Download or read book Observation of a Reversible Adsorbed Redox Couple Using Surface Enhanced Raman Scattering Pentaamminepyridineosmium III II at Silver Electrodes written by Stuart Farquharson and published by . This book was released on 1983 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt: Surface-enhanced Raman scattering (SERS) has been observed for pentaamminepyridineosmium(III) adsorbed at a silver electrode as a function of electrode potential in order to examine the molecular vibrational changes of electrode potential in order to examine the molecular vibrational changes accompanying electron transfer involving a simple surface-bound redox couple. Noticeable alterations in the intensity and frequency of several vibrational bands involving osmium-ligand and pyridine ring modes were observed as the electrode potential was made more negative which are consistent with a variation of the osmium oxidation state from III to II. The effective formal potential for the adsorbed Os(III)/(II) couple determined from SERS, ca -630 mV vs sce, is in reasonable agreement with that obtained from rapid cyclic voltammetry, illustrating the value of SERS for monitoring electron-transfer processes at metal surfaces. (Author).
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1983 with total page 784 pages. Available in PDF, EPUB and Kindle. Book excerpt: Lists citations with abstracts for aerospace related reports obtained from world wide sources and announces documents that have recently been entered into the NASA Scientific and Technical Information Database.
Download or read book Government Reports Announcements Index written by and published by . This book was released on 1983 with total page 1428 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Surface enhanced Raman Scattering from a Modified Silver Electrode written by and published by . This book was released on 2002 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Electrochemical and spectroelectrochemical data was obtained for a silver electrode modified with oxazine 720. A quasi-reversible redox behaviour was observed for the modified electrode. Surface adsorption density, calculated from the measured electrochemical charge transfer, is higher than would be expected for a monolayer of flat-adsorbed oxazine 720. Surface-enhanced Raman scattering (SERS) data, in conjunction with results of a density functional theory (DFT) calculation, suggest that the molecule is adsorbed with its rings perpendicular to the electrode surface, consistent with the electrochemically estimated adsorption density. SERS was recorded in situ at different applied potentials. The SERS intensity remains relatively stable between -200 and -500 mV (versus AglAgCl Cl-sat), but decreases dramatically as the applied potential is made more negative than -500 mV. Ths is consistent with the onset of oxazine 720 reduction observed during cyclic voltammetry. The spectroelectrochemical data indicates that oxazine 720 remains adsorbed at the SERS-active sites even in its reduced form. Similar in situ SERS data was collected for rhodamine 6G and pyridine. Spectra in the Stokes and anti-Stokes regions were obtained at several applied potentials using two different laser excitation energies. Normalized ratios of the anti-Stokes to Stokes intensities were calculated for various vibrational bands of the three molecules. The measured ratios vary with changes in the excitation energy, the applied voltage and the energy of the vibrational mode being investigated. The ratios for oxazine 720 show a preferential enhancement of the Stokes scattering while the ratios for rhodamine 6G indicate an enhancement of the anti-Stokes scattering. For pyridine, the preferential enhancement changes between Stokes and anti-Stokes depending on the excitation wavelength used, the applied voltage and the vibrational band being examined. The main trends of the anti-Stokes to Stokes ratios ca.
Download or read book Government Reports Annual Index written by and published by . This book was released on 1983 with total page 1166 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Surface Enhanced Raman Scattering for Redox Active Adsorbates Pentaammineosmium III II and Pentaammineruthenium II Containing Nitrogen Heterocycle Ligands written by S. Farquharson and published by . This book was released on 1984 with total page 32 pages. Available in PDF, EPUB and Kindle. Book excerpt: Surface-Enhanced Raman Scattering (SERS) for pentaammineosmium (III) and pentaammineruthenium(II) containing pyridine (py), pyrazine (pz), or 4,4'-bipyridine (bpy) ligands adsorbed at the silver-aqueous interface has been examined as a function of electrode potential to explore vibrational changes associated with electron transfer involving simple adsorbates. SERS was observed for the pyridine complexes despite their lack of an unshared electron pair for surface binding, although more intense spectra were obtained for the pyrzine and bipyridine complexes which contain a remote nitrogen lone pair. SER vibrational bands for metal-ligand and internal ammine modes were observed in addition to those due to heterocycle ring modes. Marked shifts were observed in the frequency of several, vibrational bands for adsorbed Os(NH3)5py and Os(NH3)5pz as the electrode potential was made more negative that are consistent with the reduction fo Os(III) to Os(II). The potential-dependent concentrations of adsorbed Os(III) and Os(II) as determined using SERS are in good agreement with those obtained from rapid cyclic voltammetry. The bulk-phase Raman spectra exhibit resonance enhancement.
