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Open Access Publications from the University of California

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

  • Author(s): Lam, RK
  • England, AH
  • Sheardy, AT
  • Shih, O
  • Smith, JW
  • Rizzuto, AM
  • Prendergast, D
  • Saykally, RJ
  • et al.

© 2014 Published by Elsevier B.V. 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.

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