Direct visual evidence of end-on adsorption geometry of pyridine on silver surface investigated by surface enhanced Raman scattering and density functional theory calculations

Fourier transform Raman (FT-Raman) spectra of neat pyridine (Py) and surface enhanced Raman scattering (SERS) spectra of Py with silver nanoparticles (AgNPs) solution at different molar concentrations (X = 1.5 M, 1.0 M, 0.50 M, 0.25 M, and 0.125 M) were recorded using 1064 nm excitation wavelength. The intensity of Raman bands at similar to 1003 (nu(11)) and similar to 1035 (nu(21)) cm(-1) of Py is enhanced in the SERS spectra. Two new Raman bands were observed at similar to 1009 (nu(12)) and similar to 1038 (nu(22)) cm(-1) in the SERS spectra. These bands correspond to the ring breathing vibrations of Py molecules adsorbed at the AgNPs surface. The value of intensity ratios (I-12/I-11) and (I-21/I-22) is increased with dilution and attains a maximum value at X = 0.5 M and upon further dilution (0.25 and 0.125 M) it drops gradually. The theoretically calculated Raman spectra were found to be in good agreement with experimentally observed Raman spectra. Both, experimental and theoretical investigations have confirmed that the Py interacts with AgNPs via the end-on geometry. (C) 2015 Elsevier B.V. All rights reserved.