Download or read book Interference Problems on Wing fuselage Combinations in Inviscid Incompressible Flow written by Aeronautical Research Council (Great Britain) and published by . This book was released on 1974 with total page 1212 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Surface enhanced Raman Scattering from a Modified Silver Electrode written by Aaron Craig Sanderson and published by . This book was released on 2007 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Effect of Low Illumination During Oxidation Reduction Cycles Upon Surface Enhanced Raman Scattering from Silver Electrodes written by F. Barz and published by . This book was released on 1982 with total page 16 pages. Available in PDF, EPUB and Kindle. Book excerpt: The intensity of surface-enhanced Raman scattering from thiocyanate and chloride adsorbed at silver electrodes is shown to depend critically on whether the electrode is illuminated during the oxidation-reduction cycle (ORC) used to pretreat the electrode. The nature and magnitude of the photoeffect is dependent upon the type of surface vibrational mode, the adsorbate, and the wavelength of the irradiation during the ORC. (Author).
Download or read book Observation of Surface Enhanced Raman Scattering for Transition Metal Hexaammine Cations at the Outer Helmholtz Plane Implications for Enhancement Mechanisms at Electrochemical Interfaces written by M. A. Tadayyoni and published by . This book was released on 1983 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt: The recent observation of surface-enhanced Raman scattering (SERS) for a variety of adsorbates at silver in electrochemical and gas-phase environments has generated a plethora of theoretical models to account for the remarkable (ca. 1,000,000 fold) observed enhancement of the Raman scattering intensities. These models can be divided into those demanding only the presence of the Raman scatterer at or close to the metal surface ('physical models'), and those requiring specific adsorbate-surface interactions ('chemical models'). Prompted in part by the especially intense SERS seen for specifically adsorbed species at silver electrodes, a widely held viewpoint is that the enhancement is due in part to chemical interactions between the Raman scatterer and the metal surface, possibly involving as adsorbate-adatom 'complex'. The report examines SERS of inorganic adsorbates at silver-aqueous interfaces. One objective is to examine systematically how the SER spectra are influenced by the nature of the adsorbate-surface interactions. A valuable class of adsorbates for this purpose is provided by substitutionally-inert Cr(III), Co(III), Ru(III) and Os(III) ammine complexes containing ligands such as thiocyanate, bromide, or pyrazine that bind strongly to silver electrodes.
Download or read book Surface Enhanced Raman Scattering from OH Adsorbed on a Ag Electrode in Dilute Mg 2 Electrolytes written by Paul B. Dorain and published by . This book was released on 1987 with total page 21 pages. Available in PDF, EPUB and Kindle. Book excerpt: Surface enhanced Raman scattering (SERS) has been used to probe the adsorption of OH( - ) on a silver electrode immersed in .01 to .001 M MgC12 containing micromolar quantities of either KMnO4 or dissolved C12. Strong spectra due to adsorbed OH( - ), nearly identical to those obtained previously in> or = 1M MgC12 solutions, were obtained only if the oxidizing agent present. Besides the O-H stretching modes near 3600/cm, the low frequency modes due to the metal oxygen stretch are observed. A model is proposed in which adsorbed Mg+2 provides positive surface charge densities which are sites for absorbing OH( - ). Three distinct absorption sites are predicted which is in accord with the observation of three O-H species during H2 production. These results, together with those previously obtained for alkali halides, indicate that corrosion processes in dilute aqueous media proceed by pathways dependent on the concentration and composition of dissolved salts which strongly affect the surface of water and its derivatives. Keywords: Surface enhanced Raman scattering, Adsorbed, Hydroxides, Magnesium ions.
Download or read book Surface Enhancement Factors for Raman Scattering at Silver Electrodes Role of Adsorbate Surface Interactions and Electronic Structure written by M. J. Weaver and published by . This book was released on 1985 with total page 31 pages. Available in PDF, EPUB and Kindle. Book excerpt: The integrated Raman band intensities for internal vibrational modes of various adsorbates at roughened silver electrodes are combined with surface concentrations obtained electrochemically to yield surface Raman scattering cross sections. These data together with the corresponding bulk-phase Raman intensities provide estimates of the degree of enhancement of the vibrational bands at the silver surface with respect to the bulk medium, i.e., the surface enhancement factors (SEF). For surface-attached thiocyanate, isothiocyanate-bridged Cr(III) complexes, and also for Cr(III) and Co(III) hexammines that are electrostatically attracted to chloride-coated silver, SEF values are obtained that are relatively insensitive to both the vibrational mode and the adsorbate, even though substantial (up to 500 fold) variations are observed in the Raman cross sections. This finding applies to stretching modes involving nonbridging ammine groups as well as to bridging thiocyanate modes, although the frequencies of the latter, but not of the former, are perturbed strongly by the silver surface. Comparisons were also made between Raman cross sections, surface enhancement factors, and excitation profiles for pyrazinepentaammineosmium(III) and (II) to explore the influence of electronic resonance since the Os(II) form displays an intense charge-transfer band in the vicinity of the laser wavelengths (460-650 nm) employed. A pronounced peak in the Os(II) excitation profile, absent for Os(III), is obtained that is markedly (ca. 100 nm) red shifted for the adsorbed versus bulk complex.
