The hfs of the ground state of ${}_{}{}^3{}_{}{}^{}\mathrm{He}_{}^{+}{}_{}{}^{}$ has been studied using the spin-dependent collision processes between stored ${}_{}{}^3{}_{}{}^{}\mathrm{He}_{}^{+}{}_{}{}^{}$ ions and a polarized beam of Cs atoms. All possible hfs transitions have been measured in a magnetic field of about 7.13 G. A consecutive-pulse multiple-resonance scheme was developed to detect the only weakly field-dependent transition $(F=0, m_F=0)\leftrightarrow (F=1, m_F=0)$ in an almost ideally isolated and pure atomic system. Magnetic-resonance disorientation is observed as a change in the number of ions remaining in the rf quadrupole ion trap after a fixed interaction time with both the resonant rf fields and the polarized atomic beam. For the detection of an ion-number signal, the ion macromotion at ${\overline{\omega }}_z$ was coherently excited by a homogeneous electric field at ${\overline{\omega }}_z+\Omega$, where $\Omega$ is the frequency of the inhomogeneous rf field used for trapping. Linewidths of 10 Hz have been measured for the (0, 0) ↔ (1, 0) hfs transition, when the transition was induced during a time of the order of half the electron-spin orientation time in a weak atomic beam. The value for the zero-magnetic-field hfs splitting is $\Delta \nu =(8\mathrm{}665649867\pm 10)$ Hz. Rate equations for the populations of the hfs Zeeman levels in the presence of the polarized atomic beam and transitions caused by various rf fields are given. Features of the line shape caused by the consecutive-pulse multiple-resonance scheme are also considered. Several mechanisms which may ultimately limit the precision are discussed. A comparison of the experimental result with current theories of the hfs of hydrogenic systems is presented.

• Received 13 March 1969

DOI:https://doi.org/10.1103/PhysRev.187.5