Electron-ion geminate escape probability in anisotropic media

The diffusion-controlled electron-hole geminate escape probability in anisotropic media has been calculated by numerical solution of the adjoint equation for that probability after a series of simplifying transformations. Relative to the crystalline axes the anisotropies of both dielectric constant and mobility, which generally have different principal directions, are important. The escape probability depends on the magnitude and direction of the initial electron-hole separation. Applied to anthracene the implied experimental escape probability ≈0.01 is attained at initial separations 4.0, 4.0 and 3.2 nm along the a, b, c′ crystal directions respectively.     

Ejection of high-energy photoelectrons by intense laser light

The mechanism by which a high-energy photoelectron acquires its large drift momentum is analyzed. Ejection by circularly polarized light is found to be most efficient, in accord with experimental observations.     

Transient nutations of photoelectrons from alkali metal anions

Transient nutations of the magnetization of photoelectrons ejected from rubidium and cesium anions are described. The nature of the nutations requires that the time between photoexcitation and appearance of the photoelectron is less than ≈10^?7 s.     

On methods to determine the surface areas of molecules

The known methods to determine the surface areas of molecules are discussed and a new method is proposed based on the molecule representation in the form of a molecular Voronoi-Dirichlet polyhedron. A linear correlation is found between the surface areas of molecules calculated using the molecular Voronoi-Dirichlet polyhedra and determined by the already known methods. The efficiency of the use of molecular Voronoi-Dirichlet polyhedra for the analysis of intermolecular interactions in crystal structures is demonstrated by concrete examples.     

重视演示实验 提高化学教学质量

演示实验是使学生获取知识、活跃思维、激发兴趣、培养能力的重要手段。它既可以及时提供必要的化学事实供学生验证所学的理论知识并加强记忆,又可以使学生学到化学实验的技巧,还可以使教学按辩证唯物主义认识论的原理进行,事半功倍地帮助学生形成概念、掌握知识、培养观察现象、分析问题、解决问题的能力,从而提高化学教学质量,圆满完成教学任务。     

Thermal studies to determine the accelerated ageing of flares

Summary Thermal analysis is an interesting technique to determine kinetic parameters of separate components, and also of a complete system to receive adequate information on the ageing process of pyrotechnic compositions. The investigated tracer is a tracking tracer of a Swiss missile. It is attached to a missile and produces during burning a red flame. The missile system is already in use for 15 years. Periodic inspections of the system take place every three years. These inspections, however only give information on the actual state of the tracer and not on the future state. The aim of this investigation is to predict the ageing behaviour of the tracer system to give additional information about the future use of the missile system. After two ageing profiles the tracer systems were tested on the test range at Armasuisse in Thun. The results of the testing show that an ageing period of 4 weeks at 60°C gives no changes in performance (light output and burning time). On the other side also a quite heavy ageing period of 4 weeks at 150°C was applied on tracer systems, which gives a dramatically change in burning time. The light output was even higher after this ageing profile, although the intensity changes a lot.     

Photoelectron spectroscopy without photoelectrons: twenty years of ZEKE spectroscopy

Zero Kinetic Energy (ZEKE) spectroscopy, originally developed as a high resolution form of photoelectron spectroscopy, promised a means to the unambiguous determination of ionic (ro)vibrational states. Since its original development, it has spawned numerous methodological offshoots and has become one of the default methods of choice for high resolution spectroscopy of the ion. This tutorial review describes the historical development of the method, provides some insight into how it works and assesses the impact of the technique by reviewing some of the highlights of the past 20 years as well as some of the more recent developments and applications.     

Correcting electronic spectra for distortions caused by inelastic collisions of photoelectrons

A procedure is developed for correcting X-ray photoelectron spectra for distortions caused by inelastic collisions of photoelectrons, leading to an intense tail on the side of higher bond energies. The procedure was used to correct the form of the valence band X-ray photoelectron spectra of pure copper and a Ti-Ni-Cu alloy. Translated fromZhurnal Struktumoi Khimii, Vol. 39, No. 6, pp. 1145–1146, November–December, 1998.     

