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Cool Interstellar Physics and Chemistry
Published in Leonid Khriachtchev, Physics and Chemistry at Low Temperatures, 2019
Alexander G. G. M. Tielens, Louis J. Alternandola
Interstellar ice composition in protostellar regions is particularly important since this is where new planets are also forming. The material surrounding these star-forming regions dominates the absorption spectrum because the gas and dust is orders of magnitude more concentrated here than it is along the rest of the line of sight. These are the regions in which the OCN−, CO2, and CH3OH bands become important. The presence of methanol in these ices is of pivotal importance since it drives a rich interstellar ice photochemistry,9,97,98 is important in ice segregation,99 and plays an important role in gas-phase chemistry after evaporation near a newly formed star.7,87 The discussion below will focus on the photochemistry of mixed molecular ices comprised of the most abundant interstellar ice species as described in Section 2. There is now a large body of work on ice photochemistry of various ice mixtures, many of astronomical interest,10,100–102 but the kinetic parameters required to extrapolate the experiments to astrophysical conditions have not been studied in detail. This is an area in which much laboratory work is needed.
New measurement of the diffusion of carbon dioxide on non-porous amorphous solid water
Published in Molecular Physics, 2023
Jiao He, Paula Caroline Pérez Rickert, Tushar Suhasaria, Orianne Sohier, Tia Bäcker, Dimitra Demertzi, Gianfranco Vidali, Thomas K. Henning
Molecule diffusion is crucial for the chemistry on/in interstellar ice. However, laboratory measurements of diffusion are lacking, limiting the accuracy of astrochemical modeling of grain surface processes. The current study builds on prior studies [14, 17] to measure the diffusion energy barrier and prefactor for CO on np-ASW surface simultaneously. A whole set of isothermal experiments were carried out to quantify the diffusion rate at different temperatures, from which the energy barrier and the prefactor for diffusion were then obtained.