Extensive water cluster fragmentation after low energy electron ionization

Water clusters (H2O)N from the size range N ¯ ≈ 10 –150 have been investigated by electron ionization (EI) and photoionization after Na-doping (NaPI) under identical experimental conditions. The NaPI yields cluster sizes in good agreement with a semiempirical formula derived previously. The EI leads to large cluster fragmentation even at electron energies near the ionization threshold at 13 eV. The fragmentation does not change significantly between 15 eV and 90 eV. For N ¯ = 138 the mean cluster ion fragment size corresponds to only about 10% of the original neutral cluster size.