Spectroscopic Studies of Homogeneous Precursors to Atmospheric Acids and Aerosols

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A newly constructed, pulsed-nozzle Fourier transform microwave spectrometer will be used to determine the structures, dipole moments, and reaction energetics of a variety of gaseous species that are precursors to certain atmospheric aerosols and acids. Particular emphasis will be placed on adducts of sulfur trioxide (SO3), which is the immediate precursor to sulfuric acid (H2SO4) in the atmosphere. Additional studies will focus on complexes involving water vapor, sulfur trioxide, ammonia, sulfur dioxide, sulfuric acid, nitrogen oxides, and nitric acid. The data from these spectroscopic investigations will provide new molecular-level detail about the chemical mechanisms that produce sulfuric acid and nitric acid aerosols. Because aerosols influence the earth's albedo and precipitation patterns, this research will impact our understanding of climate. Many of the adducts targeted for study are expected to involve bonding forces that are intermediate between van der Waals and covalent. Consequently, this research will explore the role of unconventional bonding in complexes involved in postulated processes of atmospheric importance. Extensions of the initial project will include studies of radical intermediates and selected tertiary clusters that represent the next step beyond dimers in the homogeneous nucleation process.