Changes In Band Shape Research Articles

Deriving column-integrated thermospheric temperature with the N<sub>2</sub> Lyman–Birge–Hopfield (2,0) band

Abstract. This paper presents a new technique to derive thermospheric temperature from space-based disk observations of far ultraviolet airglow. The technique, guided by findings from principal component analysis of synthetic daytime Lyman–Birge–Hopfield (LBH) disk emissions, uses a ratio of the emissions in two spectral channels that together span the LBH (2,0) band to determine the change in band shape with respect to a change in the rotational temperature of N2. The two-channel-ratio approach limits representativeness and measurement error by only requiring measurement of the relative magnitudes between two spectral channels and not radiometrically calibrated intensities, simplifying the forward model from a full radiative transfer model to a vibrational–rotational band model. It is shown that the derived temperature should be interpreted as a column-integrated property as opposed to a temperature at a specified altitude without utilization of a priori information of the thermospheric temperature profile. The two-channel-ratio approach is demonstrated using NASA GOLD Level 1C disk emission data for the period of 2–8 November 2018 during which a moderate geomagnetic storm has occurred. Due to the lack of independent thermospheric temperature observations, the efficacy of the approach is validated through comparisons of the column-integrated temperature derived from GOLD Level 1C data with the GOLD Level 2 temperature product as well as temperatures from first principle and empirical models. The storm-time thermospheric response manifested in the column-integrated temperature is also shown to corroborate well with hemispherically integrated Joule heating rates, ESA SWARM mass density at 460 km, and GOLD Level 2 column O/N2 ratio.

Skeletal Structure of the Chromophore of Photoactive Yellow Protein in the Excited State Investigated by Ultraviolet Femtosecond Stimulated Raman Spectroscopy.

We studied ultrafast structural dynamics of photoactive yellow protein (PYP) using ultraviolet femtosecond stimulated Raman spectroscopy. By employing the Raman pump and probe pulses in the ultraviolet region, resonantly enhanced, rich vibrational features of the excited-state chromophore were observed in the fingerprint region. In contrast to the marked spectral change reported for the excited-state chromophore in solution, in the protein, all of the observed Raman bands in the fingerprint region did not show any noticeable spectral shifts nor band shape changes during the excited-state lifetime of PYP. This indicates that the significant skeletal change does not occur on the chromophore in the excited state of PYP and that the trans conformation is retained in its lifetime. Based on the femtosecond Raman data of PYP obtained so far, we discuss a comprehensive picture of the excited-state structural dynamics of PYP.

Application of Infrared Reflectance Spectroscopy on Plastics in Cultural Heritage Collections: A Comparative Assessment of Two Portable Mid-Fourier Transform Infrared Reflection Devices.

Plastics have been increasingly used to create modern and contemporary art and design, and nowadays, museum collections hold numerous objects completely or partially made of plastics. However, the preservation of these materials is still a challenging task in heritage conservation, especially because some plastics show signs of degradation shortly after their production. In addition, different degradation mechanisms can often take place depending on the plastic composition and appropriate environmental and packaging conditions should be adopted. Therefore, methods for in situ and rapid characterization of plastic artifacts' composition are greatly needed to outline proper conservation strategies. Infrared (IR) spectroscopy, such as attenuated total reflection Fourier transform infrared spectroscopy (ATR FT-IR), is a well-established method for polymeric material analysis. However, ATR FT-IR requires an intimate contact with the object, which makes its application less appropriate for the in situ investigation of fragile or brittle degraded plastic objects. Mid-FT-IR reflectance spectroscopy may represent a valid alternative as it allows in situ measurements with minimum or even no contact, and IR data can be acquired rapidly. On the other hand, spectral interpretation of reflectance spectra is usually difficult as IR bands may appear distorted with significant changes in band maximum, shape, and relative intensity, depending on the optical properties and surface texture of the material analyzed. Presently, mid-FT-IR reflection devices working in external reflection (ER FT-IR) and diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) modes have been used in cultural heritage research studies. As the collected vibrational information depends on the optical layout of the measuring system, differences between ER FT-IR and DRIFT spectra are thus expected when the same polymer is analyzed. So far, ER FT-IR and DRIFT spectroscopy have been individually explored for the identification of plastic objects, but comparative studies between the application of two reflectance FT-IR modes have not been presented yet. In this work, the use of two portable FT-IR spectrometers equipped with ER FT-IR and DRIFTS modes were compared for plastics identification purposes for the first time. Both references of polymeric materials and historical plastic objects (from a Portuguese private collection) were studied and the differences between ER FT-IR and DRIFT spectra were discussed. The spectra features were examined considering the two different optical geometries and analytes' properties. This new insight can support a better understanding of both vibrational information acquired and practical aspects in the application of the ER FT-IR and DRIFTS in plastic analysis.

