Showing papers on "Ionization published in 1972"
914 citations
TL;DR: In this paper, the authors derived the probability that a pulse initiated by n electrons in a uniformly multiplying semiconductor diode will result in a total number of electrons (or holes) m, to give a gain m/n, and for the probability Q n,m} that the gain will be m/m or greater.
Abstract: Expressions are derived for the probability P_{n,m} that a pulse initiated by n electrons (or holes) in a uniformly multiplying semiconductor diode will result in a total number of electrons (or holes) m , to give a gain m/n , and for the probability Q_{n,m} that the gain will be m/n or greater. It is shown that the distributions are far from Gaussian. The gain distribution P_{1,m} for a single photoelectron, for example, is shown to have a maximum value for m = 1 for any value of the average gain M=m/n . The derivations are valid for any electric field distribution and assume only that the hole ionization coefficient \beta(E ) can be approximated by the relation \beta(E) =k\alpha(E) , where \alpha(E) is the electron ionization coefficient and k is a constant. A method of determining an effective value of k , for cases where \beta=k\alpha is not a good approximation, is presented. The results can be used to calculate the average gain and the mean square deviation from the average, giving results in agreement with previously published relations [1], [2]. The implications of this theory on the use of avalanche diodes for low-level photodetection are discussed. It is shown that in the near infrared, cooled avalanche photodiodes can compare favorably with the best available photomultiplier when used either in a photon-counting mode, or for the reliable detection of low-level laser pulses.
507 citations
TL;DR: In this paper, a transmission experiment is used to observe structure in the total electron-impact cross section for He, Ne, Ar, Kr, and Xe below the respective ionization potentials, and also in the region of autoionizing states.
Abstract: A transmission experiment is used to observe structure in the total electron-impact cross section for He, Ne, Ar, Kr, and Xe below the respective ionization potentials, and also in the region of autoionizing states The positions of the resonances are tabulated and compared with the results of other investigators In both neon and argon, relatively large isolated resonances exist near the edge of the Rydberg series involving inner-shell autoionizing states, ie, near 475 and 29 eV, respectively
396 citations
TL;DR: In this article, the hole states of O 2 +, obtained by ionization of the oxygen molecule, have been examined theoretically in three approximations: (i) the frozen orbital approximation, which consists of single configuration calculations in terms of the Hartree-Fock orbitals for the neutral O2 molecule; (ii) direct hole state calculations in which g or u inversion symmetry is imposed on each molecular orbital; (iii) direct HO state calculations without the restriction in (ii).
Abstract: The hole states of O 2 +, obtained by ionization of the oxygen molecule, have been examined theoretically in three approximations: (i) The frozen orbital approximation, which consists of single configuration calculations in terms of the Hartree‐Fock orbitals for the neutral O2 molecule; (ii) direct hole‐state calculations in which g or u inversion symmetry is imposed on each molecular orbital; (iii) direct hole‐state calculations without the restriction in (ii). For the 1s 4Σ− hole state the three approximations yield the following ionization potentials: (i) 563.5 eV; (ii) 554.4 eV; (iii) 542.0 eV. The experimental ionization potential is 543.1 eV, and it is concluded that the hole state is localized on one of the two oxygen atoms.
331 citations
317 citations
TL;DR: In this paper, a limiting intensity for light propagation in transparent liquids and solids is determined by avalanche ionization over a wide range of pulse durations, wavelengths, and band gaps, based on the thickness dependence of the dc breakdown.
Abstract: A limiting intensity is shown to exist for light propagation in transparent liquids and solids. In pure bulk materials it is determined by avalanche ionization over a wide range of pulse durations, wavelengths, and band gaps. The ionization rate per unit time is deduced from the thickness dependence of the dc breakdown. The negative real part of the index of refraction of the carriers stabilizes the size of self-focused filaments.
287 citations
264 citations
TL;DR: In this article, the Bethe asymptotic formula involving two parameters that represent important atomic properties has been used to describe the energy dependence of the measured cross sections of ionization cross sections.
