Inner shell excitation of CH 3F,CH 3Cl,CH 3Br and CH 3I by 2.5 keV electron impact

Small angle inelastic scattering of 2.5 keV electrons was used to study inner shell excitation in the methyl halides at energy transfers between 50 and 700 eV. Discrete peaks due to the excitation of carbon K, fluorine K, chlorine L, bromine M_{4, 5} and iodine N _{4, 5} electrons were observed. Correlations through the methyl halide series were used to aid in the assignment of features in the carbon K-shell spectra. A comparison of halogen inner-shell excitation structures with the carbon K-shell excitation structure in the same molecule allowed a complete assignment of all spectral features. The assignments proposed involve promotions of inner shell electrons to unoccupied valence and Rydberg orbitals. On the basis of our assignments of the chlorine L- and carbon K-shell electron energy loss spectra of CH ₃Cl we propose an alternate assignment of the previously reported CH ₃Cl chlorine K-shell photoabsorption spectrum.     

K-shell excitation spectra of CO,N2 and O2

Electron energy loss spectra of CO, N₂ and O₂ have been recorded in the regions of carbon, nitrogen and oxygen K-shell excitation and ionisation. These results are compared to previous energy loss, photoabsorption and theoretical studies of the same spectral regions. Several inconsistencies in the published spectra are clarified in the present work. Comparisons with recent calculations of the K-shell continua of these molecules are presented. Vibrational structure in the K → π * transitions of CO (C 1s) and N₂ (N 1s) has been resolved in high-resolution studies (< 0.1 eV FWHM) of these species.     

Systematic trends in the radiative emission rates for low- and medium-Z elements in high-temperature plasmas

The power radiated by an optically thin, low-density (N_e ≤ 10¹⁴ electrons/cm³) plasma has been calculated for the electron temperature range 1–10⁶ eV taking into account resonance line emission, direct recombination radiation, dielectronic recombination radiation, and bremsstrahlung from the ions of a given element. The ionization structure has been determined by using a corona equilibrium model in which collisional ionization and inner-shelled excitation followed by autoionization are balanced by direct radiative and dielectronic recombination. Based on the results for respresentative elements from carbon through nickel, graphs are presented of the maximum radiated power, the maximum emission temperature, and the mean charge at the maximum for each shell as functions of the atomic number Z. Assuming that the maximum emission temperature can be achieved, aluminum and iron are predicted to be the most efficient K-shell radiators for Z ≤28.     

Electron energy loss spectra of the silicon 2p, 2s, carbon 1s and valence shells of tetramethylsilane

Inner shell excitation spectra of tetramethylsilane, (CH₃)₄Si, have been measured in the silicon 2s, 2p (L_I,II,III-shell) and carbon is (K-shell) regions using electron energy-loss spectroscopy at an impact energy of 2.5 keV and a scattering angle of ~1°. The high-resolution valence shell spectrum has also been observed at an impact energy of 3 keV and a zero degree scattering angle. The silicon 2p spectra are compared and contrasted with published photoabsorption spectra of SiF₄, SiH₄, and other related Si-containing molecules with varying ligands.     

Effects of the overlap between wave functions of impurity centers on the activation energy of hopping conduction

The hopping conductivity σ₃ has been studied in samples of slightly counterdoped crystalline Si: B with a boron concentration of 2×10¹⁶ cm^?3<N<10¹⁷ cm^?3 and a compensation of 10^?4≤K≤10^?2. It is found that at K≤10^?3 the activation energy ε₃ is not lower (as it must be according to classical notions at finite K) but larger than the value ε_N=e ² N ^1/3/κ, where e is the electronic charge and κ is the dielectric constant. With decreasing N, the energy ε₃ drops slower and, with decreasing K, grows faster than follows from the standard theory. At K≤10^?4, ε₃ is higher than ε _N by a factor of 1.5–2. The result is explained by the effect of the overlap between wave functions of neighboring impurity centers on the structure of the impurity band.     

Electronic excitations in phosphorus-containing molecules. I. Inner shell electron energy loss spectra of PH3, P(CH3)3, PF3 and PCL3

Electron energy loss Spectroscopy has been used to obtain the inner shell electronic excitation spectra of PH₃, PF₃, PCl₃ and P(CH₃)₃ in the phosphorus L-shell (P 2p, 2s) region as well as the respective ligand K -shells (F 1s, C 1s) and L-shell (Cl 2p and 2s) regions. The spectra were obtained under small momentum transfer conditions so that dipole-allowed transitions dominate. An impact energy of 2.5 ke V was used and inelastically scattered electrons were detected at a typical scattering angle of about 1°. A dipoleforbidden transition of unusual character is observed at 135.11 eV in the P 2p spectrum of PCl₃. Although optically forbidden, as indicated by its absence in a soft X-ray absorption spectrum, the intensity of this transition rises very rapidly with increase in momentum transfer.     

