Hydroxylation by solar wind protons has been simulated in our laboratory on Apollo 17 lunar sample 78421, a very mature regolith sample that is rich with agglutinates (68%). The goal of this study was to determine the rate of hydroxyl formation and their thermal stability by monitoring changes in the SiOH (hydroxyl) stretching band near 3 μm using diffuse reflectance FTIR spectroscopy (DRIFTS). A 2 keV H₂⁺ ion beam was used to simulate proton implantation on 78421 and on a crushed fused silica sample. We find that the OH band does not change unless the samples have been annealed in vacuum prior to irradiation. Qualitatively, the OH bands for the fused silica and 78421 are very different. The OH band for fused silica is centered at 2.74 μm and is relatively sharp ranging from 2.67 ‐ 3.1 μm at full‐width‐at‐half‐maximum (FWHM), while the OH band for 78421 is centered at 3.0 μm and ranges from 2.74 ‐ 3.37 μm at FWHM. The increase in wavelength and broadened nature of the OH band in 78421 may be associated with the OH’s proximity to surface defects and/or lattice vacancies. The lack of the H₂O bending mode at 6.1 μm indicates that any adsorbed terrestrial H₂O is below our detection limit, and therefore the H₂O stretching mode at 2.9 μm is not significantly contributing to the broad 3 μm OH band and implies that proton implantation by itself does not lead to water formation. To simulate the maximum dayside temperature on the lunar surface, the lunar sample was heated after proton irradiation. The proton induced OH concentration was reduced by as much as 25% after heating to 400 K (127 °C).

中文翻译：

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太阳风质子对阿波罗17号土壤样品78421的羟化作用

在我们的实验室中，对阿波罗17号月球样品78421进行了模拟，模拟了太阳风质子引起的羟化反应，这是一种非常成熟的长石块样品，富含凝集素（68％）。这项研究的目的是通过使用漫反射FTIR光谱仪（DRIFTS）监测3μm附近的SiOH（羟基）拉伸带的变化来确定羟基形成的速率及其热稳定性。A 2 keV H ₂ ⁺离子束用于模拟质子在78421和压碎的熔融石英样品上的注入。我们发现，除非样品在辐照之前已在真空中退火过，否则OH谱带不会改变。定性上，熔融石英和78421的OH谱带非常不同。熔融石英的OH谱带中心在2.74μm处，并且在半峰全宽（FWHM）范围内从2.67到3.1μm相对较锐利，而78421的OH谱带中心在3.0μm处并且在2.74范围内‐在FWHM处为3.37μm。78421中OH波段的波长增加和加宽性质可能与OH接近表面缺陷和/或晶格空位有关。在6.1μm处缺少H ₂ O弯曲模式表明任何吸附的地面H ₂O低于我们的检测极限，因此2.9μm的H ₂ O拉伸模式对3μm宽的OH谱带没有显着贡献，并且暗示质子注入本身不会导致水的形成。为了模拟月球表面上的最高日间温度，质子辐照后将月球样品加热。加热至400 K（127°C）后，质子诱导的OH浓度降低了25％。