MRCI investigation of different isomers of Ni2O2H2

The geometrical and electronic structures of different isomers of Ni2O2H2+ are investigated by multireference configuration interaction (MRCI) calculations using natural atomic orbital basis sets. The lowest-lying isomer, Ni-2(OH)(2)(+), has a rhombic shape with two OH groups bridging the Ni atoms. The next isomer in energetic order with a relative energy of 0.29 eV consists of a linear NiONi(OH2)(+) chain. Other structures with a rhombic shape, (NiH)(2)O-2(+), with H bound to the Ni atoms have considerably higher energies, above 4 eV. Especially the low-lying isomers are characterised by a large number of low-lying electronic terms. The product Ni2O2H2+ of the reaction of Ni2O2+ with small alkanes is likely to have the rhombic Ni-2(OH)(2)(+) structure. The reaction energy of the reaction Ni2O2+ + H-2 -> Ni-2(OH)(2)(+) is estimated to be about -3.5 eV.