Methane as a reddish coating agent.

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 C bonds on planets and moons with a solid surface and a methane-containing atmosphere. [Display omitted] • Quartz grains in a quartz ampoule with methane are mechanically activated. • The activation mimics saltation and mediates triboelectric charging. • The activation process gives the grains a reddish color, reminiscent of the color on Triton, Pluto and Charon • The reddish color is investigated by XPS, Raman and AFM-IR experiments. • A model based on an anchored polydiene can reproduce the spectroscopic data. [ABSTRACT FROM AUTHOR]