Survival of molecular information under surfaced‐enhanced resonance Raman (SERRS) conditions

Abstract

In the present paper, we discuss the molecular information that can be derived from surface-enhanced resonance Raman Scattering (SERRS) experiments performed with different excitation wavenumbers, which are close to resonance with an excited electronic state of the molecule [surface-enhanced Raman dispersion spectroscopy (SERADIS)]. We specifically consider the situation, where a molecule is physisorbed to a site characterized by a local electric field with a direction independent of the direction of the external, exciting field. The molecular information available in this experimental situation is compared with the information available in a corresponding Raman dispersion spectroscopy (RADIS) experiment performed on a free molecule or a molecule physisorbed to a site, where the local field is isotropic. The consequences for resonance Raman scattering (RRS) and RADIS, when the molecule is adsorbed in the highly anisotropic hot spot (HS), are discussed; here it is shown that only the molecular information originating from the symmetric part of the scattering tensor can survive in SERRS and in SERADIS. Besides, it is shown that the depolarization ratio can no longer be used to discriminate between totally and non-totally symmetric modes in the polarized surface-enhanced Raman scattering (SERS) spectra. These results have implications for the resonance Raman spectra, but even more important for the application of the resonance Raman effect in the investigation of excited vibronic molecular states, in general, and in the investigation of electronic states in larger bio-molecules, such as the various metallo-porphyrins.

Experimental study on polarized surface enhanced resonance Raman scattering of rhodamine 6G adsorbed on porous Al2O3 substrates

“…The polarization parameter will, when considering the molecules adsorbed in the highly anisotropic local electric field in the hot-spots, only depend on the properties of the hot-spot. 23 The polarization parameter is, therefore, independent of the nature of the Raman modes and will not depend on whether the molecules are oriented or randomly oriented. As opposed to this, the polarization parameter will depend on the nature of the Raman modes, when the molecules are adsorbed in the isotropic sites, both when the molecules are oriented and randomly oriented in the site.…”

Quick detection of contaminants leaching from polypropylene centrifuge tubes with surface‐enhanced Raman spectroscopy and ultraviolet absorption spectroscopy

“…As a label-free and noninvasive technique, Raman spectroscopy can provide information on the vibrational mode and symmetry of a molecule and thus can identify the chemical species. [7] Compared to normal Raman spectroscopy, SERS can enhance the Raman signal by several orders of magnitude, which allows this technique to be sensitive enough to detect single molecules. [8] Ultraviolet (UV) absorption spectrometry is another simple and fast quantitative technique for molecular detection and identification but it is not as sensitive as SERS and may damage the structures of organic compounds due to its high photon energy.…”

Polarization characteristics of surface-enhanced Raman scattering from a small number of molecules at the gap of a metal nano-dimer

“…Several interesting polarized SERS studies have been carried out. [5][6][7][8][9][10][11][12][13][14][15][16][17] If one assumes a symmetrical single nano-dimer structure in which only the localized electromagnetic field at the gap contributes to the enhancement, SERS depolarization is not observed because the polarizations for excitation and scattering are the same. Linearly polarized scattered light was observed in a metal nano-dimer system.…”