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Surface diffusion of carbon atoms as a driver of interstellar organic chemistry


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 C–C 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 30 K and produced C2 molecules. The activation energy for C-atom surface diffusion was experimentally determined to be 88 meV (1,020 K), indicating that the diffusive reaction of C atoms is activated at approximately 22 K on interstellar ice. The facile diffusion of C atoms at temperatures above 22 K 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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Fig. 1: Summary of C-atom chemistry in a molecular cloud.
Fig. 2: Determination of Esd based on the steady-state PSD-REMPI measurements.
Fig. 3: Determination of Esd based on the decay measurements.
Fig. 4: TPD spectra obtained for C- and H-atom-irradiated ASW and ethane on ASW.
Fig. 5: Ethane formation yields and steady-state C-atom intensities as a function of temperature.
Fig. 6: Diffusive area of C atoms on interstellar ice with different Esd.

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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.


  1. van Dishoeck, E. F. & Black, J. H. The photodissociation and chemistry of interstellar CO. Astrophys. J. 334, 771 (1988).

    Article  ADS  Google Scholar 

  2. Snow, T. P. & McCall, B. J. Diffuse atomic and molecular clouds. Annu. Rev. Astron. Astrophys. 44, 367–414 (2006).

    Article  ADS  Google Scholar 

  3. Langer, W. The carbon monoxide abundance in interstellar clouds. Astrophys. J. 206, 699–712 (1976).

    Article  ADS  Google Scholar 

  4. Keene, J., Blake, G. A., Phillips, T. G., Huggins, P. J. & Beichman, C. A. The abundance of atomic carbon near the ionization fronts in M17 and S140. Astrophys. J. 299, 967–980 (1985).

    Article  ADS  Google Scholar 

  5. Papadopoulos, P. P., Thi, W.-F. & Viti, S. Ci lines as tracers of molecular gas, and their prospects at high redshifts. Mon. Not. R. Astron. Soc. 351, 147–160 (2004).

    Article  ADS  Google Scholar 

  6. Burton, M. G. et al. Extended carbon line emission in the galaxy: searching for dark molecular gas along the G328 sightline. Astrophys. J. 811, 13 (2015).

    Article  ADS  Google Scholar 

  7. Zmuidzinas, J., Betz, A. L., Boreiko, R. T. & Goldhaber, D. M. Neutral atomic carbon in dense molecular clouds. Astrophys. J. 335, 774 (1988).

    Article  ADS  Google Scholar 

  8. Qasim, D. et al. An experimental study of the surface formation of methane in interstellar molecular clouds. Nat. Astron. 4, 781–785 (2020).

    Article  ADS  Google Scholar 

  9. Lamberts, T. et al. Methane formation in cold regions from carbon atoms and molecular hydrogen. Astrophys. J. 928, 48 (2022).

    Article  ADS  Google Scholar 

  10. Molpeceres, G. et al. Carbon atom reactivity with amorphous solid water: H2O-catalyzed formation of H2CO. J. Phys. Chem. Lett. 12, 10854–10860 (2021).

    Article  Google Scholar 

  11. Potapov, A., Krasnokutski, S. A., Jäger, C. & Henning, T. A new “non-energetic” route to complex organic molecules in astrophysical environments: the C + H2O → H2CO solid-state reaction. Astrophys. J. 920, 111 (2021).

    Article  ADS  Google Scholar 

  12. Krasnokutski, S. A., Chuang, K.-J., Jäger, C., Ueberschaar, N. & Henning, T. A pathway to peptides in space through the condensation of atomic carbon. Nat. Astron. 6, 381–386 (2022).

  13. Fedoseev, G. et al. Hydrogenation of accreting C atoms and CO molecules–simulating ketene and acetaldehyde formation under dark and translucent cloud conditions. Astrophys. J. 924, 110 (2022).

  14. Duflot, D., Toubin, C. & Monnerville, M. Theoretical determination of binding energies of small molecules on interstellar ice surfaces. Front. Astron. Space Sci. 8, 645243 (2021).

