Oscillator strengths for the shape resonances in the N K absorption spectrum of NaNO3 measured with the use of synchrotron radiation

Spectral dependences of the total absorption cross sections near the N K(ls) ionization threshold have been measured in transmission for the first time for solid-phase sodium nitrate NaNO₃ using synchrotron radiation of the Russian-German soft x-ray beamline at the electron storage ring BESSY-II. On the basis of these measurements, which were performed with correct consideration of the background and instrumental distortions, partial N K absorption cross sections and the oscillator strengths for the π and σ shape resonances were determined for NaNO₃.     

Study of cross sections for the loss of outer 1s, 2s, and 2p electrons by fast ions and atoms of light elements

In the case of light-element ions propagating with velocities V = 1.83 and 3.65 au in H₂, He, N₂, Ne, and Ar, the loss cross sections σ_{i, i+m} for m electrons (m = 1, 2, 3) are considered. The partial loss cross sections σ_i(nl) for one of the outer 1s, 2s, or 2p electrons are determined using the obtained data. It is shown that the experimental cross sections for the loss of the 1s and 2s electrons by positive ions qualitatively agree with the theoretical values calculated in the Born approximation. In the case of the ion velocity V = 1.83 au, the cross sections σ_i for 2p electrons are greater than the cross sections σ_i (1s) and σ_i (2s) by a factor of 1.2–3 for the same binding energies of electrons in the ion (I _nl > 20 eV). It is found experimentally that, at V = 1.83 au, the cross sections σ_i (2p) for I _nl ～ 10–20 eV are less than the cross sections σ_i (1s) by a factor of 2–3, which is probably caused by a decrease in the screening parameter (θ_2p < 1) of the outer shell of atoms.     

Excitation of the 1s 2- and 1s 4-levels of neon and argon by He+-impact at energies between 100 keV and 1000 keV

The excitation of the 1s ₂- and 1s ₄-levels of neon and argon by He⁺-impact has been studied in the energy range of 100 keV to 1000 keV. The total emission cross sections for the 1s ₂ levels show pronounced maxima at about 350 keV impact energy, whereas the cross sections for the 1s ₄ levels increase with decreasing energy.     

Broadening of a two-photon resonance in a zinc atom in collisions with CO<Subscript>2</Subscript>, CO,and NO molecules

The broadening of a two-photon resonance is studied experimentally at the 4s¹S₀?6s³S₁ transition in a zinc atom upon absorption of two waves with a small detuning from an intermediate state in collisions with CO₂, CO, and NO molecules. The measured absolute values of broadening cross sections greatly exceed gas-kinetic cross sections and are (9.4±2.4, 6.5±1.6, and 3.9±1.0)×10^{? 14}cm² for CO², CO, and NO, respectively. Anomalously large rate constants and cross sections obtained in experiments are explained by the efficient resonance quenching of the excited states of zinc atoms in collisions with molecules accompanied by transfer of the energy of excited atoms to vibrational-rotational degrees of freedom of molecules.     

K-vacancy production by 3.6-, 4.75-, and 5.9-MeV/amu238U Ions

Projectile (Z ₁) and target (Z ₂)K-vacancy production cross sections induced by 3.6-, 4.75-, and 5.9-MeV/amu²³⁸U ions in selected targets between C and U are reported. The cross sections are discussed within the context of the molecular model of inner-shell vacancy production in heavy-ion-atom collisions. The measured 1sσ and 2pσ excitation cross sections are compared with semiempirical formulas, and with the perturbed-stationary-states calculations of Betz et al. The dependence of these cross sections onZ _u =Z₁+Z ₂ agrees well with the Betz calculations. However, the measured cross sections are factors of 2 to 4 (1sσ) and 4 to 5 (2pσ) larger than the theoretical values.     

