CALCULATION OF STIMULATED NUCLEAR-POLARIZATION IN SHORT-LIVED BIRADICALS AND COMPARISON WITH EXPERIMENT

A theoretical model is presented which allows one to calculate stimulated nuclear polarization (SNP) (and RYDMR) in short-lived flexible biradicals. It is based on the numerical solution of the stochastic Liouville equation for spin density matrix and takes into account distance-dependent exchange interaction. For description of polymethylene chain conformational motions the "restricted diffusion" model is used. This approach is shown to allow adequate description of SNP spectra of acyl-alkyl biradicals formed in the photolysis of cycloalkanones. The influence of different parameters on calculated SNP spectra is considered. From the comparison with experimental data it is concluded that SNP technique is very sensitive to the magnitude of exchange interaction. Parameters of the latter are discussed.