Surface-enhanced raman scattering of pyrazine at the junction between two Ag ₂₀ nanoclusters

In this work we present a detailed time-dependent density functional theory (TDDFT) investigation of the absorption and Raman spectra of a pyrazine molecule located at the junction between two Ag ₂₀ clusters. Surface-enhanced Raman scattering enhancements of the order of 10 ⁶ have been found for the junction system, which are similar to enhancements of 10 ⁵ found for individual silver nanoparticles. Surprisingly, the chemical enhancement is found to account for as much as 10 ⁵, suggesting that this mechanism might be more important than previously believed, in particular for nanoparticle aggregates. Moreover, TDDFT calculations suggest that unlike larger nanoparticles, the junction between small Ag ₂₀ tetrahedral clusters does not provide an electromagnetic "hot spot".