Experimental and Theoretical Studies of the C₆H₅ + C₆H₆ Reaction

The absolute rate constants for the C₆H₅ + C₆H₆ and C₆D₆ reactions have been measured by cavity ringdown spectrometry at temperatures between 298 and 495 K at a constant 40 Torr Ar pressure. The new results, which reveal no detectable kinetic isotope effect, can be represented by the Arrhenius equation, k₁ = 10^{(11.9±91±0.13)} exp[-(2102 ± 106)/T] cm³/(mol s). Our low-temperature data for the addition/stabilization process, C₆H₅ + C₆H₆ → C₁₂H₁₁, can be correlated with those obtained in a low-pressure, high-temperature Knudsen cell study for the addition/displacement reaction, C₆H₅ + C₆H₆ → C₁₂H₁₀ + H, by the RRKM theory using the molecular and transition-state parameters computed at the B3LYP/6-311G(d,p) level of theory. Combination of these two sets of data gives k₁ = 10^{(11.98±0.03)} exp[-(2168 ±34)/T] cm³(mol s) covering the temperature range 298-1330 K. The RRKM theory also correlates satisfactorily the forward reaction data with the high-temperature shock-tube result for the reverse H-for-C₆H₅ substitution process with 2.7 and 4.7 kcal/mol barriers for the entrance (C₆H₅ + C₆H₆) and reverse (H + C₁₂H₁₀) reactions, respectively. For modeling applications, we have calculated the forward reaction rate constants for the formation of the two competing products, H + C₁₂H₁₀ and C₁₂H₁₁, at several pressures covering 300 K < T < 2500 K.