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Stability and Struc...
Stability and Structure of Protonated Clusters of Ammonia and Water, H+(NH3)(m) (H2O)(n)
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Hvelplund, P. (author)
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Kurten, T. (author)
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Stochkel, K. (author)
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- Ryding, Mauritz Johan, 1981 (author)
- Gothenburg University,Göteborgs universitet,Institutionen för kemi,Department of Chemistry
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Nielsen, S. B. (author)
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Uggerud, E. (author)
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(creator_code:org_t)
- 2010-06-22
- 2010
- English.
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In: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 114:27, s. 7301-7310
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Abstract
Subject headings
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- Mass spectrometric experiments show that protonated mixed ammonia/water clusters predominant exist in three forms namely H+(NH3)(4)(H2O)(n), H+(NH3)(5)(H2O)(n), and H+(NH3)(6)(H2O)(n) (n = 1-25). For the first two series the collisional activation mass spectra are dominated by loss of water, whereas ions of the latter series preferably lose ammonia. The quantitative characteristics of these observations are reproduced by quantum chemical calculations that also provide insight into the geometrical structures of the clusters. Although the experiments and the calculations agree that clusters with five ammonia are thermodynamically preferred, this does not indicate a rigid tetrahedral structure with one central ammonium covered with an inner solvation shell of four ammonia molecules, with water outside, Instead, water and ammonia have comparable affinities to the binding sites of the first shell, with a preference for ammonia for the first two sites, and water for the last two. The "leftover" ammonia molecules bind equally strong as water molecules to sites in the second shell due to synergistic hydrogen binding. Finally, it is discussed whether the observation of enhanced stability of the H+(NH3)(5)(H2O)(20) in terms of magic numbers and associated geometries may be related to a tetrahedral ammonium core encapsulated in a dodecahedral (H2O)(20) structure, typically found in clathrates.
Subject headings
- NATURVETENSKAP -- Kemi -- Fysikalisk kemi (hsv//swe)
- NATURAL SCIENCES -- Chemical Sciences -- Physical Chemistry (hsv//eng)
Keyword
- gas-phase solvation
- set model chemistry
- magic number
- collisional activation
- atmospheric-pressure
- mass-spectrometry
- binary clusters
- global minima
- ab-initio
- ions
Publication and Content Type
- ref (subject category)
- art (subject category)
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