Abstract: Resonance ionization spectroscopy, RIS, is a multistep photon absorption process in which the final state is the ionization continuum of an atom. The RIS process can be saturated with available pulsed lasers, so that one electron can be removed from each atom of the selected type. This method was first applied to the determination of the absolute number of Hes(2/sup 1/S) excited states produced when pulsed beams of protons interacted with helium gas. Laser schemes for RIS are classified into five basic types; with these, nearly all of the elements can be detected with commercially available lasers. A periodic table is included showing schemes applicable to all of the elements except He, Ne, F, and Ar. A compact theory of the RIS process is presented which delineates the conditions under which rate equations apply. Questions on the effects of collisional line broadening, laser coherence time, and nonresonant multiphoton ionization processes are discussed. The initial demonstration of one-atom detection of Cs is described. By using laser beams to saturate the RIS process and proportional counters as single-electron detectors, one-atom detection is made possible. With RIS, one-atom detection is highly selective, has the ultimate in sensitivity, and has excellent space and timemore » resolution. Furthermore, a modification of the technique in which single electrons (or single ions) are detected with a channel electron multiplier permits single-atom detection in a vacuum. The authors describe how RIS can be used for photophysics measurements such as far wing collisional line broadening, measurements of photoionization cross sections for excited states, and collisional redistribution among excited states.« less

Abstract: The theory of Coulomb ionization of $L$ shells by low-velocity heavy charged particles whose atomic number is small compared to the atomic number of the target atom is extended to projectiles with velocities comparable to or larger than the $L$-shell orbital velocities. At large impact parameters projectiles polarize the shell, and at small impact parameters they increase the binding energies of the electrons to be excited. The polarization effect is incorporated in accordance with the perturbed stationary-state (PSS) approximation. The effect of the repulsion between the projectile and the target nucleus is accounted for by a Coulomb-deflection factor (C). This CPSS theory is developed further to include relativistic effects (R) of the target wave function through a procedure that reproduces the results of numerical calculations for heavy target atoms. With electron capture by the projectiles as an additional channel of ionization, the CPSSR theory is compared with experiment.

Abstract: Increases in the solar ultraviolet flux (wavelengths shorter than 1250A) over the past five years of rising solar activity have been larger than anticipated. This increase in UV flux dramatically affects the production of ionization of the various constituents in the thermosphere. Measurements of the solar UV flux by the Atmosphere Explorer satellites are used to determine ionization frequencies for the major thermospheric species for various dates exhibiting notably different levels of solar activity. For the convenience of users of such data, a reduced set of cross-section and flux data is presented for the wavelength range below 1027A, consisting of 37 wavelength intervals

Abstract: Calculations of the optical and UV emission-line intensities and column densities of ions observable in the optical and UV are presented for plane-parallel steady-state shock waves in the interstellar medium. The range of shock velocities considered is from 50 to 200 km/s, and preshock densities are between 1 and 300 per cu cm. The ionization state of the preshock gas is found to be an important parameter, and several sets of elemental abundances corresponding to various amounts of depletion onto grains are used. The results are compared with observations of the Cygnus Loop, the Vela supernova remnant, and Herbig-Haro objects.

Abstract: We have calculated α and η, the ionization and attachment coefficients, and (E/N) *, the limiting breakdown electric‐field–to–gas‐density ratio, in SF6 and SF6 mixtures by numerically solving the Boltzmann equation for the electron energy distribution. The calculations require a knowledge of several electron collision cross sections. Published momentum transfer and ionization cross sections for SF6 were used. We measured various attachment cross sections for SF6 using electron‐beam techniques with mass spectrometric ion detection. We determined a total cross section for electronic excitation of SF6 by comparing the predicted values of α, η, and (E/N) * with our measured values obtained from spatial current growth experiments in SF6 in uniform fields over an extended range of E/N. With this self‐consistent set of SF6 cross sections, together with published He and N2 cross sections, it was then possible to predict the dielectric properties of SF6‐He and SF6‐N2 mixtures. Published experimental values of α for the SF6‐He mixtures lie between the values of α calculated with and without ionization of SF6 by excited He atoms. Published experimental values of (E/N) * agree with our calculations to within 5% in both the SF6‐He and the SF6‐N2 mixtures.

