Electron attachment to molecules and clusters of atmospheric relevance: Oxygen and ozone

Highly monochromatized electrons are used in a crossed beams experiment to investigate electron attachment to oxygen clusters (O-2)(n) at electron energies from approximately zero up to 2 eV. At energies close to zero the attachment cross section for the reaction (O-2)(n) + e --> O-2(-) varies inversely with the electron energy, indicative of s-wave electron capture to (O-2)(n) Peaks in the attachment cross section present at higher energies can be ascribed to vibrational levels of the oxygen anion, The vibrational spacings observed can be quantitatively accounted for. In addition, electron attachment to ozone and mixed oxygen/ozone clusters has been studied in the energy range up to 4 eV. Absolute attachment cross sections for both fragment ions, O- and O-2(-), from ozone could be deduced. Moreover, despite the initially large excess of oxygen molecules in the neutral oxygen/ozone clusters the dominant attachment products are undissociated clusters ions (O-3)(m)(-) including the O-3(-) monomer while oxygen ions (O-2)(n)(-) appear with comparatively low intensity.