Showing papers on "Ionization published in 1982"

The ionization equilibrium of astrophysically abundant elements

Abstract: The paper presents new calculations of ionization equilibrium fractions of 11 abundant elements (C, N, O, Ne, Mg, Si, S, Ar, Ca, Fe, Ni) as functions of temperature. Convenient coefficients for fitting the rates of collisional ionization, radiative recombination, and dielectronic recombination are also tabulated. Many of the ionization rates are based on recent experimental measurements of cross sections for collisional ionization and autoionization following inner-shell excitation. These rates are used elsewhere in computations of nonequilibrium ionization, radiative cooling, radiative shock models, and plasma emission diagnostics.

X-ray nebular models

Abstract: Theoretical models are presented for the temperature and ionization structure of spherically symmetric, constant density, gaseous nebulae surrounding compact X-ray sources and for the optical, UV, and X-ray spectra emerging from the nebulae. The structure is determined by assuming a local balance between heating and cooling in the gas, and the radiation field is found by solving a simplified equation of transfer. The calculations include an accurate and comprehensive treatment of the atomic processes affecting the state of the gas and the radiation field. The destruction of line radiation during resonance scattering causes models to be significantly hotter and more highly ionized than previous models of the same type. Model results are presented for a wide variety of gas densities and X-ray source spectra, scaling laws which allow these results to be generalized to a wide variety of astrophysical solutions are discussed, and column densities of multiply charged species are tabulated.

Enhancement of electron impact ionization in a superlattice: A new avalanche photodiode with a large ionization rate ratio

Abstract: The first superlattice avalanche photodiode (APD) is reported. The high field region of this p‐i‐n structure consists of 50 alternating Al0.45Ga0.55As (550 A) and GaAs (450 A) layers. A large ionization rate ratio has been measured in the field range (2.1–2.7)×105 V/cm, with α/β≃10 at a gain of 10 giving a McIntyre noise factor Fn = 3. The ionization rate ratio enhancement with respect to bulk GaAs and AlGaAs is attributed to the large difference in the band edge discontinuities for electrons and holes at the heterojunction interfaces. The superlattice APD is a new device concept which can be used to develop low noise APD’s in a variety of III‐V materials including long wavelength 1.3–1.6‐μm semiconductors.

Introduction to the Theory of Laser-Atom Interactions

Abstract: Basic Ideas. States in a Weak-Near-Resonant Field. More General States of an Atom in a Laser Field. Spontaneous Radiation by Atoms in Lasers. Deflection of Atoms in Laser Fields and External Fields. Potential Scattering of Charged Particles in a Laser Field. Multiphoton Ionization. Electron-Atom Scattering in a Laser Field. Atom-Atom Scattering in the Field of a Laser. Index.

An empirical approach to K-shell ionisation cross section by electrons

Abstract: The working out of an empirical expression for the cross section for production of atomic K-shell vacancies by electrons is described. The basis is a critical analysis of the existing experimental data. The ranges for which the function is evaluated are 6

Electronic energy-levels in dense plasmas

Abstract: Modern inertial-confinement fusion experiments subject matter to extreme physical conditions previously studied only in theoretical astrophysics. At very high plasma density, atomic energy states are significantly altered by electric fields of neighboring ions and by free electrons; the resulting phenomena of pressure ionization and continuum lowering may be analyzed with a sequence of models, each adding new subtleties to a complex picture. In this paper, we develop a simple parameterization of pressure ionization, discuss limitations of the Debye-Huckel model for plasma perturbations, and survey an approximate description of X-ray spectra based on the WKB approximation. WKB theory leads to a simple derivation of the screened hydrogenic model for plasma ionization and radiative properties. Electron eigenvalues are obtained from the total ion energy in agreement with Koopman's theorem, and the representation of spectral terms is improved by a new set of screening coefficients.

Energy Loss of Energetic Partons in Quark - Gluon Plasma: Possible Extinction of High p(t) Jets in Hadron - Hadron Collisions

Abstract: Hi& energy quarks and gluons propagating through quark-gluon plasma suffer differential energy loss via elastic scattering from quanta in the plasma. lhis mechanism is very similar in structure to ionization loss of charged particles in ordinary matter. 'ihe dE/dx is roughly proportional to the square of the plasma temperature. For hadron-hadron collisions with high asscoiated multiplicity and with transverse energy dET/dy in excess of 10 GeV per unit rapidity, it is possible that quark-gluon plasma is produced in the collision. If so, a produced secondary high-p, quark or gluon might lose tens of GeV of its initial transverse momentum while plowing through quark-gluon plasma produced in its local environment. High energy hadron jet experiments should be analysed as function of associated multiplicity to search for this effect. An interesting signature may be events in which the hard collision occurs near the edge of the overlap region, with one jet escaping without absorption and the other fully absorbed.