Inclusive cross sections in the central region and the supercritical pomeron

Using the double-Regge formalism and a supercritical pomeron with α_P(0)=1+Δ, we analyse the energy dependence of inclusive cross sections for negatively charged particles (c⁻) and K_s⁰ at CM rapidity y=0 in the CERN PS-Sp̄pS collider energy range. The values of Δ(c⁻)=0.170±0.008 and Δ(K_s⁰)=0.167±0.024 are found to be very close to each other and compatible with estimates of Δ derived from the total cross sections.     

Angular distribution and polarization of photons during resonant above-threshold scattering on an atom

The effect of the resonant structure in the continuous spectrum induced by an external laser field due to the coupling of continuum states with the 1s4s ¹ S level in helium on cross sections of elastic and inelastic scattering of probe radiation on an atom in the metastable 1s2s ¹ S state at an energy above the ionization threshold is theoretically studied. Explicit expressions for the angular distribution and the degree of polarization of scattered photons as functions of probe and laser radiation characteristics are derived in the rotating wave approximation. Frequency, angular, and polarization dependences of the cross sections of scattering into final 1s ^{2 1} S, ¹ s2s ¹ S, and 1s4s ¹ S atomic states are calculated.     

About the effect of a bound state on ionization cross sections in ion-atom collisions

The cross sections σ_nl for ionization of hydrogen-like ions by heavy particles from the nl = 3s, 3p, 3d, 4s and 4p states have been calculated in the Born approximation. A structure in the energy dependence of the cross sections σ_nl and the ratios of the cross sections σ_nl/σ_1s due to the radial wave function of a bound state is discussed.     

Measurements ofK-shell ionization with132Xe and208Pb projectiles in the energy range of 1.4–5.9 MeV/u

Projectile and targetK-shell ionization cross sections induced by 3.6-, 4.7-, and 5.9 MeV/u¹³²Xe ions and 1.4-, 3.6-, 4.7-, and 5.9 MeV/u²⁰⁸Pb ions from the UNILAC in thin solid targets between C and U are measured. The cross sections are discussed in terms of the molecular model of innershell vacancy production in heavy ion-atom collisions. The sharing of 2p _1/2σ vacancies between theK shells of the two collision partners in these very heavy ion-atom collisions is found to deviate from the Meyerhof-Demkov formula forR≦10^?2. The measured ionization cross sections are compared with theoretical calculations for 1sσ and 2p _1/2σ excitation cross sections. AZ _UA=Z₁+Z ₂ dependence is found independent ofZ ₁/Z ₂. Outer-shell vacancy configurations measured in these close encounters are reported.     

Charge exchange and excitation cross sections at collisions of alpha particles with be-like impurity oxygen ions in a plasma

The charge exchange and excitation cross sections at collisions of alphas with O⁴⁺(1s ²2s ²) impurity atoms in a hot plasma for striking energies E _c varying from 20 keV to 2 MeV are determined for the first time. The cross sections are calculated using the method of close-coupling equations with 13 singlet four-electron quasi-molecular states taken as a basis. The partial cross sections of charge transfer to the 1s, 2s, and 2p states of a He⁺ ion and for O⁴⁺(1s ²2s ²) → O⁴⁺(1s ²2lnl’) (n = 2, 3) electronic excitation of an oxygen ion are found. The maximal value of the charge exchange total cross section roughly equals 2.2 × 10^?16 cm² at E _c ≈ 0.7 MeV. The excitation total cross section has a maximum of ≈ 7.7 × 10^?16 cm² at E _c ≈ 80 keV for single-electron excitation and ≈6.5 × 10^?16 cm² at E _c ≈ 0.7 MeV for two-electron excitation.     

Three particle correlation function of metal ions in tetrahedral coordination determined by XANES

The three particle correlation function of local atomic distribution at metal ion sites in solutions has been extracted from XANES (X-ray absorption near edge structure) spectra of [CrO₄]²⁻ and [MnO₄]⁻ ions measured by using synchrotron radiation. The absorption cross section for 1s core level excitation is calculated in the real space multiple scattering approach using the Hedin and Lundqvist energy dependent potential. We show that in these systems the expansion of the total absorption cross section in terms of contributions of higher order scattering processes is possible over a large energy range. This gives a unified theory of XANES and EXAFS and allows the third order correlation function to be extracted from experimental data.     

