Backward electron transfer , spin

The theory of geminate recombination experienced a similar evolution from primitive exponential model and contact approximation [19,20], to distant recombination carried out by backward electron transfer [21], However, all these theories have an arbitrary parameter initial separation of reactants in a pair, / o. This uncertainty was eliminated by unified theory (UT) proposed in two articles published almost simultaneously [22,23], UT considers jointly the forward bimolecular electron transfer and subsequent geminate recombination of charged products carried out by backward electron or proton transfer. The forward transfer creates the initial condition for the backward one. This is the distribution of initial separations in the geminate ion pair/(ro), closely analyzed theoretically [24,25] and inspected experimentally [26,27], It was used to specify the geminate recombination kinetics accompanied by spin conversion and exciplex formation [28-31], These and other applications of UT have been covered in a review published in 2000 [32],... 

The shape of the kernels (3.651) is rather obvious from the physical point of view. The kernels R and R are exactly the same as in Eq. (3.369) of the spinless theory. When spin conversion during encounter is negligible, the backward electron transfer to the ground state remains the single channel of geminate ion recombination. Therefore, the kernel R is 4 times smaller than... 

A. I. Burshtein. Diffusional and spin-dependent theory of chemiluminescence resulting from backward electron transfer. Chem. Phys., 289(2-3) 251-261, 2003. 

The rate constants (activation enthalpies) for the forward and backward reactions are kt = 0.019 0.002 s-1 (AH = 31 2 kJ mol"1) and k t = 0.041 0.003 s-1 (AH = 81.5 0.4 kJ mol-1) respectively. These results demonstrate that high-spin hemes are much less efficient in long distance electron transfer than low-spin analogue. 

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