Abstract: For the collisional-radiative model applied to helium, two alternative formulations are presented in which non-linear process such as ionization due to metastable-metastable collisions may be included. The atomic data, including dielectronic,recombination, employed in the calculations are summarized. The collisional-radiative calculation is applied to a positive-column plasma for which both the nonlinear processes and radiation trapping are taken into account. The calculated population densities of excited levels for a low-pressure and low-current discharge plasma show good agreement with a measurement made using the hook method. The population density distribution among excited levels is interpreted in terms of excitation-ionization mechanisms in the plasma. This leads to a grouping of the excited levels into two phases for the discharge plasma considered: the corona phase applies to the lower-lying levels and the quasi-saturation phase to the higher-lying levels. The importance of the ladder-like excitation-ionization mechanism is noted for this class of plasmas.

Abstract: Cross sections have been calculated for electron-impact ionization of singly excited states of the rare gases (neon, argon, krypton, xenon), cadmium, and mercury. The calculations are based upon the symmetric binary-encounter model, together with a semiempirically determined momentum distribution function for the bound, excited electron. Good agreement is obtained with the available experimental data, as well as with existing theoretical results, in the low- to intermediate-energy range.

Abstract: The evolution of H II regions is calculated with a two-dimensional hydrodynamic numerical procedure under the assumption that the exciting star is born within a cool molecular cloud whose density is about 10/sup 3/ particles cm/sup -3/. As the ionization of the cloud's edge is completed, a large pressure gradient is set up and ionized cloud material expands into the ionized low-density (1 particle cm/sup -3/) intercloud medium, with velocities larger than 30 km s/sup -1/.The calculations are made under the simplifying assumptions that (i) within the H II region, ionization equilibrium holds at all times, (ii) the ionization front is a discontinuity, thus its detailed structure is not calculated, (iii) the temperature of each region (H II region, neutral cloud, and intercloud medium) is constant in time, (iv) all ionizing photons come radially from the exciting star. Four cases are calculated and compared with observations: (1) the edge of the cloud is overrun by a supersonic ionization front, (2) the initial Stroemgren sphere surrounding the star lies deep inside the cloud, thus the cloud's edge is ionized by a subsonic ionization front, (3) the ionization front breaks through two opposite faces of the same cloud simultaneously, (4) the flowmore » encounters an isolated globule of density 10/sup 3/ particles cm/sup -3/ shortly after emerging from the molecular cloud.The phenomena here considered show how evolving H II regions are an important input of kinetic energy to the interstellar medium.« less

Abstract: Gold disks have been irradiated with 1.06 μm laser light at intensities between 7 × 1013 and 3 × 1015 W/cm2, and pulse lengths between 200 and 1000 psec. Due to the high Z and long pulse, inverse bremsstrahlung becomes an important absorption mechanism and competes strongly with resonance absorption and stimulated scattering. In addition to measured absorptions, data on the temporal, spatial, angular, and spectral characteristics of the x‐ray emission are presented. Temporally and spectrally resolved back‐reflected light, and polarization‐dependent sidescattered light are detected, providing estimates for the amount of stimulated scattering and of the coronal electron temperature. Inhibited electron thermal conduction and nonlocal thermodynamic equilibrium ionization physics play key roles in bringing numerical simulations of these experiments into agreement with all of the above‐mentioned data.

Abstract: The major photochemistry consisted of solar EUV and photoelectrons comprising 70 percent and 30 percent respectively, of the initial source of CO2(+) and O(+). The energetic O2(+) provided a substantial source of energy to the ambient ions, distributing of the order of 1.6 x 10 to the -7 power W/sq m at an average of 160 km. This input can be compared to that from the ambient electrons of 1.3 x 10 to the -7 power W/sq m with average deposition at 145 km and from the calculated thermal conduction of 1 x 10 to the -9 power W/sq m at 270 km and 1 x 10 to the -8 power at 230 km for assumed dip angles of 2 deg and 12 deg respectively, for a 10nT magnetic field. At altitudes above 250 km upward, vertical fluxes of the order 6 x 10 to the 10th power/sq m/sec for the thermal ions were calculated. The net ionization of O(+) and CO2(+) by charge exchange with incoming solar wind protons varied from 5 x 10 to the 8th power to 5 x 10 to the 12th power /sq m/sec for assumed field strengths of 50nT to 2nT on the dayside of the planet.

