Investigating the stable structures of yttrium oxide clusters: Y_<i>n</i> clusters as promising candidates for O₂ dissociation

This study presents threshold photoionization (PI) spectra for a series of yttrium oxide clusters (Y_<i>n</i>O_<i>m</i>, n = 2-8, m = 2-4) in the photon energy range of 192 to 300 nm (6.46 to 4.13 eV). Density functional theory (DFT) is employed to explore the stable structures of these clusters. For Y_<i>n</i>O₂ clusters, experimental PI spectra are compared with calculated spectra for the lowest-energy and near-lowest-energy structural isomers. Stable structures contributing to the experimental PI spectra are identified. Experimentally corrected adiabatic ionization energies for Y_<i>m</i>O₂ clusters are determined. The newly identified lowest-energy structure for Y₂O₂ differs from those in previous literature studies, while larger clusters show better agreement, primarily varying in oxygen binding sites. Molecular oxygen-absorbed configurations of yttrium oxide clusters are generally unstable or energetically unfavorable, with O₂ activation occurring <i>via</i> charge transfer from yttrium to oxygen. Climbing image nudged elastic band (CI-NEB) calculations indicate that Y_<i>n</i>O₂ forms in the ground state when an O₂ molecule is absorbed onto low- or under-coordinated sites such as corners or edges of Y_<i>n</i> clusters. This process involves the dissociation of the O-O bond, followed by the adsorption of individual O atoms at different sites on the Y_<i>n</i> clusters. Analysis of the total density of states (TDOS) and partial density of states (PDOS) reveals an increased orbital density near the Fermi level, indicating a strong reaction affinity between Y and O atoms.