Maize Stalk Material for On-Site Treatment of Highly Polluted Leachate and Mine Wastewater.

New research applications involving the use of cellulosic material derived from maize stalk for on-site treatment of leachate were evaluated for specific removal of Cu(II) and Fe(III) from real, highly polluted tailing pond and mine wastewater samples. Two major issues generated by anthropic mining activities were also tackled: wastewater metal content decrease to improve water quality and subsequently metal specific recovery, increasing the economic efficiency of metal production by using a green technology for residual management. Rapid saturation of the maize stalk mass determined in batch studies and the mine pilot experiment led to diminished metal concentrations in the second pilot experiment, where Cu(II) and Pb(II) from synthetic solutions were monitored in order to test biomaterial performances. In addition, in the second pilot experiment, maize stalk removed Pb(II) in the first 36 h, below the determination limit of the analytical method. The biomaterial bed in the column was saturated after 252 h of inflow solution. FTIR-ATR, TG and SEM techniques probed the interaction between maize stalk polar groups C=O, –OH, C–O and tailing water metallic ions by large FTIR band displacements, intensity decrease and shape changes, modification of thermal stability and by changes in the appearance of adsorbent microstructure images owing mainly to ion exchange mechanism.

Effects of micrometer-scale surface roughness on thermal infrared emittance spectra of silica glass

Surface roughness is known to decrease thermal infrared (TIR) absorption band intensity, but studies of the effect on geologically relevant samples are relatively limited. To determine the effect of surface roughness (with features smaller than ~2/3 of the wavelength) on TIR spectra, we investigated two glass compositions with prepared roughened surfaces: (1) high purity fused silica and (2) soda-lime glass (73 wt% SiO2). We roughened the surfaces of the glasses by sandblasting and polishing with grit paper. The surfaces were characterized with scanning electron microscopy and stylus profilometry. We then analyzed the roughened glasses with TIR emittance spectroscopy. Micrometer-scale roughness causes a decrease in TIR absorption band intensity, relative to a specular surface. No significant changes in band shape or shifts in wavelength were detected. As roughness increases, empirical results show a logarithmic decrease in TIR absorption band intensity. The logarithmic trends of the two glass compositions are different; empirical roughness calibrations do not translate across different compositions. A linear, least-squares spectral deconvolution using two endmembers, specular and blackbody, predicts model spectra of roughened glass surfaces with relatively low error. This is of consequence to orbital TIR measurements of poorly constrained targets, such as the martian surface, because micrometer-scale roughness is adequately modeled by the addition of a blackbody spectrum to the deconvolution endmember matrix.

CaF2: An Ideal Substrate Material for Infrared Spectroscopy?

CaF2 seems to be the ideal substrate material for the infrared spectroscopy of organic and biological layers, since its refractive index is very similar to that of these materials. As a consequence of this similarity, the baseline, i.e., the signal strength in nonabsorbing regions, is nearly flat and does not show notable interference fringes. Nevertheless, as absorption is always accompanied by changes of the refractive index, the refractive indices of substrate and layer can substantially deviate around absorption bands. As a consequence, changes in band intensity, shape, and position result, which aggravate a correct interpretation of the spectra. For layers with thicknesses between 1 and 2 μm, we show experimentally, that deviations from the Beer-Lambert law of up to ±10% occur. Calculations reveal that for thinner layers these deviations are even higher. These results suggest the application of a wave-optics based formalism to correct the deviations. We introduce such a formalism and prove that it is able to remove the errors. In addition, it also corrects band shape and position changes.

Removing interference-based effects from infrared spectra - interference fringes re-revisited.