Abstract: Ionization cross sections of forty gases have been measured for electrons of kinetic energies 0.1-2.7 MeV. The measurements are absolute and extensive precautions have been taken to minimize systematic and accidental errors. The energy dependence of the measured cross sections is accurately described by the Bethe asymptotic formula involving two parameters that represent important atomic properties. Comparisons have been made between ${\mathrm{H}}_{2}$ and ${\mathrm{D}}_{2}$ and between C${\mathrm{H}}_{4}$ and C${\mathrm{D}}_{4}$; the observed differences are of the order of 1% and too small to be resolved with certainty. A close comparison has been made between positrons and electrons in Ar at 0.67 and 1.1 MeV; the cross sections are observed to be equal within a probable error of 0.5%.
236 citations
TL;DR: In this article, the authors compared the predictions of a simple point charge model with and without corrections for polarization and repulsion for the removal of various electrons from the alkali chlorides and the sodium and cesium halides.
Abstract: We have measured ionization potentials for the removal of various electrons from the alkali chlorides and the sodium and cesium halides. These binding energies are compared with the predictions of a simple point charge model with and without corrections for polarization and repulsion. The simple model predicts and the data show that the spacings of the energy levels for a given ion are independent of what crystal it is in and are the same as for the free ion. The point charge model also allows us to calculate the difference between cation and anion energy levels in the same crystal. There is, however, a disagreement between the predicted and experimental values of this difference that ranges from about 1.8 eV for LiCl to −0.2 eV for RbCl. This discrepancy is markedly reduced by inclusion of polarization effects. The point charge model with polarization and repulsion corrections predicts absolute ionization potentials for the alkali and halide ions that differ in a systematic way from those observed. For the sodium halides, the difference between calculated and experimental energies decreases monotonically from about −4 eV for NaF to about 0.9 eV for NaI. The origin of these discrepancies is apparently due to charging of the samples and their trend is directly attributable to the size of the respective bandgaps. We show that the electrostatic model can be used to provide a comparison between experimental binding energies for inner electrons in a crystal and Hartree‐Fock calculations for binding energies of inner electrons in free atoms. Finally, using the point charge model we show that the binding energy of an electron on a highly charged ion in an ionic crystal is only slightly different from the binding energy of the same electron in the neutral atom.
213 citations
TL;DR: Using an energy-resolved electron beam, appearance potentials for, and fragment ions from hydrocarbons of formula C 3H4, C3H6, C4H8, and C5H10 have been measured in this article.
Abstract: Using an energy-resolved electron beam, appearance potentials for,, and fragment ions from hydrocarbons of formula C3H4, C3H6, C4H6, C4H8, and C5H10 have been measured. In each case the fragment ap...
206 citations
TL;DR: In this article, the observed π-orbital energies ϵv,j = −Iv,j derived from the vertical ionization potentials obtained by a photoelectron spectroscopic investigation of the acenes benzene A, naphthalene A(2), anthracene A (3), naphthacene A/4 and pentaceneA/5 have been compared with three different approximations: (a) the standard Huckel HMO model; (b) a first-order perturbation treatment, based on (a),
Abstract: The ‘observed’ π-orbital energies ϵv,j = −Iv,j derived from the vertical ionization potentials obtained by a photoelectron spectroscopic investigation of the acenes benzene A(1), naphthalene A(2), anthracene A(3), naphthacene A(4) and pentacene A(5) have been compared with π-orbital energies calculated by three different approximations: (a) the standard Huckel HMO model; (b) a first-order perturbation treatment, based on (a), that takes into account bond length changes which follow the ionization process; (c) a SCF π-electron model of the type proposed by Pople and by Pariser & Parr. In agreement with previous experience it is found that model (b) yields the most satisfactory parametrization of the experimental data.
TL;DR: In this paper, the high-resolution HeI electron spectra of Ni(C5H5), Fe(C 5H5)2, Mn(Mn) and Cr(Cr5H7)2 have been recorded and analyzed in terms of a molecular orbital description of the electronic structure.
