Abstract
We report on an experimental study on the formation of water, through the D + O2 pathway, on a sample of amorphous solid water, i.e. a realistic analogue of the surface of the interstellar grains of dense clouds. For improving our experimental conditions we use deuterium instead of hydrogen. We obtain, using both Temperature-Programmed Desorption Spectroscopy and Infrared Spectroscopy, that the morphology of the nascent water ice is mostly compact. We compare our results with those obtained previously by Oba et al. and show that the first technique is more effective in probing the morphology of amorphous water ice. We propose that the formation of compact ice is due to the heat of reactions which lead to the formation of water molecules. Water is synthesized, through the D + O2 pathway, on a film of compact amorphous solid water and on a porous substrate for comparison purposes. We show that in this latter case a gradual compaction of the sample takes place upon formation of new water molecules. We compare this reduction of water ice porosity with that one obtained by Accolla et al., due to recombination of deuterium atoms sent on the surface of an amorphous porous ice sample, and show that the compaction of the sample as a consequence of the water formation appears clearly more efficient.
Highlights
The space between the stars is far from being empty
The iteration of the three steps described in the previous section enable us to study the morphology of the sample as the solid water synthesized is gradually formed on the c-amorphous solid water (ASW) substrate
To confirm that formation of water molecules leads to a change in the morphology of ASW from porous to compact we investigate the morphology of the water formed through the O2 + D pathway on a porous ice sample
Summary
The space between the stars is far from being empty. Ions, atoms and molecules in the gas phase and small solid particles, mixed with the gas, constitute the so-called interstellar medium, or ISM. 7 per cent of the mass of our Galaxy, within 15 kpc of the centre, is in the form of interstellar gas, mostly hydrogen and helium (Draine 2011). This gas is not uniformly diffused, instead it aggregates into structures known as interstellar clouds. In diffuse clouds, which are structures with number densities around 100 hydrogen nuclei cm−3 and temperatures around 50 K, the gas is mainly in atomic form, few molecules are present. Water may form through the following reaction scheme (Duley & Williams 1984): H2 + cosmic rays → H2+ + e−
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
