Application of decelerated bare nuclei to precision spectroscopy of one-electron ions

Bare Cl nuclei were decelerated and then allowed to capture a single electron in a He-gas target. By this method pure hydrogenlike Cl ions were prepared in an excited state from which the 2p-1s transition wavelength could be accurately ({}10^-5) measured without distortion by spectator electrons. After Doppler correction by utilizing measurements at four different ion velocities (v/c{}0.038--0.067), fine-structure splitting and 1s Lamb-shift values were determined within 15% error bars, which, while far from the potential possible limits of our method, are in agreement with theoretical results.