Thermal dissociation of alkyl nitrites and recombination of alkyl radicals

Abstract

The thermal dissociations of three alkyl nitrites (C3H7ONO, n-C4H9ONO, and i-C4H9ONO) have been studied in a diaphragmless shock tube by laser schlieren densitometry over 700 < T < 1000 K and 60 < P < 250 Torr. The nitrites act as clean, thermal sources of alkyl radicals that create the radicals at much lower temperatures than are accessible with other precursors. The decomposition of the three nitrites proceeds via a common mechanism, which is discussed. Rate coefficients for dissociation of the alkyl nitrites to an alkoxy radical and NO, k1, were obtained with an uncertainty of 30%. Rice–Ramsperger–Kassel–Marcus/Master Equation (RRKM/ME) calculations for dissociation of the nitrites were performed and provide excellent simulations of the experimental results. The high-pressure limit rate coefficients from the RRKM/ME calculations are: k1,C3H7ONO=(5.69±1.71)×1021T−1.60exp(−21458/T)s−1; k1,n−C4H9ONO=(9.91±2.97)×1021T−1.59exp(−21588/T)s−1; k1,i−C4H9ONO=(3.92±1.18)×1021T−1.58exp(−21162/T)s−1. At the low temperatures of this work, the alkyl radicals are thermally stable and thus their recombination reactions were also studied. The recombination rate coefficients for ethyl, n-propyl and i-propyl radicals (uncertainties of 50%) are in excellent agreement with literature values, particularly recent theoretical results, and extend the range of experiments to higher temperatures.