High‐temperature kinetics of the reaction between CN and hydrocarbons using a novel high‐enthalpy flow tube

Abstract

International audienceMore than 70 molecules of varied nature have been identified in the envelopes of carbon-rich stars through their spectral fingerprints in the microwave or far infrared regions. Many of them are carbon chain molecules and radicals, and a significant number are unique to the circumstellar medium. The determination of relevant laboratory kinetics data is critical to keep up with the development of the high spectral and spatial resolution observations and of the refinement of chemical models. Neutral-neutral reactions of the CN radical with unsaturated hydrocarbons could be a dominant route in the formation of cyanopolyynes, even at low temperatures and deserve a detailed laboratory investigation. The approach we have developed aims to bridge the temperature gap between resistively heated flow tubes and shock tubes. The present kinetic measurements are obtained using a new reactor combining a high-enthalpy source with a flow tube and a pulsed laser photolysis-laser-induced fluorescence system to probe the undergoing chemical reactions. The high-enthalpy flow tube has been used to measure the rate constant of the reaction of the CN radical with propane (C3H8), propene (C3H6), allene (C3H4), 1,3-butadiene (1,3-C4H6), and 1-butyne (C4H6) over a temperature range extending from 300 to 1200 K. All studied reactions of CN with unsaturated hydrocarbons are rapid, with rate coefficients greater than 10−10 cm3 * molecule−1 * s−1 and exhibit slight negative temperature dependence above room temperature. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 753-766, 201

High temperature reaction kinetics of CN(v = 0) with C2H4 and C2H6 and vibrational relaxation of CN(v = 1) with Ar and He

“…24 More recently, the source has finally been adapted to measure the kinetics of reactions of interest for hot atmospheres. 9 All of the components of the reactor and their functions were detailed in the former paper. 9 The buffer gas contained in a high-pressure reservoir (P res ∼ 600 mbar) is heated up by traveling through the hot porous walls of the graphite rod, before ending its course in the rod cavity.…”

“…9 All of the components of the reactor and their functions were detailed in the former paper. 9 The buffer gas contained in a high-pressure reservoir (P res ∼ 600 mbar) is heated up by traveling through the hot porous walls of the graphite rod, before ending its course in the rod cavity. The gas is then evacuated into a 38 mm flow tube in which a low pressure (P ch ∼ 4-5 mbar) is maintained by a Roots pump.…”

“…This apparatus has been recently employed to measure the reaction kinetics of the CN radical with propane, propene, allene, 1,3-butadiene, and 1-butyne over the 300-1200 K temperature range. 9 We use it in the present work to pursue the investigation of the reaction kinetics of CN with C 2 H 4 and C 2 H 6 over the same temperature range.…”

“…In particular, the reaction of CN with a selection of hydrocarbons exhibits a variety of temperature dependencies and products (see Ref. 9 and references therein) that deserve investigation.…”

Insights into gas-phase reaction mechanisms of small carbon radicals using isomer-resolved product detection

“…97 In the astrochemical context, the production of CN radical is generally attributed to the photolysis of HCN. 98 For higher temperatures, experimental techniques have measured kinetics of CN reactions with small linear hydrocarbons up 1200 K. 17,18 In combustion chemistry, the CN radical is a key species in the incorporation of nitrogen into large carbon structures and is also implicated in the fate of NO and many other reactions. 64 Nitrile species are also important in the combustion of biofuels.…”