Intensity measurements on Σ-hyperonic and kaonic atoms

σ-hyperonic X-ray lines have been observed in 8 elements and their intensities as well as those of the accompaning kaonic X-ray lines have been determined. The σ-atomic cascade has been found to be similar to those of other exotic atoms. The production of σ^? hyperons per stoppedK ^? has been measured by comparing their X-ray intensities. For the first time the intensity attenuation due to the strong absorptive σN interaction could be measured in four cases, and simple optical model calculations have been performed in order to reproduce the data.     

Shifts of X-ray characteristic L lines of free atoms of rare-earth metals

Results of the study of X-ray characteristic spectra of free atoms of a number of rare-earth metals from Ce to Ho are reported. L _α1 and L _β1 lines were studied, and the shifts of the peaks of emission lines of free atoms relative to their positions in the case of emission by the solid aggregate state were measured. The data obtained enable one to use the corresponding X-ray characteristic lines as references with the accuracy Δλ/λ≈10^?5. The Z-dependences of shifts are plotted.     

Anomalous H/D isotope effect on 35Cl NQR frequencies in piperidinium p-chlorobenzoate

Anomalous isotope effects were detected in the ³⁵Cl nuclear quadrupole resonance (NQR) frequency of piperidinium p-chlrobenzoate (C₅H₁₀NH· ClC₆H₄COOH) by deuteration of hydrogen atoms. The atoms were determined to form two kinds of N–H···O type H-bonds in the crystal structure. Large frequency shifts of the ³⁵Cl resonance lines reaching 288 kHz at 77 K and 278 kHz at room temperature were caused upon deuteration, in spite of the fact that the Cl atoms in the molecule do not form hydrogen bonds in the crystal. Results of single crystal X-ray diffraction measurements and density-functional-theorem calculations suggest that a dihedral-angle change of 1.8° between benzene and the piperidine ring contributes to ³⁵Cl NQR anomalous frequency shifts.     

Collisional deexcitation of exotic hydrogen atoms in highly excited states

The atomic cascades in μ^- p and p atoms have been studied in detail using new results for the cross-sections of the scattering of highly excited exotic atoms from molecular hydrogen. The cascade calculations have been done with an updated version of the extended standard cascade model that computes the evolution in the kinetic energy from the beginning of the cascade. The resulting X-ray yields, kinetic energy distributions, and cascade times are compared with the experimental data.     

Paramagnetische Wasserstoffzentren in Kaliumjodid

After irradiation with ultraviolet light at low temperature KJ crystals doped with SH^? or SeH^? ions show the ESR spectra of interstitial hydrogen atoms (U ₂ centers). The behavior of the spectra is studied at 9 and 35 GHz respectively, and the parameters of the spin Hamiltonian have been determined. Forbidden transitions with changes Δm=±1 of the nuclear quantum number are found to occur with appreciable intensity in KJ. Above 95 K the hydrogen atoms become unstable and react to new paramagnetic hydrogen centers.     

Calculations of the cascade characteristics for hadronic hydrogen atoms based on a quantum-classical approach

The quantum–classical Monte Carlo cascade calculation model for the muonic (non-hadronic) hydrogen atom has been modified for exotic pK ^??? and $p\bar p$ atoms with strong interaction. The radiative and collision transitions were taken into account only because in such a case of “heavy” atoms the effects of exotic molecule formation are not essential. The radiative cascade was considered within the framework of quantum mechanics whereas the collisions of exotic atoms in excited states with hydrogen were described by methods of classical mechanics. The yields for the K-series X-rays in pK ^??? and $p\bar p$ atoms have been calculated and compared with the experimental data.     

Formation of highly excited hydrogen atoms in a beam-foil interaction

The production of highly excited hydrogen atoms by passing a proton beam though a thin carbon foil has been investigated within the energy range 5–30 keV. The population of atoms in states with principal quantum number, n, between 14 and 25 have been determined using the field ionization technique and found to scale as n^?4.35±0.2.     

