Electron Exchange in Spurs

In order to understand the origin of the ERP effect, consider a simple two-pair spur in the absence of other coherent and incoherent effect, which can exhibit two types of correlation the first type considers two singlet correlated radical pairs (type 1) and the second considers two triplet correlated radical pairs (type 2). 

Two singlet correlated radical pairs Considering the type (1) first, the wavefunction xjf for the two ion-pair spur can be written as 

Equation (8.12) has two important features (i) The wavefunction is still overall singlet but has an overall probabiUty of 75% triplet and 25% singlet for pairs (1,4) and (2, 3). (ii) If radical pair 2,3 reacts and is found to be triplet, then pair (1,4 must also be triplet as there is no component in the wavefunction in Eq. (8.12), where one pair is singlet and the other triplet. This incoherent change in the spin state of the disjoint radical pair is hypothesised to act as an extra source of relaxation. It can be seen that this non-local effect is independent of the distance between radical pairs and any magnetic interactions. 

Two triplet correlated radical pairs The second type of action at a distance concerns type (2) spurs where a triplet encounter between 1,4 (which occurs in 75% of the cases in spurs) causes the disjoint pair 2,3 to adopt the same spin multiplicity. The normaUsed wavefunction after removing the singlet terms becomes 

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The preceding sections have illustrated the main concepts behind the TR MFE technique and how electron exchange in spurs can influence the spin dynamics of radical pairs. This section will now present in detail the computational model used to investigate the ERP effect on the spin-lattice relaxation time within the IRT framework, using the algorithm as discussed in Sect. 4.4 of this work. 

Although analytical formulations are available to calculate the intensity of fluorescence, they lack the ability to predict the effect of electron exchange in spurs and their contribution to the spin relaxation times. Currently the only viable method to take these into account is to use numerical simulations such as IRT or Monte Carlo... 

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