Photodissociation of Mass-Selected(CO2)n−Clusters: Evaporation Leading to Magic Numbers in Fragment-Ion Distributions

Photodissociation of mass-selected ${{\left({\mathrm{CO}}_2\right)}_n}^{-}$ clusters, $n<~40$ at 355 and 308 nm reveals that the same "magic numbers" are present in the fragmentation pattern as in the mass spectrum, demonstrating that these intensity anomalies are due to relative ionic stabilities. The photon energy dependence of the fragmentation pattern shows that photodissociation proceeds by an evaporative mechanism and yields an upper bound, 0.22 ± 0.01 eV, for the binding energy of a neutral C${\mathrm{O}}_2$ onto the ionic cluster in the large-cluster limit.