کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
4753876 | 1417593 | 2017 | 8 صفحه PDF | دانلود رایگان |
- Dependence of concentration, temperature and oxygen on photoreaction of metamitron.
- Oxygen dependent quantum yields in aqueous solution.
- Confirmation of a photoreaction from the triplet state.
- Recommendation of metamitron as an actinometer.
The dependence of the quantum yield of metamitron on oxygen concentration in the range cO2 = (0.005-12.6)· 10â4 M in aqueous solution was investigated with a polychromatic Xe-light source in the wavelength region 270-376 nm. The quantum yield of Φ = 0.022 ± 0.002 mol molâ1 at T = (293 ± 3) K and cO2=2.8·10â4 M is independent from metamitron concentration in the range of cM = 8 ·10â8 â 1.8 · 10â4 M. A weak temperature dependence of the photolysis of metamitron at constant oxygen concentration was found with an activation energy of EA = (3 ± 1) kJ molâ1. The yield (ν = 0.91) of the main product desamino-metamitron does not depend on start concentration of metamitron, oxygen concentration or temperature (in the range of T = 281.5-327 K). Oxygen is necessary in the photolysis of metamitron. Quantum yields for the photoreaction of metamitron increase from practically zero at low oxygen concentrations (Φ = 0.002 mol molâ1 at cO2<3·10â6 M) to a maximum of Φmax = 0.042 mol molâ1 at cO2=5.1·10â5 M and declines with increasing oxygen concentration to a value of Φ = 0.006 mol molâ1 in oxygen saturated solutions. Two reaction sequences with a reaction from the triplet state T1 and from a recently proposed transient triplet state T1â² were used to explain the oxygen-dependent rate constants of metamitron. Both sequences explain the oxygen dependence equally well and it was not possible to distinguish between both mechanisms. Aqueous solutions of metamitron are recommended as a promising actinometric system, especially suitable for measurements in sunlight.
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Journal: Journal of Photochemistry and Photobiology A: Chemistry - Volume 347, 1 October 2017, Pages 138-145