Small charged water clusters: Cations

Nonempiric calculation (MP2/UHF/4-31++G**) shows the presence of inherent H 3O and OH fragments in small water cluster cations. According to the arrang ement of these fragments, the structures of cations are divided into two gr oups: either OH fragment acts exclusively as a proton acceptor in all its h ydrogen bonds, or it is directly bonded to H3O and acts also as a proton do nor in the H-bond with a water molecule. At the external effect of about 0. 4 eV, the former cations can dissociate into free or quasifree OH radical a nd a protonated water cluster of the corresponding size. An extrapolation o f the adiabatic ionization potentials of water clusters to an infinite clus ter size provides the value of 8.5 eV close to the experimental photoelectr ic threshold of amorphous ice. When the adiabatic hydration of the electron knocked out is taken into account, the energy of 6.8 eV should be sufficie nt for the ionization of an ice specimen.