Chromophore Interacting with Phonons and TLSs Which Are not in Thermal Equilibrium
The equations for the density matrix derived in Part III take into account the interaction with phonons and those TLSs which have already reached thermal equilibrium. These equations were used in the last part of the book, when studying the photon echo. Let us generalize them to the density matrix and take into account interactions with TLSs whose relaxation rate is slower than the electronic relaxation rate. Such TLSs will approach thermal equilibrium during the course of optical measurements. From the mathematical point of view, this means that tunneling processes must be taken into account in the equation for the density matrix. The relevant theory was derived by the author in  and  and is discussed in this chapter.
KeywordsQuantum State Density Matrix Guest Molecule Electronic Excitation Ground Electronic State
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