Improvement of the parametric method of the theory of vibronic spectra of polyatomic molecules: Absorption spectra and the structure of butadiene, hexatriene, and octatetraene in the excited state

The structure of the excited states and absorption spectra of butadiene, hexatriene, and octatetraene are calculated by the parametric method of the theory of vibronic spectra using models of the first-and second-order approximations. It is shown that these molecular models adequately reflect the molecular structure and allow one to predict quantitatively the shape and fine vibrational structure of the absorption spectra. When passing to the second-order approximation, only two additional (angular) parameters are used. These parameters are transferable in the series of polyenes. Compared to the first-order approximation model, the second-order approximation model more accurately takes into account the angular deformations of polyenes upon their excitation and describes the intensity distribution in the vibrational spectrum, including weak lines. In addition, the calculations also quantitatively predict spectral variations in the molecular series. The parametric method is more efficient for modeling polyatomic molecules in the excited states and their vibrational spectra compared to other semiempirical and ab initio methods.     

Modeling of the vibrational structure of the vibronic spectra of diphenylpolyenes by the parametric method

The structures of the electronic-vibrational spectra and of the excited states of a number of diphenylpolyene molecules are determined within the framework of the second approximation of the parametric method. The system of parameters of the structural fragments of molecules is improved and good agreement with spectral experiment is obtained. It is shown that there is a high degree of transferability of the polyene and acene parameters of the method and that the models obtained are adequate to the real structure of molecules. It is also shown that the method proposed makes it possible to perform predictive qualitative and quantitative calculations of the spectra of these molecules, as well as of the spectral characteristics necessary for modeling photochemical molecular transformations. In the series of diphenylpolyene molecules, an interpretation of the vibrational structure of the spectra is proposed and the specific features of variation of the geometry upon excitation of molecules are considered.     

Modeling of the vibrational structure of the vibronic spectrum and an excited state of the dinaphthylethylene molecule

The vibrational structure of the fluorescence spectrum and the structure of a dinaphthylethylene molecule in an excited state are calculated in the first and second approximations of the parametric method employed in the theory of vibronic spectra. The calculated spectra are in quantitative agreement with experimental data. The role of the angular parameters of the parametric method in the quantitative prediction of the vibrational structure of the fluorescence spectrum and changes observed in the geometry of the dinaphthylethylene molecule under excitation is determined. It is demonstrated that the polyene and acene parameters of the parametric method possess a high degree of transferability and that the models obtained are quite adequate to the real structures of the molecules under investigation. The proposed approach permits qualitative predictions and quantitative predictive calculations of the spectra of the studied molecules, as well as the spectral characteristics necessary for simulation of photochemical molecular transformations.     

Calculation and interpretation of the vibronic spectra of pyridine and <Emphasis Type="Italic">trans</Emphasis>-1,2-di(2′-pyridyl)ethylene in the second approximation of the parametric method

The structures of pyridine and dipyridylethylene molecules in an excited state and their vibronic spectra are calculated within the second approximation of the parametric method. The system of parameters obtained, including parameters of the σ and π types, ensures a quantitative agreement between the theoretical and experimental spectra of the pyridine and dipyridylethylene molecules. This agreement indicates that the proposed model is adequate to the real structure of the molecules. The parameterization is sufficiently complete and provides a means for quantitatively modeling the vibrational structure of the spectra of complex molecules containing fragments similar to those characterized by the σπ* and ππ* transitions. It is demonstrated that, after such essential substitutions of atoms in the molecules, the system of parameters of the acene and polyene fragments retains the high stability. The vibrational structure of the electronic spectra of the pyridine and dipyridylethylene molecules is interpreted, and the changes observed in the geometry of these molecules under electronic excitation are analyzed.     

Modeling vibronic spectra and excited states of polyenes with a parametric method

The structural-dynamic models of excited states and vibronic structure of absorption spectra of linear polyenes (R-(CH=CH)_n-R, R=H, CH₃, n=4, 5, 7) are calculated using the parametric method of the theory of vibronic spectra of such molecules. Good agreement is obtained between the calculated and experimental spectra. It is shown that the system of parameters of the method for the polyenes has a high degree of transferability in the series of related polyenes. The constructed models adequately reflect the real structure of the molecules in excited states and allow one to predict quantitatively the fine vibrational structure of the spectra, including relatively weak effects related to the methyl substitution. The dynamic of structural changes of the molecules upon their excitation is studied in the series of polyenes.     

