How acids behave in ultracold interstellar space
Researchers from the Cluster of Excellence Ruhr Explores Solvation (Resolv), together with partners from the FELIX Laboratory, have investigated how acids interact with water molecules at extremely low temperatures ( below 10 Kelvin/ -263 degrees Celsius), like in interstellar space. Using spectroscopic analyses and computer simulations, the team found out that at extremely low temperatures hydrochloric acid sometimes releases its proton, depending on the order in which the team brought the water and hydrochloric acid molecules together. The results are crucial for understanding how more complex chemical molecules formed in space – long before the first precursors of life came into existence.
“We would like to know whether the same acid-alkali chemistry as we know on earth also exists in the extreme conditions in interstellar space. The acids are thus able to dissociate, but this does not necessarily have to happen – both processes are two sides of the same coin, so to speak,” summarises Martina Havenith, speaker for the Cluster of Excellence Resolv.
The researchers assume that the result can also be applied to other acids, i.e. it represents the basic principle of chemistry under ultracold conditions. “Chemistry in space is by no means simple; it might even be more complex than chemistry under ambient conditions,” says Professor Dominik Marx. After all, it depends not only on the mixing ratios of the reacting substances but also on the order in which they are added to each other. “This phenomenon needs to be taken into consideration in future experiments and simulations under ultracold conditions,” says the researcher.
Create interstellar space in the lab
In order to replicate the extremely low temperatures in the laboratory, the researchers had the chemical reactions take place in a droplet of superfluid helium. They monitored the processes using a special type of infrared spectroscopy, which can detect molecular vibrations with low frequencies. A laser with especially high brightness, as is available at the FELIX Laboratory, was needed for this. Computer simulations enabled the scientists to interpret the experimental results.
The team has shown that even at low temperatures, such as in interstellar space and in stratospheric clouds, acids can be found. Whether or not it becomes acidic does not only depend on the temperature, but also sequence matters.
The team consisted of a group led by Professor Martina Havenith, Chair of Physical Chemistry II and Professor Dominik Marx, Chair of Theoretical Chemistry, from Ruhr-Universität Bochum, and a group led by Dr. Britta Redlich, director FELIX Laboratory.
The work was supported financially by the German Research Foundation as part of the Cluster of Excellence Resolv (EXC1069, EXC2033) and has received funding from the European Union's Horizon 2020 research and innovation programme (Laserlab-Europe EU-H2020 654148).
Devendra Mani et al., "Acid solvation versus dissociation at “stardust conditions”: reaction sequence matters!", Science Advances (2019) DOI: 10.1126/sciadv.aav8179
Dr. Britta Redlich