Electron paramagnetic resonance hyperfine coupling

Electron paramagnetic resonance (EPR) spectra are also discussed by Valentine et al. in reference 21. The splitting of the gy resonance is due to hyperfine coupling between the unpaired electron on Cu(II) and the nuclear spin of the copper nucleus... 

Electron-nuclear double resonance (ENDOR) spectroscopy A magnetic resonance spectroscopic technique for the determination of hyperfine interactions between electrons and nuclear spins. There are two principal techniques. In continuous-wave ENDOR the intensity of an electron paramagnetic resonance signal, partially saturated with microwave power, is measured as radio frequency is applied. In pulsed ENDOR the radio frequency is applied as pulses and the EPR signal is detected as a spin-echo. In each case an enhancement of the EPR signal is observed when the radiofrequency is in resonance with the coupled nuclei. 

HMO) formalism, because its singly occupied molecular orbital (SOMO) is constrained by symmetry to be on those atoms. More sophisticated molecular orbital analysis finds not only equal, positive spin densities on the end carbons but also a small negative 7T-spin density on the central carbon due to spin polarization. At the UB3LYP/6-31G level, the spin density p ) - p(C3) = +0.700, mostly from 7T-spin contributions, and p(C2) = -0.275.27 The experimental numbers estimated for TT-spin density (not overall spin density) are p(C ) = p(C3) = +0.582 and p(C2) = -0.164 from electron paramagnetic resonance (EPR) studies of 13C hyperfine coupling (hfc).28... 

The paramagnetic d ion VO + is an excellent probe for electron paramagnetic resonance (EPR) spectroscopy. In combination with proton potentiometry and/or electron absorption spectrometry (UV-Vis), species distribution schemes for VO + in the presence of various ligands have been obtained, comparable to those discussed in Section 2.2.1 for vanadate(V) systems derived on the basis of NMR plus potentiometry. EPR also allows, via the anisotropic hyperfine coupling constant in field direction (A or An,... 

Deuterium quadrupole coupling constants can also be obtained from electron nuclear double resonance (ENDOR).19 30 An observation of the hyperfine structure caused by quadrupole coupling in the electron paramagnetic resonance (EPR) spectrum, as for many lanthanide complexes, has not been reported for deuterium. The determination of nuclear quadrupole coupling constants from Mossbauer spectroscopy is not applicable to the deuterium nucleus. 

Electron Paramagnetic Resonance (EPR) can be used to measure the spin-densities in radicals. It is then assumed that the hyperfine coupling constants for the hydrogen atoms are proportional to the spin-density of the adjacent carbon atom [70]. Measurements on the allyl radical [71] give with such an analysis ratio of —0.282 between the spin-densities of the central and the end carbon atom. The CASSCF value is 0.311. One would suspect that methods that include spin polarization of the a skeleton would give better values. The UHF value is, however, — 0.717. What is the reason for this large difference Let us take a closer look at the CAASCF wave function. It contains three terms ... 

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