Absorption Spectra Of Powders Research Articles

First results from a dispersive EXAFS beamline developed at INDUS-2 synchrotron source at RRCAT, Indore, India

A dispersive extended X-ray absorption fine structure (EXAFS) beamline employing an elliptically bent crystal and a position-sensitive CCD detector has been developed at the BL-8 bending magnet port of INDUS-2 synchrotron source at RRCAT, Indore, India. The beamline enables simultaneous measurement of X-ray absorption spectra over the range of 5–20 keV in a short span of time. The beamline performance has been investigated by measuring the absorption spectra of metal foils and oxide powders. The EXAFS measurements on crystalline Pb 5Ge 3O 11 samples were performed for the first time in literature. The average Pb–O bond length obtained from these measurements is found to agree well with the theoretically estimated value.

SU‐GG‐T‐155: Quality Assurance for IMRT in Belgium: Verification of the Integral Delivered Dose with Alanine‐ESR Dosimetry

Purpose: To face IMRT treatments with confidence, a federal QA program is set up in Belgium to verify the integral delivered dose for the routine technique as it is applied in the individual centers. The measured dose is compared to the TPS calculated dose as stated by the participant. Method and Materials: The integral IMRT‐delivered dose is measured at 3 locations within a phantom: at the center of two CTV's and at the center of one OAR in between. Dose is measured with alanine detectors which are read out in a desk top ESR‐spectrometer. Alanine dosimetry shows a linear variation with dose, no energy dependence nor fading. Dose is measured as the intensity of the central line in the powder absorption spectrum of alanine. The alanine pellets are calibrated in terms of “dose to water” between 1 Gy and 50 Gy by irradiation in a Co‐60 beam against water The participants are asked to pass the phantom through their routine process in order to perform a “end‐to‐end‐test”: acquiring CT scans for imaging, defining 2 cylindrical CTV's and one OAR as well to outline the detector volume. Complete freedom is given to the local staff in making a treatment plan: number of beams, optimization criteria, constraints, irradiation mode…). The only restriction is to deliver 10 Gy at the two CTV's and 3 Gy to the OAR. Finally the phantom is placed and lined up on the treatment couch using the routine procedure and irradiated. Results: up to now 6 centers are visited for which 10 tests with different IMRT techniques were performed: Tomotherapy(5), Segmented MLC(4), Dynamic MLC(1). The mean value of the ratio between stated and measured dose for CTV1 is 0.989 (sd=0.024); for CTV2 0.992 (sd=0.019); and 0.958 (sd=0.092) for OAR.

THz-Wave Spectroscopy Applied to the Detection of Illicit Drugs in Mail

A series of experiments in the field of THz-wave spectroscopy is described. The measurement of absorption spectra of solid samples, powders, and liquids is demonstrated using various optical setups. One of the sources we used is a widely tunable coherent THz-wave generator relying on an optical parametric process: nanosecond Q-switched Nd : YAG laser light scattering from the polariton mode of a MgO-doped LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> crystal. For the measurement of the absorption of THz waves in liquids, a train of waves is allowed to oscillate inside a silicon prism. A liquid placed on a total internal reflection surface lowers the quality factor of the resonator, which allows determining the complex refraction index of the sample by frequency scanning. We have also developed a technique for THz chemical imaging, by introducing the component spatial pattern analysis. The spatial distribution of the chemicals, such as illicit drugs concealed in an envelope, is obtained from terahertz multispectral transillumination images and absorption spectra. To compensate for the low imaging speed, a prescreening step is proposed, by first detecting the presence of powders in the envelopes, which is achieved by measuring in real time the amount of scattering produced by the envelopes. Details and examples are provided.

Temperature dependence of ultrafast photoinduced ring-opening and -closure reactions of spironaphthooxazine in crystalline phase

To investigate the dynamics of photoinduced ring-opening and -closure reactions in crystalline phase, we measured transient absorption spectra of spironaphthooxazine microcrystalline powder by femtosecond diffuse reflectance spectroscopy and examined their temperature dependence. The lifetimes of the excited state of the spiro form and the subsequent non-planar open form were about 3 ps and 3 ns at room temperature, respectively. The temperature dependence of their decay constant showed the Arrhenius type behavior and the activation energy of the ring-opening and -closure reactions are estimated to 7 and 12 kJ mol −1, respectively. The yield of the non-planar open form became smaller at lower temperature, and it was zero below about 140 K. The experimental results and kinetic analysis indicate that a short-lived species having a molecular conformation different from the non-planar form should be considered as an intermediate in the ring-opening reaction.

