Molecular-Orbital Framework of Two-Electron Processes: Application to Auger and Intermolecular Coulomb Decay

Area of Science:

• Atomic and Molecular Physics
• Quantum Chemistry
• X-ray Spectroscopy

Background:

• Core- or inner-shell vacancies, often induced by high-energy photons, decay via two-electron processes.
• These relaxation processes include Auger decay, intermolecular Coulomb decay, and electron-transfer-mediated decay.
• Such processes are fundamental to understanding X-ray spectroscopies.

Purpose of the Study:

• To bridge the gap between many-body wave functions and the molecular orbital picture of electronic decay processes.
• To introduce a novel concept for interpreting complex quantum chemical calculations.
• To provide chemical insight into core-level hole relaxation mechanisms.

Main Methods:

• Development and application of natural Auger orbitals (NAOs).
• NAOs are derived from a two-step singular value decomposition of two-body Dyson orbitals.
• Utilizing the Feshbach-Fano treatment to calculate decay rates.

Main Results:

• NAOs successfully connect initial and final many-body states with molecular orbitals.
• The study demonstrates the utility of NAOs in interpreting ab initio calculations.
• NAOs provide a chemically intuitive understanding of Auger decay and related phenomena.

Conclusions:

• Natural Auger orbitals offer a powerful new tool for analyzing electronic relaxation processes.
• This approach enhances the interpretation of complex quantum chemical calculations in atomic and molecular physics.
• NAOs facilitate a deeper understanding of chemical bonding and electronic structure through spectroscopy.