Direct measurement of the reaction pair C 6H 5NO→C 6H 5+NO by a combined shock tube and flow reactor approach

Abstract

The dissociation of nitrosobenzene in a shock tube and the corresponding association of phenyl radicals () and NO in a flow reactor have been investigated. From the shock tube, high-temperature absorption spectra were obtained for nitrosobenzene and its decay products. The absorption coefficients of these species around 275 nm are sufficiently different to permit the direct measurement of the rate of the nitrosobenzene decay. The rate coefficient for the reaction C6H5NO→C6H5+NO in the temperature range 800–1000 K at pressures between 2.0 and 2.2 bar was determined to be k1-1015.29±0.53 exp(−(24.720±1110)/T)s−1 Variation of the pressure between 0.9 and 4.4 bar showed k1 to be independent of pressure, which indicates that reaction (1) is close to its high-pressure limit. In a complementary set of experiments, the recombination reaction C6H5+NO→C6H5NO was studied in a fast flow reactor under pseudo-first-order conditions. Helium was used as the carrier gas, the pressure was 10 mbar, and the temperature was varied from 420 to 820 K. The pyrolysis of nitrosobenzene was used as a reliable source of phenyl radicals. Under the experimental conditions, the reaction was close to its high-pressure limit for T<500 K. At higher temperatures, it exhibits a significant falloff. By using a falloff formalism, both sets of experiments could be fitted very well. An expression krec,02=6.2×1012×e233/T cm3/mol/s was deduced. The heat of reaction required for these calculations is in good agreement with the thermochemical literature data for C6H5NO, C6H5, and NO.