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Methane as a reddish coating agent

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Experiments in quartz ampoules that simulate the saltation of quartz grains in a methane atmosphere show that the solid phase acquires a reddish color, reminiscent of the color observed on Triton, Pluto, and Charon. Reflection spectroscopy of the coated grains show a wide, continuous absorption spectrum peaking at near-UV wavelengths, in line with the reddish color. X-ray photoelectron spectroscopy indicates the grains are coated with a substance containing C–C and C–O bonds, and estimates the average thickness of the surface layer to 2.3 Å. Solid state Raman measurements of the coating shows a transition at 1540 cm−1. A model is proposed to describe these measurements. The model is a polydiene, anchored to the quartz surface. Electron structure calculations show that a polydiene with around 8 CH units reproduces the measurements. AFM-IR experiments support this result. Our findings suggest a pathway for synthesis of complex molecules with C[dbnd]C bonds on planets and moons with a solid surface and a methane-containing atmosphere.

OriginalsprogEngelsk
Artikelnummer115023
TidsskriftIcarus
Vol/bind382
ISSN0019-1035
DOI
StatusUdgivet - aug. 2022

Bibliografisk note

Funding Information:
The numerical results presented in this work were obtained at the Centre for Scientific Computing , Aarhus, Denmark, http://phys.au.dk/forskning/cscaa . We thank Dr. N. C. W. Hansen at this Centre for providing an efficient and problem free computational environment. We also thank Dr. Steen U. Pedersen for providing initial Solid State Raman spectra. Kai Finster acknowledges the Villum Foundation for support (Villum Experiment grant No. 36213 ). Thaddeus W. Golbek thanks the Lundbeck Foundation (postdoc grant R322-2019-2461 ).

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