Reactant and product coordinate systems

The single biggest problem in quantum reactive scattering theory is that there are inevitably at least two coordinate systems involved in a calculation. The coordinate system which is best suited to the reactant arrangement is different from that which is best for the product arrangement. In figure 8.1, the two coordinate systems are shown schematically for the reaction A-hBC AB+C. 

The initial conditions must be specified in the reactant coordinates, while any final state analysis, needed for instance to determine the quantum state distribution of the products, must be performed in product coordinates. 

In the past we used to start the calculation off in reactant coordinates. At some strategic time, when the wavepacket was concentrated in the strong 

More recently we discovered that it was possible to propagate starting from t=0 in product coordinates. It is also possible to compute total reaction probabilities by using reactant coordinates only. This may be done by computing the flux of particles which do not react. The total flux, minus the non-reacting flux, is then equal to the flux of particles which does react. 

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