When large molecules are excited by absorption of one or several photons, or by the impact of electrons, ions, atoms, or other particles, they may relax by emitting electrons, photons and/or by fragmentation. In statistical
fragmentation, where the internal energy is statistically distributed on all
vibrational modes prior to decay, the fragmentation channels corresponding to the lowest dissociation energies and/or the lowest energy barriers dominate strongly. However, fragmentation may also occur before the excitation energy is distributed across the internal degrees of freedom. When an atom collides with a molecule it may knock out one or more of the molecule's individual atoms in billiard-ball-like processes which will yield different, generally more reactive, fragments than those formed in statistical processes. Such non-statistical fragmentation processes have been observed in several experiments by the Atomic Physics group.
