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We present an experimental and theoretical investigation of the reaction of vibrationally excited CN ( v = 1) with isomers of butadiene at low temperature. The experiments were conducted using the newly built apparatus, UF-CRDS, which couples near-infrared cw-cavity ring-down spectroscopy with a pulsed Laval flow. The well-matched hydrodynamic time and long ring-down time decays allow measurement of the kinetics of the reactions within a single trace of a ring-down decay, termed Simultaneous Kinetics and Ring-down (SKaR). The pulsed experiments were carried out using a Laval nozzle designed for the 70 K uniform flow with nitrogen as the carrier gas. The measured bimolecular rates for the reactions of CN ( v = 1) with 1,3-butadiene and 1,2-butadiene are (3.96 ± 0.28) × 10 −10 and (3.06 ± 0.35) × 10 −10 cm 3 per molecule per s, respectively. The reaction rate measured for CN ( v = 1) with the 1,3-butadiene isomer is in good agreement with the rate previously reported for the reaction with ground state CN ( v = 0) under similar conditions. We report the rate of the reaction of CN ( v = 1) with the 1,2-butadiene isomer here for the first time. The experimental results were interpreted with the aid of variable reaction-coordinate transition-state theory calculations to determine rates and branching of the addition channels based on a high-level multireference treatment of the potential energy surface. H-abstraction reaction rates were also theoretically determined. For the 1,2-butadiene system, theoretical estimates are then combined with literature values for the energy-dependent product yields from the initial adducts to predict overall temperature-dependent product branching. H loss giving 2-cyano-1,3-butadiene + H is the main product channel, exclusive of abstraction, at all energies, but methyl loss forming 1-cyano-prop-3-yne is 15% at low temperature growing to 35% at 500 K. Abstraction forming HCN and various radicals is important at 500 K and above. The astrochemical implications of these results are discussed.
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Kinetic study of the CN radical reaction with 2‐methylfuran
Abstract The gas phase reaction of the ground state cyano‐radical (CN (X2∑+)) with 2‐methylfuran (2‐MF) is investigated in a quasi‐static reaction cell at pressures ranging from 2.2 to 7.6 Torr and temperatures ranging from 304 to 440 K. The CN radicals are generated in their ground electronic state by pulsed laser photolysis of gaseous cyanogen iodide (ICN) at 266 nm. Their concentration is monitored as a function of reaction time using laser‐induced fluorescence at 387.3 nm on the B2∑+(ν′ = 0) ← X2∑+(ν″ = 0) vibronic band. The reaction rate coefficient is found to be rapid and independent of pressure and temperature. Over the investigated temperature and pressure ranges, the rate coefficient is measured to be 2.83 (± 0.18) × 10−10cm3molecules s−1. The enthalpies of the stationary points and transition states on the CN + 2‐MF potential energy surface are calculated using the CBS‐QB3 computational method. The kinetic results suggest the lack of a prereactive complex on the reaction entrance channel with either a very small or nonexistent entrance energy barrier. In addition, the potential energy surface calculations reveal only submerged barriers along the minimum energy path. Based on comparisons between previous CN reactions with unsaturated hydrocarbons, the most likely reaction pathway is CN addition onto one of the unsaturated carbons followed by either H or methyl elimination. The implications for the transformation of biomass‐derived fuels in nitrogen‐rich flames is discussed.
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- PAR ID:
- 10455694
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- International Journal of Chemical Kinetics
- Volume:
- 52
- Issue:
- 11
- ISSN:
- 0538-8066
- Page Range / eLocation ID:
- p. 838-851
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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