Ultraviolet Absorption Spectrum of Toluene-D8

The near ultraviolet absorption spectrum of toluene-d₈ has been recorded with the help of a E₁ large quartz spectrograph. The (O,O) band has been identified at 37672 cm^?1. The spectrum has been analysed with the help of the excited state fundamentals 282, 378, 431, 454, 508, 700, 926, 1150 and 1432 cm^?1. These frequencies have been correlated with the corresponding frequencies of the normal molecule. The ration R = ν(C₆H₅CH₃)/ν(C₆D₅CD₃) has been calculated for each excited state mode of vibration and compared with the corresponding value of R found for the ground state vibrations.     

Dehydrochlorination of poly(vinyl chloride)

PVC has been dehydrochlorinated with alcoholic alkali in soution at 7°C for different lengths of time. At early stages of dehydrochlorination the dominant reaction is intramolecular removal of HCl and this gives rise to two intense Raman bands at ～ 1126 (ν₁) and ～ 1518 cm^?1 (ν₂) and following UV irradiation, to a quadruplet ESR spectrum. Increasing polyene sequence length and intermolecular removal of HCl at later stages of reaction alters the quadruplet signal to a singlet, shifts ν₁ and ν₂ to lower frequencies and increases the molecular weight. The presence of polyene units stiffens the chain and increases the elastic modulus. The T_g is, however, lowered slightly due to the removal of bulky chlorine atoms which relieves steric hindrance and dipole interaction between neighboring chains. The β-transition is also rendered less distinct.     

Microstructure and Thermal Properties of Polylactides with Different L‐ and D‐Unit Sequences: Importance of the Helical Nature of the L‐Sequenced Segments

A series of polylactides (PLA) with different stereo sequences are prepared by the copolymerization of L ‐lactide and DL ‐lactide. It is confirmed that the glass transition temperature (T_g) of the PLA decreases with decreasing optical purity of the lactate units (%ee) according to the Fox's equation. Analysis of the FT‐IR spectra of these PLA samples reveals that the absorbance at 1 265 cm^?1 (δCH + νCOC) decreases with increasing L ‐content while the absorbance at 1 210 cm^?1 (ν_asCOC + r_asCH₃) increases with increasing L ‐content. These changes in absorbance are reasonably correlated with the randomness and helical nature of the L ‐sequenced segments involved in PLA. Namely, the PLA chains with higher L ‐content comprise a higher number of short helical blocks that are made of several L ‐lactate units. This difference in helical nature causes the opposite dependences of T_g and density on the L ‐content of PLA; i.e., the increased T_g and decreased density with increasing L ‐content.

FT‐IR spectra of a PDLLA film, NO‐PLLA, and BO‐PLLA.     

Effect of matrix chain entanglement on toughening mechanism evolution of acrylic impact modifier toughened methyl methacrylate-N-phenylmaleimide copolymers

The toughening mechanism evolution of acrylic impact modifier (AIM) toughened methyl methacrylate-N-phenylmaleimide copolymers (PMMA-PMI) was investigated in terms of matrix chain entanglement density (ν_e), especially within the range of matrix ν_e?≈?0.1 mmol/cm³. After respectively blended the PMMA-PMI having designed ν_e with the same content preformed AIM, it was showed that the notched impact strength of the blends increase with PMMA-PMI ν_e enhancement. The morphological analyses revealed that the extent of shear yielding gradually enlarged when matrix ν_e is higher than 0.1061 mmol/cm³. Whereas, in the AIM/PMMA-PMI blend with lower matrix ν_e, the toughening mechanism transformed into matrix crazing triggered by PBA cavitation. The results suggest that the response of the matrix with different ν_e to the rubber particle cavitation dominate toughening mechanism and mechanical performance of AIM/PMMA-PMI blends, and it is believed that matrix ν_e is an inherent factor to toughening mechanism evolution.     

Modeling the Electronic,Structural and Vibrational Properties of Cubic SiC Nanocrystals Built from Diamondoid Structures

Silicon carbide diamondoids are used as building blocks of cubic SiC nanocrystals. Density functional theory (DFT) at the generalized gradient approximation level of Perdew, Burke and Ernzerhof (PBE) with 6-31G(d) basis is used to investigate the electronic structure of these diamondoids up to 12 cages. The results show that the energy gap and bond lengths generally decrease with shape fluctuations as the number of atoms increases. Electronic and structural properties are in good agreement with both previous experimental and theoretical results. Vibrational modes converge to the SiC experimental bulk limit of the radial breathing mode while hydrogen related modes are nearly constant in their frequencies. It is suggested in this work to identify SiC-diamondoids from their hydrogen vibrational modes finger print in the range (1000-3000 cm^?1) and identify the size of the diamondoid from low frequency vibrational modes (0-1000 cm^?1) such as radial breathing modes.     

The Stretching Frequencies of Isotopic Arsenate and Permanganate Ions in Aqueous Solutions

The infrared absorption of crystalline powders and D₂O solutions of normal and 84.5 atom % ¹⁸O-labelled sodium arsenate as well as normal and 83.3 atom % ¹⁸O-labelled sodium permanganate was measured in the 780–980 cm^?1 region. The ν₁ and ν₃ fundamentals of the aqueous As¹⁸O₄^3? ion appear at 834(sh) and 866(s) cm^?1 while the respective As¹⁸O₄^3? values are 808 and 822 cm^?1 These as well as other data are shown to indicate that the water molecules which hydrate this ion are attached to its As atom. The ν₃ frequency of the aqueous Mn¹⁸O₄^? ion is observed at 917 cm^?1 and that of hydrated Mn¹⁸O₄^? at 878 cm^?1.     

Modeling pKa of the Brønsted Bases as an Approach to the Gibbs Energy of the Proton in Acetonitrile

A simple but efficient computational approach to calculate pK_a in acetonitrile for a set of phosphorus, nitrogen, and carbon bases was established. A linear function that describes relations between the calculated ΔG’_a.sol(BH⁺) and pK_a values was determined for each group of bases. The best model was obtained through the variations in the basis set, in the level of theory (density functionals or MP2), and in the continuum solvation model (IPCM, CPCM, or SMD). The combination of the IPCM/B3LYP/6-311+G(d,p) solvation approach with MP2/6-311+G(2df,p)//B3LYP/6-31G(d) gas-phase energies provided very good results for all three groups of bases with R² values close to or above 0.99. Interestingly, the slopes and the intercepts of the obtained linear functions showed significant deviations from the theoretical values. We made a linear plot utilizing all the conducted calculations and all the structural variations and employed methods to prove the systematic nature of the intercept/slope dependence. The interpolation of the intercept to the ideal slope value enabled us to determine the Gibbs energy of the proton in acetonitrile, which amounted to −258.8 kcal mol⁻¹. The obtained value was in excellent agreement with previously published results.     

Structural optimization and vibrational analysis of an antidiabetic drug: tolbutamide

The purpose of this study is to investigate the vibrational spectrum of tolbutamide by ab initio techniques in combination with experimental studies. The Fourier transform infrared spectra (400–4000?cm^?1) and Laser-Raman spectra (100–4000?cm^?1) of tolbutamide have been obtained in the solid phase. Assignments have been found by the combination of the vibrational frequencies and the contribution of the potential energy distributions. Assignments have been compared with the theoretical and experimental results of similar structures as reported in the literature. Structural parameters such as bond lengths and angles, frequencies and infrared intensities and Raman activities of tolbutamide have been computed by density functional theory and Hartree–Fock methods using 6–311G++(d,p) and 6–31G(d) basis sets. The computed vibrational frequencies and optimized structural parameters are consistent with the corresponding experimental results. In addition, the images of tolbutamide frontier molecular orbitals (highest occupied and lowest unoccupied) and its energy gaps have been interpreted with the assistance of quantum chemical calculations.     