Study of the absorption characteristics of molecular oxygen in the Schumann-Runge system at high temperatures: II. Experiment and comparison with calculation

Absorption cross sections of oxygen molecules in the UV spectral range are experimentally determined in the temperature range 1600–6000 K. The absorption cross sections are measured in oxygen or in its mixtures with argon behind the shock wave front. Measurements are performed for the spectral range 190–270 nm, which pertains to the electronic transition X ³Σ _g ^? → B ³Σ _u ^? of the Schumann-Runge system. The absorption cross sections are also measured at temperatures 291 and 3300 K in the range 160–185 nm. The measured absorption cross sections are compared with the calculated spectra of the O₂ molecule.     

Magnetic coherence transfer induced by discharge radiation and the effect of radiation trapping on the lifetime of the hidden alignment of Ne terms

The dichroism of a neon gas discharge plasma in a weak magnetic field is investigated by scanning the 3s ₂-2p ₄ transition by monochromatic laser radiation. Magneto-optical resonances of the intrinsic macroscopic alignment and hidden alignment of the 2p ₄ level are separated. Against the background of these resonances, resonances attributed to coherence transfer from the 1s _{2, 4, 5} levels and the birefringence of the wings of the nearest absorption lines from the 1s _{4, 5} levels are observed. A new type of alignment is revealed—integral hidden alignment, whose lifetime, in contrast to the case with macroscopic alignment, increases without bound with increasing radiation trapping.     

Disalignment collision cross sections of the neon levels 2p 4 and 2s 2 obtained by mode crossing

Alignment destroying collision cross sections of the Ne levels 2p ₄ and 2s ₂ were measured by investigation of the zero-field mode crossing resonances of a multimode He/Ne-laser operating on the 3s ₂→2p ₄ (λ=633nm) and 2s ₂→2p ₁ (λ=1.52μm) Ne transitions respectively. The measurements were carried out with the aid of a small sample cell which was placed inside the laser cavity and filled with pure Neon or a mixture of the He and Ne. Comparison of the measured cross sections concerning the 2p ₄ level with corresponding Hanle effect measurements shows that in multimode operation velocity changing collisions do not produce an additional broadening of the mode crossing resonances. The alignment destroying cross section is almost temperature independent in the case of He collisions; it decreases, however, with increasing temperature in the case of Ne. Due to the allowed dipol transition between the 2s ₂ and the ground state of Ne, radiation trapping and resonance interaction takes place if the gas filling contains Ne. The effect on the mode crossing resonance width is investigated.     

Energy dependence of backward π−d elastic scattering in the 1–2 GeV region

Differential cross sections for backward π^?d elastic scattering (?1 ≦ cos θ_c.m ≦ ?0.98) have been measured at fourteen momenta from 0.98 to 1.76 GeV/c and at 2.45 GeV/c. Energy dependence of the cross section exibits a new wide structure at √s ≈ 2.9 GeV. Possible mechanisms of the reaction accounting for this structure are presented. Experimental data are compared with theoretical calculations.     

