Abstract: Rate coefficients for excitation of the b 1Σ+g state of O2 by low energy electrons have been measured using a drift tube technique. The time dependence of the absolute intensity of the 762 nm band emission was measured for O2 densities between 1016 and 2×1018 molecules/cm3. When corrected for electron attachment, ionization, and metastable diffusion, the number of b 1Σ+g molecules produced per centimeter of electron drift and per O2 molecule calculated from the 762 nm emission varied from 1.3×10−18 cm2 at E/N=5×10−17V cm2 to 2.1×10−16 cm2 at E/N=2×10−15V cm2. These values of electric field to oxygen density ratio E/N correspond to mean electron energies of 0.75 and 6 eV, respectively. Measured decay constants for the 762 nm radiation yield a value for the product of the diffusion coefficient and the O2 density of (5.0±0.3) ×108 cm−1 sec−1 and a quenching coefficient for the b 1Σ+g state of (3.9±0.2) ×10−17 cm3 sec−1. Comparison of measured excitation coefficients with values calculated using a recommended...

Abstract: Experimental K-shell ionization cross sections of /sub 13/Al and /sub 28/Ni are reported for ions of /sup 1//sub 1/H, /sup 2//sub 1/H, /sup 4//sub 2/He, /sup 6//sub 3/Li, and /sup 7//sub 3/Li with kinetic energies in the range from 2 to 36 MeV, and of /sub 28/Ni for ions of /sup 12//sub 6/C, /sup 16//sub 8/O, and /sup 19//sub 9/F in the range from 4 to 90 MeV. The theory of direct Coulomb K-shell ionization, as developed in an earlier paper (Phys. Rev. A 7, 983 (1973)) for projectiles of atomic number Z/sub 1/, small compared to the target atomic number Z/sub 2/, and of velocities v/sub 1/ small compared to the target K-shell electron velocity v/sub 2K/, i.e., v/sub 1/ very-much-less-than v/sub 2K/, is extended to intermediate velocities v/sub 1/ approx. = v/sub 2K/. New effects appear. They add to the Z/sup 2//sub 1/-proportional cross sections one derives from linear-response theories for direct ionizations. They are attributed to the polarization of the target K shell in the field of the projectile, and to electron capture by the projectile. Guided by the perturbed stationary-state theory of atomic collisions, the polarization effects are incorporated so that the theory retains the unifyingmore » aspects of the cross sections derived in the plane-wave Born approximation, but the variables now contain the nonlinear effects as scaling factors. Electron-capture cross sections are added. When v/sub 1/ >> v/sub 2K/, such contributions subside, and one retrieves the cross sections of the linear-response approximation. The theory predicts K-shell ionization cross sections for projectiles with Z/sub 1//Z/sub 2/ < 0.5 at all velocities in a comprehensive manner. It agrees with experimental data covering six orders of magnitude for collisions partners with Z/sub 1//Z/sub 2/ ranging from 0.03 to 0.3 and v/sub 1//v/sub 2K/ from 0.07 to 2.« less

Abstract: Absolute measurements are reported of the electron impact ionisation cross sections of ground-state atoms of helium, carbon, nitrogen and oxygen for electron energies ranging from 7 to 1000 eV. The method used was that of crossed beams in which fast beams of atoms are produced by charge capture of 2 to 4 keV ions in a gas target. The data for helium atoms above 100 eV are in excellent agreement (+or-5%) with the absolute data of Rapp and Englander-Golden (1965) who used a static gas target technique. However, the present data are smaller in magnitude at lower energies. Data for oxygen and nitrogen atoms are in adequate agreement with data from earlier crossed-beams experiments that employed thermal-energy atom beams.

