15min:

S. W. HUNT, C. S. BRAUER, M. CRADDOCK, K. R. LEOPOLD, Department of Chemistry, University of Minnesota, Minneapolis, MN 55455.

Previous reports of atmospheric sulfate aerosol formation indicate significantly enhanced nucleation rates in the presence of elevated concentrations of ammonia. Computational studies predict the most stable structure for NH₃-SO₃- H₂O ternary system is the hydrogen bonded complex, H₂SO₄-NH₃, but a second minimum, only 0.4 kcal/mol higher in energy occurs for the hydrated form of sulfamic acid (H₃N-SO₃) H₂O. In this report, we present microwave spectroscopic results obtained in a supersonic jet seeded with H₂O, NH₃, and SO₃. A-type rotational spectra of a near-prolate asymmetric top requiring the simultaneous presence of NH₃, H₂O, and SO₃ in the jet have been observed. The transitions correlate with the intensity of known H₃N-SO₃ spectra, and spectroscopic constants are consistent with those predicted for (H₃N-SO₃) H₂O.^b Assignment to H₂SO₄-NH₃, however, cannot be ruled out on the basis of data corresponding to the parent isotopic form alone. Isotopic work is in progress, and spectral results will be reported. A novel, dual-injection arrangement, in which two gases are independently admitted into the early phases of the supersonic expansion, has been developed and will be described as well.