Calculations of inelastic cross sections for rotational excitation

Cross sections for scattering of N₂ (j=0) molecules on He atoms have been calculated for relative energies below 5 · 10^?3 eV (58 °K). The time independent scattering formalism ofArthurs andDalgarno was used together with an assumed Lennard-Jones type potential with anisotropicP ₂(cos?) terms in the attractive and repulsive parts. The resulting system of coupled differential equations was solved in the distorted wave and close coupling approximations for the differential and integral cross sections for elastic and inelastic (j=0→j=2) scattering. In the integral inelastic cross section several sharp resonances were found to contribute 40% to the cross section at energies below 40 °K. The resonance peaks are attributed to orbiting or short-lived compound states since they are also observed in the elastic cross section at energies which are lower by the excitation energy of 1.5 · 10^?3 eV. Finally, the effect of varying the potential parameters on the integral inelastic cross section was studied at 50 °K and a rough formula for the cross section as a function of the parameters is obtained. The formula shows that a certain ratio of repulsive and attractive anisotropies leads to a small inelastic cross section indicating a mutual cancellation.     

Energy and angular distributions of electrons ejected from CH<Subscript>4</Subscript> and C<Subscript>3</Subscript>H<Subscript>8</Subscript> under 16.0 keV electron impact

Relative cross sections, differential in energy and angle, for electrons ejected from CH₄ and C₃H₈ molecules under 16.0 keV electron impact have been measured. Electrons were analyzed by a 45° parallel plate electrostatic analyzer at emission angles varying from 60° to 135° with energies from 50 eV to 1000 eV. The angular distributions of electrons exhibit structures which are found to arise from Coulomb and non-Coulomb interactions. Furthermore, the double differential cross sections of electrons ejected from C₃H₈ molecule are found to be higher in magnitude than those from CH₄. This result supports the fact that the number of ejected electrons participating in collisions with C₃H₈ molecules is more than that in CH₄. Also, the angular distributions of C-K-shell Auger electrons emitted from the target molecules have been studied and shown to be isotropic within the experimental uncertainty     

Excitation of a singly charged Sr Ion by e-Sr collisions

Excitation of spectral lines of SrII, including laser lines, is studied experimentally in collisions of slow electrons with strontium atoms. Twenty-one excitation cross sections are measured at an energy of electrons of 30 eV. Five optical excitation functions are recorded at an energy ranging from 0 to 200 eV. Direct-excitation cross sections for the 5p ² P°_{1/2, 3/2} levels and the contribution to their population by cascade transitions are calculated. Excitation cross sections of two laser transitions in the IR spectral region are determined using known branching ratios. The results obtained are compared with data of previous experiments.     

The dissociative excitation of odd doublet cobalt atom levels in collisions of electrons with cobalt dichloride molecules

The extended crossed beam method was used to measure the dissociative excitation cross sections in e-CoCl₂ collisions for 91 transitions from odd doublet levels of cobalt atoms. The dissociative and direct CoI excitation cross sections were compared. Possible reaction channels at low electron energies were considered. The results were used to calculate the total dissociative excitation cross section of CoI levels at an exciting electron energy of 100 eV. For the z ² F°, z ² G°, and y ² G° levels, cascade population contributions were also determined.     

Absolute triple differential cross sections for electron impact ionization of helium: Comparison between experimental and theoretical results at 256 eV collision energy

Triple differential cross sections have been measured for electron impact ionization of helium at 256 eV collision energy, 3 eV energy of the slow outgoing electrons and scattering angles of the fast outgoing electrons of 4°, 6°, 8°, and 10°. The data have been put on absolute scale by extrapolating the generalized oscillator strength to zero momentum transfer. In this optical limit the triple differential cross sections can be normalized by using the well-known cross sections for photoionization. The experimental data are compared with results of different theoretical approaches. For nearly all calculated curves rather good agreement with the measurements is obtained for the relative shape of the binary peak, while often its absolute cross section is overestimated. Concerning the recoil peak, larger discrepancies are found with respect to both, relative shapes and cross sections. A perceptible improvement can be stated for calculations which have been performed in a distorted wave approximation and in second Born approximation.     

