Structure, Energetics, Reaction Dynamics and Vibrational Spectra of Gaseous Ions

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The general objectives of our research over the next grant period will be to expand the understanding of the nature of inter- and intra-molecular interactions found in the novel bonding environments frequently displayed by gas phase ions and to probe both the unimolecular and bimolecular reaction dynamics of gas phase ions. In order to address these objectives we will use a four-pronged approach combining both experimental and computational studies. The first of the experimental methods used is High Pressure Mass Spectrometry (HPMS), which permits the study of gas-phase ion-molecule reactions and equilibria as a function of temperature. In this way, accurate experimental values of ΔHo and ΔSo can be obtained for these processes leading to an accurate, quantitative understanding of the potential energy landscapes involved. The second experimental approach involves Fourier Transform Ion Cyclotron Resonance Spectrometry (FTICR) which permits confinement of ions in an electromagnetic trap for extremely long periods of time at low pressures. The third technique exploited is Infrared Multiple Photon Dissociation (IRMPD) experiments involving a Free Electron Laser (FEL). Finally, all of our experimental work is accompanied by computational studies using electronic structure methods which greatly aid in the understanding of bonding and energetics as well as in the interpretation of vibrational spectra. An accompanying RTI application also proposes to add an OPO laser system to our laboratory to permit IRMPD experiments to be carried out at Waterloo. The principle experiments to be carried out are of several different types. We have demonstrated recently the significant insight into small biomolecule structure and dynamics that can be gained from gas phase bimolecular H/D reactions using FTICR experiments. As an example, the Na+(Ala)n series of sodiated polyalanines (n = 2-14) have been found to exhibit a surprising consistency in the number and speed of H/D exchange dynamics despite significant changes in the structures of the polyalanines as the number of amino acid residues increases. H/D exchange experiments are also currently in progress for protonated glutathione and its protonated dimer. Another area of study involves the formation and characterization of some novel gas phase clusters. We are investigating a series of alkylammonium chlorides which show the capability of forming extended networks resembling the formation of salt crystals in the gas phase. In addition, guanidinium chloride is found to form very large clusters which take on progressively greater extents of bowl and ball like shapes as the cluster size increases. Finally, a new type of systems involving ionic adducts of all-cis hexafluorocyclohexane and related substituted cyclohexanes are under investigation as they exhibit extremely strong ion binding interactions. IRMPD spectra aid in their characterization.