Abstract
Many interstellar complex organic molecules (COMs) are believed to be produced on the surfaces of icy grains at low temperatures. Atomic carbon is considered responsible for the skeletal evolution processes, such as CâC bond formation, via insertion or addition reactions. Before reactions, C atoms must diffuse on the surface to encounter reaction partners; therefore, information on their diffusion process is critically important for evaluating the role of C atoms in the formation of COMs. In situ detection of C atoms on ice was achieved by a combination of photostimulated desorption and resonance-enhanced multiphoton ionization methods. We found that C atoms weakly bound to the ice surface diffused above approximately 30âK and produced C2 molecules. The activation energy for C-atom surface diffusion was experimentally determined to be 88âmeV (1,020âK), indicating that the diffusive reaction of C atoms is activated at approximately 22âK on interstellar ice. The facile diffusion of C atoms at temperatures above 22âK on interstellar ice opens a previously overlooked chemical regime where the increase in complexity of COMs is driven by C atoms. Carbon addition chemistry can be an alternative source of chemical complexity in translucent clouds and protoplanetary disks with crucial implications in our current understanding on the origin and evolution of organic chemistry in our Universe.
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The authors confirm that the data supporting the findings of this study are available within the article and its supplementary materials. The numerical data are available from the corresponding author upon reasonable request.
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Acknowledgements
This work was partially supported by JSPS KAKENHI grant nos. JP23H03982, JP22H00159, JP21H01139, JP18K03717, JP22F22013, JP20H05847 and JP17H06087. We acknowledge support from the JSPS International Fellowship Program (grant no. P22013).
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M.T. and N.W. conceived the study. M.T. performed all experiments and analyses. M.T. drafted the manuscript. All the authors reviewed the draft manuscript and critically revised it for intellectual content.
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Tsuge, M., Molpeceres, G., Aikawa, Y. et al. Surface diffusion of carbon atoms as a driver of interstellar organic chemistry. Nat Astron 7, 1351â1358 (2023). https://doi.org/10.1038/s41550-023-02071-0
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DOI: https://doi.org/10.1038/s41550-023-02071-0
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