    Article  Google Scholar 

  15. Wakelam, V., Loison, J.-C., Mereau, R. & Ruaud, M. Binding energies: new values and impact on the efficiency of chemical desorption. Mol. Astrophys. 6, 22–35 (2017).

  16. Shimonishi, T., Nakatani, N., Furuya, K. & Hama, T. Adsorption energies of carbon, nitrogen, and oxygen atoms on the low-temperature amorphous water ice: a systematic estimation from quantum chemistry calculations. Astrophys. J. 855, 27 (2018).

    Article  ADS  Google Scholar 

  17. Minissale, M. et al. Thermal desorption of interstellar ices: a review on the controlling parameters and their implications from snowlines to chemical complexity. ACS Earth Space Chem. 6, 597–630 (2022).

    Article  ADS  Google Scholar 

  18. Masel, R. I. Principles of Adsorption and Reaction on Solid Surfaces (John Wiley & Sons, 1996).

    Google Scholar 

  19. Watanabe, N. & Tsuge, M. Experimental approach to physicochemical hydrogen processes on cosmic ice dust. J. Phys. Soc. Jpn. 89, 051015 (2020).

    Article  ADS  Google Scholar 

  20. Tsuge, M. & Watanabe, N. Behavior of hydroxyl radicals on water ice at low temperatures. Acc. Chem. Res. 54, 471–480 (2021).

    Article  Google Scholar 

  21. Miyazaki, A., Tsuge, M., Hidaka, H., Nakai, Y. & Watanabe, N. Direct determination of the activation energy for diffusion of OH radicals on water ice. Astrophys. J. Lett. 940, L2 (2022).

    Article  ADS  Google Scholar 

  22. Sakai, N. & Yamamoto, S. Warm carbon-chain chemistry. Chem. Rev. 113, 8981–9015 (2013).

    Article  Google Scholar 

  23. Ruffle, D. P. & Herbst, E. New models of interstellar gas-grain chemistry—I. Surface diffusion rates. Mon. Not. R. Astron. Soc. 319, 837–850 (2000).

  24. Garrod, R. T., Belloche, A., Müller, H. S. P. & Menten, K. M. Exploring molecular complexity with ALMA (EMoCA): simulations of branched carbon-chain chemistry in Sgr B2(N). Astron. Astrophys. 601, A48 (2017).

    Article  ADS  Google Scholar 

  25. Das, A., Sil, M., Gorai, P., Chakrabarti, S. K. & Loison, J. C. An approach to estimate the binding energy of interstellar species. Astrophys. J. Suppl. Ser. 237, 9 (2018).

    Article  ADS  Google Scholar 

  26. Kobayashi, H. et al. Hydrogenation and deuteration of C2H2 and C2H4 on cold grains: a clue to the formation mechanism of C2H6 with astronomical interest. Astrophys. J. 837, 155 (2017).

    Article  ADS  Google Scholar 

  27. Lindstrom, P. J. & Mallard, W. G. (eds) NIST Chemistry WebBook, NIST Standard Reference Database Number 69 (National Institute of Standards and Technology, accessed 26 January 2023);

  28. Jenniskens, P. et al. Carbon dust formation on interstellar grains. Astron. Astrophys. 273, 583 (1993).

    ADS  Google Scholar 

  29. Harada, N. et al. Molecular-cloud-scale chemical composition. III. Constraints of average physical properties through chemical models. Astrophys. J. 871, 238 (2019).

  30. Weingartner, J. C. & Draine, B. T. Dust grain-size distributions and extinction in the Milky Way, Large Magellanic Cloud, and Small Magellanic Cloud. Astrophys. J. 548, 296 (2001).

    Article  ADS  Google Scholar 

  31. Kouchi, A. et al. Transmission electron microscopy study of the morphology of ices composed of H2O, CO2, and CO on refractory grains. Astrophys. J. 918, 45 (2021).

    Article  ADS  Google Scholar 

  32. Hasegawa, T. I. & Herbst, E. New gas–grain chemical models of quiescent dense interstellar clouds: the effects of H2 tunnelling reactions and cosmic ray induced desorption. Mon. Not. R. Astron. Soc. 261, 83–102 (1993).

