Ion-Atom Merged-Beams Experiment (Electron-Capture)

The ORNL ion-atom merged-beams apparatus has been successful in performing benchmark electron capture cross section measurements for the multicharged ions (B⁴⁺, C⁺, C³⁺, C⁴⁺, N²⁺, N³⁺, N⁴⁺, N⁵⁺, O³⁺, O⁴⁺, O⁵⁺, and Si⁴⁺) on H(and D) from 20 meV/amu to 5000 eV/amu, over five orders of magnitude in collision energy. (see publication list) In this energy range the relative nuclear motion between collision partners is slow compared to the orbital motion of active electrons in the system. Electrons of the quasimolecule formed in the collision have sufficient time to adjust to the changing interatomic field as the nuclei appraoach and separate. Simple scaling laws which exist at higher collision energies (v ~ 1 a.u.) do not exist at eV/amu energies. Fully quantal coupled- channel molecular-orbital calcualtions are considered most accurate at these energies but are difficult to perform and have only recently been tested in detail.

Merged-beams measurements have provided critical comparison with theory and experiment. A brief summary is given here. Select a collision system of interest from the Index. A brief abstract will be presented after which the data can be viewed in either graph or table format. The graph contains comparsion with other experiment or theory when available.

Using a simple multi-grid energy analyzer in the merged-beams apparatus, measurements of state-selective cross sections and angular distributions are now possible at eV/u energies. These