Affiliations: [a] Grupo de Química – Física Teórica, Instituto de Química, Universidad de Antioquia, Medellín, Colombia | [b] Escuela de Ciencias y Humanidades, Departamento de Ciencias Básicas, Universidad Eafit, Medellín, Colombia | [x] Centro de Química, Instituto Venezolano de Investigaciones Científicas, IVIC, Caracas, Venezuela | [y] Departamento de Química, Instituto Universitario de Tecnología FRP, Caracas, Venezuela
Correspondence:
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Corresponding author: Albeiro Restrepo, Grupo de Química–Física Teórica, Instituto de Química, Universidad de Antioquia, AA 1226, Medellín, Colombia. E-mail: albeiro@exactas.udea.edu.co.
Abstract: A detailed study of the interactions leading to stabilization of the NH3(H2O)n=1,2 clusters is presented in this work. The Potential Energy Surface for the trimers was explored using an adapted version of the simulated annealing optimization procedure that produced cluster candidate structures that were further optimized, refined, and characterized at the MP2/6–311++G(d, p) level. Our results indicate that hydrogen bonding of the N⋯H type is stronger and more covalent than of the O⋯H type. We provide evidence that suggests that the topological complexity of the electron distributions is directly correlated with cluster stability and that most of the stabilization energy originates in electrostatic and exchange contributions. Our calculated trimerization enthalpy, ΔH°298 −41.75 kJ/mol, is in excellent agreement with the experimental enthalpy of adsorption of NH3 into surface water, reported to be −(41 ± 5) kJ/mol.
