Effect of instantaneous and spectral diffusions on the pulsed EPR SECSY signal of an electron-nuclear spin-coupled system in a gamma-irradiated malonic acid single crystal

Abstract

Abstract The many-body effects of instantaneous and spectral diffusions due to electronic dipolar interactions of an observer electron spin of an electron-nuclear spin-coupled system of a molecule in a gamma-irradiated malonic acid single crystal, characterized by the electronic spin ½ and the nuclear spin ½, with the electrons of the other molecules in the crystal in the vicinity on the SECSY signal are investigated rigorously by numerical computation. The spectral diffusion is taken into account by considering the relevant relaxation matrix elements in the Liouville von Neumann equation, specifically, that caused by a random spin flip of the interacting electronic dipole moment in the crystal vicinity, using the analytical expression, derived by Salikhov et. al. [J. Magn. Reson (1969), 42(2), pp.255–276. (1981)]. On the other hand, the instantaneous diffusion of the observer electron due to the dipolar interaction with the electrons in the crystal vicinity, which are at, or close to, resonance of the observer electron, is taken into account by considering their random spin flips by a probability determined by the Monte-Carlo technique. It is found that the instantaneous diffusion together with the spectral diffusion, brings a better agreement of the calculated signal with the experiment.