Abstract: 1. Introduction.- 2. Quantum Electrodynamics in Strong and Supercritical Fields.- 2.1 The Electrodynamics of High-Z Electronic Atoms.- 2.1.1 Lamb Shift in Hydrogenlike Ions.- 2.1.2 Lamb Shift in Heliumlike Ions.- 2.1.3 Quantum Electrodynamics in High-Z Neutral Atoms.- 2.1.4 High-Z Atoms and Limits on Nonlinear Modifications of QED.- 2.1.5 Wichmann-Kroll Approach to Strong-Field Electrodynamics.- 2.2 The Electrodynamics of High-Z Muonic Atoms.- 2.2.1 General Features.- 2.2.2 Vacuum Polarization.- 2.2.3 Additional Radiative Corrections.- 2.2.4 Nuclear Effects.- 2.2.5 Electron Screening.- 2.2.6 Summary and Comparison With Experiment.- 2.2.7 Muonic Helium.- 2.2.8 Nonperturbative Vacuum Polarization Modification and Possible Scalar Particles.- 2.3 Quantum Electrodynamics in Heavy-Ion Collisions and Supercritical Fields.- 2.3.1 Electrodynamics for Z?>1.- 2.3.2 Spontaneous Pair Production in Heavy-Ion Collisions.- 2.3.3 Calculation of the Critical Internuclear Distance.- 2.3.4 Calculation of the Spontaneous Positron Production Rate.- 2.3.5 Induced Versus Adiabatic Pair Production.- 2.3.6 Vacancy Formation in Heavy-Ion Collisions.- 2.3.7 Nuclear Excitation and Other Background Effects.- 2.3.8 Radiative Corrections in Critical Fields.- 2.3.9 Coherent Production of Photons in Heavy-Ion Collisions.- 2.3.10 Self-Neutralization of Matter.- 2.3.11 Very Strong Magnetic Field Effects.- 2.4 Conclusion.- References.- 3. Relativistic Effects in Highly Ionized Atoms.- 3.1 Background.- 3.2 Interactions.- 3.2.1 Relativistic Interactions.- The Dirac Equation.- Two-Body Interactions.- The Central Field Approximation.- 3.2.2 Nonrelativistic Interactions.- 3.3 Transition Operators.- 3.3.1 The Interaction.- 3.3.2 Effective Transition Operators.- 3.3.3 Dipole Oscillator, Line, and Momentum Strengths.- 3.4 Calculation of Wave Functions and Energies.- 3.4.1 1/Z Expansion.- 3.4.2 Parametric Potentials.- 3.4.3 Hartree-Fock.- 3.5 Results.- References.- 4. Theory of Inelastic Atom-Atom Collisions.- 4.1 Quantum-Mechanical Treatment of Nuclear Motion.- 4.1.1 Expansion in a Finite Basis.- 4.1.2 The First Born Approximation for Excitation and Ionization.- 4.1.3 Incident Bare Nucleus.- 4.1.4 Incident Neutral Atom or Ion Carrying Electrons.- 4.1.5 Comments on the Validity of the PWBA.- 4.1.6 The Binary Encounter Approximation.- 4.1.7 Charge Exchange in Fast Collisions.- 4.1.8 Slow Collisions of Atoms.- 4.2 Classical Treatment of Nuclear Motion.- 4.2.1 Coupled Equations in the Impact Parameter Method.- 4.2.2 Expansion in Target Eigenfunctions.- 4.2.3 Eigenfunction Expansions on More Than One Center.- 4.2.4 Molecular Eigenfunction Expansion.- References.- 5. Excitation in Energetic Ion-Atom Collisions Accompanied by Electron Emission.- 5.1 Historical Background.- 5.2 General Considerations.- 5.3 Outer-Shells.- 5.3.1 Target Ionization.- 5.3.2 Projectile Ionization.- 5.4 Inner-Shells.- 5.4.1 Auger Spectra.- 5.4.2 Direct Excitation.- 5.4.3 Electron Promotion.- 5.4.4 Vacancy Sharing.- References.- 6. X-Ray Production in Heavy Ion-Atom Collisions.- 6.1 Measurement of X-Rays.- 6.1.1 Atomic Transitions, Fluorescence Yields, and Lifetimes.- 6.1.2 X-Ray Detectors.- 6.1.3 High Resolution X-Ray Data.- 6.2 Direct Ionization.- 6.2.1 Coulomb Excitation, Simple Description.- 6.2.2 Perturbation Improvements for Coulomb Ionization.- 6.2.3 Impact Parameter Dependent Direct Ionization.- 6.2.4 Electron Capture.- 6.2.5 Complex Excitation.- 6.3 Quasi-Molecular Excitation, Z1 ~ Z2.- 6.3.1 The Electron Promotion Model.- 6.3.2 K-Shell Ionization.- 6.3.3 Impact Parameter Dependence.- 6.3.4 L- and M-Shell Excitation.- 6.4 Quasi-Molecular Radiation.- 6.4.1 General Considerations.- 6.4.2 The Double Collision Mechanism - The L-MO Radiation.- 6.4.3 The Quasi-Atomic Approximation - The M-MO Radiation.- 6.4.4 Collision Broadening Effects - The K-MO Radiation.- 6.4.5 MO Emission Characteristics and Anisotropies.- 6.5 Bremsstrahlung and Radiative Electron Capture.- 6.5.1 Electron Bremsstrahlung.- 6.5.2 Nucleus-Nucleus Bremsstrahlung.- 6.5.3 Radiative Electron Capture.- References.- 7. Extensions of Beam Foil Spectroscopy.- 7.1 Extension of the Dynamic Range of Lifetime Measurements Using the Beam-Foil Technique.- 7.2 Target Ion Recoil Spectroscopy.- 7.3 Projectile Electron Spectroscopy and Lifetime Measurements.- References.- 8. Atomic Collisions in Solids.- 8.1 Channeling.- 8.1.1 Atomic Interactions from Planar Channeling Measurements.- 8.1.2 Hyperchanneling.- 8.2 Charge State Distributions.- 8.2.1 Effects of Channeling.- 8.3 Stopping Power.- 8.4 Inner-Shell Ionization.- 8.4.1 Exit Channel Effects.- 8.4.2 Level Shifting Effects.- 8.4.3 Solid-State Effects on Vacancy Lifetimes.- 8.4.4 Effects on the Relaxation of Target Atom Vacancies.- 8.4.5 Relation of Inner-Shell Vacancies to Emergent Charge State Distributions.- References.