Analysis of gamma-ray continuum spectra to determine the chemical composition

Neutron induced -ray spectra from various geological samples were analyzed to evaluate the usefulness of continuum spectra in deriving the chemical composition information. A fast Fourier transform technique has been used to estimate the signal content of selected energy bands of the continuum spectra. Monte Carlo calculations have been performed using the major -ray energy sources (due to Fe, Ca, Si and Al) to generate the corresponding detected -ray spectra. The experimental spectra are compared to the simulated spectra to check the consistency of the signal distribution between the peak and the continuum. The continuum above and below a chosen -ray line is calculated to find what fraction of the lower energy continuum is due to that line. The accuracy of the relative elemental concentrations determined by this method is confirmed through comparison with laboratory elemental analysis of the samples. It is found that using the continuum could greatly increase the sensitivity and precision of the measurement of elemental concentrations determined from -ray spectra of thick target sources, for spectra having peaks of poor statistical significance. However, for thin target sources or spectra with very good statistics in their peaks, this method may not be very advantageous.     

Basis and optimization of the indooxine method to determine oximes

Summary Consideration is given to a spectrophotometric method for determining oximes that involves acid hydrolysis followed by reaction of liberated hydroxylamine with 8-quinolinol to form a dye, indooxine (5-[(8-hydroxy-5-quinolyl)imino]-8-(5H)-quinolone). The various steps of the method, applied to pyruvic oxime (2-oximinopropanoic acid) as representative of -oximino acids, were investigated and optimized, leading to improvements in reproducibility and sensitivity over the existing procedure. Incomplete liberation of hydroxylamine from oximes is due largely to incomplete hydrolysis at equilibrium in acid solution. An additional cause with -oximino acids, as opposed to simple oximes, is decarboxylative dehydration to form the corresponding nitrile. Hydrolysis is more complete and nitrile formation less favored the lower the pH, at least in the pH range 0 to 2.5. The importance of calibration curves and the control of pH, time of hydrolysis and temperature in quantitative application of the method is emphasized. The method can be used quantitatively for determination of a single oxime but only semiquantitatively or qualitatively for determination of total oximes in an unknown mixture of oximes.     

Angular distribution of photoelectrons with regard to non-dipole effects in photoionization and elastic electron scattering in solids

The angular distribution of photoelectrons from a semi-infinite solid sample is considered with regard to non-dipole transitions in photoionization with polarized and unpolarized radiation and elastic scattering. Non-dipole transitions are taken into account up to the octupole approximation. Calculations were carried out based on transport theory and Monte Carlo methods. Good agreement between two independent approaches is obtained. All angular parameters, necessary to calculate the angular dependence of intensities of photoelectrons for all elements Z < 100 in a wide range of ionizing radiation energies, are calculated in the relativistic approximation.     

建设课外开放实验拓宽实践育人途径——以课外化学开放实验为例

Constructing the extracurricular chemistry open experiments for non-major students would help to raise the participation of students in practice instruction, thus benefiting more students. This paper has introduced the construction measures and practical experience about extracurricular chemistry open experiment for non-major students from the following aspects:the attentions in constructing the extracurricular chemistry open experiments for non-major students, the diversified construction of teaching resources and the teaching methods reform.     

A method to determine and classify the chirality of the water medium

A new numerical method to determine the chirality of water configurations is developed. It consists in the comparison of matrices composed for both initial configuration and its mirror image based on the information of four bound water molecules. The method developed enables the rapid and unambiguous determination of the chirality of an aqueous system.     

Perturbation theory to determine the stable isomer of triatomic linear molecules

The electronegativity perturbation theory up to the fourth order has been used to study the preferred isomer of linear triatomic molecules. Systems with 10–16 valence–electron systems are discussed and our results are in good agreement with the experiment. The only exception is the isomers of PNO. The usefulness of the perturbation theory is briefly discussed. © 1993 John Wiley & Sons, Inc.