Optical Oscillator Strengths of Hydrogen Chloride in the Energy Region of 5.5-20 eV

Absolute optical oscillator strength density (OOSD) spectrum of HCl in the valence shell energy region of 5.5-20eV has been determined by the high resolution fast electron energy loss spectrometer (EELS). The optical oscillator strengths for the broad A^1Ⅱ 1^3∑^ dissociation peak and the discrete transitions of b^aⅡ(ν′= 0),C^1Ⅱ ( ν′ = 0, 1,2) and M^1 Ⅱ ( ν′ = 0) are reported.     

Study of (e, 2e) process on potassium at 6 eV—60 eV above threshold in second-order Born approximation

The standard distorted wave Born approximation (DWBA) method has been extended to second-order Born amplitude in order to describe the multiple interactions between the projectile and the atomic target. Second-order DWBA calculations have been preformed to investigate the triple differential cross sections (TDCS) of coplanar doubly symmetric (e, 2e) collisions for alkali target potassium at excess energies of 6 eV-60 eV. Comparing with the first-order DWBA calculations before, the present theoretical model improves the degree of agreement with experiments, especially for backward scattering angle region of TDCS. This indicates that the present second-order Born term is capable to give a reasonable correction to DWBA model in studying coplanar symmetric (e, 2e) problems in low and intermediate energy range.     

Theoretical investigations of collision dynamics of cytosine by low-energy(150–1000 eV) proton impact

Using a real-space real-time implementation of time-dependent density functional theory coupled to molecular dynamics(TDDFT-MD) nonadiabatically,we theoretically study both static properties and collision process of cytosine by150-1000 eV proton impact in the microscopic way.The calculated ground state of cytosine accords well with experiments.It is found that proton is scattered in any case in the present study.The bond break of cytosine occurs when the energy loss of proton is larger than 22 eV and the main dissociation pathway of cytosine is the breaks of C_1 N_2 and N_8 H_(10).In the range of 150 eV≤E_k≤360 eV,when the incident energy of proton increases,the excitation becomes more violent even though the interaction time is shortened.While in the range of 360 eVE_k≤1000 eV,the excitation becomes less violent as the incident energy of proton increases,indicating that the interaction time dominates mainly.We also show two typical collision reaction channels by analyzing the molecular ionization,the electronic density evolution,the energy loss of proton,the vibration frequency and the scattering pattern detailedly.The result shows that the loss of electrons can decrease the bond lengths of C3 NS and CSN6 while increase the bond lengths of C_4 H_(11),C_5 H_(12) and C_4 C_5 after the collision.Furthermore,it is found that the peak of the scattering angle shows a little redshift when compared to that of the loss of kinetic energy of proton.     

Two-photon vibronic spectroscopy of allene at 7.0–10.5 eV: experiment and theory

2?+?1 resonance-enhanced multiphoton ionization (REMPI) spectra of allene at 7.0–10.5?eV have been observed. The excited vibronic symmetry has been determined from polarization-ratio measurements. Based on the vibronic energies and peak intensities calculated using ab initio MO and time-dependent density functional theory, the very congested REMPI spectra have been assigned as due to π*?←?π, 3p?←?π, 4s?←?π, 4p?←?π, and 4d?←?π transitions. Vibrational progressions related to the CH₂ twisting (ν₄ ～770?cm^?1) have been observed for several excited electronic states. Calculated Franck–Condon factors also confirm that CH₂ twisting is the most active mode in the vibronic spectra of allene. In this study, theoretical calculations of two-photon intensities and polarization ratios have been made through the ab initio computed one-photon transition dipole moments to various electronic states as intermediates. As a starting point to interpret the complicated vibronic spectrum of allene, the theoretical approach, without vibronic couplings, has been applied to predict the peak positions, spectral intensities, and polarization ratios of Rydberg states, and qualitatively shows a considerable agreement with experimental observations.     