Substantial refractive index mismatches between substrate and layers lead to undulating baselines, which are known as interference fringes. These fringes can be attributed to multiple reflections inside the layers. For thin and plane parallel layers, these multiple reflections result in wave interference and electric field intensities which strongly depend on the location within the layer and wavenumber. In particular, the average electric field intensity is increased in spectral regions where the reflectance is reduced. Therefore, the most important precondition for the Beer-Lambert law to hold, absorption as the single reason for electric field intensity changes, is no longer valid and, since absorption is proportional to the electric field intensity, considerable deviations from the Beer-Lambert law result. Fringe removal is consequently synonymous with correcting deviations from the Beer-Lambert law in the spectra. Within this contribution, we introduce an appropriate formalism based on wave optics, which allows a particularly fast and simple correction of any interference based effects. We applied our approach for correcting transmittance spectra of Poly(methyl methacrylate) layers on silicon substrates. The interference effects were successfully removed and correct baselines, in good agreement with the calculated spectra, were obtained. Due to its sound theoretical foundation, our formalism can be used as benchmark to test the performance of other methods for interference fringe removal.

Vibrational Relaxation and Redistribution Dynamics in Ruthenium(II) Polypyridyl-Based Charge-Transfer Excited States: ACombined Ultrafast Electronic and Infrared Absorption Study.

Ultrafast time-resolved electronic and infrared absorption measurements have been carried out on a series of Ru(II) polypyridyl complexes in an effort to delineate the dynamics of vibrational relaxation in this class of charge transfer chromophores. Time-dependent density functional theory calculations performed on compounds of the form [Ru(CN-Me-bpy) x(bpy)3-x]2+ ( x = 1-3 for compounds 1-3, respectively, where CN-Me-bpy is 4,4'-dicyano-5,5'-dimethyl-2,2'-bipyridine and bpy is 2,2'-bipyridine) reveal features in their charge-transfer absorption envelopes that allow for selective excitation of the Ru(II)-(CN-Me-bpy) moiety, the lowest-energy MLCT state(s) in each compound of the series. Changes in band shape and amplitude of the time-resolved differential electronic absorption data are ascribed to vibrational cooling in the CN-Me-bpy-localized 3MLCT state with a time constant of 8 ± 3 ps in all three compounds. This conclusion was corroborated by picosecond time-resolved infrared absorption measurements; sharpening of the CN stretch in the 3MLCT excited state was observed with a time constant of 3.0 ± 1.5 ps in all three members of the series. Electronic absorption data acquired at higher temporal resolution revealed spectral modulation over the first 2 ps occurring with a time constant of τ = 170 ± 50 fs, in compound 1; corresponding effects are significantly attenuated in compound 2 and virtually absent in compound 3. We assign this feature to intramolecular vibrational redistribution (IVR) within the 3MLCT state and represents a rare example of this process being identified from time-resolved electronic absorption data for this important class of chromophores.

Temperature-dependent hygroscopic behaviors of atmospherically relevant water-soluble carboxylic acid salts studied by ATR-FTIR spectroscopy

Model of aerosols and cloud formation processes requires extensive data on hygroscopic properties of water soluble organic species at lower troposphere relevant temperatures, which are ubiquitously found in atmospheric aerosols. Recent field studies (Kerminen et al., 1998) have revealed that sea salt aerosols can be efficiently chemically processed by water soluble carboxylic acids and lead to chloride depletion and formation of carboxylic acid salts. In this study, we report hygroscopic properties of four carboxylic acid salts, namely, sodium formate, sodium acetate, sodium oxalate and sodium succinate at temperatures commonly encountered in the lower troposphere ranging from 295.8 K to 270.0 K for the first time via attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Deliquescence relative humidity (DRH) and efflorescence relative humidity (ERH) of these carboxylic salts as a function of temperature were derived using both changes in water-to-solute (WSR) data and changes in band positions and shapes of carboxylate asymmetric and symmetric stretch modes. Hygroscopic data were also fitted by polynomial and corresponding coefficients were obtained. Our results have shown that these carboxylic acid salts exhibit strong temperature dependence and they would deliquesce at a lower humidity and are more likely to remain deliquesced when they are elevated in the troposphere. Since all these carboxylic acid salts present very different hygroscopic behaviors at lower temperatures from that of NaCl, chemically processed sea salt aerosols by carboxylic acids are expected to have fairly different phase state, size, and water content, consequently affecting their reactivity, lifetime, and ability to serve as cloud condensation nuclei.

