Electrons exchange interactions

OIDEP usually results from Tq-S mixing in radical pairs, although T i-S mixing has also been considered (Atkins et al., 1971, 1973). The time development of electron-spin state populations is a function of the electron Zeeman interaction, the electron-nuclear hyperfine interaction, the electron-electron exchange interaction, together with spin-rotational and orientation dependent terms (Pedersen and Freed, 1972). Electron spin lattice relaxation Ti = 10 to 10 sec) is normally slower than the polarizing process. 

The electron exchange interaction [see Eq. (6.16)] requires overlap of the electronic wave functions of the donor and acceptor. Dexter<31) evaluated the exchange expectation value equation and obtained the following result ... 

In contrast to the dipole-dipole interaction, the electron-exchange interaction is short ranged its rate decreases exponentially with the donor-acceptor distance (Dexter, 1953). This is expected since, for the electron exchange between D and A, respective orbital overlap would be needed. If the energy transfer is envisaged via an intermediate collision complex or an exciplex, D + A—(D-------A)- D + A, then Wigner s rule applies there must be a spin com-... 

In PET, an electron is transferred between an excited-state species and a ground-state species, and Figures 6.18 and 6.19 show that electron transfer processes occur by electron-exchange interactions and so require orbital overlap. 

Eqs 2 and 12 can be applied to the data for activationless ET processes to give a rough estimate of the electron exchange interaction and the spatial separation of donor and acceptor... 

The efficiency of Forster energy transfer depends mainly on the oscillator strength of the A -> A and B -> B radiative transitions, whereas the efficiency of energy transfer by the electron exchange interaction cannot be directly related to an experimental quantity. 

Higher multipole-multipole interaction terms decrease at higher inverse powers of the intermolecular separation, but become important when the dipole-dipole interaction is symmetry forbidden, e.g., in benzene where the octupole-octupole interaction is dominant [161]. The electron-exchange interaction requires overlap of the electronic wave functions of M d and Ma, and it is therefore of short range (<1.5 nm). Due to an exponential decrease in the overlap of electronic wave functions with intersite distance, the energy transfer rate is expected to decrease more rapidly and, in fact, it can be expressed as (see e.g., Ref. 162)... 

The initial state valence electrons of a ferromagnet are unequally populated by majority (t) and minority (J electrons, which result from electron exchange interactions. This can result in fairly substantial spin polarization. For instance, studies of the amorphous alloys FegoB2o and Co77B23 reveal polarization as high as 20% when excited by 35-eV synchrotron radiation [36]. A recent report of Co(100)... 

The electron-exchange interaction can be described 155) as resulting from the mixing of the charge transfer state F with the initial state I,... 

The Hamiltonian for interradical interactions can be decomposed into two terms corresponding to the electron exchange interaction and the electron dipolar interaction... 

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