Quadrupolar dip in proton relaxation dispersion of poly(vinyl chloride)

NMR Study of Phase Transitions in New Ferroelectric Crystal—(C5H5NH)5Bi2Br11

“…The theoretical second moment value was calculated using van Vleck's formula [14] for four motional states of the pyridinium cation [11]: rigid, performing the C 2 reorientation around the axis perpendicular to the pyridinium ring, performing the C 2 reorientation about a pseudodyad axis located in the ring, and performing the C 6 reorientation about the axis perpendicular to the cationic ring ( Table 1). The highest observed M 2 value (4.9 G 2 ) at 30.4 K is nearly the same as the estimated total second moment value for (C 5 H 5 NH) 6 Bi 4 Cl 18 [15], giving the interaction part as 1.25 G 2 . Instead of a plateau a small decrease in the second moment is observed.…”

“…Generally, the relaxation processes in this system are due to dipolar interaction between proton spins I and quadrupole nuclei spins S and to quadrupole interaction of the S spins with the electric field gradients of the sample. The evolution in time of the magnetizations I Z and S z in the system is as follows [6][7][8][9][10]:…”

Fast-field-cycling NMR: Applications and instrumentation

“…The expression "QDs" is associated with local minima in proton T, relaxation profiles when a Zeeman transition of the observed spin system crosses a quadrupolar transition of another nucleus contained in the same molecule [1,4,131]. QDs are extremely sensitive to molecular dynamics and structure [38,105,106,[132][133][134][135][136][137][138][139][140][141][142][143][144][145][146][147][148][149][150]. They can also be used to detect molecular order at the macroscopic level in mesomorphic systems like thermotropic liquid crystals [113,114,151].…”

Quadrupole-enhanced proton spin relaxation for a slow reorienting spin pair: (I)–(S). A stochastic Liouville approach

“…The theoretical analysis presented in the literature is generally limited to the static regime. For instance, the QD's was observed and analysed in the plastic crystals phases of CFCl 3 [32], in the biaxial smectic mesophase of HpAB [33], and for amide protons or water in immobilized proteins [1], [34]- [39]. Nuclear quadrupole resonance (NQR) studies are relevant for the theory of cross relaxation, because at zero field, the spin quantisation is defined by the molecular fixed principal axes of the 4 F o r P e e r R e v i e w O n l y electric field gradient, NQR reports directly on the quadrupole spin system.…”