Model-Based Analyses of Confined Polymer Electrolyte Nanothin Films Experimentally Probed by Polarized ATR–FTIR Spectroscopy

Orientational ordering within nanoscale (70–8 nm) thickness fluorinated ionomer films on Si substrates was investigated through the use of attenuated total reflection Fourier transform infrared (ATR–FTIR) spectroscopy in conjunction with electromagnetic field calculations. A spectral model was developed for Nafion thin films across the 1400–950 cm–1 region from frequency-dependent, isotropic optical constants derived from Kramers–Kronig analysis of ionomer transmission infrared spectra. The model considered infrared light propagation within the parallel boundary regions between the Ge ATR crystal, the ionomer film, and the Si substrate supporting the film. The calculations reproduced overall polymer thickness-dependent changes in peak frequencies and band shapes observed in experimental spectra recorded with p- and s-polarized light. General trends were traceable to effects of anomalous dispersion and electric field enhancement within the nanoscale gap separating the Ge and Si phases. However, optical eff...

A chemometric cleanup using multivariate curve resolution in liquid chromatography: Quantification of pesticide residues in vegetables

Both extraction and chemical cleanup are steps performed when the official AOAC 2007.01 QuEChERS method is used. The chemical cleanup step is required because many co-extractives may still be present after the whole samples extraction; however, it may reduce recovery of certain analytes due to non-selectivity of this step. In addition, unexpected constituents may still interfere with the analysis even when chemical cleanup is carried out, impairing univariate quantification. A chemometric cleanup using MCR-ALS is proposed as an alternative to the QuEChERS chemical cleanup. The performance of the proposed approach was demonstrated through quantification of seven pesticide residues (Carbendazim, Thiabendazole, Fuberidazole, Carbofuran, Carbaryl, 1-naphthol, and Flutriafol) in four non-spiked vegetable samples using HPLC-DAD. With the proposed strategy, it was possible to perform a reliable quantification despite the presence of co-eluted constituents (analytes and interferents), peak shift, band shape changes and avoiding the chemical cleanup with low analyte losses and LOD.

Interstellar ice analogs: H2O ice mixtures with CH3OH and NH3in the far-IR region

Context. New spectroscopic observations in the far-infrared (IR) range are expected from future planned missions. Although water ice is the only species detected so far in interstellar ices in this range, the presence of ice mixtures requires laboratory characterization of the corresponding spectra.Aims. We present an investigation on far-IR spectra of binary ice mixtures relevant in various astrophysical environments. The foremost goal is to compare the spectroscopic features of the ice mixtures to those of pure ices, and to search for changes in peak frequencies, intensities, and band strengths of the main bands.Methods. Mixtures H2 O:CH3 OH and H2 O:NH3 of different ratios have been deposited on a diamond substrate at astrophysically relevant conditions. We measured the spectra in the near- and mid-IR regions to derive ice column densities that were subsequently used to calculate the apparent band strengths in the far-IR region. We also designed theoretical models to study these mixtures and to predict their spectra.Results. We recorded spectra of amorphous phases for H2 O:CH3 OH mixtures of different compositions, that is 1:1, 3:1, and 10:1 at 8 K, and compared these mixtures to those obtained after warming. This process involves the appearance of new spectral features and changes in band shapes and band strengths. We also compared the spectra to those of the pure species and to theoretical predictions. We measured apparent band strengths for all the observed features. For H2 O:NH3 mixtures, the ratios selected were 3:1, 1:1, and 1:3. In this case the spectral variations are even more marked than for the water:methanol samples. Conclusions. Band strengths in the far-IR are missing in astrophysics literature for ice mixtures. The results presented here are valuable for detecting the presence and composition of such mixtures from future space observations in this spectral region.

