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Intermolecular Dipole-Dipole Spin Relaxation of Xenon-129 Dissolved in Benzene. A Molecular-Dynamics Simulation Study

par Luhmer, Michel ;Moschos, A.;Reisse, Jacques
Référence Journal of Magnetic Resonance, Series A, 113, 2, page (164-168)
Publication Publié, 1995-04

Article révisé par les pairs

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Résumé :

By use of molecular-dynamics simulations for xenon dissolved in liquid benzene, it is confirmed that the intermolecular dipole-dipole spin-relaxation mechanism contributes significantly to the relaxation of 129Xe. The calculated dipolar relaxation time (750 ± 160 s) lies in the range of the experimental determinations, which are 390 and 870 s. The time correlation function of the Xe-H spin dipole-dipole interaction displays a fast decay between 0 and 5 ps, decreases exponentially between 5 and 15 ps, and follows a t^(−3/2) power law at longer times. The Xe-H correlation function can be, in very good approximation, factored into distance and angular contributions; the latter is found to be the major contribution. The influence of the rotational dynamics of the solvent molecules is investigated on the basis of comparisons between the Xe-H time correlation functions and the corresponding functions for spins located at the center of mass of the benzene molecules. Finally, the relaxation of 129Xe and 131Xe are compared. It is shown that the quadrupole relaxation of 131Xe depends essentially on the rotational motions of the solvent molecules while the dipolar relaxation of 129Xe is largely dependent on the translational motions.