In this review, papers related to the study of the spectral properties of ketocyanine dyes are considered from the viewpoint of the theory of chromophore interaction. It is shown that the use of this theory makes it possible to describe the properties of a number of bichromophoric polyenic donor-acceptor compounds and to predict their molecular configuration and spectral features.

The composition and temperature of molten metal in a furnace are important parameters in metallurgical industrial processing. Laser-induced breakdown spectroscopy (LIBS) is a promising technique for the in-situ quantitative composition analysis of molten metal, and infrared radiation from molten metal can be used for temperature measurement. A near-infrared spectrometer was added to a LIBS system in this work. The LIBS signal and temperature information were recorded by the same optical system and optical fiber, and the temperature and the elemental content of the molten metal could be measured simultaneously. Molten carbon steel was used to verify the system performance. The measured temperature exhibited a good consistency with the temperature that was obtained by using a commercial pyrometer, with a relative root mean square error of 0.95%. The relative standard errors of Cr and Mn composition detection were lower than 10%. These results prove that it is possible to monitor composition and temperature in a molten metal process by a LIBS systems imultaneously.

The possibility of formulating and solving the problem of the probabilities of chemical reactions as a problem of the energy levels of molecular objects and the probabilities of transitions between them is considered. The features of using multiminimum Gaussian potentials in such problems are discussed. The algorithm for ab initio calculating the probabilities of chemical transformations with given initial conditions and a list of structures participating in the process is proposed. It is shown that the algorithm can be constructed using a variational procedure on the basis of the functions corresponding to the solutions of both one-dimensional problems with a multiminimum potential and problems for each well separately.

The geometrical structure of the phthalocyanine molecules (MgPc, H₂Pc) and their b-octaphenyl derivatives (MgPcPh₈, H₂PcPh₈) was calculated by the DFT PBE/TZVP method, and the calculations of the excited electronic states were carried out by the modified INDO/Sm method. Taking into account the data for the porphyrazines MgTAP and H₂TAP, the detailed consideration of bond lengths was performed. It was shown that the weight of the internal 16-atom macroheterocycle in the electronic structure of MgPc and MgPcPh₈ increases as compared to MgTAP, while the contribution of the 18-atom azacyclopolyene for the free bases H₂Pc and H₂PcPh₈ becomes weaker as compared to H₂TAP. The two lowest unoccupied MOs and the highest occupied MO of the molecules considered are 70% localized on the internal 16-atom macrocycle (INDO/Sm data); as for the lower-energy filled MOs, there is strong mixing of the p AOs of the 16-atom macrocycle with the p MOs of the annelated benzene rings (MgPc and H₂Pc) and additionally with the p MOs of the phenyl rings (MgPcPh₈ and H₂PcPh₈). The Q state energies calculated by the INDO/Sm method agree with the experimental data with an accuracy of 200-400 cm^-1. It is emphasized that the observed broad absorption spectrum in the range 27000-37000 cm^-1 (Soret band) of phthalocyanines should be, first of all, assigned to several pp* transitions for which both the local excitation of the 16-atom macrocycle and the electron transfer of the type of the 16-atom ring « the benzene fragments are characteristic. If only, two most intense pp* transitions are taken into account, there is a qualitative agreement between the calculation and the experiment, but the calculated energies are overestimated by ~3000 cm^-1. For MgPcPh₈, the calculated energy of the most intense transition is in good agreement with the experimental maximum of the Soret band (an over-estimation is only 900 cm^-1).

Coal tar is a complex mixture of a large number of polycyclic aromatic hydrocarbons (PAHs) and heterocyclic compounds. The terahertz (THz) spectral properties of coal tar are studied by terahertz time-domain spectroscopy (THz-TDS). The absorption coefficient, refractive index, and relative permittivity of coal tar in the range of 0.2-2.5 THz are determined. Compared with pure cyclic hydrocarbons such as benzene, quinolone, and carbazole that are able to be extracted from coal tar, it is surprising to find that coal tar has a higher transmittance to THz waves than its pure components.

