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.     

Enhanced forward scattering in the case of two crossed laser beams interacting with a plasma

The nonlinear enhancement of large-angle forward scattering of two identical laser beams propagating in a preformed plasma has been observed experimentally. The spectral analysis of the forward-scattered light shows two components, one which is unshifted with respect to the initial laser light frequency, and the other which is redshifted by a few angstroms. The redshifted component is found to be strongly enhanced in the case of crossed beam interaction in comparison with that of one beam illumination. Two-dimensional numerical simulations show that this enhancement is due to large-angle forward stimulated Brillouin scattering in which each beam serves as seed for the forward scattering of the other.     

Electron scattering from trans 1,3-butadiene molecule: cross-sections, oscillator strength and VUV photoabsorption cross-sections

Electron energy-loss spectra for the butadiene molecule were measured in the scattering angular range of 2.0° to 8.0°, in an energy-loss range from 2 to 50 eV, using 1000 eV incident electrons. The absolute generalized oscillator strength (GOS) and inelastic cross section have been determined for the \hbox{$\tilde{\rm X}^{1}$}?X1A _g  → 1¹B _u transition. The absolute elastic differential cross section was also determined spanning an angular range from 2.0° to 40.0°. From a small angle electron energy-loss spectrum, the optical oscillator distribution (photoabsorption spectrum) for the butadiene molecule was obtained in the 2 to 100 eV photon energy range. Accurate ab initio calculations have been performed, within the First Born Approximation, for generalized oscillator strength (GOS) and excitation energies for the \hbox{$\tilde{\rm X}^{1}$}?X1A _g  → 1¹B _u and \hbox{$\tilde{\rm X}^{1}$}?X1A _g  → 2¹A _g transitions. Our results emphasize the importance of using highly correlated wavefunctions and accurate methodologies in the calculation of the GOS for electron impact-induced electronic transitions in molecules.     

Raman scattering from plasmon-LO phonon coupled modes in ZnTe

Raman scattering spectra of LO phonon-plasmon coupled modes were observed at various temperatures below 400 K. The contributions of plasmon damping and phonon damping were analyzed by the use of the theoretical expression of the cross section and of Hall data. The temperature dependence of the calculated LO-phonon damping was discussed.     

声子频率对同位素掺杂硅声子散射的影响

点缺陷对声子的散射是影响电绝缘体热导率的重要机制之一,其中声子频率是影响声子散射的重要因素．本文主要研究声子频率对同位素掺杂硅声子散射的影响。首先产生一个窄频率范围的声子波包,然后使用分子动力学(MD)模拟声子在同位素掺杂硅中的散射过程,在原子尺度下清晰展示了声子对同位素掺杂的散射过程,并对能量的透射率和反射率进行分析。将模拟结果和已发表的理论结果相比较,在单个同位素掺杂缺陷下,在临近共振频率区域内用改进的R.O.Pohl公式成功的拟合了MD结果,这一结果会对在较宽频率包括非色散和色散声子范围内构造声子热传导公式有帮助.对于在较高的掺杂浓度下,声子频率对声子散射特性的影响还需要更进一步的研究。     

Local effective polarization and absorption potentials from cross-sections for e-atom scattering

A possibility of obtaining local, effective, energy-dependent polarization and absorption potentials from experimental cross-sections for electron scattering is investigated. Potentials have been fitted with the help of the genetic algorithm on large sets of experimental data for e-He, e-Ne and e-Ar elastic scattering at impact energies 20-3000 eV. The obtained potentials reproduce the cross-sections within experimental errors.     

Infrared safety in factorized hard scattering cross-sections

The rules of soft-collinear effective theory can be used naïvely to write hard scattering cross-sections as convolutions of separate hard, jet, and soft functions. One condition required to guarantee the validity of such a factorization is the infrared safety of these functions in perturbation theory. Using e⁺e⁻$e^{+}{e}^{-}$ angularity distributions as an example, we propose and illustrate an intuitive method to test this infrared safety at one loop. We look for regions of integration in the sum of Feynman diagrams contributing to the jet and soft functions where the integrals become infrared divergent. Our analysis is independent of an explicit infrared regulator, clarifies how to distinguish infrared and ultraviolet singularities in pure dimensional regularization, and demonstrates the necessity of taking zero-bins into account to obtain infrared-safe jet functions.     

