Cascade Processes in Muonic Hydrogen Atoms

The QCMC scheme created earlier for cascade calculations in heavy hadronic atoms of hydrogen isotopes has been modified and applied to the study of cascade processes in the μp muonic hydrogen atoms. The distribution of μp atoms over kinetic energies has been obtained and the yields of K-series X-rays per one stopped muon have been calculated. Comparison with experimental data indicated directly that for muonic and pionic atoms new types of non-radiative transitions are essential, while they are negligible for heavy (kaonic, antiprotonic, etc.) atoms. These processes have been considered and their probabilities have been estimated. This revised version was published online in August 2006 with corrections to the Cover Date.     

Near resonance charge transfer from a laser excited donor state

A laser induced charge transfer from Na(3p) to hydrogen-ions at different kinetic energies has been studied. An enhancement factor of about 90% in the production rate of Lyman-α radiation has been demonstrated to occur only with H⁺ and Na(3p) atoms reaction; no enhancement was observed with either H ₂ ⁺ or H ₃ ⁺ ions. Absolute cross-section for the production of Lyman-α radiation during the collision of H⁺, H ₂ ⁺ and H ₃ ⁺ ions and Na(3p) and Na(3s) atoms have been measured in the energy range 1–600eV. The charge exchange reactions involving hydrogen-ions and Na(3p) atoms created by two different methods have also been compared.     

Dipole and quadrupole cascades in the yrast region of 143Gd

The high spin states of ¹⁴³Gd have been studied via the ¹¹¹Cd(³⁵Cl,1p2n) reaction at 170 MeV. One dipole cascade has been newly found and two dipole cascades have been extended to higher spin states. A relatively long E2 cascade consisting of irregular transition energies has been found, which has only weak connections to the other dipole and quadrupole cascades. This resembles the ones recently found in ^142,143,144Eu and ¹⁴⁴Gd. The dipole and quadrupole cascades have been found to appear by turns in an energy increment of about 0.2 MeV above the yrast line. Received: 1 November 1997     

Comments on the physical significance of E1 values for excited sputtered atoms

Measurements of parameters associated with the emitted photons from a number of elements have indicated that the kinetic energies of sputtered excited atoms may be of the order of 10²–10³ eV. A recent result of Yu et al. [Phys. Rev. Letters 48 (1982) 427] is in contradiction to those results. We argue that the high energy values reported are the result of cascade repopulation of the upper level of the observed transition, distorting the experimental observations. Cascade corrections could reduce the energy values to the order of 10 eV, similar to the most probable energy of secondary ions.     

Historical overview and introduction

The complex balance of processes occurring at the cascade of exotic H-atoms is usually described by the so-called standard cascade model, but this model neglects variations of the kinetic energy T of the exotic atom during the cascade which are crucial for the analysis of several important experiments. New experimental results on T _μp at H₂ pressures between 0.063 and 4 hPa demonstrate the importance of acceleration due to Coulomb de-excitation processes at highly excited μp levels n > 9. The data at the lowest density are sensitive to the initial values of the kinetic energy and n-levels at the moment of atomic capture. From the measured low-energy tail of the T _μp-distribution it can be concluded that a considerable part of the μp(2s) atoms is metastable at pressures of a few hPa. This revised version was published online in August 2006 with corrections to the Cover Date.     

Electron-impact excitation of the 3 P o and 3 D o levels of a nickel atom

The excitation cross sections of transitions from the ³ P ^o and ³ D ^o levels of a nickel atom in electron-atom collisions at an exciting-electron energy of 50 eV have been analyzed by the method of extended crossing beams with detection of the optical signal from excited atoms. Eleven optical excitation functions have been recorded in the electron-energy range of 0?C200 eV. The direct excitation cross sections of the energy levels and the contribution of the cascade transitions were calculated using the data obtained.     

Electron-stimulated desorption of potassium and cesium atoms from an oxidized molybdenum surface

The yield and energy distributions of potassium and cesium atoms emitted in electron-stimulated desorption (ESD) from a molybdenum surface, oxidized to different extent and maintained at 300 K, have been measured by the time-of-flight technique with a surface ionization detector. The ESD threshold for potassium and cesium atoms lies around 25 eV, irrespective of molybdenum oxidation state. In the case of molybdenum coated by an oxygen monolayer, secondary thresholds at ∼40 and ∼70 eV have been observed, as well as atomic energy distribution tailing down to very low energies. The most probable kinetic energies of the atoms are a few tenths of one eV. The results are explained within a model involving Auger neutralization of the adsorbed alkali metal ions after the filling of the 2s O, 4s Mo, and 4p Mo core holes. The possibility of ESD of a neutral species as a result of oxide-cation core-level ionization has been demonstrated for the first time. Fiz. Tverd. Tela (St. Petersburg) 39, 758–761 (April 1997)     

The energy distributions of atoms sputtered from HfC

The energy spectra of Hf and C atoms sputtered from an HfC target with a 6 keV Xe⁺ beam have been measured. It was found that the target constituents of widely different masses were sputtered with energy distributions of the same form. The results are compared with the collision cascade theory for compound targets.     