It is shown that the Frank-Condon principle, the thermal equilibrium population of sublevels of the initial electronic state, and the independence of the probability of elementary transitions of the temperature permit to find the frequency of the electronic 0-0-transition (n₀₀) not only from the dependence of the cross-section spectra s(n) on frequency, but also from their relative changes with the variation of the temperature. In this case, n₀₀ corresponds to the minimum of the dependence of the sum of the average energies of combining states on the frequency or to the extremum of the function ±hn/2 - ¶ln(s(n))/¶(1/kT) (the signs“+” and “-“ should be used for the absorption and emission, respectively) on the same parameter. The approach is tested on vapor spectra of some substances and show better precision than that by frequency dependence, especially for overlapped spectra.

He absorption and luminescence spectra of 7-azaindole in vapors are measured. The absorption spectrum in the 240-300 nm region has a wide band, against which a sequence of vibrational maxima is observed. Two bands are observed in the luminescence spectrum, one of which relates to fast fluorescence with a maximum of λ_mаx=305 nm, the second band with λ_mаx = 520 nm refers to long-lasting luminescence. The fluorescence spectrum under excitation in the 0-0-transition region (λ_ex = 289 nm) has a quasilinear structure. At other excitation wavelengths, the fluorescence spectrum is diffuse. The long-lasting luminescence in the microsecond time range is interpreted as the luminescence of free radicals formed due to the triplet-triplet annihilation. Excited states of free radicals are populated by nonradiative energy transfer from the triplet states of 7-azaindole to the doublet states of free radicals.

The majority of studies on silicate glass spherules containing fly ash deal only with the determination of their chemical composition. Nearly 70 vol.% of fly ash is comprised of silicate glass spherules. Here, we report spectroscopic properties of silicate glass spherules using the laser micro-Raman and Fourier transform infrared techniques coupled with refractive index measurements, X-ray diffraction, and electron probe micro analysis to better ascertain their physical and chemical properties. Glass spherules show similar refractive indices (1.499-1.510) and a bell-shaped diffraction pattern with 5-10 vol.% of crystallites observed on microscopic and submicroscopic scales. The bulk chemical composition of fly ash spherules is predominantly silica-rich (SiO₂: 70.96-74.13 wt.%) with a subordinate amount ofAl₂O₃(0.11-0.69 wt.%), FeO_(Total)+MgO (3.6-4.94 wt.%), and CaO + Na₂O + K₂O (20.83-22.62 wt.%). The infrared spectra suggest the presence of a dissolved -OH- bearing fluid phase in the studied fly ash spherules. The spectra also show symmetric stretching peaks of C-O-C due to the atmospheric CO₂ adsorption at 2350 cm^-1. The Raman spectra show broad amorphous and/or short-ordered phases.

Based on laser atomic emission spectroscopic analysis, a technique has been developed for the rapid determination of carbon content in low-alloy steels. The C I 909.483 nm carbon line in the near infrared region of the spectrum was chosen as an analytical one. Optimization of the conditions for the spectrum recording in this region is carried out. It is shown that the transition to a double-pulse mode of excitation enhances the intensity of the spectral lines of the elements included in the composition of the analyzed sample, and reduces the intensity of lines of the elements included in the composition of the air, which allows the analysis of the line under normal atmospheric conditions. The calibrated dependence for carbon steels is linear for the practically important concentration range of the determining component of this steel grade. The measurement error of the carbon concentration, and also the influence of pollution of atmosphere of a working environment by this element on its determination are estimated.

Photoconductive and photovoltaic properties of film composites based on the new oligomer polyepoxypropylpyridobenzothiazole were compared with the known poly-N-epoxypropylcarbazole, which contains the squarylium dye as a photoconductivity sensitizer. It is found that these composites have a photoconductivity of the hole type, and the internal photoelectric effect is determined by the photogeneration of charge carriers from dye molecules and transport of the holes over donor fragments of the polymer matrix. The photoconductivity and photovoltaic response increase with the transition to a new oligomer with the more efficient conjugation system in the donor fragments.

