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

•First X-ray absorption spectrum of dissolved CO2.•Fast-flow liquid microjet mixing system used to generate dissolved CO2 via the decomposition of aqueous carbonic acid.•Hydration structure determined in conjunction with first principles XCH calculations. 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 >2.67Å and the carbonyl oxygens serve as weak hydrogen bond acceptors, thus locally enhancing the tetrahedral water hydrogen bonding structure.