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.     

Analysis of the Resonance Raman Scattering Spectra and Line Spectra of Tetrabenzoporphin Metal Complexes

On the basis of the calculations of normal vibrations of Zn– and Cu–tetrabenzoporphin, the literature spectra of resonance Raman scattering of the above compounds and the fluorescence spectra of Zn–tetrabenzoporphin are interpreted. The nonmirror character of the fluorescence and fluorescence excitation spectra is noted for some B _1g symmetry type vibrations of the point group of symmetry D _4h caused by the symmetry breakdown of a molecule in its electronic state S ₁ due to the Jahn–Teller effect.     

Frequency Dependence of the Components of Dielectric Permeability and Characteristic Losses of Fluorite

The ₁(E), –Im^–1, and Re^–1 spectra of the fluorite crystal are calculated on the basis of the experimental (10–35 eV) and theoretical spectra ₂(E) (10–27 and 8–20 eV). They were employed to decompose the ₂(E) and –Im^–1 spectra into elementary components. The most intense transverse and longitudinal components of transitions and their parameters have been determined. The correlation between two types of components of transitions and their distinguishing features have been established.     

Finitized Conformal Spectra of the Ising Model on the Klein Bottle and Möbius Strip

We study the conformal spectra of the critical square lattice Ising model on the Klein bottle and Möbius strip using Yang–Baxter techniques and the solution of functional equations. In particular, we obtain expressions for the finitized conformal partition functions in terms of finitized Virasoro characters. This demonstrates that Yang–Baxter techniques and functional equations can be used to study the conformal spectra of more general exactly solvable lattice models in these topologies. The results rely on certain properties of the eigenvalues which are confirmed numerically.     

Apparent conflicting indications on the conformation of dimethylether–argon from the rotational spectra of the d6 and C species

The rotational spectra of dimethylether–d₆–Ar and dimethylether–¹³C–Ar have been investigated by molecular beam Fourier transform microwave spectroscopy. The obtained rotational constants, when compared to those of the normal species, give contrasting indications on the conformation of the complex. We believe the indications given by the dimethylether–Ar/dimethylether–¹³C–Ar pair to be the correct ones. They suggest the Ar atom to lie in the σ_ν symmetry plane of dimethylether perpendicular to the C–O–C plane, shifted towards the oxygen atom. This conformation is in agreement with several kinds of theoretical calculations. Probably isotopic substitution effects make the data from dimethylether–d₆–Ar not directly compatible with those of the other species.     

Mössbauer and infrared studies of the Cu-Cr ferrites

Ferrites of the system CuCr_xFe_2–x O₄, wherex=0,0.2,0.4, 0.6 and 0.8, have been studied by Mössbauer and IR absorption spectra. Mössbauer spectra were recorded at room temperature. The spectra of all samples showed two well defined Zeeman patterns corresponding to A and B sites. The effect of the variation of chromium substitution on the various hyperfine interactions has been discussed. The cationic distribution makes clear that all Cr³⁺ ions occupy octahedral sites. The IR spectra in the range 200–4000 cm^–1 showed the presence of four bands. The high and low frequency bandsv ₁ andv ₂ belong to the tetrahedral and octahedral sites, respectively. Small bandsv ₃ andv ₄are observed around v₂ and are assigned to the octahedral divalent metal-oxygen ion complexes and the lattice vibrations of the system, respectively.     

Photoinduced Oxidation of Diphenylbisanthene and Its Spectral Manifestations

The absorption and fluorescence spectra of diphenylbisanthene (DPB) in n-octane and benzene at 300 and 77 K have been investigated. The appreciable Stokes shift of the fluorescence band (180 cm^–1 in n-octane and 440 cm^–1 in benzene) points to the nonplanar character of the aromatic skeleton of DPB, which has been confirmed by results of the optimization of the molecule geometry by the AMI quantum-mechanical method. It has been found that spectral manifestations of the products of photoinduced transformations of DPB molecules are observed in the UV region (200–350 nm), and it has been shown that the observed photochemical process is two orders of magnitude less effective than for diphenylhelianthrene. On the basis of the experimental data and the results of the quantum-chemical calculations of the electronic spectra of molecules of DPB and endoperoxides (ZINDO/S method), it has been concluded that the end products of DPB phototransformations are its endobiperoxides in which —O—O— groups are added to the phenyl-substituted benzene rings of the aromatic skeleton.     

Fine Structures of the Permittivity and Characteristic Losses of Electrons in Fluorite

Experimental-computational spectra of the permittivity and characteristic losses –Im^–1 for energies in the range 5–21 eV at a temperature of 4.2 K and theoretical spectra of and –Im^–1 of a fluorite crystal are resolved into elementary transition bands. The parameters of transition bands (energies of their maxima E _i, band halfwidths H _i and areas S _i, and oscillator forces f _i) are determined. A correlation of the spectral bands of and –Im^–1is established, and their specific features are elucidated.     

