Electron spin resonance hyperfine calculations

Knight, L. B., Kaup, J. G., Petzold, B., Ayyad, R., Ghanty, T. K., Davidson, E. R., 1999, Electron Spin Resonance Studies of 45Sc170, 89Y170, and 139La170 in Rare Gas Matrices Comparison With Ab Initio Electronic Structure and Nuclear Hyperfine Calculations , J. Chem. Phys., 110, 5658. 

The electron spin resonance (ESR) spectra of free radicals obtained by electrolytic or microsomal reduction of several potential antiprotozoal 1,2,5-oxadiazoles were characterized and analyzed. Ab initio MO calculations were performed to obtain the optimized geometries, and the theoretical hyperfine constant was carried out using Zerner s intermediate neglect of differential overlap (ZINDO) semi-empirical methodology. DFT was used to rationalize the reduction potentials of these compounds <2003SAA69>. 

Copper porphyrin is one of the best-characterized of the metalloporphyrins, and its electron spin resonance (ESR) spectrum has been known for a quarter of a century.(17) More recently, electron nuclear double resonance (ENDOR) investigations have provided the complete hyperfine tensors for the metal, the nitrogens and the pyrrole protons.(18) We have used this detailed knowledge earlier(, ) to assess the quality of scattered-wave calculations. 

Compute from this both the distribution of the sum of all the tt electrons, i.e. the distribution iv of the overall electron density over the three carbon atoms in the radical, as weU as the distribution qr of charge over the ions. Calculate the distribution Qr of electron spins in the radical. This quantity is called the spin density g>r- It can be determined for example from the hyperfine structure of electron-spin resonance (ESR) spectra. 

Electron spin resonance spectroscopy The ESR spectrum of humic and fulvic acids consists of a single line identified by its position and width. In general, the ESR spectra are devoid of hyperfine splitting. The ESR spectra of humic substances result from only a small fraction of the total number of molecules that comprise the humic and fulvic acids. The number of free radicals per unit weight, the g value and the line width can be calculated. The predominant radicals are semiquinones. Comparison of the ESR properties among humic fractions reveals that fulvic acids contain greater quantities of free radicals than humic acids. 

H. M. Quiney, P. Belanzoni. Relativistic calculation of hyperfine and electron spin resonance parameters in diatomic molecules. Chem. Phys. Lett., 353 (2002) 253-258. 

Simulation of the Electron Spin Resonance Spectra of Polycrystalline Samples Calculated Isotropic and Anisotropic Hyperfine Coupling Constants of Transition Metal Ions Rotational Properties of Electron Spin Resonance Spectra Vibrational Structure of EPR Spectra... 

Hyperfine splitting due to interaction with ligand nuclei with 7 > 0 reflects the extent of spin delocalization onto neighboring atoms and can be used to characterize the types and numbers of such nuclei. In cases where these couplings are too small to be resolved in the EPR spectra, electron nuclear double resonance (ENDOR) or electron spin echo envelope modulation (ESEEM) can be used to measure the couplings as discussed in Chapter 2.3. Modern calculational tools are approaching the capabilities required to calculate g and A values from electronic wave functions. However, much of the spectroscopy that has been performed to date has used empirical correlations to interpret g and A values. 

Later [38, 39], oxygen vacancies (Fig. 2.2) and E point defects present in glassy Si02 could be studied in great detail, including also full ab-initio calculations of the hyperfine parameters experimentally detected by electron-nuclear double resonance (ENDOR) experiments. Indeed, these types of measurements are nowadays routinely done to identify this class of paramagnetic defects. In the ENDOR technique, some Si atoms are substituted with their isotopes Si. This confers anon-zero nuclear spin I to the atomic nucleus that couples to the electron spin S via a tensor A. On the theoretical front, the calculation from first principles DFT approaches does not pose particular problems since the hyperfine interaction is still a ground state property which can be expressed in terms of the electronic density p x). The interaction between an electron spin (S) and a nuclear (I) spin is in fact described by the Hamiltonian... 

---