Probing chirality across the electromagnetic spectrum with the full semi-classical light-matter interaction

Area of Science:

• Theoretical Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• Electronic Circular Dichroism (ECD) is a powerful spectroscopic technique.
• Relativistic effects and higher-order light-matter interactions are crucial for accurate ECD calculations, especially at higher energies.

Purpose of the Study:

• To develop and implement a relativistic quantum chemical method for calculating anisotropic and isotropic ECD.
• To investigate the importance of beyond-first-order interactions and relativistic effects on ECD spectra.
• To analyze ECD in simple disulfides (H2S2, (CH3S)2) across various electronic transitions.

Main Methods:

• Utilized a four-component relativistic framework with the full semi-classical light-matter interaction operator.
• Implemented calculations for both isotropic and oriented ECD.
• Compared results with a truncated formulation in the Coulomb gauge (velocity representation).

Main Results:

• The relativistic formalism allows for gauge-origin invariant calculations in the velocity representation, distinguishing electric and magnetic multipole contributions.
• Beyond-first-order treatment is essential for soft X-ray energies, significantly impacting differential absorption profiles.
• A first-order approach overestimates differential absorption by a factor of two and fails to predict signs at higher energies (>1000 eV).

Conclusions:

• The developed relativistic method accurately describes ECD across a wide spectral range.
• Higher-order contributions are mandatory for precise ECD calculations in the soft X-ray region.
• Relativistic effects and advanced interaction treatments are critical for interpreting complex ECD spectra.