A molecular beam mass-spectrometric study of isopropyl nitrate pyrolysis reactions at short residence times and temperatures up to 700 K

Abstract

The pyrolysis of isopropyl nitrate in the presence of NO was studied in a molecular beam mass spectrometer apparatus, with residence times in the hot part of the quartz reactor of ca. 30 ms. This method gives rapid quenching of the reaction and direct sight-line sampling, and is designed to optimize detection of intermediates and radicals. Temperatures up to 700 K and pressures of 200–300 mbar were used in this study. NO was added in the reactor at a partial pressure of 5–10 mbar. In the experiments, which give information on the very first reaction steps, isopropyl nitrite is shown to be a stable intermediate up to 490 K. From this molecule, several other species are formed by dissociation or reaction with methyl radicals and NO, and the nitrate reactions are thus similar to the nitrite reactions. In previous studies of isopropyl nitrate pyrolysis reactions the products very strongly with temperature. Our results show that this temperature variation is due to the existence of thermally labile species like isopropyl nitrite and methyl nitrite. More stable molecules like hydrocarbons provide sinks for the flux in the reaction scheme. Tentative identification of nitrosomethane CH₃NO at intermediate temperatures and HCN at temperatures above 600 K is also made.