The hyperfine interaction in a hydrogen atom between the magnetic dipole moment of the proton and the spin magnetic dipole moment of the electron splits the ground level into two levels separated by 5.9 x 10-6eV.
(a) Calculate the wavelength and frequency of the photon emitted when the atom makes a transition between these states and compares your answer to the value given at the end of Section 41.3. In what part of the electromagnetic spectrum does this lie? Such photons are emitted by cold hydrogen clouds in interstellar space; by detecting these photons, astronomers can learn about the number and density of such clouds.
(b) Calculate the effective magnetic field experienced by the electron in these states (see Fig. 41.4). Compare your result to the effective magnetic field due to the spin-orbit coupling calculated in Example 41.6.