Experimental and theoretical studies of Raman spectroscopy on 4-mercaptopyridine aqueous solution and 4-mercaptopyridine/Ag complex system

Raman scattering and surface-enhanced Raman scattering (SERS) have been used to study the behavior of 4-mercaptopyridine (4-Mpy) dissolved in water and adsorbed on silver mirrors. In order to gain the actual structure and the theoretical modes of the 4-Mpy dissolved in water and adsorbed on the surface of silver mirror, ab initio calculation at the Hartree-Fock (HF) level and density functional theory (DFT) at Beck's three-parameter Lee-Yang-Parr (B3LYP) level were performed to calculate the vibrational modes and wavenumbers. 4-Mpy/2H ₂O and 4-Mpy/Ag complex systems were optimized, and then the corresponding Raman spectra were calculated and analyzed. Compared with the experimental results, the calculated results of 4-Mpy and 4-Mpy/2H₂O complex systems obtained from DFT method were more accurate. Among the results calculated with HF method, the one with three Ag atoms was economical, which took less computer time but gave equivalent results to those with more noumber of Ag atoms.