（e, 2e） triple-differential cross sections for Ag＋（4p, 4s） in coplanar symmetric geometry

The (e, 2e) triple-differential cross sections of Ag + (4p, 4s) are calculated based on the three-body distorted-wave Born approximation considering post-collision interaction in coplanar symmetric geometry. The energy of the outgoing electron is set to be 50, 70, 100, 200, 300, 500, 700, and 1000 eV, and the intensity and splitting of forward and backward peaks are discussed in detail. Some new structures are observed around 15° and 85° for 4p and 4s orbitals. Structures in triple-differential cross sections at 15° are reported for the first time. A double-binary collision is proposed to explain the formation of such structures. The structures at 85° are also considered as the result of one kind of double-binary collision.     

Die Winkelabhängigkeit der Resonanzstreuung niederenergetischer Elektronen an N2

Results of scattering experiments with monochromatic electrons in the energy range from a few tenth of an eV to about 16 eV are reported. Below 1.8 eV collision energy no resonance structures have been found either in the total scattering (transmitted current) or in the elastic and inelastic differential cross sections. The resonances above 1.8 eV have been measured in the elastic and inelastic channels (up to vibrational quantum numberν=8 of the N₂-molecule) in the angular range from 10° to 110°. In the inelastic channelsν≧2 especially the first resonance peak appears asymmetric, as predicted by calculations of the associated Franck-Condon-factors. In all inelastic channels the angular dependence (due to the pure resonance scattering) shows maxima at 0° and 90° and a minimum around 55°, probably indicating gerade-symmetry of the associated N ₂ ^? -state. Excitation functions of three states of N₂ were measured between their thresholds (between 11 and 12 eV) and 15 eV, one of them showing several new resonance structures.     

KTa0.4Nb0.6O3 nanoparticles synthesized through solvothermal method

Potassium tantalate niobate (KTa_0.4Nb_0.6O₃, KTN) nanoparticles of perovskite structure were successsfully synthesized by a solvothermal method. The KTN nanoparticles synthesized at 250 °C for 8 h with 1 to 4 M KOH concentration using isopropyl alcohol [(CH₃)₂ CHOH] as the solvent was composed of a single phase of cubic perovskite structure. Futhermore, the KTN powers synthesized at the same conditions besides of using (CH₃)₂CHOH/H₂O as a solvent compose of a single phase of tetragonal perovskite structure. The nanoparticles exhibit a mixture of cubic and prism-like shapes with lengths of 100 nm to 500 nm and average cross sections of 200×200 nm². The solvent dependence of the powder formation is discussed. X-ray diffraction and electron diffraction results show that the powders have the needed tetragonal perovskite structure. The band gap of KTN nanoparticles is determined to be 3.26 eV from the optical absorption spectra.      

Angular distributions of scattered excited muonic hydrogen atoms

Coulomb deexcitation differential cross sections of excited muonic hydrogen in collisions with the hydrogen atom are studied for the first time. In the fully quantum-mechanical close-coupling approach, both the differential cross sections for the nl → n′l′ transitions and l-averaged differential cross sections have been calculated for the initial exotic atom states with n = 2–6 at kinetic energies of E _cm = 0.01–15 eV and for scattering angles of ϑ_cm = 0°–180°. The vacuum polarization shifts of the ns states are taken into account. The differential cross sections of the elastic and Stark scattering obtained in the same approach are also presented. The main features of the calculated differential cross sections are discussed, and a strong anisotropy of Coulomb deexcitation cross sections is predicted. The text was submitted by the authors in English.     