XAFS studies of the local structure and charge state of the Pr impurity in SrTiO3

Solid solutions of (Sr_{1 ? x} Pr _x )TiO₃ have been studied using X-ray methods. It has been shown that, with an increase in the praseodymium concentration, the temperature of the structural phase transition to the phase with space group I4/mcm increases and, at x ?? 0.15, the structure at 300 K is tetragonal. X-ray absorption fine structure (XAFS) spectroscopy studies have revealed that Pr ions are predominantly in the charge state 3+ and occupy the Sr sites. No indications of the off-centering of Pr atoms at the Sr sites have been revealed. The local environment of Pr atoms is characterized by a strong relaxation of the oxygen atoms, the value of which corresponds to the difference between the ionic radii of Pr³⁺ and Sr²⁺. It has been found that, in the second shell, there occurs a significant repulsion of the Pr³⁺ and Ti⁴⁺ ions, which is responsible for the weak dependence of the lattice parameter in the solid solution on the praseodymium concentration.     

The configuration of the hydrogen atoms in HfV2Hx compounds at low temperatures: A NMR study

The ⁵¹V nuclear electric quadrupole interaction and the shape of the proton resonance line in the low temperature phase of the HfV₂H_x (0≤x≤4) compounds has been studied by NMR. The data yield information about the hydrogen arrangement in the low temperature phase. They confirm the results of recent neutron diffraction studies that for x=4 and ordered super lattice of the hydrogen atoms exists, with the hydrogen atoms occupying only tetrahedral interstitial sites formed by two Hf and two V atoms. Our results show that in the lower concentration compound the hydrogen atoms most probably also occupy the same type of interstices, but without crystallographic order.     

Kinetic energy distributions in pionic hydrogen

A framework for analyzing the Doppler broadening of the X-ray lines in pionic hydrogen is proposed. It is shown that the kinetic energy distributions at the instant of the (n = 2-4) radiative transitions are related to each other. In order to establish the connection, the collisional processes for pionic hydrogen scattering from hydrogen atoms and molecules have been calculated in different models. The proposed method can be used to determine reliably the strong interaction width of the ground state of pionic hydrogen from the X-ray line profiles measured recently at the Paul-Scherrer-Institut.Received: 6 August 2004, Published online: 28 September 2004PACS: 34.50.-s Scattering of atoms and molecules - 36.10.Gv Mesonic atoms and molecules, hyperonic atoms and molecules     

X-ray photoelectron spectra and structure of iron polynuclear complexes

Iron trimethylacetate complexes with different ligands have been investigated by X-ray photoelectron spectroscopy (XPS). The Fe 2p, Fe 3p, C 1s, O 1s, and N 1s spectra obtained at successive replacement of the Fe-O coordination bonds with Fe-N bonds have been analyzed. A satellite component is found in the spectra of iron trimethylacetate complexes, which is indicative of the high-spin state of Fe^II and Fe^III iron atoms. The XPS data made it possible to determine the degree of covalence of the metal-ligand bonding and reveal two nonequivalent states for iron atoms.     

Structural and magnetic transformations in the GdMn2Hx hydrides

Powder samples of GdMn₂H_x hydrides, with 0⩽x⩽4.3, have been characterized by X-ray analysis and SQUID magnetometry for temperatures ranging between 4 and 375 K. The observed phase transformations as a function of temperature and hydrogen concentration are discussed and explained. The correlated changes of magnetization and susceptibility have been analyzed and the temperature dependent development of magnetic ordering of Mn and Gd atoms as a function of temperature and hydrogen content has been discussed. The structural and magnetic phase diagrams have been proposed.     

Nitrogen 1s electron binding energy assignment in carbon nitride thin films with different structures

Carbon nitride thin films deposited by dc unbalanced magnetron sputtering have been analyzed by high-resolution X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The XPS data show that N 1s binding states depend on substrate temperature (T_s). By comparison with the Raman spectra, N 1s binding states are assigned in which nitrogen atoms are mainly bound to sp² and sp³ carbon atoms at T_s = 100°C, whereas at T_s = 500°C nitrogen atoms are mainly bonded to sp², sp³ and sp¹ carbon atoms.     

Detection of hydrogen in nominally pure GaP:Zn by optically detected electron nuclear double resonance

Optically detected electron nuclear double resonance (ODENDOR) measurements of the triplet antisite center P_Ga³⁺ in GaP:Zn have revealed the presence of hydrogen atom impurities in a nominally pure sample. Strong ligand ³¹P signals have also been observed. Assuming a uniform distribution of hydrogen the intensity ratio of the ³¹P to ¹H lines sets a rough lower limit of between 1–10 ppm on the hydrogen concentration. The possibility that the H¹ atoms form part of the antisite defects is also discussed.     

