Simulation of the Resonance Raman Spectra for 5-Halogenated (F, Cl, and Br) Uracils

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-1 excited state is computed at the CAMB3LYP/aug-cc-pVTZ level of theory in the conductor-like polarizable continuum model for water (C-PCM, H2O), based, on the equilibrium geometry determined using PBEO/aug-cc-pVTZ in H2O (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 term 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.