Acousto-optical effect in the luminescence excitation spectrum of HgI2

A study of the photoluminescence excitation spectrum in a crystal of mercury diiodide is reported. Each of the two luminescence bands peaking at 543 and 572–575 nm investigated was found to have its own excitation spectrum. The excitation spectrum of the 575-nm line in the long-wavelength doublet band has been observed to be sensitive to strong ultrasound vibrations and preliminary irradiation of the sample by 590-nm light. This line is associated with radiative recombination of photocarriers at intrinsic point defects (vacancies or iodine and mercury interstitials) located close to dislocations. The binding energy of the photosensitive center to a dislocation was estimated from the change in the excitation spectrum. Fiz. Tverd. Tela (St. Petersburg) 41, 1965–1968 (November 1999)     

Fluorescence polarization of helical molecules cooled in a supersonic jet

The β-binaphthylene oxide molecules studied under supersonic cooling conditions have a number of specific properties due to their nonplanarity. Low-frequency vibrations of the molecules in the excited S1 state are higher than the frequencies for the S0 state, and conversely the high-frequency vibrations have lower frequencies. The S₀-S₂ fluorescence excitation spectrum is structureless. The absence of a Q branch in the rotational contour of the line for the purely electronic transition indicates that it is substantially broadened and shifted toward shorter wavelengths as a result of rotational perturbations of the helical structure of the molecule. Multiplet lines in the spectra of β-binaphthylene oxide complexes with argon, krypton, and xenon correspond to different isomeric complexes. Their bond energies are below those observed previously for planar polycyclic molecules such as perilene, fluorene, and carbazole. The greater number of isomers with xenon is due to strengthening of the bond in the van der Waals complex and the nonequivalence of the position of the xenon atoms on the outside and inside of the helical molecule. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 473–477, July–August, 2006.     

Radiation from particles in crystal undulators with allowance for a polarization of the medium

The radiation from relativistic particles channeled in a microscopic undulator created by applying transverse ultrasonic vibrations to a single crystal is investigated. The results of numerical investigations are presented for real crystal undulators. The calculations show the radiation spectra in the particle and photon energy ranges where narrowing of the spectrum occurs when the particle energy is close to a definite threshold energy. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 6, 437–441 (25 September 1998)     

Formation of color centers during growth of alkali-earth fluoride crystals

New bands within the ranges of 1900–2200 and 700–1000 cm^–1 have been discovered in the IR absorption spectra of crystalline alkali-earth fluorides. It is found that the defects responsible for the high frequency bands facilitate the formation of color centers during crystal growth. These bands are presumably caused by valence vibrations of CO molecules. The low frequency bands are attributed to molecular complexes which contain oxygen-vacancy dipoles.     

Spectral characteristics of heterocyclic compounds with a chain structure, cooled in an ultrasonic jet

We have recorded the fluorescence excitation spectra of three heterocyclic compounds with a chain structure [BPO (2-phenyl-5-(4-diphenylyl)oxazole), POPOP (1,4-di[2-(5-phenyloxazolyl)]benzene, and TOPOT (1,4-di[2-(5-n-tolyloxazolyl)]benzene] and the fluorescence spectra of POPOP, under conditions where the molecules were cooled in an ultrasonic helium jet. A line structure is observed in the spectra of POPOP and TOPOT; for the BPO molecules, whose configuration changes considerably during electronic excitation, vibrational structure is apparent only in the low-frequency region of the excitation spectrum, and a diffuse spectrum is recorded starting from ν ₀ ⁰ + 200 cm⁻¹. For all the compounds, in the spectra we recorded vibrations with frequencies up to 100 cm⁻¹, arising due to the flexibility of the molecular structure. The rotational contours of the lines for the electronic and vibronic transitions of the POPOP molecules (T_rot = 10.5 K) and TOPOT molecules (T_rot = 15 K) are structureless and bell-shaped. The degree of polarization of the fluorescence P_fl for the jet-cooled POPOP molecules for excitation of vibrations along the absorption band up to 2000 cm⁻¹ above ν ₀ ⁰ is practically constant (∼8.4%) and matches P_fl for high-temperature vapors. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 728–734, November–December, 2006.     

Molecular mechanism of gelation with ethylene glycol added to a solution of polyacrylonitrile in dimethylsulfoxide

The mechanism of solidifying a solution of polyacrylonitrile (PAN) in dimethylsulfoxide (DMSO) into which ethylene glycol is added is studied by the method of Raman spectroscopy. In the absence of ethylene glycol, DMSO molecules produce dipole-dipole bonds to PAN molecules. Upon adding ethylene glycol, DMSO molecules form hydrogen bonds with it and a line at 1000 cm⁻¹ appears in the Raman spectrum, which is assigned to the valence vibrations of S=O bonds involved in the hydrogen bonds. After DMSO is removed, ethylene glycol molecules produce hydrogen bonds with two neighboring PAN molecules, giving rise to a band at 2264 cm⁻¹, which is assigned to the valence vibrations of C≡N bonds involved in these hydrogen bonds. A high-viscosity gel consisting of PAN molecules arises in which these molecules are bonded to each other through ethylene glycol molecules.     

