Observational and Laboratory Studies in Astrobiology: Phosphorus, Carbon Nanostructures, and Distant Organic Molecules
Author
Bernal, Jacob JeromeIssue Date
2021Advisor
Ziurys, Lucy M.
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The University of Arizona.Rights
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction, presentation (such as public display or performance) of protected items is prohibited except with permission of the author.Abstract
The period of time, beginning with ejection of molecular material into a circumstellar envelope and ending in the formation of a new solar system, allows for rich, intricate chemistry. In between, molecules will face shocks, ion and high energy photon bombardment, potential condensation on to dust grains and surface reactions, extreme temperature ranges and fluctuations, and potentially GYr timescales to reexperience these events. The molecular species most pertinent to astrobiology contain so-called “NCHOPS” elements, the six most abundant elements in biology. A combination of millimeter-wave astronomical observations using the Submillimeter Telescope (SMT) and 12-m Telescope of the Arizona Radio Observatory, as well as in situ laboratory Transmission Electron Microscope (TEM) measurements have been conducted in order to constrain important NCHOPS-containing species, and their progression from circumstellar environments to star-forming regions. Observations of phosphorus monoxide (PO) and phosphorus mononitride (PN) towards the circumstellar envelopes (CSE) of O-rich supergiant and AGB stars resulted in a 100% detection rate, indicating gas-phase phosphorus species are common in CSEs. ARO 12m observations were used to complete a 3mm spectral survey towards the star-forming region Orion-KL, which resulted in the first-ever detection of PO in the source. The line profiles and LSR velocities of the observed PO and PN transitions indicate formation in the Plateau region. This region is dominated by shock chemistry, and this shock formation mechanism can be applied to a majority of the other molecular clouds where PO is detected. To determine if there is a change in abundance of NCHOPS-containing Complex Organic Molecules (COMs) with respect to galactocentric distance, 12m observations of methanol transitions were conducted towards 20 molecular clouds. A methanol detection rate of 95% was found, with the farthest detection 23.5 kpc from the galactic center. These results indicate that COMs are present even at the very edge of the galaxy, in low metallicity regions. The largest known COMs are fullerenes such as C60 and C70, which are seen in planetary nebulae and the ISM. In situ TEM heating and ion bombardment experiments were conducted at Argonne National Laboratory and the University of Arizona on analog silicon carbide (SiC) presolar grains. The heating and ion bombardment experimental results indicate that when SiC was heated to ~1275 K, Si atoms leach from the crystal lattice, leaving graphene layers on the grain surface. The graphene layers distorted, forming carbon nanobuds with the same diameter as C60. The implications of these results on interstellar fullerene formation are discussed. Finally, the implications of the experimental results on the presence of larger COMs such as carbon nanotubes are presented.Type
textElectronic Dissertation
Degree Name
Ph.D.Degree Level
doctoralDegree Program
Graduate CollegeChemistry