Production of metastable singlet O2 photosensitized by NO2

Energy transfer from electronically excited NO2 to O2 has been studied. The NO2* is produced by irradiation with light having 7000 < λ < 4050 Å. Observations of light emission from O2(a1Δg, v′ = 0), O2(a1Δg, v′ = 1), and O2(b 1Σg+, v = 0) have been made, and from these measurements at various pressures, rates have been measured for production of O2(a 1Δg, v = 0) and O2(b 1Σg+, v = 0) by energy transfer from NO2*, for quenching of O2(b 1Σg+) by O2, NO2 and wall collisions, and for quenching of O2(a 1Δg, v = 0) by NO2. The efficiency for Δg1 production is 7.5% ± 2.5%, per collision quenching NO2*, and for Σg+1 production, 0.14% ± 0.02%. The Δg1 production efficiency reported here is considerably greater than our preliminary value of 1%. The metastable O2 generated in an urban atmosphere by energy transfer from NO2* is 1%–5% as effective as ambient O(3P) in initiating the oxidation of alkylated aromatic hydrocarbons and 0.1% or less as effective in the case of small, unsubstituted olefins.