The hydration structure of aqueous carbonic acid from X-ray absorption spectroscopy

• Published in: Chemical Physics Letters
• Main Authors: Lam, Royce K, England, Alice H, Sheardy, Alex T, Shih, Orion, Smith, Jacob W, Rizzuto, Anthony M, Prendergast, David, Saykally, Richard J
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: eScholarship, University of California 2014
• Subjects: Physical Sciences; Chemical Sciences; Technology; Chemical Physics; Carbonic acid
• Online Access: https://escholarship.org/uc/item/8km10634; https://escholarship.org/content/qt8km10634/qt8km10634.pdf; https://doi.org/10.1016/j.cplett.2014.09.052

Despite much effort, aqueous carbonic acid (H2CO3) remains poorly characterized because it is very short-lived. We describe the detection and characterization of aqueous H2CO3 by X-ray absorption spectroscopy, wherein protonation of a bicarbonate solution continuously generates the acid under ambient conditions. Accompanying first principles calculations of the carbon K-edge transitions facilitate spectral assignment and interpretation in terms of the H2CO3 π∗ orbital, which exhibits a small (0.2 eV), systematic blueshift relative to that of bicarbonate. These results establish the detailed hydration properties of this short-lived molecule and will thereby facilitate future studies of carbonate chemistry in biological and geological system.