Chemical interactions of pyridine and cyanide with silver

From a quantitative determination of pyridine and cyanide adsorbed on a silver electrode, by a radiochemical technique, we have shown that the two adsorbate - silver systems are different. After a dissolution - redeposition electrochemical cycle the quantity of pyridine adsorbed depends on the charge transfer. For low charge transfer (<50 mC cm^?2) the quantity increases from three to nine monolayers and depends on the nature of the supporting electrolyte, which suggests the formation of new bonds between pyridine, Ag and the anion of the supporting electrolyte. For high charge transfers the quantity of pyridine increases, the rate of increase depending on the supporting electrolyte (KI>KCl>KClO₄); in our opinion this is due to a trapping of pyridine in the salt formed between the support electrolyte anion and silver. The quantity of pyridine adsorbed at the silver electrode which can be as large as 100 equivalent monolayers can explain part of the enhancement of the Raman signal observed for this system.After a dissolution - redeposition electrochemical cycle the quantity of cyanide adsorbed remains constant, the cyanide - silver system is reversible and the Raman enhancement observed at the rest potential, is due only to Ag-CN interactions.     

Resonance Raman spectra of β-carotene and its molecular structure in the excited electronic state

The resonance Raman spectra of β-carotene have been obtained at low temperature. The excitation profiles of ν₁ (1525 cm^?1) and 2ν₁ (3043 cm^?1) are analysed in terms of the Albrecht theory. The overlap integrals between the vibrational wavefunctions of the ground and the first excited electronic states are shown to be the most important factor in determining the resonance Raman intensities of this molecule. Information on the structure of the electronically excited state has been obtained.     

IR,Raman, and Surface‐enhanced Raman Spectroscopic Study on Triruthenium Dipyridylamide Diruthenium Nickel Dipyridylamide Family: Metal‐metal Bonding and Structures

We report the infrared, Raman, and surface‐enhanced Raman scattering (SERS) spectra of triruthenium dipyridylamido complexes and of diruthenium mixed nickel metal‐string complexes. From the results of analysis on the vibrational modes, we assigned their vibrational frequencies and structures. The infrared band at 323–326 cm^?1 is assigned to the Ru₃ asymmetric stretching mode for [Ru₃(dpa)₄Cl₂]^0–2+. In these complexes we observed no Raman band corresponding to the Ru₃ symmetric stretching mode although this mode is expected to have substantial Raman intensity. There is no frequency shift in the Ru₃ asymmetric stretching modes for the complexes with varied oxidational states. No splitting in Raman spectra for the pyridyl breathing line indicates similar bonding environment for both pyridyls in dpa^– , thus a delocalized structure in the [Ru₃]^6–8+ unit is proposed. For Ru₃(dpa)₄(CN)₂ complex series, we assign the infrared band at 302 cm^?1 to the Ru₃ asymmetric stretching mode and the weak Raman line at 285 cm^?1 to the Ru₃ symmetric stretching. Coordination to the strong axial ligand CN^– weakens the Ru‐Ru bonding. For the diruthenium nickel complex [Ru₂Ni(dpa)₄Cl₂]^0–1+, the diruthenium stretching mode ν_Ru‐Ru is assigned to the intense band at 327 and 333 cm^?1 in the Raman spectra for the neutral and oxidized forms, respectively. This implies a strong Ru‐Ru metal‐metal bonding.     

Kinetics of silver electrodeposition from thiocarbamide solutions at a regular surface coverage with sulfide ions

Kinetics of silver electrodeposition in the presence of sulfide ions is studied on electrodes renewed by cutting off a thin surface layer, at a controlled time of contact of the “fresh” surface with the electrolyte. Solutions containing 10^?2 M AgNO₃, 0.1 M thiocarbamide, 0.5 M HClO₄, and from 2 × 10^?6 to 1.5 × 10^?5 M Na₂S are studied. It is shown that under the studied conditions, the effect of silver electrodeposition on the surface concentration of sulfide ions is insignificant. As the concentration of sulfide ions in solution and their coverage on the electrode surface θ increase, the cathodic polarization decreases. Tafel curves plotted for θ = const are used in estimating the exchange current i ₀ and the transfer coefficient α. It is shown that α ≈ 0.5 and weakly depends on θ, whereas the exchange current increases with the increase in θ by an approximately linear law from 10^?5 A/cm² at θ ? 0 to 10^?4 A/cm² at θ = 0.43. The obtained data are compared with the results of kinetic studies of silver anodic dissolution in similar solutions.     

