Nuclear magnetic relaxation of spinI=1/2 scalar coupled to a quadrupolar nucleus in the presence of cross-correlation effects

Kupriyanova, G. S.

doi:10.1007/bf03166802

Cited by 5 publications

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“…With the aim of studying the characteristic features of relaxation for a quadrupolar nucleus in a strong magnetic field and identifying the factors affecting involvement of high rank multipoles in the relaxation process, in this paper it is proposed to use equations obtained within second-order perturbation theory in the operator representation [9,10].…”

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“…From a theoretical standpoint, interference terms for interference between these interactions may contribute to the relaxation. In secondorder perturbation theory, the basic relaxation equation for the "observable" (the mean value of a parameter determined by the operator Q) may be written in the form [10]:…”

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“…1 shows the time dependence of the longitudinal spin orders for spin S = 1 in the presence of slight CSA, obtained from solution of Eqs. (10). The contribution due to only Q-CSA cross correlations can be estimated from Fig.…”

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Relaxation of a quadrupolar nucleus in a strong magnetic field

Kupriyanova

2006

J Appl Spectrosc

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539.294Longitudinal relaxation of spin systems (S = 1, 3/2, 3) containing isolated quadrupolar nuclei are studied. The characteristic features of the relaxation behavior are identified in strong magnetic fields in the presence of chemical shift anisotropy. Two mechanisms are established that favor involvement of high rank multipoles in the relaxation process: an autocorrelation mechanism and a cross correlation mechanism. Multipoles of odd rank are involved in the relaxation of nuclei with spin S > 1 as a result of the autocorrelation mechanism (in this case, due to quadrupole interactions). The cross correlation mechanism, due to correlations between the chemical shift anisotropy and the quadrupole interactions, favors the appearance of multipoles of even rank. Expressions are presented for the multipole cross relaxation and longitudinal relaxation rates for spin systems with S = 1, 3/2, 3. Introduction.In studying the relaxation of quadrupolar nuclei with spin S > 1 in isotropic molecular systems, it has been observed [1] that in the slow molecular motion region, multipoles of high rank are involved in the relaxation process. This leads to multiexponential decay of the corresponding curve. It has been shown that decay of the magnetization is described by (S + 1/2)-exponential functions for half-integral spin and by S exponents for integral spin [1]. It has been demonstrated in [2,3] that in spin systems with S = 3/2, 5/2, and 7/2, the effect of multipoles depends on the parameters of the pulse sequences used and on the initial magnetization state. Analysis of the results of experiments carried out in different magnetic fields has led to contradictory conclusions even when studying the same sample. The effect of high rank multipoles on the lineshape and longitudinal relaxation of spin S = 3 has been studied as a function of the molecular motion correlation time [4,5]. For a sample of Na 2 B 12 H 11 SH (BSH) 95% enriched in 10 B and dissolved in glycerol, where the condition for slow molecular motion ω 0 τ c > 1 is satisfied over a broad temperature range in a magnetic field with induction B = 14 T ( 10 B NMR, ω 0 = 64 MHz), experimental results showed [4] that the longitudinal relaxation is described by a multiexponential function while the lineshape behaves like the lineshape for half-integral spins. In [5], the longitudinal relaxation and transverse relaxation of 10 B were studied in the same sample for a weaker magnetic field B = 11.7 T ( 10 B NMR, ω 0 = 53.73 MHz). It was shown that longitudinal relaxation is described well by a single exponent over a broad range of molecular motion correlation times. An increase in the line asymmetry is observed when comparing the NMR spectra for the 10 B nucleus that were recorded in magnetic fields of 11.7 T and 14 T. We should take into account the fact that when studying magnetic relaxation of quadrupolar nuclei in strong magnetic fields, interactions become important that are connected with the effect of chemical shift anisotropy (CSA). This question has not been previ...

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Relaxation of a quadrupolar nucleus in a strong magnetic field

Kupriyanova

2006

J Appl Spectrosc

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“…An alternative approach to a study of the relaxation processes based on the operator method was suggested by Abragam [7] who studied relaxation in spin systems with I = 1/2 and by Goldman [8] who examined heteronucleus spin systems with a spin of 1/2 in the presence of the cross-correlation relaxation mechanisms. This approach was subsequently developed in [9,10] for multipole spin systems. It is attractive because it allows the relaxation equations to be derived directly for quantities observed in experiments.…”

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“…In the present study, we use the operator approach [9] that obviates the necessity of an a priori determination of the basis functions to study the influence of cross-correlation effects on the relaxation processes in two-spin systems (I = 1/2 and S = 1). However, in contrast with [1], we use the angular momentum operators defined in the actual three-dimensional space to derive the relaxation equations.…”

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