Dipole resonances of an ionized cluster

We study the resonance properties of an ionized spherical cluster that interacts with an optical radiation field in terms of linear hot-plasma polarizability models. Based on a generalization that includes spatial dispersion in the well-known Mie problem of the diffraction of a plane wave by a small-size plasma sphere, we calculate the eigenfrequencies, the radiative and collisional damping constants, and the resonance amplitudes of the cluster surface and bulk plasmon fields. The role of collisionless dissipation processes is analyzed in terms of a one-dimensional kinetic model. The latter allows the corresponding damping constants for both types of plasmons to be determined as functions of the characteristic electron-plasma boundary collision frequency. We show that both types of plasmons in certain domains of cluster and external-radiation parameters can undergo a strong resonance that causes both the amplitude of the scattered wave and the absorbed power and the field inside the cluster to increase significantly.     

Formation of small water cluster anions by attachment of very slow electrons at high resolution

Using a high resolution laser photoelectron attachment method, we have studied the formation of (H ₂ O) _q ^- (q = 2, 6, 7, 11, 15) cluster ions in collisions of slow free electrons (E = 1-80 meV) and Rydberg electrons (n = 12-300) with water clusters. Resonances at zero energy have been observed, the shapes of which are strongly dependent on cluster size. The results are discussed in terms of the formation of metastable negative ions. Received 8 March 1999     

Thermal electron capture by some chlorobromopropanes

Thermal electron attachment rate constants for CH₂ClCHBrCH₃ and CH₂ClCH₂CH₂Br have been measured using electron swarm method. Corresponding rate constants are equal to 3.5×10^-10 and 2.5×10^-10 cm³ molec^-1 s^-1, respectively. Parallely, negative ion mass spectra of these compounds as well as CH₂FCH₂Br, CH₂ClCH₂Br, CH₂BrCH₂Br and CF₃CHClBr has been measured with negative ion mass spectrometry method. The rate constants have been compared with the negative ion mass spectra.     

Dipole moment of a small water cluster. The effect of size,temperature, and electric field

A molecular dynamics simulation of neutral clusters (H₂O) _{n ≤ 21} has been performed in the framework of the flexible polarized model. The formation and evolution of the dipole moment of the cluster have been investigated with a change in the size and temperature of the cluster and an external electric field. It has been shown that at low electric fields corresponding to the experiments on the deflection of clusters in the transverse inhomogeneous electrostatic field (Moro et al., 2006), the induced polarization of the cluster is determined by the orientational polarizability of the “rigid” cluster, rather than by the intracluster reorientation of the molecules. The calculated dependence of the effective polarizability of the cluster in the low field on n qualitatively reproduces the experimental results, but the calculated polarizability is numerically much higher than the experimental value by, e.g., a factor of 4 for n ≈ 20.     

低能He2+-He反应中单电子俘获微分散射过程的实验研究

利用冷靶反冲离子动量谱仪装置系统研究了20-40 keV He2+-He碰撞体系的态选择单电子俘获过程,实验获得了单电子俘获过程的态选择截面以及角微分截面.在所研究的能区范围,电子俘获到L壳层的截面最大,为主要的反应道,这与分子库仑过垒模型的反应窗理论的预测一致.实验测量的态选择截面与原子轨道紧耦合的计算结果很好地符合,与光谱方法的测量结果存在一定的差别,主要原因是光谱方法不能测量完整的反应通道信息.实验结果表明,总角微分截面在小角度范围主要来源于电子俘获到基态的贡献,在大角度范围主要来自电子俘获到激发态的贡献;电子俘获到基态的和激发态的角微分截面均出现振荡结构,这种振荡来源于电子俘获反应中分子轨道之间的相干效应.实验测量的角微分截面与其他实验和紧耦合方法的计算结果进行了比较和分析.     

Positronium formation by electron capture from hydrogen-like ions

Two different impulse approximations are provided for the problem of fast positron collisions with hydrogen-like ions. One of the impulse approximations is formulated by making a consistent expansion of the scattering wave function in powers of the weak interaction to the strong. The other impulse approximation is formulated by making a consistent expansion of theT-matrix in powers of the weak interaction to the strong. In this impulse approximation, the opposite limits of the target nuclear charge tending to zero and to infinity are examined. Differential and angle-integrated cross sections are computed for ground-state positronium formation from hydrogen within the impulse approximations. The full peaking approximation is employed in the evaluation of theT-matrix. By 300 eV, the impulse approximations for the angle-integrated cross section are in close agreement with the strong potential Born and the exact second Born calculations.     

Isomer triggering via nuclear excitation by electron capture

Triggering of long-lived nuclear isomeric states via coupling to the atomic shells in the process of nuclear excitation by electron capture (NEEC) is studied. NEEC occurring in highly charged ions can excite the isomeric state to a triggering level that subsequently decays to the ground state. We present total cross sections for NEEC isomer triggering considering experimentally confirmed low-lying triggering levels and reaction rates based on realistic experimental parameters in ion storage rings. A comparison with other isomer triggering mechanisms shows that, among these, NEEC is the most efficient.     

