DETAILED RATE COEFFICIENTS AND THE ENTHALPY CHANGE OF THE EQUILIBRIUM REACTION OH + C2H4 (M)REVERSIBLE HOC2H4 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 reversible HOC2H4 + M. The temperature dependence of the equilibrium constant led to the enthalpy of reaction DELTA-H = - (30.3 +/- 0.8) kcal mol-1 and the entropy of reaction DELTA-S = - (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 ion 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) X 10(-13) exp[(1200 +/- 800)/T] cm3 molecule-1 s-1, k(r) = (6.2 +/- 1.0) X 10(11) exp[- (11 900 +/- 400)]T] s-1, and k(a) = (8.8(-1.5)+25) X 10(9) exp[-10 400(-400)+1600)/T] s-1, respectively.