The absolute rate of the recombination of three hydrogen atoms is calculated entirely theoretically. The manner in which rotation determines the dimensions of the activated complex in cases having little or no activation energy is discussed. The theoretical data are in good agreement with the experimental rates of Steiner and of Amdur. An immediate consequence of the theory is that energy transfer occurs most effectively among particles which can react with each other, free atoms being more efficient than molecules. A qualitative application of potential surfaces to the problem of energy transfer as met in velocity of sound experiments and in experiments on maintenance of high pressure rates of unimolecular reactions is made.