Anisotropy of arrival directions of E 0 ⩾ 8 × 1018 eV cosmic rays and cosmic microwave background

Results are presented that were obtained by analyzing the arrival directions of E ₀ ? 8 × 10¹⁸ eV primary cosmic rays recorded at the Yakutsk array over the period between 1974 and 2003 and at the SUGAR array (Australia). The greatest primary-cosmic-ray flux is shown to arrive from the region of visible intersection of the planes of the Galaxy and the Supergalaxy (local supercluster of galaxies) at a galactic longitude of about 137°. On a global scale, the lowest temperature of the cosmic microwave background is typical of this region.     

Muons in extensive air showers of energies E 0=1016.6–1019.8 eV

Data on muons with the threshold energy E _μ≈1.0×secθ GeV in extensive air showers of energies E ₀≥4×10¹⁶ eV measured on the Yakutsk and Akeno arrays are jointly analyzed. The results are compared with the calculations by the quark-gluon-string model with jets. It is shown that this model does not contradict the data measured for energies E ₀≤10¹⁸ eV on both arrays under the assumption that the primary particle composition differs from the composition where heavy nuclei dominate over protons. Experimental data for energies E ₀≥3×10¹⁸ eV indicate that the shower development differs from that predicted by the quark-gluon-string model with jets.     

Optical Spectra of Zinc Oxide in the Wide Energy Range 0–30 eV

A full set of spectra of the optical functions of a zinc oxide crystal in the range 0–30 eV has been calculated on the basis of the experimental spectrum of characteristic losses –Im ^–1. The ₂, ₁ and Im ^–1, Re ^–1 spectra were decomposed into elementary components. The most intense transverse and longitudinal components of transitions and their parameters have been determined. The data obtained were compared with theoretical calculations of the bands.     

New N2+Electronic States in the Region of 23–28 eV

Threshold photoelectron spectra of N₂⁺were measured between 23.4 and 27.6 eV with high resolution and high intensity by using the penetrating field technique and synchrotron radiation. Five vibrational progressions were observed. The first of these progressions was theC²Σ_u⁺state. The second progression was identified as the transition to the second state of²Π_gsymmetry found by P. Baltzer, M. Larsson, L. Karlsson, B. Wannberg, and M. Carlsson (1992.Phys. Rev. A46,5545). The third progression, which was discovered by F. Merkt and P. M. Guyon (1993.J. Chem. Phys.99,3400), can be designated as the²Σ_u⁻state by comparison with previous theoretical study (E. W. Thulstrup and A. Andersen, 1975.J. Phys. B8,965). The fourth and fifth progressions were designated as the²Δ_uand 2²Π_ustates by similar comparison with previous theories.     

Optical Oscillator Strengths of Hydrogen Bromide in the 4.5-20 eV Excitation Energy Region

The absolute optical oscillator strength density spectrum of HBr in the valence shell energy region of 4.5-20eV has been determined by a high-resolution fast electron energy loss spectrometer. The optical oscillator strengths for the broad a^3∏ A^1∏ dissociation peak and the discrete transitions orb ^3∏1 (v′=0) and C^1∏(v′=0,1,2) are     

Optical spectra of triglycine sulfate crystals in the range of 7–33 eV and its changes at phase transition

Pseudo-dielectric functions ?ε₁(E)? and ?ε₂(E)? of triglycine sulfate (TGS) crystal have been obtained in the range of 7–33 eV for different temperatures close to ferroelectric phase transition by spectral ellipsometry using the synchrotron radiation source BESSY II. These dielectric functions ε₁(E) and ε₂(E) have also been calculated from first principles using CASTEP CAmbridge Serial Total Energy Package code together with the band structure and density of electronic states of the crystal. Experimental and theoretical dielectric functions agree satisfactorily. A characteristic decrease of temperature dependences of the dielectric losses tgδ(T) and related values just below the phase transition temperature T _c have been found and discussed.     

