Electronic structure computations hyperfine coupling constants

The quantitative theory of CIDNP enables one to compute the intensity ratios of CIDNP spectra on the basis of reaction and relaxation rates and characteristic parameters of the radical pair (initial spin multiplicity, p), the individual radicals (electron g factors, hyperfine coupling constants, a), and the products (spin-spin coupling constants, J) [122-126]. Conversely, the patterns of signal directions and intensities observed for different nuclei of a reaction product can be interpreted in terms of the hyperfine coupling constants of the same nuclei in the radical cation intermediate. This feature has proved significant for the assignment of radical cation structures. 

The fact that FDE was able to provide subsystem-localized electronic structures was known since its early application to systems with unpaired electrons [60-62, 102]. Later, this ability of FDE was explored for the computation of diabatic states for electron transfer [48, 49, 67, 103] and to compute hyperfine coupling constants [60, 61]. 

When ZnTPP (TPP2- = teteraphenylporphyrin dianion 5.0 X 10-4 M) is oxidized by exactly 1 equiv. of Ru(bpy)3+ (bpy = 2,2 -bipyridine 5.0 X 10 4 M), ZnTPP+ is produced without leaving any neutral species. In such a case, no self-exchange electron transfer of ZnTPP+ with ZnTPP occurs when the ESR spectrum of ZnTPP+ detected at 233 K exhibits well-resolved hyperfine structures as shown in Fig. 13.2a. The hyperfine coupling constants (hfc) are determined by comparison of the observed spectrum with the computer simulation spectrum as shown in Fig. 13.2b. 

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