Calculation of Absolute Resonance Raman Intensities

Open Access
Author:
Kane, Krista Ann
Graduate Program:
Chemistry
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 30, 2009
Committee Members:
  • Lasse Jensen, Thesis Advisor
Keywords:
  • Short-time Approximation
  • Resonance Raman Spectroscopy
  • Vibronic Theory
Abstract:
We present the resonance Raman (RR) spectra of uracil, rhodamine 6G (R6G) and iron(II) porphyrin with imidazole and CO ligands (FePImCO) calculated using density functional theory (DFT). The absolute RR intensities were determined using both the vibronic theory and the short-time approximation. We found that the absolute RR intensities calculated using the short-time approximation are overestimated compared to those calculated using the vibronic theory. This is attributed to the sensitivity of the short-time approximation to the damping parameter. Uracil is not affected by vibronic coupling and so the absolute RR intensities calculated using both methods should be comparable. Despite the agreement obtained in the relative RR intensities, the absolute RR intensities calculated using the short-time approximation are severely overestimated compared to those calculated using the vibronic theory. In addition, the absolute RR intensities of R6G, computed using the vibronic theory, are only slightly underestimated compared to experiment, which is attributed to the neglect of solvent effects in the calculations. The absolute RR intensities calculated using vibronic theory correctly resulted in an increase in the relative RR intensity of the low-frequency Raman bands for molecules that experience vibronic coupling (i.e. R6G and FePImCO), but was not observed in the RR spectra calculated using the short-time approximation.