Electrochemical Surface-Enhanced Raman Spectroscopy for Aniline Adsorbed on Silver Electrodes: A DFT Study of the Anharmonic Effects of Amino Wagging Vibrational Modes

Abstract

Aniline molecules exhibit a special amino wagging vibrational mode on the surface of the silver electrode. The corresponding Raman peak not only displays enhanced Raman signals in surface-enhanced Raman spectroscopy (SERS) experiments but also shows a shift toward higher wavenumbers. This work adopts a molecule-metal cluster model to investigate the normal Raman spectra of aniline molecules and their SERS spectra adsorbed on silver electrode surfaces by density functional theory (DFT) approaches. Based on the harmonic approximation, the influence of anharmonic effects on the normal Raman and SERS spectra of aniline is further considered. Our calculated results of the anharmonic Raman spectra of free aniline molecules show that their anharmonic effect mainly comes from the amino wagging vibrational mode. Then, the anharmonic Raman spectra of aniline binding to neutral and positively charged silver clusters were calculated and compared with the harmonic Raman spectra. It was found that the coupling effect between vibrational modes also greatly affects the Raman spectral characteristics. Finally, the excited state energy gap and pre-resonance Raman spectra of the aniline−silver cluster complexes are studied, and it is believed that there may be a charge-transfer enhancement mechanism.

Uncovering the Dissociative Adsorption of the Leveler Janus Green B on Cu Electrodes at the Molecular Level

“…In the high wavenumber region, in addition to the downward ν­(O–H) free peak caused by squeezing surface Cl – , two upward peaks belonging to ν as (N–H) and ν s (N–H) of the NH 2 group were observed at 3301 and 3154 cm –1 , respectively. This suggests that the NH 2 group is not protonated and that the lone pair of electrons on the NH 2 group is directly bonded to Cu, as reported elsewhere. , In addition, only the A 1 and B 2 vibrational modes were observed for the adsorbed B species. By comparing the relative peak intensities of the IR spectra for the dissolved B with those for adsorbed B (Figure S7), we can deduce the adsorption configuration for B and depict it, where α = 70° and β = 0°.…”

“…This suggests that the NH 2 group is not protonated and that the lone pair of electrons on the NH 2 group is directly bonded to Cu, as reported elsewhere. 41,42 In addition, only the A 1 and B 2 vibrational modes were observed for the adsorbed B species. By comparing the relative peak intensities of the IR spectra for the dissolved B with those for adsorbed B (Figure S7), we can deduce the adsorption configuration for B and depict it, where α = 70°and β = 0°.…”