Experimental investigation of structural OH/H2O in different lunar minerals and glass via solar-wind proton implantation

Abstract The possibility of OH/H2O formation on the lunar surface has been proposed because of the interaction between protons from the solar wind and oxygen in the regolith. In this study, we examined olivine, pyroxene, plagioclase, and volcanic glass samples together irradiated with 7 keV H+ at a dose of 1017 ions/cm2 under the same experimental conditions to simulate the solar-wind proton implantation process on the Moon. By comparing the infrared spectral characteristics of these samples before and after H+ implantation through an infrared spectrometer, we confirm that OH forms in all minerals and glass after H+ implantation, with a remarkable amount of OH/H2O found in plagioclase. This indicates that plagioclase can capture more H+ than other silicate phases to form the OH/H2O. The absorption characteristics of OH/H2O formed by H+ implantation are distinct and associated with the mineral structure. The efficiency of OH/H2O formation by H+ implantation is affected by crystal structure. We conclude that OH/H2O formed by solar-wind implantation in the lunar soil is likely to be mainly preserved in plagioclase, and the estimated OH/H2O absorption strength from 0.7 to 3.6% at 3356 cm−1 and from 0.9 to 4.8% at 3622 cm−1 of plagioclase is consistent with those found by recent lunar spacecraft missions.