On the separation of timescales in chemically activated reactions

Abstract

Chemically activated reactions are important in describing the composition of reactive gases including flames, planetary atmospheres, and the interstellar medium (ISM). In a chemically activated reaction, two reactants combine to populate a vibrationally excited well that can undergo unimolecular transformations (isomerization, dissociation) or be thermalized through collisions with the bath gas. Once a well has been thermalized, it may still have sufficient energy to undergo further unimolecular reaction, in a purely thermal process. If the timescale for the thermally activated process is sufficiently short, such that it approaches that of the chemically activated reaction, the two concurre..