Fermi resonance of optical one-phonon and acoustic two-phonon vibrations in light metals

It is shown that the anharmonicity of crystal lattice vibrations in light metals such as beryllium, can give rise to a Fermi resonance of optical one-phonon and acoustic two-phonon vibrations. New hybridized vibrational states are formed as a result of such a resonance interaction: biphonon and quasibiphonon vibrations and renormalized optical vibrations. Depending on the wave vector, these vibrational states can be both damped and stationary. The corresponding dispersion equation is obtained, whose solution made it possible to determine the spectrum of these vibrations (dispersion curves and the wave vector dependence of the damping for damped vibrations). It is shown that ultrafast damping of optical vibrations, similar to the well-known superradiance effect for Frenkel’ and Wannier-Mott excitons, is possible. Fiz. Tverd. Tela (St. Petersburg) 39, 542–546 (March 1997)     

Localized vibrational modes in an <Emphasis Type="Italic">A</Emphasis><Subscript>3</Subscript><Emphasis Type="Italic">B</Emphasis> two-dimensional perfect crystal

The possibility of existence of nonlinear localized vibrational modes in an A₃B two-dimensional crystal with pairwise interatomic bonds is demonstrated. Such modes are easily realized when the difference between masses of atoms A and B is significant and the spectrum of small-amplitude crystal vibrations has a sufficiently wide gap. The influence of the uniform tension/compression deformation on the small-amplitude crystal vibration spectrum and on the existence of nonlinear localized modes is investigated. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 73–79, August, 2008.     

Specific features of the dielectric spectra of the liquid crystal 5CB in the decimeter wavelength range

The dispersion and anisotropy of the permittivity of the liquid crystal 5CB in the solid, nematic, and isotropic phases are investigated at frequencies ranging from 50 to 1000 MHz using discretely tunable hybrid microstrip cavities. Resonance features which grow with increasing temperature are observed in the dielectric spectra. It is found that the section of the dispersion which is due to oriented vibrations of the mesophase molecules covers the frequency range almost up to 300 MHz, and the resonances found could be due to conformational vibrations of the molecules. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 4, 251–253 (25 August 1997)     

A study of the molecular structure of DL-serine with the method of low-temperature IR spectroscopy

Use of low-temperature IR spectroscopy in studies of compounds with a developed system of hydrogen bonds such as DL-serine revealed a complete set of vibrational frequencies. The region of manifestation of stretching vibrations of OH groups involved in the formation of strong hydrogen bonds was found. It is shown experimentally that in a crystal some of the molecules of SL-serine exist in the nonionized form. On the basis of analysis of experimental data, frequency ranges of stretching deformation and torsional vibrations of NH ₃ ⁺ , COO⁻, and OH groups were determined more accurately. It is found that in the crystals there exist molecules of DL-serine with different spatial orientation of NH ₃ ⁺ COO⁻, and COH groups. It is shown that conformational diversity of molecular structures is also preserved at T=18 K. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 864–868, November–December, 1998.     

Interaction of acoustic and optical branches via a Lifshitz-type invariant

It is shown that the interaction of the acoustic and soft optical branches of the spectrum of normal vibrations of a crystal via a gradient invariant of the Lifshitz-invariant type explains the characteristic temperature dependences of these branches as the point of a transition from the initial phase into an incommensurate phase is approached. A comparison is made with the experimental data for betaine calcium chloride dihydrate — BCCD. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 9, 707–710 (10 May 1997)     

IR spectroscopic study of surface properties of amorphous water ice

The state of the surface of amorphous ice with a specific surface area of about 160 m²/g obtained by the condensation of water vapor at 77 K is studied by IR spectroscopy. As the temperature increases to 130–160 K, absorption bands of surface hydroxyl groups vanish, whereas changes in bands characteristic of hydroxyl groups in the bulk of ice are indicative of a phase transition of ice from amorphous to the polycrystalline structure. The surface sites of amorphous ice are characterized with low-temperature adsorption of carbon monoxide. It is shown that there are two types of CO adsorption sites, free hydroxyl groups and oxygen atoms of surface coordinately unsaturated water molecules. Upon adsorption of nitrogen, methane, and carbon monoxide, in addition to the perturbation of surface OH groups, reversible changes in the spectrum are observed in the region of vibrations of bulk hydroxyls, which indicate that the strength of hydrogen bonds between water molecules in the surface layer of icy particles increases approaching the strength of these bonds in the crystal and that the ice surface becomes less amorphous. These results indicate that the properties of the ice surface layer substantially depend on the presence of adsorbed molecules.     

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.     

