Low-Energy-Electron Attachment to Oxygen Clusters Produced by Nozzle Expansion

Abstract

Electron attachment to ${\mathrm{O}}_{2}$ clusters gives two homologous series, ${{({\mathrm{O}}_{2})}_{n}}^{\ensuremath{-}}$ and ${({\mathrm{O}}_{2})}_{n}{\mathrm{O}}^{\ensuremath{-}}$. Measured relative attachment-cross-section functions show significant differences, i.e., ${({\mathrm{O}}_{2})}_{n}{\mathrm{O}}^{\ensuremath{-}}$ ions show a similar behavior to ${\mathrm{O}}^{\ensuremath{-}}$ from ${\mathrm{O}}_{2}$ (a single peak at \ensuremath{\sim}7 eV), whereas ${{({\mathrm{O}}_{2})}_{n}}^{\ensuremath{-}}$ ions show an additional peak at \ensuremath{\sim}0 eV. The latter result explains the large thermal-electron attachment rates observed in high-pressure and low-temperature swarm experiments.