For reactions such as vibrational energy transfer processes, the Arrhenius form of the rate expression Equation 4–5 is often not used. Instead, it is common to use the Landau-Teller expression,

(4–33)

In addition, we have provided the possibility to blend the Arrhenius expression with the Landau-Teller expression in the general expression, as follows:

(4–34)

Clearly, by setting and to zero, the Arrhenius expression is recovered, and by setting and to zero, the standard Landau-Teller expression is recovered. If appropriate, however, all the parameters can be used together to provide more flexibility in the reaction-rate expression than could be afforded by one of the forms alone.