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Complexes of Molecular and Ionic Character in the Same Matrix Layer: Infrared Studies of the Sulfuric Acid/Ammonia System

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journal contribution
posted on 16.06.2011, 00:00 by Mark Rozenberg, Aharon Loewenschuss, Claus J. Nielsen
The atmospherically important interaction products of sulfuric acid and ammonia molecules have been firstly observed by matrix isolation Fourier transform infrared spectroscopy (MIS-FTIR). Infrared spectra of solid argon matrix layers, in which both H2SO4 and NH3 molecules were entrapped as impurities, were analyzed for bands not seen in matrix layers containing either of the parent molecules alone. Results were interpreted on the basis of spectral changes, experimental conditions, and semiempirically scaled frequencies from the B3LYP/aug-cc-pVTZ and B3LYP/aug-cc-pVQZ calculations. Bands were assigned to complexes of the H2SO4·NH3 and H2SO4·[NH3]2 general formulas. They differ significantly: the 1:1 H2SO4·NH3 complex is a strongly hydrogen bonded complex, an analogue of the H2SO4·H2O complex, studied previously. For the 1:2 H2SO4·[NH3]2 complex, spectral results indicate an almost complete proton transfer forming a complex of essentially the two ionic moieties HSO4 and [H3N···H···NH3]+, an analogue of the [H2O···H···OH2]+ “Zundel ion”.