Anharmonic Effects in Ammonium Nitrate and Hydroxylammonium Nitrate Clusters
| Autor: | Malika Kumarasiri, Sharon Hammes-Schiffer, Chet Swalina |
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| Rok vydání: | 2007 |
| Předmět: |
Models
Molecular Quantitative Biology::Biomolecules Nitrates Molecular Structure Proton Chemistry Anharmonicity Ionic bonding Hydroxylamine Vibration Potential energy Surfaces Coatings and Films chemistry.chemical_compound Models Chemical Computational chemistry Covalent bond Chemical physics Ionic liquid Physics::Atomic and Molecular Clusters Materials Chemistry Quantum Theory Density functional theory Physical and Theoretical Chemistry Hydroxylammonium nitrate |
| Zdroj: | The Journal of Physical Chemistry B. 111:4653-4658 |
| ISSN: | 1520-5207 1520-6106 |
| DOI: | 10.1021/jp065569m |
| Popis: | The covalent and ionic clusters of ammonium nitrate and hydroxyl ammonium nitrate are characterized using density functional theory and second-order vibrational perturbation theory. The most stable structures are covalent acid-base pairs for the monomers and ionic acid-base pairs for the dimers. The hydrogen-bonding distances are greater in the ionic dimers than in the covalent monomers, and the stretching frequencies are significantly different in the covalent and ionic clusters. The anharmonicity of the potential energy surfaces is found to influence the geometries, frequencies, and nuclear magnetic shielding constants for these systems. The inclusion of anharmonic effects significantly decreases many of the calculated vibrational frequencies in these clusters and improves the agreement of the calculated frequencies with the experimental data available for the isolated neutral species. The calculations of nuclear magnetic shielding constants for all nuclei in these clusters illustrate that quantitatively accurate predictions of nuclear magnetic shieldings for comparison to experimental data require the inclusion of anharmonic effects. These calculations of geometries, frequencies, and shielding constants provide insight into the significance of anharmonic effects in ionic materials and provide data that will be useful for the parametrization of molecular mechanical force fields for ionic liquids. Anharmonic effects will be particularly important for the study of proton transfer reactions in ionic materials. |
| Databáze: | OpenAIRE |
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