Long-range dipolar interactions

Long range dipolar interactions between an unpaired electron and nuclear spins on adjacent atoms will not normally be resolved in conventional powder EPR spectra.The pulse technique of electron spin echo modulation (ESEM) is in favourable cases able to detect very weak hyperfine interactions not seen in CW EPR. The method measures modulation of the electron spin echo signal by dipolar hyperfine coupling in the time domain at fixed magnetic field. Until recently,... 

Consider a linear chain of N identical molecules coupled through long range dipolar interactions. The molecules are assumed to be parallel to each other and perpendicular to the stacking axis. In the localized site representation, the electronic Hamiltonian is written as... 

The localization / delocalization behavior of exeitons is illustrated in Figs. 1 and 2 for a disordered linear chain of N=100 molecules eoupled through long-range dipolar interactions. For a given realization of the disorder, the average number of sites covered by the excitation is represented by segments eentered around the mean exciton position for weak disorder (cr/F = 0.01) or for rel-... 

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