Pathways and Dynamics of Dissociation of Ionized ( H 20 ) 2

The energetics, geometrical and electronic structure, ionization processes, dynamics, and dissociation pathways of neutral and singly and doubly ionized water dimers are investigated with simulations employing the BomOppenheimer local-spin-density functional molecular dynamies (BO-LSD-MD) method. Vertical and adiabatic ionization potentials and dissociation energies and barriers are calculated for various dissociation channels of the singly and doubly ionized dimer. A new bound ground-state, (H20)2+(a), with a hydrazine-like configuration, whose energy is lower by 0.22 eV than that of the disproportionated-ion isomer, (OH)(H@)+, is found for the singly charged dimer cation. A state with a similar geometry is found for a bound metastable state of the doubly ionized water dimer, whose dissociation into 2(H20+) involves a barrier of -0.68 eV. The dissociation pathways of the singly ionized dimer depend on the internal energy of the parent neutral and on the excitation energy, with the OH + H30+ channel dominating at low energies. Fission of the doubly ionized dimer into the H20+ + H20+ and OH+ + H30+ channels can be influenced by the ionization process; direct double ionization of the neutral leads mainly to fission into the first channel, while sequential double ionization can lead to the other.