Formation of higher-order fullerene dianions in collisions with Na atoms

We have measured electron capture cross sections in collisions between higher order fullerene anions C_n ^- (n=76, 78, 82, 84, 86, 90 and 96) and Na atoms. The ions were produced in an electrospray ion source (ESI) and accelerated to an energy of 50 keV. The measured cross section for dianion formation is three times larger for C₉₆ than that for C₆₀. The latter cross section was earlier found to be 36 ?². The dramatic increase of the cross section with fullerene size is explained by means of the curve crossing model for electron transfer.     

Statistical theory of nuclear neutrino capture: (II). Inclusion of first-forbidden transitions

The statistical theory of nuclear neutrino capture is extended to include first-forbidden transitions. A comparison with the theory of Bahcall and Frautschi is made. It is found that the present theory predicts neutrino capture cross sections which are smaller than those of Bahcall and Frautschi by a factor 2–3 for neutrino energies less than 50 MeV when first-forbidden transitions are dominant. Calculation of the cross section is made for the process in which ³⁷Cl nuclei capture electron neutrinos that are emitted in muon decay. The present calculation gives a cross section which is around one half of that of Donnelly and Haxton. Finally the contributions of the highly excited states in ³⁷Ar to the neutrino capture cross section are evaluated. It is shown that the contributions from the highly excited states (E > 6.02 MeV) to the neutrino capture cross section amount to 60% for E_v = 50 MeV.     

The contribution ofK-electron capture for the production of highly charged Ne recoil ions by 156 MeV bromine impact

The recoil ion production cross sections in 2MeV/amu Br ⁿ⁺+Ne⁰→Br ^n′++Ne ^q+ were measured using a projectile ion — recoil ion coincidence technique where the final charge states of both collisions partners were detected simultaneously. Multiple ionization was found to be the dominant process for the production of low charge state recoil ions whereas the production of highly charged recoil ions is accompanied by electron capture from the Nek-shell. The derived ratio of single to double Ne-k electron capture probabilities indicates deviations from a binomial statistics distribution.     

Ionization of hydrogen and helium atoms by highly charged fast ions in collisions with small momentum transfer

Ionization of hydrogen and helium atoms is studied for the case of “soft” collisions with highly charged fast ions with v≲Z≪v² and v≫v ₀, where Z is the ion charge, v is the collision velocity, and v ₀∼1 is the characteristic velocity of the electron in the ground state of the atom. Analytical expressions are derived for the singly and doubly differential cross section for ionization of a hydrogen atom accompanied by the ejection of a slow electron v _e≲v ₀, where v _e is the velocity of the ejected electron with respect to the recoil ion). The results are generalized to the case of single ionization of helium. It is shown that soft collisions provide the main contribution to the hydrogen ionization cross section and for all practical purposes determine the cross section for single ionization of helium. The asymmetry in the angular distribution of the ejected slow electrons and the properties of momentum exchange in such collisions are discussed. Finally, a formula for the cross section for single ionization of helium is proposed. Zh. éksp. Teor. Fiz. 112, 1966–1977 (December 1997)     

Single and double electron capture processes in slow Ne q+-He (q=10, 6) collisions

The cross sections for single and double electron capture to the states Ne⁹⁺ n) with n=3–6 and Ne⁸⁺(3l,n′l′), Ne⁸⁺(4l,n′l′) with n′⩾4 and also the cross sections for single electron capture to the states Ne⁵⁺(3) in collisions of Ne¹⁰⁺ and Ne⁶⁺ with He atoms are calculated for collision energies in the interval from 10 to 150 keV. The calculation is carried out in the multichannel Landau-Zener, Nikintin, and Landau-Zener-Chaplik models with allowance for the radial coupling of the channels at crossing points of the energies of the quasidiabatic twoelectron states of the quasimolecule. The energies of the two-electron states are calculated in the effective potential method to first order in perturbation theory in the residual electron-electron interaction. The energies of the adiabatic states in the neighborhoods of the crossings of quasidiabatic terms are determined by the configuration interaction method. It is found that in Ne¹⁰⁺-He collisions the electron is captured mainly to the n=5 state of the Ne⁹⁺ ion. The cross section for double electron capture to the 3lnl′ state (n⩾4) of the Ne⁸⁺ ion is an order of magnitude smaller than the cross section for single electron capture. The contribution to the total cross section for double electron charge transfer from the 4l4l′ 4l5l′, and 4l6l′ states is approximately 25%. The dependence of the cross sections for double electron charge transfer on the values of l and l′ is investigated. Zh. Tekh. Fiz. 69, 15–28 (January 1999)     

Absolute cross sections for electron capture into (n, 1) subshells of N VI by VUV spectroscopic study of the N6+-He collision

Absolute cross sections for electron capture into different (n, 1) subshells have been determined for N⁶⁺-He collision at 4.2 keV/amu. The n = 3 level is predominantly populated. The total one electron charge exchange excitation cross section is deduced.     