On the stability of parameters of molecular models in the parametric method of the theory of vibronic spectra

We have studied the stability of the system of parameters used in the parametric method of the theory of vibronic spectra of polyatomic molecules with respect to whether the initial structural-dynamic model of the ground state of a molecule is formed either by the fragmentary method or by direct quantum-chemical calculation. Modeling of excited states and spectra of the stilbene-h ₁₂ and stilbene-d ₁₂ molecules showed that, although the initial models of the ground states are significantly different, calculated changes in the geometry that occur upon excitation and electronic-vibrational spectra of the models are close and quantitatively agree with experiment. This indicates that the parameters of the method are stable and are applicable for performing predictive calculations of vibronic spectra based on models of the ground states created by different methods. We show that the fragmentary method has a considerable advantage, since models created by this method take into account the continuity of the structure in series of related compounds and calculations can be easily performed for molecules of arbitrarily high complexity. We show that direct quantum-chemical calculations are important in the case of molecules with unknown structural-dynamic models of fragments in the ground states.     

Fluorescence of pyrene in galactolipid liposomes and native membranes of etioplasts

The fluorescence parameters of pyrene and pyrenedecanoic acid in lipid micelles and native membranes of etioplasts whose basic lipid components are mono- and digalactosyldiacylglycerol (MGDG and DGDG) have been investigated. The vibrational structure of the emission spectra of pyrene (λ_exc = 337 nm) in the 370–400-nm range points to the hydrophilic microsurrounding of pyrene molecules in all types of the investigated membranes. The absence of MGDG from liposomes leads to a decrease in the degree of excimerization of a probe. In native membranes, this parameter increases with increasing content of pigments. Pyrene covalently bound to decanoic acid is found in the membranes of prolamellar bodies and in artificial monolayer micellae in an even more hydrophilic microsurrounding than the molecules of a free probe, and a decrease in the degree of eximerization is observed thereby. The specific features of localization of the investigated probes in plastid membranes are discussed. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 3, pp. 344–349, May–June, 2000.     

Relaxation processes of water confined to AlMCM-41 molecular sieves. Influence of the hydroxyl groups of the pore surface

A series of AlMCM-41 molecular sieves was prepared with constant composition (Si/Al = 14.7) and presumably same pore structure but different pore diameters (from 2.3 to 4.6 nm). The pore size distribution is narrow for each sample. The rotational fluctuations of water molecules confined inside the pores were investigated applying broadband dielectric spectroscopy (10⁻²–10⁷ Hz) over a large temperature interval (213–333K). A relaxation process, slower than that expected for bulk water, was observed which is assigned to water molecules forming a surface layer on the pore walls. The estimated relaxation time has an unusual non-monotonic temperature dependence, which is rationalized and modeled assuming two competing processes: rotational fluctuations of constrained water molecules and defect formation (Ryabov model). This paper focuses on the defects and notably the influence of the hydroxyl groups of the pore walls. The Ryabov model is fitted to the data and characteristic parameters are obtained. Their dependence on pore diameter is considered for the first time. The found results are compared with those obtained for other types of molecular sieves and related materials.     

IR spectra temperature changes and conformational structure of 4-butyl-4′-cyanobiphenyl

IR spectra of 4-butyl-4′-cyanobiphenyl in the liquid and solid-crystal states were measured in the 400–4000 cm^–1 region at 28–70°C. Changes of the spectra as a function of temperature are due to the conformational fluxionality of the molecules according to calculated IR spectra of the possible 4-butyl-4′-cyanobiphenyl conformers. Calculations were carried out using the method of fragments and the LEV-100 program package. Bands sensitive to the conformational changes in the molecular structure were found. IR spectra have been interpreted. Conclusions have been made about the conformations of the sample in the solid-crystal and liquid phases. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 3, pp. 325–333, May–June, 2009.     

Schemes for excitation of rare earth monoxides in flame laser-induced molecular ionization spectrometry

Laser-induced ionization spectra of PrO, TbO, and CeO molecules in a flame were recorded in the wavelength ranges 440–480 nm and 535–575 nm. Based on study of the spectra, we propose a two-step scheme for excitation of PrO and CeO molecules in which in the first step, the molecule goes to the excited electronic state, while the excitation energy in the second step is selected so that the total energy imparted to the molecule corresponds to its ionization potential. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 544–546, July–August, 2006.     

Relationship between the Structure and Photostability of Decahydroacridine Derivatives

The absorption and photoluminescence spectra of a number of derivatives of 3,3,6,6-tetramethyl-N-phenyl-decahydroacridine-1,8-dione with a regular change in the structure of molecules are investigated. Their electronic structure is calculated. The nature of some of the spectral bands is established. Significant differences in the efficiency of the processes of photochemical transformations of dyes exposed to UV irradiation have been revealed; these changes are attributable to the different donor-acceptor properties of the substituents introduced. A mechanism of phototransformations that agrees with both calculations of the electronic structure of molecules and the spectral-luminescent characteristics of the initial and irradiated compounds is suggested. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 4, pp. 454–459, July–August, 2005.     

