Zeeman splitting exchange interactions

In the spin-correlated RP the two radicals interact via electron-electron dipolar and exchange interaction which leads to line splitting. The ET process creates the RP in a strongly spin-polarized state with a characteristic intensity pattern of the lines that occur either in enhanced absorption (A) or emission (E).144 145 The spectrum is therefore very intense and can directly be observed with cw EPR (transient EPR) or by pulse methods (field-swept ESE).14 To study the RPs high field EPR with its increased Zeeman resolution proved to be very useful the first experiment on an RP was performed by Prisner et al. in 1995146. From the analysis of the RP structure detailed information about the relative orientation of the two radicals can be extracted from the interaction parameters. In addition kinetic information about the formation and decay of the RP and the polarization are available (see references 145,147). 

The first term of Eq. 4 represents the electronic Zeeman term, Si and 2 the spin operators for tvro triplet carbenes, and the second term represents the electronic exchange interaction. If Si and 2 couple to a quintet state (S = 2), ( 1 + 2) = S = S(S + 1) = 6. If they couple to a singlet, S = 0. Therefore, this term directly results in the energy level scheme, indicated in the inset of Fig. 9.13. The pure singlet and the pure quintet states are split by Assq which turns out to be the characteristic property of each dicarbene. The third term of Eq. 4 represents the magnetic dipole-dipole coupling of the two triplet carbenes ... 

As shown in Figure 5.6, the Zeeman splits for the A and B valence bands in the wurtzite structure are suggested to have opposite polarities. When the spin-orbit coupling and the p-d exchange interaction anisotropies are neglected, simple expressions can be obtained for the Zeeman splitting energies of the A and B bands [7, 62] ... 

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