Size-Dependent Onset of Nitric Acid Dissociation in Cs+·(HNO3)(H2O) n=0–11 Clusters at 20 K

We report the water-mediated charge separation of nitric acid upon incorporation into size-selected Cs+·(HNO3)(H2O) n=0–11 clusters at 20 K. Dramatic spectral changes are observed in the n = 7–9 range that are traced to the formation of many isomeric structures associated with intermediate transfer...

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Bibliographic Details
Published in:	The journal of physical chemistry letters 2021-04, Vol.12 (13), p.3335-3342
Main Authors:	Mitra, Sayoni, Yang, Nan, McCaslin, Laura M, Gerber, R. Benny, Johnson, Mark A
Format:	Article
Language:	eng
Subjects:	Acid dissociation Infrared spectroscopy INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY Mass spectrometry Physical Insights into Chemistry, Catalysis, and Interfaces
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Summary:	We report the water-mediated charge separation of nitric acid upon incorporation into size-selected Cs+·(HNO3)(H2O) n=0–11 clusters at 20 K. Dramatic spectral changes are observed in the n = 7–9 range that are traced to the formation of many isomeric structures associated with intermediate transfer of the acidic proton to the water network. This transfer is complete by n = 10, which exhibits much simpler vibrational band patterns consistent with those expected for a tricoordinated hydronium ion (the Eigen motif) along with the NO stretching bands predicted for a hydrated NO3 – anion that is directly complexed to the Cs+ cation. Theoretical analysis of the n = 10 spectrum indicates that the dissociated ions adopt a solvent-separated ion-pair configuration such that the Cs+ and H3O+ cations flank the NO3 – anion in a microhydrated salt bridge. This charge separation motif is evidently assisted by the electrostatic stabilization of the product NO3 –/H3O+ ion pair by the proximal metal ion.
ISSN:	1948-7185 1948-7185