Fragmentation of ionized liquid helium droplets: A new interpretation

Pure liquid helium droplets of mean size [N] = 100-15000 atoms ionized by e lectron impact show surprisingly similar ion fragment distributions. For al l cluster sizes He-2(+) is the most probable cluster ion fragment, accounti ng for 30%-70% of the total ion yield. The high relative intensity of He-2( +) for the larger clusters shows that the droplets dissipate the ionization energy through an impulsive process, which ejects He-2(+) from me cluster, rather man by thermal evaporation. The other helium ion fragments that hav e been the focus of previous studies ate most likely formed by a similar me chanism. (C) 1998 American Institute of Physics. [S0021-9606(98)00547-9].