7.4:
Atomic Nuclei: Nuclear Spin State Overview
NMR-active nuclei have energy levels associated with their nuclear magnetic moment orientations called 'spin states'.
In the absence of a magnetic field, the nuclear magnetic moments are randomly oriented, and the spin states are degenerate.
When an external magnetic field is applied, there are only 2I + 1 available orientations.
The orientations aligned against the field are higher energy than the orientations aligned with the field, so the spin states are quantized in a phenomenon called Zeeman splitting.
The energy difference between any two spin states, ΔE, is directly proportional to the strength of the applied magnetic field.
This energy difference and the ambient temperature affect the number of nuclei that occupy each spin state.
As the temperature decreases, lower-energy spin states are more populated than the higher-energy spin states.
7.4:
Atomic Nuclei: Nuclear Spin State Overview
NMR-active nuclei have energy levels called 'spin states' that are associated with the orientations of their nuclear magnetic moments. In the absence of a magnetic field, the nuclear magnetic moments are randomly oriented, and the spin states are degenerate. When an external magnetic field is applied, the spin states have only 2
+ 1 orientations available to them. A proton with = ½ has two available orientations. Similarly, for a quadrupolar nucleus with a nuclear spin value of one, the nuclear magnetic moment has three possible orientations.
The orientations aligned against the field are higher energy than those aligned with the field. The quantization of spin states is a phenomenon called Zeeman splitting. The energy difference between the two spin states is proportional to the strength of the applied magnetic field. However, at temperatures close to absolute zero, the lower energy spin state is more populated than the high energy spin state.