Reddish materials synthesized on ice show two or more components in UV–visible.
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Net production rate of reddish materials decreased at higher irradiation temperature.
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Reddish materials destroyed below thermal dissociation temperature by irradiation.
Abstract
We recently reported on the reddish coloration of a CH3OH/H2O ice irradiated by cryoplasma, which is similar in appearance to the reddish surfaces seen on some icy bodies in the outer Solar System, and is sustained only at cryogenic temperatures. In this study, we analyzed the time evolution of absorption spectra during irradiation of this ice at temperatures of 70–90 K, and found that the nominal production rates of the reddish materials decreased with increasing temperature. We conducted kinetic analysis, which revealed that although the formation of the materials that absorb at 500 nm showed no temperature dependence, their disappearance under cryoplasma irradiation showed a positive temperature dependence. This finding indicates that the interactions of excited plasma species with the reddish materials, coupled with thermally-driven processes, can increase the rates of disappearance of the reddish materials and result in their destruction even at temperatures below their thermal dissociation temperatures, which was found to be 120–150 K in our previous study. These results suggest that the effects of radiation-driven chemistry and thermally-driven chemistry in concert can influence the formation and stability of reddish materials such as those synthesized in this study.
