Complexes of molecular and ionic character in the same matrix layer: infrared studies of the sulfuric acid/ammonia system.

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 center dot NH3 and H2SO4 center dot[NH3](2) general formulas. They differ significantly: the 1:1 H2SO4 center dot NH3 complex is a strongly hydrogen bonded complex, an analogue of the H2SO4. H2O complex, studied previously. For the 1:2 H2SO4 center dot[NH3](2) complex, spectral results indicate an almost complete proton transfer forming a complex of essentially the two ionic moieties HSO4- and [H3N center dot center dot center dot H center dot center dot center dot NH3](+), an analogue of the [H2O center dot center dot center dot H center dot center dot center dot OH2](+) "Zundel ion".