Download or read book The Surface Enhanced Raman Scattering of the Protonated Forms of DABCO at a Silver Electrode written by David A. Guzonas and published by . This book was released on 1988 with total page 48 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Surface Enhanced Raman Spectra of the aliphatic diamine 1.4 diazabicyclo2.2.2octane (DABCO) from a silver electrode have been measured as a function of the bulk solution pH. The SER spectrum of the diprotonated DABCO molecule at pH = 1.8 is almost identical to the normal Raman spectrum of the bulk solution at the same pH, in contrast to the SER spectrum of the unprotonated DABCO molecule at pH=12, which shows large differences from the spectrum of the bulk solution at pH = 12. It is proposed that the diprotonated DABCO molecule is co-adsorbed with specifically adsorbed anions, e.g. CT, and that its spectrum is enhanced by the electromagnetic enhancement mechanism alone. At intermediate pH values, all three possible forms (di, mono and unprotonated) of DABCO are observed, in amounts strongly dependent upon the electrode potential. Both band deconvolution and factor analysis were used to quantify relative populations. (AW).
Download or read book Surface Enhanced Raman Spectroscopy of Electrochemically Characterized Interfaces Transition Metal Isothiocyanate Adsorbates at Silver Adsorbates written by M. A. Tadayyoni and published by . This book was released on 1984 with total page 32 pages. Available in PDF, EPUB and Kindle. Book excerpt: Surface-enhanced Raman (SER) spectra have been obtained at the silver-aqueous interface for nine Cr III, Co III, Ru II, and Rh III ammine or ethylenediamine complexes containing one or more thiocyanates as surface bridging groups. These complexes provide stereochemically well-defined adsorbates having at least one sulfur surface binding site but with electronic properties that differ substantially from thiocyanate itself. The dependence of the SER spectra were examined in each case over a potential range where the complexes are stable with respect to reduction or oxidation, and where the adsorbate coverage remained close to a monolayer. The adsorbate coverage could be evaluated in several cases from the faradaic charge required for one-electron reduction. SER spectra were obtained using a spectrograph-optical multichannel analyzer (OMA) as well as a conventional scanning spectrometer. This enabled the rapid reversible component of the SERS potential dependence to be separated from the irreversible signal decay associated with surface rearrangement. SERS bands due to metal ammine and internal ammine vibrations were observed in addition to those associated with internal thiocyanate and ligand-surface vibrations.
Download or read book Surface Enhanced Raman Spectroscopy of Pentaammineosmium III II and Pentaammineruthernium II Containing Pyridine Pyrazine Or 4 4 Bipyridine Ligands at Silver Electrodes Vibrational Assignments written by S. Farquharson and published by . This book was released on 1984 with total page 32 pages. Available in PDF, EPUB and Kindle. Book excerpt: Detailed vibrational assignments are described for Surface Enhanced Raman (SER) spectra of pentaamminoeosmium(III), (II) and pentaammineruthenium(II) containing pyridine (py), pyrazine (pz), and 4,4'-bipyridine (bpy) ligands adsorbed at the silver-aqueous interface. The assignments are based on group symmetry analysis, deuteration effects, and by comparison with corresponding normal Raman and infrared spectra for the solid-phase complexes and surface and bulk Raman spectra for the corresponding free ligands. Most bands present in the normal Raman and/or infrared spectra also appear in the SER spectra. This results from the high intensity of the SER spectra along with the relaxation of vibrational selection rules for adsorbed molecules. The appearance of intense SER spectra for Os(NH3)5py(III)/(II) and RuII(NH3)5py is noteworthy since unlike free pyridine, these lack an available nitrogen for surface coordination. The results illustrate the virtues of electrochemical SER spectroscopy for examining the detailed vibrational properties of coordination compounds, including those in oxidation states (such as Os(II) here) that are difficult to obtain pure in bulk media. (Author).
Download or read book Surface Enhanced Raman Scattering from Silver Electrodes written by Gary Richard Trott and published by . This book was released on 1981 with total page 122 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book An Examination of the Relationship Between Surface Enhanced Raman Scattering SERS Intensities and Surface Concentration for Pyridine Adsorbed at the Polycrystalline Gold Aqueous Solution Interface written by L. Stolberg and published by . This book was released on 1990 with total page 49 pages. Available in PDF, EPUB and Kindle. Book excerpt: Surface enhanced Raman scattering (SERS) data are presented for pyridine adsorbed onto both smooth and roughened polycrystalline gold electrode surfaces. It was found that, for smooth surfaces, time independent (stable to within 10% of the initial value) intensities of the totally symmetric ring breathing mode of pyridine could be measured by applying slow oxidation-reduction cycles between each intensity measurement. The potential and concentration dependence of the intensity of the band was therefore determined. Independently, the isotherms for pyridine adsorption at smooth polycrystalline gold surfaces were obtained using chronocoulometry. The SERS data are compared to the surface concentration coverages and deviate, becoming inverse, above half coverage concentrations. Lastly, the effect of surface roughness on the potential and concentration dependence of pyridine SERS was studied. No correlation between the SERS data from rough electrode surfaces and adsorption isotherms determined at a smooth surface was found. Keywords: Surface enhanced Raman scattering; Gold surfaces; Correlation; Surface concentration; Electrochemical measurements; Raman intensity. (jes).
