Cascade, directed excited-state energy

Fig. 5 Cascade systems with directed excited-state energy transfer. On each step, the emission spectrum shifts to longer wavelengths...

The third class of mechanisms, involving either direct ionization of the liquid or electron ejection via field-emission, has been used to study the behavior of quasifree, localized, and solvated electrons. In contrast to the photoselectivity of the previous two schemes, a cascade of events occurs when high-energy electrons impart energy to a liquid. The resulting ions, excited states, and excess electrons provide a complex spectrum to unravel. However, the temporal evolution of each of the various species differs significantly and we are able to focus on the primary picosecond event, electron localization, with little interference. 

The random occurrence of inelastic collisions may be expected to lead to a complex pattern of displacements of the polymer chain. The overall motion of the chain may be described by a superposition of two forms of displacement Segmental and normal mode motion. The former is usually associated with the movement of a block of the chain relative to the main backbone change from structure (2) to (l). The only restrictions placed on such a motion is that sufficient energy should be available from inelastic collisions for the intramolecular interactions restricting free rotation of the polymer backbone to be overcome. It is implicit in this definition of segmental motion that the relaxation process involves direct activation from the lowest energy state via a cascade mechanism which may lead to excitation of the other thermal vibrational states. 

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