Photodissociation-Photoionization Mass Spectrometry

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This project is in the general area of analytical and surface chemistry and in the subfield of mass spectrometry. During the tenure of this three-year continuing grant, Professor Johnston and his students will use the recently developed technique of photodissociation-photoionization mass spectrometry (PDPI/MS) to investigate mechanisms of photochemical reactions of organic molecules in the gas phase. In PDPI/MS, neutral molecules are photodissociated with an ultraviolet pulsed laser beam. A second pulsed laser generates coherent vacuum ultraviolet radiation which then ionizes the parent molecules and neutral photoproducts from the initial laser pulse. The resulting ions are then detected with a quadrupole mass spectrometer. The two primary goals of this research, which builds upon accomplishments of the Johnston group under NSF grant CHE-9096266, are the (1) development of improved experimental methods for making innovative photochemical measurements by PDPI/MS and (2) fundamental studies of mechanisms of decomposition of large organic molecules. %%% The successful attainment of the goals of this project will provide a rational framework for understanding how large organic molecules undergo gas phase photofragmentation. This knowledge will facilitate the rapid and reliable determination of the structures of technologically important complex molecules.