Reactivity of sodium arenesulfinates in the substitution reaction to γ‐functionalized allyl bromides

The kinetics of nucleophilic bimolecular substitution reactions of γ‐functionalized allyl bromides with non‐substituted and p‐substituted sodium arenesulfinates has been studied. Both the structure of allyl bromides and nucleophilicity of arenesulfinate ions exerted a significant effect on the values of the kinetic parameters such as the second‐order rate constants k, activation energy E_A, and changes in the entropy ΔS^≠, enthalpy ΔH^≠, and free energy ΔG^≠ of the formation of the activated complex from reactants. Based on the evaluation of kinetic parameters, the reactants could be arranged, according to their decreasing reactivity in the S_N2‐reactions as follows: p‐toluenesulfinate ion > benzenesulfinate ion > p‐chlorobenzenesulfinate ion and 4‐bromo‐2‐butenenitrile > 1,3‐ dibromopropene, respectively. Comparison was also made between the kinetic data obtained and some delocalization reactivity indexes for both the substrates and nucleophiles. The enthalpy–entropy compensation effect was observed for the reactions of sodium arenesulfinates with γ‐functionalized allyl bromides. Copyright © 2009 John Wiley & Sons, Ltd.     

Theoretical study of the MgAr molecule and its ion Mg<Superscript>+</Superscript>Ar: potential energy curves and spectroscopic constants

The adiabatic potential energy curves of the low-lying electronic states of the MgAr molecule dissociating into Mg (3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p)+Ar have been investigated. The electronic structure of the Mg-Ar molecule is calculated using [Mg²⁺] and [Ar] core pseudopotentials complemented by the core polarization operators for both atoms, considering the molecule to be a two-electron system. The derived spectroscopic constants of the ground state and lower excited states are in good agreement with available experimental and theoretical work. In addition, for the purpose of checking the pseudopotential accuracy on a simpler related system, low lying potential energy curves of the single active electron Mg⁺Ar ion are also reported and the corresponding molecular constants are compared with those in the existing literature.     

Hund's rules and the interpretation and common misinterpretation of energy differences

With a Z expansion formalism which is exact in non-relativistic quantum mechanics it has been shown that for multiplets of neutral atoms and of many positive ions the state of the highest energy has the lowest expectation value for the interelectronic repulsion energy. This reversed order of the repulsion energy occurs for cases which obey Hund's first rule as well as for cases which obey the second of Hund's rules. It can be shown that the energy differences are in all cases dominated by the difference in electron nuclear attraction energy and not by the difference in electron repulsion energy.

The lowest ¹Π _u and ³Π _u states of the H₂ molecule have similar features. At many internuclear distances, including the equilibrium ones, the ¹Π _u state has the highest energy but the lower kinetic energy and electron repulsion energy but again the higher electron nuclear attraction energy. These results contradict clearly the usual theories for energy differences between spectroscopic states in atoms and molecules.     

X-ray spectra induced in highly charged 40Arq+ interacting with Au surface

By use of optical spectrum technology, the spectra of X-ray induced by highly charged ⁴⁰Ar ^q+ ions interacting with Au surface have been studied. The results show that the argon Kα X-ray were emitted from the hollow atoms formed below the surface. There is a process of multi-electron exciting in neutralization of the Ar¹⁶⁺ion, with electronic configuration 1s² in its ground state below the solid surface. The yield of the projectile Kα X-ray is related to its initial electronic configuration, and the yield of the target X-ray is related to the projectile kinetic energy.     

Nuclear model calculations on the production of <Superscript>125,123</Superscript>Xe and <Superscript>133,131,129,128</Superscript>Ba radioisotopes

In this study, production rates of ^125,123Xe and ^{133,131,129,128}Ba medical isotopes produced by ¹²⁷I(p, 3n)¹²⁵Xe, ¹²⁷I(p, 5n)¹²³Xe, ¹³³Cs(p, n)^133mg Ba, ¹³³Cs(p, 3n)^131mg Ba, ¹³³Cs(p, 5n)¹²⁹Ba, and ¹³³Cs(p, 6n)¹²⁸Ba reactions have been investigated up to 100 MeV incident proton energy. The preequilibrium calculations involve the hybrid model, the geometry-dependent hybrid model and the cascade exciton model. The calculated results are compared with the experimental data taken from the literature.     

