ENDOR of quintet states

The spin Hamiltonian Tls.i of a qimitet dicarbene coupled to one individual proton, numbered i, is 

The first term in Eq. 10 is given by Eq. 4 and the second is the nuclear Zeeman energy. I, is the nuclear spin operator for nuelear spin 1/2. The third term is the hyperfine interaction of the individual proton i, as defined by the hyperfine tensor At. S is the total electron spin operator, S = Si -I- 2. As nuclear dipole-dipole interaction can be neglected we will omit the index i in the following. 

The first order perturbation theory of the nuclear terms calculates the shift Av of the individual proton Larmor frequency with respect to the free proton Larmor frequency vp (ENDOR shift)  

For a quintet state one should observe 5 different ENDOR lines per proton. This is illustrated in Fig. 9.14 where the observed NMR transitions in the ENDOR experiment are indicated by the ciphers (n) = (1), (2), (3), (4), and (5) the first order ESR transitions are indicated by the lower case letters (a), (b), (c), and (d). 

The ENDOR shift anisotropy is shown in Fig. 9.16 for the strongly coupled protons i = 1, 2, 3, and 4. This anisotropy is mainly due to the anisotropy of the effective spin Seff. The lines were calculated (via Eqs. 12 and 13) by fitting Ai- In total we have analyzed 22 protons, the hyperfine tensors Ai of which are presented in Tab. 9.4. Two features can be 

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