Electron Attachment Cross-Sections to Protons and Positrons Incident on the Fluids He and H₂

Abstract

Recent experimental data by Tang and Surko on the angular and energy dependences of positronium formation in molecular H₂ has prompted us to bring them into contact with total cross-sections as a function of energy in the energy range up to 125 eV (20 aJ). Data for protons incident on H₂ are also compared and contrasted with the positron results. Two regimes are delineated: one around the maximum in the total cross-section and the second in the high energy tail. The positron data of Tang and Surko correspond to the tail regime.

Finally, contact is also made with He data, plus some brief comments on the heavier noble gases. Here, the maximum cross-sections are shown to correlate roughly quadratically with polarizability.

Key Words:

• Positronium
• polarizability
• electron attachment
• atomic and molecular fluids