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Recent insights are presented in the Journal of Physical Chemistry A by JILA Fellow and Physics Professor at the University of Colorado Boulder, Heather Lewandowski, and former graduate student Olivia Krohn. They have developed experiments using Coulomb crystals-cold pseudo-crystalline structures-to simulate ISM conditions and observe the interactions between ions and neutral molecules.
Their experiments employ precise laser cooling and mass spectrometry to control quantum states, successfully replicating ISM chemical reactions. "The field has long considered which chemical reactions are crucial in understanding the ISM's composition," states Krohn. "Ion-neutral molecule reactions are a key group, and our experimental setup is ideal for studying these reactions at relatively cold temperatures."
The Lewandowski group initiated their experiment by loading an ion trap with various ions in an ultra-high vacuum chamber, introducing neutral molecules separately. Despite knowing the reactants, the resulting products were not always predictable, enhancing the mystery and intrigue of ISM chemistry.
Krohn adds, "CCl+ ions, derived from tetrachloroethylene and expected in various space regions, were part of our tests. The challenge lies in their synthesis, which involves UV lasers that break down tetrachloroethylene, creating complex ion fragments."
After the initial filtration, the researchers used Doppler cooling to slow the ions, arranging them into Coulomb crystals within the vacuum chamber's electric fields. This process allowed them to maintain the ions in a trapped state for extended periods, facilitating real-time reaction monitoring.
The experimental trifecta also included time-of-flight mass spectrometry (TOF-MS), enabling the team to analyze the trapped ions and determine the reaction products and their masses. "This technique allows us to substitute hydrogens with deuterium or other isotopes, helping us understand the discrepancies in deuterium-containing molecules observed in the ISM compared to the atomic deuterium-to-hydrogen ratio," explains Krohn.
This comprehensive approach not only deepens our understanding of space chemistry but also opens new avenues for exploring the cosmic chemical landscape. The research is supported by the National Science Foundation and the Air Force Office of Scientific Research.
Research Report:Cold ion-molecule reactions in the extreme environment of a Coulomb crystal
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