Electron-stimulated cations desorption from water and perfluorocarbons at cryogenic temperature

The yields of electron-stimulated cations desorption from the condensed C6F12 layer are found to be about two orders of magnitude higher than those from the C6F6 layer. The H+(H2O)n yields from the H2O molecules adsorbed on the C6F12 layer are about 30 times as high as those on the C6F6 layer at temperature of 10 K. The overlapping of π orbitals is responsible for the relatively small cations yield from the C6F6 layer. With increasing temperatures from 10 K to 140 K, the H+(H2O)n yields from water adsorbed on the C6F12 layer decay by two orders of magnitude, as a consequence of the surface diffusion of H2O molecules and the formation of larger clusters. These behaviors are explicable in terms of the localization/delocalization of valence holes in dissociative ionization via Coulomb explosion of perfluorocarbons and that of cluster size effect of water.