Direct Observation of the Spontaneous Emission of the Hyperfine TransitionF=4toF=3in Ground State HydrogenlikeH165o66+in an Electron Beam Ion Trap

We report the first direct laboratory measurement of the spontaneous emission due to the hyperfine splitting of the ground state of a highly charged hydrogenlike ion excited by electron collisions. The transition between the $F=4\mathrm{}$ and $F=3\mathrm{}$ levels of the $1s{}_{}{}^2{}_{}{}^{}S_{1/2}^{}{}_{}{}^{}$ configuration of hydrogenlike ${}_{}{}^{165}{}_{}{}^{}H{o}^{65+}$ was observed and its wavelength was determined to $5726.4\pm 1.5Å$. After taking into account relativistic, nuclear charge distribution, Bohr-Weisskopf, and QED corrections, we observe a significant deviation from commonly tabulated values of the nuclear dipole magnetic moment of this nucleus.