Theoretical Studies On The Effect Of Silver Clusters On Surface-enhanced Raman Scattering Spectroscopy

Recent years, with the development of computer technology, quantum chemistrywas used in many areas. In particular, the density functional theory (DFT) methodswere widely used in the molecular structure, properties and vibrational spectra.Density functional theory and time-dependent density functional theory (TDDFT)methods were used to calculate the chemical structure, Raman spectra and molecularproperties. We studied the enhancement mechanism of surface enhanced Ramanscattering by means of the calculated static polarizability, charge distribution andabsorption spectroscopy.The introduction of silver cluster influenced the Raman spectra of1,4-Benzenedithiol (1,4-BDT). The adsorption sites and silver cluster size werediscussed to give insight in the surface enhanced Raman scattering enhancementmechanism for1,4-BDT. We simulated the Raman spectra of1,4-BDT-Ag2,1,4-BDT-Ag4and1,4-BDT-Ag6complexes. In addition, we adopted Ag2cluster toanalyze the different adsorption models of1,4-BDT-Ag2. There were two models, vis,1,4-BDT binding to Ag2cluster through carbon or sulfur atom, respectively. And wecompared the results of the simulation and the measured experimental spectra. Weconducted comprehensive1,4-BDT molecular vibrational modes assignments. As canbe seen from the simulated Raman spectra of different complexes, the Raman spectralargely depended on the metal clusters size and adsorption site. From the aboveresearch findings it can be seen that static polarizability directly affects the strength ofthe Raman spectra and the molecular charge redistribution because of the introductionof metal clusters. On the basis of results, the Raman spectra of1,4-BDT-Au2,1,4-BDT-Ag2and Ag2-1,4-BDT-Au2complexes were calculated. The adsorptionbehavior of1,4-BDT on metal cluster has been investigated by means of DFT. Wecalculated the excited states of Ag2-1,4-BDT-Au2with time dependent densityfunctional theory. And we studied surface enhanced Raman enhancement mechanismby simulating the absorption spectroscopy and orbital transition. We got the chargetransfer state of Ag2-1,4-BDT-Au2by calculating electron cloud distribution of beforeand after excitation. The results had a good practical significance on the study ofresonance Raman spectroscopy.In addition, we conducted experimental and theoretical researches on Ramanspectra of melamine. We simulated the Raman spectra of melamine and melamine-metal complexes. And we researched the differences of Raman spectrabecause of the introduction of metal cluster.