Barbara Pergolese

Gold/Palladium and Silver/Palladium Colloids as Novel Metallic Substrates for Surface-Enhanced Raman Scattering

New surface-enhanced Raman scattering (SERS) substrates, composed of gold or silver colloidal nanoparticles doped with palladium, were prepared. These novel colloids are stable and maintain a satisfactory SERS efficiency, even after long aging. The interest in doping the coinage metal nanoparticles with palladium is due to the well-known catalytic activity of this metal. Transmission electron microscopy (TEM) and ultraviolet–visible absorption spectroscopy were used to characterize the shape and size of the metal particles. It was found that these bimetallic colloidal nanoparticles have a core–shell structure, with gold or silver coated with palladium clusters.

Surface enhanced Raman spectroscopic studies of 1H-indazole on silver sols

The SER spectra of 1H-indazole adsorbed on silver hydrosol were recorded in the 1800-100 cm(-1) and in the 3200-2800 cm(-1) regions. The SERS data were interpreted on the basis of previous vibrational assignments, with the help of the results of DFT calculations carried out using the 6-31G** basis. From the comparison of SER and normal Raman spectra it can be deduced that 1H-indazole is non-dissociatively adsorbed on metal surface and that it interacts with silver sol via nitrogen atoms and ring pi-system. The molecular plane assumes a tilted orientation with respect to the silver surface. The effect of varying the concentration of adsorbate was also evaluated. The observed changes of the relative intensities of some enhanced bands suggest that the molecule assumes a more tilted orientation upon lowering the concentration of the adsorbate.

Study by SERS spectroscopy of the adsorption of 1H-1,2,4-triazole-3-thione on silver sols

Surface enhanced Raman scattering (SERS) spectra of 1H-1,2,4-triazole-3-thione (TAS) adsorbed on silver sols were recorded. From the comparison between the SERS and normal Raman spectra of TAS in aqueous and in NaOH solutions, it can be deduced that the substance adsorbs in the ionized thiolic form (TASA) on the silver surface. From the description of the vibrational normal modes related to the most enhanced bands in the SERS spectra, it can be deduced that the interaction with the silver sol occurs via the lone pairs of the sulphur and of one of the nitrogen atoms and that the orientation of the tetrazole ring is inclined with respect to the metal surface.

2 H and 14 N Nmr of Cetylpyridinium Bromide Lyotropic and Thermotropic Liquid Crystals

2 H and 14 N NMR spectra of the cationic head group have been recorded for liquid crystalline systems of CPB (cetylpyridinium bromide), pentanol and NaBr brine, at low surfactant content. The 2 H quadrupolar splittings provided the order parameters of the aromatic ring at various temperatures. Using these order parameters, the experimentally determined 14 N quadrupolar splittings allowed the evaluation of the principal values of the nitrogen quadrupole coupling tensor, |C Q |= 0.41 MHz and m =0.39. 2 H quadrupolar splittings measured for the thermotropic liquid crystal given by pure CPB above 71C allowed to calculate the ring order parameters also for this phase. These parameters and the 14 N |C Q | and m values led to 14 N splitting values in very good agreement with those actually observed for this thermotropic ionic liquid crystal.

Vibrational assignments and theoretical calculations of 1-phenyl-5-mercaptotetrazole and 1-phenyl-5-mercaptotetrazolate

The infrared and Raman spectra of 1-phenyl-5-mercaptotetrazole (PMT) and 1-phenyl-5-mercaptotetrazole sodium salt in the solid state and in solution have been measured. Detailed vibrational assignments of PMT and 1-phenyl-5-mercaptotetrazolate (PMTA) have been performed. In order to give a firmer basis to the interpretation of the vibrational spectra, harmonic wavenumbers of PMT and PMTA have been calculated by means of MP2 and DFT/BPW91 calculations. The DFT calculations provide a satisfactory agreement between the calculated and observed wavenumbers without using scaling factors. Experimental evidence shows that PMT is present in the thione tautomer both in the solid state and in solution of polar solvents.

Polarized Infrared and Raman Spectra and Ab-Initio Calculations of 2-(Methylthio)Benzothiazole

Abstract The infrared spectra of 2-(methylthio)benzothiazole have been measured from 4000 to 180 cm−1 for liquid and polycrystalline samples, polarized spectra of oriented films have also been obtained. the Raman spectra of polycrystalline and liquid samples have been investigated. the structural parameters, energies and vibrational frequencies have been calculated from ab-initio RHF calculations using the 6-31G** basis set for various conformations. a detailed assignment of most of the observed bands has been proposed on the basis of the infrared dichroism, Raman polarization data and frequency calculations.