Transition state theory, configuration and potential energy

1 Transition state theory, configuration and potential energy 

The reacting molecules and products are described in terms of all the atoms in a single reaction unit made up of all the reacting species and products, e.g. the reaction 

When the geometrical configuration changes, the potential energy, PE, of the reaction unit also changes, and a PE surface summarizes these changes. 

For the general reaction e.g. A + B — C + D, where A, B, C and D are polyatomic molecules, the PE surface is /(-dimensional. Fortunately, all the basic properties of an /(-dimensional surface of relevance to kinetics can be exemplified by the simpler three-dimensional surface. This describes the reaction e.g. X + YZ — XY + Z, where 

Y and Z are atoms, and where a linear approach of X to YZ and recession of Z is assumed, implying a linear configuration for the reaction unit  

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