Electron spin decoupling

Conversion of magnetic hyperfine coupling constants A into internal fields for Fe When the nuclear spin is decoupled from the electronic spin by application of an external field, the hyperfine coupling, according to (4.76), is defined as... 

During the last few years the versatility of ENDOR spectroscopy has been improved by a number of new techniques which make use either of special types of pumping fields (CP-ENDOR, PM-ENDOR), of more than one rf field (DOUBLE ENDOR, multiple quantum transitions, nuclear spin decoupling) or a different display of the spectrum (EI-EPR). In addition to these techniques, alternative methods have been developed (electron spin echo and electron spin echo ENDOR) which are able to supplement or to replace the ENDOR experiment under certain conditions. The utility of all these various advanced techniques, particularly in studies of transition metal compounds, has recently been demonstrated. 

We will discuss this technique again in Chapter 12, but for now we can say that spin decoupling allows us to electronically erase the effect of H/C coupling, greatly simplifying the appearance of the spectrum. Can this same technique be used to decouple all homonuclear coupling H spectra No, not exactly. But in Chapter 13 we will see an indirect way to accomplish this feat ... 

Paschen-Back effect - In atomic spectroscopy, the decoupling of electron spin from orbital angular momentum as the strength of an external magnetic field is increased. 

F=J+l=S+L+I Pf=tt(F(F+ )) -, field projections 0,...,hF Hyperfine spectrum (hfs) J levels split due to nuclear spin I Hfs F-levels split into 2F+1 levels (Zeeman effect) Electron-nucleonq.n.decouple,producing(2J+1)(2/+ l)levels Electron spin-orbit decouple, producing separate 5- andZ.-levels... 

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