Alexia Simon Public Thesis Defense

Описание: "Decoding Solar System Volatile Compositions: Laboratory Investigations of Ice Entrapment and Deuterium Fractionation"

Abstract: Stars and planets form within molecular clouds where dust grains are coated with icy mantles of simple molecules such as water, carbon dioxide, and methane. These ices store and process volatile elements that later shape the composition of comets and planets. Through laboratory experiments, this thesis investigates three key processes that control the chemical and isotopic evolution of astrophysical ices. First, desorption studies reveal how hyper-volatile species like CO and CH₄ become trapped within water and carbon dioxide ices, shaping how these volatiles are distributed between gas and ice phases in planet-forming disks. Second, UV irradiation of mixed water and methane ices showing hydrogen–deuterium exchange proceeds efficiently but remains incomplete, challenging the idea that all volatile species are inherited from molecular clouds. Finally, oxygen-atom insertion into methane produces methanol and its deuterated forms under cold conditions, revealing a new route to isotopic enrichment that helps interpret recent observations. Together, these results explain how ice structure and photochemistry regulate volatile entrapment, isotopic fractionation, and the formation of complex molecules during planet formation.

Advisor: Karin Oberg