Abstract: Publisher Summary The study of (e, 2e) collisions has expanded rapidly since the first coincidence measurements of the two emitted electrons in the electron impact ionization of helium This chapter focuses on the symmetric (e, 2e) reaction at high and intermediate energies—that is, the regime of (e, 2e) collisions that can yield reliable information on the momentum distribution of the struck electrons for transitions to definite final ion states This chapter deals with only those experiments designed to yield detailed information on the electronic structure of atoms and molecules This is the regime of symmetric kinematics at intermediate and high electron energies The chapter outlines some of the experimental techniques employed in these investigations The basic theory necessary for describing the reaction mechanism and for extracting all the structure information is developed The theory for atoms is extended to cover the case of molecular targets The reaction mechanism at intermediate to high energies is investigated in the chapter for atomic targets in both the coplanar and noncoplanar symmetric geometry Some of the structure information that has been obtained on atoms and molecules that include electron–electron correlation effects in both the target and final ion states are also discussed in the chapter

Abstract: It is shown that ions in a low-density plasma has an excited-state population density described by corona equilibrium or by the capture-cascade scheme; for hydrogen-like ions both have the same p -dependence ( p is the principal quantum number) of n ( p )/ g ( p ) ∝ p -0.5 ( n ( p )/ g ( p ) is the population density per unit statistical weight) for an optically thin high-temperature plasma. For an equilibrium condition, relative contribution is about 10:1, verifying the corona model commonly assumed. For a low-temperature equilibrium plasma, however, the capture-cascade component dominates over the corona one for high-lying levels. In the high-density limit partial LTE holds only if the plasma is in ionization equilibrium or in complete LTE. In view of the fact that the equilibrium plasma is a rather exceptional case in actual situations, the theory is generalized: a plasma is decomposed into purely-ionizing- and purely-recombining-plasma components.

Abstract: The energy levels of the calcium atom in all of its stages of ionization, as derived from the analyses of atomic spectra, have been critically compiled. In cases where only line classifications are reported in the literature, level values have been derived. Electron configurations, term designations, J‐values, experimental g‐values, and ionization energies are included. Calculated percentages of the two leading components of the eigenvectors of the levels are given.

Abstract: It is shown conclusively that electron impact ionization of the C $1s$ and O $1s$ core levels of CO adsorbed on W(100) leads to C${\mathrm{O}}^{+}$ and ${\mathrm{O}}^{+}$ desorption, respectively, and that soft-x-ray photons induce the same processes by an intrinsic photoeffect. Disintegration of the adsorption complex which becomes multiply charged by Auger decay of the core hole is assumed as explanation.

Abstract: Previous work on the determination of the photoionization threshold ( I sol ) of tryptophan has now been extended to indole as a solute, both in tetramethylsilane (TMSi) and H 2 O solvents. In TMSi, electron scavenging by N 2 O or photoconductivity measurements lead to the same I sol value: 4.95 ± 0.1 eV. In water, I sol is found equal to 4.35 ± 0.1 eV. From these experiments, information on the ionization mechanism, on the oxidized solute and on the solvent can be gained: (i) the scavenger electron affinity does not intervene in the energy balance providing I sol ; (ii) an “effective” ionic radius of indole (1.40 A) is estimated which suggests that the positive charge remains highly localized on the N-atom of the indole ring; (iii) a value of −1.2 ± 0.1 eV can be deduced for V o , the conduction band edge of water; (iiii) from the above findings, the energy gap E G of pure water, considered as a semi-conductor, would be close to 7 eV. Such a result is discussed in terms of literature data pertaining to electron ejection in pure liquid water and X-ray photoelectron spectroscopy of amorphous ice.

