Infrared Spectroscopy of Size-Selected Hydrated Carbon Dioxide Radical Anions CO (H O) (n=2-61) in the C-O Stretch Region.

Understanding the intrinsic properties of the hydrated carbon dioxide radical anions CO (H O) is relevant for electrochemical carbon dioxide functionalization. CO (H O) (n=2-61) is investigated by using infrared action spectroscopy in the 1150-2220 cm region in an ICR (ion cyclotron resonance) cell cooled to T=80 K. The spectra show an absorption band around 1280 cm , which is assigned to the symmetric C-O stretching vibration ν . It blueshifts with increasing cluster size, reaching the bulk value, within the experimental linewidth, for n=20. The antisymmetric C-O vibration ν is strongly coupled with the water bending mode ν , causing a broad feature at approximately 1650 cm . For larger clusters, an additional broad and weak band appears above 1900 cm similar to bulk water, which is assigned to a combination band of water bending and libration modes. Quantum chemical calculations provide insight into the interaction of CO with the hydrogen-bonding network.