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.