Effects of solvation and core switching on the photoelectron angular distributions from (CO2)n− and (CO2)n−⋅H2O

Abstract

Photoelectron images are recorded in the photodetachment of two series of cluster anions, (CO(2))(n)(-), n=4-9 and (CO(2))(n)(-).H(2)O, n=2-7, with linearly polarized 400 nm light. The energetics of the observed photodetachment bands compare well with previous studies, showing evidence for switching between two anionic core structures: The CO(2)(-) monomer and covalent (CO(2))(2)(-) dimer anions. The systematic study of photoelectron angular distributions (PADs) sheds light on the electronic structure of the different core anions and indicates that solvation by several CO(2) molecules and/or one water molecule has only moderate effect on the excess-electron orbitals. The observed PAD character is reconciled with the symmetry properties of the parent molecular orbitals. The most intriguing result concerns the PADs showing remarkable similarities between the monomer and dimer anion cluster-core types. This observation is explained by treating the highest-occupied molecular orbital of the covalent dimer anion as a linear combination of two spatially separated monomeric orbitals.

Photodetachment, photofragmentation, and fragment autodetachment of [O2n(H2O)m]− clusters: Core-anion structures and fragment energy partitioning

“…A similar dimer-to-monomer anion core switching has been discussed in the case of heterogeneous ͑CO 2 ͒ n − ͑H 2 O͒ m clusters. 29,34 However, the strong intensities of the O 2 − and O 2 − ͑H 2 O͒ photofragments observed in the ͓O 2n ͑H 2 O͒ m ͔ − case, combined with the structure of the corresponding photoelectron spectra, argue in favor of a preserved O 4 − core. Upon photon absorption, this core is promoted to an excited state correlating with the O 2 − +O 2 dissociation fragments.…”

“…This has been demonstrated, for example, in our group's work on solvent-mediated reactivity of the ͑CO 2 ͒ n − ͑H 2 O͒ m clusters. 29,33,34 The expected decrease in photodetach with increasing cluster size will tend to increase the fraction defined by Eq. ͑1͒, thus competing with the monotonic decrease expected from the statistical model.…”

IR photodissociation spectroscopy of (OCS)n+ and (OCS)n− cluster ions: Similarity and dissimilarity in the structure of CO2, OCS, and CS2 cluster ions

“…For homo-dimer radical ions, it is often seen that the intermolecular charge resonance interaction occurs in them, giving a symmetrical species; the charge is equally shared by the two components. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] The dimer ion form is kept as a dimer ion core in some homo-molecular cluster ions, such as (benzene) n + . 13,14 However, the charge distribution of cluster ions is not predictable so easily on the basis of IE, PA, or EA.…”

The interaction of negative charge with carbon dioxide – insight into solvation, speciation and reductive activation from cluster studies

“…At n ¼ 6, this balance tips in favour of a solvated monomer anion as the charge carrier [107]. Interestingly, angular distributions measured in photoelectron imaging experiments [109] show strong similarities regardless whether the charge carrier is CO À 2 or C 2 O À 4 . The origin of this similarity is the fact that the HOMO of C 2 O À 4 can be treated as a linear combination of two monomer units.…”

“…Interestingly, replacing water with methanol as the perturbing molecule in the cluster, the C 2 O À 4 core ion exists only for ½ðCO 2 Þ 2 Á CH 3 OH À [178,179], while all other cluster sizes seem to exhibit a CO À 2 charge carrier. While the presence of one or two water molecules in CO 2 cluster anions changes the switching point between monomer and dimer cores, it does not significantly change the shape of the HOMO in either core, as was shown by photoelectron imaging spectroscopy experiments [109].…”