Absorption Spectra of Excited Ruby Crystals

We have investigated the absorption spectra of excited laser single crystals of ruby. The longlived increase in absorption depending on the degree of excitation is observed in optically excited crystals of ruby in a wide spectral range. Moreover, in the absorption spectrum of a postexcited ruby we discovered the excitationinduced longlived kinetic instability, namely, the noiselike quasiline component variable in time and over the spectrum and imposed on the smooth spectral curve.     

Absorption Spectra of Pyrene Aggregates in Saturated Solutions

The longwave part of the absorption spectra of saturated pyrene solutions in a number of organic solvents is measured. The interpretation of the longwave trail in these spectra as a band of aggregative nature with a complex mechanism of its formation is proposed.     

Spectral Complex for Controlling the Parameters of the Plasmachemical‐Reactor Working Medium

An automated spectral complex for controlling the parameters of the plasmachemicalreactor working medium by the emission and absorption spectra in the 200–1100 and 2000–5000nm ranges has been developed. To record radiation, a CCD array and a pyroelectric detector are used. Control of the spectral device functions, data recording, and the obtaining of results reflecting the workingmedium parameters and the concentration in it of components being measured are carried out by means of a personal computer. The complex makes it possible to study the temporal behavior of the workingmedium parameters being measured with a resolution of up to 10^–2 sec.     

Profile Shape of Absorption Spectra in the IR Spectra of Carbohydrates

In the IR spectra of mono-, di-, and polysaccharides, the profile shapes of eight absorption bands have been investigated. They turned out to be symmetric and very close to the dispersion one for all the bands considered. It has been found that in mono- and disaccharides the minimum halfwidth of the bands is 10 cm^–1 and in polysaccharides it is higher by a factor of two or more. The halfwidth ratios of different bands in one and the same spectrum can differ severalfold. As is shown, double differentiation of the IR spectra makes it possible to investigate the profile shape of absorption bands when there is marked background absorption or these bands significantly overlap with other bands.     

Absorption and fluorescence of 8-azasteroids in the gas phase

Extensive studies of the spectral-luminescent characteristics of four 8-azasteroids and a model compound 2-(3,3-dimethyl-1,2,3,4-tetrahydro-1-isoquinolidene)-5,5-dimethyl-1,3-cyclohexanedion in the gas phase have been made. From the analysis of the dependences of the absorption spectra on the vapor pressure (T_low) and the fluorescence spectra on T_low and the exciting radiation wavelength (_exc) a conclusion on the presence in the vapors of the investigated 8-azasteroids of three absorption and fluorescence centers (S-, M-, and L-centers) has been drawn. The absorption spectra of these centers strongly overlap. Their long-wave absorption boundaries have been determined. The dependence of the fluorescence spectra of all three centers on _exc, which is inherent in rarefied gases of individual organic molecules, is observed. The S-centers are the molecules of the initial steroids, and the M- and L-centers are the molecules of thermo- and phototransformations of the initial steroids. The model compound in the gas phase is characterized by the same dependences of the fluorescence spectra on T_low and _exc as those inherent in 8-azasteroids. Taking into account the additional data obtained as a result of investigation of the absorption and fluorescence spectra of solutions of the substances extracted from vacuum cells after the investigation of 8-azasteroids and the model compound in the gas phase, conclusions on the nature of the M- and L-centers have been drawn.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 1, pp. 48–57, January–February, 2005.     

Mid-infrared absorption measurements of liquid hydrocarbon fuels near

Quantitative absorption spectra for several hydrocarbon fuels in the liquid phase at are presented. Measurements of toluene, n-dodecane, n-decane, and three samples of gasoline were made over the spectral region 2700–3200 to support the development of mid-infrared laser-absorption diagnostics for measurements of fuel vapor in the presence of liquid films and aerosols. A procedure for quantitative Fourier transform infrared (FTIR) absorption measurements of strongly absorbing liquids is described and the resulting absorption spectra are compared with previously measured absorption spectra in the vapor phase. The measured absorption spectra for liquid gasoline are shown to scale with the volume percent of olefin, alkane, and aromatic hydrocarbons in each sample. Finally, the observed frequency shift of in the spectra of vapor and liquid hydrocarbons is discussed, including the potential for measurements of fuel vapor in the presence of liquid films.     

Difference in the Nonlinearity of Absorption in Natural and Synthetic Coals

It is established that on an increase in the SHF radiation power for powder anthracite, a more rapid increase in the amplitude of the EPR line is observed in comparison to the case of linear absorption, whereas for carbon obtained by deposition of the products of pyrolysis of deuterobenzene (C₆D₆) on the surface of -Al₂O₃ there occurs saturation of absorption. At an air pressure of 10^–3 mm Hg, saturation of resonance absorption is observed in both samples. The linear effects observed can be understood within the framework of the formalism of a three-level scheme possible in the case of the triplet ground state of the paramagnetic centers of powder anthracite.     

