  Neutral alkali clusters efficiently capture low-energy electrons with the aid
of long-range polarization attraction. Upon attachment, the electron affinity
and kinetic energy are dissipated into vibrations, heating the cluster and
triggering evaporation of atoms and dimers. This process offers a novel means
to explore nanocluster bonding and evaporation kinetics. The present work
investigates the formation of ${Na}_N^-$. A crossed-beam experiment reveals
that relative anion abundances become strongly and nontrivially restructured
with respect to the neutral precursor beam. This restructuring is explained in
quantitative detail by an analysis of evaporative cascades initiated by the
attachment. The analysis thus furnishes a complete description of the electron
attachment process, from initial attraction to final rearrangement of the
cluster population. In addition, the paper describes a systematic derivation of
cluster evaporation kinetics and internal temperature distributions; a new
relation between the dissociation energies of cationic, neutral and anionic
metal clusters; and a scenario for inferring the neutral cluster population in
the supersonic beam from the cationic mass spectrum.