Carbon K-shell excitation spectra of linear and branched alkanes

The electron energy loss spectra of ethane, propane, n-butane, n-pentane, n-hexane, isobutane, isopentane and neopentane in the region of carbon K-shell excitation have been recorded under dipole-dominated conditions (2.8 ke V impact energy, small angle). The spectra are dominated by transitions to unoccupied valence π¹(CH₂, CH₃) and σ¹(C-C) levels. Additional weak features are assigned to Rydberg transitions. The position of the main continuum feature in each spectrum is consistent with the predictions of an empirical relationship with bond length. Systematic variations of spectral intensities are observed which support our assignments. The dominant feature in the K-shell spectrum of ethane, which was previously assigned to C 1s → 3p Rydberg transitions, is reassigned to excitation to a 3p/π¹(CH₃ ), mixed Rydberg/valence orbital (of antibonding σ-¹(C-H) character), in comparison to the other alkane spectra. An improved calibration value of 290.74(5) eV for the energy of the C 1s → π¹ transition in CO₂ is also obtained.     

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.     

Impact parameter dependence ofL- andK-shell excitation in I-Ag collisions

The impact parameter dependence of theL- andK-vacancy production of target and projectile was measured in I-Ag collisions at 40 MeV and 63 MeV in a X-ray particle coincidence experiment. A largeL-vacancy production is found for impact parametersb smaller than theL-shell radius with a pronounced increase forb<250fm. TheL-shell excitation is discussed in terms of 4fσ excitation and vacancy transfer in the 3pσ, 3dπ, 3dσ molecular orbitals through 3pπ-3pσ and 3dδ-3dπ-3dσ rotational-couplings. The 2pσ excitation probability is obtained from the summedK-vacancy production probability, and compared with the prediction of 2pσ excitation in a multiple collision process. The latter is determined by folding the measured IL-shell excitation probability with the impact parameter dependence of the 2pπ-2pσ rotational coupling. The discrepancy observed at small impact parameters suggests an enhanced 2pπ and 2pσ excitation at small impact parameters in a one-collision process. TheL- andK-vacancy sharing probabilities are found to be impact parameter independent over a large impact parameter range.     

On the assignment of the carbon K-shell spectra of the methyl halides

Electron energy loss spectra of the methyl halides in the region of carbon K-shell excitation have been obtained at higher resolution than those previously reported. The existence of two electronic transitions between 288 and 290 eV in CH₃F is demonstrated. This result conflicts with a recent SCF calculation which suggests that the σ* (C–F) level in CH₃F is unbound and thus predicts the existence of only one electronic transition in this spectral region. Studies of the carbon K-shell spectra of CH₃Br and CD₃Br demonstrate the vibrational origin of some spectral features. These new results support our earlier tentative assignments for the carbon K-shell spectra of the methyl halides.     

Determination of the electron concentration and temperature,as well as the reduced electric field strength,in the plasma of a high-voltage nanosecond discharge initiated in atmospheric-pressure nitrogen by a runaway electron beam

We report on the results of spectroscopic measurements of electron concentration N _e and temperature T _e , as well as the reduced electric field strength E/N in the plasma of a high-voltage nanosecond discharge in the gap with a strongly nonuniform electric field distribution, which is filled with nitrogen under the atmospheric pressure. The possibility of using the method for determining T _e and E/N, which is based on the determination of the ratio of the peak intensities of the ionic N ₂ ⁺ (λ = 391.4 nm) and molecular N₂ (λ = 394 nm) nitrogen bands, is proved. We detected the mean values of quantities N _e , T _e , and E/N amounting to ～2 × 10¹⁴ cm^?3, ～2 eV, and ～240 Td, respectively. In addition, the dynamics of these quantities is determined.     

Inner shell excitation,valence excitation and core ionization in NF3 studied by electron energy-loss and X-ray photoelectron spectroscopies

Electron energy-loss Spectroscopy (EELS) at impact energies of 2.5–3 keV has been used to obtain the electron excitation spectra for the N 1s (K-shell), F 1s (K-shell) and valence shell regions of NF₃. The inner shell spectra were recorded using small angle scattering (?1° ) while the valence shell spectrum was obtained at zero degree scattering angle. The inner shell excitation spectra show a strongly enhanced 1s→ δ^* type transition and continuum features which are typical for molecules with highly electronegative ligands. One of the peaks in an earlier published photoabsorption study of the N 1s region has been shown to be due to a N₂ impurity. The valence shell electron energy-loss spectrum shows a number of transitions which are considered to be mainly due to valence-valence type transitions, with also some evidence of Rydberg structure.The X-ray photoelectron spectra (XPS) of the N 1s and F 1s electrons along with their associated satellite structures have also been recorded using Al Kα (1486.58 eV) radiation. The vertical ionization potentials for the N 1s and F 1s electrons were found to be 414.36 (10) eV and 693.24 (10) eV, respectively. Both spectra exhibit a rich and different satellite structure. These “shake-up” features in the satellite XPS spectra are compared with continuum features of the inner shell electron energy-loss spectra and also with the valence shell spectrum.     