Vibrational Structure of the Absorption Spectra and a Model of the HNO and DNO Molecules in the Excited State

The vibrational structure of the absorption spectra of the first n–^*–electron transitions of the HNO and DNO molecules is calculated in the Franck–Condon approximation. A structural model of the molecules in the excited electronic state is constructed on the basis of correlations and with the aid of a method of hybrid atomic orbitals. Evaluation of the influence of deuterium substitution on the intensities of the vibrational components upon electronic excitation is made. A comparison of the experimental and theoretical absorption spectra calculated for different models of the molecules is carried out.     

The Effect of a Magnetic Field on Photoinduced Electron Transfer in Solutions of Chlorophyll and Porphyrins

It is found that, with the action of photoexcitation and a variable magnetic field on halide-containing porphyrin solutions, a differential absorption is observed, whose spectra conform to the absorption spectra of cation radicals of pigments. It is shown that the effect increases linearly with an increase in the strength of a supplementary magnetic field (H) up to saturation (H _max 200 G). The scheme of the photophysical and photochemical deactivation of the energy of electronic excitation for chlorophyll-like pigments in the presence of CCl₄ is analyzed with allowance for the effect of the magnetic field on the intercombination conversion in an ion–radical pair. It is shown that solvate-separated ion radicals of the pigments in halide-containing solutions can be formed from the singlet state of tetrapyrrole molecules.     

Laser Raman Spectroscopy of Crystals with the Structure of Sillenite

The experimental data of the past 10–15 years for the vibrational spectra of crystals with the structure of sillenite Bi₁₂M _x O_20± obtained by the methods of laser Raman scattering and infrared (IR) absorption are generalized. Correlations between the chemical composition and crystal structure of the compounds (variations of the cation M) and their vibrational spectra are established. It is shown that the main contribution to formation of the highfrequency part of the spectrum of two, three, and fourphonon absorption is given by phonons related to vibrations of the [MO₄]^n- complexes. On the basis of the analysis of Raman spectra, the effective use of crystals with the structure of sillenite in acoustooptics is justified.     

Quantitative treatment of the effect of solvent on the electronic absorption and fluorescence spectra of substituted coumarins: Evaluation of the first excited singlet-state dipole moments

The electronic absorption and fluorescence spectra of coumarin and 11 substituted coumarins were measured in several solvents (dioxane, ethyl ether, ethyl acetate, ethanol, dimethylformamide, acetonitrile, and dimethyl sulfoxide). Ground-state dipole moments were determined in dioxane at 298 K. The results were used to obtain the first excited singlet-state dipole moments of the coumarins under study by the solvatochromic shift method (Bakhshiev, Kawski-Chamma-Viallet, McRae, and Suppan correlations). Also, the ground- and the first excited singlet-state dipole moments were calculated using a combination of the PPP method (-contribution) and the vector sum of the -bond and group moments (-contribution). In general, the first excited singlet-state dipole moments of the coumarins are noticeably higher than the corresponding ground-state values, indicating a substantial redistribution of the-electron densities resulting in a more polar excited state. There is a reasonably good agreement between the calculated and the experimental dipole moments.Presented, in part, at the 2nd International Conference on Solar Energy Storage and Applied Photochemistry, Cairo, Egypt, January 6–11, 1993. For a preliminary communication, see Ref. 1.     

Effect of γ-Irradiation on the Absorption Spectra of the Solutions of Acid Dyes

The absorption spectra of -irradiated solutions of some acid dyes in various solvents are investigated. The characteristic times of radiation-induced destruction of dyes in the solutions are determined. It is shown that irreversible radiative discoloration of solutions occurs as a result of the interaction of the dye molecules with the oxygen-containing radicals formed in radiolysis of solvents. Practical recommendations for increasing the radiation stability of the solutions of acid dyes and for using them as detectors of a dose of hard radiation are given.     

Interaction of Anionic Forms of Fe-Octaethylporphyrin With Methanol

The electron absorption spectra of protonation products of ClFe(III) anions-octaethylporphyrin (Fe(III)OEP) have been investigated. The spectra of monoanions (Fe(II)OEP) and dianions (Fe(I)OEP) in tetrahydrofuran remain practically unchanged on protonation of these reduced forms by methanol, whereas in the spectra of protonation products of tri- and tetraanions absorption bands characteristic of -monoanions and Zn-phlorins are observed. These data are interpreted as proof of the -anionic character of the ligand, i.e., the excess electron density in three- and four-electron reduced forms of FeOEP is concentrated not only on the d-orbitals of the Fe ion, but also in the cyclic system of the tetrapyrrole ligand.     

