The enthalpy change and the detailed rate coefficients of the equilibrium reaction OH+C₂H₂⇌HOC₂H₂ over the temperature range 627-713 K

The reaction between OH and C₂H₂ in He has been studied over the pressure range 414-864 Torr and the temperature range 627-713 K by means of the laser-photolysis/laser-induced-fluorescence technique. Analysis of the temporal profile of [OH] yielded the forward and the reverse rate coefficients, hence the equilibrium constant for the reaction OH+C ₂H₂+⇌HOC₂H₂+M. The temperature dependence of the equilibrium constant yielded the enthalpy of reaction ΔH(670±43 K) = -(34.2±1.0) kcal mol^-1 and the entropy of reaction AS(670±43 K) = -(30.5±1.2) cal K ^-1 mol^-1 near 670 K; consequently, ΔH⁰ (298 K) = -(33.6±1.2) kcal mol^-1 and ΔS⁰ (298 K) = -(28.9±1.5) cal K^-1 mol^-1 were derived for the reaction, in agreement with theoretical prediction. The temperature dependence of the rate coefficients for the forward, the reverse, and the adduct-loss (isomerization/decomposition other than the reverse) reactions near 1 atm have been determined to be k_f = (1.1 ± 0.2) × 10-¹³ exp[(1460 ± 500)/T] cm³ molecule^-1 s^-1, k_r = (2.2 ± 0.4) × 10¹² exp[ - (15 100 ± 600)/T] s^-1, and k_a = (7.4 _-5.6^+0.2) × 10¹⁰ exp[ - (13 200 _-1700⁺⁷⁰⁰)/T]s^-1, respectively.