A systematic treatment of quantum mechanical reaction coordinates

The problem of constructing an orthogonal curvilinear coordinate system which retains the intuitive clarity of the reaction path concept is treated by canonical point transformation. The Hamiltonian describing the collision process is transformed rigorously onto the reaction-coordinate net; no linearization or approximation is employed. Difficulties inherent in earlier work (e.g., triple-valued regions, restriction to regions very close to the reaction path, etc.) do not occur. The transformed momenta and Hamiltonian are obtained in general. A simple, yet useful, example transformation is worked out in detail and applied to a realistic problem, the LEPS potential surface for H+Cl ₂→HCl+Cl. The example transformation is also used in a comparison of our method with that of Marcus. The canonical mapping of Connor and Marcus is shown to be a special case of the present method. Applications of the procedure to polydimensional surfaces, dissociative reactions, and actual dynamical calculations are discussed.