The Effect of Superstoichiometric Components on the Luminescence of Undoped Zinc Selenide Crystals

The evolution of photoluminescence spectra and X-ray rocking curves is analyzed for zinc selenide crystals annealed at 400–1000 °C in saturated Zn and Se vapor. The defect-formation mechanisms and radiative-transition diagrams are proposed.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 56–60, January, 2005.     

Reinvestigation of the (4, 20) band of the O2 second negative system

High resolution absorption spectra of the (4, 20) band in the second negative system (A²Π_u–X²Π_g) of O₂⁺ cation were measured and analyzed in the range of 11 900–12 300 cm^–1 via optical heterodyne velocity modulation spectroscopy. Precise molecular constants of the levels involved were obtained by a nonlinear least-squares fitting procedure combining with our previous spectra of the (4, 19) and (6, 20) bands.     

Spectral-Luminescence Characteristics of Carbazole, Dibenzofuran, and Dinaphthofuran in the Gas Phase in Excitation by Electrons and Photons

The spectra of electron-energy loss, the excitation functions, and the fluorescence spectra in excitation of carbazole, dibenzofuran, and dinaphthofuran by monoenergetic beams of electrons of different energies are determined. The singlet-triplet transitions S ₀–T ₁ and the singlet-singlet transitions up to S ₀–S ₇ are recorded, which covers the region 2–11 eV. In the spectra of electron-energy loss, bands that refer to the n^ast and ^* transitions are identified. The replacement of the heteroatom of nitrogen by the atom of oxygen in the five-membered ring has no substantial effect on the spectra of electron-energy loss.     

Optical Properties of the (CuInSe2) x ·(2ZnSe)1−x and (CuInTe2) x (·2ZnTe)1−x Solid Solutions

Crystals of the compounds CuInSe₂, CuInTe₂, ZnSe, and ZnTe, and the solid solutions (CuInSe₂) _x ·(2ZnSe)_1–x and (CuInTe₂) _x ·(2ZnTe)_1–x were grown by the Bridgman and chemical transport reactions methods. Their transmission and reflection spectra in the region of the main absorption line edge were studied. The forbidden band gap of the indicated materials was determined and its concentration dependences were built for the solid solutions. It is established that the forbidden band gap changes linearly with the x composition and is satisfactorily described by the square-law dependence.     

Anharmonic resonances in the vibrational spectra of pyrazine

The quartic force field of pyrazine has been calculated in the B3LYP/6-31G(d) hybrid density-functional approximation. Based on the results of this calculation, the total IR (250–3800 cm^–1) and Raman (400–3200 cm^–1) spectra of pyrazine have been interpreted with consideration for the Fermi and Darling-Dennison resonances and their spectral manifestations. A precision method is proposed for anharmonic analysis of the vibrational states of polyatomic molecules on the basis of consideration of their theoretical anharmonicity constants in combination with the corresponding experimental frequencies. The method of linear scaling of frequencies has been theoretically substantiated.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 1, pp. 13–22, January–February, 2005.     

Singlet–triplet oscillations and far-infrared spectrum of four-minima quantum-dot molecule

We study ground states and far-infrared spectra (FIR) of two electrons in four-minima quantum-dot molecule in magnetic field by exact diagonalization. Ground states consist of altering singlet and triplet states, whose frequency, as a function of magnetic field, increases with increasing dot–dot separation. When the Zeeman energy is included, only the two first singlet states remain as ground states. In the FIR spectra, we observe discontinuities due to crossing ground states. Non-circular symmetry induces anticrossings, and also an additional mode above ω₊ in the spin-triplet spectrum. In particular, we conclude that electron–electron interactions cause only minor changes to the FIR spectra and deviations from the Kohn modes result from the low-symmetry confinement potential.     

