Experimental and Theoretical Studies of the C₆H₅ + C₆H₆ Reaction

Abstract

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(11.91±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.