Collision cross-sections for scattering of electrons from NO molecule

Electron-NO scattering is investigated in the energy range 2–1000eV by using a parameter-free spherical complex optical potential (SCOP) approach in the fixed nuclei approximation. The real part of the optical potential consists of three potentials namely, the static, the exchange and the polarization. For the imaginary part of the SCOP, we employ a semi-empirical model absorption potential. The molecular charge density function is calculated from a single-configuration molecular orbital based on Slater type orbitals. The various potential terms are then determined from these charge density functions. Calculations of the elastic (with and without absorption effects), total absorption, momentum transfer and differential cross-sections are obtained and compared with the available theoretical results and experimental measurements.     

Many-particle-effects in the theory of the extended X-ray absorption fine structure

The Lee-Beni-procedure for the calculation of the extended X-ray absorption fine structure (EXAFS) is extended so as to include the effects of the electronic charge density outside the localized muffin-tin potentials. In our scheme EXAFS is caused by back-scattering of an elementary excitation of a homogeneous electron gas by localized energy dependent many-particle muffin-tin potentials. The difference between the two schemes is negligible at large k's, as expected from physical grounds. However, at small and intermediate k-values the difference is quite large. The effect of the outer electrons as compared to the Lee-Beni-model is twofold. First, they renormalize the scattered electron in the usual way. Second, they are missing within the scattering muffin-tins. Hence, we avoid to count some of the electrons twice. Results are presented for Cu as an example.     

Optical absorption and refraction index change of a confined exciton in a spherical quantum dot nanostructure

Electronic energies of an exciton confined in a strained Zn_1−x Cd _x Se/ZnSe quantum dot have been computed as a function of dot radius with various Cd content. Calculations have been performed using Bessel function as an orthonormal basis for different confinement potentials of barrier height considering the internal electric field induced by the spontaneous and piezoelectric polarizations. The optical absorption coefficients and the refractive index changes between the ground state (L = 0) and the first excited state (L = 1) are investigated. It is found that the optical properties in the strained ZnCdSe/ZnSe quantum dot are strongly affected by the confinement potentials and the dot radii. The intensity of the total absorption spectra increases for the transition between higher levels. The obtained optical nonlinearity brings out the fact that it should be considered in calculating the optical properties in low dimensional semiconductors especially in quantum dots.     

Struktur- und Absorptionspotentiale von KCl und NaCl aus Beugungsaufnahmen im konvergenten Elektronenbündel

By improvement of an earlier published preparation method for producing thin single crystals soluble in water, it is possible to determine structure and absorption potentials of some reflections of KCl and NaCl crystals by a convergent beam diffraction technique. The structure potentials evaluated on the basis of the two-beam dynamical theory are found to depend on the thickness of the crystals used. The structure potentials corrected for relativistic, thermal and many-beam effects are compared with theoretical values. The measured (220)- and (420)-absorption potentials of NaCl are in good agreement with theoretical values. Radiation damage in KCl and NaCl crystals by electron beams is observed.     

Multi-photon behaviors of shot noise in a quantum dot system under the perturbation of two microwave fields

We have investigated the shot noise affected by the perturbation of two microwave fields (MWFs) with frequencies ω₁ and ω₂, which can be classified as the commensurate and incommensurate external ac fields. The time-dependent current correlation function and the spectral density of shot noise have been obtained. They are very different compared with the single-field applied system in the nonlinear regime of the ac potentials. The different photon absorption and emission processes induce different kinds of noise spectral density. We have performed the numerical calculations for both commensurate balanced and unbalanced photon absorptions and emissions. The multi-photon procedure can be seen clearly from the resonance of shot noise. Different commensurate number q = ω₂/ω₁ contributes to different photon absorption and emission behaviors. It is found that the asymmetric configuration of shot noise is intimately associated with the commensurate number q. The differential conductance appears symmetric and asymmetric behaviors, and the channel blockade exhibits. The shot noise is large enough to surpass its saturated value for the unbalanced photon absorption case. The sensitive behaviors of Fano factor associated with different commensurate numbers and amplitudes of ac fields signify that the shot noise can be controlled by external MWFs significantly.     

Pion-nucleus optical potential: The pion-absorption contribution

The real and imaginary parts of pion-nucleus optical potential arising from pion absorption channel have been computed. A two-nucleon model of pion absorption which includesπ andρ rescattering andS-wave interaction has been used. The effects of short-range nucleon-nucleon correlations, Pauli blocking and formfactors have been included. The threshold values of imaginary absorption potential are reasonably close to density-squared terms of phenomenological potentials. The real part ofP-wave potential is attractive and that ofS-wave potential is weakly attractive at lower pion energies and changes sign as pion energy is increased. The calculation shows that the real part of absorption is significantly affected by short-range correlations and Pauli-blocking.     

Optical model potential of 800 MeV/c K+ meson for12C and40Ca by the method of inversion

The elastic scattering differential cross-sections of 800 MeV/c K⁺ mesons from¹²C and Ca have been analyzed using the Ericson’s parametrization for the phase shift. It is found that the parameter values obtained by our analysis are significantly different from those obtained from the closed expression for K⁺-nucleus amplitude derived by the strong absorption approximation. Next, using the phase shift obtained from the present analysis we calculate the K⁺ optical model potentials for¹²C and⁴⁰Ca by the method of inversion. The calculated potentials are compared with the recently determined phenomenological ones.     

