10/07/2019 Actinometer - Wikipedia
Actinometer
Actinometers are instruments used to measure the heating power
of radiation. They are used in meteorology to measure solar radiation
as pyranometers, pyrheliometers and net radiometers.
An actinometer is a chemical system or physical device which
determines the number of photons in a beam integrally or per unit
time. This name is commonly applied to devices used in the
ultraviolet and visible wavelength ranges. For example, solutions of
iron(III) oxalate can be used as a chemical actinometer, while
bolometers, thermopiles, and photodiodes are physical devices giving
a reading that can be correlated to the number of photons detected.
Contents
History
Chemical actinometry
Choosing an actinometer Actinometer instrument designed by Jules
Chemical actinometry in the visible range Violle and used to estimate the
References temperature of the Sun's surface.
History
The actinometer was invented by John Herschel in 1825; he introduced the term actinometer, the first of many uses of
the prefix actin for scientific instruments, effects, and processes.[1]
The actinograph is a related device for estimating the actinic power of lighting for photography.
Chemical actinometry
Chemical actinometry involves measuring radiant flux via the yield from a chemical reaction. It requires a chemical
with a known quantum yield and easily analyzed reaction products.
Choosing an actinometer
Potassium ferrioxalate is commonly used, as it is simple to use and sensitive over a wide range of relevant wavelengths
(254 nm to 500 nm). Other actinometers include malachite green leucocyanides, vanadium(V)–iron(III) oxalate and
monochloroacetic acid, however all of these undergo dark reactions, that is, they react in the absence of light. This is
undesirable since it will have to be corrected for. Organic actinometers like butyrophenone or piperylene are analysed
by gas chromatography. Other actinometers are more specific in terms of the range of wavelengths at which quantum
yields have been determined. Reinecke’s salt K[Cr(NH3)2(NCS)4] reacts in the near-UV region although it is thermally
unstable.[2] [3][4] Uranyl oxalate has been used historically but is very toxic and cumbersome to analyze.
Recent investigations into nitrate photolysis[5][6] have used 2-nitrobenzaldehyde and benzoic acid as a radical
scavenger for hydroxyl radicals produced in the photolysis of hydrogen peroxide and sodium nitrate. However, they
originally used ferrioxalate actinometry to calibrate the quantum yields for the hydrogen peroxide photolysis. Radical
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10/07/2019 Actinometer - Wikipedia
scavengers proved a viable method of measuring production of hydroxyl radical.
Chemical actinometry in the visible range
Meso-diphenylhelianthrene can be used for chemical actinometry in the visible range (400–700 nm).[7] This chemical
measures in the 475–610 nm range, but measurements in wider spectral ranges can be done with this chemical if the
emission spectrum of the light source is known.
References
1. Science, American Association for the Advancement of (April 25, 1884). "Notes and News" (https://books.google.
com/books?id=h6zq_tFWAvUC&pg=PA527&dq=herschel+actinometer#v=onepage&q=herschel%20actinometer&
f=false). Science. 3 (64): 527. Bibcode:1884Sci.....3..524. (http://adsabs.harvard.edu/abs/1884Sci.....3..524.).
doi:10.1126/science.ns-3.64.524 (https://doi.org/10.1126%2Fscience.ns-3.64.524).
2. Calvert, Jack G; James N Pitts (1966). Photochemistry. New York: Wiley and Sons. ISBN 0-471-13091-5.
3. Taylor, H. A. (1971). Analytical methods techniques for actinometry in Analytical photochemistry and
photochemical analysis. New York: Marcel Dekker Inc.
4. Rabek, J. F. (1982). Experimental methods in Photochemistry and Photophysics. Chicester: Wiley and Sons.
ISBN 0-471-90029-X.
5. Anastasio, Cort; McGregor K.G. (2001). "Chemistry of fog waters in California's Central Valley: 1. In situ
photoformation of hydroxyl radical and singlet molecular oxygen". Atmospheric Environment. 35 (6): 1079–1089.
Bibcode:2001AtmEn..35.1079A (http://adsabs.harvard.edu/abs/2001AtmEn..35.1079A). doi:10.1016/S1352-
2310(00)00281-8 (https://doi.org/10.1016%2FS1352-2310%2800%2900281-8).
6. Chu, L; Anastasio, C. (2003). "Quantum Yields of Hydroxyl Radical and Nitrogen Dioxide from the Photolysis of
Nitrate on Ice". Physical Chemistry A. 107 (45): 9594–9602. Bibcode:2003JPCA..107.9594C (http://adsabs.harvar
d.edu/abs/2003JPCA..107.9594C). doi:10.1021/jp0349132 (https://doi.org/10.1021%2Fjp0349132).
7. Brauer H-D; Schmidt R; Gauglitz G; Hubig S (1983). "Chemical actinometry in the visible (475-610 nm) by meso-
diphenylhlianthrene". Photochemistry and Photobiology. 37 (6): 595–598. doi:10.1111/j.1751-
1097.1983.tb04526.x (https://doi.org/10.1111%2Fj.1751-1097.1983.tb04526.x).
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