Infrared Spectroscopy of Size‐Selected Hydrated Carbon Dioxide Radical Anions CO₂^.−(H₂O)_n (n=2–61) in the C−O Stretch Region

Abstract

Understanding the intrinsic properties of the hydrated carbon dioxide radical anions CO2.−(H2O)n is relevant for electrochemical carbon dioxide functionalization. CO2.−(H2O)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 νs. It blueshifts with increasing cluster size, reaching the bulk value, within the experimental linewidth, for n=20. The antisymmetric C−O vibration νas is strongly coupled with the water bending mode ν2, 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 CO2.− with the hydrogen‐bonding network.

Infrared Multiple Photon Dissociation Spectroscopy of Hydrated Cobalt Anions Doped with Carbon Dioxide CoCO2(H2O)n−, n=1–10, in the C−O Stretch Region

“…The weaker absorption band observed experimentally at 1570–1730 cm −1 lies in the range of the H 2 O bending mode and the antisymmetric stretching mode of CO 2 − . The presence of an intact water molecule, isomers Ig and Ih , can be ruled out.…”

“…However, the band broadens with increasing n so that the band is smeared out for n ≥6, resulting in a raised baseline as seen in Figure . For larger clusters, the band might be explained by a combination of H 2 O bending ν 2 , H 2 O libration ν L2 , and bending of H 2 O triplets ν T2 , as seen before in the spectra of CO 2 − (H 2 O) n …”

“…The measurements were performed in the range of 1250–2234 cm −1 where characteristic C−O stretching modes are typically observed. Details on the experimental laser setup can be found elsewhere . The present experiments are lacking information on the number of photons required for dissociation, thus we determine the IRMPD yield, which is total photofragment intensity divided by total ion intensity, irradiation time and laser power.…”

“…Raman spectroscopy of CO 2 − in bulk aqueous solution places the symmetric stretching mode of hydrated CO 2 − at 1298 cm −1 . In our recent IR study on gas phase clusters CO 2 − (H 2 O) n , we observed very similar values already around n= 20 . Some hydrated metal ions M + (H 2 O) n , M=Mg, Cr, Co, pick up exactly one CO 2 molecule, indicating that electron transfer from the metal to carbon dioxide takes place .…”

“…[4][5][6][7] This has been repeatedly confirmed by quantum chemical calculations. [3,[7][8][9] In interaction with ar are gas matrix [10] or as olvation shell such as (CO 2 ) n À [6,11,12] or CO 2 (H 2 O) n À , [13,14] the radical anion is stabilized. [4] The same is true in as alt environment where the interaction with positive chargec enters is responsible for the stabilization.…”