Detailed rate coefficients and the enthalpy change of the equilibrium reaction OH+C2H4=MHOC2H4 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 kf =(4±3)×10−13 exp[(1200±800)/T] cm3 molecule−1 s−1, kr =(6.2±1.0)×1011 exp[−(11 900±400)/T] s−1, and ka=(8.8+25−1.5)×109 exp[−(10 400+1600−400)/T] s−1, respectively.