Abstract
The association of benzene molecules to form dimers has been studied at temperatures between 15 and 123 K in a CRESU (Cinétique de Réactions en Ecoulement Supersonique Uniforme) apparatus with helium as the buffer gas. Second-order rate coefficients (k2) for the formation of dimers have been determined for temperatures between 15 and 88 K. The effective third-order rate coefficients (no study of fall off behavior has been undertaken) obtained by dividing the values of k2 by [He] show a strong negative temperature dependence. Further evidence for the formation of dimers at critical concentrations of benzene has been obtained from a study of the CH+C6H6 reaction and from LIF spectra. Modelling calculations indicate that any systematic errors in the results arising from the formation of higher oligomers are small. Based on a model in which it is assumed that the benzene molecules in the dimer are free to rotate, third-order rate coefficients have been calculated for dimerization and are in good agreement with the experimental values for T⩾30 K, where effects of falloff should not be too great.
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