Ground-based direct-sun DOAS and airborne MAX-DOAS measurements of the collision-induced oxygen complex, O<sub>2</sub>O<sub>2</sub>, absorption with significant pressure and temperature differences

Abstract. The collision-induced O2 complex, O2O2, is a very important trace gas for understanding remote sensing measurements of aerosols, cloud properties and atmospheric trace gases. Many ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements of the O2O2 optical depth require correction factors of 0.75 ± 0.1 to reproduce radiative transfer modeling (RTM) results for a nearly pure Rayleigh atmosphere. One of the potential causes of this discrepancy is uncertainty in laboratory-measured O2O2 absorption cross section temperature and pressure dependencies due to difficulties in replicating atmospheric conditions in the laboratory environment. This paper presents ground-based direct-sun (DS) and airborne multi-axis (AMAX) DOAS measurements of O2O2 absorption optical depths under actual atmospheric conditions in two wavelength regions (335–390 and 435–490 nm). DS irradiance measurements were made by the Washington State University research-grade Multi-Function Differential Spectroscopy Instrument instrument from 2007 to 2014 at seven sites with significant pressure (778 to 1013 hPa) and O2O2 profile-weighted temperature (247 to 275 K) differences. Aircraft MAX-DOAS measurements were conducted by the University of Colorado (CU) AMAX-DOAS instrument on 29 January 2012 over the Southern Hemispheric subtropical Pacific Ocean. Scattered solar radiance spectra were collected at altitudes between 9 and 13.2 km, with O2O2 profile-weighted temperatures of 231 to 244 K and nearly pure Rayleigh scattering conditions. Due to the well-defined DS air-mass factors during ground-based measurements and extensively characterized atmospheric conditions during the aircraft AMAX-DOAS measurements, O2O2 "pseudo" absorption cross sections, σ, are derived from the observed optical depths and estimated O2O2 column densities. Vertical O2O2 columns are calculated from the atmospheric sounding temperature, pressure and specific humidity profiles. Based on the ground-based atmospheric DS observations, there is no pressure dependence of the O2O2 σ within the measurement errors (3%). Two data sets are combined to derive the peak σ temperature dependence of the 360 and 477 nm dimer absorption bands from 231 to 275 K. DS and AMAX-derived peak σ ( O2O2) as a function of T can be described by a quadratic function at 360 nm and linear function at 477 nm with about 9% ± 2.5% per 44 K rate. Recent laboratory-measured O2O2 cross sections by Thalman and Volkamer (2013) agree with these "DOAS apparent" peak σ( O2O2) at 233, 253 and 273 K within 3%. Changes in the O2O2 spectral band shape at colder temperatures are observed for the first time in field data. Temperature effects on spectral band shapes can introduce errors in the retrieved O2O2 column abundances if a single room temperature σ( O2O2) is used in the DOAS analysis. Simultaneous fitting of σ( O2O2) at temperatures that bracket the ambient temperature range can reduce such errors. Our results show that laboratory-measured σ( O2O2) (Hermans, 2011, at 296 K and Thalman and Volkamer, 2013) are applicable for observations over a wide range of atmospheric conditions. Column densities derived using Hermans (2011) σ at 296 K require very small correction factors (0.94 ± 0.02 at 231 K and 0.99 ± 0.02 at 275 K) to reproduce theoretically calculated slant column densities for DS and AMAX-DOAS measurements. Simultaneous fitting of σ( O2O2) at 203 and 293 K further improved the results at UV and visible wavelengths for AMAX-DOAS.

Measurements of the absorption cross section of (13)CHO(13)CHO at visible wavelengths and application to DOAS retrievals.

The trace gas glyoxal (CHOCHO) forms from the atmospheric oxidation of hydrocarbons and is a precursor to secondary organic aerosol. We have measured the absorption cross section of disubstituted (13)CHO(13)CHO ((13)C glyoxal) at moderately high (1 cm(-1)) optical resolution between 21 280 and 23 260 cm(-1) (430-470 nm). The isotopic shifts in the position of absorption features were found to be largest near 455 nm (Δν = 14 cm(-1); Δλ = 0.29 nm), whereas no significant shifts were observed near 440 nm (Δν < 0.5 cm(-1); Δλ < 0.01 nm). These shifts are used to investigate the selective detection of (12)C glyoxal (natural isotope abundance) and (13)C glyoxal by in situ cavity enhanced differential optical absorption spectroscopy (CE-DOAS) in a series of sensitivity tests using synthetic spectra, and laboratory measurements of mixtures containing (12)C and (13)C glyoxal, nitrogen dioxide, and other interfering absorbers. We find the changes in apparent spectral band shapes remain significant at the moderately high optical resolution typical of CE-DOAS (0.55 nm fwhm). CE-DOAS allows for the selective online detection of both isotopes with detection limits of ∼200 pptv (1 pptv = 10(-12) volume mixing ratio), and sensitivity toward total glyoxal of few pptv. The (13)C absorption cross section is available for download from the Supporting Information.

