Core Ion Structures in CO2- and N2O-Based Cluster Anions Studied by Infrared Photodissociation Spectroscopy

The interactions of anionic species with other molecules opens up new avenues to study the process of bond formation or charge transfer. Gas phase clusters are a useful tool for studying such systems in the absence of competing effects in condensed phase. Cluster ions can be studied as model analogues to more complex condensed phase systems. The majority of this thesis focuses on gas phase cluster ions of the form [M(CO2)n] (M=Bi, Sn, Mn, Fe). These clusters consist of a charged molecular anion surrounded by weakly bound \textquotedblleftsolvent\textquotedblright CO<sub>2</sub> species. IR photodissociation spectroscopy is used to probe the infrared spectra of the molecular core ions.</p> <p>[Bi(CO<sub>2</sub>)n]- and [Sn(CO<sub>2</sub>)n]- clusters are studied as model systems of the reduction of CO<sub>2</sub> at a corner or edge site of a Bi or Sn electrode surface. The structures of the core ions for these clusters give insight into potential docking motifs of the CO<sub>2</sub> species. In both species, the formation of an ɳ1-C docked CO<sub>2</sub> species results in a metal carboxylate complex. These structures have characteristic CO<sub>2</sub> stretching frequencies that can be used to identify these species in the condensed phase. These species also exhibit oxalate ligand formation, which is interesting since it requires the formation of a C-C bond.

[Mn(CO<sub>2</sub>)n]- and [Fe(CO<sub>2</sub>)n]- clusters are studied to understand how a change in the electron configuration of the metal affects the binding motifs of the CO<sub>2</sub>. As in other first row transition metals, these species exhibit a rich collection of interaction motifs, among which the ɳ<sup>2</sup>(C,O), where M-C and M-O bonds are formed, is most prevalent. In addition, oxalate ligands also are present.</p> <p>We also investigated the structure and charge distributions of neat and heterogeneous N<sub>2</sub>O clusters [(N<sub>2</sub>O)n- and (N<sub>2</sub>O)nO-]. In heterogeneous N<sub>2</sub>O clusters, we find that initially the core ion is an NNO<sub>2</sub>- molecular anion. We find that this core ion switches to an O- core ion at larger cluster sizes. We also find an N<sub>2</sub>O- core ion for neat anionic clusters of N<sub>2</sub>O and report for the first time frequencies of the N-N and N-O stretches of the N<sub>2</sub>O- anion.
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Department of Physics
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University of Colorado Boulder
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