The potential energy surface of the (N2O center dot H2O)(+) cluster cation

The ground state potential energy surface of the (N2O . H2O)(+) cluster cat ion is explored with ab initio and density functional theories. B3LYP optim izations are used to determine the structure of the products of the dissoci ation of the cluster ions as well as possible structures for the clusters t hemselves and transition states that connect various minima. Energetics for all optimized structures are determined with the G2M(RCC,MP2) method. The results are used to interpret collision-induced dissociation (CID) experime nts which study the cluster ion, and which find that the cluster dissociate s to form H2O++N2O, N2OH++OH, and N2O++H2O products. The calculations an (N 2O-OH2)(+) complex as well as a similar (H2O-N2O)(+) complex, and show that these complexes access the experimentally observed H2O++N2O products and N 2OH++OH products without any intervening reverse barrier. The stability of both these complexes, approximately -20 kcal/mol relative to the H2O++N2O p roducts, agrees well with experimentally determined CID thresholds for all products. Additional calculations of the ground state potential energy surf ace of the cluster investigate the possibility of the formation of other pr oducts. Some preliminary studies of the excited states of the cluster catio n are also performed; the results of these calculations lend insight into e xperimental photodissociation studies of the cluster ions. Mechanisms for t he formation of H2O++N2O, N2OH++OH, and N2O++H2O products following photoex citation of the cluster ions are discussed; the H2O++N2O and N2OH++OH produ cts must be formed from a surface-hopping from an excited electronic state to states which correlate to ground state products. Similarly, N2O++H2O pro ducts may be formed from collision induced dissociation of clusters only by means of a surface-hopping mechanism. (C) 1999 American Institute of Physi cs. [S0021-9606(99)30241-5].