Abstract: Production of SF−5 by dissociative attachment of very low energy electrons to SF6 is known from previously reported work to be strongly enhanced by increasing the gas temperature. Data on this effect is presented and analyzed to give an activation energy of ea=0.2 eV for the reaction. The expectation that this effect can be produced by direct optical excitation of the ν3 vibrational mode is confirmed by using a tunable cw CO2 laser focused collinearly with an electron beam inside a collision chamber. The product ions are monitored using a quadrupole mass filter. By chopping the laser beam and monitoring ion signals and electron current during the laser on, and laser off, periods it is possible to isolate the desired signals from the interfering effects of heating of the collision chamber and the electron gun filament, caused by the laser beam. The observed enhanced of the SF−5 signal by the radiation is strongly dependent on the laser wavelength, and is confined to the attachment peak at very low (<0.1 eV...

Abstract: The photoelectron spectra of the azabenzenes s-tertrazine, s-triazine, pyrimidine, pyrazine, pyridazine and pyridine are interpreted on the basis of many-body Green's function caculations both for the outer and the inner valence region. Koopmans' appromximation is in general totally useless for supplying an ordering of ionic states. The calculations confirm that ionization of the first n-electron occurs at lower energy than of the first π-electron (for pyridine both ionization energies are equal). At fairly low energies (about 16 eV) the familiar orbital picture of ionization breaks down. Between about 16 and 22 eV the lines are split into 2 to 4 components in general, whereas at higher energies the intensity becomes distributed over many lines. The orbital picture of ionization thus can break down for ionization from valence orbitals which are not of 2s character for atoms from the first row of the periodic table.

Abstract: Unsynchronized exponentially growing V79 monolayer cultures were exposed to high-energy accelerated heavy-ion beams (/sup 12/C, /sup 20/Ne, /sup 40/Ar) at various positions in their unmodified Bragg ionization curves. High-LET particle beams proved to be much more effective in causing a G/sub 2/ + M block, measured by the method of flow microfluorometry, than low-LET radiation. The number of cells arrested in G/sub 2/ + M increased linearly with dose up to at least 75% of the maximum effect. In this domain, the RBE values were LET-dependent with a maximum (RBE/sub 50/ = 8.3) at about 100 keV/..mu..m. In contrast to ..gamma.. and x rays, heavy ions with high LET did not affect cell traverse through the G/sub 1/ and S phase. Though the RBE values for G/sub 2/ + M block are much higher than the RBEs for survival, there was a linear relationship between accumulation of cells in G/sub 2/ + M and cell killing.

Abstract: Binding energies and wave functions of inner-shell electronic states in superheavy quasimolecules with (Z/sub p/ + Z/sub t/) ..cap alpha.. > 1 are calculated. Ionization during a collision of very heavy ions is investigated within a molecular basis generated by the solutions of the two-center Dirac equation. Transitions to vacant bound states as well as direct excitation to the continuum are taken into account. We present theoretical values for the ionization probability as a function of impact parameter, bombarding energy, and combined nuclear charge. Our computed results are compared with recent experimental data. It is suggested that relativistic binding energies of electrons in superheavy quasimolecules can be determined experimentally via the impact-parameter dependence of ionization and the anisotropy of quasimolecular radiation.

Abstract: The energy levels of the titanium atom in all of its stages of ionization, as derived from the analyses of atomic spectra, have been critically compiled. In cases where only line classifications are reported in the literature, level values have been derived. Term designations, experimental g‐values, and ionization energies are included. Calculated percentages of the two leading components of eigenvectors of the levels are given.

Abstract: The coupled-cluster variational-like direct approach to the calculation of ionization and electron attachment energies and of excitation energies is applied to several π-electron model systems, using the PPP Hamiltonian with various parametrizations. A simple approximation, which represents the triexcited clusters in terms of disconnected W1T2 terms, is employed. All the necessary diagrams for both excitation energy and ionization potential (electron affinity) calculations are given in the compact Hugenholtz nonoriented form. The results of the calculations for benzene, trans-butadiene, all-trans-hexatriene, and fulvene are compared with the corresponding full CI results, and the conclusions about the validity and efficiency of this approach are drawn.