A Raman spectroscopic study of the antimonite mineral peretaite Ca(SbO)4(OH)2(SO4)2·2H2O

Raman spectra of mineral peretaite Ca(SbO)₄(OH)₂(SO₄)₂·2H₂O were studied, and related to the structure of the mineral. Raman bands observed at 978 and 980 cm^?1 and a series of overlapping bands observed at 1060, 1092, 1115, 1142 and 1152 cm^?1 are assigned to the SO₄^2? ν₁ symmetric and ν₃ antisymmetric stretching modes. Raman bands at 589 and 595 cm^?1 are attributed to the SbO symmetric stretching vibrations. The low intensity Raman bands at 650 and 710 cm^?1 may be attributed to SbO antisymmetric stretching modes. Raman bands at 610 cm^?1 and at 417, 434 and 482 cm^?1 are assigned to the SO₄^2? ν₄ and ν₂ bending modes, respectively. Raman bands at 337 and 373 cm^?1 are assigned to O–Sb–O bending modes. Multiple Raman bands for both SO₄^2? and SbO stretching vibrations support the concept of the non-equivalence of these units in the peretaite structure.     

Microstructural and Potential Dependence Studies of Urease-Immobilized Gold Nanoparticles–Polypyrrole Composite Film for Urea Detection

Gold nanoparticle–polypyrrole nanocomposite film was electrochemically deposited in a single-step polymerization of pyrrole in the presence of 3-mercaptopropionic acid (MPA)-capped gold nanoparticles (GNPs) and p-toluenesulfonic acid (pTSA) on the surface of an indium tin oxide (ITO)-coated glass plate. The carboxyl functional groups surrounding the GNPs within the polymer matrix were utilized for the immobilization of urease enzyme through carbodiimide coupling reaction for the construction of a Urs/GNP(MPA)–PPy/ITO-glass bioelectrode for urea detection in Tris–HCl buffer. The resulting bioelectrode film was characterized by atomic force microscopy (AFM), high-resolution transmission electron microscopy (HRTEM), contact angle measurement, Fourier transform infrared spectroscopy (FTIR), and electrochemical techniques. The potentiometric response of the bioelectrode made of polymer nanocomposite films of two different thicknesses prepared at 100 and 250 mC cm^?2 charge densities, respectively, was studied towards the urea concentration in Tris–HCl buffer (pH 7.4). The thin polymer nanocomposite film-based bioelectrode prepared at 100 mC cm^?2 charge density exhibited a comparatively good potentiometric response than a thick 250 mC cm^?2 charge density film with a linear range of urea detection from 0.01 to 10 mM with a sensitivity of 29.7 mV per decade.     

Raman and Photoluminescence Spectroscopic Detection of Surface‐Bound Li+O2− Defect Sites in Li‐Doped ZnO Nanocrystals Derived from Molecular Precursors

We present a detailed study of Raman spectroscopy and photoluminescence measurements on Li‐doped ZnO nanocrystals with varying lithium concentrations. The samples were prepared starting from molecular precursors at low temperature. The Raman spectra revealed several sharp lines in the range of 100–200 cm^?1, which are attributed to acoustical phonons. In the high‐energy range two peaks were observed at 735 cm^?1 and 1090 cm^?1. Excitation‐dependent Raman spectroscopy of the 1090 cm^?1 mode revealed resonance enhancement at excitation energies around 2.2 eV. This energy coincides with an emission band in the photoluminescence spectra. The emission is attributed to the deep lithium acceptor and intrinsic point defects such as oxygen vacancies. Based on the combined Raman and PL results, we introduce a model of surface‐bound LiO₂ defect sites, that is, the presence of Li⁺O₂^? superoxide. Accordingly, the observed Raman peaks at 735 cm^?1 and 1090 cm^?1 are assigned to Li? O and O? O vibrations of LiO₂.     

