Organic Chemistry In The H2-bearing, CO-rich Interstellar Ice Layer At Temperatures Relevant To Dense Cloud Interiors

By Keith Cowing
Status Report
January 11, 2024
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Organic Chemistry In The H2-bearing, CO-rich Interstellar Ice Layer At Temperatures Relevant To Dense Cloud Interiors
IR difference spectra obtained upon irradiation of a similar incident energy with 2 keV electrons of CO:15N2:H2 ice samples in Experiments 4−6. The IR difference spectra were baseline-corrected using a spline function with the IDL software. IR band assignments are indicated in the panels. Tentative assignments are indicated in grey. Grey asterisks indicate possible baseline artifacts that were not subtracted. — astro-ph.GA

Ice chemistry in the dense, cold interstellar medium (ISM) is probably responsible for the formation of interstellar complex organic molecules (COMs).

Recent laboratory experiments performed at T=4 K have shown that irradiation of CO:N2 ice samples analog to the CO-rich interstellar ice layer can contribute to the formation of COMs when H2 molecules are present. We have tested this organic chemistry under a broader range of conditions relevant to the interior of dense clouds by irradiating CO:15N2:H2 ice samples with 2 keV electrons in the 4-15 K temperature range.

The H2 ice abundance depended on both, the ice formation temperature and the thermal evolution of the samples. Formation of H-bearing organics such as formaldehyde (H2CO), ketene (C2H2O), and isocyanic acid (H15NCO) was observed upon irradiation of ice samples formed at temperatures up to 10 K, and also in ices formed at 6 K and subsequently warmed up and irradiated at temperatures up to 15 K.

These results suggest that a fraction of the H2 molecules in dense cloud interiors might be entrapped in the CO-rich layer of interstellar ice mantles, and that energetic processing of this layer could entail an additional contribution to the formation of COMs in the coldest regions of the ISM.

Rafael Martín-Doménech, Alexander DelFranco, Karin I. Öberg, Mahesh Rajappan

Subjects: Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2401.04024 [astro-ph.GA] (or arXiv:2401.04024v1 [astro-ph.GA] for this version)
Submission history
From: Rafael Martín-Doménech
[v1] Mon, 8 Jan 2024 17:02:39 UTC (643 KB)
Astrobiology, Astrochemistry

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