Knowledge Bank

Ortho-para transitions have been observed directly in $CH4$ for the first time. These normally forbidden transitions were observed in the ground electronic, ground vibrational, and J = 2 rotational state by combining a simple level-crossing technique with the conventional molecular beam magnetic-resonance method. It is shown how this spectrum can be used to measure, for certain tetrahedral molecules, the interaction constants which appear in the Zeeman, nuclear-hyperfine and rotational-distortion Hamiltonians.