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Abstract:
The reaction of cobalt cluster anions Con– (3 ≤ n ≤ 17) with CO2 was studied experimentally and theoretically to explore the size-specific activation mode of CO2 by Con–. Mass spectrometric measurements revealed that the reactivity depends strongly on cluster size: the reactivity emerges abruptly at n = 7, peaks at n = 8–10, and then gradually decreases with increasing n. Infrared multiple photon dissociation spectra of ConCO2– exhibit a single peak at ∼1870 cm–1, similarly to the previously reported spectra of ConCO–. Density functional theory calculations for Co7CO2– as an example revealed that the dissociative adsorption of CO2 into CO and O is energetically more favorable than nondissociative adsorption. The infrared spectra calculated for dissociated isomers Co7(CO)O– reproduced the experimental results, whereas those for nondissociated isomers Co7CO2– did not. The photoelectron spectra of ConCO2– were shifted dramatically toward higher energies relative to those of Con–, suggesting electron transfer from Con– to the CO and O ligands. These results indicate that the CO2 molecule adsorbs dissociatively on Con–, in sharp contrast to its nondissociative adsorption onto the Co monomer anion.
