Hyperfine level
= Hyperfine level
{title2=$F=|I-J|,\ldots,I+J$}
An <energy level> resolved by coupling the <nuclear spin> $I$ to electronic total <angular momentum> $J$. For a rotationally invariant <Hamiltonian>, a fixed $F$ has $2F+1$ degenerate <magnetic sublevels>. Spectral component counts identify the number of upper <hyperfine levels> only when lower <hyperfine structure>, <selection rules>, unresolved overlaps and missing lines have been accounted for.