The isotopic composition of water is an important indicator of its quality and determines its suitability for human use in space missions. The features of the infrared (IR) spectra in the middle region of various isotopic forms of water (–OH, –OD, H2O, HDO, and D2O) included in the crystal structure and adsorbed on the surface of the main rock-forming mineral of the lunar crust, anorthite, are considered. The results of numerical simulation of the main molecule’ vibrations using the ALT/CUSTEP module (Biovea Materials Studio) and experimental studies using an FT-801 IR Fourier spectrometer (Simex, Novosibirsk), as well as an inVia Reflex Raman spectrometer (Renishaw, United Kingdom), are presented. Numerical calculations of the lattice stability have shown that anorthite can contain both hydroxyl groups –OH(D) and molecular water H(D)2O in its crystal structure. The possibility of retaining various isotopic forms of molecular water by anorthite has been experimentally verified, and the corresponding mid-IR spectra of mineral grains with an aqueous film have been obtained. The presence of “light” isotopic forms of water on the lunar surface is confirmed by data from the SOFIA Stratospheric Infrared Observatory (NASA/GAS), but additional research will be required to detect “heavy” water.
Voropaev et al. (Wed,) studied this question.