The nonradiative electron-capture process was investigated for 66.3-MeV/u hydrogenlike cesium ions colliding with ${\mathrm{N}}_2$, Ar, Kr, and Xe gas targets at the internal gas-jet-target terminal of the Heavy Ion Research Facility at Lanzhou-Cooling Storage Ring. For each target, the cesium $K$-shell x-ray emissions were measured at ${35}^{\circ }$ relative to the projectile beam. These spectra contain contributions from He-like cesium formed through single-electron capture, as well as from H-like cesium produced via $1s$-electron excitation. From the measured x-ray spectra, the intensity ratio of x rays emitted from H-like cesium to those from He-like cesium was extracted and found to decrease rapidly with increasing target atomic number. Based on these ratios, the absolute electron-capture cross sections into $n>1$ were determined in combination with calculated electron excitation cross sections. The results were compared with predictions from the relativistic eikonal approximation and continuum distorted-wave theory. The experimental data exhibit reasonable agreement with the continuum distorted-wave calculations, whereas the relativistic eikonal approximation overestimates systematically the measured cross sections.

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• Atomic & molecular collisions
• Charge-transfer collisions
• Scattering of atoms, molecules, clusters & ions
• Atoms
• Ions
• Atom & ion cooling
• X-ray emission spectroscopy