Structure analysis methods lines split

In the spin-correlated RP the two radicals interact via electron-electron dipolar and exchange interaction which leads to line splitting. The ET process creates the RP in a strongly spin-polarized state with a characteristic intensity pattern of the lines that occur either in enhanced absorption (A) or emission (E).144 145 The spectrum is therefore very intense and can directly be observed with cw EPR (transient EPR) or by pulse methods (field-swept ESE).14 To study the RPs high field EPR with its increased Zeeman resolution proved to be very useful the first experiment on an RP was performed by Prisner et al. in 1995146. From the analysis of the RP structure detailed information about the relative orientation of the two radicals can be extracted from the interaction parameters. In addition kinetic information about the formation and decay of the RP and the polarization are available (see references 145,147). 

The solution of a typical structural analysis problem by nmr methods utilizes at least four kinds of information obtained directly from the spectrum. They are chemical shifts (8), line intensities (signal areas), spin-spin splitting patterns (line multiplicities), and coupling constants (/). We already have shown how chemical shifts are used in the absence of spin-spin splitting. We now will illustrate how more complex spectra may be analyzed. 

In order to make practical use of Child s semiclassical method, it is necessary to have absolute rotational assignments for the sharp lines. This is a nontrivial problem since the usual rotation-vibration branch and band structures are shattered beyond recognition. However, the sharpest lines will have appreciable fluorescence quantum yields, thus enabling rotational assignments to be made on the basis of resolved R(J — 1) - P(J +1) = B"(4J + 2) splittings in laser-excited fluorescence spectra. It is fortunate that the theoretical analysis is based on the sort of assignment information that is most accessible in the simplest tunable laser experiment. 

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