Paramagnetism Quantum Approach

In the classical picture, we assumed that the magnetic moments of the electrons were randomly distributed in all possible orientations relative to the magnetic field. Of coruse, only discrete orientations are allowed quantum mechanically. Therefore, we must sum over these orientations rather than integrate over a continuum. The z-component of the magnetic dipole moment = —gfL sAj and the energy is If = —/AzF = —giL Mj, 

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Breaking with convention, the book broaches quantum mechanics from the perspective of biological relevance, emphasizing low-symmetry systems. This is a necessary approach since paramagnets in biomolecules typically have no symmetry. Where key topics related to quantum mechanics are addressed, the book offers a rigorous treatment in a style that is quick to grasp for the nonexpert. Biomolecular EPR Spectroscopy is a practical, all-inclusive reference sure to become the industry standard. 

The ESR method is useful in two aspects for studies of photochemical processes involving paramagnetic species the qualitative mechanistic aspect and the quantitative rate measurement. For the mechanistic approach we have seen from Section IV how transient radicals can be observed during photolysis. The major disadvantages are (a) It is not practical to determine accurately the quantum efficiency of radical production. Thus the radical process evidenced by ESR can well have been a very minor photochemical process, due to the high sensitivity of the modern ESR spectrometer. (b) In static... 

Neese, E. (2007) Quantum Chemical Approaches to Spin Hamiltonian Parameters, in Electron Paramagnetic Resonance (eds B.C. Gilbert, M.J. Davies and D.M. Murphy), Royal Society of Chemistry, Cambridge, 20, p. 73. 

Quantum chemical calculations on metal clusters in zeolite A [12] and semi-empirical ligand field interpretations of spectroscopic data of transition metal ions [6] have proven to be successful in structural characterizations of molecular sieves and their guest species. The present tendency in catalysis towards a more fundamental approach justifies the expectation that ESR, combined with other spectroscopic techniques, will become important. However, this requires an accurate and unambiguous parameterization of the ESR spectra. The parameter set thus obtained forms a firm basis for a theoretical investigation of the coordination environment of the paramagnetic entity. 

The pulse Fourier transform approach to magnetic resonance spectroscopy has been extensively developed and successfully applied to systems of one-half spin and their mutual interactions. But resonance spectroscopy of spin systems with the higher half- and integer spin quantum numbers is commonplace, for example, in the case of alkali metal nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) of transition metal compounds involving multi-quantum transitions. Similarly, magnetic resonance at zero field entails the observation of multi-quantum transitions. 

We now turn to the quantum mechanical approach to the phenomenon of paramagnetism and discuss first the orbital contribution to a magnetic moment. It is convenient at this point to make a few general statements which will be explained by the subsequent discussion. 

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