Topologically disordered films based on binary mixtures of SiO₂ nanoparticles with CdS quantum dots on their surfaces with different surface and volume concentrations are studied. For the first time, a percolation transition of excitons has been observed in the CdS quantum dots array on a quasi-two-dimensional surface and the features of its formation have been described qualitatively. A percolation transition of excitons in a film based on a binary mixture of pure SiO₂ and coated with quantum dots (SiO₂/CdS), which is analogous to the phase transition of metal and dielectric macroparticles, has also been observed. It is shown that the percolation transition in such a system occurs at a critical concentration of nanoparticles of one sort (n_c ~ 0.6), which is almost twice as high as in the macroparticle system (~0.29). This is due to the interaction between nanoparticles (van der Waals forces and electrostatic forces) and the chemical nature of the binding ligand.

The rapid analysis of 6-benzylaminopurine (6-BAP) residue by surface-enhanced Raman spectroscopy with a portable Raman spectrometer is reported. The results showed that the Raman signals of 6-BAP can be significantly enhanced when mixed with a gold nanoparticle colloid substrate. The typical Raman shifts of 6-BAP extraction were at 1002, 1318, and 1336 cm^-1and the intensities of normalized characteristic band at 1002 cm^-1 (I₁₀₀₂to I₇₃₈) showed high correlation with 6-BAP concentrations. The concentration linear range was 0.1-5.0 μg/mL. The coefficient of determination (R²) was about 0.99, and calculated RSDs below 10%. The SERS data matched well with the HPLC results.

The Japanese roof iris, Iris tectorum Maxim., is used as the research object, and we analyze the spectral characteristics of the aquatic vegetation in outdoor mesocosms under different coverage percentages. A field spectrometer was used to measure the irises’ vegetation canopy spectral reflectance. Experimental results showed that decreases in the iris coverage led to corresponding decreases in the canopy spectral reflectance. Differences in the iris canopy spectral reflectance under different coverage percentages were most pronounced in the 740-1350 and 1450-1800 nm band ranges. Linear relation models were constructed for the coverage and reflectance data at selected wavelengths, and high correlation coefficients were obtained. The results of the study are intended to provide model support for the monitoring of wetland aquatic vegetation using spectroscopy and are combine with remote sensing technology to aid in image interpretation and classification.

The accuracy of the extracted optical constants by terahertz time domain spectroscopy critically depends on the accuracy of the sample thickness. However, due to the large number of optimization steps, it is time consuming to extract the optical constants over a broad frequency range and determine the sample thickness simultaneously using conventional algorithms. With particular emphasis on thin liquid samples, a three-dimensional optimization algorithm was used to obtain the optical constants and sample thickness simultaneously , significantly reducing the calculation time. In the experiments, the THz signals of 200-mm-thick water in a known cuvette were measured, and its accurate thickness and optical constants were determined by the algorithm, validating the effectiveness of the approach.

A real-time comparative measurement method is proposed to enhance the measurement accuracy of Raman shifts. Several experimental configurations are presented and demonstrated. The error sources in Raman shifts are also analyzed. The method is tested on a Raman spectrometer by measuring a sample of monocrystalline silicon and a sample of polystyrene. Experimental results indicate that the accuracy limit of the method is 0.07 cm^{- 1} . The measurement uncertainty of the Raman shift of the silicon is 0.2 cm^{- 1} (k = 2), and the measurement uncertainty of the polystyrene is also improved. It is shown that the real-time comparative measurement method can remarkably enhance the measurement accuracy of Raman shift, and it applies to Raman spectrometers regardless of whether their exact laser wavelengths are known or not.

The spectral-luminescence properties of the 4-cyano-4'-pentylbiphenyl CH₃(CH₂)₄(C₆H₄)₂CN (5CB) liquid crystal has been studied in the temperature range 4.2-297 K. It is shown that at increasing temperature the fluorescence spectra are shifted to the red side. The spectral long-wavelength shifts are also analyzed. A comparison of the temperature behaviour position of the emission of the band maxima l_max and their half-widths Δl/2 in the fluorescence spectra and the results of the DSC-investigation show that phase transitions occur in 5CB liquid crystals at T ~ 230 and 260 K.

