The hydration structure of dissolved carbon dioxide from X-ray absorption spectroscopy

Abstract The dissolution of carbon dioxide in water and its subsequent hydrolysis reactions comprise one of the most central processes in all of science, yet it remains incompletely understood despite enormous effort. We report the detailed characterization of dissolved CO2 gas through the combination of X-ray spectroscopy and first principles theory. The molecule acts as a hydrophobe in water with an average hydrogen bond number of 0.56. The carbon atom interacts weakly with a single water at a distance of >2.67 Å and the carbonyl oxygens serve as weak hydrogen bond acceptors, thus locally enhancing the tetrahedral water hydrogen bonding structure

Detection of oxygen isotopic anomaly in terrestrial atmospheric carbonates and its implications to Mars

The debate of life on Mars centers around the source of the globular, micrometer-sized mineral carbonates in the ALH84001 meteorite; consequently, the identification of Martian processes that form carbonates is critical. This paper reports a previously undescribed carbonate formation process that occurs on Earth and, likely, on Mars. We identified micrometer-sized carbonates in terrestrial aerosols that possess excess 17O (0.4–3.9‰). The unique O-isotopic composition mechanistically describes the atmospheric heterogeneous chemical reaction on aerosol surfaces. Concomitant laboratory experiments define the transfer of ozone isotopic anomaly to carbonates via hydrogen peroxide formation when O3 reacts with surface adsorbed water. This previously unidentified chemical reaction scenario provides an explanation for production of the isotopically anomalous carbonates found in the SNC (shergottites, nakhlaites, chassignites) Martian meteorites and terrestrial atmospheric carbonates. The anomalous hydrogen peroxide formed on the aerosol surfaces may transfer its O-isotopic signature to the water reservoir, thus producing mass independently fractionated secondary mineral evaporites. The formation of peroxide via heterogeneous chemistry on aerosol surfaces also reveals a previously undescribed oxidative process of utility in understanding ozone and oxygen chemistry, both on Mars and Earth