Contributions to Atmospheric Chemistry by Photochemical Reactions of Cluster Molecules

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Small aggregates of molecules often have properties unique and different from their respective isolated molecules or bulk phase. The simplest aggregate is the two molecule complex or dimer. Low concentrations of dimers are expected in the atmosphere, but their numbers may be sufficient to influence certain atmospheric chemical processes. Little is known about the properties of dimers containing species of atmospheric relevance. The project will explore the hypothesis that the photolysis of weakly bound molecular dimers may be an important source for some atmospheric species. The study will use both conventional methods in which quantum yields are measured for photolysis of gas mixtures at a variety of partial pressures and temperatures and the method of supersonic jet expansion with Fourier Transform spectroscopy and multiphoton ionization coupled with mass spectrometric detection. This approach will obtain fundamental physical parameters such as shifts in absorption spectra, absorption cross-sections, dimer binding energies, and entropies of formation. The data obtained will be directly applicable to computer models of atmospheric chemistry.