Congratulations to PhD Student Duncan Mifsud who has just published two articles describing our new experimental set-up for ice astrochemistry in Debrecen (Hungary)!
Overview
These papers, published in the journals Review of Scientific Instruments and The European Physical Journal D, introduce the Ice Chamber for Astrophysics-Astrochemistry (ICA). The ICA is an ultra-high vacuum compatible chamber with an oxygen-free, high thermal conductivity copper sample holder containing a series of zinc selenide substrate discs. The chamber itself can be pumped down to an internal pressure of a few 10–9 mbar via the use of a turbomolecular pump and a dry rough vacuum pump, and the substrates can be cooled down to 20 K using a closed-cycle helium cryostat. Such conditions simulate those encountered in the interstellar medium. Astrophysical ice analogues can be synthesised on the substrate discs via the background deposition of dosed gases and vapours, and monitored in situ via Fourier-transform infrared absorbance spectroscopy (the zinc selenide substrates being transparent to infrared light).
Once deposited, the ices may be processed in three ways which simulate astrophysical phenomena. Firstly, thermal annealing of the ices may be achieved by means of a temperature regulator and simulates the warming that interstellar ices undergo when in proximity to a nascent or evolving star. The ICA is also equipped with an electron gun which allows electron impact radiolysis of ices to be studied. Finally, the ICA is connected to a 2 MV Tandetron accelerator which permits ion irradiations of and implantations into the ices using projectiles of various natures and energies. Ion and electron radiolysis of ices replicates the processing astrophysical ices undergo as a result of interaction with galactic cosmic rays, the solar wind, or planetary magnetospheric plasmas. Thermal and radiolytic processing of the ices results in physico-chemical changes such as chemical reactions, crystallization, and amorphization, all of which may be monitored using infrared spectroscopy. It is also possible to monitor changes in the gas-phase composition – which may occur as a result of sputtering or desorption from the ice – using a quadrupole mass spectrometer attached to the chamber.
These publications also detail our preliminary results. For example, we have shown that irradiation of methanol ice at 20 K using energetic protons and sulphur ions results in the destruction of the deposited methanol along with the concomitant formation of various molecular products, such as carbon dioxide, carbon monoxide, formaldehyde, and methane. Such reactions were also observed to take place when the irradiation was performed with electrons. We have also characterised the thermal reactions taking place between frozen water and sulphur dioxide, which were shown to result in the formation of solid-phase sulphuric acid. These initial results are merely a starting point, and we intend to further exploit the functional advantages of the ICA to study, among other things, the formation of complex prebiotic molecules relevant to the origins of life, as well as to probe unsolved problems in astrochemistry such as the depletion of sulphur in dense intermolecular clouds.
References (highlighted names provide links to CAPS group members)
P. Herczku, D. V. Mifsud, S. Ioppolo, Z. Juhász, Z. Kaňuchová, S. T. S. Kovács, A. Traspas Muiña, P. A. Hailey, I. Rajta, I. Vajda, N. J. Mason, R. W. McCullough, B. Paripás, B. Sulik (2021): The Ice Chamber for Astrophysics-Astrochemistry (ICA): A New Experimental Facility for Ion Impact Studies of Astrophysical Ice Analogues. Rev. Sci. Instrum. 92, 084501.
D. V. Mifsud, Z. Juhász, P. Herczku, S. T. S. Kovács, S. Ioppolo, Z. Kaňuchová, M. Czentye, P. A. Hailey, A. Traspas Muiña, N. J. Mason, R. W. McCullough, B. Paripás, B. Sulik (2021): Electron Irradiation and Thermal Chemistry Studies of Interstellar and Planetary Ice Analogues at the ICA Astrochemistry Facility. Eur. Phys. J. D 75, 182.