Photostability of Molecules of Aromatic Amines in a Polymeric Matrix

In the temperature range T = 5–295 K, the spectralluminescent properties and curves of thermostimulated luminescence (TSL) of molecules of triphenylamine (TPA), trirtolylamine (TTA), triranisolamine (TAA), and N,N'diphenylbis(3methylphenyl)(1,1'biphenyl)4,4'diamine (TPD) in polystyrene and 4Brpolystyrene matrices have been investigated. It has been found that photoirradiation at room temperature in the region of the lowest electron transition of molecules leads to a decrease in the intensities of the luminescence, photoluminescence, and TSL bands, as well as to the formation of new deep traps for charge carriers. At equal irradiation doses these changes in TPD are noticeably less pronounced than in TPA, TTA, and TAA. The higher photochemical stability of TPD molecules compared to TPA, TTA, and TAA is attributed to the difference in the mechanisms of nonradiative deactivation of the triplet states of molecules.     

Absorption Spectra of Gasolines in the Region 1090–1220 nm

The difference absorption spectra of different grades of gasoline (A-76, AI-92, and AI-95) with octane numbers lying within 76–85 have been investigated experimentally in comparison with hydrocarbons: isooctane, benzene, and n-heptane. The spectra obtained contain absorption bands of the CH₃, CH₂, and CH groups and supposedly of the olefin double bond. The possibility of determining the octane number of an unknown grade of gasoline by using the absorption of a measured difference spectrum at one selected wavelength is shown.     

Two-electron absorption in a biased quantum well

Linear light absorption of 2D electrons confined within a biased quantum well is studied theoretically. We demonstrate that for light polarization perpendicular to the 2D plane, in addition to conventional absorption peak at frequency ω≈Δ, where Δ is the intersubband energy distance, there exists a peak around a double frequency ω≈2Δ. This additional peak is entirely due to electron–electron interactions, and corresponds to excitation of two electrons by one photon. The magnitude of two-electron absorption is proportional to U², where U is the applied bias.     

Spectral Manifestations of Anion-Cation Interactions of Water-Soluble Porphyrins

The influence of anion-cation interactions on the structure and electronic absorption spectra of cationic 5,10,15,20-tetrakis-(4-N-methylpyridyl)porphyrin and anionic 5,10,15,20-tetrakis-(4-sulfonatophenyl)porphyrin has been investigated by absorption spectroscopy and molecular modeling. It is shown that the shifts of bands in the electronic absorption spectra appearing when passing from aqueous solutions to solutions in organic solvents are due to the interaction of ionized peripheral substituents of the porphyrin macrocycle with counterions. The bathochromic shift of the Q _x transition is due to the influence of counterions on the energy characteristics of the molecule itself, primarily, as a result of Coulomb interactions changing the relative position of the orbitals and the distribution of electron density on them. The hypsochromic shift of the Q _y transition is a consequence of the increase in the dihedral angle between the plane of the porphyrin macrocycle and the aromatic rings with ionized groups due to the decrease in the -electron interaction between them under the action of counterions.     

Resonance absorption of gamma-quanta in one- and two-dimensional crystals

The resonance absorption of gamma-quanta in undisturbed one- and two-dimensional crystals is studied, the form of the resonance lines is determined and the question of the possibility of the existence of the Mössbauer effect in such models is studied. It is found that for one-dimensional crystals the Mössbauer effect is zero with the exception of the case of the perpendicular incidence of gamma-rays on the linear chain and for two-dimensional crystals this effect would be possible in addition only at absolute zero temperature.The authors would like to thank Dr. . Muziká for suggesting the work and for many discussions.     

Multiple trapping of random walkers on periodic lattices

Formulas are obtained for the mean absorption time of a set ofk independent random walkers on periodic space lattices containingq traps. We consider both discrete (here we assume simultaneous stepping) and continuous-time random walks, and find that the mean lifetime of the set of walkers can be obtained, via a convolution-type recursion formula, from the generating function for one walker on the perfect lattice. An analytical solution is given for symmetric walks with nearest neighbor transitions onN-site rings containing one trap (orq equally spaced traps), for both discrete and exponential distribution of stepping times. It is shown that, asN , the lifetime of the walkers is of the form Ta_kN², whereT is the average time between steps. Values ofa _k, 2 Sk 6, are provided.     

Millimeterwave spectra of some superionic conductors

Using a quasi-optical continuously tunable spectrometer in the frequency range of 40–90 GHz (=7.5-3.3 mm) the absorption spectra of the superionic conductors Na-alumina, Ag-alumina,-AgI and CuTeBr have been measured at various temperatures. In the measured spectral range all the materials showed a monotonic increase in the absorption as a function of frequency. These results are discussed in the light of existing theoretical models.Alfred P. Sloan Foundation Fellow