Bird’s total collision energy model: 4 decades and going strong

The focus of this work is the total collision energy model of chemical reactions, derived through the application of the collision theory in pioneer work of Bird in 1977–1978. Several aspects of the model, such as the inclusion of the internal degrees of freedom, the detailed balance, and some numerical limitations, are considered. The use of the model for exchange and dissociation reactions, its connection to other chemistry models of the direct simulation Monte Carlo method, and the applicability to different problems of rarefied gas dynamics are discussed.