An international team of scientists from The Hebrew University of Jerusalem (HUJI) in Israel, the Max Planck Institute for Nuclear Physics (MPIK, Heidelberg), and the FLASH free electron laser facility at DESY, Hamburg, has made an important discovery in molecular physics, revealing unexpected symmetry-breaking dynamics in ionized carbon dioxide dimers. Published in Nature Communications, this study uncovers new insights into the structural changes that occur when these molecular clusters are exposed to extreme ultraviolet (EUV) radiation. The collaborative effort has demonstrated that ionized CO₂ dimers undergo asymmetric structural rearrangements, leading to the formation of CO₃ moieties. The discovery has significant implications for atmospheric and astrochemistry, offering a deeper understanding of molecular behaviour under extreme conditions.
Key Findings: Symmetry-breaking dynamics and structural rearrangement
In environments such as cold outer space and atmospheric settings, carbon dioxide molecules can form symmetrically shaped pairs. According to quantum mechanics, the wave function of these pairs should preserve symmetry even after ionization. However, in a new experimental study at the FLASH free electron laser facility, the researchers from HUJI and MPIK observed a phenomenon known as symmetry breaking.
Two well-established quantum chemistry models were used to predict the behaviour of the ionized dimers. The first model suggested that the molecules would move in unison, maintaining their symmetrical shape. In contrast, the second model predicted that ionization would break the symmetry, causing one of the molecules to slowly rotate around its axis and point toward its partner within approximately 150 femtoseconds. Through the use of ultrafast EUV pulses produced by the FLASH free electron laser, the researchers confirmed the second model, showing that the ionized dimers indeed undergo asymmetric structural rearrangement.
This symmetry-breaking leads to the formation of CO3 moieties, which could play a crucial role in the chemical evolution of more complex species in cold outer space environments.
Quantum mechanics and the symmetry-breaking phenomenon
A key question arising from this study is how symmetry-breaking occurs despite quantum mechanics forbidding it. The researchers explain that, similar to Schrödinger's famous cat, the pair of carbon dioxide molecules exists in a superposition of two symmetry-broken states. The system preserves symmetry until the quantum wave function collapses, resulting in one of the CO2 molecules rotating relative to the other.
Broader implications and future research
Daniel Strasser (HUJI), the study's lead author, highlighted the significance of the findings: "Our research demonstrates the power of combining cutting-edge experimental techniques with advanced theoretical modelling to uncover unexpected molecular behaviour. These insights into the dynamics of ionized carbon dioxide dimers could open new avenues for carbon dioxide chemistry and contribute to our understanding of planetary and atmospheric processes."
Roi Baer (HUJI), who led the theoretical modelling, commented: “By directly comparing theory with experimental measurements, we improve our ability to simulate and predict the outcome of chemical reactions that occur in remote environments and are not possible to experimentally test in a laboratory.
The study's results have significant implications for atmospheric chemistry, astrochemistry, and provides new insights about the atmospheric carbon dioxide cycle. The discovery of asymmetric structural rearrangements, formation of a CO3 moiety, and time-resolved dynamics provides a deeper understanding of molecular processes in extreme conditions.
This research was made possible through international collaboration and the use of modern facilities, including the reaction microscope developed and built by MPIK Heidelberg and employed at the FLASH2 free electron laser at DESY in Hamburg, Germany. “The team’s innovative approach paves the way for further investigations into the behaviour of molecular clusters under extreme conditions, states group leader Robert Moshammer from the department of Thomas Pfeifer at MPIK: “This demonstrates the future potential for applications ranging from atmospheric science to laser-controlled chemistry.”
(HUJI/MPIK)
Original publication:
Symmetry-breaking dynamics of a photoionized carbon dioxide dimer
Ester Livshits, Dror M. Bittner, Florian Trost, Severin Meister, Hannes Lindenblatt, Rolf Treusch, Krishnendu Gope, Thomas Pfeifer, Roi Baer, Robert Moshammer and Daniel Strasser
Nature Communications 15, 6322 (2024). DOI: 10.1038/s41467-024-50759-2
Weblinks:
Group "Ionizing Atoms and Molecules in Strong Fields" in the Pfeifer Division at MPIK
Group of Daniel Strasser at the HUJI
Free Electron Laser FLASH at DESY
