Investigating Pt atom addition to gas phase Ce(2)O(n) clusters using photoionization efficiency spectroscopy and density functional theory

Photoionization efficiency spectra for PtCe₂O(n) (n = 0–1) clusters were recorded and compared with simulations based on density functional theory to determine adiabatic ionization energies (IE) and verify cluster structures. Calculated structures were also presented for PtCe₂O₂–₅, though no comparison with experiment was made due to nondetection of these species in the mass spectrum. The IEs of PtCe₂ and PtCe₂O were determined to be 4.59 and 4.55 eV, respectively. The calculated IEs for PtCe₂O₂–₅ sharply rise to >5.95 eV, coinciding with the HOMO of the clusters being lower energy Pt 6s-like, Ce 4f-like, and Pt 5d-like orbitals, from the higher energy Ce 6s-like HOMOs of PtCe₂O₀,₁. The sharp increase in IE also explains the lack of PtCe₂O₂–₅ ionization products observed in the experiment, though photodissociation is found to be a less likely possibility. As the level of oxidation in the clusters increased the charge on the Pt atom in the cluster became more positive, representing a transition from Ce → Pt to Pt → Ce charge transfer. This transition coincided with the formation of the first Pt–O–Ce structural motif and the sharp decrease in O bond dissociation energy in PtCe₂O₃. PtCe₂O₄ and PtCe₂O₅ each possess a second Pt–O–Ce site formed with the latter also having a sharp increase in calculated IE to 7.71 eV due to the low-energy Pt localized 5d-like HOMO.Aidan M. Karayilan and Gregory F. Meth