Infrared Spectroscopy at Three and Six Microns of Water Ices Mixtures of Astrochemical Interest
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Buffo, Christina Evelina
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Abstract
Water ice exists in many cold regions of the solar system, from our own Earth’s poles to comets far past the orbit of Pluto. On the moon, stable ice can exist for billions of years in the cold permanently shadowed polar regions, but water has also been detected in sunlit areas, furthering debate over its origins and morphology. Similarly ancient ice exists elsewhere: comets may be the least modified reservoirs of ice and dust from the early solar system. Wherever ice is found, its formation mechanism and heating history can greatly influence its structure. The presence and composition of minerals can also shape ice’s structure, and trapped volatile species can reveal even more about the ice’s provenance. The underlying structure of water ice can be determined remotely or in the laboratory through infrared absorption observations, especially at the 3 µm (3300 cm-1) O-H stretch and the 6 µm (1600 cm-1) H-O-H bend.
This thesis examines the role of formation method and mineral composition on water ice structure as revealed by its infrared features. Water ice formed through liquid aerosol injection and vapor deposition appears different at cryogenic temperatures between 91-165 K. The presence of 5 wt% mineral is sufficient to modify the resulting ice structure from mineral-free water, and spectral differences depend on mineral composition. At 50 wt% mineral, ice appears more amorphous with greater olivine weight percentage. Water sublimation from mineral-containing ice is complete by 200 K, demonstrating that adsorption is insufficient to retain water in sunlit lunar regions. Finally, implications of the isotopic composition of noble gases trapped in cometary ice are explored in a mission concept for comet surface sample return.
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2025-12
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Dissertation (PhD)