Fragmentation Analysis of Size Selected Sodium Clusters

AbstractWe investigate the fragmentation behaviour of size selected sodium clusters Nan, n ≤ 4, for different ionization methods. The experimental technique, size selection by means of scattering the cluster beam from a helium target beam and subsequent time resolved measurement of the scattered particles, enables us to find a unique correlation between the detected cluster ions and their neutral precursors. In the case of photoionization we use the light from a Xe‐arc lamp in a broad spectral range down to a wavelength of about 220 nm, whereas for the pulsed, frequency doubled dye laser the wavelength is tuned to 290 nm. Electron impact ionization has been examined with an electron energy of 25 eV, which is far above the ionization threshold of all sodium clusters. The ionization by electron impact with the large excess energy results in a total fragmentation of the sodium trimer. In the case of photoionization the fragmentation probabilities do not follow always the energetically favoured pathways, which will be demonstrated for the sodium tetramer.