 Orthohydrogen

Orthohydrogen uses the three symmetric spin-one-half triplet states,These three states give a nuclear-spin multiplicity of three, in addition to the rotational multiplicity $2J+1$. Thus the lowest orthohydrogen level, $J=1$, has nine states, whereas the lowest parahydrogen level, $J=0$, has one. The familiar high-temperature $3:1$ ratio is not the ratio $9:1$ of these two lowest levels: at high temperature, many even and odd rotational levels contribute.