Abstract: The surface chemistry of cleaved GaAs(110) (and, to a lesser extent, InP and GaSb) is studied as a function of oxygen exposure (both unexcited and excited) with soft-x-ray photoemission spectroscopy. When the cleaved GaAs (110) surface is exposed to molecular oxygen in the ground state, chemisorption to only the arsenics takes place. No back bonds are broken even for large exposures. Room-temperature oxidation of the surface can be induced by exciting the oxygen, e.g., by an ionization gauge. The adsorption of excited oxygen is initially the same as for the unexcited, except 500 times faster. However, after g 20% of a monolayer has been adsorbed, further exposure to excited oxygen causes back bonds to be broken and ${\mathrm{As}}_{2}$${\mathrm{O}}_{5}$ and ${\mathrm{Ga}}_{2}$${\mathrm{O}}_{3}$ are formed. Larger doses of excited oxygen result in the formation of thicker oxides composed primarily of ${\mathrm{Ga}}_{2}$${\mathrm{O}}_{3}$ with small amounts of elemental As (or As bound to only one Ga) and ${\mathrm{As}}_{2}$${\mathrm{O}}_{3}$, most of which has subilimed from the surface. No ${\mathrm{As}}_{2}$${\mathrm{O}}_{5}$ is seen in the thicker oxide because there is a deficiency of oxygen, and any partially oxidized Ga present will reduce the arsenic oxides. The escape depth for GaAs(110) was measured for electron kinetic energies between 20 and 200 eV. This range includes the minimum in the escape depth which is about 6 \AA{} at 60 eV. No chemical shift in the core levels between the atoms on the surface and in the bulk was observed. GaSb (110) and InP (110) surfaces were also studied. InP behaves like GaAs, whereas the GaSb is oxidized immediately even when exposed to only unexcited oxygen. The oxygen uptake curves for GaSb and GaAs were compared and found to be quite different with a sticking coefficient, at zero coverage, of 2 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$ for GaSb and 8 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}10}$ for GaAs.

