Investigating Pt Atom Addition to Gas Phase Ce2On Clusters Using Photoionization Efficiency Spectroscopy and Density Functional Theory

Photoionization efficiency spectra for PtCe2On (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.