Surface-enhanced Raman scattering of uracil and uracil dimer on silver by density functional method.

The adsorbed structures, Surface-enhanced Raman scattering (SERS) and pre-resonance Raman spectra of the U-Ag and U〈 〉U-Ag complexes are calculated using density-functional theory (DFT) method with B3LYP/6-311g (d, p) (C, H, O)/Lanl2dz (Ag) basis set. The uracil and uracil dimer prefer to a perpendicular orientation adsorbed on the Ag surface via atom O8 site. The SERS of the U-Ag and U〈 〉U-Ag complexes are similar with the normal Raman spectra of the isolated uracil and uracil dimer but with an enhancement factor less than 10. The enhancement mechanism is ascribed to the ground state static chemical enhancement from the static polarizability changes. The pre-resonance Raman spectra of the complexes are obtained at 316 nm and 315 nm, in which the enhancement factors are up to 103–104. The greatest enhancement factor is observed for the C2=O8 stretching vibration, caused by the electron transfer from the molecules to Ag atom. The charge transfer resonant enhancement plays the major role in the molecule–metal system. [ABSTRACT FROM AUTHOR]