Spectroscopic investigations of Nd3+ doped flouro- and chloro-borate glasses

Spectroscopic and physical properties of Nd(3+) doped sodium lead flouro- and chloro-borate glasses of the type 20NaX-30PbO-49.5B(2)O(3)-0.5Nd(2)O(3) (X=F and Cl) have been investigated. Optical absorption spectra have been used to determine the Slater Condon (F(2), F(4), and F(6)), spin orbit xi(4f) and Racah parameters (E(1), E(2), and E(3)). The oscillator strengths and the intensity parameters Omega(2), Omega(4) and Omega(6) have been determined by the Judd-Ofelt theory, which in turn provide the radiative transition probability (A), total transition probability (A(T)), radiative lifetime (tau(R)) and branching ratio (beta) for the fluorescent level (4)F(3/2). The lasing efficiency of the prepared glasses has been characterized by the spectroscopic quality factor (Omega(4)/Omega(6)), the value of which is in the range of 0.2-1.5, typical for Nd(3+) in different laser hosts. Nephelauxetic effect results in a red shift in the energy levels of Nd(3+) for chloroborate glass. The radiative transition probability of the potential lasing transition (4)F(3/2)-->(4)I(11/2) of Nd(3+) ions is found to be higher for flouroborate as compared to chloroborate glass.     

Spectroscopic investigations of Fe2+ complexation on nontronite clay

Diffuse reflectance (visible) and attenuated total internal reflection Fourier-transform infrared (ATR-FTIR) spectroscopies were used to examine a colloidal nontronite clay in the presence of Fe2+(aq). pH-dependent changes are observed in both types of spectra. In the visible region, a broad feature at approximately 750 nm appears as the pH is raised to circumneutral values. This absorbance band overlaps with a portion of the spectrum of the chemically reduced clay which is dominated by an intervalence charge-transfer transition between Fe2+ and Fe3+ within the mineral structure. The similarities between these spectra suggest that Fe2+(aq) adsorbs to the clay in such a way that it can undergo charge transfer with structural Fe3+ within the clay. ATR-FTIR spectra at pH 5-8 reveal a transformation in the Si-O stretching region between pH 6 and pH 7 with a shift of the component peaks to lower frequency. Taken together, these spectroscopic studies indicate that Fe2+ forms an inner-sphere complex with the clay at higher pH values. The pH threshold for these observed changes in physical and electronic structure is in good agreement with the point of zero charge (pzc) of the hydroxyl groups on the edge surfaces of the clay, suggesting that complexation of Fe2+ to deprotonated edge sites leads to the observed spectroscopic features.     

ChemInform Abstract: Thorium Fluorides ThF,ThF2, ThF3, ThF4, ThF3(F2), and ThF5‐ Characterized by Infrared Spectra in Solid Argon and Electronic Structure and Vibrational Frequency Calculations.

Laser‐ablated Th atoms are reacted with different F₂ concentrations to produce ThF_x (x = 1, 2, 3, 4), ThF₃(F₂) and ThF₅^‐.     

Spectroscopic investigations of polyacrylonitrile thermal degradation

PAN undergoes chemical decomposition in stages on thermal treatment. In the literature, several mechanisms were proposed for the degradation process. However, the decomposition pathway and the structural rearrangement of solid residue in relation to the loss of volatile products are not fully understood. The degradation process has therefore received further attention in this work by employing a combination of FT-IR, high-resolution solid-state ¹³C-NMR, pyrolysis GC-MS, and microelemental analysis. These investigations have established that PAN decomposes to gaseous and volatile products over a range of temperatures (150–590°C) with concurrent stabilization of the structure of residual matter occurring on a parallel course. While linear polymerization of nitrile group is the principal reaction in the decomposition process, cyclization followed by extended conjugation is the notable exothermic process. No evidence has been obtained for the formation of oxygen-containing chromophores either as intermediates or as part of the chemical structure of the residue. Temperature sensitivity of oligomer formation has been established through pyrolysis–GC-MS studies. The overall decomposition profile of PAN has thus been established. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2503–2512, 1998     

Spectroscopic investigations of halogenated aluminas and silica aluminas

In contrast with the different activities of fluorinated and chlorinated aluminas, the OH-bands of γ- and η-Al₂O₃ are almost identical after halogenation with F, Cl, Br and I for lower coverages (θ<1), but excessive fluorination with imigration into the lattice causes greater changes.From a discussion of the OH-bands of silica-aluminas it may be concluded that a surface phase Al₂O₃-SiO₂ is formed, and SiO-bands at 1632, 1865 and 1970 cm⁻¹ may be used to determine the SiO₂-content of silica-aluminas.     

Spectroscopic investigations and structural confirmation studies on thiourea

The Fourier transform infrared and Raman spectra of thiourea have been studied in the region 4000–400 and 4000–10 cm^?1, respectively. A complete vibrational analysis on the molecular structure of thiourea has been made on the basis of C_2υ point group symmetry. The validity of the vibrational assignments on the structure of thiourea is supported by evaluating the molecular constants and the potential energy distribution.     

