Linear Vibronic Coupling Approach for Surface-Enhanced Raman Scattering: Quantifying the Charge-Transfer Enhancement...

Area of Science:

• Surface-enhanced Raman scattering (SERS)
• Plasmonics
• Quantum chemistry

Background:

• SERS amplification arises from plasmonic (PL) and charge-transfer (CT) mechanisms.
• Accurately modeling CT enhancement factors is theoretically challenging due to complex state couplings.

Purpose of the Study:

• To simulate electrochemical SERS spectra considering coupled PL and CT states.
• To investigate the influence of external electric fields on CT mechanisms in SERS.
• To theoretically estimate CT enhancement factors.

Main Methods:

• Quantum dynamical propagation of nuclear wavepackets.
• Linear vibronic coupling models parametrized using fragment-based maximum-overlap diabatization.
• Simulation of pyridine on silver clusters under an external electric field (E⃗).

Main Results:

• A direct relationship exists between population transfer to CT states and total scattered intensity.
• Electric fields effectively tune CT states relative to PL states, matching experimental observations.
• CT enhancement factors were estimated to be between 10^5 and 10^6.

Conclusions:

• The theoretical model accurately reproduces experimental SERS behavior under varying electric fields.
• CT mechanisms play a crucial role in SERS, comparable to PL mechanisms when in resonance.
• This work provides a pathway for understanding and predicting SERS enhancement through combined PL and CT effects.