REACTIVE SPECIES BY FTMS: FREE RADICALS AND ELECTRON-DEFICIENT MAIN GROUP ATOMS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We are investigating pyrolysis of suitable precursors seeded into a supersonic beam as a means to follow reactions of ions with radicals and other reactive species. Our test reaction is that of the benzene radical cation, stored in an FTMS cell, and the allyl radical generated by pyrolysis of 1,5-hexadiene. All reactions were performed in a specially designed FT mass spectrometer, following on-line pyrolysis of 1,5-hexadiene at T = 1273 K in the nozzle. Studies using deuterated benzene and semiempirical MO calculations at the PM3 level give insight to mechanism. When the pyrolysis is incomplete, both the starting 1,5-hexadiene and the product allyl radical are observed. The production of adduct ions indicate the presence of allyl radical. Studies in which an electron beam is used for ionization of the reactive beam showed that both charge exchange and formation of ions of m/z 91 occur at the time the seeded radical beam enters the FT-ICR cell. The [adduct - H], however, does not track the onset of the radical beam; instead, it is delayed by 3 ms. The reactive species must travel a considerably longer distance than that from the nozzle to the cell before reacting. Now that the instrumentation is built and the system working, we intend to characterize better the experimental system and expand to reactions of electron-deficient silicon-containing systems and to biological systems where free radical damage can cause serious modification in biological function. We are also using ion trap technology to follow directly the reactions of other reactive species (e.g., CBr+, SiH+, PBr+) with small organic molecules. In addition, we are augmenting these experimental studies with theoretical calculations by using density functional theory which is implemented through the Gaussian 98 suite running on a small Dell cluster.