Simulating surface-enhanced Raman optical activity using atomistic electrodynamics-quantum mechanical models.

Area of Science:

• Chemical Physics
• Spectroscopy
• Computational Chemistry

Background:

• Raman optical activity (ROA) is vital for molecular geometry analysis.
• Surface-enhanced Raman scattering (SERS) mechanisms suggest potential for enhanced ROA (SEROA).
• Experimental SEROA, especially for enantiomers, remains challenging.

Purpose of the Study:

• To develop advanced computational methods for simulating SEROA.
• To move beyond point-dipole approximations in SEROA modeling.
• To understand factors hindering experimental SEROA measurements.

Main Methods:

• Developed a dressed-tensors model (point-dipole and point-quadrupole).
• Implemented a discrete interaction model/quantum mechanical (DIM/QM) model considering full molecular charge density.
• Evaluated model performance for small and medium-sized molecules (e.g., 2-bromohexahelicene).

Main Results:

• The dressed-tensors model is adequate for small molecules but fails for medium-sized ones.
• The DIM/QM model provides a more comprehensive approach.
• SEROA spectra are highly sensitive to local electric fields, molecular orientation, and plasmonic properties.

Conclusions:

• Advanced computational models are necessary for accurate SEROA simulation.
• The sensitivity of SEROA to experimental conditions explains the difficulties in obtaining enantiomer-specific spectra.
• Findings provide insights into overcoming experimental challenges in SEROA spectroscopy.