Surface enhanced Raman spectra of nucleic acid components adsorbed at a silver electrode

High-resolution vibrational spectra of nucleic acid components adsorbed on a silver electrode were obtained using a spectroelectrochemical method based on the large-intensity enhancement for Raman scattering at electrode surfaces.The laser surface Raman spectra of purine, adenine, adenosine, deoxyadenosine, adenine mononucleotides, adenylyl-3′, 5′-adenosine and polyriboadenylic acid were recorded in the range of 150–3500 cm^?1. The intensities of the vibrational bands were highly dependent upon the electrochemical preparation of the electrode, the applied potential and the nature of the adsorbate species. High-intensity spectra in rather dilute bulk solutions were obtained.The phosphate derivatives of adenosine exhibited strongly enhanced Raman scattering. Spectral band frequencies corresponded closely with normal Raman spectra of these molecules in solution. The adenine ring breathing mode at 740 cm^?1 and the adenine ring skeletal vibration at 1335 cm^?1 produced prominent Raman scattering. A strong band at about 240 cm^?1 for the adenine mononucleotides was attributed to silver/adsorbed phosphate group vibrations.     

Microspectrometric investigation of active substrates for surface enhanced Raman scattering

The results of investigations of several new active silver substrates and some previously reported active silver substrates for surface enhanced Raman spectrometry (SERS) using a Raman microprobe are given. Filter-papers of different composition and porosity, silver membranes and glass slides are evaluated as supports for SERS active substrates. Methods of silver preparation include evaporation and chemical reduction. The Raman microprobe facilitates the acquisition of SER spectra of the adsorbate over the metal microstructure being observed on a TV monitor. This capability allows the establishment of practical relationships between the surface morphology and SERS activity which can be used as guidelines for SERS experiments with the microprobe. For the most monodisperse substrates, it is possible to establish a linear relationship between SERS intensity and adsorbate concentration. In the lower extreme of the calibration graph, the amount of adsorbate being observed under the microscope objective is only 0.3 amol or 1.9 × 10⁵ molecules.     

Raman analysis of SF6 molecular beams excited by a cw CO2 laser

In a molecular beam the effects of vibrational pumping of SF₆ (ν₃ = 948 cm^?1) are studied, using a line-tunable cw CO₂ laser. Intracavity spontaneous Raman scattering is used for analysis. For excitation in the collision regime (x_E/D ≤ 1), a thermal redistribution of the ν₃ excitation over all vibrational modes is found, together with an average absorption up to six photons per molecule. The infrared absorption profile shows a red-shift of 6 cm^?1. For excitation in the relatively rare collision regime (x_E/D ? 4), a structured non-thermal ν₁ Raman spectrum is observed, especially in the case of seeded molecular beams (10% in He). The observed hot-band peaks can be explained in terms of single-photon absorptions and collision-induced near-resonant V-V energy transfer, leading to single, double and triple excitations of the ν₃ mode. The value of T_rot in the beam is found to influence sensitively the non-resonant energy-transfer rate [e.g. hν₃(948 cm^?1)+ΔE_rot → h(ν₄ + ν₆)(962 cm^?1) relative to the near-resonant transfer rate (hν₃ + hν₃ → 2hν₃ + 3.5 cm^?1)].     

Vibrational spectrum and conformation of cyclopropyldichloroborane

The infrared (3500-40 cm^?1) and Raman spectra (3200-0 cm^?1) have been recorded for cyclopropyldichloroborane in both the gaseous and solid states. Additionally, the Raman spectrum of the liquid was recorded and qualitative depolarization values obtained. Only one conformation has been found in all three physical states and, on the basis of the polarized nature of the Raman band assigned as the BCl₂ antisymmetric stretch, this conformer has been identified as being the bisected structure with C_s molecular symmetry. A complete vibrational assignment is proposed based on Raman depolarization data, infrared gas phase band contours, and group frequencies. These results are compared with the corresponding data in other organoboranes.     

