Department or Program

Chemical Physics

Primary Wellesley Thesis Advisor

Chris Arumainayagam

Additional Advisor(s)

Dr. Karin Öberg (Harvard Center for Astrophysics)


The recent Rosetta and Giotto missions to comets have detected the presence of a surprisingly large amount of O2 within cometary comae. Most comet formation models suggest that comet compositions preserve conditions in the early solar system, so one possible origin of this diatomic oxygen is formation within ice layers on small dust particles in space before or during solar system formation. One common ice component is carbon dioxide, and this thesis focuses on O2 formation from UV photolysis of CO2 ices. Viewed in the context of the evolution of related molecules, CO and O3, we examine O2 production as a function of UV photon fluence and ice temperature. We report that the ideal conditions for O2 production are a large photon fluence and ice temperatures in the range of 20-25 K, which are reasonable conditions for the interstellar medium. In light of these findings, we propose that interstellar regions with significant CO2 ice could partially explain the large abundance of O2 in comets.