Determination of the temperature and pressure dependence of the reaction OH + C2H4 from 200–400 K using experimental and master equation analyses

Abstract

The pressure and temperature dependence for the reaction of OH + C₂H₄ was studied over the range of conditions: 200–400 K and 5–600 Torr by laser flash photolysis, laser-induced fluorescence (FP-LIF). Additional experiments were conducted at room temperature by laser flash photolysis, cavity ring-down spectroscopy to facilitate determination of the high pressure limit. One-dimensional master equation calculations were conducted to test the temperature and pressure dependence of the reaction in He and in N₂. The energetics of the reaction and geometries of intermediate species were calculated by ab initio calculations (DFT-BH&HLYP/6-311+G(3df,2p) and CBS-APNO level along DFT-IRC, respectively. An investigation into the importance of a pre-reaction van der Waals complex on the kinetics over the pressure range of the troposphere is discussed. The high pressure rate coefficient was extracted by fitting the master equation calculations to the data and yields k_∞ = 5.01 × 10⁻¹² exp(148/T) cm³ molecule⁻¹ s⁻¹. The master equation calculations were then optimized for the pressure fall-off in He and N₂ by varying the average downward energy transfer parameter (〈ΔE〉_down) for the different collision partners and finally fitted to a Troe expression to determine k_o and F_cent for use in atmospheric modeling.