The Reactions of Bromide with Ozone Towards Bromate and the Hypobromite Puzzle: A Density Functional Theory Study

Taking the solvent water into account, the energetics of the reactions of O₃ with Br^? leading to BrO₃ ^? have been calculated by Density Functional Theory at the B3LYP/6–311+G(d)/SCRF =COSMO level. Br^? reversibly forms an adduct, BrOOO^?, (ΔG?=?+6 kJ mol^?1) that decays spin allowed into BrO^? and O₂(¹Δ_g) (ΔG?=?+13 kJ mol^?1). BrO^? undergoes an oxidation to BrO₂ ^? and a reduction to Br^?. This may be accounted for if two different adducts, OBrOOO^? and BrOOOO^?, decay into BrO^? plus O₂ and Br^? plus 2 O₂. After cyclization, OBrOOO^? may also lead to Br^? plus 2 O₂.     

Preparation and characterization of Co2+ substituted Li–Dy ferrite ceramics

Stoichiometric compositions of ferrites with the chemical formula Li_0.5?0.5xCo_xFe_2.4?0.5xDy_0.1O₄ with x=0, 0.25, 0.5, 0.75, 1.0 were prepared by the standard double sintering ceramic method. X-ray diffraction analysis confirmed the cubic spinel structure of the prepared samples. The structural, morphological and magnetic properties were studied by X-ray diffraction, infra-red spectroscopy (IR), scanning electron microscopy (SEM), vibrating sample magnetometry (VSM) and ac susceptibility measurements. Lattice constant, grain size and density increase whereas porosity decreases with the increase in Co²⁺ substitution. IR measurements show the characteristic ferrite bands. Spectral absorption bands were observed in IR spectroscopic analysis at ν₁=564?601 cm^?1, ν₂=486?519 cm^?1 and ν₃=551?578 cm^?1. The cation distribution estimated by the X-ray diffraction is supported by magnetization and susceptibility studies. The saturation magnetization decreases from 44.25 to 17.14 emu/g whereas coercivity remarkably increases from 240.69 to 812.14 emu/g with increasing Co²⁺ substitution. The mechanisms involved are discussed.     

A Theoretical Study on the Mechanism and Kinetic of the Reaction between Ozone and Benzene

Ozone has been widely used to degrade volatile organic compounds (VOCs) in combination with other methods such as ultraviolet light, adsorption, thermal and catalytic incineration. Despite its fundamental importance, the mechanism and kinetics of the reaction between ozone and VOCs are still lacking of detailed investigation. It is well known that quantum chemical calculation is a well-established method for investigating the chemical reactions. In this paper, quantum chemical calculation is employed to investigate the mechanism and kinetics of the reaction between ozone and VOCs exemplified by benzene. The microcosmic reaction process was depicted and discussed in detail based on geometry optimizations made using the UB3LYP/6-31G (d) method. According to the mechanism study, the kinetic parameters were also calculated by the classical transition state theory (TST). The calculated activation energy is 14.90 kcal/mol at the QCISD(t)/6-311g(d,p)//UB3LYP/6-31G(d) level of theory, while the obtained Arrhenius expression is that, k=1.05×10¹¹ exp(-61527/RT) (cm³·mole^?1·s^?1). Both the activation energy and the Arrhenius expression are in good agreement with the experimental results, which indicated that the mechanism and kinetic study of the reaction between benzene with ozone by employing quantum chemical calculation was reasonable and reliable.     

Characterization of crystallographic orientation and lattice disorder in hydroxyapatite thin films by Raman scattering

This report presents the way of evaluating the crystallographic orientation and crystallinity of hydroxyapatite (HAp) thin films by Raman scattering spectroscopy. According to the Raman selection rule, the symmetric stretching mode (ν₁) of P?O bonds in an isolated PO₄^3? units is Raman active, whereas the asymmetric stretching mode (ν₃) is not. Nevertheless, a weak ν₃ signal is usually observed in the Raman spectra of HAp powder crystals. We will show that the ν₃ signal is entirely absent for uniaxially oriented HAp films, whereas it appears in the case of randomly-oriented ones. This principle is feasible for discriminating the uniaxial orientation from a random one in HAp crystals. Another simple approach for evaluating crystallinity is exploiting the line width of the ν₁ PO₄^3? Raman signal. If the full-width at half maximum (FWHM) of the ν₁ signal is smaller than 7.4 cm^?1, the HAp crystal is uniaxially oriented in one direction, whereas if the FWHM value is larger than 7.4 cm^?1, the film is composed of randomly-oriented crystallites.     

