Observations of IR features of ices towards low mass young stellar objects show that ices that coat dust grains are made of water with significant fractions of simple molecules such as CO and CO2. Mid-IR features indicate the presence of such molecules in different binding arrangements and aggregation states. The study of diffusion and aggregation of molecules in ices is important in the understanding of the thermal and chemical evolution of ices in the interstellar medium (ISM). Using temperature programmed desorption and in-situ infrared spectroscopy (RAIRS- reflection absorption infrared spectroscopy) we investigated the elementary steps of adsorption, diffusion, aggregation, and desorption of simple molecules on amorphous solid water (ASW), an analog of ices coating dust grains in the ISM. We were able to characterize sticking and desorption at very low coverage and at low temperature so as to make the results relevant to conditions encountered in interstellar environments. In the study of diffusion of CO2 and CO on non-porous ASW, we find that CO wets the surface while CO2 aggregates in clusters. Using a simulation, we obtain the energy barrier to diffusion of CO2 on np-ASW. These and other results can be used to characterize and interpret the thermal evolution of and catalytic processes in ices in the ISM.

Adsorption, diffusion, aggregation, and desorption of simple molecules (CO2, CO, O2, etc.) on interstellar ice analogs

253rd National Meeting (2017)

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