Abstract: The high resolution HeI electron spectra of Ni(C5H5)2, Fe(C5H5)2, Mn(C5H5)2, and Cr(C5H5)2 have been recorded and analyzed in terms of a molecular orbital description of the electronic structure. The ground state electronic configurations have been assigned by considering the feasible ground state configurations, determining the number and type of ionic states obtained from ionization of these configurations, and then comparing the predicted transitions with those observed experimentally. The ground state configuration and adiabatic first ionization potential of these molecules are: Cr(C5H5)2, ··· (e2g)3(a1g)1, 3E2g, I.P.=5.50 eV; Mn(C5H5)2, ··· (e2g)4 (a1g)1, 2A1g, I.P.=6.55 eV; Fe(C5H5)2, ··· (a1g)2 (e2g)4, 1A1g, I.P.=6.72; Ni(C5H5)2, ··· (a1g)2 (e2g)4 (e1g)2, 3A2g, I.P.=6.2 eV. Vibrational structure has been observed in the spectrum of ferrocene and is assigned to progressions in ν4, the symmetric ring‐metal stretching mode.
TL;DR: In this paper, an improved and simplified analytical characterization of differential cross sections leading to secondary electrons following bombardment at a fixed primary electron energy is presented, which can describe phenomenologically the falloff in the production of secondary electrons at low and at high energies more accurately.
TL;DR: The titration calorimetry (TC) method as discussed by the authors can be used in any solvent to determine equilibrium constants for proton ionization and metal ion interactions over a large pH range for simple and complex equilibria.
TL;DR: In this article, the lifetime of associative ionization of He* (1s2s 3S) + H(1s 2s 2S) was calculated as a function of internuclear distance, and cross sections for associative and penning ionization were determined for low collision energies.
Abstract: The width Γ (or lifetime ℏ/Γ) for autoionization of He* (1s2s 3S) + H(1s2S) has been calculated as a function of internuclear distance, and cross sections for Penning and associative ionization (He*+H → He+H++e−, HeH++e−) have been determined for low collision energies Associative ionization is 22% of the total ionization cross section in the limit of zero collision energy; this fraction decreases with increasing energy, being ·18% at a collision energy corresponding to 300°K The distribution in energy of the ionized electron is also calculated, and it is seen that measurement of this quantity should lead to a good estimate of the well depth of the He*–H potential Comparison of these results with those obtained by an orbiting model shows that the model (suitably scaled) is adequate in predicting the total ionization cross section, but is less accurate for the more detailed collision properties
TL;DR: In this article, the first ionization potentials of ferrocene have been computed in the LCAO-MO-SCF scheme as the difference of the total energy for the neutral molecule and the positive ion.
Abstract: The first ionization potentials of ferrocene have been computed in the LCAO-MO-SCF scheme as the difference of the total energy for the neutral molecule and the positive ion. The corresponding sequence of ionization potentials is found to be IP.(e
2g
)
TL;DR: In this article, the radial profiles of ionized helium flux and protons are calculated, and certain physical effects ignored in previous treatments are taken into account, such as charge exchange processes, which provide a loss mechanism as well as a way of converting solar-wind alpha particles to He+, and contribution of fluctuating electrostatic fields to the radial-diffusion coefficient.
Abstract: The comparison of radial diffusion of magnetospheric helium ions and protons is a sensitive test of the diffusion process assumed (magnetic or electrostatic fluctuations) and thus valuable as a probe of magnetospheric dynamics for protons, electrons, and heavy ions, as well as for the helium ions themselves. In this paper radial profiles of ionized helium flux and protons are calculated, and certain physical effects ignored in previous treatments are taken into account. These effects include (a) charge-exchange processes (He++ → He+ → He or He++), which provide a loss mechanism as well as a way of converting solar-wind alpha particles to He+, and (b) contribution of fluctuating electrostatic fields to the radial-diffusion coefficient. Like nearly all other treatments of radial diffusion, other processes such as pitch-angle scattering have been omitted for lack of quantitative knowledge. The combination of a solar-wind source, of losses dominated by charge exchange, and of electrostatic radial diffusion (with a plausible power spectrum for the fluctuations) leads to (a) fast conversion of alphas to He+, and (b) a radial-diffusion coefficient proportional, at fixed energy per nucleon, to (Z/A)². Thus helium and other heavier ions (C, N, O) diffuse much more slowly than protons in the magnetosphere, and this slow diffusion can explain the very small α/p ratios observed near L = 3.