Kinetic energy of π− p-atoms in liquid and gaseous hydrogen

We have measured the Doppler broadening of neutron time-of-flight spectra from the reaction π⁻ p → π⁰ + n in atomic states. From the data, we infer that the kinetic energy distribution of π⁻ p-atoms in liquid and gaseous hydrogen contains discrete ‘high-energy’ components with energies as high as 200 eV attributed to Coulomb de-excitation. In liquid hydrogen, evidence for Coulomb de-excitation transitions with Δn = 2 has been found. This revised version was published online in August 2006 with corrections to the Cover Date.     

Electron Transitions during the Capture of an Electron by a He<Superscript>2+</Superscript> Ion at the Argon Atom

We have measured the absolute values of the total cross section of the one-electron capture by He²⁺ ions in the kinetic energy range 2–30 keV at the Ar atoms. The absolute values of the differential scattering cross sections of He⁺ ions formed during the one-electron capture and the electron capture with ionization at energies of 2.2, 5.4, and 30 keV have been determined. The electronic states of the formed ions have been determined using collision spectroscopy based on analysis of the change in the kinetic energy of He⁺ after the interaction. We have measured doubly differential (with respect to the kinetic energy and the scattering angle) cross sections of the formation of free electrons. The free electron formation channels (direct ionization and electron capture with ionization) have been analyzed by calculating the electron terms of the (HeAr)²⁺ system. The calculated cross section of capture with ionization is in conformity with the cross section measured using collision spectroscopy.     

Ionization of fast rydberg atoms in longitudinal and transverse electric fields

The main properties of longitudinal and transverse electric field ionizers for fast Rydberg atoms n=21–40 have been investigated. The dispersion and the background due to collisional processes between fast atoms and residual gas molecules have been measured and calculated. The kinetic energy spread of ions formed by field ionization of Rydberg atoms and their trajectories have been calculated. The potassium beam energy was 3.9 keV.     

Spectrum of Kelvin-wave turbulence in superfluids

We derive a type of kinetic equation for Kelvin waves on quantized vortex filaments with random large-scale curvature, that describes step-by-step (local) energy cascade over scales caused by 4-wave interactions. Resulting new energy spectrum E _LN(k) ∝ k ^−5/3 must replace in future theory (e.g., in finding the quantum turbulence decay rate) the previously used spectrum E _KS(k) ∝ k ^−7/5, which was recently shown to be inconsistent due to nonlocality of the 6-wave energy cascade.     

反冲原子对低速离子轰击Si表面时电子发射产额的影响

在兰州重离子加速器国家实验室电子回旋共振离子源高电荷态原子物理实验平台上,用低能(0.75keV/u≤EP/MP≤10.5keV/u,即3.8×105m/s≤vP≤1.42×106m/s)He2+,O2+和Ne2+离子束正入射到自清洁Si表面时二次电子发射产额的实验结果.结果表明电子发射产额γ近似正比于入射离子动能EP/MP.在相同动能下,γ(O)γ(Ne)γ(He),对于原子序数ZP比较大的O2+和Ne2+离子,ZP大者反而γ小,这与较高入射能量时的结果截然不同.通过计算不同入射能量下入射离子的阻止能损S,发现反冲原子对激发二次电子的作用随入射离子能量的降低显著增大,这正是导致在较低能量范围内二次电子发射产额与较高入射能量时存在差异的主要原因.     

Electron-stimulated desorption of sodium atoms initiated by their reverse motion

This paper reports on the first measurement of the yield and energy distributions of sodium atoms in electron-stimulated desorption at T = 160 K from sodium layers adsorbed on tungsten with a gold film atop. The Na atom yield has a resonant pattern with an appearance threshold of 30 eV, which can be attributed to exciton excitation in the Na 2p level. The Na yield is associated with the formation of a semiconducting Na _x Au _y film at T ∼ 300 K and sodium and gold coverages in excess of one monolayer. Sodium atoms are desorbed through Auger neutralization of Na²⁺ ions in their reverse motion toward the surface and is limited by the resonant ionization of Na atoms as they pass through the adsorbed layer of Na⁺ ions. The energy distributions of Na atoms are bell shaped with a maximum at about 0.56 eV.