There has been a long-standing quest to observe chemical reactions at low temperatures where reaction rates and pathways are governed by quantum mechanical effects. So far this field of Quantum Chemistry has been dominated by theory. The difficulty has been to realize in the laboratory low enough collisional velocities between neutral reactants, such that the quantum wave nature could be observed. Recently we have demonstrated a new way of studying cold reactive collisions by magnetically merging two fast neutral supersonic beams. After 40 years where the reactive scattering temperature was limited to above 5 K we were able to continuously tune collision energies from hundreds of Kelvin down to 10 mK temperature, a reduction of almost three orders of magnitude [A. B. Henson et. al, Science 338, 234, 2012]. Importantly, we were able to show that at low temperatures quantum effects start dominating reactive dynamics with the first observation of orbiting resonances in a reactive collision. We propose to extend our novel method to study chemical reactions in the regime of Cold Chemistry where the reactants’s de Broglie wavelength becomes larger compared to the characteristic interaction range. Theoretical predictions at low temperatures are extremely sensitive to the parameters used, routinely differing by orders of magnitude leading to contradictions waiting to be settled by experiment.
Our ability to reach low enough collision energies and resolve scattering resonances will be used to bring a radical change to transient species spectroscopy. We believe that our work will not only test the central tenets of Quantum Chemistry, but will also provide valuable information to other fields, such as Astrochemistry helping to understand the synthesis of various molecules in interstellar space at temperatures 10 K and below.
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