Mechanism of the intramolecular charge transfer state formation in all-trans-β-apo-8'-carotenal: influence of solvent polarity and polarizability.

In this work we analyzed the infrared and visible transient absorption spectra of all-trans-β-apo-8'-carotenal in several solvents, differing in both polarity and polarizability at different excitation wavelengths. We correlate the solvent dependence of the kinetics and the band shape changes in the infrared with that of the excited state absorption bands in the visible, and we show that the information obtained in the two spectral regions is complementary. All the collected time-resolved data can be interpreted in the frame of a recently proposed relaxation scheme, according to which the major contributor to the intramolecular charge transfer (ICT) state is the bright 1Bu(+) state, which, in polar solvents, is dynamically stabilized through molecular distortions and solvent relaxation. A careful investigation of the solvent effects on the visible and infrared excited state bands demonstrates that both solvent polarity and polarizability have to be considered in order to rationalize the excited state relaxation of trans-8'-apo-β-carotenal and clarify the role and the nature of the ICT state in this molecule. The experimental observations reported in this work can be interpreted by considering that at the Franck-Condon geometry the wave functions of the S1 and S2 excited states have a mixed ionic/covalent character. The degree of mixing depends on solvent polarity, but it can be dynamically modified by the effect of polarizability. Finally, the effect of different excitation wavelengths on the kinetics and spectral dynamics can be interpreted in terms of photoselection of a subpopulation of partially distorted molecules.

Effect of Au and Ru in Au@Pd and Ru@Pd Core@Shell Nanoparticles for Direct Formic Acid Fuel Cells

The study of Pd-based core@shell bimetallic catalysts with Pd as the shell and another transition metal as the core has generated great interest in the field of PEM fuel cells because their electronic and chemical properties are completely different from pure Pd. As the anode catalyst in direct formic acid fuel cells (DFAFCs), an enhanced activity has been obtained for these Pd-based core@shell nanoparticles compare to pure Pd for formic acid oxidation [1,2]. However, there is a lack of understanding of how these added transition metals interact with Pd, namely by influencing their electronic structure and chemical property toward electrochemical oxidation of formic acid. It is important to fill this knowledge gap and find out a trend between the effect of the transition metals and the activity. This will help developing more efficient and less cost DFAFCs.In this study, Au@Pd and Ru@Pd core@shell nanoparticles with same thickness of Pd are synthesized via a two-step process. Non-supported nanoparticles are used for TEM and X-ray photoelectron spectroscopy (XPS) analysis. TEM is used to characterize the structure and morphology of the nanoparticles. XPS is used to differentiate the chemical shifts due to charge transfer between Pd and Au (or Ru). XPS analysis shows a different binding energy shift for Pd peak of Au@Pd and Ru@Pd compare to that of pure Pd nanoparticles. In addition, a change of the XPS valence band shape and down-shift of the d-band center are also observed. This different binding energy shift indicates that Au and Ru core interact with Pd shell and significantly influence the electronic structure of Pd. Electrochemical measurements (cyclic voltammetry and chronoamperometry) are used to investigate the electrochemical activity of carbon supported Au@Pd and Ru@Pd core@shell nanoparticles toward formic acid oxidation. The Pd loading of the carbon supported samples is 40wt%. Based on CV results shown in Figure 1, Au@Pd shows the best activity toward formic acid oxidation, which is about twice higher than that of Pd/C. The relationship between the electronic perturbation and electrochemical activity will be elucidated in this paper. Furthermore, a real direct formic acid fuel cell test will be also operated with these Au@Pd and Ru@Pd core@shell nanoparticles under the various fuel cell operating conditions.

