Abstract: Experimental $K$-shell ionization cross sections are reported for low-velocity heavy projectiles of atomic number small compared to the target atomic number. For such projectile-target combinations, the Coulomb interaction between the projectile nucleus and the $K$-shell electrons dominates the $K$-shell ionization process at all projectile velocities. The data can disagree by orders of magnitude with the primary predictions of the nonrelativistic quantum theory in the plane-wave Born approximation. Important physical processes are shown to be at the root of the discrepancies. They derive from the finite charge of the moving projectile, and thus do not contribute in the plane-wave Born approximation. They are the Coulomb deflection of the projectile in the field of the target nucleus and the perturbation of the target atomic states by the projectile. A theory for these processes is developed in an approximate manner. When incorporated with the theory in the plane-wave Born approximation, it accounts quantitatively for the data. A method results for reducing cross-section data in a comprehensive way. A universal graph of cross sections emerges which, in effect, constitutes an extrapolation of the data to the conditions of zero projectile charge. It comprises cross sections ranging over six orders of magnitude measured on different targets for various projectiles with a wide range of velocities, mostly below the mean $K$-shell velocities. The locus of this universal graph coincides with the prediction of the plane-wave Born approximation.

Abstract: The net erosion rate at the cathode spots of 100‐A vacuum arcs has been determined experimentally for Cd, Zn, Ag, Cu, Cr, Fe, Ti, C, Mo, and W electrodes. Ion currents to the metal walls surrounding each of these cathode materials have also been investigated. For each material, the dependence of the wall ion current on the electrode spacing and anode geometry is consistent with an arc model which assumes predominant vapor ionization in the cathode regions, with subsequent isotropic free flight motion from these regions. Comparison of the net erosion rate with the wall ion current indicates that, for high‐vapor‐pressure materials such as Cd and Zn, ≈ 15% of the vapor leaves the cathode regions ionized. For low‐vapor‐pressure materials such as C, Mo, and W, this fractional ionization is almost 100%. The ion current magnitudes observed at long electrode spacings are similar for each material, and lie in the range 7–10% of the arc current. Ion currents of this magnitude are also predicted for Mg, Al, and Ni u...

Abstract: Ionization rates for electrons and holes are extracted from photomultiplication measurements on silicon p+n mesa diodes for electric fields of 2·0 × 105−7·7 × 105 V/cm at temperatures of 22, 50, 100 and 150°C. These results are particularly pertinent to the analysis of high-frequency (∼ 100 GHz) silicon IMPATT diodes. The rates obtained here are in reasonable agreement with previously published data of van Overstraeten and DeMan, although slightly larger in magnitude. Calculated curves of breakdown voltage vs background doping level are presented using the room temperature ionization rates. Also a comparison is made to previously reported rates. The new rates provide a closer agreement between predicted and measured breakdown voltages for breakdown voltages less than 70 V.

Abstract: Numerical results are presented for the characteristics of heavy‐ion laser‐produced plasmas. A conversion ratio defined as x‐ray power/absorbed power is then computed. Collisional‐radiative equilibrium is assumed for the ionization model. In the case of low radiation emission, a relation between laser flux and plasma temperature is derived. The one‐dimensional geometrical model is then corrected in the expansion by assuming that the emission occurs, in fact, over a length L only. Results are given and compared with experimental ones. The influence of the laser wavelength is also discussed and conclusions on the possible applications of these laser‐produced plasmas are drawn.

Abstract: Transition rate equations for atomic hydrogen are solved to obtain coefficients for population of excited levels and for ionization and recombination. The results are based upon more accurate transition rates, cover a wider range of plasma parameters, and are obtained by a more general solution of the rate equations than previously available compilations. Diagnostic applications for laboratory plasmas are discussed.

Abstract: Reaction rate constants for the quenching of electronic energy in metastable argon (3P0,2) by Kr, Xe, and a number of simple molecules have been measured A hollow, cold‐cathode discharge excites the metastables in a flow apparatus The concentration of metastables was followed by absorption spectroscopy as a function of time and of quenching molecule concentration Quenching of Ar*(3P2) by Kr, CO, N2, CF4, and H2(D2) proceeds at rates between 06 and 7 × 10−11 cm3 molecule −1 · sec−1 Except for Kr, Xe, N2, CO, and CH4, the 3P0 metastable level is quenched slightly more rapidly than the 3P2 level With the aid of data in the literature, the contribution from the product channels (Penning and associative ionization) are considered for quenching by NO and C2H2 These channels appear not to be of major importance for quenching since the ionization efficiency of these two reactions is low: ∼ 02 for NO and ∼ 01 for C2H2 The quenching mechanism is discussed in terms of both a curve crossing and a ``golden r

