Epr Line Broadening

Anionic radical ligand derived from alloxan D shows epr which are markedly affected by coordination to diamagnetic Mg, Ca and Zn + ions. 

The splitting patterns due to ligand protons and nuclei differ in the free ligand and the complexes. There is rapid intramolecular exchange of between two possible sites (shown in 13) and this leads to line broadening which can be used to measure the exchange rate constants (5 x 10 s to 2 x 10 s ). See Table 7.4. 

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As was the case with ll g, the rates of inversion of the oxiranyl radicals, 12J, and 12J, could be measured by EPR line broadening over a wide range of temperatures... 

The conducting phase of TMQ /16/. Microwave conductivity experiments, performed at low temperature on the samples used for the pressure experiment, have succeeded in showing an increase by a factor 10 from 300 K down to loo K, /41/. The possibility of susceptibility measurement via low field method is limited by the EPR line broadening occurring at low temperature and under pressure. The spin susceptibility was derived from a fit of the EPR absorption line shape with a Lorentzian curve. The proton relaxation time was measured under pressure at low field lOe- with a pulse spectrometer. Figures... 

Dipolar interaction can lead to an EPR line broadening (Fig. 6). The spectrum of the interacting spins can be treated as the convolution of the non-interacting powder pattern spectrum with a dipolar broadening function which is known as Pake pattern in randomly oriented samples. 

Most applications use EPR as a detection method for reactants or products. Various flow methods can be coupled with EPR to monitor the time dependence of EPR-active species. It is also possible to use EPR line broadening to measure exchange rates, and in this area the time scale is in the range of 10" to 1(T s. 

Fe(CN)6] binds axially to [Cu(II)(H 2Aib3)] with a stability constant of 8.1 and the exchange rate calculated from EPR line broadening, 2 X 10 M s is comparable with the value for exchange of [IrC ] . Relatively small AS values contrast with those for ruthenium reduction and suggest that the copper center is solvated after the transition state. 

In a similar study also using EPR spectroscopy, cyclic voltammetry and chronoamperommetry was reported for the spin probe TEMPONE in [bmim][BF4]. A linear dependence of the EPR line broadening versus the concentration of the spin probe at constant temperature was found. 

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