Simulation
of the Resonance Raman Spectrum for Uracil
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Abstract
The resonance Raman spectrum of uracil
is simulated using the Herzberg–Teller
short-time dynamics formalism. The ground-state geometry is optimized
at the levels of PBE0/aug-cc-pVTZ and B3LYP/aug-cc-pVTZ, respectively.
The gradient of the bright excited state is computed using time-dependent
density functional theory and spin-flip time-dependent density functional
theory. The excited-state calculations are carried out in both the
gas phase and implicit water using the conductor-like polarizable
continuum model. The ground-state equilibrium structure is found to
impact the resulting resonance Raman spectrum significantly. The simulated
resonance Raman spectrum using the long-range corrected functionals,
that is, CAMB3LYP and LC-BLYP, and based on the PBE0/aug-cc-pVTZ optimized
ground-state structure shows better agreement with the experimental
spectrum than using standard hybrid functionals, that is, PBE0 and
B3LYP. The solvation effect leads to a change in the energetic order
of the <i>n</i> → π* and π → π*
excited states, and it improves the agreement with the experimental
spectrum, especially with regard to the relative intensities of the
peaks with frequencies greater than 1600 cm<sup>–1</sup>