Interwell transition

For small noise intensities the system spends most of the time fluctuating near the stable positions, and interwell transitions occur only occasionally. Q((o) can then be represented as the sum of partial contributions from vibrations about the equilibrium positions x weighted with the populations of the corresponding stable states wn, and from interwell transitions. The intrawell contribution takes the form... 

As interwell transitions can be neglected, the calculation of the RFs reduces to the consideration of each well separately as in Ref. [4], We consider the spin-orbit coupling as our perturbation. It is then convenient to use CG coefficients for the 7)-type of perturbation this introduces. Within the 7) orbital states, the CG coefficients are... 

However, the case of il being exactly zero is to some extent an exception. At any finite Q, one has to remember that the time X is exponential in a that is, it grows infinitely with cooling the system. Therefore, at low temperatures the interwell transition is completely frozen, and the situation is governed by intrawell relaxation. The latter is sensitive to the details of the potential near the bottom of the well, and for the system in question is determined by the infinite eigenvalue spectrum A of the kinetic equation (4.225) for k > 3. 

Some estimations on the magnitude of the SR effect are given in Refs. Ill and 112. We would like also mention an extension of the framework presented for the case of the excited field nonparallel to the particle anisotropy axis. As shown in Ref. 113, despite the absence of interwell transitions for the components of the particle magnetic moment perpendicular to the anisotropy... 

Such a replacement reduces all the magnetic dynamics to the interwell transition, ignoring all the intrawell motions. For this reason, the blocking... 

In all these systems, the transfer takes place between chemically identical acceptor sites, the equivalence of which is destroyed only by the environment (or in some instances by a peripheral chemical substitution). The theoretical study of PT in such symmetric PES is simplified and is of special interest, since the observation of coherent tunneling provides additional information that can be compared with numerical calculations. Detailed experimental studies have been made for isolated small molecules and molecular complexes [61-67, 111]. In condensed phases, coherent tunneling was observed for proton translations in only a few systems, where the delocalization of the wave function over both wells is sufficient to observe interwell transitions (see below). 

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