High resolution electron attachment to CO2clusters

Electron attachment to CO2 clusters performed at high energy resolution (0.1 eV) is studied for the first time in the extended electron energy range from threshold (0 eV) to about 10 eV. Dissociative electron attachment (DEA) to single molecules yields O− as the only fragment ion arising from the well known 2Πu shape resonance (ion yield centered at 4.4 eV) and a core excited resonance (at 8.2 eV). On proceeding to CO2 clusters, non-dissociated complexes of the form (CO2)n− including the monomer CO2− are generated as well as solvated fragment ions of the form (CO2)nO−. The non-decomposed complexes appear already within a resonant feature near threshold (0 eV) and also within a broad contribution between 1 and 4 eV which is composed of two resonances observed for example for (CO2)4− at 2.2 eV and 3.1 eV (peak maxima). While the complexes observed around 3.1 eV are generated via the 2Πu resonance as precursor with subsequent intracluster relaxation, the contribution around 2.2 eV can be associated with a resonant scattering feature, recently discovered in single CO2 in the selective excitation of the higher energy member of the well known Fermi dyad [M. Allan, Phys. Rev. Lett., 2001, 87, 0332012]. Formation of (CO2)n− in the threshold region involves vibrational Feshbach resonances (VFRs) as previously discovered via an ultrahigh resolution (1 meV) laser photoelectron attachment method [E. Leber, S. Barsotti, I. I. Fabrikant, J. M. Weber, M.-W. Ruf and H. Hotop, Eur. Phys. J. D, 2000, 12, 125]. The complexes (CO2)nO− clearly arise from DEA at an individual molecule within the cluster involving both the 2Πu and the core excited resonance.