Hyperfine Structure of2sHe+3by an Ion-Storage Technique

An electrostatic confinement device has provided resonance linewidths ≃ 1 kHz for the hyperfine transition $F=1\mathrm{}$, $m_F=0\mathrm{}$ to $F=0\mathrm{}$, in metastable $2s$ ${}_{}{}^3{}_{}{}^{}\mathrm{He}_{}^{+}{}_{}{}^{}$. The state-selection and resonance-detection scheme is the same used in an earlier ion-beam experiment; however, ion storage has yielded a resonance linewidth narrower by a factor of 100. Our result for the $2s$ hyperfine structure is $\Delta {\nu }_2=1083.354\mathrm{}969\left(30\right)\mathrm{}$ MHz. Comparison with the $1s$ hyperfine structure yields a test of state-dependent terms in the theory.