Concentration-dependent SERS and DFT investigation of N-(5-Chloropyrazin-2-yl)-2-hydroxybenzamide (CHB) adsorbed on Ag6 cluster: Insights into adsorption mechanism and electronic properties

This study investigates the vibrational, electronic, and adsorption properties of N-(5-Chloropyrazin-2-yl)-2-hydroxybenzamide (CHB) using surface-enhanced Raman spectroscopy (SERS) and density functional theory (DFT). Concentration-dependent SERS spectra (10−3–10−6 M) reveal strong interactions between CHB and silver colloids. DFT calculations at the B3LYP level, including an Ag6 cluster model, support experimental findings, showing good agreement in vibrational features and adsorption-induced spectral shifts. The carbonyl (C=O) and amine (N-H) groups are identified as primary binding sites, contributing to charge transfer and enhancement mechanisms. Electronic analyses (HOMO-LUMO, DOS, and UV–Vis) indicate reduced energy gaps and increased delocalization upon adsorption. MEP, ELF, LOL, and RDG analyses highlight stronger interaction at the carbonyl site, while thermodynamic results suggest energetically favorable NH adsorption. Overall, adsorption is exothermic and feasible, providing insights into molecule-metal interactions and aiding the design of efficient SERS-based sensing systems.