This paper considers the rate constants for the following processes: Aromatic Radical + Methyl double left right arrow AromaticCH(3)(+) double right arrow AromaticCH(2) + H AromaticCH(3) where M is the collision partner and aromatic CH3 is toluene, 1-methylnaphthalene or 1-methylphenanthrene. Rate constants are derived over a range of temperatures and pressures. Primary interest is focused on the effect of molecular size on temperature as well as pressure dependent rate constants. Results are based on the toluene system where comparisons can be made with experimental data and ab initio and RRKM calculations from the literature. A general strategy for deriving rate constants for chemical activated as well as thermal reactions, which is readily extendable to larger molecules, has been validated. The special feature of these reactions is the formation of resonance stabilized aromatic molecules. The results demonstrate the necessity of considering chemical activation processes in most of the cases where excited adducts are formed. These include oxygen addition to radicals as well as soot formation processes involved in ring growth. Chemical activation processes are intimately related to thermal process and their inclusion in current databases where thermal processes are properly represented is mandatory. Published by Elsevier Inc. on behalf of The Combustion Institute.