Chemical Coupling SERS Properties of Pyridine on Silver-Caged Metal Clusters M@Ag12 (M = V-, Nb-, Ta-, Cr, Mo, W, Mn+, Tc+, Re+)

Using density functional theory, this work presents a comprehensive analysis of nonresonant surface-enhanced Raman scattering enhancement of pyridine on M@Ag-12 (M = V-, Nb-, Ta-, Cr, Mo, W, Mn+, Tc+, Re+). Computational results indicate that the chemical enhancement of pyridine on M@Ag-12 is closely associated with the charge properties of silver-caged clusters. Pyridine on negative clusters exhibits the strongest chemical enhancement with a factor of about 10(3), while the chemical enhancement is only about 10(2) for pyridine on neutral clusters and 10 for pyridine on positive clusters. The polarizability analyses elucidate the nature of the chemical enhancement that delocalized electrons of negative adsorption systems occupy higher molecular orbitals than those of neutral and positive adsorption systems, which can lead to stronger nonresonant chemical enhancement.