Murov etal, 1993). According to Brandi etal. (2003), changes in concentration inside the recycling system were obtained from... 

The necessary equipment is easily available and the experimentation does not pose any particular problem (Figure 8) detection is in general by spectrophotometry, and the measurement of the intensity of the flashes can be made by actinometers of ferrioxalate or uranyl oxalate. 

Weigh out 0.74 g of your preparation, add 10 cm dilute sulphuric acid and make up to 250 cm with water. Irradiate an aliquot of your solution using a low pressure mercury lamp. Pipette 10 cm of the irradiated solution, add 5.0 cm of the acetate buffer solution used above and 2.0 cm of 0.1% phenanthroline solution, shake well and measure the absorbance at the wavelength of maximum absorption determined in Sec. 13.4.1. Repeat using uranyl oxalate solution described in Sec.2.10.2 but irradiate for a longer period. From O of the latter actinometer, determine d> for the trisoxalatoferrate(III) actinometer. 

The quantum efficiency is usually determined by using a chemical reaction of known efficiency (actinometer) as a standard. The most commonly used reaction is the uranyl-ion-catalyzed decomposition of oxalic acid into water, carbon dioxide, and carbon monoxide, which has a quantum efficiency of 0.55 and is essentially independent of wavelength between 200 and 400 m. The apparatus consists of a solution of uranyl sulfate (0.01 M) and oxalic acid (0.05 M) maintained at 25° and contained in a cell of sufficient thickness to permit adsorption... 

The most studied system consists of a solution containing the uranyl and oxalate ions. This combination has received extensive study because of its widespread use as a chemical actinometer. Photolysis of such solutions lead to the formation of both carbon monoxide and carbon dioxide. The two principal reactions that lead to product formation (Eqs. (8.6) and (8.7)] do not involve reduction of the uranyl ion.< ... 

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