Actinometer ferrioxalate

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 ... 

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 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 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 method just described is not usually applicable in the ultraviolet because ultraviolet lamps of known spectral distribution are not readily available at present. The spectral sensitivity caii be calculated directly if the values of B L and P, are known. The first of these is obtained from the dispersion curve of the monochromator the second is somewhat difficult to measure—for prism instruments over restricted wavelength regions above 250 m t it is often reasonably constant. The photomultiplier sensitivity, P can be determined by comparison with a thermopile or with the ferrioxalate actinometer.11 12 Direct calculation of S, is subject to inaccuracies due to the accumulation of errors in the measurement of the three separate quantities B L and P,. A more convenient... 

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 ... 

This result may be substituted into Eq. 15-40 to calculate Oir(A). Classical actinometers that are used in this way include the potassium ferrioxalate actinometer that can be employed both in the uv and visible spectral region the Reinecke s salt actinometer (visible region), and the ort/io-nitrobenzaldehyde actinometer (uv region). For further description of these actinometers we refer to the literature (e.g., Leifer, 1988, pp. 148-151). 

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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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 azobenzene actinometer has been calibrated for intensity measurements with pulsed nitrogen, excimer, and Nd YAG lasers. Comparative actinometric measurements of the radiation intensity of a weak nitrogen laser (337.1 nm, 5 ns, and <5mJ/pulse) utilizing ferrioxalate (vide supra) and a dilute (10" M) azobenzene solution resulted in an isomerization quantum yield identical to that obtained using the 334-nm mercury line (14). Thus, we conclude that a concentrated (6.4x 10" M) azobenzene solution can be used in the same way as described for actinometric measurements of the mercury line at 334 nm (15) with an calibration factor of W=3.6x 10 Einsteincm [see Eq. (14)]. 

In summary, concentrated azobenzene solutions represent reliable chemical actinometers for pulsed UV sources, such as the nitrogen laser line at 337.1 nm, the third harmonic output of Nd YAG lasers at 355 nm, or the XeCl excimer laser line at 308 nm. In contrast to the ferrioxalate actinometers, the azobenzene actinometers are not restricted to low-energy lasers but can measure laser pulse energies up to 150 mJ. 

An experimental setup similar to the Zimmerman photolysis cell was utilized by Lazare et al. (60) to determine the quantum yield for the photoreaction of a substrate adsorbed on silica gel. The photolysis cell consists of an aluminum dish for the powdered silica gel sample, which is covered by a double-walled hemispherical Pyrex cap filled with ferrioxalate actinometers solution. The sample is irradiated through a quartz light pipe, which enters the photolysis cell through a hole at the top of the cap. Thus, nearly all scattered light from the silica gel sample is absorbed by the surrounding actinometer solution, and the amount of light absorbed by the substrate (which is adsorbed on the silica gel surface) is determined by a similar subtraction method as described in the Zimmerman experiment (vide supra). 

Gruter H. Measuring the pulse energy of a nitrogen laser with the potassium ferrioxalate actinometer. J Appl Phys 1980 51 5204—5206. 

Demas JN, Bowman WD, Zalewski EF, Velapoldi RA. Determination of the quantum yield of the ferrioxalate actinometer with electrically calibrated radiometers. J Phys Chem 1981 85 2766-2771. 

C. G. Hatchard and C. A. Parker, A new sensitive chemical actionometer. II. Potassium ferrioxalate as a standard chemical actinometer, Proc. Roy. Soc. (London) A235, 581 (1956). 

Procedures. Continuous irradiations of halocarbon solutions were conducted with monochromatic radiation in a merry-go-round apparatus (12) or in a Schoeffel reaction chemistry system. Reactions were followed through analysis for remaining halocarbon or analysis of chloride ions produced by the photoreactions. Dark controls were used in all cases to correct for thermal production of chloride ions. Ferrioxalate actinometers were used to determine the irradiance (16). The irradiance at the photoreaction cell surface was typically about 10 nanoeinsteins/cm2,s. The Fe(II) concentrations were determined by using a modified version of the ferrozine procedure described by Stookey (17). Electronic absorption spectra were obtained by using a Shi-madzu model 265 spectrophotometer. 

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