摘要:

AbstractThe derivation of various components of the Hamiltonian operator used to describe high‐resolution NMR experiments is presented, with an emphasis on time‐dependent interactions that can produce relaxation of a spin system (dipole‐dipole, chemical shift anisotropy) or that lead to excitation of a spin system (radio‐frequency

ISSN:1043-7347    

DOI:10.1002/cmr.1820040302

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractA fitting procedure for the extraction of the characteristic NMR parameters from solid‐state NMR powder patterns is described at an introductory level. The Levenberg‐Marquardt nonlinear least‐squares algorithm is recoded in Matlab, a vector‐oriented programming language, so that the NMR simulation programs are more condensed than are those in traditional programming languages. Three examples of line‐shape fitting are shown: the deuterium powder pattern for the bridging deuterium site in [Et4N] [2HCr2(CO)10], the proton‐coupled13C powder pattern for the bridging methylene site in cis‐(μ‐CH2)(μ‐CO)[FeCp(CO)]2, and the (14N,195Pt)‐coupled13C powder pattern for the Pt‐CN system in K2Pt(CN)4· 3H2O. The results provide information about quadrupolar, dipolar, and chemical‐shielding tensors. In each case, the line‐shape is calculated from the spin Hamiltonian expressed in a simple, uncoupled basis set. The variables in each case are a small set of NMR parameters: the quadruple‐coupling constant and the asymmetry parameter. The effects of finite pulse‐lengths or anisotropic cross‐polarization are not included in the line‐shape simulations. The line‐shapes are powder patterns; averaging over the Euler angles, θ andx, is done either with constant angle step size o

ISSN:1043-7347    

DOI:10.1002/cmr.1820040303

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe impedance‐matched condition and its relation to the reflection coefficient are discussed. Some important properties of transmission lines for impedance‐matching are considered. Resonance tank circuits in NMR probes are discussed with analogies to microwave cavity resonances. By analyzing reflection coefficients in terms of Q factors, the impedance‐matched condition is re‐derived in a manner that highlights practical considerations for high‐frequency app

ISSN:1043-7347    

DOI:10.1002/cmr.1820040304

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractInterest in the nuclear Overhauser effect (NOE) has increased enormously in recent years because of its wide application to the structure determination of molecules in the liquid state, particularly large molecules, such as biomolecules. Most NOE studies are carried out in spin systems that exhibit splittings because of indirect spin‐spin (J) couplings, but the most common NMR analyses ignore I splitting. We focus attention on the presence of J coupling and particularly on selective perturbation of a transition of coupled spins. Both steady‐state and transient NOE have been calculated in closed form. There is a large multiplet effect that results from the direct pumping effect that is observed in the intensities, careful measurement of which requires the use of small‐angle pulses. The use of a 90° pulse obliterates the multiplet effect. As an extension, cross‐correlation effects in the three‐spin system and the three‐spin effect in NOE spectra also are discussed. A brief analysis of spin diffusion in a multiple‐spin system is

ISSN:1043-7347    

DOI:10.1002/cmr.1820040305

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

ISSN:1043-7347    

DOI:10.1002/cmr.1820040306

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

ISSN:1043-7347    

DOI:10.1002/cmr.1820040307

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

ISSN:1043-7347    

DOI:10.1002/cmr.1820040301

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY