G. Sbrana

Vapour and crystal spectra in polarized light of pyrimidine-d0 and pyrimidine-d4

Abstract The infra-red spectra of pyrimidine- d 0 and - d 4 have been measured between 4000 and 300 cm −1 in gas, liquid and solid phases. Since the analysis of the rotational band envelopes alone was not sufficient for a definite assignment, useful information was gained from the interpretation of the crystal spectra in polarized light of both isotopic species. A new vibrational assignment is presented which differs from that given previously by L ord et al. for the six fundamentals ν 6 a , ν 19 a , ν 6 b , ν 18 b , ν 19 b , ν 4 . The experimental evidence for the new assignment is discussed in detail.

Spectroscopic investigation and normal mode analysis of As4S4 polymorphs

Abstract Tetra-arsenic tetrasulfide polymorphs have been investigated by IR, Raman and UV-visible spectroscopies. The mineral realgar ( α -As 4 S 4 ) and the high-temperature phase β -As 4 S 4 transform to pararealgar by exposure to monochromatic laser light with a reaction rate depending on the wavelength of the exciting radiation. The photoinduced alteration process has been monitored by Raman spectroscopy, following in real time the spectral changes of the samples undergoing irradiation. A satisfactory assignment of realgar, β -As 4 S 4 and pararealgar was obtained by employing a simplified valence force field which provided a complete set of normal coordinates suitable for describing the vibrational spectra of these As 4 S 4 polymorphs.

Infrared Spectra of Crystalline and Matrix Isolated Pyridine and Pyridine‐D5

Infrared spectra of pyridine‐H5 and pyridine‐D5 in the solid state were measured between 4000 and 200 cm− 1. Frequencies and polarization of fundamental absorptions were established for oriented thin films of freshly crystallized samples. Behavior of the bands in polarized light aided in clarifying several assignments. The multiplicity of several of the bands was accounted for by close‐lying overtones and combinations. Some of the components of ν26 are due to the existence of appreciable amounts of 13C isotope species clearly observable in a nitrogen matrix at 5°K. For pyridine‐D5 a phase transition was clearly observable after several hours of annealing of thin films at about − 60°C, but similar transformation could not be induced in normal pyridine. The infrared crystal data are consistent with an orthorombic factor group established by x‐ray analysis with no molecule on any symmetry element of the crystal. Raman spectra of liquid and solid pyridines are also reported.

Phase transition in crystalline pyrazine. Infrared and Raman spectra

The phase transition of crystalline pyrazine‐d0 and ‐d4 has been investigated by means of the infrared and Raman spectra at various temperatures. The spectra of the low temperature phase (form II) are consistent with x‐ray structure. Inferences on the unknown structure of the high temperature phase (form I) are given, and arguments in favor of an orthorhombic or monoclinic structure are discussed. The complex pattern of several bands is described and attributed to interaction with combination levels.

IR and Raman spectra of A 2,2′-bipyridine single crystal: internal modes☆

The polarized light IR and Raman spectra of 2,2′-bipyridine single crystals were obtained. The oriented gas model was applied and the proportionality factors for the intensity of the IR and Raman bands calculated and compared with experiment. The difficulties encountered while applying the oriented gas model to molecules with C2h symmetry and to monoclinic structures were discussed. An assignment of the internal modes based on the polarized light spectra has been given. The far infrared spectrum of the molecule was also measured and the ring—ring torsional model of Au species was identified at 73 cm−1.

Normal mode analysis of 2,2′-bipyridine—II. Crystal vibrations

Abstract A normal mode analysis of the crystal spectrum of 2,2′-bipyridine was carried out using a previously determined intramolecular force field and an intermolecular potential described in terms of interactions among non-bonded atoms. New i.r. and Raman data in the region of lattice vibrations are presented, which can be satisfactorily accounted for by frequency calculations in the rigid-body approximation. Frequency splittings and shifts of internal modes, mixing with external vibrations and relative intensity of out-of-plane modes are analyzed through calculations at k = 0 which include all vibrational degrees of freedom.

Infra-red and Raman spectra of five-membered heterocyclic molecules—oxazole and thiazole

Abstract The infra-red and Raman spectra of oxazole and thiazole have been measured in different conditions in order to get definite evidence for a complete assignment of the normal vibrations of these ring compounds. The vibrational assignment of oxazole and thiazole is then discussed on the basis of the collected experimental results. The correlation with the normal modes of similar ring molecules is substantiated and discussed.

Surface enhanced Raman scattering of pyrazine adsorbed on silver colloidal particles

Abstract The surface enhaced Raman scattering of pyrazine in a silver sol was investigated. Strong enhancement of the g modes and appearance of Raman forbidden vibrations were observed, in agreement with existing results obtained on electrode surface. Chemical reactions of pyrazine on Ag were monitored by Raman and mass spectroscopy.

Spectroscopic and potentiometric study of copper(II) complexes with l-histidyl-glycyl-l-histidyl-glycine in aqueous solution

Abstract The complex formation between copper(II) and the tetrapeptide l -histidyl-glycyl- l -histidyl-glycine (HL) has been studied in aqueous solution in the pH range 2–10.5, by potentiometric and spectroscopic methods (visible, CD, EPR, 1 H NMR and Raman scattering). Between pH 3 and 6 the species [CuHL] 2+ and [CuH −1 L] have been detected. The former complex co-ordinates through two nitrogen and two oxygen atoms in the equatorial plane while, for the latter, the spectroscopic data (particularly Raman spectra) suggests an unusual structure with the two imidazole rings and two peptide NH in the plane. The species at pH 7, [CuH −2 L] − , is involved in the co-ordination by the amino group, the His 1 imidazole and two peptide nitrogens, while, for the complex [CuH −3 L] 2− , which seems to be predominant in alkaline medium, a third deprotonated backbone NH, replaces the imidazole nucleus.

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.