First observation of K X-rays from pp atoms

K and L series X-rays have been observed from p$\text{p}$ atoms formed in hydrogen gas at NTP in association with annihilations into neutral particles. The total K X-ray yield is (6.5 ± 3.2) × 10^?3 per stopped antiproton. A model-dependent fit of the K X-ray spectrum gives a K_α energy of 8.9±0.3 keV, corresponding to a strong interaction shift of (?0.5±0.3) keV.     

Stepwise ionization in a non-equilibrium,steady-state hydrogen plasma

The paper considers a non-equilibrium, steady-state hydrogen plasma with 10¹⁰ ? N_e, cm^-3 ? 10¹⁷ and 8000 ? T_e, °K ? 64,000. The following two cases are analyzed: (1) the plasma is optically thin for all atomic lines and (2) the plasma is optically thick towards the Lyman lines and optically thin for all other lines. Analytical expressions have been obtained for populations and ionization frequencies of excited levels. Populations of the excited levels obtained from the analytical formulas are in good agreement with numerical calculations.     

The contribution of dissociative processes to the production of atomic lines in hydrogen plasmas

The contribution of molecular dissociative processes to the production of atomic lines is considered for a steady-state hydrogen plasma. If the contribution of dissociative processes is dominant, a substantial simplification in plasma diagnostics can be achieved. Numerical calculations have been performed for the production of Balmer α, β, and γ lines in hydrogen plasmas with medium and large degrees of ionization (x ? 10^-4) and for 5000 ? T_e, K ? 45,000 and 10¹⁰ ? N_e, cm^-3 ? 10¹⁶.     

Calculation of X-ray and Auger transition rates, lifetimes, X-ray wavelengths, and fluorescence yields of variously ionized silicon atoms

X-ray and Auger transition rates, X-ray wavelengths, and fluorescence yields are calculated for variously ionized silicon atoms with configurations 1s2s^m2pⁿ, m=0-2, n=1-6. The calculation has been performed using the Hartree-Fock atomic model. Intermediate coupling and configuration interaction have been taken into account. The energies and widths are found to be strongly affected by configuration mixing. The results from the present calculation have been compared with those available in the literature. The theoretical K_α hypersatellite and satellite spectra fall into several well-separated regions, corresponding to each of the possible number of spectator electrons in the 2s and 2p shells. The dependence of radiative rates and fluorescence yields on the number of spectator electrons is also investigated.     

Study of the dependence of the radiative properties of high-frequency electrodeless lamps in an Hg-Ar mixture on the pressure of mercury vapor

The radiative characteristics of high-frequency electrodeless lamps in a mixture of mercury and argon have been studied theoretically and experimentally as functions of the cold spot temperature (the pressure of mercury vapor). The intensity of the mercury lines at 404.7, 435.8, and 546.1 nm, corresponding to the triplet transition (7³ S ₁-6³ P _0,1,2) in the visible spectral region, as well as the intensity of the UV resonance line (6³ P ₁-6¹ S ₀) at 253.7 nm, has been measured. A model describing the physical processes in the discharge plasma and including the kinetics of excited states of mercury and argon atoms has been suggested. The parameters of the discharge plasma and the electromagnetic field have been calculated self-consistently through the numerical solution of the system of equations of electron density and energy balance and population balance of excited levels of argon and mercury atoms, as well as the Maxwell equations. The model developed has allowed us to calculate the intensities of the mercury emission lines at 253.7, 404.7, 435.8, and 546.1 nm and to compare the results with experimental data. The relative intensities of the mercury spectral lines corresponding to the triplet transition 7³ S ₁-6³ P _0,1,2 have been calculated for the first time on the basis of a self-consistent model of the discharge.     

Scattering of Light Exotic Atoms in Excited States

The scattering of light exotic atoms in excited states (n = 2–5) from hydrogen has been calculated in a close-coupling model. For the first time, the absorption cross sections for hadronic atoms due to Stark collisions have been calculated by taking the shifts and widths of the nS states into account in a self-consistent quantum mechanical framework. A classical-trajectory Monte Carlo method has been used to calculate the scattering of exotic atoms from molecular hydrogen for n≥8. The Coulomb transitions with Δn>1 are found to be the dominant deexcitation mechanism at the initial stage of the cascade.