Triplet ground state tunneling reactions

Interestingly, it was possible to probe the spin-forbidden component of the tunneling reaction with internal and external heavy atom effects. Such effects are well known to enhance the rates of intersystem crossing of electronically excited triplets to ground singlet states, where the presence of heavier nuclei increases spin-orbit coupling. Relative rates for the low-temperature rearrangements of 12 to 13 were... 

Fig. /. The four-state model used for the description of triplet energy transfer in the RC according to Angerhofer (1997). For detailed explanation, see text. The filled arrows denote the rates that have been observed and described in the literature. The broken arrows depict rates that are either unknown (from and to BS) or speculative (k3 -i for bypass reaction, and k4 -2 for tunneling). The rates defined by arrows between different molecules (P, B, and Car) are in reality second order rates, i.e. they depend on the ground state concentrations of the molecule the excited state of which they point to. In the case of low excitation densities, i.e., when double excitation of the RCs can be neglected these rates can be assumed to be first order as for example done by Frank et al. (1996b).

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