Fourier-transform infrared and UV–vis spectroscopes of nickel phthalocyanine thin films

The Fourier-transform infrared (FT-IR) technique has been applied to identify the polymorphs of phthalocyanine molecules. The infrared absorption (IR) spectra were recorded in the spectral range 400–1000 cm −1. A comparison of absorption spectra of powder, as-deposited and annealed films is presented. The powder absorption spectrum was identified as rich of β-NiPc, where the thermally deposited films at room temperature were identified as the rich of α-NiPc. Moreover, the main spectral peaks of the films, annealed at 573 K, were defined as rich of β-form. The absorption measurements recorded in the UV–vis region showed two well-defined absorption bands of phthalocyanine molecule, namely the Soret band (B) and the Q-band. The Q-band showed its characteristic splitting (Davydov splitting), and Δ Q was obtained as 0.21 eV. Some of the important optical absorption parameters such as the molar extinction coefficient, the oscillator strength, and the electric dipole strength have been evaluated.

UV–vis Absorption Spectra of Powdered Materials: Direct Measurements by Optical Waveguide Spectroscopy

Abstract UV–vis absorption spectra of powders of naphthalene and salicylideneaniline were obtained using optical waveguide spectroscopy. It is demonstrated that the optical waveguide spectroscopy is an excellent method for the measurement of UV–vis absorption spectra of powdered materials as they are, without any treatment.

Broadened Far-Infrared Absorption Spectra for Hydrated and Dehydrated Myoglobin

The far-infrared absorption spectra of myoglobin powder at hydration levels between 3.6 and 42 wt % were measured with terahertz time-domain spectroscopy and Fourier transform infrared spectroscopy. Absorption is dominated by the water content, but even the driest specimens have a nearly continuous spectrum without identifiable sharp features. Inhomogeneous broadening plus the intrinsically high spectral density of vibrational modes in the region below 2.0 THz apparently combine to obscure the lowest frequency vibrational modes expected for protein molecules of this size. A continuous absorption spectrum for hydrated protein powders suggests that the absorption mechanisms are similar to those in liquid water, and hinders the spectroscopic identification of biomolecules in this frequency range.

Strain and local heterogeneity in the forsterite?fayalite solid solution

Infrared powder-absorption spectra of nine natural and five synthetic olivine samples across the forsterite–fayalite join have been investigated at room temperature in the range 70–1400 cm−1. Variations of peak positions as a function of Fe content are close to linear for those vibrational bands whose trend could be followed across the solid solution. Line-broadening has been quantified by autocorrelation analysis. Positive deviations from linearity of the line-broadening parameter, Δcorr, for groups of bands at low energies are consistent with the existence of local elastic strain heterogeneities at intermediate compositions in the solid solution. It also appears that the structure of forsterite is more homogeneous than Fe-rich olivines in relation to local elastic strain effects. Positive deviations from linearity of the line-broadening parameter for the low-energy regions scale linearly with calorimetric data for the enthalpy of mixing. This close correlation between line-broadening in IR spectra and calorimetric enthalpies of mixing has now been observed for four different binary solid solutions, and there is a further, qualitative correlation with bulk modulus.

Nonlinear optical properties of some derivatives of stilbene and vinyl cyanide

Three derivatives of stilbene: 3-hydroxy-4-methoxy-4′-nitrostilbene (HMONS), 3-methoxy-4-hydroxy-4′-nitro-stilbene (MOHNS), 2-cyano-3-indole-propenoic acid ethyl ester (CIP-ethyl), and one derivative of vinyl cyanide: p-1,1-dicyano-vinyl-dimethylaminoaniline (DVDA) were designed and synthesized. The powder second-harmonic generation and absorption spectra of these four compounds were measured. First principle calculation of the molecular first hyperpolarizabilities of HMONS were calculated and compared with those of 3-methyl-4-methoxy-4′-nitrostilbene (MMONS, Appl. Phys. Lett. 56 (1990) 423) in order to elucidate their structural origin of the optical nonlinearity.

Sonochemical Synthesis of Cerium Oxide Nanoparticles—Effect of Additives and Quantum Size Effect

Cerium oxide (CeO2) nanoparticles were prepared sonochemically, by using cerium nitrate and azodicarbonamide as starting materials, and ethylenediamine or tetraalkylammonium hydroxide as additives. The additives have a strong effect on the particle size and particle size distribution. CeO2 nanoparticles with small particle size and narrow particle size distribution are obtained with the addition of additives; while highly agglomerated CeO2 nanoparticles are obtained in the absence of additives. Monodispersed CeO2 nanoparticles with a mean particle size of ca. 3.3 nm are obtained when tetramethylammonium hydroxide (TMAOH) is used as the additive and the molar ratio of cerium nitrate/azodicarbonamine/TMAOH is 1/1/1. Blue shifts of the absorption peak and the absorption edges of the products are observed in the UV-Vis absorption spectra as a result of the quantum size effect. The samples have been characterized using powder XRD, TEM, DLS, and absorption spectra.

