Probing symmetry-driven DEA dynamics in ozone investigated by velocity slice imaging technique

Abstract

We report the results of a comprehensive experimental investigation of dissociative electron attachment (DEA) to ozone using the velocity slice imaging technique. We reveal several channels that yield both O^− and O^−2 from negative-ion resonances formed by electron attachment. Our results demonstrate that DEA to ozone proceeds through competition between symmetric and asymmetric dissociation pathways. This is governed by excitation of symmetric, asymmetric, and bending vibrational modes and likely involves vibronic coupling between the symmetry of the negative ion resonance states. At 1.6 eV, symmetric dissociation results in vibrationally excited O2 and O^−2 with near-thermal kinetic energies. An additional asymmetric dissociation pathway driven by overlapping contributions from ^2A1 and ^2 B2 states producing rotationally excited O2 with enhanced translational energy is identified. DEA from the second resonance yields both O^− and O^−2 with considerable internal energies arising from a single anionic state (^2B2) proceeding via an asymmetric dissociation mechanism. In the 4.1 − 4.4 eV region, overlapping resonances with A1 and B2 symmetry lead to asymmetric dissociation, accompanied by a notable increase in internal excitations of the molecular moieties. This also provides experimental evidence for the previously proposed ^2A1 shape resonance at 4.2 eV. At higher energies around 6.9 eV, angular distribution analysis reveals a contribution from an additional ^2A1 state, in contrast to the theoretically predicted ^2B2 state. These findings establish a unified picture of competing symmetric and asymmetric dissociation mechanisms that produce highly internally excited and chemically reactive fragments.