Determination of the quantum yields of the potassium ferrioxalate and potassium iodide–iodate actinometers and a method for the calibration of radiometer detectors

Abstract

The quantum yields for two actinometers have been determined using a tunable laser light source at the National Institute of Standards and Technology (NIST) in Gaithersburg, MD. The power of this light source has been calibrated against an absolute cryogenic radiometer, considered accurate with an uncertainty better than 0.1% at a coverage factor k = 2. The quantum yield at 253.7 nm for the ferrioxalate actinometer was found to be 1.38 ± 0.03, which compares favorably with the value 1.40 ± 0.03 determined by Goldstein and Rabani. The quantum yield at 253.7 nm for the KI/KIO 3 actinometer was found to be 0.69 ± 0.02 at 23.5 °C. Again this compares favorably with 0.72 ± 0.03 determined by Goldstein and Rabani and 0.73 ± 0.02 determined by Rahn et al. Based on the determinations to date, including the present investigation, the recommended values for the quantum yields at 253.7 nm are 1.39 ± 0.02 (temperature independent) for the ferrioxalate actinometer and [(0.71 ± 0.02) + (0.0099 ± 0.0004)( t − 24)] for the KI/KIO 3 actinometer, where t is the temperature (°C) of the actinometer solution. Finally, a protocol is recommended for the use of the KI/KIO 3 actinometer to calibrate radiometer detectors at 253.7 nm.