Pressure and Temperature Dependence of the Reaction of Vinyl Radical with Ethylene

Abstract

This work reports measurements of absolute rate coefficients and Rice-Ramsperger-Kassel-Marcus (RRKM) master equation simulations of the C2H3+C2H4 reaction. Direct kinetic studies were performed over a temperature range of 300-700 K and pressures of 20 and 133 mbar. Vinyl radicals (H2C=CH) were generated by laser photolysis of vinyl iodide (C2H3I) at 266 nm, and time-resolved absorption spectroscopy was used to probe vinyl radicals through absorption at 423.2 nm. Measurements at 20 mbar are in good agreement with previous determinations at higher temperature. A weighted three-parameter Arrhenius fit to the experimental rate constant at 133 mbar, with the temperature exponent fixed, gives k=(7+/-1)x10(-14) cm3 molecule(-1) s(-1) (T/298 K)2 exp[-(1430+/-70) K/T]. RRKM master equation simulations, based on G3 calculations of stationary points on the C4H7 potential energy surface, were carried out to predict rate coefficients and product branching fractions. The predicted branching to 1-methylallyl product is relatively small under the conditions of the present experiments but increases as the pressure is lowered. Analysis of end products of 248 nm photolysis of vinyl iodide/ethylene mixtures at total pressures between 27 and 933 mbar provides no direct evidence for participation of 1-methylallyl.

Pressure and temperature dependence of the reaction of vinyl radical with alkenes II: Measured rates and predicted product distributions for vinyl+propene

“…The product of this rate constant with the initial concentration of vinyl is with 25% of the two values for k 2 reported in Table S1. In contrast, if the rate of vinyl + vinyl iodide at 298 K is approximated by the previously reported [5] rate for vinyl + ethene, or 5 Â 10 À16 cm 3 molecules À1 s À1 , then the product of this rate with the initial concentration of vinyl iodide is several orders of magnitude smaller than k 2 . Thus, the zero-propene intercept is chiefly attributable to the vinyl self-reaction.…”

“…The experimental apparatus has been described previously [5], therefore only a brief summary will be given in this paper.…”

“…To facilitate comparison with other work on vinyl + alkenes, the data for vinyl + ethene [5] was refit with a temperature exponent of 1.6, yielding k v+e = 7.6 Â 10 À13 cm 3 molecule À1 s À1 (T/1000) 1.6 exp[À1600/T]. It is expected that the rate for vinyl + ethene would have a larger A-factor than k 1 , since (i) the reaction path degeneracy is twice that of vinyl + propene, and (ii) rotational constants for ethene are larger than those of propene.…”

The neutral photochemistry of nitriles, amines and imines in the atmosphere of Titan

“…C 2 H 3 CN + H reaction is generally taken from Monks et al (1993). However the data of Monks et al (1993), at room temperature only, are very imprecise and their rate constant for the C 2 H 3 + HCN reaction is notably higher than the rate constant of reactions of C 2 H 3 with unsaturated hydrocarbons (Wang and Frenklach, 1994;Knyazev et al, 1996;Callear and Smith, 1986;Ismail et al, 2007) which is a surprising result as several other atoms and radicals (C 2 , C 2 H, CN, OH, F, Cl) are significantly less reactive with HCN (Frost et al, 1986;Hoobler and Leone, 1997;Fukuzawa and Osamura, 1997;Sander et al, 2011) than with unsaturated hydrocarbons (Nesbitt et al, 1994;Li et al, 2006a,b;Paramo et al, 2008;Daugey et al, 2008;Canosa et al, 2007;Lee et al, 2000;Vakhtin et al, 2001;Sims et al, 1993;Gannon et al, 2007;Atkinson et al, 2004;McKee et al, 2007;Nesbitt et al, 1999;Gu et al, 2006;Mebel et al, 2006;Bouwman et al, 2012;Golden, 2012). We performed theoretical calculations for this reaction finding a barrier in the entrance valley equal to 18.0 kJ/mol at the DFT level (M06-2X/cc-pVTZ), in good agreement with Petrie (2002), and classical transition state theory leads to a rate constant equal to k(C 2 H 3 +HCN) = 1.0 Â 10 À12 exp (À2300/T) cm 3 molecule À1 s À1 , a much lower value than Monks et al (1993).…”

Kinetic Modeling of Ethane Pyrolysis at High Conversion

“…Comparison of measured overall rate constants for the reaction of vinyl with ethylene to that calculated in this study. Data: Shestov et al, 47 Ismail et al, 48 Fahr and Stein. 46 The Journal of Physical Chemistry A ARTICLE order of ∼4 kcal/mol.…”