Theory of Electron-Tunnelon Optical Band
The interaction of the electronic excitation of a guest molecule with phonons, and the manifestation of this interaction in electron-phonon bands have been examined in previous chapters. However, in polymers and glasses there is an additional type of low energy excitation which accompanies tunneling transitions of atoms or molecules from one potential well to another. These excitations are described within the framework of the two-level system (TLS) model. Some details of the TLS model have been discussed in Sect. 6.5. Since the excitation in the TLS is realized via a tunneling transition through a potential barrier, the excitation quantum in the TLS was called a tunnelon. Tunnelons are low frequency excitations of a few cm−1. Because they exist in all polymers and glasses, they influence low temperature properties of these materials. Due to the electron-tunnelon interaction, tunnelons can be created and annihilated upon electronic excitation of the chromophore of a guest molecule. These electron-tunnelon optical bands are the topic to be considered in last part of this book.
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