Two important steps in the gas-phase formation of water in diffuse interstellar clouds proceed faster than previously assumed. This is the result of measurements at low temperatures, performed by researchers at the MPI for Nuclear Physics in Heidelberg. Complementary calculations, using a novel method that takes quantum effects into account, are in excellent agreement. The combined results have far-reaching implications for the understanding of interstellar chemistry and the theoretical treatment of low-temperature reactions.
Accumulations of gas and dust in space can be observed with telescopes as interstellar clouds. Despite the low temperatures and densities, a rich variety of molecules has been found in these environments. The backbone of the cold interstellar chemistry is a network of reactions between charged and uncharged atoms or molecules, so-called ion-neutral reactions.
Simplified interstellar chemistry network, showing the gas-phase water formation chain (blue) in front of the Orion nebula.
MPI für Kernphysik / background: NASA
In today´s universe, ion-neutral reactions in the gas phase can lead to the production of complex molecules, from protonated water (H₃O⁺) to organic compounds. When one of the protonated and therefore positively charged molecules encounters an electron, it can be neutralized and usually breaks up into neutral fragments. This process leads to the formation of neutral molecules in space, ranging from water (H₂O) to more complex species, like alcohol and other organics.
But how effective are these processes? To answer this question, it is crucial to find out how often a collision between the reaction partners at low temperature actually leads to a chemical reaction, because collisions are rare in the thin medium. To shed light on these processes, laboratory experiments have to be performed under true interstellar conditions. As these conditions are difficult to realize, present astrochemical models are mostly based on data that have been measured at much higher temperatures and densities, and accordingly are only of limited validity.
Water forms in diffuse interstellar clouds – where reactions on the surface of interstellar dust play a minor role – via a chain of processes started by cosmic rays. Intermediate products are the hydroxyl ion (OH⁺) and the water cation (H₂O⁺), which both react with hydrogen molecules, attaching one hydrogen atom and releasing the other one. The ERC-funded ‘Astrolab’ group of Holger Kreckel at the MPI for Nuclear Physics succeeded to measure the reaction rates of these two important steps in the gas-phase formation of interstellar water at low temperatures.
The scientists trapped the ions in a cryogenic radiofrequency ion trap, in which temperatures down to 10 degrees above absolute zero are accessible. Up to 100 milliseconds after adding a defined amount of hydrogen gas, they determined how many of the initial ions were still present. From the data, they derived so-called rate coefficients for both reactions, which are a measure of the efficiency of the reactions between the collision partners. It turned out that in both cases practically every collision leads to a chemical reaction.
In parallel, colleagues from Cyprus and the USA performed theoretical calculations using a novel method. In an elegant way, this approach employs analogies between quantum systems and the properties of ring-shaped molecules to account for quantum effects which are particularly relevant at low temperatures. The calculated rate coefficients are in excellent agreement with the measured values.
Compared to previous measurements at room temperature, the new values are considerably “faster”. This has implications for the understanding of interstellar chemistry, reaching far beyond the water formation chain. “Our results show once again that it is imperative to use rate coefficients that have been measured under interstellar conditions for astrochemical models“, says Holger Kreckel.
“Since this is experimentally often difficult and time-consuming, it is also important to develop theoretical procedures that can cope with quantum effects which are relevant for low-temperature processes, and to benchmark them with measurements. In this case, the strength of our work lies in the combination of experimental and theoretical methods that are appropriate for interstellar conditions.“
Low temperature rates for key steps of interstellar gas-phase water formation
Sunil S. Kumar, Florian Grussie, Yury V. Suleimanov, Hua Guo, Holger Kreckel
Science Advances 4, eaar3417 (2018) doi: 10.1126/sciadv.aar3417
Dr. Holger Kreckel
Stored and Cooled Ions Division, Professor. Dr. Klaus Blaum
Max Planck Institute for Nuclear Physics, Heidelberg, Germany
Tel.: +49 6221 516 517
http://www.mpi-hd.mpg.de/mpi/astrolab - Astrolab group homepage at the MPI for Nuclear Physics
Dr. Gertrud Hönes | Max-Planck-Institut für Kernphysik
Double layer of graphene helps to control spin currents
18.10.2019 | University of Groningen
Analysis of Galileo's Jupiter entry probe reveals gaps in heat shield modeling
17.10.2019 | American Institute of Physics
A very special kind of light is emitted by tungsten diselenide layers. The reason for this has been unclear. Now an explanation has been found at TU Wien (Vienna)
It is an exotic phenomenon that nobody was able to explain for years: when energy is supplied to a thin layer of the material tungsten diselenide, it begins to...
Researchers at Ludwig-Maximilians-Universitaet (LMU) in Munich have explored the initial consequences of the interaction of light with molecules on the surface of nanoscopic aerosols.
The nanocosmos is constantly in motion. All natural processes are ultimately determined by the interplay between radiation and matter. Light strikes particles...
Particles that are mere nanometers in size are at the forefront of scientific research today. They come in many different shapes: rods, spheres, cubes, vesicles, S-shaped worms and even donut-like rings. What makes them worthy of scientific study is that, being so tiny, they exhibit quantum mechanical properties not possible with larger objects.
Researchers at the Center for Nanoscale Materials (CNM), a U.S. Department of Energy (DOE) Office of Science User Facility located at DOE's Argonne National...
A new research project at the TH Mittelhessen focusses on the development of a novel light weight design concept for leisure boats and yachts. Professor Stephan Marzi from the THM Institute of Mechanics and Materials collaborates with Krake Catamarane, which is a shipyard located in Apolda, Thuringia.
The project is set up in an international cooperation with Professor Anders Biel from Karlstad University in Sweden and the Swedish company Lamera from...
Superconductivity has fascinated scientists for many years since it offers the potential to revolutionize current technologies. Materials only become superconductors - meaning that electrons can travel in them with no resistance - at very low temperatures. These days, this unique zero resistance superconductivity is commonly found in a number of technologies, such as magnetic resonance imaging (MRI).
Future technologies, however, will harness the total synchrony of electronic behavior in superconductors - a property called the phase. There is currently a...
02.10.2019 | Event News
02.10.2019 | Event News
19.09.2019 | Event News
18.10.2019 | Power and Electrical Engineering
18.10.2019 | Medical Engineering
18.10.2019 | Physics and Astronomy