Scattering cross section velocity distribution function

The experimentalist interested in reaction dynamics dreams of the day when it will be possible to select all, or nearly all, of the initial parameters for potentially reactive collisions and, at the same time, observe the products scattered at particular angles as a function of their quantum states. (In this ideal experiment, the distribution of final relative velocities could be obtained through the equation of energy conservation, since the total energy will be defined and the distribution of final internal energies will be measured.) These experiments would yield detailed (or state-to-state) differential cross sections. Of course, the reaction dynamicists millenium, like most others, is some way off and, until such time as this dream is fulfilled, we only have the... 

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