Migration of molecules in p-bromochlorobenzene with vacancies in its structure

Based on polarization measurements of the low-frequency Raman spectra of p-bromochlorobenzene and calculations of the frequency spectra of lattice vibrations by the Dean method it is shown that the structure may contain vacancies. Their presence affects the appearance of additional lines in the low-frequency spectrum, particularly in the vicinity of 70 cm⁻¹, and their positions depend weakly on the orientational disorder of the molecules with respect to the para substituents. The activation energies for diffusion in a randomly disordered p-bromochlorobenzene crystal with vacancies in the structure is calculated from atom-atom potentials. It is shown that the value of the activation energy varies along a selected direction and depends on the arrangement of the p-bromochlorobenzene molecules with respect to the para substituents, in contrast to the results for ordered p-dibromobenzene and p-dichlorobenzene. Fiz. Tverd. Tela (St. Petersburg) 40, 1835–1838 (October 1998)     

Christiansen effect in an Al2O3 particles – liquid crystal system

We have studied the optical transmission of a small aluminum oxide particles – liquid crystal (4-methoxybenzylidene-4′-butylaniline) system. We have observed that at room temperature, in the spectrum we observe a transmission band with maximum at 1896 cm^–1, which is shifted toward shorter wavelengths on application of a voltage and depends on temperature. The experimental results are explained by the optical homogeneity of the system in a narrow frequency interval when the refractive indices of the particle material and the matrix are close, and also by reorientation of the liquid crystal molecules when a voltage is applied.     

2-Nitroimidazole derivative studied by means of35Cl-NQR spectroscopy and molecular dynamics simulations

³⁵Cl nuclear quadrupole resonance as well as quantum chemical calculations were applied to study electronic structure and molecular dynamics of the imidazole derivative 1-(2-hydroxy-3-chloroprophyl)-2, 3-dinitro-5-methyl-imidazole. The spectra of this compound taken at 77 and 293 K show only one line, which means that there are no physically inequivalent positions of the chlorine atoms in the elementary cell. The line width was of about 28 kHz at 77 K and the relaxation time was about 320 ms at liquid-nitrogen temperature and about 8 ms at room temperature. As follows from the spin-lattice relaxation time measurements performed for the compound studied, in the range 77–200 K the libration mechanism of molecular vibrations is active, while above 200 K the activation process related to reorientation of the CH₂Cl group begins. The activation energy is 18.82 kJ/ mol. The activated process of the CH₂Cl group reorientations exerts rather insignificant effect on the averaging of the electric field gradient in the vicinity of the resonant³⁵Cl nucleus.     

Effect of mode interaction on spectroscopic parameters of molecular vibrations with combination frequencies

An equation has been obtained for excited vibrations with combination frequencies by modifying the equation for the normal vibrations of the molecules, using the direct product operation and its properties for the eigenvalues and eigenvectors of the cofactor matrices within matrix perturbation theory. From the solution of the equation, the elements of the vibrational mode tensor are determined, for which formulas are written (in terms of projectors of the matrix of the dynamic coefficients) that take into account their changes for excited vibrations. Using these formulas makes it possible to study the effect of perturbations on the change in the intramolecular and spectroscopic parameters of combination vibrations of the molecules. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 421–425, July–August, 2006.     

Trends in the spectral distribution of the absorption coefficient of complex organic molecules

General trends in formation of the observed vibrational spectra are analyzed by calculating spectral distributions of the absorption coefficient in the IR region for 45 molecules of different classes ignoring the electrooptical paramaters of particular bonds and structural groups. It is shown that for many molecules, only vibrations of peripheral X-H bonds make a prevailing contribution to the total integral absorption in a wide spectral range. The effect of increasing intensities of some bands is clearly observed for skeleton vibrations, when optical parameters of external X-H bonds are zero. V. I. Vernadski Institute of Geochemistry and Analytical Chemistry of the Russian Academy of Sciences, 19, Kosygin St., Moscow, 117975, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 4, pp. 491–496, July–August, 1998.     

Analysis of the ir absorption profile of hydrargillite in the region of the valent vibrations of hydroxyl groups

An analysis of the complex absorption profile of hydrargillite in the region of stretching vibrations of the OH bond has been performed with the use of the method of direct fitting of the second-derivative curve. The observed profile is shown to contain an intense broad absorption band masked by eight mutually overlapping relatively narrow bands of structural OH groups of aluminum trihydroxide. The revealed broad absorption band is apparently due to the stretching vibrations of water molecules localized in the trihydroxide structure and the stretching vibrations of structural OH groups interacting with them via the hydrogen bond. An estimation of the basic spectral characteristics of the absorption bands forming the complex profile has been performed. Translated from Zhurnal Prikladnoi Spekroskopii, Vol. 67, No. 3, pp. 306–311, May–June, 2000.     

ESR spectroscopy of La2Ga5SiO14:Cr single crystals

The ESR spectrum of La₃Ga₅SiO₁₄ single crystals activated by chromium ions is investigated. It is shown that chromium ions are incorporated into the La₃Ga₅SiO₁₄ crystal lattice in the trivalent state at laoctahedric positions. Orientations of the principal magnetic axes are determined, and parameters of the spin Hamiltonian are estimated. The effect of disorder of the crystal structure of the matrix on line widths and shapes of the ESR spectrum of impurity Cr³⁺ ions is discussed. I. Franko L’vov State University, 50, Dragomilov St., L’vov, 290005, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 942–946, November–December, 1998.