Vibrational analysis of the A′1Π state of barium oxide using two isotopes

Barium vapor is reacted with N₂¹⁶O and N₂¹⁸O at 0.7 Torr to produce clearly distinguishable isotopic bands of BaO A′¹Π-X¹Σ in the wavelength region of 320–415 nm. The unique vibrational numbering is determined by measuring the isotopic shift in the bandheads between Ba¹⁶O and Ba¹⁸O. Spectroscopic constants for the A′¹Π state are determined from the present analysis to be ν₀₀ = 17 588 ± 15 cm^?1, ω_e = 442.45 ± 0.3 cm^?1, and ω_ex_e = 1.652 ± 0.009 cm^?1. Uncertainties represent three standard deviations.     

The Compton profile of Bismuth excited below the K absorption edge

A cylindrically symmetric Compton profile spectrometer stimulates resonant Raman scattering at the L₂, L₃, M and N edges in a Bi target when using a ¹⁰⁹Cd γ-ray source with energy 2.50 keV below the K-shell binding energy of Bi. Similarly, an ²⁴¹Am source (E_γ = 59.536 keV) excites a resonance response at the L₃ and M edges of Yb (B.E. = 61.332 keV) but not in Lu (B.E. = 63.314 keV).     

Magnetic properties of the compounds N(CH3)4MnIIMIII(CN)6 ·8 H2O(MIII = Mn,Fe)

In the isostructural cyanobridged chain compounds N(CH₃)₄Mn^IIM^III(CN)₆ · 8H₂O high spin Mn(II) ions couple antiferromagnetically to low spin Mn(III) of Fe(III) ions. The Mn^II–Mn^III compound orders ferrimagnetically below T_N = 28.5 ± 1 K. The tetragonal a and b axes are easy ones for the magnetic moments. In the Mn^II–Fe^III compound antiferromagnetic order occurs below T_N = 9.3 K, with spins aligned along the tetragonal c axis. The compound undergoes a meta-magnetic transition from the antiferromagnetic to a ferrimagnetic phase. This occurs at 2 K for a field H_crit ≈ 1.2 T. The temperature dependence of H_crit, which vanishes at T_N, is followed. The tricritical temperature T¹ is ～ 5 K.     

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.     

Negative ion effects in CO2 convection laser discharges

Negative ions are computed to be formed on a time scale and in quantities such that they may be a cause of plasma instability observed in low pressure electrical discharge convection CO₂ lasers. In a typical CO₂?N₂?He?H₂O laser mixture the principal ions are CO ₃ ^? , CO ₄ ^? and H^? with the total negative ion densityn _? given by 0.1n _e <n _?<n _e , wheren _e is the electron density: but if the gases are re-cycled or if there is an air leak NO ₂ ^? and NO ₃ ^? are formed in significant amounts andn _? can become greater thann _e in a time considerably less than the gas dwell time in the electrical excitation discharge. CO is effective in reducingn _? in a system without re-cycling, but is ineffective in a re-cycled system with the oxides of nitrogen present.     

Light nuclei as distinct probes for transient magnetic fields

Salient features of transient magnetic fields are brought out from nuclear spin precession measurements on light ions penetrating polarized Fe-, Ni- and Gd-hosts. At low velocities ion fractions with singleK-shell vacancies, at high velocities H-like charge state fractions, can account for the observed precessions. The data suggest a sharp reduction of theK-shell field at a velocityv _ion?0.5v ₀. Large degrees ofK-shell polarization have been derived for C- and O-ions. Measurements in different ferromagnets show that the transient fields scale with the polarized electron density of the host.     

Secondary ion emission from Si under nitrogen ion bombardment

The yield and energy distribution of positive secondary ions emitted from Si under N₂⁺ ion bombardment were measured. The obtained mass peaks correspond to three types of secondary ion species, that is, physically sputtered ions (Si⁺, Si₂⁺), chemically sputtered ions (SiN⁺ Si₂N⁺) and doubly charged ions (Si²⁺). The dependence of secondary ion emission on the primary ion energy was studied in a range of 2.0–20.0 keV. The yields of physically and chemically sputtered ions were almost independent of the primary ion energy. The yield of the doubly charged ion strongly depended on the primary ion energy. The energy distribution of secondary ions of the three types showed the same dependence on the primary ion energy. The most probable energy of the distribution increased with the primary ion energy. On the other hand, for the energy distribution curves of sputtered ions, the tail factors N in E^?N were constant and showed a m/e dependence.     

Effects of radiator motion on plasma-broadened hydrogen lyman-β

For the hydrogen line L-β, broadening in an Ar⁺-plasma (N_e = 7.2 × 10¹⁶ cm^?3, T = 12,200 K) has been investigated with the help of a computer simulation of ion broadening taking full account of radiator motion. The anisotropy in Stark broadening for a moving radiator is found to be negligible under these conditions, but Stark profiles depend markedly on the radiator speed. The final line profile (including Stark and Doppler broadening) is nearly the same as the profile obtained by convolution of the Doppler profile with the Stark profile for radiators at rest and fictitious ions with the reduced mass of the atom-ion pair.