Theoretical Study of Doubly Charged [ X ( H 2 O ) ] and [ X ( NH 3 ) ] ( X = Si , Ge , Sn , Pb ) Molecular Ions * Pablo López - Tarifa

Ab initio calculations have been used to study the structure and stability of several doubly charged molecular ions in the gas phase. In particular the complexes of water and ammonia with Si, Ge, Sn and Pb have been studied. Geometries have been obtained at B3LYP/6-31G(d) level and final energies at CCSD(T)/6-311+G(3df,2p) level. Different fragmentation channels have been considered. The loss of X (X = Si, Ge, Sn, Pb) is the most favorable one, except for [Si(H2O)] where the loss of a H has a lower energy cost. Water complexes are thermodynamically stable, while loss of X in ammonia complexes are exothermic processes. In ammonia complexes a Coulomb barrier prevents the systems from spontaneous dissociation; to obtain these barriers the potential energy curves for the loss of Si or Pb in [Si(NH3)] and [Pb(NH3)] complexes have been obtained at CCSD(T)/6-311+G(3df,2p) level, the corresponding vibrational states have been located and their lifetimes evaluated using the exterior complex scaling. The barriers for dissociation of [X(NH3)] complexes are similar to the ones obtained for [X(H2O)] complexes.