![Effect of substrate morphology and composition on the UV photodesorption of water ice at 12 K. (A) Evolution of the XPS-derived ice coverage as a function of photon fluence for an initial coverage of approximately 4 ML deposited on planar gold, planar olivine crystal, olivine microparticle powder, and soot at 12 K. Linear fits to the coverage curves give photodesorption yields of 1.5 × 10−3 , 1.8 × 10−3 , 7.2 × 10−4 , and 7.2 × 10−5 molecule photon−1 , respectively (see Table 1). (B) Scanning electron microscopy image of the olivine powder film, showing micrometer- and submicrometer-sized angular particles. (C) Scanning electron microscopy image of the soot film, showing highly aggregated carbon nanoparticles with a much finer and more ramified morphology. (D) Coverage derived from XPS measurements as a function of UV fluence at 12 K for 2 ML ice films deposited at 120 K (nonporous ice) and 12 K (porous ice), giving photodesorption yields of 4.6 × 10−5 and 1.4 × 10−5 molecule photon−1 , respectively -- [astro-ph.IM]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/11/Suppression.png?fit=1200%2C674&ssl=1)
[astro-ph.IM] Ultraviolet (UV) photodesorption regulates the partitioning of water between interstellar ice mantles and the gas phase, yet laboratory yields are generally measured on planar substrates rather than on surfaces representative of cosmic dust.
We investigate how grain morphology affects UV photodesorption from thin H2O ice films of 2-6 monolayers deposited on planar gold and olivine, soot nanoparticles, and olivine microparticles. Samples were irradiated at 12 and 60 K with a microwave-discharge hydrogen lamp, and ice depletion was monitored by X-ray photoelectron spectroscopy and reflection-absorption infrared spectroscopy.
On planar gold, the photodesorption yield increases approximately linearly with ice coverage, from ∼5×10−4 to ∼2×10−3 molecule photon−1 between 2 and 6 monolayers, consistent with increasing UV absorption in optically thin ice; planar olivine gives comparable yields.
In contrast, photodesorption is suppressed on particulate olivine and, more strongly, on soot, where yields are up to a factor of ∼40 lower than on gold at 12 K. Both experimental techniques confirm the strong suppression of ice depletion on soot. These results show that UV photodesorption depends not only on ice coverage but also strongly on grain morphology.
The pronounced suppression on soot may reflect heterogeneous ice growth and altered energy redistribution within nanoscale ice domains, implying that yields measured on planar substrates may substantially overestimate photodesorption from the thin ice mantles of cosmic dust.
Ph. Parent, C. Laffon
Comments: 9 pages, 4 figures
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2611.09308 [astro-ph.IM] (or arXiv:2611.09308v1 [astro-ph.IM] for this version)
https://doi.org/10.48550/arXiv.2611.09308
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From: Philippe Parent Dr
[v1] Fri, 6 Nov 2026 10:59:46 UTC (941 KB)
https://arxiv.org/abs/2611.09308
Astrobiology,
