Based on a surface from our group, trajectory calculations were performed to analyze the effects of vibrational versus translational energy on the dynamics of the F + CH4 reaction, in comparison with the F + CH2D2. For this 'early transition state' reaction, translational energy is more effective in driving the reaction than an equivalent amount of energy in vibration, consistent with an extension of Polanyi's rules. This behaviour is the opposite to that found for the similar F + CH2D2 reaction using the same surface, indicating that, in polyatomic reactions, the application of the Polanyi's rules which are well established in atom - diatom reactions, is neither straightforward nor always valid. (C) 2010 Elsevier B.V. All rights reserved.