Farbzentren rhombischer und monokliner Symmetrien in NaF

A number of zero-phonon absorption lines ofF aggregate color centers is studied inx-irradiated NaF crystals under uniaxial stress. The color centers associated with the lines are found to exhibit rhombic (D_2h, D₂, C_2v; rotation axes along 〈110〉 and 〈100〉) and monoclinic (C_2h, C₂, C_s; rotation axis along 〈110〉) symmetries. The transitions of the rhombic color centers correspond to 〈100〉 and 〈110〉 dipoles, those of the monoclinic centers to 〈112〉 and 〈110〉 dipoles. The most prominent line at 5803 Å is due to a 〈112〉 dipole transition within a monoclinic color center. Several models of centers are discussed.     

The 313 nm band system of SeO2. Part 2: rotational structure

Rotational analyses of the first four bands in the ν₁ progression of the transition of SeO₂ at 312.7 nm are reported. The gas phase sample, which contained selenium isotopes in natural abundance, was formed in a free jet expansion from a heated nozzle source. The rotational constants for the state show a rather erratic dependence on v₁^′, consistent with the identification of small, local perturbations in the rotational structure. The A-rotational constant shows a particularly irregular dependence on v₁^′. The r₀ structure was therefore determined from the B and C values of ⁸⁰SeO₂ to be:

     

A theoretical study of BrCN in the Π electronic ground state: Large amplitude bending motion

We have calculated the three-dimensional potential energy surfaces for the 1 ²A′ and 1 ²A″ states of BrCN⁺ at the MR-SDCI_DK+Q/[QZP-ANO-RCC (Br, C, N)] level of theory, where MR-SDCI_DK means ‘multi-reference single and double excitation configuration interaction calculation with Douglas-Kroll Hamiltonian.’ These ab initio potential energy surfaces have a common minimum (corresponding to the state) at a linear equilibrium structure with r_e(Br-C) = 1.735 Å and r_e(C-N) = 1.199 Å. Variational RENNER calculations yield a zero-point averaged structure (with the structural parameters calculated as expectation values over rovibrational wavefunctions) with 〈r(Br-C)〉₀ = 1.739 Å, 〈r(C-N)〉₀ = 1.204 Å, and 〈∠(Br-C-N)〉₀ = 172(4)°. A severe Fermi resonance between 2ν₂ and ν₃ has been found theoretically for the ²A″ potential energy surface. Comparing the ab initio zero-point averaged structure with a recent, experimentally derived r₀ structure, it is concluded that the effects of large-amplitude bending motion should be taken into account explicitly in the process of deriving the r₀ structure from the experimental values of the rotational constants. The electronic structure of BrCN⁺ has also been discussed.     

New heavy mesons as hadronic molecules

We discuss a possible interpretation of the , D_s1(2460), and B_s1(5778) mesons as hadronic molecules. Using an effective Lagrangian approach we calculate their weak, strong and radiative decays. The new impact of the molecular structure of these states is the presence of u(d) quarks in the K, D^(∗) and B^(∗) mesons which gives rise to the direct strong isospin-violating transitions and in addition to the modes generated by η−π⁰ mixing as was considered before in the literature.     

Application of the two-mode squeezed coherent state representation in deriving generalized optical Collins formula

We propose a new two-mode squeezed coherent state representation |z₁, z₂〉_g which is characteristic of the correlation between the squeezing and the displacement. Based on it and using the technique of integration within an ordered product of operators we obtain a generalized two-mode Fresnel operator (GTFO), which is an image of the mapping from (z₁, z₂) to in |z₁, z₂〉_g representation. The matrix element of GTFO in the coordinate representation leads to a generalized two-dimensional Collins formula (Huygens-Fresnel integration transformation describing optical diffraction) in entangled form.     

Theory of the microstructure of disordered <Emphasis Type="Italic">AA</Emphasis>′BO<Subscript>3</Subscript> and <Emphasis Type="Italic">ABB</Emphasis>′O<Subscript>3</Subscript> perovskite-structure solid solutions

A model is considered in which atoms A and A′ or B and B′ of disordered solid solutions A _x A _1?x ^′ BO₃ and AB _x B _1?x ^′ O₃ are distributed over a regular system of points 1(a) and 1(b) of the symmetry group O _h ¹ characterizing the ideal perovskite structure. The probabilities P(G _i |x) of unit cells having crystal-field symmetry at their center lowered to G _i =T _d , D_3d, C_3v, C_4v, D_2h, C_2v, C _s , or C₂ are calculated as a function of the concentration x. The limits for x in which the Jahn-Teller and/or dipole ordering mechanism is probable are determined. In the approximation taking into account only effective pair interactions, the scattering amplitude F _hkl is found to depend on a single parameter r₀. The theory predicts that the dependence of the intensities of even and odd reflections on sin θ/λ is nonmonotonic and that the distributions of nonuniform strains and of values of the lattice parameters in solid solutions are discrete.     