Structural and electrical characterization of annealed Si1−xCx/SiC thin film prepared by magnetron sputtering

Si-rich Si1—xCx /SiC multilayer thin films are prepared using magnetron sputtering, subsequently followed by thermal annealing in the range of 800–1200 °C. The influences of annealing temperature (Ta) on the formation of Si and/or SiC nanocrystals (NCs) and on the electrical characteristics of the multilayer film are investigated by using a variety of analytical techniques, including X-ray diffraction (XRD), Raman spectroscopy and Fourier transform infrared spectrometry (FT-IR), current—voltage (I—V) technique, and capacitance-voltage (C—V) technique. XRD and Raman analyses indicate that Si NCs begin to form in samples for Ta ≥ 800 °C. At annealing temperatures of 1000 °C or higher, the formation of Si NCs is accompanied by the formation of SiC NCs. With the increase in the annealing temperature, the shift of FT-IR Si—C bond absorption spectra toward a higher wave number along with the change of band shape can be explained by a Si—C transitional phase between the loss of substitutional carbon and the formation of SiC precipitates and a precursor for the growth of SiC crystalline. The C—V and I—V results indicate that the interface quality of Si1—xCx/SiC multilayer film is improved significantly and the leakage current is reduced rapidly for Ta ≥ 1000 °C, which can be ascribed to the formation of Si and SiC NCs.

Determination of five pesticides in juice, fruit and vegetable samples by means of liquid chromatography combined with multivariate curve resolution

The aim of this work was to quantify five commonly used pesticides (propoxur, carbaryl, carbendazim, thiabendazole and fuberidazole) in real samples as: tomato, orange juice, grapefruit juice, lemon and tangerine. The method used for the determination of these analytes in the complex matrices was high-performance liquid chromatography with diode array detection. In order to work under isocratic conditions and to complete each run in less than 10min, the analysis was carried out applying multivariate curve resolution coupled to alternating least-squares (MCR–ALS). The flexibility of this applied multivariate model allowed the prediction of the concentrations of the five analytes in complex samples including strongly coeluting analytes, elution time shifts, band shape changes and presence of uncalibrated interferents. The obtained limits of detection (in μgL−1) using the proposed methodology were 2.3 (carbendazim), 0.90 (thiabendazole), 12 (propoxur), 0.46 (fuberidazole) and 0.32 (carbaryl).

Surface plasmonic contribution to SEIRA and asymmetrical band

The Surface Enhanced InfraRed Absorption (SEIRA) band reaches its the maximum intensity and the band shape becomes asymmetric at the just percolated metal thin films. To explain for them, various models (e.g. the Fano model) have been proposed. However, no model can explain them completely. In this paper, we conducted a classical model calculations (Fresnel’s formula and the Bruggemann effective medium theory) for SEIRA and asymmetric bands. The calculated SEIRA spectra were good agreement with the experimentally spectra. Therefore, the asymmetrical SEIRA band might not be attributable to Fano model. Moreover, we specifically addressed the relation between effective dielectric constants of a metal–insulator composite thin film and SEIRA band shape change. Although the sign of the real part switched from positive to negative and although the imaginary part became metallic, the asymmetrical band shape did not change. The sign of the real part is

Solvent versus Temperature Control over the Infrared Band Shape and Position in Fe(CO)3(η4-Ligand) Complexes

The solute-solvent interactions between Fe(CO)3(η(4)-cyclooctatetraene) (FeCOT) and 27 solvents were examined by infrared (IR) spectroscopy. The observed change in band shape and position of the carbonyl bands as a function of solvent was found to be very similar to that previously observed in temperature-dependent IR experiments of Fe(CO)3(η(4)-norborndiene) (FeNBD). While for FeNBD the change in band shape results from dynamic exchange of carbonyl ligands, temperature-dependent IR experiments in ethyl acetate show that the observed changes are not a result of carbonyl ligand site exchange for FeCOT. We therefore concluded that the solvent dependence of the IR spectra must be a consequence of a static solute-solvent interaction. We find that the linear solvation energy model (J. Am. Chem. Soc. 1977, 99, 6027-6038; Chem. Soc. Rev. 1993, 22, 409-416) provides a satisfactory account for the spectral changes due to the solvent. From this model, we are able to conclude that the solute-solvent interactions of this system are influenced by the solvent's polarizability and hydrogen bonding acidity. We also observed interdependence between the change in fwhm and band positions for all three carbonyl bands, which brings us to the conclusion that the observed changes in the IR carbonyl band shape of FeCOT are a consequence of the solute-solvent interactions, rather than any solvent friction effects. This implies that care must be taken to separate the effects of chemical dynamics and solvatochromism when examining IR spectra of molecules suspected of exhibiting dynamically broadened vibrational spectra.