Electron impact ionization cross sections of the CO2 clusters

The modified Jain–Khare semi-empirical formalism for the evaluation of differential and integral electron impact ionization cross sections for molecules has been extended to the evaluation of cross sections for the electron ionization of CO₂ clusters: (CO₂)₂₄₀ and (CO₂)₁₇₀₀. The energy dependent differential cross sections are evaluated at the incident electron energies of 50, 100 and 200 eV. The integral total ionization cross sections have been calculated in the energy range varying from ionization thresholds to 1000 eV which revealed a good agreement with the available experimental and the theoretical data. The ionization rate coefficients have also been evaluated using the presently calculated ionization cross sections and Maxwell–Boltzmann energy distributions.     

The elastic scattering of low energy electrons from Xenon

Calculations are presented of angular distributions for electrons elastically scattered from xenon in the energy range 5.5 to 10 eV. The potential describing the xenon atom is determined by the X_α-approximation. The relative dependence with energy of the differential cross section at 30° scattering angle has been calculated in the range 30 to 200 eV. The theoretical results are in very good agreement with experimental data.     

Dynamical treatment of binding,polarization and recoil in asymmetric ion-atom collisions

The cross sections for quenching the lowestn ² P states of the alkali atoms Li, Na, K., and Rb by the inert gases He, Ne, Ar, Kr, and Xe are presented for 5 eV≦E _c.m.≦ 100 eV. These cross sections are derived from the corresponding cross sections for collisional excitation by applying the principle of microreversibility. Upper estimates for the quenching cross sections at thermal energies are given; in all studied cases the quenching cross sections are <8·10^?3Ų. These new upper limits are in most cases much lower than those obtained from other methods previously.     

Theoretical study of (e,2e) triple differential cross sections of pyrimidine and tetrahydrofurfuryl alcohol molecules using multi-center distorted-wave method

We report theoretical studies of electron impact triple differential cross sections of two bio-molecules,pyrimidine and tetrahydrofurfuryl alcohol,in the coplanar asymmetric kinematic conditions with the impact energy of 250 eV and ejected electron energy of 20 eV at three scattering angles of-5°,-10°,and-15°.Present multi-center distorted-wave method well describes the experimental data,which was obtained by performing(e,2e)experiment.The calculations show that the secondary electron produced by the primary impact electron is strongly influenced by the molecular ionic multi-center potential,which must be considered when the low energy electron interacts with DNA analogues.     

Ne原子与H2分子碰撞的同位素替代效应研究

使用密耦近似（Close-Coupling）方法、采用Tang-Toennies势模型计算了惰性气体原子Ne与H₂分子及同位素D₂分子在碰撞能量为83.8 meV时的微分散射截面及分波截面, 并与实验值和文献值进行比较.计算得到的微分散射截面值与实验值符合得较好,分波截面值与文献值也相符合.使用同样的方法和模型,文中对Ne-H₂(D₂,T₂)三个体系的微分截面和分波截面进行了系统计算和比较分析,得出对称同位素替代碰撞体系的散射截面规律.     

非共面几何条件下102eV电子碰撞He原子电离的全微分截面

利用DS3C模型研究了非共面几何(垂直平面与垂直动量转移平面)条件下,散射电子的散射角θ₁取不同固定值时,102eV的电子碰撞He原子单电离反应过程的完全微分截面(FDCS),将其计算结果与3C,CCC等理论模型及实验数据进行了比较.结果表明DS3C模型能够较好地定性描述非共面几何(垂直平面与垂直动量转移平面)条件下的碰撞结果,说明对于非共面几何条件下的碰撞过程,出射道三粒子间的动力学关联效应是比较强的. 关键词： 非共面几何 单电离 全微分截面     

