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1THz-IR spectroscopy of astrophysical ices: recent achievements and challenges
A.A. Gavdush'*, F. Kruczkiewicz2,3, B.M. Giuliano2, B. Müller2, G.A. Komandin', K.I. Zaytsev', A.V. Ivlev2, P. Caselli2
1-Prokhorov General Physics Institute of the Russian Academy of Sciences, Russia, 119991 Moscow, Russia 2- Max-Planck-Institut für Extraterrestrische Physik, Gießenbachstraße 1, Garching 85748, Germany 3- Aix-Marseille Univ, CNRS, CNES, LAM, Marseille, France
Solutions of relevant astrophysical problems [1-4] require the knowledge of the physical properties of interstellar and circumstellar ices. Among them are large-scale issues such as the evolution of molecular clouds and the genesis of stellar systems as well as local problems related to the formation of new molecular compounds in space and their prevalence. Most of the interstellar matter in the Universe is represented by ice of various molecular composition, including many organic compounds. Ices form mantles on the surface of dust particles; they can be found on the surface of satellites and asteroids, as a part of comets. Without the knowledge of the broadband dielectric properties of ices, it is impossible to determine molecular composition during the analyzes of astronomical observational data. Scattering in ices must also be taken into account when modeling radiative transfer in dense and cold University regions.
The observations of the interstellar medium are preferred to be taken in the far infrared (IR) and terahertz (THz) ranges in last decades. This approach allows to increase the number of possible objects under study due to their emission in the considered frequency ranges. Despite the importance of THz-IR dielectric properties of ices, there are still no data on the absolute values of the complex dielectric permittivity of astrophysical ice analogues in a wide spectral range, as well as their scattering properties. In the first works [5,6] in a series of publications we have focused on the developing of new approaches to reconstruct the complex dielectric response of astrophysical ice analogues in THz-IR ranges. We have shown the possibility of direct reconstruction of the ices complex dielectric permittivity in the broad spectral range, taking into account the existing amplitude and phase information for THz pulsed spectroscopy (TPS) measurements, merging of the TPS and Fourier-transform IR spectroscopy (FTIR) data and estimating phase information for FTIR data based on the Kramers-Kronig relations and TPS phase. Complex dielectric properties of several ices (CO, CO2, N2) are studied in the THz-IR range. The obtained results are parameterized using classical models of complex dielectric permittivity. First estimates for the scattering in ices are proposed which based on the assumptions of the porous structure of ices under study. The developed approach to study scattering in ices makes it possible to approximately obtain the properties of bulk ice, taking into account the use of the effective medium theory.
This work was supported by the Russian Science Foundation (RSF).
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[2] S.L. Widicus Weaver, Millimeterwave and Submillimeterwave Laboratory Spectroscopy in Support of Observational Astronomy, Annual Review of Astronomy and Astrophysics, vol. 57(1), pp. 79-112 (2019).
[3] D.V. Mifsud, et al, The Role of Terahertz and Far-IR Spectroscopy in Understanding the Formation and Evolution of Interstellar Prebiotic Molecules, Frontiers in Astronomy and Space Sciences, vol. 8 (2021).
[4] D.V. Mifsud, et al, Sulfur Ice Astrochemistry: A Review of Laboratory Studies, Space Science Reviews, vol. 217(1), pp. 14 (2021).
[5] B.M. Giuliano, et al, Broadband spectroscopy of astrophysical ice analogues: I. Direct measurement of the complex refractive index of CO ice using terahertz time-domain spectroscopy, Astronomy & Astrophysics, vol. 629, pp. A112 (2019).
[6] A.A. Gavdush, et al, Broadband spectroscopy of astrophysical ice analogues: II. Optical constants of CO and CO2 ices in the terahertz and infrared ranges, Astronomy & Astrophysics, vol. 667, pp. A49 (2022).
