2010ApJ...722.1598O

We present the experimental results of carbonic acid (H₂CO₃) formation through surface reactions of CO molecules with non-energetic hydroxyl (OH) radicals at 10-40 K. The formation of H₂CO₃ was clearly identified both in the IR spectra and in the thermally programmed desorption mass spectra. The H₂CO₃ yield was rather high, amounting to approximately 40%-70% relative to that of CO₂ formed by the reaction of CO with OH. The structure of H₂CO₃ formed by reactions of CO with OH may differ from that formed by energetic processes such as UV irradiation, ion irradiation, and electron irradiation of H₂O/CO₂ binary ices. In this paper, we envisage some of the possible roles H₂CO₃ may have in the interstellar medium, such as enriching grain mantles of new molecules via acid-base reactions with basic species and contributing to the formation of the unidentified band at 6.8 µm; we suggest possible reasons for its non-detection yet and discuss the restoration of carbonic acid molecules in the gas phase.