(Georgia Institute of Technology, 2019)
Jones, Brant M.; Aleksandrov, Aleksandr; Dyar, M. Darby; Hibbitts, Charles; Orlando, Thomas M.
Desorption activation energies of chemisorbed water on Apollo lunar samples 14163 and 10084 were determined by temperature program desorption (TPD) experiments conducted under ultra-high vacuum conditions. Desorption at the grain/vacuum interface and desorption/transport of water though the porous medium with re-adsorption were found to reproduce the experimental TPD signal. Signal from the grain/vacuum interface yielded desorption activation energies and site probability distributions. Highland sample 14163 exhibited a broad distribution of binding site energies peaking at 60 kJ mol-1 while mare sample 10084 exhibited a narrower distribution of binding site energies peaking at 65 kJ mol-1. Water desorption from the lunar surface over a typical lunar day was simulated with the measured coverage dependent activation energies of the mare and highland samples. The resulting desorption profile of water through a lunar temperature cycle is in general agreement with Lunar Reconnaissance Orbiter (LRO) Lyman-α Mapping Project (LAMP) spacecraft-based observations of trends for both highland and mare assuming ~1% submonolayer coverage and that photostimulated desorption is neglected.