Rubidium-87 ground-state hyperfine structure
= Rubidium-87 ground-state hyperfine structure
{title2=$5S_{1/2}:\ F=1,2$}
Ground-state electronic <angular momentum> $J=1/2$ couples to nuclear <spin> $I=3/2$, giving $F=1,2$. For contact <hyperfine interaction> $A\mathbf I\cdot\mathbf J/\hbar^2$, their zero-field energies are $-5A/4$ and $3A/4$. The splitting is $2A$. Electronic weak-field contributions give $g_{F=1}\simeq-1/2$ and $g_{F=2}\simeq+1/2$; the small nuclear contribution refines these numbers.