中低速C3+与He，Ne，Ar原子相互作用过程中单电子转移绝对截面的测量

实验测量了1.7v₀—4.2v₀(v₀为玻尔速度,v₀=2.19×10⁸cm/s)的C³⁺与He,Ne,Ar原子碰撞过程中单电子转移绝对截面.将实验结果与多体经典轨道蒙特卡罗模拟计算结果做了比较,发现测量结果与多体经典轨道蒙特卡罗模拟计算结果在趋势上相符.当入射离子速度在1.7v₀—2 关键词： 离子-原子碰撞 单电子转移 绝对截面     

质子与He+,Li++高能碰撞过程中电子俘获截面的理论计算

用OBK近似和CDW近似计算了H⁺+He⁺和H⁺+Li⁺⁺碰撞过程中电子俘获到激发态的分截面与俘获到基态分截面的比值，结果发现用OBK近似给出的比值和用CDW方法所给出的相应比值在高能区符合得很好．由此提出了一种用于计算高能H⁺与任一类氢离子碰撞的电子俘获总截面及任一激发态分截面的方法 关键词：     

Electron spectrometry study of associative and penning ionization in laser excited sodium vapor

The first observation, by electron spectrometry, is reported in laser-excited sodium vapor of the primary low energy electrons produced by associative ionization and by Penning ionization of sodium atoms in highly excited n1 states. The sequential heating of these primary electrons has been observed in 1, 2 or 3 superelastic collisions with Na(3p) atoms. The variation of associative ionization was measured as a function of the excited state density by using inner-shell photoionization produced by synchrotron radiation. Finally, an associative ionization cross section of 3.8 X 10^-17 cm² and a Penning ionization cross section for the 5s state of 1.1 X 10^-12 cm² were found (within 50% uncertainty) for an oven temperature of 520 K.     

Sub-leading flow modes in PbPb collisions at sNN = 2.76 TeV from the HYDJET++ model

Recent LHC results on the appearance of sub-leading flow modes in PbPb collisions at 2.76 TeV, related to initial-state fluctuations, are analyzed and interpreted within the HYDJET++ model. Using the newly introduced Principal Component Analysis (PCA) method applied to two-particle azimuthal correlations extracted from the model calculations, the leading and sub-leading flow modes are studied as a function of the transverse momentum (p_T) over a wide centrality range. The leading modes of the elliptic (v₂⁽¹⁾) and triangular (v₃⁽¹⁾) flow calculated with the HYDJET++ model reproduce rather well the v₂{2} and v₃{2} coefficients measured experimentally using the two-particle correlations. Within the p_T ≤ 3 GeV/c range, where hydrodynamics dominates, the sub-leading flow effects are greatest at the highest p_T of around 3 GeV/c. The sub-leading elliptic flow mode (v₂⁽²⁾), which corresponds to the n = 2 harmonic, has a small non-zero value and slowly increases from central to peripheral collisions, while the sub-leading triangular flow mode (v₃⁽²⁾), which corresponds to the n = 3 harmonic, is even smaller and does not depend on centrality. For n = 2, the relative magnitude of the effect measured with respect to the leading flow mode shows a shallow minimum for semi-central collisions and increases for very central and for peripheral collisions. For the n = 3 case, there is no centrality dependence. The sub-leading flow mode results obtained from the HYDJET++ model are in rather good agreement with the experimental measurements of the CMS Collaboration.     

Production of projectile and targetK X-rays by single and multiple electron-capture in collisions of Si14+ and Si13+ ions with argon atoms at 4.5 and 5.5 MeV/amu

Projectile and target X-ray cross-sections have been measured in collisions of bare and hydrogenlike Silicon ions with argon atoms. Projectile energies are 125 MeV and 153 MeV, i.e. the intermediate velocity region forK-shell capture. Coincidence measurements between X-ray photons and the scattered Si ⁿ⁺ projectiles with charge statesn-1,n-2 andn-3 have been made. The relative contribution of charge exchange and direct ionization (or excitation) of the targetK-shell has been obtained directly by this new method. DoubleK-shell electron transfer is demonstrated to be very large in the case of fully stripped Si ions. A thorough theoretical analysis of the data is carried out and multiple capture processes are evaluated using an independent electron model.     

Double electron capture in H+ + Mg collisions

The cross section for double electron capture in H⁺ + Mg collisions has been measured over the proton energy range 1.1 keV to 80 keV. The cross section exhibits structure at low energies and is rising below 2.8 keV. Results are discussed and compared with recent multichannel Landau-Zener calculations and with previous measurements.     

