Detailed rate coefficients and the enthalpy change of the equilibrium reaction OH+C ₆ H ₆ ↔ ^M HOC ₆ H ₆ over the temperature range 345-385 K

The reaction between OH and C ₆ H ₆ in He has been studied over the pressure range 250-500 Torr and the temperature range 345-385 K by means of the laser-photolysis/laser-induced-fluorescence technique. Analysis of the temporal profile of [OH] yielded the detailed rate coefficients and the equilibrium constant for the reaction OH+C ₆ H ₆ +M↔ HOC ₆ H ₆ +M. The temperature dependence of the rate coefficients for the forward, the reverse, and the adduct-loss reactions have been determined to be k _f =(2.0±0.1)×10 ^-14 exp[(1420±250)/T] cm ³ molecule ^-1 s ^-1 , k _r =(3.0±0.2)×10 ¹² exp[-(8240±320)/T] s ^-1 , and k _a =(1.7±0.3)×10 ⁶ exp[- (3500±360)/T] s ^-1 , respectively. The temperature dependence of the equilibrium constant led to the enthalpy of reaction ΔH(365±20 K)=-(20.0±1.2) kcal mol ^-1 and the entropy of reaction ΔS(365±20 K)=-(33.6±2.5) cal K ^-1 mol ^-1 , greater than previously reported values; after correction for temperature dependence, ΔH ⁰ (298 K)=-(19.9±1.2) kcal mol ^-1 and ΔS ⁰ (298 K)=-(33.4±2.6) cal K ^-1 mol ^-1 .