TL;DR: In this article, the Hartree-Fock wavefunctions were calculated for the ground state of the water molecule using both Slater and contracted Gaussian basis sets; these energies are estimated to be within 0.003±0.002 hartree of the Hartreesfock limit.
Abstract: Near Hartree‐Fock wavefunctions have been calculated for the ground state of the water molecule using both Slater and contracted Gaussian basis sets. Total energies of −76.063 hartree were obtained with a (5s4p1d/3s1p) Slater basis and a [6s5p2d/3s1p] contracted Gaussian basis derived from an (11s7p2d/5s1p) primitive set; these energies are estimated to be within 0.003±0.002 hartree of the Hartree‐Fock limit. The Hartree‐Fock wavefunctions account for ∼70% of the dissociation energy of water. The Hartree‐Fock vertical ionization potentials (in electron volts), 11.1(2B1), 13.3(2A1), and 17.6(2B2), are too low by 1–1.5 eV as expected. With the Gaussian basis set a potential surface was computed and the equilibrium geometry and harmonic force constants were calculated. The calculated bond length, 0.941 A, and bond angle 106.6°, are in good agreement with the experimental values, 0.957 A and 104.52°. In spite of the rather good agreement for the geometry, the force constants are in error by 15%–20%. This is a...
TL;DR: The multiple signals in the 3D region of seven lanthanum(III) compounds are explained by the possibility of simultaneous transfer of an electron from the neighbour atoms to the empty 4f shell during the ionization.
TL;DR: Born-approximation calculations of the ionization of aluminum $L$-shell electrons have been performed using Hartree-Slater wave functions as discussed by the authors, and the results show a delayed maximum above threshold, and the ramifications of this phenomenon are discussed.
Abstract: Born-approximation calculations of the ionization of aluminum $L$-shell electrons have been performed using Hartree-Slater wave functions. Generalized oscillator strengths and proton energy-loss cross sections from threshold to ionized-electron energies of 128 Ry have been calculated. The results show a delayed maximum above threshold, and the ramifications of this phenomenon are discussed. Comparison is made with hydrogenic results and good agreement is found at intermediate and large energy loss, but the hydrogenic calculation is totally inadequate near threshold. The implications of this for stopping-power calculations and subshell corrections is discussed. The Bethe asymptotic cross section is obtained and the variation of parameters therein is investigated.
TL;DR: In this article, the consequences of electron impact on water vapor in terms of the microscopic details of excitation, dissociation, ionization, and combinations of these processes are examined.
Abstract: Examination of the consequences of electron impact on water vapor in terms of the microscopic details of excitation, dissociation, ionization, and combinations of these processes Basic electron-impact cross-section data are assembled in many forms and are incorporated into semianalytic functions suitable for analysis with digital computers Energy deposition in water vapor is discussed, and the energy loss function is presented, along with the 'electron volts per ion pair' and the efficiencies of energy loss in various processes Several applications of electron and water-vapor interactions in the atmospheric sciences are considered, in particular, H2O comets, aurora and airglow, and lightning
TL;DR: In this article, the effect of the Jahn-Teller effect on the ionization of doubly degenerate π and σ orbitals was investigated and the results showed that in the π system, because of their much weaker binding properties, the correspondingly weak Jahn−Teller forces are just strong enough to cause excitation of e-type vibrations without giving rise to any electronic splitting.