近赤外分光法による医薬品原料粉体の判別

Near-infrared spectroscopy was employed in order to make a qualitative analysis of various pharmaceutical powders for the purpose of conducting a confirmation test for accepting raw pharmaceutical powders. The near-infrared spectrophotomater was used to determine the absorption spectra of powder, followed by the analysis of principal components of the spectra to calculate primary and secondary components, which are used as judgment criteria. A two-dimensional judgment model was also proposed. As a result it was shown that the near-infrared spectroscopy does not require pretreatment of powders and offers non-destructive and quick (about 1min) analysis of active ingredients in excipients. Consequently, a facilitated validation method of quality control for accepting raw powdery materials was proposed. It was then demonstrated that the excipients and major active ingredients were subjected to near-infrared spectroscopy for determining principal components, which satisfy the two-dimensional judgment model with a highaccuracy. Furthermore, comparative evaluation was made for the peaks appearing when the weighting factors of the principal components were subjected to loading plot as well as for chemical assignment derived from the absorption band at near-infrared region, which resulted in determination of the principal components to be judged.

Infrared powder-absorption spectroscopy of Ca-free P21/c clinopyroxenes

AbstractInfrared powder-absorption spectra of ten synthetic P21/c pyroxenes with compositions in the clinoenstatite–clinoferrosilite system have been collected at room temperature in the range 50–1500 cm−1. Variations of peak positions as a function of Fe content have been obtained for those vibrational bands whose trend could be followed across the solid solution. Local elastic strains arising from cation substitution have been quantified by means of the autocorrelation function, which gives a measure (Δcorr) proportional to the line width of the IR bands. The structure of clinoenstatite appears to be very homogeneous, whereas Fe-rich pyroxenes have high degrees of local structural hetereogeneities. A positive deviation from linearity of the Δcorr values is observed in the spectral region between 100 and 250 cm−1 and may be indicative of a positive excess enthalpy of mixing of this solid solution. At higher energies the large changes in the phonon spectra as Fe content increases are associated with rotation and deformation of the tetrahedral chains for accommodating the larger cation. The results are compared with similar studies on other chain silicates.

Synthesis and characterization of polyacrylonitrile–silver nanocomposites by γ-irradiation

The nanocomposites of stable nanosilver particles embedded in polyacrylonitrile matrix were synthesized by γ-irradiation, in which the monomer acrylonitrile was polymerized and the silver ions were reduced simultaneously by γ-irradiation to form composites in situ. The strong interactions between silver ions with –CN groups of polyacrylonitrile are found, which were confirmed by X-ray powder diffraction, IR spectrum and absorption spectra.

Autocorrelation analysis of infrared spectra from minerals

The autocorrelation function, Corr(α, ω′) = \({\int}_{{-}{\infty}}^{{\infty}}\) α(ω + ω′)α(ω)dω, may be used to parameterise effective line widths of absorption bands in IR spectra. It has the advantage of not requiring any peak fitting to the primary spectra and can be applied to individual bands or groups of bands in a spectrum. A new procedure for analysing autocorrelation spectra which result from the application of the autocorrelation function to primary spectra is presented. The approach is well suited for quantifying line width variations in powder absorption spectra from sequences of samples with varying composition, degree of cation order or structural state. Worked examples are set out to illustrate different applications of the approach, including the characterisation of structural phase transitions in tridymite, Al/Si ordering under non-equilibrium conditions in Mg-cordierite, short range Al/Ge order in BaAl 2 Ge 2 O 8 feldspar and mixing behaviour in the jadeite-augite solid solution.

Temperature dependence of infrared spectra of [Pd(dddt) 2] 2AuBr 2 and [Pd(dddt) 2] 2SbF 6 salts

Polarised reflectance and transmittance spectra of two isostructural charge-transfer salts [Pd(dddt) 2] 2AuBr 2 and [Pd(dddt) 2] 2SbF 6 (where dddt=5,6-dihydro-1,4-dithiin-2,3-dithiolate ligand) have been measured over the frequency range 650–6500 cm −1 as a function of temperature (90–300 K). Additionally, powder absorption spectra of both compounds have been studied in the region 400–40000 cm −1 at room temperature. Plasma-edge-like dispersion observed in the reflectance spectra is analysed in terms of a Drude–Lorentz model. A metal–insulator phase transition in [Pd(dddt) 2] 2SbF 6 at T≈200 K is observed in the spectra and discussed. Temperature dependence of vibrational bands, especially those related to the coupling of electrons with the totally symmetric vibrations of Pd(dddt) 2, is investigated.

