Water interactions with micronized lunar surrogates JSC-1A and albite under ultra-high vacuum with application to lunar observations

[1] Interactions of molecular water with two lunar regolith surrogates (micronized JSC-1A and albite) were examined using temperature program desorption (TPD) and diffuse reflectance infrared Fourier transform spectroscopy. TPD revealed water desorption during initial heating to 750 K under ultrahigh vacuum and diffuse reflectance infrared Fourier transform spectroscopy indicated possible water formation via recombinative desorption of native hydroxyls above 425 ± 25 K. Dissociative chemisorption of water (i.e., formation of surface hydroxyl sites) was not observed on laboratory time scales after controlled dosing of samples (initially heated above 750 K) with 0.2–500 L exposures of water. However, preheated samples of both types of surrogates were found to have a distribution of molecular water chemisorption sites, with albite having at least twice as many as the JSC-1A samples by mass. A fit to the TPD data yields a distribution function of desorption activation energies ranging from ~ 0.45 to 1.2 eV. Using the fitted distribution function as an initial condition, the TPD process was simulated on the time scale of a lunation.