Abstract: Photoelectron spectra of all the fluorobenzenes (except 1,2,3-trifluorobenzene) have been obtained with photon energies up to 40.8 eV. The changes in spectral features arising from the progressive substitution of fluorine, as well as those associated with the various stereoisomers of these molecules, illustrate clearly many important features of the benzene orbitals and assist in their correct assignment. The nature of the Jahn–Teller effect in states arising from the ionization of the doubly degenerate π and σ orbitals is shown to be markedly different, and this in turn differs from the effect of substitutional splitting in these degenerate orbitals.The analysis leads to the following reassignment of adiabatic ionization potentials for C6H6; (1a2u)–1, 11.490 eV; (3e2g)–1, 11.570 eV; (3a1g)–1, 15.446 eV and (2b1u)–1, 16.848 eV. Other changes relative to previous band assignments arise from the recognition of large electronic Jahn–Teller splittings in the σ systems. In the π systems, because of their much weaker binding properties, the correspondingly weak Jahn–Teller forces are found to be just strong enough to cause excitation of e-type vibrations without giving rise to any electronic splitting. A study of the isotopic blue shifts of the band origins observed for benzene-d6 reflects the bonding character and hydrogen dependence of the orbitals and supports the analysis. Selective enhancement of (3e2g)–1 relative to (1a2u)–1 in the C6D6 spectrum obtained with Ne I radiation was used to identify these states.
TL;DR: In this paper, the angular distribution of direct photoionization is quite different depending on whether or not the ionization is accompanied by a rotational transition, and the results are compared with available experimental data, which may serve as a basis for extensions to electronic and vibrational autoionization processes.
Abstract: Fano's theory of photoabsorption by ${\mathrm{H}}_{2}$ near the ionization threshold is extended to yield photoelectron angular distributions above as well as between the ionization thresholds for alternative rotational states of the ${\mathrm{H}}_{2}^{+}$ ion. In accordance with recent measurements, the angular distribution of direct photoionization is quite different depending on whether or not the ionization is accompanied by a rotational transition. In the autoionization range between rotational thresholds the angular distribution oscillates along each Rydberg line of the rotational autoionization spectrum, resulting in Beutler-Fano resonance profiles which depend strongly on angle of observation. The results are compared with available experimental data. Angular distributions provide very sensitive tests of the theory. The calculation may serve as a basis for extensions to electronic and vibrational autoionization processes.
TL;DR: In this article, total K-shell ionization cross sections by electron bombardment have been measured for copper silver and gold at various energies up to 140 keV, and total L III -shell ionisation cross sections for gold.
TL;DR: The electron impact spectra of methane, methyl fluoride, methylene fluoride, fluoroform, and tetrafluoromethane have been obtained out to 22 eV energy loss using electrons incident at 400 eV and scattered through small angles as discussed by the authors.
TL;DR: Using the concept of the generalized oscillator strength in the Born-Bethe approximation together with semiphenomenological techniques previously developed, the authors synthesize a diverse body of experimental and theoretical data on molecular hydrogen into sets of analytical electronimpact cross sections.
Abstract: Using the concept of the generalized oscillator strength in the Born‐Bethe approximation together with semiphenomenological techniques previously developed, we synthesize a diverse body of experimental and theoretical data on molecular hydrogen into sets of analytical electron‐impact cross sections. We include in our analysis discrete, vibrational, and dissociative excitations, together with direct and dissociative ionization. Once the important cross sections are known, it is then possible to trace the energy degradation of an incident electron upon molecular hydrogen. We give results for the electron loss function, efficiencies, and eV/ion pair together with comparison to available experimental data.
TL;DR: In this paper, a scheme for obtaining the statistical total energy in the multiple scattering formalism is presented, which is then carried out on the water molecule, which has been thoroughly investigated by ab initio LCAO MO SCF and experimental methods, in order to test the reliability of the method.
Abstract: A scheme for obtaining the statistical total energy in the multiple scattering formalism is presented. Calculations are then carried out on the water molecule, which has been thoroughly investigated by ab initio LCAO MO SCF and experimental methods, in order to test the reliability of the method. The one‐electron energies, ionization potentials, and vibrational potential curves are reported. Some advantages and limitations of the method are discussed in light of these results.
TL;DR: In this paper, the He I photoelectron spectra of the isoelectronic series of substituted benzenes toluene, aniline, phenol, and fluorobenzene have been measured and the ionization bands in the low binding energy region of the spectra have been identified and assigned.