Discussion on energy distribution in molecules in relation to chemical reactions

It often happens that the empirical observations of chemistry reveal the working of principles which can be easily interpreted in terms of physical theories, but which might have been difficult to predict. One need only mention the question of the nature of valency as one of the most conspicuous examples. For this reason it is useful if problems lying on the border line of physics and chemistry are discussed from both points of view. The present theme is the distribution of energy in molecules and its relation to the phenomena of chemical change. We know that the transference of energy from one molecule to another and, in particular, the accompanying interconversion of translational and internal energy depend upon specific mechanisms which give rise to phenomena of great interest. I need only mention the influence of hydrogen and certain other gases in maintaining the energy distribution in unimoleculer reactions, the variation of the velocity of sound with frequency, due to the finite time required for the establishment of equilibrium in the energy distribution among the internal degrees of freedom, and lastly that curious inability of solvent molecules to degrade the light energy absorbed by fluorescent substances.