Gaseous Carbonic Acid Trapped And Analyzed

Carbonic acid, an elusive but important compound in geochemical, physiological, and atmospheric processes, has been trapped and analyzed spectroscopically in the gas phase by a team of researchers headed by chemists in Austria (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201004729). H₂CO₃ plays key roles in regulating blood pH, acidifying oceans, and dissolving minerals. The compound has been studied previously as a solid, but the gaseous species had escaped direct detection because it rapidly decomposes to water and carbon dioxide. That conventional wisdom needs to be updated, according to Thomas Loerting of the University of Innsbruck, Hinrich Grothe of Vienna University of Technology, and coworkers. The team reports that it has trapped gas-phase carbonic acid molecules in a noble-gas matrix at cryogenic temperatures and that the molecule is stable above 200 K. In addition, on the basis of infrared spectroscopy studies, the group proposes that H₂CO₃ exists as a mixture with a 1:10:1 ratio of two monomeric conformers (cis-trans and cis-cis) and a cyclic dimer, respectively. These results could aid the search for gas-phase carbonic acid in astrophysical environments, the researchers say.