Formation of O2(a 1Δg) by electronic energy transfer in mixtures of NO2 and O2

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Abstract
The production of O2(a 1Δg) has been observed when mixtures of NO2 and O2 are irradiated with light in the wavelength region 330–590 nm. The dependence of the signal on light intensity and concentrations suggests that the O2(a 1Δg) is produced by transfer of electronic energy from excited NO2 to O2. The absolute energy transfer efficiency was measured at 366 nm by direct calibration against the amount of NO produced simultaneously by NO2 photolysis. The efficiency measured at other wavelengths was then related to this absolute value. The O2(a 1Δg) production efficiency depended on the wavelength of the light used to excite the NO2, reaching a maximum of 4.5% at 390 nm. A plot of this efficiency as a function of wavelength did not show any apparent discontinuity at 398 nm, the wavelength that corresponds to the first dissociation limit of NO2.