The influence of reaction orders and of changes in the total number of moles on the conversion in a periodically operated CSTR

Conversion improvements are calculated for the reaction scheme ν₁A₁ + ν₂A₂ → ν₃A₃ with the power law rate r = kc₁^n₁c₂^n₂ and compared with theoretical a priori criterions. It turns out that improvements are possible even in the first quadrant of the n₁-n₂ space. A reaction with a decreasing total number of moles (ν₃ < ν₁ + ν₂) increases this region for conversion improvements.     

Study of the Electrochemical Behavior of N-Substituted-4-Piperidones Curcumin Analogs: A Combined Experimental and Theoretical Approach

The electrochemical behavior of N-methyl- and N-benzyl-4-piperidone curcumin analogs were studied experimentally and theoretically. The studied compounds present different substituents at the para position in the phenyl rings (-H, -Br, -Cl, -CF₃, and -OCH₃). We assessed their electrochemical behavior by differential pulse and cyclic voltammetry, while we employed density functional theory (DFT) M06 and M06-2x functionals along with 6-311+G(d,p) basis set calculations to study them theoretically. The results showed that compounds suffer a two-electron irreversible oxidation in the range of 0.72 to 0.86 V, with surface concentrations ranging from 1.72 × 10⁻⁷ to 5.01 × 10⁻⁷ mol/cm². The results also suggested that the process is diffusion-controlled for all compounds. M06 DFT calculations showed a better performance than M06-2x to obtain oxidation potentials. We found a good correlation between the experimental and theoretical oxidation potential for N-benzyl-4-piperidones (R² = 0.9846), while the correlation was poor for N-methyl-4-piperidones (R² = 0.3786), suggesting that the latter suffer a more complex oxidation process. Calculations of the BDEs for labile C-H bonds in the compounds suggested that neither of the two series of compounds has a different tendency for a proton-coupled electron transfer (PCET) oxidation process. It is proposed that irreversible behavior is due to possible dimerization of the compounds by Shono-type oxidation.     

Linear sweep voltammetry of manganate(VII), manganate(VI), and manganate(V) in alkaline media

Electrochemical reactions were assigned to the voltammetric waves obtained in alkaline KMnO₄ and K₂MnO₄ solutions. Plots of i_p (AC°ν^{$\text{1}\text{2}$})^?1 and i_api_cp^?1 νs log ν indicate that at slow potential scan rates in MnO^?₄ solutions ranging from 0·07 to 0·19 F in NaOH the first step in MnO^?₄ reduction is a l-electron reversible charge transfer with no coupled chemical reaction; at fast scan rates (? V s^?1 the process becomes quasi-reversible. The standard rate constant and the activation energy for the MnO^?₄/MnO^2?₄ charge transfer step were estimated. Plots of i_p (AC°ν^{$\text{1}\text{2}$})^?1 and i_api_cp^?1 νs log ν indicate that in 4·O F KOH and at potential scan rates between 0·005 and 2·V s^?1 the reduction of MNO^2?₄ to MnO^3?₄ is a reversible charge transfer with no coupled chemical reaction. The diffusion coefficients of MnO^?₄ and MnO^2?₄ in alkaline solutions are reported.     

Spatial ions distribution of the bonding interface in YAG/Nd:LuAG composite laser ceramic

Composite YAG/Nd:LuAG transparent ceramics were fabricated by a thermal bonding process. The spatial distribution of ions around the original bonding interface of the YAG/Nd:LuAG composite laser ceramic was investigated. Around the original bonding interface, Lu³⁺ and Y³⁺ ions were replaced with each other in dodecahedral symmetry sites. Results from X‐ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS) quantitative chemical analyses positively show that the distance of Y³⁺ ions diffused in the LuAG part is about 35 μm, while Lu³⁺ ions’ diffused distance in the YAG part is about 5 μm. This corresponds to the diffusion coefficient of Y³⁺ ions and Lu³⁺ ions (D_Y=2.43 ×10^?10 cm²/s and D_Lu=0.56×10^?10 cm²/s at 1750°C). The formation of Y_xLu_(3?x)Al₅O₁₂ polycrystal in the bonding section explains the complete combination of LuAG and YAG without a bonding interface. Moreover, no diffusion phenomenon of Nd³⁺ ions was detected near the original bonding interface.     

