Gas Phase Solvation of the Ammonium Ion by NH₃ and H₂O and Stabilities of Mixed Clusters NH₄⁺ (NH₃)_n(H₂O)_w

Abstract

The gas phase equilibria were measured with a pi~lsed electron beam high pressure ion source mass spectrometer. The ion source contained pure ammonia or mixtures of ammonia and water vapor at pressures in the T o r r range. Determination of the temperature dependence of the equilibrium constants led to the evaluation of AGO, A H 0 , and AS0 values for the equilibria from t~ = 1 to 4 and \v = 1 to 5. The AGO values for the NH4+(NH3),, equilibria were in good agreement with previous determinations from this laboratory. Fair agreement was observed for the A H 0 and AS0 values. Comparison with the corresponding results for NH4+(HzO),, showed that the AH ,,,,,-, and AGO ,,,,,-were larger than AH , , . , -, and AGO ,,.,,-,. The difference was largest for the first step (1,O) and decreased progressively until a reversal with water values becoming larger occurred at the (5,4) step. The stronger hydrogen bonds of NH3 to N H 4 + for low ligand numbers is explained by the greater basicity of N H , . As the ionic charge becomes dispersed and more distant stronger interactions are obtained with water which gives stronger H bonds in the absence of positive ionic charge. Breaks in theAH,,.,,-values indicateexistenceof a relatively stabIeNH4+(NHJ)., symmetric ion. A much smaller and less distinct break is observed with pure water ligands.The mixed ammonia-water clusters show similar effects. The addition of a N H 3 molecule to a pure water ligand complex gives the strongest interaction. The addition of H 2 0 to a pure ammonia cluster gives the weakest interaction. The above effect is strongest at lowest ligand numbers. The difference decreases gradually and becomes reversed for more than four ligands. [Traduit par le journal]Can.

Intermolecular interactions: Elaboration on an additive procedure including an explicit charge‐transfer contribution

“…20. The computed interaction energy -20.8 kcal/mol, compares very satisfactorily with the gas-phase complexation enthalpy of NHi-H20 [25] when the zero-point energy correction, about 3 kcal/mol is taken into account [9].…”

A simulation experiment of photochemical reactions in the mesosphere.

“…4) is supposed to be the main channel to form NH4+. (H2O)n the conclusion of a previous work (LINEBERGER and PUCKETT, 1969b) PUCKETT and TEAGUE, 1971;PAYZANT et al, 1973) and the importance of ammonia cluster ions in the lower atmosphere has been suggested (e. g., FEHSENFELD and FERGUSON, 1973). In this experiment, the behavior of NH4+.…”

Ion conductance and ion selectivity of potassium channels in snail neurones

“…Because this ion has tetrahedrally disposed hydrogens which form hydrogen bonds with surrounding molecules, the high permeability of ammonium is revealing. In water, the ammonium ion would normally form four hydrogen bonds, one with each hydrogen, and each with an energy on the order of 10 kilocalories per mole (Payzant, Cunningham & Kebarle, 1973). If within the pore ammonium ions formed fewer than four hydrogen bonds at the selectivity site, the energy barrier for them would be expected to be at least several kilocalories per mole higher than a comparably sized "nonreactive" ion.…”