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

We investigate anionic [Co,CO2,nH(2)O](-) clusters as model systems for the electrochemical activation of CO2 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 CO2 and H2O are activated in a significant fraction of the [Co,CO2,H2O](-) 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,CO2,nH(2)O](-), n >= 2, undergo IRMPD through loss of H2O 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.