Theoretical Vibrational Raman and Surface‐Enhanced Raman Scattering Spectra of Water Interacting with Silver Clusters

Abstract

In this study, we analyzed the Raman spectrum of a water molecule adsorbed on a cluster of 20 silver atoms, and the plasmonic electromagnetic effect of the silver surface was also considered to give a theoretical prediction of the surface-enhanced Raman scattering spectrum. The calculations were performed at the density functional theory (DFT) level by using both frozen and unfrozen silver clusters. Two different models were used to consider the plasmonic enhancement; one of them was a modified classical (dipole) model and the other was the coupled perturbed Hartree-Fock method with excitation frequencies obtained from time-dependent DFT calculations and with proper detuning of these frequencies. The importance of small geometrical distortions of the silver surface in the orientation of the adsorbed water was shown. Moreover, it was shown how the symmetry of the transition dipole moment and the symmetry of the vibrational modes influence the Raman intensities of the SERS spectrum.

On the mechanism responsible of Raman enhancement on carbon allotropes surfaces: the role of molecule‐surface vibrational coupling in SERS

“…Raman intensities are usually represented by the differential Raman scattering cross section, which is directly calculated from the Raman activity (or Raman scattering factor). However, we have directly employed in this work the Raman activities (given in Å 4 /amu) to represent the spectra as the relative intensities are quite similar to those obtained from Raman scattering cross sections . The Raman activity for a given vibrational mode k , R k , is obtained from the following expression, where and are the isotropic and anisotropic invariants of the Raman tensor, .…”

“…Those transitions from the ground state with larger oscillator strength were chosen as excitation wavelengths for the calculation of the Raman activities. However, the calculation of the frequency‐dependent polarizabilities can diverge at exact resonance conditions and can be solved following two ways: introducing a damping parameter into the frequency‐dependent polarizability expression or using a small detuning of the excitation frequency . In this work, we have followed the second way and a detailed effect of the excitation wavelength on the Raman spectra of the pyridine–C54 complex was performed.…”

SERS Chemical Enhancement of Water Molecules from Halide Ion Coadsorption and Photoinduced Charge Transfer on Silver Electrodes

“…31 Recently, Sancheź-Lozano et al investigated the SERS spectra of water interacting with a 20-atom silver cluster, and proposed that the symmetry of the dipole moment and the symmetry of the vibrational modes influence the Raman intensities of the SERS spectrum. 32 All these above studies focused on the Raman signals of water molecule or hydrated species interacting directly with metal cathodes only. Furthermore, Zhang et al calculated electronic ground and excited states of water molecules on silver clusters and discussed the influence of the photoinduced electron transfer (PICT) excitation on dissociation of water.…”

“…Then, the charge transfer from the interfacial electron to a hydrated proton were proposed to contribute to the SERS signals of interfacial water . Recently, Sanchéz-Lozano et al investigated the SERS spectra of water interacting with a 20-atom silver cluster, and proposed that the symmetry of the dipole moment and the symmetry of the vibrational modes influence the Raman intensities of the SERS spectrum . All these above studies focused on the Raman signals of water molecule or hydrated species interacting directly with metal cathodes only.…”