Effect of exchange-coupling interaction on anisotropy of grain in nanoscaled magnets

The effect of inter-grain exchange-coupling interaction on the anisotropy of grain in nanoscaled magnets has been investigated by putting forward an expression of anisotropy at grain boundary, , which is suitable for different coupling conditions, and expresses well the coherency between soft and hard grains. The average anisotropy of grain 〈K^ij〉 has been calculated based on and the theory of partial exchange-coupling interaction. It has been found that the average anisotropy of hard or soft grain, 〈K^hh〉 or 〈K^ss〉, increases with increasing grain size D monotonously when hard-hard or soft-soft grains couple. When soft-hard grains touch each other, with increasing D, the variation of average anisotropy of soft-hard grain 〈K〉 depends on the anisotropy at grain interface , which denotes the affection degree of hard grain on the anisotropy of soft grain. Compared with other results, it is more reasonable that ranges from to . The variations of anisotropy with D we calculated are consistent with those of coercivities given by other authors when is fixed in a certain range.     

On the formulation of D = 11 supergravity and the composite nature of its three-form gauge field

The underlying gauge group structure of the D = 11 Cremmer-Julia-Scherk supergravity becomes manifest when its three-form field A₃ is expressed through a set of one-form gauge fields, , , η_1α, and E^a, ψ^α. These are associated with the generators of the elements of a family of enlarged supersymmetry algebras parametrized by a real number s. We study in detail the composite structure of A₃ extending previous results by D’Auria and Fré, stress the equivalence of the above problem to the trivialization of a standard supersymmetry algebra E^(11|32) cohomology four-cocycle on the enlarged superalgebras, and discuss its possible dynamical consequences. To this aim we consider the properties of the first order supergravity action with a composite A₃ field and find the set of extra gauge symmetries that guarantee that the field theoretical degrees of freedom of the theory remain the same as with a fundamental A₃. The extra gauge symmetries are also present in the so-called rheonomic treatment of the first order D = 11 supergravity action when A₃ is composite. Our considerations on the composite structure of A₃ provide one more application of the idea that there exists an extended superspace coordinates/fields correspondence. They also suggest that there is a possible embedding of D = 11 supergravity into a theory defined on the enlarged superspace .     

Compositional dependence of the physical properties in a-Ge-Se-In glassy semiconductor

Physical properties viz. mean bond energy (〈E〉), glass transition temperature (T_g), cohesive energy (CE), average heat of atomization , density (ρ), molar volume (V_m) and compactness (δ) of Ge₂₀Se_80−xIn_x (x=0, 5, 10, 15, 20) bulk glassy alloys have been examined theoretically. Mean bond energy (〈E〉) is proportional to glass transition temperature (T_g). The cohesive energy (CE) of the investigated samples has been calculated using the chemical bond approach (CBA) method. The relation between photon energy (E₀₄) is discussed in terms of average heat of atomization and average coordination number (〈r〉). The compactness (δ) of the structure of the glass is determined from measured density of the glasses in order to display the chemical threshold in the system using Phillips-Thorpe topological models. Maximum of the compactness has been observed at floppy to rigid transition point occurring in networks. Molar volume (V_m) has been calculated from the experimentally measured densities and on the basis of number of atoms per unit volume (N); V_m follows the same trend as that of optical band gap.     

Substantially low desorption barriers in recombinative desorption of deuterium from a Si(1 0 0) surface