Electron and hole impact ionization coefficients in InP determined by photomultiplication measurements

Abstract: The electron and hole ionization coefficients α and β in (100) InP have been determined through analysis of photomultiplication data on p+‐n and n+‐p junctions grown by liquid phase epitaxy (LPE). A special device structure is described which allows reproducible thinning of the substrate in order to achieve pure carrier injection from either side of the p‐n junction. By fabricating wafers with depletion layer doping levels from 1.2×1015 to 1.2×1017 cm−3, α and β have been determined over a wider range of electric fields than previously reported. The ratio of β/α decreases from 4.0 to 1.3 as the electric field is increased from 2.4 to 7.7×105 V/cm.

Extended adiabatic blast waves and a model of the soft X-ray background

Abstract: An analytical approximation is generated which follows the development of an adiabatic spherical blast wave in a homogeneous ambient medium of finite pressure. An analytical approximation is also presented for the electron temperature distribution resulting from coulomb collisional heating. The dynamical, thermal, ionization, and spectral structures are calculated for blast waves of energy E sub 0 = 5 x 10 to the 50th power ergs in a hot low-density interstellar environment. A formula is presented for estimating the luminosity evolution of such explosions. The B and C bands of the soft X-ray background, it is shown, are reproduced by such a model explosion if the ambient density is about .000004 cm, the blast radius is roughly 100 pc, and the solar system is located inside the shocked region. Evolution in a pre-existing cavity with a strong density gradient may, it is suggested, remove both the M band and OVI discrepancies.

Ionization Potential and Appearance Potential Measurements, 1971-1981,

Abstract: : A compilation is presented of the ionization potential and appearance potential measurements which appeared in the referred literature in the time period 1971-1981. The data are sorted according to the identity of the ionic species formed in the ionization process. Precursor molecules or radicals are identified by a structural formula and, in the case of compounds containing rings, by name according to the Chemical Abstracts system of nomenclature. Chemical Abstracts Registry Numbers are provided where available. A complete bibliography and author index are provided. (Author)

Electronic correlation and the Si(100) surface: Buckling versus nonbuckling

Abstract: Theoretical cluster calculations for the Si(100) surface show that the use of doubly occupied orbital wavefunctions, such as the closed‐shell Hartree–Fock (HF), lead to an asymmetric dimer description of the surface. The inclusion of electron correlation produces a symmetric dimer description with a ground state ∠1.0 eV below the minimum of the HF buckled dimer. There are two low‐lying states of the symmetric dimer (a singlet and a triplet) with very different geometries. Energy minimization calculations indicate that a (2×1) structure is favored over a c(2×2) structure. We also report ionization potentials for surface and Si(2p) core electrons that are consistent with current experimental data.

Experiments concerning electron capture and loss to the continuum and convoy electron production by highly ionized projectiles in the 0.7 - 8.5-MeV/u range transversing the rare gases, polycrystalline solids, and axial channels in gold

Abstract: Velocity spectra of electrons emitted into the forward direction have been measured for 0.7--8.5-MeV/u projectile ions traversing He, Ne, and Ar targets, polycrystalline solids (C, Al, Ag, Au), and axial channels in gold. Spectral shapes and yields are compared and contrasted with one another and with theories which seek to account for the cusp-shaped peaks observed in terms of electron capture and loss to low-lying projectile-centered continuum states. We report the results of both singles and coincidence measurements, where the dependence of cusp shapes and yields on the emergent-ion charge state are examined. For electron capture to the continuum (ECC), variance is noted with respect to the simple, first-order theory of Dettmann, Harrison, and Lucas. The ECC yields are compared to experimental and theoretical studies of bound-state capture, especially to high Rydberg states. For electron loss to low-lying continuum states (ELC), variance is noted with respect to the corresponding theories of Briggs, Drepper, and Day, and ELC cross sections are compared to total electron-loss cross sections. For convoy electron production in solids, no known theory accounts for the results. As in ELC processes, convoy cusp widths are observed to be velocity independent. Convoy electron yields are also observed to bemore » independent of emergent-ion charge state.« less

Comparative Study of Electron Energy Deposition and Yields in Water in the Liquid and Vapor Phases

Abstract: Dual sets of Monte Carlo computations were made for electrons in water to assess differences due to the state of condensation. The GSF computer code was used for the vapor and the ORNL code for the liquid. The underlying physical differences specifically incorporated into the liquid code are discussed. At electron energies greater than or equal to 50 eV, ionization is considerably more efficient in the liquid than in the vapor, the high-energy W values for the two phases being 24.6 and 30.0 eV/ip. Above 50 eV, the Fano factor is about half as large in the liquid as in the vapor. The single-collision spectrum in the liquid is harder, giving a greater stopping power in the range 50 to 10/sup 4/ eV, beyond which the liquid and vapor stopping powers merge. Slowing down spectra for 10/sup 3/- and 10/sup 4/-eV electrons and depth-dose curves for 1-keV electrons are calculated. In addition, the radial dose distributions around electron paths in liquid and vapor are compared.