Development of a femtosecond diffuse reflectance spectroscopic system, evaluation of its temporal resolution, and applications to organic powder systems

An ultrafast time-resolved diffuse reflectance spectroscopic system has been developed as a potential instrument for analyzing photophysical and photochemical dynamics of light scattering materials such as powder and opaque suspension, using an amplified femtosecond Ti:sapphire laser as a light source. Transient absorption spectra of organic powder, covering the wavelength region from 400 to 760 nm, were precisely obtained by using a stable and bright femtosecond white-light continuum as a probe light. An ultrashort light pulse is temporally broadened owing to numerous times of refraction, reflection, and diffraction in scattering materials. This affects the temporal resolution of transient absorption measurements, which was examined and discussed in detail by using a simple numerical model with time-dependent light propagation of a short pulse. From the simulation and experimental results, it was shown that the temporal resolution of transient absorption measurement is less than a few ps under a certain measurement condition, although it strongly depends on the optical properties of the sample; scattering and absorption coefficients. Some applications to the analysis of excited dynamics of organic molecules in polymer latex and molecular microcrystalline powder are also demonstrated.

Hard mode infrared spectroscopy of cation ordering and substitution in a chain silicate

Infrared powder-absorption spectra of natural ordered (P2/n) and disordered (C2/c) as well as experimentally disordered pyroxenes lying in the binary join augite-jadeite were recorded at room temperature in the frequency region 70–1400cm−1. Frequency shifts and linewidth variations as a function of composition and degree of order were examined in particular detail over the spectral ranges 100–200cm−1 and 610–800 cm−1. Phonon signals at low frequencies are very sensitive to both changes in composition and degree of order, and are indicative of a non-ideal mixing behaviour for the C2/c solid solution. Phonons at high frequencies depend on the average composition of the samples and not on local configurational changes related to the order—disorder transition. A linear correlation between the short-range order parameter obtained by IR analysis and the long-range order parameter obtained by structural refinements of X-ray single crystal diffraction data was found. Substantial line broadening in C2/c samples with intermediate compositions is interpreted in terms of local structural heterogeneities.

Electronic and Vibrational Spectra of Et$\mathsf{_4}$N[ Au(dmit)$\mathsf {_4}$TCNQ] Crystals

We present the results of spectral studies of Et 4 N[Au(dmit) 2 TCNQ] salt containing alternating stacks of Au(dmit)2 and TCNQ molecules. The polarized transmission spectra of single crystals are measured in the IR region (650 to 6500 cm -1 ) as a function of temperature (90 to 300 K). Moreover, the powder absorption spectra in the frequency range (400 to 40000 cm -1 ) are reported. From spectral evidence results that transferred electrons are localized on Au(dmit)2 molecules in the mixed stacks. The intrastack charge transfer between Au(dmit)2 and TCNQ molecules (∼ 8000 cm -1 ) and the interstack charge transfer transition between Au(dmit) 2 molecules (∼ 5500 cm -1 ) are found. Interactions of electrons with intramolecular vibrations of TCNQ (a g modes) and Au(dmit)2 (C = C and C = S stretching) are suggested and discussed.

Electrical and spectral properties of some bis(oxapropylenedithio)tetrathiafulvalene (BOPDT‐TTF) salts

Three new organic charge transfer salts formed by the organic donor bis(oxapropylenedithio)tetrathiafulvalene (BOPDT-TTF or OTT) and ClO4, BrO2 and Bri2 anions have been synthesised. These crystals are semiconductors, σdc (300 K) being equal to 0.12, 10 and 5 × 10−6 S cm−1 for the salts with ClO4, BrO2, BrI2 anions, respectively. The electrical conductivity is of activated type (BrO2 and BrI2 salts) or is fitted well with the variable-range hopping model (ClO4 salt). Room temperature powder absorption spectra within the frequency range 400–40,000 cm−1 have been measured. From the position of charge transfer bands it results that Coulumb interactions in BOPDT-TTF salts are stronger than in other analogous compounds. The FT-NIR Raman spectrum of neutral BOPDT-TFF in the region of C(SINGLE BOND)C stretching has also been studied.

Spectroscopic Investigations of Charge Transfer Salt VINΦ2(TCNQ)2

VINΦ2(TCNQ)2 is a salt with two different, non-parallel TCNQ stacks. The polarized reflectance spectra from single crystals in the IR region 660-5200 cm-1, the powder absorption spectra 400-45000 cm -1 and FT—NIR Raman spectra of VINΦ2(TCNQ)2 are measured at room temperature. Moreover, the temperature dependence of powder absorption spectra in the frequency range 400-7900 cm -1 are studied. The nature of electronic bands, the anisotropy of optical conductivity, the temperature dependence of some vibrational bands and the charge distribution on different TCNQ stacks are discussed. PACS numbers: 71.38.+i, 78.30.Jw, 78.40.—q