Spectroscopic investigations of solvent effect on chiral interactions

The spectrophotometric method was used to determine the mechanism of chiral interactions between a known chiral selector, tert-butyl carbamoylated quinine (t-BuCQN), and N-derivative amino acids (DNB-Leu). Results obtained on binding constants, free energy of binding (DeltaG), and difference in free energy of binding (DeltaDeltaG) values seem to suggest that there are three possible types of interactions between DNB-Leu and t-BuCQN: electrostatic interaction between the carboxylate group of the DNB-Leu and the ammonium group of the t-BuCQN, the donor-acceptor charge-transfer type of interaction between the (acceptor) aromatic group of the amino acid and the (donor) aromatic group of the t-BuCQN, and the hydrogen-bonding interaction between the amide group of the DNB-Leu and the carbonyl group of t-BuCQN. The strongest interaction will be observed if all of three interactions are in operation as in the case of DNB-Leu. The electrostatic interaction seems to play the dominant role in the interactions. While the charge-transfer interaction is relatively weaker, it seems, however, to be responsible for enantiomeric selectivity, namely, the closer the electron acceptor dinitrophenyl group is to the electron donor quinoline group, the higher is the enantiomeric selectivity. Specifically, in solvent with high polarity, both donor and acceptor are solvated by solvent molecules, thereby preventing them from being close. As a consequence, the interaction will be weaker and, hence, lower enantiomeric selectivity. Solvation will be less in less polar solvent which, in turn, leads to stronger interaction and higher enantiomeric selectivity.     

Spectroscopic investigations of CF3Se-derivatives

The vibrational spectra of CF₃SeH, CF₃SeD, CF₃SeCl, CF₃SeBr, CF₃SeCN, CF₃SeCl₃, (CF₃)₂Se and (CF₃Se)₂ are reported, and vibrational assignments presented. N.m.r. parameters for a wide range of CF₃Se-derivatives are tabulated.     

Spectroscopic and magnetic investigations of actinide‐based nanomagnets

Magnetic exchange is an essential feature of transition‐metal nanomagnets because it combines the relatively low spin‐only moments of several ions into a “giant spin” ground state, which can make slow magnetic relaxation very favorable in an axially anisotropic environment. In contrast, most of the early research on lanthanide‐based complexes focused on single‐ion magnets, where the required large moment is generated by the unquenched orbital contribution (which is parallel to the spin in heavy rare earths). With their unfilled 5f electronic shell being on the verge between localization and itinerancy, actinides are expected to combine the best of both 3d and 4f metals in terms of exchange and anisotropy, and are therefore under consideration as potential building blocks for the next generation of single‐molecule magnets. In this Perspective, a review of the recent development in this field is given, and some discrepancies between the spectroscopic and magnetic data are discussed. © 2014 European Commission. International Journal of Quantum Chemistry published by Wiley Periodicals, Inc.     

Spectroscopic investigations on II–VI-semiconductor nanocrystals and their assemblies

This review points out that (magneto-)optical measurements may help to shine light on the recombination processes taking place in semiconductor nanocrystals. The surface capping with thiols creates a CdS shell around CdTe cores and forms a Cd site that is not fourfold-coordinated at the surface. It is pointed out how specific cappings such as thio-amines and thio-acids assist in coupling NCs and how we may distinguish between NC–NC interactions via electrostatic and covalent linking with the aid of the optical measurements. Furthermore, with static and time-resolved ODMR studies on IR-active core-shell HgTe/Hg _x Cd_1−x Te(S) particles it is demonstrated how the nature of the recombination emission being associated with a Cd–Hg mixed site is elucidated and by this yielding structural information on the NC core-shell interface. With these examples we show that and how nanomaterials of probable technological interest are studied beneficially with advanced spectroscopic techniques.     

Spectroscopic investigations of the structure of liquid water and aqueous solutions

IR spectroscopy is a powerful tool for investigating the structure of aqueous systems. Changes in vibrational frequencies and intensities of the absorption band provide information about the structure of the associated water molecules. The water molecule has C_2v symmetry when the intermolecular interaction is symmetrical to both OH bonds as in 2:1 complexes. In this case the frequency difference of the two stretching vibrations ν₃ and ν₁ is nearly constant. If the intermolecular interaction is unsymmetric to the OH bonds as in 1:1 complexes the band separation of ν₃ and ν₁ increases markedly in relation to the increase of the unsymmetry. The IR overtone region is more suitable for the study of the structure of liquid water or aqueous solutions than the IR fundamental region. The reason is the higher intensity of the absorption bands of the “free” OH vibration compared to the H-bonded OH groups. The ratio of the intensities is inverse in the fundamental region. Furthermore it is possible to measure quantitatively in the overtone region and there are no experimental difficulties. The results are estimations of the H-bonded and the free OH groups in different aqueous systems.     