A pure material proportion estimation method based on a spectral database is proposed. The method transforms the non-negative and linear constraints into a pure material proportional cost function minimization problem with a linear mixed model. The Newton algorithm is used to optimize the cost function, and the optimized extreme value is the optimal estimate of the proportion of pure material. Spectral simulation experiments are carried out for space target materials using the US Geological Survey database, and the experimental results show that the method proposed in this paper can help to estimate the proportion of pure substances in such targets quickly and accurately, especially when the number of mixed pure materials is large. Compared with some existing common algorithms, the proposed method is robust and can estimate the proportion of pure material in a space target when the signal-to-noise ratio is less than 40 dB. The accuracy of the method is 30% higher than that of the existing method.

The direct imaging of adsorption of single colloidal quantum dotes with a diameter of ~10nm (spherical semiconductor core-shell nanocrystals of CdSeS/ZnS functionalized with organic oleic acid ligands) in nanopores of a nuclear filter (a track polypropylene membrane with the pores diameter of ~500nm) has been realized using fluorescence nanoscopy. It is shown that the nanoparticles are completely retained at a depth of 10 µm when the colloidal solution passes through the membrane pores.

The dynamic Fourier spectrometer for recording Raman spectra in the near-IR range (800-1100 nm) has been developed. Stability and reliability of the spectrometer operation is ensured by the use of corner reflectors in the design as mirrors of the main channel. For detecting a weak Raman signal in the spectrometer, a white light channel is realized that provides a binding to the zero optical path difference when summing interferograms over several scans. The reference channel with a sampling frequency of l/4 makes it possible to increase the sampling accuracy and the signal-to-noise ratio of the recorded emission spectra. Using the developed spectrometer, Raman spectra of test substances with known positions of the emission lines were registered: 1,4-bis (5-phenyl-2-oxazolyl) benzene (POPOP, C₂₄H₁₆N₂O₂), stilbene (C₁₄H₁₂), acetylsalicylic acid (C₉H₈O₄). A comparison of the Raman spectra of POPOP obtained by the dynamic spectrometer and a diffraction spectrometer in the same experimental conditions has shown their qualitative agreement, while the time of the spectral recording using the dynamic Fourier spectrometer is 4 times smaller.

An iterative algorithm for narrowing the definition domain of the distribution function of the hyperfine interaction parameter is proposed. The use of this algorithm increases the resolving power of the Tikhonov regularization method for solving the inverse problem of Mossbauer spectroscopy.

The effect of the amplitude anisotropy of nanoporous alumina films and depolarization of the transmitted radiation on the phase shift between the orthogonally polarized components of the transmitted radiation was studied using Stokes-polarimetry and coherence matrix methods. The test samples were illuminated by linearly polarized radiation with the polarization azimuth of 45° in the wavelength range from 400 to 1000 nm. The systematic error introduced into the phase shift between the orthogonally polarized components of the transmitted radiation because of neglecting the material amplitude anisotropy and the depolarization of the transmitted radiation was established.

The influence of complex defects related to the presence of protons on the optical properties of LiNbO₃:Y(0.24):Mg:(0.63 mas.%) and LiNbO₃:Gd(0.25):Mg(0.75 mas.%) crystals has been studied using IR absorption spectroscopy in the region of valence vibrations of OH^- groups, photoinduced and Raman scattering of light, and laser conoscopy. It is shown that the LiNbO₃:Y(0.24):Mg:(0.63 mas.%) crystal has a larger photorefraction effect than the LiNbO₃:Gd(0.25):Mg(0.75 mas.%) crystal and a congruent crystal. An anomalously fast (<1 s) disclosure of the speckle structure of the indicatrix of photoinduced light scattering in the LiNbO₃:Y(0.24):Mg(0.63 mas.%) crystal is found.

