Title: The effect of internal energy on the addition of hydroxyl radicals and deuterium atoms to aromatic hydrocarbons
Abstract: This paper reports a study of the reactions of hydroxyl radicals and deuterium atoms with toluene and 1,3,5-trimethylbenzene under single collision conditions. The internal (vibrational and rotational) energy of the hydrocarbon was varied while the distribution of relative kinetic energies of collision was kept constant. The amount of OH–aromatic hydrocarbon complexes which reached the mass spectrometer detector decreased as the vibrational and rotational temperature of the hydrocarbon was increased. The amount of hydrogen atom displacement product and methyl radical displacement product decreased slightly. If the dynamics of the methyl radical displacement reaction are similar to the analogous F+ aromatic hydrocarbon reaction (arguments are presented which indicate that this may well be the case), then our results show that there is no significant increase in the branching ratio of the methyl radical displacement path with increased hydrocarbon temperature. This means that the complexes which reached the detector at low hydrocarbon temperature but which decomposed before reaching the detector at higher hydrocarbon temperatures decomposed back to reactants rather than to products. The amount of D–aromatic hydrocarbon complexes reaching the detector increased as the hydrocarbon temperature was increased. This result probably means that there is a barrier to complex formation and that vibrational and/or rotational energy of the hydrocarbon is effective at overcoming this barrier.