Experimental Study of the Reaction between Vinyl and Methyl Radicals in the Gas Phase. Temperature and Pressure Dependence of Overall Rate Constants and Product Yields

Abstract

The vinyl−methyl cross-radical reaction was studied by laser photolysis/photoionization mass spectroscopy. Overall rate constants and quantitative product yields were obtained in direct real-time experiments in the temperature region 300−900 K and bath gas (He) density (3−12) × 1016 molecules cm-3. The observed overall C2H3 + CH3 rate constant is independent of pressure and demonstrates a slight negative temperature dependence, which can be represented by the expression k4 = 5.1 × 10-7T-1.26 exp(−362/T) molecule-1 cm3 s-1 (The expression has ±10% uncertainty, see text for details.). Propene, acetylene, and allyl radicals were identified as primary products of the C2H3 + CH3 reaction. At room temperature propene and acetylene are the major products of the reaction, whereas at 900 K production of allyl radicals becomes the dominating channel. On the basis of these experimental results, a mechanism consisting of two major routes is proposed. One route proceeds via direct abstraction of a hydrogen atom from t...