    Article  ADS  Google Scholar 

  33. Smith, D. L. Thin-Film Deposition: Principles and Practice (McGraw-Hill, 1995).

    Google Scholar 

  34. Thi, W. F. et al. Warm dust surface chemistry. Astron. Astrophys. 634, A42 (2020).

    Article  Google Scholar 

  35. Hama, T. et al. The mechanism of surface diffusion of H and D atoms on amorphous solid water: existence of various potential sites. Astrophys. J. 757, 185 (2012).

  36. Miyazaki, A. et al. Photostimulated desorption of OH radicals from amorphous solid water: evidence for interaction of visible light with OH-ice complex. Phys. Rev. A 102, 052822 (2020).

  37. Furuya, K. et al. Diffusion activation energy and desorption activation energy for astrochemically relevant species on water ice show no clear relation. Astrophys. J. Lett. 933, L16 (2022).

    Article  ADS  Google Scholar 

  38. Le Gal, R. et al. A new study of the chemical structure of the Horsehead nebula: the influence of grain-surface chemistry. Astron. Astrophys. 605, A88 (2017).

  39. Bergin, E. A. et al. Hydrocarbon emission rings in protoplanetary disks induced by dust evolution. Astrophys. J. 831, 101 (2016).

  40. Öberg, K. I. & Bergin, E. A. Astrochemistry and compositions of planetary systems. Phys. Rep. 893, 1–48 (2021).

    Article  ADS  Google Scholar 

  41. Tielens, A. G. G. M. & Charnley, S. B. Circumstellar and interstellar synthesis of organic molecules. Orig. Life Evol. Biosph. 27, 23–51 (1997).

    Article  ADS  Google Scholar 

  42. Watanabe, N. & Kouchi, A. Efficient formation of formaldehyde and methanol by the addition of hydrogen atoms to CO in H2O-CO ice at 10 K. Astrophys. J. 571, L173–L176 (2002).

  43. Furuya, K., Lee, S. & Nomura, H. Different degrees of nitrogen and carbon depletion in the warm molecular layers of protoplanetary disks. Astrophys. J. 938, 29 (2022).

    Article  ADS  Google Scholar 

  44. Watanabe, N. et al. Direct measurements of hydrogen atom diffusion and the spin temperature of nascent H2 molecule on amorphous solid water. Astrophys. J. Lett. 714, L233–L237 (2010).

  45. Krasnokutski, S. A. & Huisken, F. A simple and clean source of low-energy atomic carbon. Appl. Phys. Lett. 105, 113506 (2014).

    Article  ADS  Google Scholar 

  46. Albar, J. D. et al. An atomic carbon source for high temperature molecular beam epitaxy of graphene. Sci. Rep. 7, 6598 (2017).

    Article  ADS  Google Scholar 

  47. Qasim, D. et al. A cryogenic ice setup to simulate carbon atom reactions in interstellar ices. Rev. Sci. Instrum. 91, 054501 (2020).

    Article  ADS  Google Scholar 

  48. Adler‐Golden, S. M., Langhoff, S. R., Bauschlicher, C. W. Jr & Carney, G. D. Theoretical calculation of ozone vibrational infrared intensities. J. Chem. Phys. 83, 255–264 (1985).

  49. Hidaka, H., Kouchi, A. & Watanabe, N. Temperature, composition, and hydrogen isotope effect in the hydrogenation of CO on amorphous ice surface at 10–20K. J. Chem. Phys. 126, 204707 (2007).

    Article  ADS  Google Scholar 

  50. Moore, L. J., Fassett, J. D., Travis, J. C., Lucatorto, T. B. & Clark, C. W. Resonance-ionization mass spectrometry of carbon. J. Opt. Soc. Am. B 2, 1561–1565 (1985).

    Article  ADS  Google Scholar 

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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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Correspondence to Masashi Tsuge.

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Nature Astronomy thanks Alexey Potapov and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Figs. 1–9, discussion and Table 1.

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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, 1351–1358 (2023).

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