Influencing the satellite transitions of half-integer quadrupolar nuclei for the enhancement of magic angle spinning spectra

Double frequency sweeps can induce spin transitions in a set of satellites of a half-integer quadrupolar nucleus by simultaneously passing through resonance for a satellite pair. It is shown that by transferring population from the outer spin levels to the inner |1/2 and |−1/2 levels an increased intensity for central transition spectra is obtained. Although Magic Angle Spinning in principle interferes with this process, and the adiabaticity of the passages is different for every crystallite in a powder, enhanced spectra with undistorted line shapes are obtained for I=3/2 (²³Na) and 5/2 (²⁷Al) spins experiencing quadrupolar interactions with ω_Q in the range 0.1–3 MHz. Even at spinning speeds up to 30 kHz significant enhancements are obtained. An analysis of the combined effects of double frequency sweeps (DFS) and MAS indeed shows strongly different effects for different crystallites in powder ranging from no gain at all to the theoretical maximum gain of 2I. As the effects are randomly distributed over all orientations on a sphere this is averaged over the whole line shape. Therefore, undistorted powder patterns are obtained enhanced by the average gain over the individual crystallites. Saturation of the satellite transitions, which can only be achieved if spin–spin relaxation is sufficiently strong, leads to identical results. Optimization of the sweeps should be toward an optimal effect on the population transfer to the central levels and chosen short with respect to spin–lattice relaxation times.     

Dependence on temperature of homogeneous broadening of InGaAs/InAs/GaAs quantum dot fundamental transitions

We report systematic temperature-dependent measurements of photoluminescence spectra in self-assembled InGaAs/InAs/GaAs quantum dots (QDs). We have studied the rise in temperature of the ground-state homogeneous linewidth.A theoretical model is presented and accounts for the phonon-assisted broadening of this transition in individual QD. We have estimated the homogeneous linewidth of an individual QD from PL spectra of self-organized InAs/GaAs QDs by isolating the PL of each individual QD and fitting the narrow line associated with self-organized QDs through a Lorentzian convoluted by a Gaussian. We have observed a strong exciton–LO–phonon coupling (γ_LO) which becomes the dominating contribution to the linewidth above the temperature of 45 K. We have also derived the activation energy (ΔE) of the exciton–LO–phonon coupling, zero temperature linewidth (Γ₀) and the exciton-LA-phonon coupling parameter (γ_Ac). We report that our values are close to the values found in the literature for single InGaAs QD and InAs QD.     

Computation of the oscillator strength and absorption coefficients for the intersubband transitions of the spherical quantum dot

The electronic structure and optical properties of one-electron Quantum Dot (QD) with and without an on-center impurity were investigated by assuming a spherically symmetric confining potential of finite depth. The energy eigenvalues and the state functions of QD were calculated by using a combination of Quantum Genetic Algorithm (QGA) and Hartree–Fock Roothan (HFR) method. We have calculated the binding energy for the states 1s,1p,1d,1f, oscillator strengths, the linear and third-order nonlinear optical absorption coefficients as a function of the incident photon energy and incident optical intensity for the 1s–1p, 1p–1d and 1d–1f transitions. The existence of the impurity has great influence on the optical absorption spectra and the oscillator strengths. Also we found that the magnitudes of the total absorption coefficients of the spherical QD increase for transitions between higher states.     

Absorption spectra of benzophenone derivatives containing donor groups

The absorption spectra of benzophenone derivatives with donor groups have been examined and measured in alcohol and benzene at concentrations of 10^–2210^–5 and 10^–3–10^–5 mole/l respectively. The characteristics of the spectra are explained by the participation in the light absorption of conformations, in which either one or both of the rings are noncoplanar, relative to the plane of the carbonyl.     

Conversion of FexCo1–x Si and FexMn1–x Si Weak Band Magnetic Materials Caused by the Electron Concentration

The resistance of Fe_xCo_1–x Si and Fe_xMn_1–x Si weak band magnetic materials in the temperature interval 4.2–300 K is measured. Based on the experimental data, the conversion from semiconducting and submetallic materials with negative temperature resistance coefficients (TRC) to materials with positive TRC caused by the electron concentration is described. It is demonstrated that the main reason for the conversion of the electronic structure is splitting of s-, p- and d-electronic spectra in fluctuating exchange fields. As a result, the number of current carriers increases significantly with the temperature. The competition of this effect with electron-phonon scattering is the basic mechanism of forming resistive states with abnormally low TRC in the examined weak band magnetic materials.     

Effect of the Electron-Vibrational Interaction on the Second Electron Transition of Tetraazaporphin and Tetraazachlorin Molecules

We have traced the change in the complex structure of the intense 0–0 band of the electronic S ₂ S ₀ transition in the quasi-line absorption spectra (n-octane, 77 K) for individual types of impurity centers in the series of compounds tetraazaporphin–tetraazachlorin–di(tert-butylbenzo)barrelene-substituted tetraazachlorin. It has been concluded that the reason for the appearance of this structure is the interaction of the pure electronic S ₂ state with the vibronic S ₁ states rather than the Franck–Condon manifestation of low-frequency vibrations. Attempts to detect the short-wave S ₂ S ₀ fluorescence for all three compounds were unsuccessful. The reasons for the difference from the case of bacteriochlorin, in which such a fluorescence was observed earlier, are discussed.