Nuclear Magnetic Resonance Spectroscopy:

Figure 35.02: Schematic arrangements of spins in ground and excited states.

Upon radiating with microwaves, the alignment of nuclear spins from the low energy aligned state is flipped to the higher energy spin opposed state, resulting in an excited state. As derived earlier, the energy required for making this transition depends on the magnitude of the applied magnetic field, as demonstrated in Figure 35.03.

The two spin states have same energy when the external field is zero, but as the field increases so does the separation of energies of the spin states and therefore so does the frequency required to cause the spin-flip. At a field equal to H₀, the formula for the energy difference is given.