About the character of the “Knee” at E⋍3×1015 eV in the energy spectrum and the mass composition of primary cosmic rays in the energy range 1015–1017 eV

The method of rescaling from the muon-multiplicity spectrum to the extensive-air-shower spectrum as a function of the total muon number n _μ is presented. The method allows a direct comparison of data obtained in different experiments with muon groups. A direct comparison of data at n _μ>1800 and n _μ=76–660 has been performed. The data in the region n _μ=75–3500 agree better with the assumption that the slope change in the energy spectrum of primary cosmic rays occurs approximately at the same energy per nucleus, E _c=3×10¹⁵ eV, and the mass composition in the energy range 10¹⁵–10¹⁷ eV is close to that observed at 10¹⁴ eV.     

Generation of 1015–1017 eV photons by ultrahigh-energy cosmic rays in the Galactic magnetic field

It is shown that the expected dip in the diffuse photon spectrum above the threshold of e ⁺ e ⁻ pair production, i.e., at energies 10¹⁵–10¹⁷ eV, may be absent due to the synchrotron radiation by the electron component of the extragalactic ultrahigh-energy cosmic rays (UHE CRs) in the Galactic magnetic field. The mechanism we propose requires small (<2×10⁻¹² G) extragalactic magnetic fields and a large photon fraction in the UHE CRs. For a typical photon flux expected in top-down scenarios of UHE CRs, the predicted flux in the region of the dip is close to the existing experimental limit. The sensitivity of our mechanism to the extragalactic magnetic field may be used to improve existing bounds on the latter by two orders of magnitude. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 8, 487–492 (25 October 1999) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Estimate of the fraction of primary photons in the cosmic-ray flux at energies ∼1017 eV from the EAS-MSU experiment data

We reanalyze archival EAS-MSU data in order to search for events with an anomalously low content of muons with energies E _μ > 10 GeV in extensive air showers with the number of particles N _e ? 2 × 10⁷. We confirm the first evidence for a nonzero flux of primary cosmic gamma rays at energies E ～ 10¹⁷ eV. The estimated fraction of primary gamma rays in the flux of cosmic particles with energies E ? 5.4 × 10¹⁶ eV is ε_γ = (0.43 _?0.11 ^+0.12 )%, which corresponds to the intensity I _γ = (1.2 _?0.3 ^+0.4 ) × 10^?16 cm^?2 s^?1 sr^?1. The study of arrival directions does not favor any particular mechanism of the origin of the photon-like events.     

GaP中1.71eV发光带的研究

本文研究了GaP中普遍出现的1.71eV光致发光(PL)宽带。这是一个与多个杂质能级有关的发光带,由吸收谱和光致发光激发谱(PLE)检测到在价带上方0.37—0.089eV范围内与该发光带有关的深能级。时间分辨谱测量表明。随着衰减过程的延续,谱峰移向低能方向,说明该带起源于D—A对复合。讨论了该发光带与背景Cu杂质有关的可能性及其发光机制和激发途径。     

石英玻璃中5.0 eV吸收带的起源

从吸收强度的角度出发研究石英玻璃中５．０ｅＶ光吸收带的起源。利用实验和理论给出的非驰豫氧空位缺陷态的能级,并以第一原理计算得到的石英玻璃导带电子态密度为基础,计算了５．０ｅＶ线性吸收系数。理论结果与实验结果符合得比较好,人而支持了非驰豫氧空位缺陷态是石英玻璃中５．０ｅＶ光吸收带的起源的观点。     

Absolute Generalized Oscillator Strength Profile of Negative Ion Resonance at 8.9 eV in C2F6

A temporary negative ion resonance at 8.9eV in C2F6 has been clearly identified using angle-resolved electron energy loss spectroscopy at 2.5 keV impact energy, and can be attributed to electron capture into 1^2a1u, 1^2a1g, 2^2a2u, and 1^2eg ,yirtual molecular orbitals. The corresponding absolute generalized oscillator strength profile is found to have a shape characteristic of non-dipole interaction with the maximum K - 0.8 a.u. of momentum transfer.     

Second Knee on the Spectrum of Cosmic Ray at Energies ∼1017 eV by Long-Term Observations of Small Cherenkov EAS Array

Physics of Atomic Nuclei - The paper presents the cosmic ray spectrum by the Small Cherenkov Yakutsk array data for 20 years of continuous observation. It has been shown by measurements that in the...