Detailed rate coefficients and the enthalpy change of the equilibrium reaction OH+C₂H₄⇌^MHOC₂H ₄ over the temperature range 544-673 K

The reaction between OH and C₂H₄ in He has been studied over the pressure range 278-616 Torr and the temperature range 544-673 K by means of the laser-photolysis/laser-induced-fluorescence technique. Analysis of the temporal profile of [OH] yielded the equilibrium constant for the reaction OH + C₂H₄ + M⇌HOC₂H₄ + M. The temperature dependence of the equilibrium constant led to the enthalpy of reaction ΔH = -(30.3 ± 0.8) kcal mol^-1 and the entropy of reaction ΔS = -(30.9 ± 1.0) cal K^-1 mol ^-1 near 600 K, in agreement with previous predictions. Analysis of the detailed rate coefficients suggests that the H-atom abstraction reaction is relatively unimportant in the temperature range of our study; the rate coefficient determined previously for the H-atom abstraction near 673 K may have been overestimated. The temperature dependence of the rate coefficients for the forward, the reverse, and the adduct-loss reactions have been determined to be k_f = (4±3)×10^-13 exp[(1200±800)/T] cm³ molecule^-1 s^-1, k_r = (6.2±1.0)×10¹¹ exp[ - (11 900±400)/T] s ^-1, and k_a = (8.8_-1.5 ⁺²⁵) ×10⁹ exp[ - (10 400_-400 ⁺¹⁶⁰⁰)/T] s ^-1, respectively.