A Systematic Study on the Absorption Features of Interstellar Ices in Presence of Impurities


Optimized structures for (a) pure water and for the 4 : 4 concentration ratio: (b) H2O − HCOOH, (c) H2O − NH3, (d) H2O − CH3OH, (e) H2O − CO, (f) H2O − CO2, (g) H2O − H2CO, (h) H2O − CH4, (i) H2O − OCS, (j) H2O − N2, (k) H2O − O2 clusters.

Spectroscopic studies play a key role in the identification and analysis of interstellar ices and their structure. Some molecules have been identified within the interstellar ices either as pure, mixed, or even as layered structures.

Absorption band features of water ice can significantly change with the presence of different types of impurities (CO, CO2, CH3OH, H2CO, etc.). In this work, we carried out a theoretical investigation to understand the behavior of water band frequency, and strength in the presence of impurities. The computational study has been supported and complemented by some infrared spectroscopy experiments aimed at verifying the effect of HCOOH, NH3, and CH3 OH on the band profiles of pure H2O ice. Specifically, we explored the effect on the band strength of libration, bending, bulk stretching, and free-OH stretching modes. Computed band strength profiles have been compared with our new and existing experimental results, thus pointing out that vibrational modes of H2O and their intensities can change considerably in the presence of impurities at different concentrations.

In most cases, the bulk stretching mode is the most affected vibration, while the bending is the least affected mode. HCOOH was found to have a strong influence on the libration, bending, and bulk stretching band profiles. In the case of NH3, the free-OH stretching band disappears when the impurity concentration becomes 50%. This work will ultimately aid a correct interpretation of future detailed spaceborne observations of interstellar ices by means of the upcoming JWST mission.

Prasanta Gorai, Milan Sil, Ankan Das, Bhalamurugan Sivaraman, Sandip K. Chakrabarti, Sergio Ioppolo, Cristina Puzzarini, Zuzana Kanuchova, Anita Dawes, Marco Mendolicchio, Giordano Mancini, Vincenzo Barone, Naoki Nakatani, Takashi Shimonishi, Nigel Mason

Comments: Accepted for Publication in the ACS Earth and Space Chemistry Journal
Subjects: Astrophysics of Galaxies (astro-ph.GA)
DOI: 10.1021/acsearthspacechem.0c00098
Cite as: arXiv:2005.12867 [astro-ph.GA] (or arXiv:2005.12867v1 [astro-ph.GA] for this version)
Submission history
From: Ankan Das
[v1] Tue, 26 May 2020 16:58:57 UTC (3,114 KB)
https://arxiv.org/abs/2005.12867
Astrobiology, Astrochemistry

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