Theoretical study of photoionization of the isoelectronic sequence Rb<Superscript>+</Superscript>, Sr<Superscript>2+</Superscript>, and Y<Superscript>3+</Superscript>

The photoionization cross sections for the 4p shell of ions of the Kr isoelectronic sequence Rb⁺, Sr²⁺, and Y³⁺ are calculated. The configuration interaction theory and the perturbation theory are used to describe the many-electron effects. The relativistic effects are taken into account in the Pauli-Fock approximation. The calculated resonance structure of photoionization cross sections for the 4p shell in the region below the 4s threshold associated with the autoionization of the 4s-np singly excited states and the 4p4p-nln′l′ doubly excited states reproduces the results of recent measurements of total photoabsorption cross sections for the Rb⁺, Sr²⁺, and Y³⁺ ions. It is found that, as the nuclear charge in the isoelectronic sequence increases, the ratio between the direct and correlation parts of amplitudes of the 4s-(n/?)p transition changes and, as the consequence, the minimum of the photoionization cross section of the 4s shell shifts from the continuous spectrum to the region of states of discrete spectrum. This accounts for the strong changes in the shape of the 4s-np resonances in the photoionization cross sections for the 4p shell of Rb⁺, Sr²⁺, and Y³⁺, as well as the distinction between the shapes of the 4s-6p _1/2 mirror resonance in the partial 4p _1/2 and 4p _3/2 photoionization cross sections for the Y³⁺ ion which do not suppress each other in the total photoionization cross section, as is the case for similar resonances in Rb⁺ and Sr²⁺.     

Perturbative QCD calculation of jet cross sections in e+e− annihilation

We calculate the α_s² to three-jet cross sections in e⁺e^? annihilation in a scheme that uses regulator masses for the infrared and collinear divergences. Using various methods to define the three-jet region, we find that the corrections to the O(α_s) cross sections are large.     

Collisional-radiative model for non-Maxwellian inductively coupled argon plasmas using detailed fine-structure relativistic distorted-wave cross sections

Our recently developed collisional-radiative model which included fine-structure cross sections calculated with a fully relativistic distorted-wave method [R.K. Gangwar, L. Sharma, R. Srivastava, A.D. Stauffer, J. Appl. Phys. 111, 053307 (2012)] has been extended to study non-Maxwellian inductively coupled argon plasmas. We have added more processes to our earlier collisional-radiative model by further incorporating relativistic distorted-wave electron impact cross sections from the 3p ⁵4sJ = 0, 2 metastable states, (1s ₃, 1s ₅ in Paschen’s notation) to the 3p ⁵5p (3p _i ) excited states. The population of various excited levels at different pressures in the range of 1–25 mTorr for an inductively coupled argon plasma have been calculated and compared with the recent optical absorption spectroscopy measurements as well as emission model results of Boffard et al. [Plasma Sources Sci. Technol. 19, 065001 (2010)]. We have also calculated the intensities of two emission lines, 420.1 nm (3p ₉ → 1s ₅) and 419.8 nm (3p ₅ → 1s ₄) and compared with measured intensities reported by Boffard et al. [J. Phys. D 45, 045201 (2012)]. Our results are in good agreement with the measurements.     

Departures from the Hauser-Feshbach theory due to the level-level correlations in deformed nuclei

A microscopic dynamical model is used for the inelastic scattering of nucleons by deformed nuclei and the fluctuation cross sections are calculated. The case of weak absorption in all channels is considered so that the number of statistical assumptions is minimized. The results are compared with the Hauser-Feshbach expressions as regards the magnitude and structure. The partial width amplitudes calculated from the model are correlated, the simplest type of level-level correlations being due to the similar-channels effect (SCE). When the correlations are due to SCE alone, the following two results are obtained, (i) The fluctuation cross sections are increased over the Hauser-Feshbach estimates, for Γ ? D and Γ ? D, by a factor κ if the entrance and exit channels are similar. The numerical value of κ is found to be 3 for a special case and in the general case it is conjectured to lie between the limits 1 and 3, (ii) The fluctuation cross sections σ_cc′^f1 and σ^f1_cc″ exhibit correlated fluctuations if the exit channels c′ and c″ are similar. The fluctuation cross sections in the cases “SCE+direct channel-channel coupling” and “SCE+intermediate structure” are also investigated. In all cases studied direct reaction cross sections do not vanish and the channelwise factorization assumption of the Hauser-Feshbach theory fails.