Access Type

Open Access Dissertation

Date of Award

January 2016

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Chemistry

First Advisor

Arthur Suits

Abstract

This dissertation presents results of applying dc slice imaging in crossed molecular beams to probe the dynamics of the reactions of halogen atoms (chlorine and fluorine) with polyatomic hydrocarbons and alcohols such as deuterated propanes, butane isomers, pentane, alkenes and propanol. The full velocity-flux contour maps of the radical products were measured with 157nm single photon ionization at various collision eneriges. Secondary and tertiary abstractions were found in Cl with normal and deuterated propanes and butane isomers and show distinct differences. The differences were explained in terms of the nature of abstraction sites, energy disposal of the radical product, and kinetic isotope effects. For Cl reaction with butene isomers, the coupling of translational energy and center of mass angular distributions reflect the energetics of competition between direct abstraction and addition/elimination pathways in accordance with ab initio thermochemical data. A possible Cl atom roaming mediating the indirect mechanism is suggested and further addressed with investigations of Cl + isobutene reactions at various collision energies. For reaction of chlorine atoms with butenes, the combined experimental theoretical calculations result shows that Cl addition-HCl elimination occurs from an abstraction-like Cl-H-C geometry, rather than a conventional three-center or four-center transition state. This geometry is accessed exclusively by Cl atom roaming from the initial adduct.

For fluorine atom reaction with linear alkanes, i.e. propane, n-butane and n-pentane, little effect of reaction exoergicity appears in the reduced translational energy distributions. The fraction of available energy in translation for pentane is smaller than the other two. Sharp forward scattering were found in the center of mass angular distributions of all targets and the backscattering decreases in with the size of the molecule increasing. The analyzed data were compared with corresponding theoretical studies.

For fluorine atom reaction with 1-propanol, the translational energy distribution and center of mass angular distributions is quite similar to the results of F + n-butane; it is possible that the greater fraction of collision energy in translation comes from the existence of O-H group. The product scattering distributions of fluorine reaction with 1-butene and 1-hexene provide evidence of a long-lived complex mediated mechanism.

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