Date of Award

August 2020

Degree Type


Degree Name

Doctor of Philosophy (PhD)




Gianfranco Vidali

Subject Categories

Physical Sciences and Mathematics


In this thesis I explore the results of ultra-high vacuum laboratory experiments performed at the Syracuse University Astrophysics and Surface Science Laboratory on structural changes of analogs of ice mantles that cover dust grains in dense clouds in the interstellar medium. We present the experimental and analytical techniques that we used and the motivations for the investigations in the context of molecular astrophysics. The primary contribution of this thesis is the meaningful insight into the long-standing question of how molecular diffusion and formation occur in or on ices in the interstellar medium under the conditions of low pressure and low temperature. Specifically, the focus is placed on an astrophysically relevant two layer ice geometry where the first layer is primarily composed of water molecules (water-rich), while the second layer’s dominant species is CO (water-poor). We consider each layer separately, first investigating the pore surface area of the water-rich layer and correspondingly its ability to store, trap, and facilitate the formation of complex organic molecules (COMs). We then consider the water poor layer where we report the discovery of a new phase transition in carbon monoxide ice at low temperature. We use CO2 as a probe within the CO ice matrix to demonstrate how this transition causes a diffusion and clustering of CO2 and consequentially suggests the potential mechanism for molecular formation in the ISM. This information is used to build a predictive model that is applied to an astrophysically relevant parameter space within which we are able to directly relate the time scale on which this transition occurs with that of stellar evolution.


Open Access