Journal
JOURNAL OF CHEMICAL PHYSICS
Volume 129, Issue 23, Pages -Publisher
AMER INST PHYSICS
DOI: 10.1063/1.3040272
Keywords
magnetic fields; magnetisation; nuclear magnetic resonance; spin-lattice relaxation; spin-spin coupling
Funding
- European Community [011721]
- INTAS [05-100000-8070]
- Russian Foundation for Basic Research (RFBR) [06-03-32993, 07-03-00424]
- EU [IIF 22008]
- Russian Federation [MK-215.2007.3]
- Alexander von Humboldt Foundation
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A theoretical approach to the description of longitudinal (T-1) relaxation in scalar coupled systems of spin 1/2 nuclei at arbitrary magnetic field is developed, which is based on the Redfield theory. The consideration is addressed to field-cycling relaxometry experiments with high-resolution NMR detection, in which the field dependence of T-1-relaxation times, the nuclear magnetic relaxation dispersion (NMRD), can be studied for individual spins of the molecule. Our study reveals well-pronounced effects of spin-spin couplings on the NMRD curves. First, coupled spins having completely different high-field T-1 times tend to relax at low field with a common relaxation time. Second, the NMRD curves exhibit sharp features at the fields corresponding to the positions of nuclear spin level anticrossings. Such effects of spin-spin couplings show up not only for individual spins but also for the T-1-relaxation of the total spin magnetization of the molecule. The influence of spin-spin coupling is of importance as long as the coupling strength J is larger than the inverse T-1-relaxation times of the spins. Around J center dot T-1=1 there is also a coherent contribution to the relaxation kinetics resulting in an oscillatory component of the kinetic curves. Application of the theory to experimental examples will be described in subsequent publications.
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