Abstract: After one year of operation the GEOS-1 Ion Composition Experiment has surveyed plasma composition at all local times in the L range 3~8 and the energy per charge range from thermal to 16 keV/e. From measurements made in the keV range during eleven magnetic storms we find that the percentage of heavy (M/Q > 1) ions present in the outer magnetosphere increases by a factor of 3 to 10 during disturbances. We conclude that two independent sources (solar wind, characterized by 4He2+, and ionosphere, characterized by O+) give on the average comparable contributions to injected populations, although in a single event one or the other source may dominate. However, in magnetically quiet periods protons are the dominant species with a few percent of heavy ions. With the help of special satellite manoeuvres magnetic field aligned fluxes of ≈0.05–3 keV/e H+, He+, O+ with traces of O2+ have been observed which may be related to ion beams found previously at lower altitudes in the auroral zone. At still lower energies (~1 eV/e) the thermal plasma population is found to be made up of six ion species, three of which, D+, He2+ and O2+, were unknown in the magnetosphere prior to the GEOS-1 measurements. We present here a study of the evolution of doubly charged ions and their parent populations over four consecutive days. Various production mechanisms for doubly charged ions are discussed. We argue that ionization of singly charged ions by UV and energetic electrons and protons is the dominant process for plasmasphere production. Furthermore, the observed high concentrations of O2+ at high altitudes are a result of production in the upper ionosphere and plasmasphere combined with upward transport by thermal diffusion.

Abstract: Measurement of the specific conductance, pH, and zeta potential of latex dispersions upon titration with acid or base have been used by several workers to determine the number and nature of the surface ionizable groups. The ionization of latexes with single or several types of surface groups is modified by the interaction of the surface charge and potential with solute ions and is often complex and difficult to interpret in a quantitative manner. The solution of this problem requires (a) accurate estimates of the chemical and surface parameters of the particular latex dispersion, and (b) a reliable model for the potential and charge distribution at the latex/water interface. We describe the results of calculations using a general computer program for solving complex solution and surface reaction equilibria. The surface ion binding of electrolytes is shown to be a major contributing reaction for surface charge development and a new double extrapolation method for determining the intrinsic equilibrium constants for simple ionization and complex ionization reactions is outlined. Simulated titrations in which pH, specific conductivity, κ, and zeta potential, ζ, are estimated for each addition of base or acid are given and compared to reported results.

Abstract: The investigation of electronic and structural parameters of metal molecules as a function of size may be decisive for understanding and control of heterogeneous catalysis with finely divided metals. Metal-atom clusters can be prepared by several methods, most of which yield a molecular mixture only. Expansion of an atomic vapour into vacuum through a supersonic nozzle creates a complex cluster-spectrum which has been investigated by photoionization using a mass-spectrometer as selective detector. Broad band single photoionization (PI.) yields the abundances and ionization thresholds for Nax(x⩽16), Kx(x⩽12) and NaxKy(x+y⩽6). Rough indications about other deactivation channels of excited alkali-molecules are obtained from an analysis of the photoionization efficiency (PIE.) curves. Two-photon PIE. curves with narrow-band (laser) light sources give an accurate photoionization threshold value and detailed information on ionization processes. Two-photon ionization spectra via a real intermediate state reached by laser excitation are equivalent to normal absorption spectra, if the exciteation step is controlled by the true transition probabilities. By investigation of the power dependence of the ion current of Na as a function of the wavelength of the tunable cw dye laser (excitation) and of the ionizing Ar+- or Kr+-laser, conditions under which true spectra are obtained have been clarified, in good agreement with a photon-kinetic model of the processes involved. Vibronic and rovibronic spectra of several transitions in Na2 and K2 have been measured. Similarly a spectrum of Na3 has been determined mass-selectively. The scope of the new method for an absorption spectroscopy in molecular beams is discussed.

Abstract: Abstract Two-photon ionization of benzene molecules in a mass spectrometer is performed with a tunable frequency-doubled dye laser. The nonlinear ionization is resonantly enhanced by real intermediate rovibronic levels in the S1 state of the molecule. Our results show that stepwise multi-photon ionization is a very selective and versatile ionization source for a mass spectrometer.