We have studied desorption kinetics of deuterium molecules from a Si(1 0 0) surface by means of temperature-programmed desorption (TPD) spectra and isothermal desorptions.Three desorption components, denoted as β_1,A,β_1,B, and C, can be distinguished in semi-logarithmic plots of the TPD spectra.Their peak positions and intensities are strongly affected by the surface preparation methods employed, either with or without annealing to control the initial D coverage .Peak C appears at the leading edge of the TPD peak.It accounts for only about 5% of the TPD peak at and it diminishes rapidly with decreasing , vanishing at .In contrast, together the β_1,A and β_1,B peaks account for the whole TPD peak at any less than 1.0 ML. The maximum of the β_1,A peak is nearly constant at around the maximum temperature of the TPD peak.On the other hand, the β_1,B peak appears on the high-temperature side of the TPD peak and it systematically shifts to higher temperatures with decreasing .These results imply that first- and second-order kinetics are operating for the β_1,A and β_1,B desorptions, respectively.Isothermal desorption experiments confirm the above predicted kinetics for a limited region, namely .From the results for the rate curve analysis, the desorption barriers are evaluated to be 1.6 ± 0.1 eV and 1.8 ± 0.1 eV for the β_1,A and β_1,B desorptions, respectively.These values are substantially lower than the widely accepted value of ∼2.5 eV. To reproduce the measured TPD spectra we take the Arrhenius-type rate equation containing the first- and second-order rate terms for the β_1,A and β_1,B desorptions.The TPD spectra measured for can be reasonably fit with the proposed rate equation when the values given above for E_d,A and E_d,B are used. For , however, the TPD curves are not fit with the same values; rather, the best-fit curves require values for E_d,A and E_d,B larger than those given above. Combining the present kinetics results with those obtained by STM along with the studies, the β_1,A and β_1,B peaks may be attributed to desorption along the 2H path, while peak C may be attributed to desorption along the 4H path. The atomistic desorption mechanism as well as the energy relationship between the desorption barrier and isosteric heat of adsorption are discussed.     

Equilibrium structure in the presence of internal rotation: A case study of cis-methyl formate

The Born-Oppenheimer (BO) equilibrium molecular structure () of cis-methyl formate has been determined at the CCSD(T) level of electronic structure theory using Gaussian basis sets of at least quadruple-ζ quality and a core correlation correction. The quadratic, cubic and semi-diagonal quartic force field in normal coordinates has also been computed at the MP2 level employing a basis set of triple-ζ quality. A semi-experimental equilibrium structure () has been derived from experimental ground-state rotational constants and the lowest-order rovibrational interaction parameters calculated from the ab initio cubic force field. To determine structures, it is important to start from accurate ground-state rotational constants. Different spectroscopic methods, applicable in the presence of internal rotation and used in the literature to obtain “unperturbed” rotational constants from the analysis and fitting of the spectrum, are reviewed and compared. They are shown to be compatible though their precision may be different. The and structures are in good agreement showing that, in the particular case of cis-methyl formate, the methyl torsion can still be treated as a small-amplitude vibration. The best equilibrium structure obtained for cis-methyl formate is: r(C_m-O) = 1.434 Å, r(O-C_c) = 1.335 Å, r(C_m-H_s) = 1.083 Å, r(C_m-H_a) = 1.087 Å, r(C_c-H) = 1.093 Å, r(CO) = 1.201 Å, ∠(COC) = 114.4°, ∠(CCH_s) = 105.6°, ∠(CCH_a) = 110.2°, ∠(OCH) = 109.6°, ∠(OCO) = 125.5°, and τ(H_aCOC) = 60.3°. The accuracy is believed to be about 0.001 Å for the bond lengths and 0.1° for the angles.     

Gas-phase detection of discharge-generated DSOD

We report the first spectroscopic detection of perdeuterated 1-oxadisulfane, DSOD, generated in a radio-frequency plasma of D₂S and D₂O. The chain molecule DSOD produces a perpendicular-type spectrum, with well-known spectral features encountered in previous studies of geometrically related molecules, such as compact Q-branches, which are clearly recognizable. The arrangement of the transitions shaping the Q-branches usually provides sufficient proof for a clear-cut detection of a chain molecule such as DSOD. Guided by quantum chemical calculations, we have located the band center of the -branch of DSOD in the frequency region near 466.5 GHz using the Cologne terahertz spectrometer. This -branch displays both b- and c-type spectra, quite analogous to the behavior of the corresponding -branch of HSOH. In addition, we have been able to detect an internal rotational splitting of ∼0.5 MHz for c-type transitions of the -branch, which lends independent support to our present assignment. From the measurements performed on Q-branches, we derive the following differences in rotational constants: A−(B+C)/2=93331.001(15) MHz, and (B−C)/4=172.95923(29) MHz, in excellent agreement with theoretical predictions.     

