Broadband dielectric spectroscopy of astrophysicaly relevant phases of water ice
M.K. Matveyshina¹˒², A.A. Gavdush¹, K.I. Zaytsev¹
1- Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, Russia
2 -Bauman Moscow State Technical University, Moscow, Russia
Abstract
Understanding the optical properties of astrophysical ices is essential for the interpretation of astrophysical observations and for studying the evolution of molecular clouds, star-forming regions, and the formation of complex molecules in space. In this work, we focus on the optical properties of H2O ice in the hexagonal (Ih), cubic (Ic), and amorphous solid water (ASW) phases over the terahertz (THz) and infrared (IR) spectral ranges. Ice samples were deposited from the gas phase on high-resistivity silicon substrate at temperatures of 150 K, 120 K, and 8 K. Their THz optical properties were measured using THz pulsed spectroscopy (TPS). The THz response of all ices is formed by the low-frequency wings of the IR bands and the single broad low-intense THz peak around 1.8 THz, which is very similar for all phases. The experimental THz data was complemented with literature IR spectroscopy results and described using a dielectric response model based on a sum of Lorentz oscillators. The resulting experimental and model optical properties cover a broad frequency range from 0.3 to 120 THz (1 mm–2.5 μm). The observed absorption bands were assigned to the corresponding vibrational modes while accounting for symmetry breaking and the complex band shapes. In addition, initial stages of ice deposition were studied via He-Ne laser interferometry (632.8 nm). The gradual decrease in film growth rate accompanied by structural changes was shown. TPS measurements also enabled the characterization of the structural properties of the ice samples. Using Rayleigh scattering theory and the Bruggeman effective medium model, the porosity was estimated to be approximately 2% for Ih, 23% for Ic, and 35% for ASW, with effective pore radii of about 10 μm.
This work was supported by the Russian Science Foundation (RSF), Project # 25-72-00139.
Speaker
Maria Matveyshina
Prokhorov General Physics Institute of the Russian Academy of Sciences
Russia
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