The electron-two phonon scattering in germanium

The warm electron coefficient, in n-germanium has been calculated, following the method of detailed energy balance of energy taking into consideration the electron-two phonon scattering and found to be in excellent agreement with experimental observations.     

Boundedness of total cross-sections in potential scattering

If a spherically symmetric potential belongs to the Rollnik class, i.e., if $$I = \frac{1}{{(4\pi )^2 }}\smallint \frac{{|V(x)||V(x')|}}{{|x - x'|^2 }}d^3 xd^3 x'$$ is finite, the total cross-section is finite, and an explicit bound on this quantity can be given in terms ofI. We also investigate the case of non-spherically symmetric potentials, and show that ifI is less than unity, the total cross-section averaged over the directions of the incident beam at a given energy is finite.     

Raman scattering from surface optical phonon mode in gallium phosphide nanomaterials

The Raman scattering from gallium phosphide (GaP) nanoparticles (~53 nm) and nanosolids has been investigated. By means of Lorentzian fitting of the Raman scattering spectra, a surface optical phonon (SO) peak located between the transverse optical (TO) phonon and longitudinal optical (LO) phonon frequencies became observable. It has been proved by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) that a core-shell heterostructure is characteristic of the structure of GaP nanoparticles. According to electromagnetic theory, the SO frequency of the piezoelectric/semiconductor heterostructural nanomaterials was calculated.     

Determination of the phonon spectrum from coherent neutron scattering by polycrystals

As proposed by Bredovet al. [2, 3] the phonon spectrum can be obtained approximately from coherent neutron scattering by polycrystals if suitable averages over scattering angles are considered. The accuracy of this method is estimated by comparison with analytical results for simple lattice models (discussed here in particular for Aluminium). The errors are about 5% for low order moments and about 50% near van Hove singularities for “cold” neutrons (wavelength of the order of the nearest-neighbour-distance).     

Photon and phonon statistics of Brillouin scattering

The statistical properties for the couples of modes in Brillouin scattering are derived making use of the coherent state technique. Assuming the initial fields to be coherent, it is shown that periodical antibunching, bunching as well as coherent state behaviour can occur, provided that the anti-Stokes interaction prevails. This is demonstrated with the help of the photocount distributions and their reduced factorial moments.Dedicated to Professor Miroslav Trlifaj on the occasion of his sixtieth birthday.Editorial notice: We regret to record the death of Professor Trlifaj on 10. 2. 1982.The authoress would like to express her sincere thanks to Dr. J. Peina for comments and stimulating discussions.     

Raman scattering by phonon polaritons in ZnS

The experimental difficulties in recording the phonon-polariton spectra of ZnS crystals are discussed. The measured polariton dispersion in cubic ZnS is presented and is found to be in good agreement with the calculated one.     

Extraction of cross-sections of inelastic scattering from energy spectra of reflected atomic particles

REELS spectra of the electrons reflected off niobium are measured with energy resolution <0.5 eV within the 5–40 eV energy range of the probing beam. The measurements were performed for the scattering angles θ = 45° and θ = 120° by means of two electron guns. The process of energy losses is described within the framework of a model with three different energy loss laws: surface, intermediate, and bulk layers are considered. Differential cross-sections of inelastic scattering are represented in the form of simple equations.     

Far-field distribution of third-harmonic generation by two crossed beams

The far-field intensity distribution of the third harmonic generated in a thin silica plate by two laser beams crossed at a small angle comprises four peaks approximately symmetric with respect to the bisector. The measurement of the intensity ratio of the inner to the outer peaks yielded values scattered from 10 to 20, surprisingly larger than the combinatorial value 9. The phase-matching factor, as determined by the full three-dimensional calculations required by the absence of axial symmetry, accounts for the observed ratio and its fluctuations. Received: 14 November 2002 / Published online: 22 May 2003 RID="*" ID="*"Corresponding author. Fax: +7-95/1941-994, E-mail: fomichev@imp.kiae.ru     

Electron acceleration by two crossed Bessel--Gaussian beams in vacuum

The direct acceleration of electrons by using two linearly polarized crossed Bessel--Gaussian (BG) beams with equal frequency and amplitude in vacuum is proposed and studied. It is shown that two linearly polarized BG beams of the same order (0 or 1) with a \textit{\pi }-rad phase difference have a resultant non-zero longitudinal electric field on the z-axis and can be used, in principle, to accelerate electrons.