The effect of self‐consistent potentials on EXAFS analysis

A theory program intended for use with extended X‐ray‐absorption fine structure (EXAFS) spectroscopy and based on the popular FEFF8 is presented. It provides an application programming interface designed to make it easy to integrate high‐quality theory into EXAFS analysis software. This new code is then used to examine the impact of self‐consistent scattering potentials on EXAFS data analysis by methodical testing of theoretical fitting standards against a curated suite of measured EXAFS data. For each data set, the results of a fit are compared using a well characterized structural model and theoretical fitting standards computed both with and without self‐consistent potentials. It is demonstrated that the use of self‐consistent potentials has scant impact on the results of the EXAFS analysis.     

Effective potentials and threshold anomaly

The strongE andL dependence of the effective elastic channel potentials is shown to be an implicit radial kinetic energy (ε) dependence. It is also shown that this effective potential satisfies the dispersion relation inε variable at the strong absorption radius. Further, the experimental data for both elastic and fusion channels are consistent with thisL-dependence of the corresponding effective potentials. The effective transfer channel potentials derived using CRC code FRESCO are shown to exhibit strong energy dependence as a result of couplings. The energy dependence of effective transfer strength for¹⁶O+²⁰⁸Pb and¹⁶O+²³²Th systems is determined using the experimental transfer angular distributions.     

Coupled channel description of O+Nd scattering around the Coulomb barrier using a complex microscopic potential

Angular distributions of elastic scattering and inelastic scattering from 2⁺₁ state are measured for ¹⁶O+^142,144,146Nd systems at several energies in the vicinity of the Coulomb barrier. The angular distributions are systematically analyzed in coupled channel framework. Renormalized double folded real optical and coupling potentials with DDM3Y interaction have been used in the calculation. Relevant nuclear densities needed to generate the potentials are derived from shell model wavefunctions. A truncated shell model calculation has been performed and the calculated energy levels are compared with the experimental ones. To simulate the absorption, a ‘hybrid’ approach is adopted. The contribution to the imaginary potential of couplings to the inelastic channels, other than the 2⁺₁ target excitation channel, is calculated in the Feshbach formalism. This calculated imaginary potential along with a short ranged volume Woods–Saxon potential to simulate the absorption in fusion channel reproduces the angular distributions for ¹⁶O+¹⁴⁶Nd quite well. But for ¹⁶O+^142,144Nd systems additional surface absorption is found to be necessary to fit the angular distribution data. The variations of this additional absorption term with incident energy and the mass of the target are explored.     

Calculation and analytical representation of self-pressure and air pressure broadening coefficients of ozone spectral lines

The coefficients γ of broadening by self-pressure, and pressure of nitrogen, oxygen, and air are calculated for absorption lines of the rotational band and for the ν₂ band of the ozone molecule for temperatures 296, 252, and 212 K. The calculations are performed by the semiclassical method using rectilinear and exact trajectories for interacting molecules. It is shown that the experimental data obtained for the two bands at T = 296 K can be reconstructed better using different isotropic intermolecular interaction potentials. The experimental and calculated broadening coefficients of ozone absorption lines for the rotational band and for the ν₂ and ν₁ + ν₃ vibrational bands were used to determine the parameters of an analytical model, which permits one to calculate γ in a wide range of rotational quantum numbers, 0 ≤ J ≤ 45, 0 ≤ K _a ≤ 20, and temperatures of 200–296 K.     

Off-shell behaviour ofα-α interaction potentials

Off-shell behaviour of representativeα-α interaction potentials, both local and non-local separable, is compared through the partial wave Kowalski-Noyes half-off-shell functions. Parameters of the existing rank-one separable potentials are redetermined and an additional rank-two potential is constructed for this family. It is found that all these potentials show similar off-shell behaviour for higher partial waves. Their behaviour for low partial waves, however, particularly in the region far away from the energy-shell, is widely different. The off-shell correction for the (α, 2α) reaction at 140 MeV is calculated, as an application, and it is found that separable potentials predict a non-negligible effect.     

Interband optical absorption in a strained CdxZn1−xO/ZnO quantum dot

Numerical calculations of the excitonic absorption spectra in a strained Cd_xZn_1−xO/ZnO quantum dot are investigated for various Cd contents. We calculate the quantized energies of the exciton as a function of dot radius for various confinement potentials and thereby the interband emission energy is computed considering the internal electric field induced by the spontaneous and piezoelectric polarizations. The optical absorption as a function of photon energy for different dot radii is discussed. Decrease of exciton binding energy and the corresponding optical band gap with the Cd concentration imply that the confinement of carriers decreases with composition x. The main results show that the confined energies and the transition energies between the excited levels are significant for smaller dots. Non-linearity band gap with the increase in Cd content is observed for smaller dots in the strong confinement region and the magnitude of the absorption spectra increases for the transitions between the higher excited levels.     