Abstract: The probability for either exciting or ionizing an electron from a given atomic orbital as the result of a sudden vacancy in one of the atomic shells, such as might occur with photoionization, has been calculated through the use of the sudden approximation. Calculations were made for each of the subshells of neon, argon, krypton, and xenon as a function of the location of the initial vacancy. The calculations were based on relativistic Hartree-Fock-Slater wave functions. The results were generalized in terms of the change in effective charge. For example, electron shake-off in the valence shell was found to be nearly independent of the location of the initial core vacancy, increasing slightly as one goes to the lower principal quantum numbers. The ionization potentials were also found to be nearly independent of the location of the core vacancy. The results of the electron-shake-off calculations were also used to obtain an evaluation of the relaxation energy arising from the promotion of a single vacancy, and compared with values obtained from binding-energy calculations. Results of the electron-shake-off calculations are applicable to any process that leads to a sudden creation of a vacancy in an atom. However, particular emphasis is given to photoelectron spectroscopy in discussing the results.

Abstract: A procedure is developed for computing cross sections for the multiple ionization of atoms by the impact of protons or other fully stripped nuclei. The ionization probability, as a function of energy and impact parameter, $P(E,b)$, is computed at several beam energies in the binary-encounter approximation for a ground-state hydrogenic electron scattered by an incident proton. Scaling laws are given which may be used to extend these results to other projectiles, other targets, and other hydrogenlike filled atomic shells. It is shown that $P(E,O)=〈\frac{\ensuremath{\sigma}(E,r)}{2\ensuremath{\pi}{r}^{2}}〉$ for isotropic, but otherwise arbitrary, electron-density distributions. A formulation for multiple-ionization cross sections is developed in terms of the single-electron probabilities $P(E,b)$ for each atomic shell, assuming that both the electrons and the shells are mutually independent. Numerical calculations are compared to recent predictions in the semiclassical Coulomb approximation and to recent satellite and hypersatellite x-ray data. The discrepancies are generally within those resulting from uncertainties of 30-200% in the single-ionization cross sections, when the ionization probability is much less than one. Then, approximating $P(\mathrm{Eb})$ vs $b$ as a step function, the multiple-ionization cross sections are reduced to simple combinations of single-ionization cross sections. These single-ionization cross sections may be evaluated in the binary-encounter approximation by applying scaling laws to the usual universal curve that we tabulate. Multiple-ionization cross sections may thus be estimated without the aid of a computer.

Abstract: : A critical tabulation of observed spectral lines below 2000 Angstroms has been prepared from the published literature up to May 1972 It is intended principally as an aid to those physicists and astronomers who deal with the spectra of highly stripped atoms This report includes the first 36 elements The tabulation is divided into two main sections: the emission lines by spectrum, and a finding list The entries for each element give the ionization species, ground state term, and ionization potential, as well as the best values of vacuum wavelength, intensity, and classification A list of the pertinent reference sources is appended at the end

Abstract: The binary-encounter approximation (BEA) is transformed from momentum space to configuration space. In this frame the impact-parameter representation allows one to calculate a variety of quantities pertinent to the general problem of ionization. Among these are cross sections for proton ionization of hydrogen and helium; in the latter case, croas sections for ejection of both electrons are also given. A number of tables and formulas are given, enabling one to correct the simple hydrogenlike-model predictions of the BEA for effects which arise in multielectron atoms. Multiple-ionization probabilities (K + L shell) are calculated and compared to experimental results and to the predictions of the semiclassical approximation.

Abstract: The photoelectron and vacuum ultraviolet absorption spectra (200–120 nm) of CF3Cl, CF3Br, CF2HCl, CFH2Cl, CFHCl2, CF2Cl2, and CFCl3 are reported and discussed. The lowest ionization potentials belong to the chlorine or bromine lone pair orbitals, the next highest ones to the bonding orbitals of mainly C–Cl or C–Br character. In the absorption spectra the lowest freuqency bands are due to weak valence‐shell type transitions. At higher freuqencies we find much stronger Rydberg type bands related to the first ionization potential. All absorption bands up to 84 000 cm−1 depart from chlorine or bromine lone pair orbitals. Some of the bands exhibit vibrational fine structure. An increase in the number of the fluorine atoms causes a shift to either higher or lower energies of the ionization potentials belonging to orbitals of mainly C–H or C–Cl character according to the cases while the lone pair ionization potentials and the absorption spectra shift to higher energies in all cases.

Abstract: A theory recently developed for atoms and molecules is applied to the calculation of the main poles of one-particle Green's functions in the low-energy region and their pole strengths for the molecules F2, H2O, C2H2 and H2CO. The poles corresponding to occupied orbitals compare well with the experimental vertical ionization potentials (VIP's). In particular the sequence of the VIP's of F2 which is not reproduced by Koopmans' theorem (breakdown) is re-established. The corresponding pole strengths are found to have values around 0·9.

