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Indexed by:期刊论文

Date of Publication:2011-11-01

Journal:SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY

Included Journals:Scopus、SCIE、EI、PubMed

Volume:82

Issue:1

Page Number:205-212

ISSN No.:1386-1425

Key Words:Chemical mechanism via charge transfer; Theoretical study; Pre-SERS; Pyridine; Pyridine-Ag-n (n=2-8) complexes

Abstract:We investigate surface-enhanced Raman scattering(SERS) spectra of pyridine-A(n) (n = 2-8) complexes by density functional theory (DFT) and time-dependent DFT (TDDFT) methods. In simulated normal Raman scattering (NRS) spectra, profiles of pyridine-Ag-n (n = 2-8) complexes are analogical with that of isolated pyridine. Nevertheless, calculated pre-SERS spectra are strongly dependent on electronic transition states of new complexes. Wavelengths at 335 nm, 394.8 nm, 316.9 nm and 342.6 nm, which are nearly resonant with pure charge transfer excitation states, are adopted as incident light when simulating pre-SERS spectra for pyridine-Ag-n (n = 2-8) complexes, respectively. We obtain enhancement factors from 103 to 105 in pre-SERS spectra compared with corresponding NRS spectra. The obvious increase in Raman intensities mainly result from charge transfer resonance Raman enhancement. A charge difference densities (CDDs) methodology is adopted in describing chemical enhancement mechanism. This methodology aims at visualizing charge transfer from Ag-n (n = 2-8) clusters to pyridine on resonant electronic transition, which is one of the most direct evidences for chemical enhancement mechanism. (C) 2011 Elsevier B.V. All rights reserved.