Regular Article

Ionization energies and structures of small lanthanum oxide clusters (La₂O₃)_n.LaO (n = 1–3)^⋆

¹ Atomic and Molecular Physics Division, Bhabha Atomic Research Centre, Mumbai 400 085, India
² Homi Bhabha National Institute, Anushaktinagar, Mumbai 400 094, India
³ Harish-Chandra Research Institute, Chhatnag Road, Jhunsi, Allahabad 211019, India
⁴ Physics Department, Birla Institute of Technology and Science, Pilani 333031, Rajasthan, India

^a e-mail: sbhatt@barc.gov.in
^c e-mail: nakhate@barc.gov.in

Received: 11 April 2019
Revised: 22 May 2019
Published online: 25 July 2019

Abstract

Small lanthanum oxide clusters were produced in a laser-ablation molecular beam setup and studied by mass spectrometry and laser threshold photoionization spectroscopy. Mass spectrometry investigations of neutral clusters revealed certain stoichiometries, (La₂O₃)_n and (La₂O₃)_n.LaO (n = 1–6) were stable. For cation clusters, similar stoichiometric preference was reported by previous authors. The stoichiometric preference of the oxides was not affected by oxygen concentrations. Ionization thresholds and vertical ionization energies (VIEs) were measured for the (La₂O₃)_n.LaO (n = 1–3) neutral clusters from the photoionization efficiency curves. The energetically low-lying structural isomers for these clusters along with their adiabatic and vertical ionization energies were computed from the density functional theory using B3LYP and PW91GGA exchange correlation functionals. Favorable agreement between the computed and experimental ionization energies allows assignments of the ground state structures for these clusters. For La₃O₄, a C_3v-like structure has been found as the ground state built on La-O-La bonds with their usual oxidation states of +3 for La and −2 for O atoms. For larger clusters La₅O₇ and La₇ O₁₀, however, a trend towards forming more compact structures with few metal and O sites having higher coordination numbers have been found as the ground states and are suggested to be present in the molecular beam.