The Electronic Structure of the Superatom Au₃

Area of Science:

• Physical Chemistry
• Atomic and Molecular Physics
• Materials Science

Background:

• The triatomic gold cluster ion, Au₃⁺, is a fundamental building block in larger gold assemblies.
• Understanding Au₃⁺ is crucial for elucidating the photocatalytic mechanisms of gold nanoclusters.

Purpose of the Study:

• To obtain and interpret high-resolution, vibrationally resolved optical spectra of mass-selected Au₃⁺.
• To characterize the electronic structure and excited states of Au₃⁺ using advanced computational methods.

Main Methods:

• Photodissociation spectroscopy was used to record optical spectra of Au₃⁺ from 2.7-5.0 eV.
• Ab initio CASSCF calculations incorporating spin-orbit coupling were employed to interpret spectral features.

Main Results:

• Five complex band systems were observed in the optical spectra of Au₃⁺.
• Calculations revealed that closely spaced excited states, d-orbital excitations, small s-d orbital gaps, and significant vibronic and spin-orbit coupling govern the spectra.
• The electronic structure of Au₃⁺ exhibits strong multireference character.

Conclusions:

• Accurate characterization of Au₃⁺ excited states requires sophisticated multireference calculations.
• Simplified methods like DFT fail to capture the complex electronic interactions in Au₃⁺ due to d-orbital contributions.