Simulation of the Resonance Raman Spectra for 5‑Halogenated
(F, Cl, and Br) Uracils
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Abstract
The resonance Raman spectra of the
5-halogenated (F, Cl, and Br)
uracils are simulated via the Herzberg–Teller (HT) short-time
dynamics formalism. The gradient of the S<sub>1</sub> excited state
is computed at the CAMB3LYP/aug-cc-pVTZ level of theory in the conductor-like
polarizable continuum model for water (C-PCM, H<sub>2</sub>O), based
on the equilibrium geometry determined using PBE0/aug-cc-pVTZ in H<sub>2</sub>O (C-PCM). The simulated resonance Raman spectra show good
agreement with the experimental spectra in terms of both peak positions
and intensities. The differences between the resonance Raman spectra
of the three 5-halogenated uracils, caused by the effect of halogen
substitution, are examined in terms of ground-state normal-mode eigenvectors
and excited-state Cartesian gradients, according to the HT formalism.
The differences in the normal-mode eigenvectors and excited-state
Cartesian gradients between 5-fluorouracil and 5-chlorouracil are
used to interpret the dissimilarity between their resonance Raman
spectra. Meanwhile, the similarity between the spectra of 5-chlorouracil
and 5-bromouracil is explained by the correspondence between their
normal modes and excited-state gradients