Direct Spectroscopic Benchmark of Isolated Au(II) Oxidation State: Electronic Structure and Instability of AuCl3
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Updated: Oct 31, 2026

Measurement and Analysis of Atomic Hydrogen and Diatomic Molecular AlO, C2, CN, and TiO Spectra Following Laser-induced Optical Breakdown
Published on: February 14, 2014
Jingyue Wang1, Jian Zhang2, Xueying Li1
1State Key Laboratory of Precision Spectroscopy, School of Physics, East China Normal University, Shanghai200241, China.
Abstract:
Characterization of Au(II) oxidation state remains challenging because d9 Au(II) complexes readily disproportionate to Au(I) and Au(III). We report the first high-resolution cryogenic photoelectron spectroscopic characterization of an isolated mononuclear Au(II) halide anion, AuCl3-, combining cryogenic anion photoelectron spectroscopy (PES) with relativistic quantum chemical calculations. The measured adiabatic detachment energy (ADE) and vertical detachment energy (VDE) are 4.63 ± 0.04 and 4.93 ± 0.04 eV, respectively. The VDE shows a near-plateau relative to AuCl2- upon adding an electronegative chlorine ligand, deviating from conventional superhalogen trends. Electronic-structure analysis reveals a high-energy Au 5d σ-antibonding frontier orbital, its unpaired electron axially localized in the Jahn-Teller-distorted C2v structure. Comparative relativistic vs nonrelativistic calculations confirm relativistic effects suppressing the VDE increase from AuCl2- to AuCl3-. The disproportionation reaction 2AuCl3- → AuCl2- + AuCl4- is downhill by 1.48 eV. These results connect relativistic electronic structure, photodetachment energetics, and Au(II)'s electronic lability and disproportionation tendency.
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