Lattice vibrational spectra of nanocrystalline films of <Emphasis Type="Italic">para</Emphasis>-substituted benzene

We have obtained experimental low-frequency Raman spectra for para-dibromobenzene nanofilms of thickness ∼10 μm and ∼400 nm. With a decrease in the film thickness, the line frequencies are lowered, the linewidths increase, additional lines become more intense. We modeled the film structure by the molecular dynamics method and calculated the histograms of the lattice vibrational spectra by the Dean method. We found that as the film thickness decreases, the lattice parameters increase, the orientational disorder increases at its boundary. The structure of the studied film is similar to the structure of the para-dibromobenzene single crystal. In order to correctly interpret the lattice vibrational spectra, we need to take into account surface vibrations and the presence of vacancies in the structure. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 6, pp. 838–842, November–December, 2008.     

Effect of thermal blooming in second-harmonic generation in nonlinear crystals with a regular domain structure

Analytical expressions are obtained for the power of the second harmonic in nonlinear crystals having a regular domain structure with allowance for thermal blooming for a Gaussian beam of basic radiation in the quasi-stationary plane-wave approximation. Calculations were carried out in both the approximation of an assigned field of basic radiation and a substantially nonlinear regime of exhaustion of basic radiation. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 2, pp,. 257–260, March–April, 2000.     

Investigation of the optical properties of AgGaTe2 films obtained by laser deposition

We obtain thin films of AgGaTe₂ by laser vaporization of starting crystals. The compositions of the starting crystals and of the films obtained are determined by x-ray spectral analysis, with their structure and the parameters of the crystal lattice being determined by the x-ray method. The energies of interband transitions and crystalline (Δ _cr ) and spin-orbit (Δ _so ) splitting are calculated from transmission spectra in the region of the main absorption band. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 6, pp. 793–796, November–December, 1997.     

Development of diode laser absorption spectroscopy method for determining temperature and concentration of molecules in remote object

We develop a method of diode laser absorption spectroscopy for noncontact measurements of the temperature and pressure of a gas mixture under unsteady-state conditions at low signal-to-noise ratios. The method is based on the measurement of the absorption spectra of water molecules and approximation of experimental spectra by spectra simulated based on spectroscopic databases. Different approximation algorithms of experimental spectra are tested, such as fitting by individual contours and fitting by a part of the simulated spectrum. We reveal that, at small signal-to-noise ratios, the approximation of experimental data by a simulated spectrum yields more correct data on the temperature of the mixture compared to the fitting by individual contours. For the examined temperature range of 300–1300 K, the determination error of the gas temperature in the test cell proved to be approximately three times lower than upon fitting by individual contours. The developed method of recording and processing spectra is used to measure the temperature, water vapor concentration, and total pressure under the unsteady-state combustion conditions of an air-hydrogen mixture in a supersonic flow.     

Raman spectra and thermal disordering of the crystalline structure of benzene

Disordering of rotational degrees of freedom of molecules in a benzene crystal is investigated from Raman spectra. Nonuniform smearing of the spectrum of librational vibrations to the wing of the Rayleigh line is established. The changes observed are interpreted on the basis of calculations of frequencies, intensities, vibration modes, and barriers to molecular reorientations in the crystal by the method of atom-atom potentials. The line broadening in the spectrum of external vibrations by reorientations of molecules in the crystal as a function of their mode is analyzed. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 3, pp. 394–400, May–June, 1999.     

Allowance for angular divergence in the generation of the second harmonic in crystals with a regular domain structure

We obtained basic analytical expressions for the efficiency of the second harmonic in nonlinear crystals with a regular domain structure; in these expressions we took into account the angular divergence of the laser beam. The calculation was done in the geometric-optics approximation of the given field of laser radiation. We show that the expressions obtained are similar to the corresponding expressions for homogeneous nonlinear crystals. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 1, pp. 134–138, January–February, 2000.     

Interpretation of resonance Raman spectra of Zn-phthalocyanine and Zn-phthalocyanine-d<Subscript>16</Subscript> based on the density functional method

We have used the density functional method (DFT) to calculate the geometric structure and the frequencies of even (gerade) vibrations of the Zn-phthalocyanine and Zn-phthalocyanine-d₁₆ molecules, and we have refined the interpretation of the resonance Raman spectra and the fine-structure fluorescence spectra. We observed a dependence of the frequencies of both stretching and bending vibrations of the aza bridges on the nature of the central metal atom. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 3, pp. 296–299, May–June, 2007.     

Dependence of the spectral characteristics of quartz on the fluence of neutrons

The influence of radiation on the change in the optical properties of a crystalline quartz is investigated. The results of the measurement of the optical spectra of luminescence, reflection, and scattering in specimens irradiated with different fluences of neutron radiation are presented. It is shown that the corresponding spectral characteristics experience substantial changes in the region of fluences that are associated with rearrangement of the crystalline structure. The results of approximation of some radiation kinetics are given, and the trend in the process of accumulation of disordered zones is established. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 4, pp. 543–545, July–August, 2000.