Multiple quantum NMR dynamics in dipolar ordered spin systems

Doronin, S. I.; Fel’dman, É. B.; Kuznetsova, E. I.; Furman, G. B.; Goren, S. D.

doi:10.1103/physrevb.76.144405

Cited by 17 publications

(22 citation statements)

References 13 publications

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“…At the same time, this approach allows us to take into account the corrections due to the higher order terms of the averaged Hamiltonian theory [20], since these terms commute withÎ 2 as well. MQ NMR dynamics can be also investigated for systems with dipolar ordered initial state [21,22] by the suggested method.…”

Section: Discussionmentioning

confidence: 99%

Multiple quantum NMR dynamics of spin-12 carrying molecules of a gas in nanopores

Doronin

Fedorova

Fel’dman

et al. 2009

The Journal of Chemical Physics

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We consider the multiple quantum (MQ) NMR dynamics of a gas of spin carrying molecules in nanocavities. MQ NMR dynamics is determined by the residual dipole-dipole interactions which are not averaged completely due to the molecular diffusion in nanopores. Since the averaged nonsecular Hamiltonian describing MQ NMR dynamics depends on only one coupling constant, this Hamiltonian commutes with the square of the total spin angular momentumÎ 2 . We use the basis of common eigenstates ofÎ 2 and the projection of I on the external magnetic field for investigation of MQ NMR dynamics. This approach allows us to study MQ NMR dynamics in systems consisting of several hundreds of spins. The analytical approximation of the stationary profile of MQ coherences is obtained. The analytical expressions for MQ NMR coherence intensities of the five-spin system in a nanopore are found. Numerical investigations allow us to find the dependencies of intensities of MQ coherences on their orders (the profiles of MQ coherences) in systems consisting of 600 spins and even more. It is shown that the stationary MQ coherence profile in the considered system is an exponential one.

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Section: Discussionmentioning

confidence: 99%

Multiple quantum NMR dynamics of spin-12 carrying molecules of a gas in nanopores

Doronin

Fedorova

Fel’dman

et al. 2009

The Journal of Chemical Physics

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“…In all these experiments the starting condition generally was the thermodynamic equilibrium in a strong external magnetic field (Zeeman order). The dipolar ordered state has also been considered as the initial state for numerical calculations of MQ experiments [20][21][22]. A method for encoding the coherence numbers of the dipolar-ordered state in a basis (X) orthogonal to the Zeeman (Z) basis (in the rotating frame) in solids was presented by H. Cho et al [23].…”

Section: Introductionmentioning

confidence: 99%

Quasiequilibrium states in thermotropic liquid crystals studied by multiple-quantum NMR

Buljubasich

Monti

Acosta

et al. 2009

The Journal of Chemical Physics

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Previous work showed that by means of the Jeener-Broekaert (JB) experiment, two quasiequilibrium states can be selectively prepared in the proton spin system of thermotropic nematic liquid crystals (LC) in a strong magnetic field. The similarity of the experimental results obtained in a variety of LC in a broad Larmor frequency range, with crystal hydrates, supports the assumption that also in LC the two spin reservoirs into which the Zeeman order is transferred, originate in the dipolar energy and that they are associated with a separation in energy scales: a constant of motion related to the stronger dipolar interactions (S), and a second one (W) corresponding to the secular part of the weaker dipolar interactions with regard to the Zeeman and the strong dipolar part. We study the nature of these quasiinvariants in nematic 5CB (4'-pentyl-4-biphenylcarbonitrile) and measure their relaxation times by encoding the multiple quantum coherences of the states following the JB pulse pair on two orthogonal bases, Z and X. The experiments were also performed in powder adamantane at 301 K which is used as a reference compound having only one dipolar quasiinvariant. We show that the evolution of the quantum states during the build up of the quasi-equilibrium state in 5CB prepared under the S condition is similar to the case of powder adamantane and that their quasi-equilibrium density operators have the same tensor structure.In contrast, the second constant of motion, whose explicit operator form is not known, involves a richer composition of multiple quantum coherences on the X basis of even order, in consistency with the truncation inherent in its definition. We exploited the exclusive presence coherences ±4, ±6, ±8, besides 0 and ±2 under the W condition to measure the spin-lattice relaxation time T W accurately, so avoiding experimental difficulties that usually impair dipolar order relaxation measurement such as Zeeman contamination at high fields, and also superposition of the different quasiinvariants. This procedure opens the possibility of measuring the spin-lattice relaxation of a quasiinvariant independent of the Zeeman and S reservoirs, so incorporating a new relaxation parameter useful for studying the complex molecular dynamics in mesophases. In fact, we report the first measurement of T W in a liquid crystal at high magnetic fields. The comparison of the obtained value with the one corresponding to a lower field (16 MHz) points out that the relaxation of the W-order strongly depends on the intensity of the external magnetic field, similarly to the case of the S reservoir, indicating that the relaxation of the W-quasiinvariant is also governed by the cooperative molecular motions.

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“…It is shown that the growth of intensities of MQ coherence gets faster when the temperature decreases, and the intensities of multiple quantum coherences can be negative at low temperatures [16]. A few years later, it was proposed to use a so-called dipolar ordered state, a state in which nuclear spins are oriented along an internal local magnetic field [17], as the initial state in high temperature MQ NMR experiments [18] to faster form the correlations in spin systems [19,20]. As a matter of fact, it was found [19,20] that in experiments with the dipolar ordered state at high temperature the intensities of MQ coherences were several times higher than the analogous coherence in the standard MQ NMR experiment in which nuclear spins were oriented along an external magnetic field.…”

Section: Introductionmentioning

confidence: 99%

Low temperature MQ NMR dynamics in dipolar ordered state

Furman

Meerovich

2013

Solid State Nuclear Magnetic Resonance

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We investigate analytically and numerically the Multiple Quantum (MQ) NMR dynamics in dipolar ordered spin systems of nuclear spins 1/2 at low temperatures. We consider two different methods of MQ NMR. One of them is based on the measurement of the dipolar energy. The other method uses an additional resonance (π/4)y-pulse after the preparation period of the standard MQ NMR experiment in solids and allows one to measure the Zeeman energy. Both considered methods are sensitive to the contribution of remote spins in the interaction and to the spin system structure. The QS method is sensitive to the spin number in the molecule while the PS method gives very similar time dependencies of the intensities of MQ coherences for different spin numbers. It is shown that the use of the dipolar ordered initial state has the advantage of exciting the highest order MQ coherences in clusters of 4m identical spins, where m=1,2,3,…, that is impossible to do with the standard MQ method. MQ NMR methods based on the dipolar ordered initial states at low temperatures complement the standard NMR spectroscopy for better studying structures and dynamic processes in solids.

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Multiple quantum NMR dynamics in dipolar ordered spin systems

Cited by 17 publications

References 13 publications

Multiple quantum NMR dynamics of spin-12 carrying molecules of a gas in nanopores

Multiple quantum NMR dynamics of spin-12 carrying molecules of a gas in nanopores

Quasiequilibrium states in thermotropic liquid crystals studied by multiple-quantum NMR

Low temperature MQ NMR dynamics in dipolar ordered state

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