Production of metastable singlet O2 photosensitized by NO2

Abstract

Energy transfer from electronically excited NO₂ to O₂ has been studied. The ${\mathrm{NO}}_{\text{2*}}$ is produced by irradiation with light having $\text{7000 < λ < 4050\hspace{0.17em}}\mathrm{\AA }$ . Observations of light emission from ${\mathrm{O}}_2{\mathrm{(a}}^1{\Delta }_g\text{, v′ = 0),}{\mathrm{O}}_2{\mathrm{(a}}^1{\Delta }_g\text{, v′ = 1)}$ , and ${\mathrm{O}}_2{\mathrm{(b\hspace{0.17em}}}^1{\Sigma }_g^{+}\text{, v = 0)}$ have been made, and from these measurements at various pressures, rates have been measured for production of ${\mathrm{O}}_2{\mathrm{(a\hspace{0.17em}}}^1{\Delta }_g\text{, v = 0)}$ and ${\mathrm{O}}_2{\mathrm{(b\hspace{0.17em}}}^1{\Sigma }_g^{+}\text{, v = 0)}$ by energy transfer from ${\mathrm{NO}}_{\text{2*}}$ , for quenching of ${\mathrm{O}}_2{\mathrm{(b\hspace{0.17em}}}^1{\Sigma }_g^{+})$ by O₂, NO₂ and wall collisions, and for quenching of ${\mathrm{O}}_2{\mathrm{(a\hspace{0.17em}}}^1{\Delta }_g\text{, v = 0)}$ by NO₂. The efficiency for ${}^1{\Delta }_g$ production is $\text{7.5\% ± 2.5\%}$ , per collision quenching ${\mathrm{NO}}_{\text{2*}}$ , and for ${}^1{\Sigma }_g^{+}$ production, $\text{0.14\% ± 0.02\%}$ . The ${}^1{\Delta }_g$ 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 ${\mathrm{NO}}_{\text{2*}}$ is $\text{1\%–5\%}$ 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.