Abstract: Momentum distributions have been measured separately for $3p$ and $3s$ electrons in argon. The measured summed energy spectrum shows the presence of a peak which is analyzed in terms of electron-electron correlations.

Abstract: The results of an analytical treatment of the local low-frequency stability of weakly ionized molecular-gas mixtures consisting of a diatomic molecular species and an atomic diluent are presented. Plasma conditions typical of high-power electric-discharge-laser technology are emphasized. The calculations indicate that small-amplitude fluctuations present within these discharges excite several different wave modes. These have been identified as a space-charge relaxation mode, an electron thermal mode, an ionization mode, a negative-ion-production mode, an electronically-excited-species-production mode, a sound mode, a vibrational-energy relaxation mode, a heavy-particle thermal mode, and a vorticity mode. The stability of these modes is treated in detail with particular emphasis placed on illustrating the influence on stability of charged-particle kinetics, energy transfer, and transport processes. The influence of auxiliary ionization and aerodynamic techniques is also considered.

Abstract: Investigation of the mechanism for dissociative ionization of CO2 on the basis of measurements of the yields of photoions from CO2. It is found that at photon energies immediately above the molecular ionization limit of 13.773 plus or minus 0.002 eV the photoion yield curve exhibits a number of closely spaced peaks in a pattern not resembling Rydberg series. Two fragment ions, O(+) and CO(+), are observed as products of dissociative ionization. The yield of O(+) follows a weak, oscillatory curve from the thermochemical threshold at 19.07 eV to 19.39 eV, where a sudden increase in O(+) yield is observed exactly at the onset of the state CO2(+)/C 2 Sigma g (+)/, indicating predissociation of this state of the molecular ion. The magnitude of the jump in O(+) yield at 19.39 eV suggests that this predissociation is the principal mechanism for dissociative ionization.

Abstract: Angular distributions of electrons ejected from helium by proton impact are calculated in the plane-wave Born approximation using bound and continuum electron wave functions obtained from a Hartree-Fock potential. The results of this calculation are compared with experimental data and good agreement is found when the relative electron-proton velocity is larger than the proton velocity. The good agreement observed for large angles of the ejected electron is to be contrasted with previous calculations, which fell lower than the large-angle-scattering experimental data.

Abstract: The total absorption, photoionization and neutral product cross sections for H2O and D2O have been determined over the wavelength range 580 to 1050 A. The helium continuum was used as a background with a bandwidth of approximately 0.5 A. Previously observed Rydberg series converging to the (000) level of the ionic ground state have been extended and utilized to obtain ionization thresholds of H2O (982.47 ± 0.5 A, 12.619 ± 0.006 eV) and D2O (981.16 ± 0.5 A, 12.636 ± 0.006 eV). At wavelengths shorter than 1000 A, the total cross section curves for H2O and D2O exhibit a number of previously unreported bands superimposed on broad continua which have peaks at approximately 720 and 925 A. These bands are most likely due to progressions belonging to Rydberg states converging to the first and second excited states of the molecular ion. There is evidence from photographic spectra of H2O16 and H2O18 that the Rydberg states converging to the first excited state of the ion (A2A1) have an effectively linear conformation.

Abstract: Values for the ionization energies of the doubly and triply ionized rare earth atoms have been derived from interpolated spectroscopic properties of the 4fNns series, and from interpolated energy intervals relating the first series member, 4fN6s, to the ground state. The results in eV are La III19.1774(6)Tb III21.91(10)IV 39.79(20)Ce20.198(3)IV 36.758(5)Dy22.79(30)41.47(20)Pr21.624(3)38.98(2)Ho22.84(10)42.48(32)Nd22.14(30)40.41(20)Er22.74(10)42.65(21)Pm22.32(36)41.09(32)Tm23.68(10)42.69(20)Sm23.43(30)41.37(38)Yb25.03(2)43.74(20)Eu24.70(32)42.65(32)Lu20.9596(10)45.19(2)Gd20.63(10)44.01(35)Hf33.33(2) The values for the doubly ionized atoms agree to within ∼ 1% with those deduced from thermodynamic measurements on lanthanide oxides. A value for the ionization energy of Gd II of 12.09(8) eV was determined by using new spectroscopic data for Gd II and Gd III.

Abstract: In the positive column of low‐pressure gas discharges, the electron energy distribution can be markedly non‐Maxwellian, in particular in the tail of the distribution at low degrees of ionization. A method is described which enables one to account for large deviations from a Maxwellian distribution when calculating collision rates, energy flow terms, excited‐state densities, and the radiation output. Illustrative examples are given for Cs–Ar, Ar, and Hg–Ar discharges. Possible extensions and applications of the method are briefly discussed. Analytical formulas are derived for (i) the Coulomb relaxation between the electrons and (ii) the cross sections for ionization from excited states.