Temperature Dependence and Deuterium Kinetic Isotope Effects in the CH (CD) + C₂H₄ (C₂D₄) Reaction between 295 and 726 K

Abstract

Absolute rate coefficients for the reactions CH + C 2 H 4 (k 1 ), CD + C 2 H 4 (k 2 ), CH + C 2 D 4 (k 3 ), and CD + C 2 D 4 (k 4 ) have been measured by the laser photolysis/CW laser-induced fluorescence method at temperatures from 295 to 726 K. The individual rate coefficients can be described by k 1 ) (2.85 ( 0.02) (T/293) -(0.31 ( 0.02) × 10 0.21 ( 0.02) × 10 -10 cm 3 molecule -1 s -1 , where the error estimates are (2σ and reflect the precision of the fit. The slight negative temperature dependence is in good agreement with previous determinations of this reaction, and is consistent with barrierless formation of an excited C 3 H 5 adduct followed by rapid decomposition. The kinetic isotope effect for deuteration of the CH radical is k 1 /k 2 ) 1.19 ( 0.04 at room temperature, and declines somewhat with temperature. The kinetic isotope effect for deuteration of the ethylene is k 1 /k 3 ) 1.08 ( 0.04 at 290 K, and is approximately independent of temperature over the range studied. Quantum chemical calculations of the reaction path indicate that the reaction is dominated by addition, with a minor role possible for insertion.

Cyclic Versus Linear Isomers Produced by Reaction of the Methylidyne Radical (CH) with Small Unsaturated Hydrocarbons

“…The small kinetic isotope effects for the CH/CD + C 2 H 4 /C 2 D 4 reactions measured by Thiesemann et al 21 together with quantum chemical calculation by the same authors strongly suggest that the main entrance channel of the CH + ethylene reaction is the direct cycloaddition to form the cyclopropyl radical.…”

Direct detection of pyridine formation by the reaction of CH (CD) with pyrrole: a ring expansion reaction

“…An analogy can also be drawn from the study of Thiesemann and coworkers 49 on the reactions of CH/CD + C 2 H 4 . The small kinetic isotope effect measured and the characterization of the reaction path by density functional and QCISD(T) calculations strongly suggest that the mechanism of CH + C 2 H 4 is dominated by addition to the double bond.…”

“…This behavior is consistent with a barrierless reaction where the rate limiting step is the formation of the adduct. 49 Therefore, even at lower temperatures encountered in the ISM or in the atmosphere of Titan, the cycloaddition of CH radicals to the π-system of pyrrole could lead to ring expansion and formation of the pyridine molecule through H atom loss. Also, the C 5 H 5 N isomer distribution might be temperature dependent.…”

Methylacetylene (CH3CCH) and propene (C3H6) formation in cold dense clouds: A case of dust grain chemistry

“…2.! Rate constant from capture rate theory and branching ratio deduced from theoretical study of the isomeric CH + C 3 H 6 (Trevitt et al 2013, Loison & Bergeat 2009 1.6 1.6 7 7 (Butler et al 1981, Berman et al 1982, Thiesemann et al 1997, Thiesemann et al 2001, Canosa et al 1997, McKee et al 2003, Goulay et al 2009, Gosavi et al 1985, Wang & Huang 1998, Davis et al 1999, Stranges et al 2008, Zhang et al 2012, Loison & Bergeat 2009 10.! CH + C 2 H 6 → CH 3 + C 2 H 4 → H + C 3 H 6 2.8e-11 5.0e-12 -0.648 -0.648 43.6 43.6…”