Date of Award

Spring 2010

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry & Biochemistry

First Advisor

Veronica M. Bierbaum

Second Advisor

Theodore P. Snow

Third Advisor

Donald David

Abstract

Scientific studies have led to a more thorough understanding of processes directing the evolution of the Universe. In addition to observational studies with telescopes, terrestrial laboratory studies now contribute to the knowledge encompassed by astronomy and astrophysics. The laboratory-astrophysics experiments performed for this thesis focused on topics ranging from the birth of the first stars and galaxies to chemical processes important to the interstellar medium (ISM).

Models attempt to derive a better understanding of certain cosmological and astrophysical environments. Their reliability, however, depends heavily on the accuracy of data employed. Our contributions to laboratory astrophysics are based on the use of a flowing afterglow-selected ion flow tube (FA-SIFT) supported by ab initio calculations to study ion-neutral reaction kinetics.

Studies for this thesis began with carbon cation, C⁺. This species, ubiquitous throughout dense-translucent and molecular-cloud regions of the ISM, is extremely reactive and is shown to lead to more complex organic species. We have measured reactions of ground-state C⁺ with abundant interstellar neutrals. Our measurements will increase the accuracy in models of the ISM.

After the big bang, star and galaxy formation was not possible until the early Universe sufficiently cooled to enable protogalactic collapse. This process did not occur until a sufficient concentration of the first molecule, H₂, enabled efficient cooling. The dominant mechanism of H₂ formation during this epoch was associative detachment (AD). Because of high uncertainties in existing measurements, we have remeasured the rate constant of the AD reaction and obtained a significant improvement for cosmological models. We have also characterized the chemistry of H⁻ with prototypical chemical reactants, effectively mapping reactivity trends for hydride.

The recent detection of anions in the ISM suggests that these species must play a role in the evolution of astrophysical environments. However, in contrast to their positive counterparts, relatively little is known about anion chemistry. We contribute a number of studies of anionic species, continuing the characterization of the reactions of these species and their role in astrochemistry. A number of carbanions, relevant to interstellar chemistry, were studied with the most abundant atomic species of the interstellar medium, H atom.

Comments

I've used Unicode characters for the sub- and super-scripts. I may need to replace those with plain-text, if they are not functional here. JZ, 12 Jan. 2016

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