Dissociative recombination of electrons and O 2 + molecular ions in the field of intense visible laser radiation

We analyze the low-temperature dissociative recombination reaction e ^?+O ₂ ⁺ → O(¹ D)+O(³ P) in the field of visible monochromatic laser radiation. The analysis is performed in terms of the multichannel quantum defect theory using the stationary formalism of the radiative collision matrix. We calculate the dependences of the reaction cross section on the incident electron energy, the external electromagnetic field strength and frequency, and also the angle between the directions of the electron beam and the electric vector for linearly polarized radiation. The cross section is shown to increase by several orders of magnitude for a certain choice of these parameters, suggesting the possible laser stimulation of this reaction.     

Autoionization cross section of potassium atom excited by electron impact

The autoionization cross section of potassium atoms excited by electron impact is measured in the energy range from the first autoionization threshold at 18.72 eV to 202 eV. The data are obtained by deter-mining the total intensity of electron spectra resulting from the decay of the 3p ⁵ n ₁ l ₁ n ₂ l ₂ autoionizing states. The cross section has two maxima, 1.8 × 10^?16 and 2.2 × 10^?16 cm², at 21 and 32 eV, respectively. The excitation dynamics of autoionization states suggests that the first maximum is associated with the resonance character of the near-threshold excitation. The second maximum, as well as the behavior of the cross section at energies above 50 eV, reflects the dynamics of electron excitation of quartet and doublet autoionizing states. The measured autoionization cross section is compared with known data for the total single ionization cross section of potassium atom by electron impact. The relative contribution of the autoionization cross section to the total single ionization cross section is found to reach 30% at 32 eV.     

Fragmentation of polyatomic ions produced by electron-loss collisions of butane and isobutane molecules with ions of kiloelectronvolt energy

Fragmentation accompanying the loss of electrons by butane and isobutane (C₄H₁₀) molecules in collisions with energy H⁺, He²⁺, and Ar⁶⁺ ions of kiloelectronvolt energies is studied. The electron density functional technique is applied to C _n H_2n+2 alkane molecules and their respective C _n H _2n+2 ⁺ ions to carry out quantum-chemical calculations of the atomic spacing, electron total energy for the initial configuration of the ionizing molecules and ions in the ground state, and atomic bond breaking energy necessary to produce different ion fragments. The fragmentation energy is correlated with the fragmentation probability. It is shown that the relative cross sections of ion fragmentation depend primarily on the related energy consumption. However, the process cross section is also strongly affected by the initial configuration of C₄H₁₀ isomer molecules, as well as by the amount of dangling and arising atomic bonds involved in the formation of each ion fragment.     

Dipole capture of a slow electron by a water cluster

It is shown that the anomalously large cross section for attachment of a slow electron to a water cluster (H₂O) _n≥50 that is observed in molecular-beam experiments may be explained by the capture of the electron by a long-range field of the permanent electric dipole moment of the cluster. The cross section values are used to estimate the dipole moment of the cluster as a function of its diameter n. The values obtained significantly exceed the random dipole moments in the case of the proton-disordered cluster structure and indicate the ferroelectric ordering of the orientations of dipole moments of the molecules included in the cluster.     

Capture of ultracold neutrons in thin absorbing films

The dependence of the ultracold neutron capture cross section in targets with a thickness smaller than the neutron wavelength is calculated in the time-dependent quantum theory. It is shown that, for low velocities of neutrons, their capture cross section σ_c～v, i.e., tends to zero as the neutron velocity v tends to zero.     

WWψ couplings from singleW-production in polarizede + e − collisions

Using the processeψ→Wv we study theWWψ vertex ine ⁺ e ^? collisions with polarized beams at a future 500 GeV collider. The equivalent photon approximation and its accuracy are discussed for the case of polarized electron beams. The resulting photon spectrum is then used to compute the total cross section as well as verious differential distributions for the processe ⁺ e ^?→e ⁺ W ^? v. Special emphasis is put on the effects of using polarized electron beams and their influence on the sensitivity to anomalous couplings.     

Resonance effects with the photoproduction of electron-positron pairs in the field of a plane electromagnetic wave

The differential cross section is obtained for the formation of electron-positron pairs by a photon at a Coulomb center in the field of a plane electromagnetic wave whose intensity η = eA′/m? 1 and frequency Ω′/m? 1. Expressions are given for the resonance frequencies of the photon for which the emission of a virtual electron (positron) at a mass shell occurs. It is shown that resonance occurs only for electron or positron energies E > m²/Ω′. The resonance differential cross section under interference conditions is obtained. It is shown that the resonance cross section can exceed by several orders of magnitude the ordinary cross section for the photoproduction of pairs without a field.