Radiative Double-Electron Capture by Bare and One-Electron Ions on Gas Targets

Area of Science:

• Atomic and Molecular Physics
• Quantum Electrodynamics
• High-Energy Ion-Atom Collisions

Background:

• Radiative double-electron capture (RDEC) is an atomic collision process analogous to the inverse of double photoionization.
• Previous studies on RDEC have yielded mixed results, particularly when using solid targets like carbon foils, due to complications from multiple scattering.
• Understanding RDEC is crucial for validating fundamental theories of quantum electrodynamics in atomic systems.

Purpose of the Study:

• To conclusively demonstrate the existence of radiative double-electron capture (RDEC) in ion-atom collisions using gaseous targets.
• To investigate RDEC for fluorine ions (F$^{9+}$ and F$^{8+}$) at 2.11 MeV/u impacting nitrogen (N$_{2}$) and neon (Ne) targets.
• To compare experimental findings with theoretical predictions and previous experimental data obtained with different targets and projectile ions.

Main Methods:

• Experimentally studied radiative double-electron capture (RDEC) using a beam of 2.11 MeV/u F$^{9+}$ and F$^{8+}$ ions.
• Utilized gaseous targets of molecular nitrogen (N$_{2}$) and neon (Ne) to minimize complications from multiple scattering.
• Analyzed collision data to identify and confirm the signature of RDEC, characterized by electron transfer and simultaneous photon emission.

Main Results:

• Conclusively demonstrated the existence of radiative double-electron capture (RDEC) for both nitrogen and neon gas targets.
• Observed RDEC in collisions involving F$^{9+}$ and F$^{8+}$ ions, providing new experimental data for this process.
• Data for a carbon foil target showed some evidence of RDEC, but was complicated by multiple collisions affecting projectile charge states.

Conclusions:

• Gaseous targets provide a cleaner environment for observing and studying radiative double-electron capture (RDEC) compared to solid targets.
• The experimental results for RDEC in F$^{9+}$ and F$^{8+}$ collisions with N$_{2}$ and Ne align with theoretical expectations.
• This study provides robust evidence for RDEC and contributes to a better understanding of electron correlation and quantum electrodynamics in atomic collisions.