Surface-enhanced Raman scattering of pyrazine on Au5Al5 bimetallic nanoclusters

Abstract

In this study, we theoretically investigated the Raman and absorption spectra of pyrazine adsorbed on Au₅Al₅ bimetallic nanoclusters by a time-dependent density functional theory (TD-DFT) method. The surface-enhanced resonance Raman scattering (SERRS) spectra of pyrazine absorbed on different isomers and sites of the Au₅Al₅ cluster were simulated. The visualization of orbital transitions in electronic transitions was used to analyze the enhancement mechanism of SERRS spectroscopy. Compared with those of isolated pyrazine excited at 598 nm, the SERRS of pyrazine–Au–Au₄Al₅-a excited at the same incident light can be enhanced on the order of 10⁴, which is a typical charge transfer (CT) resonance excitation and charge transfer from substrate to pyrazine. Due to the fact that the intensity of ultraviolet SERRS can be significantly enhanced to 1.2 × 10⁶ A⁴ per amu for pyrazine–Au–Au₄Al₅-a model at 280 nm, the Au₅Al₅ cluster may be a good candidate for research of the ultraviolet SERRS materials. Other key factors that can change the intensity of SERRS include the resonance excitation wavelength, oscillator strength of the electronic excited state, metal–molecule binding site and structure of the substrate cluster. Hence, the optical properties of complexes can be tuned by varying these factors.