Since the energy is E=-gMbBm, then the energy absorbed will be the energy diffenrce in the two states, the jumps occur at a diference of m=1, so the energy of the photons is 2 times the magneton.
When there’s a hyperfine interaction another energy must be added, the term is +Amimj. And thats gives us E2=B/(mi*mj*h^2) times the magneton.