Nuclear reactions entrance channel

Such a process may be described as the system passing from the entrance channel (reactants) to the exit channel (products) on the electronic energy map as a function of the nuclear coordinates. For reaction A -I- BC... 

We denote the entrance and exit reaction channels by a and 3, respectively. In space-fixed coordinates, denoted by (xyz), the inter-nuclear distance vector of the reactant molecule is r and the vector of the colliding atom with respect to the centre of mass of the diatomic molecule is Ry. The angle between y and Ry is y. We define the mass-scaled coordinates... 

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