The present study proposes a novel method to discriminate the sex and species of silkworm pupae using NIR spectroscopy (800-2778 nm). The spectra from 840 silkworm pupae were collected then divided into a calibration set (700) and a test set (140) using the Kennard-Stone (KS) algorithm. The recognition models were built using the radial basis function and neural network (RBF-NN) and support vector machine (SVM) approaches. The species and sex identification results using the RBF-NN and SVM models based on full spectral data achieved a low accuracy of 5% and 33.57%, respectively. To improve the accuracy and decrease the processing time, both principal component analysis (PCA) and linear discriminant analysis (LDA) were used to reduce the data dimensions. The performance of the optimized SVM model (92.14%) was much better than the RBF-NN model (19.29%) based on PCA. Overall, the best discrimination results were obtained using the RBF-NN and SVM models based on LDA, providing an accuracy of 100%. These promising results have shown that the LDA-SVM and LDA-RBF-NN models can accurately recognize the sex and species of silkworm pupae using NIR spectroscopy.

A hyperspectral imaging system is proposed as a method to rapidly and non-destructively predict mycotoxin deoxynivalenol (DON) levels in FHB-infected wheat kernels. Standard normal variate transformation and multiplicative scatter correction (MSC) were used in spectral preprocessing. The successive projections algorithm (SPA) and random frog algorithm were used to select the optical wavelengths. Finally, the support vector machine (SVM) technique and partial least squares discriminant analysis were applied to establish different models for determining DON levels. Based on a comparison of the results, the MSC-SPA-SVM model, with the highest classification accuracy (100.00% for the training test and 97.92% for the testing set), gave the best performance, and a visualization map of the DON content level based on this model was created.

Principal components regression (PCR) and partial least squares regression (PLSR) are the two most powerful and widely used chemometric regression methods applied in laser-induced breakdown spectroscopy (LIBS) studies. In this work, we compared the analytical merits (accuracy and precision) of applying the PCR and PLRS algorithms to identical LIBS data sets. A set of stainless steel samples with multielemental concentration data was studied for this work. A detailed study of the PCR and PLSR coefficients and the corresponding spectra used to generate them was carried out to understand the role of the two algorithms in the evolution of the regression coefficient signal data. Based on this understanding, a few guidelines were proposed in this work for selecting PCR or PLSR depending on the analytical situation. This work identifies the situations wherein the PCR and PLSR application results are analytically equivalent and where one approach is superior over the other for LIBS data analysis.

The generation of high-order harmonics and single attosecond pulses from H₂⁺ has been theoretically investigated beyond the Born-Oppenheimer approximations. It is found that with the introduction of the inhomogeneous effects of the laser field in frequency and space, not only the harmonic cutoff can be remarkably enhanced, but also the single short quantum path can be selected. Further, with the increase of the initial vibrational state and by properly adding a terahertz controlling field, the harmonic yield can be enhanced by 2.5 orders of magnitude, showing a high-intensity supercontinuum with the bandwidth of 511 eV. As a result, four single attosecond pulses shorter than 28 as can be produced. Moreover, the present scheme can also be achieved in the multi-cycle pulse duration, which is much better for practical application.

The vibrational characteristics of a labdane diterpene, (E)-labda-8(17),12-diene-15,16-dial, have been studied using FT-IR, FT-Raman and surface-enhanced Raman spectroscopy (SERS). A good yield of the compound has been sourced and isolated from the seeds of Alpinia nigra. Experimentally obtained vibrational modes of the compound obtained by IR and Raman were verified by theoretical calculations at density functional theory (DFT) level using Gaussian 09 software package. Copper nanoparticles have been used to enhance the inherently weak Raman signals of the compound. In the SERS spectra, intense enhancement (up to 10³ fold) was observed in the bands at lower wavenumbers, corresponding to the in-plane deformations, which indicated perpendicular orientation of the compound on the metal surface. However, some bands were weakened by the proximity of the metal surface. This interaction was assessed by IR and visualized by electron microscopy, revealing that Cu nanoparticles lie in the vicinity of the compound, which is responsible for the SERS phenomenon.