Infrared Multiple Photon Dissociation Spectroscopy of Hydrated Cobalt Anions Doped with Carbon Dioxide CoCO 2 (H 2 O) n − , n =1–10, in the C−O Stretch Region

We investigate anionic [Co,CO 2 , n H 2 O] − clusters as model systems for the electrochemical activation of CO 2 by infrared multiple photon dissociation (IRMPD) spectroscopy in the range of 1250–2234 cm −1 using an FT‐ICR mass spectrometer. We show that both CO 2 and H 2 O are activated in a significant fraction of the [Co,CO 2 ,H 2 O] − clusters since it dissociates by CO loss, and the IR spectrum exhibits the characteristic C−O stretching frequency. About 25 % of the ion population can be dissociated by pumping the C−O stretching mode. With the help of quantum chemical calculations, we assign the structure of this ion as Co(CO)(OH) 2 − . However, calculations find Co(HCOO)(OH) − as the global minimum, which is stable against IRMPD under the conditions of our experiment. Weak features around 1590–1730 cm −1 are most likely due to higher lying isomers of the composition Co(HOCO)(OH) − . Upon additional hydration, all species [Co,CO 2 , n H 2 O] − , n ≥2, undergo IRMPD through loss of H 2 O molecules as a relatively weakly bound messenger. The main spectral features are the C−O stretching mode of the CO ligand around 1900 cm −1 , the water bending mode mixed with the antisymmetric C−O stretching mode of the HCOO − ligand around 1580–1730 cm −1 , and the symmetric C−O stretching mode of the HCOO − ligand around 1300 cm −1 . A weak feature above 2000 cm −1 is assigned to water combination bands. The spectral assignment clearly indicates the presence of at least two distinct isomers for n ≥2.