Electron capture by the image charge of a metal nanoparticle

We have measured absolute cross sections for the capture of low-energy elec trons by large free sodium nanoclusters (similar to 10(4) atoms, or 4 nm ra dius). To explain the results, it is necessary to go beyond the commonly us ed induced-dipole approximation and to employ the full image-charge interac tion potential which accounts for the finite size of the particle. This pot ential yields an exact analytical expression for the capture cross section and leads to good agreement with the data. It is suggested that electron ca pture may provide a useful tool for size characterization of nanoparticle b eams.