Quadrupole field split

Another parameter of interest is the quadrupole splitting, which arises as the result of the presence of an electric field gradient at the 57Fe nucleus. The interaction of the electric field gradient with the nuclear quadrupole moment splits the excited state of spin 3/2 into two states, so that two resonances may be observed. The quadrupole splitting is expressed as the difference in Doppler velocities corresponding to the two resonances. 

Fig. 10.12 The temperature dependence of the quadrupole splitting in GeFc204. The solid line corresponds to a trigonal-field splitting of 1650 K. [Ref. 61, Fig. 1]...

Next, consider the energy levels of a spin-3/2 nucleus in a single crystal in the presence of an applied magnetic field and an electric field gradient so that the perturbation provided by the quadrupole interaction with the applied EFG is small a first order perturbation. We already considered this case in II.D.l. where we saw that the quadrupole interaction split the single line into three by shifting the 3/2<- l/2 and the -3/2 ->-1/2 lines in opposite directions. We state without... 

DPPH = 2,2-diphenyl-l-picrylhydrazyl ENDOR= electron-nuclear double resonance EPR = electron paramagnetic resonance ESE = electron spin echoes ESEEM = electron spin echo envelope modulation FFT = fast fourier transformations FWHM = full width at half maximum HYSCORE = hyperline sublevel correlation nqi = nuclear quadrupole interaction TauD = taurine/aKG dioxygenase TWTA = traveling wave tube amplifier ZFS = zero field splitting. 

Figure 8.32. Strong field levels for the J = 1 level in CsF. An electric field produces the Stark splitting between the Mj = 0 and 1 components, and Cs quadrupole interaction splits each Stark component into four levels. Each level is two-fold degenerate the two components are labelled by their values of M/ and M/j. The eight electric dipole transitions which become allowed in the electrostatic C field are shown.

Abstract The analysis of ESR, ENDOR, and ESEEM data to extract the resonance parameters is treated. Free radicals in solution are mainly identified by their hyper-fine couplings (hfc). The analysis of ESR and ENDOR spectra by visual inspection and by computer simulation is discussed. The Schonland method to obtain the principal values and directions of the anisotropic g- and hfc- tensors from single crystal ESR and ENDOR data is presented. The modifications needed when 5 > A or / > A to obtain zero-field splitting ( i) or nuclear quadrupole coupling (nqc) tensors are considered. Examples of simulations to extract g-, hfc-, Tfs-, and n c-tensors from ESR and ENDOR spectra of disordered systems are presented. Simulation methods in pulsed ESR (1- and 2-dimensional ESEEM) studies are exemplified. Internet addresses for down-loading software for the simulation of ESR, ENDOR, and ESEEM spectra are provided. Software for the analysis of single crystal data by the Schonland method is also available. 

The Schonland procedure is also applicable for the determination of hyperfine coupling tensors by ESR and ENDOR, for the zero-field splitting tensor (S > V2) by ESR, and the nuclear quadrupole couplings for / > Vi by ENDOR and ESEEM, discussed in the following sections. 

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