Evidence for a cubic-to-icosahedral transition of quasi-free Pd-H-clusters controlled by the hydrogen content

An in situ synchrotron radiation study of quasi-free five nanometer-sized palladium clusters during hydrogen absorption is combined with molecular dynamics simulations to investigate the structural development. In the diffraction patterns, strong intensity changes are found that provide evidence for a structural phase transformation that is significantly different from the α--Pd-H bulk phase transition. The structural transition is reversible and driven by the hydrogen concentration. The intensity changes are consistent with a cubic-to-icosahedral structural phase transition obtained in molecular dynamical simulations using embedded-atom-method potentials. Received 15 October 2001 and Received in final form 7 February 2002     

Theoretical studies of the structures and optical properties of the bifluorene and its derivatives

The ground and excited structures of the molecules are compared basis on the calculated by HF and CIS, respectively. The ionization potentials (IPs), electron affinities (EAs) and HOMO–LUMO gaps (ΔE_HOMO–LUMO) of the oligomers are studied by the density functional theory (DFT) with B3LYP functional while the vertical excitation energies (E_gs) and the maximal absorption wavelength λ_abs of oligomers of bifluorene and its derivatives DFE, DFA, DFBT, FDBO, and FSCHD are studied employing the time dependent density functional theory (TD‐DFT) and ZINDO. Compared with BF, the derivatives DFE, DFA, and DFBT are better conjugated, easier to give an electron or a hole, as well as get an electron or a hole. Their HOMO–LUMO gaps are narrower and they have lower vertical excitation energies. The absorption and emission spectra of them are red shifting. However, FDBO and FSCHD are in the other way round. It is important that FDBO and FSCHD are good blue emitters. Copyright © 2007 John Wiley & Sons, Ltd.     

Untersuchungen zur normalen und anomalen Absorption von Elektronen in Silizium- und Germanium-Einkristallen bei verschiedenen Temperaturen

Absolute filtered intensities of the electrons scattered elastically in thin platelike Si and Ge crystals have been measured. From the intensities of the primary and the Bragg reflected beams measured as a function of incident direction the coefficients for normal and anomalous absorption can be obtained with good accuracy, using the two beam approximation of the dynamical theory. Moreover, for Si the foil thickness and structure potentials can be deduced which are in agreement with the thickness determined optically and with calculated structure potentials resp. The results partly are influenced by multiple beam effects, which, however, are shown to be describable by Bethe's second approximation. All absorption coefficients, measured for different reflections and different crystal temperatures, show an increase with temperature, which is rather weak for Si and stronger for Ge. This shows that there is an influence of temperature diffuse scattering on normal and especially on anomalous absorption, which increases with atomic number. The results can be interpreted quantitatively, using simple models for the various contributions to the absorption coefficients (excitation of single electrons, plasmons and phonons).     

Infinitely many shape invariant potentials and new orthogonal polynomials

Three sets of exactly solvable one-dimensional quantum mechanical potentials are presented. These are shape invariant potentials obtained by deforming the radial oscillator and the trigonometric/hyperbolic Pöschl–Teller potentials in terms of their degree ℓ polynomial eigenfunctions. We present the entire eigenfunctions for these Hamiltonians (ℓ=1,2,…) in terms of new orthogonal polynomials. Two recently reported shape invariant potentials of Quesne and Gómez-Ullate et al.'s are the first members of these infinitely many potentials.     

Optical absorption of small polarons bound in octahedral symmetry: V− type centers in alkaline earth oxides

The optical absorption of V^–-type centers in alkaline-earth oxides is explained as a light induced transfer of holes between equivalent O^2- sites near cation vacancy type defects, the excitation acting against the self-induced trapping potentials. The interplay between symmetry-breaking hole-phonon- and symmetry-restoring resonance-interaction is formulated as a Pseudo-Jahn-Teller effect. The model explains the width, oscillator strength, position and resonance splitting of the bands. The parameters explaining these features are consistent with the value of the ground state resonance interaction, known for MgO:V^–. The model furthermore predicts the existence of a relaxed stable excited state lying close to that determined experimentally for MgO:V^–. Transitions between nonequivalent orbitals at the equivalent O^2- sites lead to bands at higher energies than the previous ones, observed for all V^–-type centers. Generalisations of the treatment of these simple systems to optical absorption of free small polarons are given.     

Electrodynamics of Balanced Charges

We introduce here a new “neoclassical” electromagnetic (EM) theory in which elementary charges are represented by wave functions and individual EM fields to account for their EM interactions. We call so defined charges balanced or “b-charges”. We construct the EM theory of b-charges (BEM) based on a relativistic field Lagrangian and show that: (i) the elementary EM fields satisfy the Maxwell equations; (ii) the Newton equations with the Lorentz forces hold approximately when b-charges are well separated and move with non-relativistic velocities. When the BEM theory is applied to atomic scales it yields a hydrogen atom model with a frequency spectrum matching the Schrodinger model with desired accuracy. An important feature of the theory is a mechanism of elementary EM energy absorption established for retarded potentials.