The inversion of diatomic Born-Oppenheimer-breakdown corrections

The inversion of diatomic vibration-rotation data to give the r dependence of operators is considered. For the Born-Oppenheimer energy levels E_vJ and for the expectation values 〈vJ|X(r)|vJ〉 of an operator X(r), the inversion is unambiguous if the reduced mass is known, leading to the potential energy function V(r) and to X(r). The breakdown of the Born-Oppenheimer approximation is represented in terms of three functions Qⁱ(r), Rⁱ(r), and Sⁱ(r) for each atom i. The function Qⁱ(r) can be removed by a transformation that changes the other functions to and , which still have one degree of indeterminacy. The effects of this indeterminacy in fits to truncated Hamiltonians is considered for the extensive data for isotopomers of the LiH molecule. This discussion is relevant to a recent claim that the dipole moment and rotational g_J factor of LiH can be determined from a fit to field-free vibration-rotation spectra. The values obtained for these quantities are unreliable because they are strongly dependent on the constraints used in the Born-Oppenheimer-breakdown functions.     

The overtone spectrum of C2D2 and C2H2 by ICLAS-VECSEL near 1 μm

The intracavity laser absorption spectra (ICLAS) of dideuteroacetylene, C₂D₂, and acetylene, C₂H₂, have been recorded between 1.03 and 0.99 μm with a vertical external cavity surface emitting laser (VECSEL) leading to the observation of seven and six bands, for C₂D₂ and C₂H₂ respectively, most of them newly reported. The strong ν₁+3ν₃ band of C₂D₂ at is found accompanied by the two Π-Π hot bands with v₄=1 and v₅=1 lower state and by the ν₂+3ν₃+2ν₄ band near . This last band results from an intensity transfer from the ν₁+3ν₃ band induced by the 1/244 anharmonic interaction. The ν₁+3ν₃ band of , present in natural abundance in the sample, could also be detected at in full agreement with local mode model predictions. The different bands of both C₂H₂ and C₂D₂ were found mostly unperturbed and the spectroscopic parameters retrieved from the rovibrational analyses agree satisfactorily with the predictions of the respective effective Hamiltonian models.     

Fundamental Entangling Operators in Quantum Mechanics and Their Properties

For the first time, we introduce so-called fundamental entangling operators \(e^{iQ_{1} P_{2}}\) and \(e^{iP_{1} Q_{2} }\) for composing bipartite entangled states of continuum variables, where Q_i and P_i (i = 1, 2) are coordinate and momentum operator, respectively. We then analyze how these entangling operators naturally appear in the quantum image of classical quadratic coordinate transformation (q₁, q₂) → (Aq₁ + Bq₂, Cq₁ + Dq₂), where AD?BC = 1, which means even the basic coordinate transformation (Q₁, Q₂) → (AQ₁ + BQ₂, CQ₁ + DQ₂) involves entangling mechanism. We also analyse their Lie algebraic properties and use the integration technique within an ordered product of operators to show they are also one- and two- mode combinatorial squeezing operators.     

Ab initio calculations of elastic constants and thermodynamic properties of Li2O for high temperatures and pressures

The elastic constants and thermodynamic properties of Li₂O for high temperatures and pressures are calculated by the ab initio unrestricted Hartree-Fock (HF) linear combination of atomic orbital (LCAO) periodic approach. The lattice constant, elastic constants, Debye temperature, and thermal expansion coefficient obtained are in good agreement with the available experimental data and other theoretical results. It is found that at zero pressure the elastic constants C₁₁, C₁₂ and C₄₄, bulk modulus B and Debye temperature Θ_D decrease monotonically over the wide range of temperatures from 0 to 1100 K. When the temperature , C₁₂ approaches zero, consistently with the transition temperature 1200 K. However, with increasing pressure, they all increase monotonically and the anisotropy will weaken.     

Characterization of Tm doped mixed alkali borate glasses—spectroscopic investigations

The effect of mixed alkalis on the optical absorption spectra of Tm³⁺ in xNa₂O·(30−x)K₂O·70B₂O₃ glasses has been studied. The optical band gap values (E_opt) for both direct and indirect transitions have been obtained using Davis and Mott theory. Spectroscopic parameters like Racah (E¹, E² and E³), spin-orbit (ξ_4f) and Judd-Ofelt intensity parameters (, and ) have been calculated for different x values. Radiative transition probabilities (A_rad), radiative lifetimes (τ_R), branching ratios (β), integrated absorption cross sections (Σ) and multiphonon relaxation rates (W_MPR) are calculated for certain excited states of Tm³⁺ ion. The observed trends in the above parameters as a function of x in these borate glasses have been discussed keeping in view the effect of mixed alkalies in borate glasses. Certain potential lasing transitions have been identified for laser action among the various transitions of Tm³⁺ in these mixed alkali borate glasses.