Ne原子与H2分子碰撞的同位素替代效应研究

使用密耦近似（Close-Coupling）方法、采用Tang-Toennies势模型计算了惰性气体原子Ne与H₂分子及同位素D₂分子在碰撞能量为83.8 meV时的微分散射截面及分波截面, 并与实验值和文献值进行比较.计算得到的微分散射截面值与实验值符合得较好,分波截面值与文献值也相符合.使用同样的方法和模型,文中对Ne-H₂(D₂,T₂)三个体系的微分截面和分波截面进行了系统计算和比较分析,得出对称同位素替代碰撞体系的散射截面规律. 关键词： 2(D₂')" href="#">Ne-H₂(D₂ 2)碰撞')" href="#">T₂)碰撞 Tang-Toennies势模型 密耦方法 同位素替代     

一种考虑几何屏蔽效应的计算“电子-分子”散射总截面的可加性规则修正方法

在考虑分子内原子间的几何屏蔽效应随电子入射能量变化的基础上, 提出了一种能够在中、高能区准确计算“电子-分子”散射总截面的可加性规则修正方法. 利用这一修正后的可加性规则并使用“电子-C, H, O, N原子”散射总截面的实验数据, 在50—5000 eV内计算了电子被NO, N₂O, NO₂和C₂H₆分子散射的总截面, 且将计算结果与实验结果及其他理论结果进行了比较. 结果表明, 利用这一方法修正过的可加性规则进行计 关键词： 电子散射 可加性规则 总截面 几何屏蔽效应     

Electron Energy Loss Under Scattering by Complex Organic Compound Vapors

Abstract

Low-energy electron scattering by anthracene and 1, 4-di 2-(5-phenyloxazolyl) -benzene (POPOP) vapors at low pressures is studied. The primary electron beam energy E_O was varied between 10 and 60 eV. The scattering angle was θ = 90°. It has been found that in the electron-energy-loss spectra, bands with maxima of 3·7 and 5·41 eV for anthracene, 4.02 and 7 eV for POPOP correspond to the S_O → S₁ and S_o → S₂ transitions. Low intensity electron-energy loss due to T₂ -states excitation has been observed in the region of 2·15 eV for anthracene and 2·54 eV for POPOP. From comparison with optical absorption spectra and analysis of spectra structure changes at different E_O the nature of other bands has been determined. From the obtained results it was concluded that the probability of T₁ -state excitation is low. It is shown that the main mechanism of populating the T₁ -state by electric methods of vapor pumping is the process of intersystem crossing.

The development of free complex molecule spectroscopy under electric excitation is hindered by the lack of systematic reliable information about elementary interactions of electrons and other particles with such molecules. When excited in electric discharge or by an electron beam, the complex molecule may be in both a neutral and an ionized state. The investigation of such nonequilibrium gas system presents great difficulties due to a large number of possible elementary processes responsible for excitation, ionization, recombination, dissociation of complex molecules. To develop a kinetic model of such a system, one must know a number of cross sections or rate constants of elastic and inelastic electron collisions with the complex molecule. Unfortunately, such data are practically unavailable.

The aim of the present paper is to obtain information about probabilities of complex molecule singlet and triplet states excitation in a gas phase as a result of collision with low-energy electrons (less than 50 eV).

Most accurate data on effective cross sections of molecule (atom) collisions with electrons are provided by using an electronic spectrometer in which an electron beam with small energy spread (of the order of tens of in electron-energy-loss spectra, S₂-state excitation cross sections have a considerably greater value.     

Two-state curve crossing processes involving rotational coupling in the Na 2 + molecular ion

We examine the relative utility of the Landau-Zener, phase integral, and semiclassical Magnus approximations for processes involving a real crossing of two potential curves. As an example we consider rotational coupling in Na ₂ ⁺ . Numerical calculations for the ¦3p〉→¦3s〉 quenching process and for ¦3p〉→¦3d〉 excitation agree well with recent experiments in the energy range 20 eV≦E_K≦50 eV. Simple expressions forS-matrix elements, differential and total cross sections in these approximations depend only on accurate evaluation of a few JWKB phases. For the total cross section further simplification of the Magnus results yields a useful semiempirical formula.