Abstract: Negative ion products resulting from collisions between orthogonal, crossed beams of alkali metal atoms (Na, K, Cs), and the octahedral hexafluorides MF6 (M=S, Se, Te, Mo, W, Re, Ir, and Pt) have been examined in the energy range from ∼0 to 40 eV (lab). Studies of the dependence of the reaction thresholds upon the temperature of the target molecules SF6, SeF6, and TeF6 have provided electron affinities for these molecules; E.A.(SF6) =0.46±0.2, E.A.(SeF6) =2.9±0.2, and E.A.(TeF6) =3.3±0.2 eV. Energy loss measurements of the alkali, A, in the reaction A+MF6→A++MF−6 at small scattering angles are consistent with these values. Measurements for SF4 together with temperature dependent thresholds for the formation of SF−5 from SF6 and SF−3 from SF4 combined with known bond dissociation energies for D (SF5–F) and D (SF3–F) yield electron affinity values for the SFn series; E.A.(SF6) =0.46±0.2, E.A.(SF5) =2.71±0.2, E.A.(SF4) =0.78±0.2, and E.A.(SF3) =3.07±0.2 eV. Lower limits of ∼5 eV for the electron affinities o...

Abstract: Coupled-state calculations of proton---hydrogen-atom scattering using a scaled hydrogenic basis set have been performed, and the results are reported on in this paper. Thirty-five basis functions, centered about each proton, were included in the expansion of the electron wave function. Cross sections for direct excitation and charge transfer to the $n=1, 2, \mathrm{and} 3$ levels, and for ionization, have been calculated. The results for ionization indicate that charge transfer to the continuum dominates over direct ionization at proton energies below about 60 keV. The charge distribution has been plotted as a function of time at an energy of 40 keV and impact parameter of 1.5 a.u.; the plot illustrates the considerable distortion of the electron cloud caused by the passing proton.

Abstract: Detailed measurements have been made of the axial and radial ion currents, the electron temperature, and the plasma potential in a Hall-current plasma accelerator with an extended acceleration zone Plane Langmuir probes are used The results give a detailed picture of the processes which occur in the accelerator channel The results indicate the effectiveness of the accelerator as an ion source and show how the electron temperature, the ionization rate, and the potential distribution are related Calculations of the particle and energy balance in the accelerator channel are described

Abstract: In this article, the rare gas fluoride lasers are discussed in detail. There is a significant interest in these lasers because they are the most efficient visible/UV lasers to date. The dominant formation kinetics of KrF* and XeF* in both discharge and e -beam pumped lasers are presented. Because of the ionic upper level the formation processes are rapid and conditions can be chosen such that the branching ratios into the KrF* and XeF* levels from both the ionic and metastable levels are close to unity. With e -beam pumping of these lasers, a guide magnetic field enables the deposition of > 90 percent of the beam energy into the optical volume. Discharge pumping has the potential of being more efficient than e -beam pumping; however, the key technical issues of discharge stability and metastable production efficiency have to be addressed. Stabilization of the discharge is possible if an external source of ionization is used. The quenching of the rare gas fluorides by two- or three-body processes has been carefully measured and analyzed. The three-body quenching of KrF* leads to the eventual formation of the excited triatomic Kr 2 F* which radiates in a broad band centered at 410 nm. It has also been determined that ionic and excited state absorption in the active media is large enough to impact the extraction efficiency of these lasers. In the case of KrF, the dominant absorbing species are F 2 , F-, and Kr 2 F*, while Xe+ 2 appears to be the dominant absorber in XeF*. Finally, we have also investigated experimentally and theoretically the effects of the vibrational relaxation in the upper level and finite lifetime of the lower level on XeF* laser performance.

Abstract: Ab initio calculations of the MRD-CI type are reported for various states of the C 2 H 6 + ion in two different nuclear geometries and the results are compared with the experimentally observed ethane PES in the 14–25 eV region. The calculated vertical IP values for ionization out of the 1e u , 2a 2u and 2a 1g MO's respectively agree well with the locations of the three ionization maxima in this spectral range. The analogous findings for excitation out of the relaxed ionic ground state find several relatively low-lying species which occupy a 2pσ* MO in addition to states resulting from simple ionization of the neutral molecule. A number of Rydberg states are also calculated at the relaxed-ion geometry, from which results it is determined that the quantum defects for such species are from 0.40–0.45 units smaller than for their counterparts in neutral systems; these findings are clearly consistent with a decrease in the core penetrability of the Rydberg electron as the effective charge is increased to Z = 2.

