Collisions of mass-selected ions: I. Angular dependence and target effects on internal energy distributions in high-energy charge-changing collisions. II. Low-energy ion/molecule and ion/surface reactions
Abstract
The internal energy distributions of polyatomic ions energized in keV charge exchange and charge stripping collisions were measured as a function of scattering angle for the "thermometer molecule" tungsten hexacarbonyl. The experiments were performed using a modified MIKE spectrometer with angle-resolving slits which allow measurement of the scattering angle in the non-focusing plane of the instrument. The results show that charge-changing collisions accompanied by scattering have the potential for depositing large internal energies. The average internal energy deposited increases with the scattering angle for both charge exchange and charge stripping collisions. Charge exchange experiments were also performed using different compounds as collision gas. The internal energy deposited is derived mainly from translational energy rather than the reaction thermochemistry. The efficiency of the charge exchange process showed a strong dependence on the ionization energy of the target gas. Quadrupole mass spectrometers were used to study ion structures using ion/molecule reactions. An industrial copolymer was characterized by DCI mass spectrometry. The fragmentation of oligomers was studied by MS$\sp2$ and it was found that some of the higher oligomers were proton bound dimers. The monomer distribution was found not random and the degree of blockness of the monomers was determined. A pentaquadrupole mass spectrometer was used to study gas phase ion/molecule Diels-Alder additions. A correlation was found between the cycloaddition reactivity and the energy gap between the LUMO energy of the dienophiles and the HOMO energy of the diene. The structures of the adducts have been characterized by MS$\sp3$ experiments. For $\alpha,\beta$-unsaturated carbonyl dienophile ions, the adducts have the covalently bound six membered ring structures expected for Diels-Alder reaction products. A sector mass spectrometer was modified to facilitate ion/surface reactions and its performance was characterized. Low energy mass-selected ion beams (a few to tens of eV) were allowed to collide with a surface covered with C$\sb{60}$. Adducts were found on the surface after collision to be C$\sb{60}$O and C$\sb{60}$O + n CH$\sb2.$ When PhI was present in the surface region, the addition of 128 (HI) to C$\sb{60}$ was observed.
Degree
Ph.D.
Advisors
Cooks, Purdue University.
Subject Area
Chemistry|Analytical chemistry
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