Cross relaxation between proton and quadrupolar nuclear spins in metal-hydrogen systems

NMR analysis of nuclear relaxation mechanisms in Pd–H and Pd–Ag–H alloys

“…Following the argumentation of [2], the mechanism of cross-relaxation between proton and quadrupolar 105 Pd nuclear spins was assumed to be mostly responsible for the observed deviations from the Korringa behavior, since Pd 1−x Ag x -H y systems (i) are of destroyed cubic symmetry (due to absorbed hydrogen and alloying with silver) and (ii) contain quadrupolar spins. This term is removed at higher temperatures, at which hydrogen diffusion occurs on the NMR frequency scale.…”

“…Proton spin-lattice relaxation rates R 1 reveal an anomalous frequency dependence in several metal-hydrogen systems [1,2,6] at T < 100 K. In addition, many of the 1 H R 1 data have weaker than linear temperature dependencies. Both observations are unusual since Korringa relaxation [7] is expected what predicts relaxation rates linear in temperature and independent of resonance frequency.…”

“…Cross-relaxation due to dipolar interaction between the two spin systems (R 1cr ) can occur when the Zeeman energy splitting of an 1 H spin happens to equal some combined Zeeman-quadrupolar splitting of a nearby 105 Pd nuclear spin. The spin energy is transferred from the 1 H spin system (I) to that of the quadrupolar 105 Pd nuclei (S) (R 1cr term) and then on to the lattice (R 1S term) to give an overall relaxation rate R 1c [2]. At temperatures at which hydrogen diffusion occurs, R 1cr is progressively removed-averaged by the motion.…”

“…The total spin-lattice-relaxation rate is usually taken to be the sum of three terms [1]: R 1d is due to dipole-dipole interaction modulated by hydrogen diffusion, R 1e is the electronic (Korringa) relaxation rate, and R 1p represents relaxation due to paramagnetic impurities. In our case, there should be included the effects of yet another spin-lattice relaxation mechanism, R 1c , in which protons cross relax with quadrupolar metal nuclei, which in turn transfer energy to the lattice via their own relaxation rates [2]: R 1 = R 1d + R 1e + R 1p + R 1c .…”

Mechanism of 1 H– 14 N cross-relaxation in immobilized proteins

“…1 nucleus with a static residual quadrupole coupling, enhanced I-spin relaxation is observed at I-spin Larmor frequencies matching an eigenfrequency of the static S-spin Hamiltonian. This resonant cross-relaxation phenomenon has been widely exploited for structural and dynamic studies of solids and liquid crystals [1][2][3][4][5][6][7][8]. When observed against the background of the field-dependent longitudinal I-spin relaxation, the resonant enhancement of the Ispin relaxation induced by the S spin is commonly referred to as a quadrupole peak (Q peak, QP) in the relaxation rate or as a quadrupole dip in the relaxation time.…”