Proton‐induced hydroxyl formation on the lunar surface

The interaction of both the particle and photon component of the solar wind with the lunar surface material is expected to produce diverse chemical reactions. Experimental evidence for proton‐induced OH formation was obtained by bombarding a glass, chemically similar in composition to common silicate minerals, with high‐energy protons. The concentration of OH, before and after irradiation, was determined by infrared absorption measurements. The OH formation rate was greatest at the start of the bombardment and decreased with increasing dose. The maximum proton to OH conversion rate, at the start of the irradiation, is at least 5 or 10% and may be as high as 100%. Using this result, together with estimates of the lunar age and recent solar proton flux data, we were able to make very rough calculations of the minimum proton‐induced OH content in the lunar surface. If mixing or churning is not important, the upper centimeter could contain 4×10 16 OH per cm 3 . When protons below 40 Mev and the higher conversion rate are included in the computation, the estimated OH concentrations could increase by a factor of 10 or more. If surface mixing or churning has occurred, they should be divided by an average churning depth.