Category:NMR: Difference between revisions

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Many nuclei have an inherent, non-zero spin '''I''' and therefore a magnetic dipole moment '''μ''', conventionally along the z-axis:
:<math>
\mu_z = \gamma \textbf{I}_z
</math>
In the absence of a magnetic field, these are degenerate states. When an external magnetic field '''B'''<sub>ext</sub> is applied, the energy difference between two states is given by the following equation:
:<math>
\Delta E = \gamma \hbar \textbf{B}_{ext}
</math>
Conventionally, the z-axis is chosen for the direction of '''B'''<sub>ext</sub>. Along this axis, '''&mu;''' aligned with '''B'''<sub>ext</sub> will be slightly more energetically favorable and so populated than '''&mu;''' opposed to '''B'''<sub>ext</sub>. This is only signficant in the presence of strong magnetic fields.
In the presence of '''B'''<sub>ext</sub>, '''&mu;''' precesses at its Larmor frequency ''&omega;''<sub>L</sub>, determined by the strength of the magnetic field and the nucleus' gyromagnetic ratio &gamma;:
:<math>
\omega_L = \gamma \textbf{B}
</math>
A weak, oscillating magnetic field applied perpendicular (i.e. in the ''transverse frame'') to '''B'''<sub>ext</sub> (''reference frame''), e.g. using a radio-frequnecy (RF) pulse at frequnecy &omega;<sub>rf</sub>, can causes '''&mu;''' to oscillate with the RF. If &omega;<sub>rf</sub> is similar to &omega;<sub>L</sub>, then resonance occurs, hence nuclear magnetic resonance (NMR). '''&mu;''' flips from the reference to the transverse frame and the relaxation of '''&mu;''' back to the reference frame creates a signal that is measured in NMR.
== How to ==
== How to ==
*Chemical shift tensors: {{TAG|LCHIMAG}}.
*Chemical shift tensors: {{TAG|LCHIMAG}}.

Revision as of 09:50, 24 February 2025

Many nuclei have an inherent, non-zero spin I and therefore a magnetic dipole moment μ, conventionally along the z-axis:

In the absence of a magnetic field, these are degenerate states. When an external magnetic field Bext is applied, the energy difference between two states is given by the following equation:

Conventionally, the z-axis is chosen for the direction of Bext. Along this axis, μ aligned with Bext will be slightly more energetically favorable and so populated than μ opposed to Bext. This is only signficant in the presence of strong magnetic fields.

In the presence of Bext, μ precesses at its Larmor frequency ωL, determined by the strength of the magnetic field and the nucleus' gyromagnetic ratio γ:

A weak, oscillating magnetic field applied perpendicular (i.e. in the transverse frame) to Bext (reference frame), e.g. using a radio-frequnecy (RF) pulse at frequnecy ωrf, can causes μ to oscillate with the RF. If ωrf is similar to ωL, then resonance occurs, hence nuclear magnetic resonance (NMR). μ flips from the reference to the transverse frame and the relaxation of μ back to the reference frame creates a signal that is measured in NMR.

How to


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Pages in category "NMR"

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