Laser-enhanced ionization spectrometry

Abstract: Fundamental Mechanisms of Laser-Enhanced Ionization: The Production of Ions (O Axner & H Rubinsztein-Dunlop) Fundamental Mechanisms of Laser-Enhanced Ionization: Signal Detection (J Travis & G Turk) Analytical Performance of Laser-Enhanced Ionization in Flames (G Turk) Applications of Laser-Enhanced Ionization Spectrometry (R Green) Non Flame Reservoirs for Laser-Enhanced Ionization Spectrometry (N Zorov) Ions and Photons: Interplay of Laser-Induced Ionization and Fluorescence Techniques in Different Atomic and Molecular Reservoirs (N Omenetto & P Farnsworth) Index

Photoionization of argon clusters

Abstract: Argon clusters were produced in a free supersonic molecular beam expansion of pure argon at room temperature and the photoionization efficiency curves of the trimer through hexamer were measured in the wavelength regions from threshold to 700 A. A study of the Ar+3 photoionization efficiency curve as a function of nozzle stagnation pressure shows that fragmentation of heavier clusters can dominate the spectrum, even near threshold, and even when the nozzle conditions are such that the Ar+4 intensity is only a small fraction of the Ar+3 intensity. The Ar+3 photoionization efficiency curve, obtained using nozzle stagnation conditions such that no heavier ions were detected, exhibits several broad peaks near threshold which show similarities to bands of the dimer. At high nozzle stagnation pressures, the photoionization efficiency curves for Ar+3 to Ar+6 are nearly identical due to the effects of fragmentation. These spectra exhibit two very broad features which are similar to features observed in the solid....

Modeling of the charge transfer afterglow excited by intense electrical discharges in high pressure helium nitrogen mixtures

Abstract: In this work, we report the study of bimolecular and termolecular charge transfer and Penning ionization reactions in He–N2 mixtures excited by repetitive 3 kA, 7 ns duration discharges. He(2 3S) destruction frequencies have been determined from measurements of the optical absorption of the 2 3S→3 3P helium transition and were found to correlate with the late‐time decay rate of the N2+(B 2Σu→X 2Σg) fluorescence. The much more intense early‐time fluorescence was ascribed to charge transfer from He2+. The values found for the bimolecular and termolecular charge transfer reactions were, respectively, (1.1±0.1)×10−9 cm3 s−1 and (1.36±0.20)×10−29 cm6 s−1, while the corresponding values for the Penning reactions were (7.6±0.4)×10−11 cm3 s−1 and (3.3±0.3)×10−30 cm6 s−1. Branching ratios for producing the N2+(B 2Σu) state in these reactions are discussed. A comprehensive kinetic model of the He–N2 afterglow has been formulated which was able to reproduce all the experimental data obtained as functions of helium p...

Inclusion of core‐valence correlation effects in pseudopotential calculations. I. Alkali atoms and diatoms

Abstract: A simple procedure is developed to include the core‐valence polarization and correlation effects in small metallic clusters of alkali atoms. The fluctuation of the electric field on the polarizable core, as calculated from optimized limited valence basis sets, plays the dominant role. The atomic ionization potentials and the ground state spectroscopic characteristics of Na2, K2, Cs2, and of their positive ions are significantly improved. The method is applicable to polar compounds as well, as illustrated through a study of CsH. The relationship between the present procedure and Bardsley’s −αD/2 (r2+d2)2 potentials is discussed.

Quantum-state-specific detection of molecular hydrogen by three-photon ionization

Abstract: A sensitive method is demonstrated for determining (v'',J'') populations of H/sub 2/. Single rotational levels of the E,F /sup 1/..sigma../sup +//sub g/ state are prepared by two-photon excitation; absorption of a third quantum causes ionization. Detection of J'' levels of v'' = 0, 1, and 2 is possible while scanning the dye laser fundamental over just 5 nm. Measured rotational populations at different temperatures (295--750 K) agree well with the corresponding Boltzmann distributions. Rotational line strengths show almost no J'' dependence for this process.

Resonantly enhanced two‐photon photoionization of NO in an atmospheric flame

Abstract: Molecular multiphoton ionization experiments are reported for the first time in a flame environment. The resonantly enhanced two‐photon photoionization spectrum of NO from 270 to 317 nm in an atmospheric pressure H2/air/N2O flame is essentially identical with respect to both line position and intensity to that which is predicted for the one‐photon absorption to the intermediate A state. A model is developed here which accounts for this result by including rates for collisional repopulation of the laser depleted state. Based on this model, the rotational transfer rate constant for NO is estimated to be ⩾4×109 s−1 in the flame, corresponding to a cross section of ∼70 A2. It is found that the photoionization spectra obtained in this work have far better signal‐to‐noise and resolution than those reported for NO in flames using laser‐induced fluorescence methods and that the estimated detection limit for NO is 1 ppm.