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

Understanding the intrinsic properties of the hydrated carbon dioxide radical anions CO 2 .− (H 2 O) n is relevant for electrochemical carbon dioxide functionalization. CO 2 .− (H 2 O) n ( n =2–61) is investigated by using infrared action spectroscopy in the 1150–2220 cm −1 region in an ICR (ion cyclotron resonance) cell cooled to T= 80 K. The spectra show an absorption band around 1280 cm −1 , which is assigned to the symmetric C−O stretching vibration ν s . It blueshifts with increasing cluster size, reaching the bulk value, within the experimental linewidth, for n =20. The antisymmetric C−O vibration ν as is strongly coupled with the water bending mode ν 2 , causing a broad feature at approximately 1650 cm −1 . For larger clusters, an additional broad and weak band appears above 1900 cm −1 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 2 .− with the hydrogen‐bonding network.