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1 August 2003 Quantum Yield of the Iodide–Iodate Chemical Actinometer: Dependence on Wavelength and Concentration
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The quantum yield (QY) of the iodide–iodate chemical actinometer (0.6 M KI–0.1 M KIO3) was determined for irradiation between 214 and 330 nm. The photoproduct, triiodide, was determined from the increase in absorbance at 352 nm, which together with a concomitant measurement of the UV fluence enabled the QY to be calculated. The QY at 254 nm was determined to be 0.73 ± 0.02 when calibration was carried out against a National Institute of Standards and Technology traceable radiometer or photometric device. At wavelengths below 254 nm the QY increased slightly, leveling off at ∼0.80 ± 0.05, whereas above 254 nm the QY decreases linearly with wavelength, reaching a value of 0.30 at 284 nm. In addition, the QY was measured at different iodide concentrations. There is a slight decrease in QY going from 0.6 to 0.15 M KI, whereas below 0.15 M KI the QY drops off sharply, decreasing to 0.23 by 0.006 M KI. Calibration of the QY was also done using potassium ferrioxalate actinometry to measure the irradiance. These results showed a 20% reduction in QY between 240 and 280 nm as compared with radiometry. This discrepancy suggests that the QY of the ferrioxalate actinometer in this region of the spectrum needs reexamination.

Ronald O. Rahn, Mihaela I. Stefan, James R. Bolton, Evan Goren, Ping-Shine Shaw, and Keith R. Lykke "Quantum Yield of the Iodide–Iodate Chemical Actinometer: Dependence on Wavelength and Concentration," Photochemistry and Photobiology 78(2), 146-152, (1 August 2003).<0146:QYOTIC>2.0.CO;2
Received: 20 January 2003; Accepted: 1 May 2003; Published: 1 August 2003

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