Intermediate temperature electrical properties in 4 mol% ZnO-doped Zr0.92Y0.08O2-α/NaCl-KCl composite electrolyte

In this paper, 4?mol% ZnO-doped Zr_0.92Y_0.08O_2-α (8YSZ) and its 8YSZ+4ZnO/NaCl-KCl composite electrolyte were synthesized by a solid-state reaction. The X–ray diffraction (XRD) analysis indicates that 8YSZ+4ZnO and inorganic chlorides phases can coexist. The inorganic chlorides decrease the synthesis temperature of 8YSZ+4ZnO. The highest conductivities of 8YSZ+4ZnO and 8YSZ+4ZnO-NK are 7.0?×?10^?3 S?cm^?1 and 7.7?×?10^?2 S?cm^?1 at 700?°C, respectively. The oxygen concentration discharge cell shows that 8YSZ+4ZnO and 8YSZ+4ZnO-NK are good oxide ionic conductors under an oxygen-containing atmosphere. Finally, an H₂/O₂ fuel cell based on the 8YSZ+4ZnO-NK electrolyte reached the maximum power density (P_max) of 315.5?mW?cm^?2 at 700?°C.     

Effect of solvent on structure and optical properties of PZT nanoparticles prepared by sol-gel method, in infrared region

Single-phase perovskite Pb(Zr_0.52,Ti_0.48) nanoparticles, PZT-NPs were prepared by the sol-gel method with two different solvents, 2-methoxyethanol, EGME, and poly ethylene glycol, PEG. X-ray diffraction (XRD) was used to study of the structure of the PZT-NPs. Fourier transform infrared spectroscopy (FTIR) was used to measure the infrared reflectivity spectrum in the range of 4000-280 cm⁻¹. Infrared active vibration modes of BO₆ octahedral (ν₁ and ν₂) were observed for PZT-NPs below 600 cm⁻¹. The third vibration mode of Pb against the TiO₃ group, ν₃, occurred below the experimentally accessible range. The Kramers-Kronig method (K-K) and classical dispersion theory were applied to analyze the data and calculation of the optical constants such as reflective index (N(ω))and permittivity (?(ω)). The results showed that the structure and optical properties of PZT-NPs were changed by different type of solvent.     

Raman and X-ray photoelectron spectroscopy study on the influence of La2O3 on the melt structure of SiO2–CaO–Al2O3–MgO

In order to gain more insights into the influence of rare earth elements on the melt structure of SiO₂–CaO–Al₂O₃–MgO glass ceramics, Raman and X-ray photoelectron spectroscopy techniques were used to study the influence of La₂O₃ on the Si–O/Al–O tetrahedron structure within SiO₂–CaO–Al₂O₃–MgO–quenched glass samples in this study. Results showed that some Raman peak shapes at low frequencies (200–840 cm^?1) changed significantly after the addition of La₂O₃, compared to the high frequency (840–1200 cm^?1) region that corresponds to the [SiO₄] structure, suggesting that the depolymerization of the low-frequency T–O–T (T=Si or Al) structure was more prevalent with La³⁺ addition. Besides, the depolymerization extent of the Si–O/Al–O tetrahedral network varied when the melt composition altered. Most notably, depolymerization is the most significant at a low CaO/SiO₂ ratio (0.25) and a high Al₂O₃ content (8%). Meanwhile, La³⁺ can promote the transformation of Si–O–Si and Al–O–Al bonds to the Si–O–Al ones, thereby forming a complex ionic cluster network interwoven with Si–O and Al–O tetrahedrons.