Linear-Reactor-IR.-Matrix and Microwave Spectroscopy of the System O3/NO2/(Z)-2-Butene

Investigation of the formation of complex reaction products in the gas-phase system O₃/NO₂/(Z)-2-butene by combination of linear reactors with IR. matrix and microwave Stark Spectroscopy is reported. Besides the polyatomic products observed earlier in the gas-phase ozonolysis of (Z)-2-butene, the following products were identified; N₂O₅, HNO₃, HNO₄, CH₃NO₂, CH₃ONO, CH₃COONO₂ and CH₃COO₂NO₂ (peroxyacetyl nitrate, PAN). Matrix IR. spectra of N₂O₅, HNO₃. CH₃COONO, CH₃COONO₂ required for reference purposes are presented. It is shown that PAN-formation occurs already in the absence of light. A reaction scheme is proposed for explanation of the observed complex NO_x-containing products, which assumes methyldioxirane as a central intermediate. Particular reaction steps of the scheme will be discussed, including thermochemical estimates of reaction enthalpies.