title: Ammonia-water cation and ammonia dimer cation.
abstract: We have investigated the structure, interaction energy, electronic properties, and IR spectra of the ammonia-water cation (NH(3)H(2)O)(+) using density functional theory (DFT) and high-level ab initio theory. The ammonia-water cation has three minimum-energy structures of (a) H(2)NH(+)...OH(2), (b) H(3)N(+)...OH(2), and (c) H(3)NH(+)...OH. The lowest-energy structure is (a), followed by (c) and (b). The ammonia dimer cation has two minimum-energy structures [the lowest H(3)NH(+)...NH(2) structure and the second lowest (H(3)N...NH(3))(+) structure]. The minimum transition barrier for the interconversion between (a), (b), and (c) is approximately 6 kcal/mol. Most DFT calculations with various functionals, except a few cases, overstabilize the N...O and N...N binding, predicting different structures from Moller-Plesset second-order perturbation (MP2) theory and the most reliable complete basis set (CBS) limit of coupled cluster theory with single, double, and perturbative triple excitations [CCSD(T)]. Thus, the validity test of the DFT functionals for these ionized molecular systems would be of importance.
authors.affiliation: Pohang Jecheol High School, Pohang 790-390, Korea.
authors.forename: Hahn
authors.initials: H
authors.lastname: Kim
authors.forename: Han Myoung
authors.initials: HM
authors.lastname: Lee
mesh_terms: D000641:Ammonia / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D003198:Computer Simulation; D019281:Dimerization; D006860:Hydrogen Bonding; D008956:Models, Chemical; D011789:Quantum Theory; D014867:Water / Q000737:chemistry*
chemical_list: D002412:Cations; D014867:Water; D000641:Ammonia