Kinetics and mechanism of gold dissolution in thiourea solutions: Effect of sulfide ions

Chronoamperograms for gold in solutions containing 0.1 M thiourea, 0.5 M H₂SO₄, and catalytically active sulfide ions at the concentration c ₁ from 1 × 10^?5 to 4 × 10^?5 M are obtained at different potentials with the aid of an automated setup intended for renewing the electrode surface directly in the solution by cutting off a thin surface layer of the metal. It is shown that the results of measurements of the current practically coincide at a constant value of the product c ₁ t, where t is the time period elapsed after the renewal of the electrode surface. Such a coincidence testifies to a diffusion nature of processes that hamper accumulation of sulfide ions at the gold surface. This fact permitted the use of a procedure developed previously for the calculation of polarization curves at constant values of surface coverage θ by catalytically active ions. At θ = const, the voltammetric curves for gold in sulfide-containing thiourea solutions are shown to correspond to the Tafel equation. With the surface coverage increasing, the effective values of the exchange current i ₀, transfer coefficient α, and anodic reaction order with respect to thiourea P _a increase from the values i }~ 10^?5 A cm^?2, α }~ 0.12, and P _a = 0.2, which are characteristic of pure solutions, to 2 × 10^?4 A cm^?2, α }~ 0.5, and P _a = 1.1 (at θ }~ 0.5). An interpretation to the established regularities is given.     

Matrix Raman studies of Bin(n ⩾ 2) molecules

Resonance Raman spectra of bismuth molecules reveal two progressions with ω_e = 172 and 152 cm^?1 The metal concentration dependence allows us to assign the 172 cm^?1 band to Bi₂ and the 152 cm^?1 band to a larger molecule, most likely Bi₄. Thus the existence of an X' ground state of Bi₂ ≈ 1500 cm^?1 below the X state can be excluded.     

A Raman spectroscopic study of the low-frequency vibrations in anisole and anisole-d3

Low-frequency Raman spectra of solid anisole and of solid anisole-d₃ have been recorded at 130 K. The phenyl torsion observed at 148 cm^?1 is shifted to 133 cm^?1 upon deuteration of the methyl group. The twofold torsional barriers calculated from these frequencies are 4033 ± 110 cm^?1 and 4094 ± 123 cm^?1 indicating that coupling to other low-frequency modes in both cases is of the same order of magnitude. The methyl torsional mode was observed at 285 cm^?1 in the spectrum of solid anisole and at 183 cm^?1 in the spectrum of anisole-d₃. The threefold barriers calculated using these frequencies are 1847 ± 20 cm^?1 and 1465 ± 18 cm^?1 respectively. These barrier values indicate that the methyl torsion is coupled to another low-frequency mode. A doublet centered at 230 cm^?1 in anisole is shifted to 245 cm^?1 in anisole-d₃; it is proposed that this is due to a ring mode coupled to the methyl torsion. The splitting is interpreted as an example of Davydov splitting.     

Adsorption of cinnamaldehyde at the mercury-water interface

The adsorption of cinnamaldehyde from aqueous 1 M KCl has been determined by means of differential capacity, zero charge potential and maximum surface tension measurements. A Frumkin isotherm is obeyed with α = 2.4, corresponding to repulsive interaction, and Γ_s= 3.5 × 10^?10 mol cm^?2, which is independent of potential in the range ?350/?750 mV. The standard free energy of adsorption is a quadratic function of potential with maximum adsorption occurring at the potential of zero charge. The interaction of the molecular dipole with the electric field and the partial charge transfer between the electrode and the adsorbate are considered.     