Spectroscopic investigations on Naphthol and Tetrahydronaphthol. A theoretical approach

The computational efficiencies of the semi-empirical method have been compared with those of different ab-initio methods for positional isomers of Naphthol and Tetrahydro-naphthol type molecules. The efficiencies for computations in case of optimized structure, electronic absorption and emission properties are investigated. For that semi-empirical approach ZINDO and two different nature of ab-initio approaches such as TD-HF/6-311G(d,p) and TD-DFT/B3LYP/6-311G(d,p) were considered. The three main approaches are studied here to give the right direction of simulation. Semi-empirical AM1/ZINDO function itself can detect the trend of molecular transitions and the values obtained by simulations are more realistic than ab-initio methods. Ab-initio methods can reproduce exact values of first transitional energy with some scaling factor both in ground and in excited states of Tetrahydro-naphthol positional isomers whereas no solution or prediction could be inferred for Naphthol isomers.     

Fully relativistic calculations of ThF4

Based on the results of first‐principles density functional theory calculations of the electronic structure of ThF₄ in solid state and molecular form, the study of the Th6p, 5f, 6d, 7s and F2s, 2p states was done. We used the fully relativistic cluster discrete variational method with the local exchange‐correlation potential. The hybridization of F2p and Th5f, 6d, 7s, 7p states in the valence molecular orbitals (VMOs) in the region 0–10 eV and of F2s and Th6p states in the inner valence molecular orbitals (IVMOs) in the region 10–50 eV was studied. The results of relativistic cluster calculations are compared with those obtained for ThF₄ molecule. The energies of ionization of VMOs and of IVMOs were evaluated on the basis of the ground‐state and Slater's transition‐state calculations. The MO energy levels provide a satisfactory interpretation of experimental photoelectron spectra. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Spectroscopic investigations of phase transition in 5-chloro-2-pyridone

Spectroscopic investigation of 5-chloro-2-pyridone has been carried out in the temperature range 77–300 K. At room temperature the ³⁵Cl NQR spectrum shows a single line at 35.618 MHz, but at 250.7 K two lines appear at 35.850 MHz and 35.840 MHz respectively indicating the presence of a phase transition. IR, far-IR, laser Raman and dielectric measurements have been carried out to investigate the phase transition further. Low temperature IR studies show splitting of ν(CCl), β(NH) and ν(CO) bands at T_c. Dielectric measurements show a small, but finite, change in the value of the dielectric constant around T_c. Raman spectra at different temperatures support the existence of a new phase, as shown by the appearance of a new band at 81 cm⁻¹, the frequency of which changes slowly as T_c is approached and which disappears at T_c. The temperature dependence of the NQR frequencies has been analysed using Bayer Kushida and Brown equations toevaluate the torsional frequencies.     

Spectroscopic investigations of a novel tricyanofuran dye for nonlinear optics

A novel tricyanofuran dye was synthesized and the dye-in-polymer films were fabricated by spin-coating process. The spectroscopic properties of the dye in the solutions and polymer films were investigated by the absorption spectra and fluorescence emission spectra. It is found that the absorption and fluorescence maxima are largely red-shifted along with the increase of the solvent polarity. And the low values of fluorescence quantum yield in higher polarity solvents suggest the presence of twisted intramolecular charge transfer states of the dye. Moreover, the second order polarizability value of the novel dye was estimated based on the quantum-mechanical two-level model.     

Spectroscopic investigations of metalloporphyrin-oligopeptide systems: evidence for peptide aggregation

Anionic pentapeptides consisting of a string of four glutamic acid residues terminated by either tyrosine (Glu4Tyr) or tryptophan (Glu4Trp) were synthesized, and their aggregation properties in buffered (pH = 7.0) aqueous solutions were investigated using two different approaches. In the first approach, the effects of the concentration of peptide used as its own probe (intrinsic probe) on its fluorescence emission, circular dichroism, surface tension, and solution pH yielded similar critical peptide concentrations of around 175 microM. This particular concentration was taken as evidence for peptide aggregation. In the second approach, peptide aggregation was investigated using cationic metalloporphyrins, tetrakis(N-methyl-4-pyridyl)porphyrin (Pd(II)TMPyP(4+) and Zn(II)TMPyP(4+)), as extrinsic probes. The effect of peptide concentration on porphyrin ground-state absorption confirmed peptide aggregation, but at a lower critical peptide concentration near 125 microM. This difference was attributed to the possible distortion introduced by the association of one (or more) large metalloporphyrin molecule with the peptide aggregates. Evidence for peptide aggregation was also demonstrated from the effect of peptide concentration on Pd(II)TMPyP(4+) triplet-state decay. The fast component (k(f), associated with electron transfer from the target Tyr and Trp residues to the porphyrin triplet state) was found to be independent of peptide concentration, implying no noticeable effect of peptide aggregation on the electron-transfer event. This was attributed to the fact that species formed by excitation of porphyrin associated with ion-pair complexes or bound to peptide aggregates and the diffusion together of the separate T(1) and peptide entities in the bulk phase are kinetically similar. On the other hand, the slower component (k(s)) of the decay, which is associated with the diffuse formation of an encounter complex between the free peptide and T(1) porphyrin (bulk phase), was peptide-dependent and displayed a critical peptide concentration near 125 microM, above which it became practically independent of peptide concentration. This invariance of k(s) was taken as an indication that the free peptide concentration in the bulk phase remains constant above 125 microM, the concentration at which peptide molecules prefer to associate as aggregates.