Date of Award
Doctor of Philosophy (PhD)
Chemistry & Biochemistry
Veronica M. Bierbaum
Theodore P. Snow
J. Mathias Weber
Margaret A. Tolbert
The first polyatomic molecule was discovered in interstellar space in 1968, catalyzing the growth of a new scientific field called astrochemistry. Since its inception, collaborations among laboratory chemists, astrophysical modelers, and observational astronomers in this field have led to the detection of nearly 200 molecules in the interstellar medium (ISM). Similarly, detections of complex biomolecules in cometary dust and meteorites have sparked theories of the origin of terrestrial life, a central focus of the recently-established field of astrobiology. Chemical processing occurs in a variety of environments within our galaxy. The purpose of this work is to explore the chemistry of ions and molecules that are pertinent to a multitude of these regions including nebulae, prestellar cores, and the atmosphere of Saturn’s moon, Titan.
This thesis presents mass spectrometric investigations of gas-phase ion chemistry that contribute to the fields of both astrochemistry and astrobiology. Many gas-phase chemical reactions are initiated by ions due to the attractive forces induced by their charge on a reacting partner. This attraction often lowers the barriers of ion-neutral reactions, and can lead to high reaction rates even at low temperatures. The ions examined herein increase in complexity starting with simple species (CN–) and concluding with larger biomolecules, the deprotonated nucleobases.
This work begins with a series of Flowing Afterglow-Selected Ion Flow Tube (FA-SIFT) experiments exploring nitrogen-containing carbanion (CxNy–) chemistry and the formation of interstellar propene and methyl formate (Chapters 3 and 4). Reactions between CxNy– and H atoms reveal pathways for destruction of several CxN– and CxN2– anions, but no reactions are observed for CxN3– species. Two previously-proposed reactions between organic cations and H2 are shown to be immeasurably slow and unlikely to produce propene. Lastly, a reaction pathway producing protonated trans-methyl formate is experimentally and computationally verified. The later chapters describe studies of heterocyclic biomolecules performed using a modified ion trap apparatus. These ions include deprotonated azoles, pyrimidines, and purines (Chapters 5-7). In addition to their reactivity, the dissociation processes and fragments of these anions provide clues to potential precursors and abiotic syntheses. Notably, nearly all fragments observed are detected interstellar species.
Cole, Callie Ann, "The Ionic Building Blocks of Life: Exploring Astrochemistry through Mass Spectrometry" (2015). Chemistry & Biochemistry Graduate Theses & Dissertations (1986-2018). 151.