CN stretching and NO2 deformation vibrations and normal coordinate analysis of m-dinitrobenzene and m-dinitrobenzene-d4

Two bands appear for each CN stretching and nitro deformation vibration in the infrared and Raman spectra of m-dinitrobenzene and m-dinitrobenzene-d₄. The 907 cm^?1 bending mode in the vibrational spectra of m-dinitrobenzene undergo 30 cm^?1 upward shift upon d₄ substitution. A normal coordinate analysis pointed out that the 937 cm^?1 bending and 727 cm^?1 CN stretching vibrations as well as 18b CD in-plane deformation are mixed to a great extent. The other nitro bending mode undergo also an inverse isotopic effect (2 cm^?1 upward shift) due to coupling with the 18a CD in-plane deformation vibration.     

Resonance raman spectra of würster's cation dimers: p-phenylenediamine and 2,3,5,6-tetramethyl-p-phenylenediamine

Resonance Raman spectra have been observed for the dimers of p-phenylenediamine cation (PPD⁺) and of 2,3,5,6-tetramethyl-p-phenylenediamine cation (TMPD⁺). When the exciting light frequency approached the absorption bands characteristic of the dimers, new polarized Raman lines appeared at 161 cm^?1 for (PPD⁺)₂ and at 117 cm^?1 for (TMPD⁺)₂ with a striking resonance enhancement. The resonant behaviour as well as the frequency values indicate that they are reasonably assigned to the interradical stretching vibrations of the parallel D_2h dimer molecules.     

Raman spectra of gases: XIV. Hexachlorodisiloxane

The Raman spectra (50–1200 cm^?1) of gaseous, liquid, and solid (Cl₃Si)₂O have been recorded. The infrared spectra of the gas and solid have been recorded from 55–2000 cm^?1 . The spectra of the gas have been interpreted in detail on the basis of C_2v symmetry with the A₁ skeletal Si-O-Si bend assigned at 63 cm^?1. The spectra gave evidence that there are structural changes upon condensation of the gas and the Si-O-Si angle approaches linearity in the solid state. The opening of this angle is probably due to crystal packing factors.     

Electrosorption of β-naphthol on graphite

Isotherms for the adsorption of β-naphthol from a buffered aqueous solution of 0.5 M K₂SO₄ onto graphite were detemrined over a range of potential of 1.27 V. The adsorbent was a packed bed of ?100 + 120 mesh graphite powder. Sufficient surface area was available to calculate accurately the amount adsorbed by measuring spectrophotometrically the change in adsorbate concentration in the bulk solution.At all potentials, a Langmuir adsorption isotherm, modified for the displacement of solvent molecules, was followed up to 60–65% of monolayer coverage. The ratio of projected areas of β-naphthol and water molecules was consistent with the experimentally derived number of solvent molecules displaced, six. The largest amount of adsorption observed, 2.5×10^?10 mol cm^?2, agreed with the calculated monolayer coverage of β-naphthol molecules lying in flat orientation on the graphite surface. Adsorption increased at more positive potentials. Over the range of potential investigated, the adsorbability constant increased sixfold. Desorption was only partially reversible.     

The effect of thallium ions on the gold dissolution rate in thiosulfate electrolytes

The effect of TlNO₃ additions in the concentration (c ₁) range from 5 × 10^?6 to 1 × 10^?4 M on the anodic dissolution of gold in sodium thiosulfate solutions with the concentration (c ₂) from 0.005 to 0.2 M is studied by voltammetry on the electrode surface renewed by cutting off a thin metal layer immediately in solution and also by the quartz-crystal microbalance method. For c ₂ = 0.2 M, as c ₁ increases from 5 × 10^?6 to 1 × 10^?4 M, the gold anodic dissolution rate is observed to increase from 0.02 (in the absence of TlNO₃) to 0.75 mA/cm² for c ₁ = 7.5 × 10^?5 M according to a nearly linear law. The dissolution accelerates because the effective values of the transfer coefficient and the exchange current density increase from 0.2 and 4 ??A/cm² (in the absence of TlNO₃ admixtures) to 0.47 and 35 ??A/cm² (for c ₁ = 1 × 10^?4), respectively. Experiments with the renewal of the electrode surface in the course of electrolysis suggest that the gold dissolution is catalyzed in the presence of thallium ions by the adsorption mechanism and also as the result of the mixed kinetics of their adsorption on the electrode surface.