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Spin-spin relaxatio...
Abstract
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- We present an extension of a Redfield approach for calculating spin-spin relaxation rates of zero-field nuclear quadrupole resonance (NQR) coherences, which was published in [Kruk et al., PCCP, 2018, 20, 23414-23426]. The oversimplification of the secular approximation made in the recent paper makes the calculation invalid for zero-field NQR and has led to partially large deviations between predicted and experimental data from 209Bi-containing molecular crystals. Furthermore, these deviations led to speculations about an additional dipole-dipole relaxation mechanism besides the main electric field gradient (EFG) fluctuations. Here, we demonstrate how a complete application of the Redfield relaxation expression eliminates the deviation from experimental data without the need for additional assumptions. In particular, we point out the important role of off-diagonal elements in the Redfield relaxation matrix within the 3/2-1/2 block appearing due to degenerate energy levels. The resulting coupling between single and double coherence spin density elements leads to a faster coherence decay than for all other transitions. The pseudo rotational model for EFG fluctuations, as proposed in the earlier publication and usually applied for isotropic liquids, is extended in a second analysis by introducing a vibrational mode to account for the case of crystalline solids.
Ämnesord
- NATURVETENSKAP -- Kemi -- Teoretisk kemi (hsv//swe)
- NATURAL SCIENCES -- Chemical Sciences -- Theoretical Chemistry (hsv//eng)
Nyckelord
- Nuclear quadrupole resonance
- spin-spin relaxation
- Bloch-Wangsness-Redfield theory
- EFG fluctuations
- molecular crystals
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