Dipole instability in an electron beam in a drift space

Lenin All-Union Electrotechnical Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 31, No. 8, pp. 891–897, August, 1988.     

低能He2+-He反应中单电子俘获微分散射过程的实验研究

利用冷靶反冲离子动量谱仪装置系统研究了20—40 keV He²⁺-He碰撞体系的态选择单电子俘获过程,实验获得了单电子俘获过程的态选择截面以及角微分截面.在所研究的能区范围,电子俘获到L壳层的截面最大,为主要的反应道,这与分子库仑过垒模型的反应窗理论的预测一致.实验测量的态选择截面与原子轨道紧耦合的计算结果很好地符合,与光谱方法的测量结果存在一定的差别,主要原因是光谱方法不能测量完整的反应通道信息.实验结果表明,总角微分截面在小角度范围主要来源于电子俘获到基态的贡献,在大角度范围主要来自电子俘获到激发态的贡献;电子俘获到基态的和激发态的角微分截面均出现振荡结构,这种振荡来源于电子俘获反应中分子轨道之间的相干效应.实验测量的角微分截面与其他实验和紧耦合方法的计算结果进行了比较和分析. 关键词： 冷靶反冲离子动量谱仪 态选择电子俘获 态选择截面 角微分截面     

Kinetic theory of ionization and electron capture by a charged impurity in a semiconductor

Inelastic electron-phonon scattering in which the electron is captured or escapes from the Coulomb field of an impurity is taken into account in the kinetic equation for conduction electrons. This scattering is shown to become strong in a certain energy range. In this range, the distribution functions of free and bound electrons are correlated in such a way that there is a balance between the trapping and ionization processes. The existence of a region of strong scattering is the decisive factor in calculating the experimentally measurable trapping and ionization coefficients, which enter into the electron balance equation.     

Electron capture from atomic hydrogen by slow fully stripped lithium ions

Cross sections for electron capture by Li³⁺ ions from H atoms have been measured in the energy range 9–42 keV. Above 20 keV the data are in good agreement with the theory of Ryufuku and Watanabe while there is a discrepancy at the lower energies.     

Electret mechanism of electron beam capture by the magnetic field of a betatron

The mechanism of electron capture into acceleration that takes into account the electret properties of the accelerating chamber shell is described. The electron capture into acceleration is a self-consistent problem. It is demonstrated that the electron capture into acceleration is caused by the interaction of the injected electrons with the electric field of the charge created on the side interior wall of the chamber by electrons dropped out of the acceleration. The spectrum of the captured electrons is not normal. A large number of low-energy electrons are presented in the spectrum. Two and more peaks previously unknown are revealed in the dependence of the captured charge on the injected charge for large values of the injected charge. The results obtained are in agreement with the data of previous experimental studies. The captured charge and the dose rate of bremsstrahlung from a target correspond to their actual values for betatrons with accelerated electron energies of 6 and 10 MeV. Results of simulation can be used to design accelerating chambers and electron injection systems of betatrons and other cyclic accelerators. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 35–45, December, 2006.     

Nuclear excitation by electron capture followed by fast x-ray emission

The resonance strength of the two-step process of nuclear excitation by electron capture followed by γ decay of the nucleus can be significantly increased in highly charged ions if the resonant capture proceeds via an excited electronic state with subsequent fast x-ray emission. For fully ionized ²³⁸₉₂U and ²³²₉₀Th, the x-ray decay stabilizes the system against internal conversion of the captured electron, with an increase of both nuclear lifetimes and resonance strengths of up to two orders of magnitude compared with the case when occupied atomic orbitals prevent the x-ray de-excitation. Applications of this effect to the measurement of the not yet experimentally observed nuclear excitation by electron capture and to dense astrophysical plasmas are discussed.     

Coherent electron density distribution oscillations in electron capture by fast protons in helium

Assuming the validity of a recent model of Lyman-α beat behaviour from fast H atoms under conditions of reversal of an applied electric field, we find strong electric dipole density distribution oscillations in electron capture to n=2 levels of hydrogen by fast protons (≈ 2 au) in helium. Possibilities for testing relative orbital phase calculations in charge-transfer theory, and for making comparisons between beam-surface and single ion-atom collision models of projectile passage through solids exist.     

Cross sections of electron capture and electron capture ionization versus the impact parameter in collisions of a proton with multielectron atoms

The absolute differential cross sections of scattering of hydrogen atoms resulting from an electron capture and an electron capture ionization are measured for collisions of 4.5- and 11-keV protons with argon and xenon atoms. The range of scattering angles is 0°–2°. From the scattering differential cross section found experimentally, the probabilities of single-electron capture and electron capture ionization as a function of the impact parameter are calculated. The dependences of the incident particle scattering angle on the impact parameter (deviation function) for interactions with Ar and Xe atoms are calculated in terms of classical mechanics using the Moliére—Yukawa potential to describe the interaction of atomic particles. Analysis is given to the probabilities of electron capture and electron capture ionization versus the impact parameter and to the distribution of the electron density on different electron shells in a target atom versus a distance to the core. It is concluded that only electrons from the outer shell of the target atom are involved in the process of electron capture ionization. The cross section of electron capture ionization is calculated in the proton energy range 5–20 keV.