Nature of the Measurements Rate Coefficients and Branching Ratios or Cross Sections

Nature of the Measurements Rate Coefficients and Branching Ratios or Cross Sections 

The rate coefficient k T) of a bimolecular chemical reaction in the gas phase at a given temperature T results from the thermal average of a very large number of bimolecular reactive collisions. These collisions involve reagents in a variety of quantum states, the populations of which follow Boltzmann s law at this temperature, with a Maxwell-Boltzmann distribution of centre of mass kinetic energies Et (hereafter KEcm)- Ignoring any dependence of the reaction cross section (a) on the internal states of the reagents, the relationship between the rate coefficient and the reaction cross section is 

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