LOW-ENERGY-ELECTRON ATTACHMENT TO MIXED OZONE OXYGEN CLUSTERS/

Electron attachment to a cluster beam formed by adiabatic expansion of a mixture of O-3 (1%) and O-2 (99%) is studied in the energy range 0- 4 eV. Despite the initial large excess of oxygen molecules, the domina nt attachment products are undissociated cluster ions (O-3)(m)(-) incl uding the monomer O-3(-), while oxygen cluster ions (O-2)(n)(-) appear with comparatively low intensity, This behaviour is explained by an e nrichment of ozone in the cluster formation process and the preferenti al formation of O-3(-) from mixed clusters, The structured energy depe ndence of the cross section of O-3(-) formation is interpreted in term s of three different mechanisms, in the low-energy region by s-wave ca pture, around 1 eV via Feshbach resonances, and above 1.5 eV by self-s cavenging, i.e. inelastic scattering of the primary electron involving low-lying electronic states of neutral ozone and subsequent attachmen t of the slowed-down electron to another ozone molecule in the same cl uster.