Speaker
Description
The structure and morphology of interstellar water ice analogues play a crucial role in molecular adsorption and surface chemistry, influencing processes such as H₂ adsorption in cold astrophysical environments. In this study, we investigate the physical properties of amorphous solid water (ASW) ices deposited at 10 K under ultra-high vacuum using the COSPINU2 setup. Employing a multi-probe approach—combining near- and mid-infrared FTIR spectroscopy, He-Ne laser reflectometry, and optical imaging (Hg vapor lamp and white light)—we characterized ASW films grown via background deposition with thickness ranging from 0 to 5 μm, and at three different deposition rates.
We retrieved the optical constants of the ice films under each condition, finding lower values compared to those reported in the literature [1],[2]. Notably, for higher deposition rates, we observed an abrupt decrease in specular reflectance and increased diffuse scattering, suggesting a phase transition in the ice structure not seen at lower rates. This points toward a restructuring process during deposition, with slower rates favouring the formation of more stable morphologies.
These findings offer critical insight into the microphysical properties of water ice relevant to astrophysical environments. A better understanding of how deposition conditions influence porosity and surface structure will improve models of H₂ adsorption and desorption dynamics. This structural perspective directly supports ongoing efforts to characterize the interaction of HD, H₂ and D₂ with ASW ices and their role in spin-state chemistry and energy transfer mechanisms in cold molecular clouds.
[1] Rebecca A. Carmack et al, 2023, ApJ 942 1
[2] Emily H. Mitchell et al, 2017, Icarus 285
