A very important measurable quantity in molecular beamMolecular beam experiments is the kinetic energy of the fragments produced in a unimolecular reaction. The kinetic energy is determined by a combination of the reverse process cross section and the microcanonical temperature of the particle. The basic formalism required to solve this problem has been established in Chap. 5. We saw little difference between the expressions for the electron- and atom emission rate constants and this is true also for the distributions of relative kinetic energies created during unimolecular decays. The differences that do appear when the equations are applied are caused by the differences in the capture cross section, which is a place where the two types of decays can differ significantly.