Abstract: For a number of atoms, systematic calculations have been made of the alignment occurring in the photoionisation of inner subshells in the vicinity of the ionisation threshold. The influence of the centrifugal barrier in the effective partial potential on the alignment and on the anisotropy of the angular distribution and the polarisation of X-rays and Auger electrons is discussed. It is shown that the anisotropy is rather sensitive to the models used.

Abstract: Measurements of the relative photoionization cross sections of Rb in the presence of various strengths of external electric fields are reported. Systematic, field-dependent, resonance structure is observed not oly for energies above the classical field-ionization limit, but above the zero-field ionization limit as well. A striking dependence of the cross section upon light polarization is also observed.

Abstract: Laser spectroscopy and kinetic mass spectrometry of polyatomic isolated molecules have been carried out by using stepwise laser ionization of molecules in a mass spectrometer The optical absorption spectrum of NO(2) has been recorded, for example, by using pulsed dye-laser excitation and H(2) vacuum-ultraviolet laser ionization of molecules The kinetics of excited electron states and of the production of molecular and fragmented ions of some polyatomic molecules have been investigated with high temporal resolution The sensitivity achieved is 10(-10) cm(-1) of the absorption coefficient and 10(9) (10(5)) molecules in the ground (electronically excited) state in the irradiated volume

Abstract: The mode of ionization of a molecule has a strong influence on its behavior in the mass spectrometer and thus on the information that can be obtained from its mass spectrum. In chemical ionization a reagent gas, e.g. methane, is first ionized by electron impact. The ions formed in ion-molecule reactions, in particular [CH5]+, [C2H5]+, and [C3H5]+, then react “chemically” with the substrate M in fast acid/base type reactions to form ions of the type [MH]+, [M(C2H5)]+, etc., which subsequently fragment to various extents. Alternatively, chemical ionization can be effected by charge exchange, in that ions of a reagent gas, e.g. [He]+•, react with the substrate M to form molecular ions [M]+·. Chemical ionization can thus be conducted in a more or less mild fashion and the extent of the fragmentation can be controlled over a very wide range.

Abstract: Recent experiments and calculations have indicated that mutual collisions between excited 6 3P0, 6 3P1, and 6 3P2 atoms may be important for the ion formation in low‐pressure Hg–noble‐gas discharges. We calculate various rates for electron‐impact and for excited‐atom‐collisional ionization for a range of conditions relevant to the Hg‐Ar fluorescent lamp (pAR=3 Torr, R=1.8 cm, Twall=20–80 °C, and I=0.2–0.8 A). In the analysis use is made of experimentally determined values for particle densities and electron temperatures. Deviations from a Maxwellian electron‐energy distribution, which substantially reduce the electron‐impact ionization rates, are taken into account. We find that 6 3P–6 3P collisions become even more important for the ion formation than electron impact at the higher Hg vapor pressures. Both Hg+ and Hg+2 will be formed. The 6 3P–6 3P collisions are indicated to be mainly responsible for the well‐known decrease in uv efficiency of the Hg–noble‐gas discharge at temperatures above 40 °C.

Abstract: The negative ion products resulting from collisions between orthogonal beams of alkali atoms (Na, K, Cs) and the methane derivatives CH3CN, CH3NO2, CF3Br, and CF3I have been studied in the energy range from reaction thresholds to ∼40 eV (LAB). Stable negative ions with masses corresponding to the last three molecules were detected and the following electron affinities are derived from measurements of the energy threshold for the ion pair production reactions: E.A.(CH3NO2) =0.44+0.1−0.2 eV; E.A.(CF3Br) =0.91±0.2 eV, and E.A.(CF3I) =1.57±0.2 eV. From measurements of the difference between the energy threshold for the appearance of various fragment ions and the parent ion, the following bond dissociation energies are deduced: D(CH3–NO−2) =0.56±0.2 eV; D(CF3–Br−) =0.54±0.2 eV and D(CF3–I−) =0.32±0.2 eV. An argument is presented which adds further strength to the suggestions of Williams et al. and Jordan and Wendoloski that electron binding to CH3CN is dominated by the dipole field.