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Resonance Raman scattering of rhodamine 6G as calculated using time-dependent density functional theory
Lasse Jensen1, George C Schatz
1Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, USA. l. jensen@chem.northwestern.edu
The Journal of Physical Chemistry. A
|May 5, 2006
Summary
This study presents the first calculation of the resonance Raman scattering (RRS) spectrum for rhodamine 6G (R6G) using time-dependent density functional theory (TDDFT). The findings offer insights into RRS spectra, crucial for advancing surface-enhanced Raman scattering (SERS) techniques.
Area of Science:
- Physical Chemistry
- Spectroscopy
- Computational Chemistry
Background:
- Rhodamine 6G (R6G) is a key molecule for surface-enhanced Raman scattering (SERS) studies.
- Understanding RRS spectra is vital for interpreting SERS experiments, especially near absorption maxima where fluorescence interferes.
Purpose of the Study:
- To perform the first theoretical calculation of the resonance Raman scattering (RRS) spectrum of rhodamine 6G (R6G).
- To investigate the applicability of a time-dependent density functional theory (TDDFT) method with a short-time approximation for RRS calculations.
- To provide insights into RRS spectra of R6G, particularly under conditions where experimental measurements are challenging due to fluorescence.
Main Methods:
- Utilized a recently developed time-dependent density functional theory (TDDFT) method.
- Employed a short-time approximation to calculate the Raman scattering cross section.
- Calculated both normal and resonance Raman scattering (RRS) spectra for R6G.
Main Results:
- The calculated normal Raman spectrum showed good agreement with experimental data.
- The calculated RRS spectrum qualitatively matched SERS results for S(1) state excitation.
- Significant differences were observed between calculated and measured RRS spectra for vibronic sideband excitation of S(1).
- Calculated resonance enhancements were on the order of 10^5.
Conclusions:
- The TDDFT method provides valuable insights into the RRS spectrum of R6G, especially in the challenging spectral region near the absorption maximum.
- The calculated resonance enhancements suggest a surface enhancement factor of approximately 10^10 is needed for single-molecule detection of R6G via SERS.
- Despite discrepancies, the study advances the understanding of RRS and its application in SERS.
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