Showing papers on "Ionization published in 1991"
TL;DR: In this paper, a review of applications of corona discharge induced plasmas and unipolar ions is presented, focusing on one of two aspects of the discharge: the ions produced or the energetic electrons producing the plasma.
Abstract: Applications of corona discharge induced plasmas and unipolar ions are reviewed. Corona process applications emphasize one of two aspects of the discharge: the ions produced or the energetic electrons producing the plasma. The ion identities depend on the polarity of the discharge and the characteristics of the gas mixture, specifically on the electron attaching species. The electron energies depend on the gas characteristics and on the method of generating the corona. In general, in an application using ions, the corona induced plasma zone will occupy a small fraction of the total process volume, while a process using the electrons will fill most of the volume with the plasma. Current state-of-the knowledge of ionized environments and the function of corona discharge processes are discussed in detail. >
820 citations
TL;DR: In this article, the dispersion relation for helicon waves in a uniform, bounded plasma is derived with both collisional and Landau damping, and it is shown that the latter can explain the very high absorption efficiency of helicon wave in plasma sources and can lead to plasma generators with a controlled primary electron energy.
Abstract: The dispersion relation for helicon waves in a uniform, bounded plasma is derived with both collisional and Landau damping. It is shown that the latter can explain the very high absorption efficiency of helicon waves in plasma sources and can lead to plasma generators with a controlled primary electron energy. The wave pattern and other features of helicon waves are pointed out.
531 citations
TL;DR: In this paper, cross sections for elastic, excitation, and ionization collisions of N+, N+2, N, and N2 with N2 and for Ar+ and Ar with Ar for laboratory energies from 0.1 eV to 10 keV are presented.
Abstract: Graphical and tabulated data and the associated bibliography are presented for cross sections for elastic, excitation, and ionization collisions of N+, N+2, N, and N2 with N2 and for Ar+ and Ar with Ar for laboratory energies from 0.1 eV to 10 keV. Where appropriate, drift velocities and reaction or excitation coefficients are calculated from the cross sections and recommended for use in analyses of swarm experiments and electrical discharges. In the case of N+ in N2, cross sections for momentum transfer, charge transfer, electronic excitation, and electron production are recommended. Drift velocity calculations predict runaway for N+ in N2 for electric field to gas density ratios E/n greater than 4.3×103 Td, where 1 Td (townsend)=10−21 V m2. For N+2 in N2, the cross sections include those for N+ and N+3 formation, electronic excitation, and electron production. Drift velocities and average cross sections are calculated for E/n≥500 Td. In the case of N in N2, only cross sections for momentum transfer are ...
520 citations
TL;DR: In this article, the isotopic abundances of tungsten with natural isotopic composition were determined by negative thermal ionization (NTI) in a double-filament ion source.
492 citations
TL;DR: In this article, a 1.053-μm, 1-psec Nd:glass laser was used to study the ionization of noble gases in the tunneling regime.
Abstract: Laser ionization of noble gases was studied with a 1.053-μm, 1-psec Nd:glass laser. A systematic scan of intensities from mid-1013 W/cm2 to mid-1016 W/cm2 was performed, resulting in the production of charge states as high as Xe12+. Ionization occurs exclusively in the tunneling regime. We compare experimental ion production rates with those predicted by several different theories. Agreement between experimental ion-production curves and theoretical predictions is good for two theoretical models: (1) an elaboration of the Keldysh tunneling model, developed by Ammosov et al. [ Sov. Phys. JETP64, 1191 ( 1986)] and (2) a much more primitive model, based on Coulomb-barrier suppression, in which tunneling and other quantum-mechanical effects are ignored completely. The success of the more primitive model suggests that a new term, barrier-suppression ionization, rather than tunneling or multiphoton ionization, may be the most appropriate at this wavelength and in this range of intensities.
416 citations
TL;DR: The electron momentum spectroscopy (EMS) as mentioned in this paper is a technique that uses electron-impact ionization reactions near the Bethe ridge at total energies of the order of 1000 eV or higher.
Abstract: Unique information about the motion and correlation of valence electrons in atoms, molecules and their ions is obtained from electron-impact ionization reactions near the Bethe ridge at total energies of the order of 1000 eV or higher. This is electron momentum spectroscopy. The history, theory and practice of the field are discussed and its value is shown by numerous examples.
416 citations
TL;DR: In this paper, a new mass selective method was developed for the determination of the optical spectra of molecular ions and for the production of state selected ions, which can be used for mass selection.
Abstract: The developement of a new mass selective method is reported for the determination of the optical spectra of molecular ions and for the production of state selected ions.(AIP)
372 citations
TL;DR: In this paper, the analytical expressions for the probability of tunnel ionization of atoms and atomic ions and for the energy and angular electron spectra in a strong low-frequency electromagnetic field are obtained.
Abstract: The analytic expressions for the probabilities of tunnel ionization of atoms and atomic ions and for the energy and angular electron spectra in a strong low-frequency electromagnetic field are obtained. The adiabatic approximation of quantum mechanics is used. The cases of linear and circular polarization of the field are considered.
344 citations
TL;DR: Improved estimates of the nonrelativistic stationary nucleus correlation energies of the ground-state atomic ions with three to ten electrons and up to 20 are derived by combining experimental data and improved calculations with relativistic complete-valence-space Hartree-Fock energies.
Abstract: Improved estimates of the nonrelativistic stationary nucleus correlation energies of the ground-state atomic ions with three to ten electrons and Z up to 20 are derived by combining experimental data and improved ab initio calculations. Unlike previous work in this area, we focus on the correlation contribution to individual ionization energies, computed by comparing experimental data with relativistic complete-valence-space Hartree-Fock energies.
317 citations
TL;DR: In this article, the MgKα X-ray and He(I)/He(II) ultraviolet (UPS) photoelectron spectra of several thin films of C 60 (one to three monolayers) prepared by vapor deposition on gold are reported.
305 citations
Patent•
IBM1
TL;DR: In this article, a hollow cylindrical sputter target is disposed between an end sputter and a substrate to create intense, plasma regions near the interior surface of the target and thereby causing ionization of sputtered neutrals.
Abstract: A sputter deposition system includes a hollow, cylindrical sputter target 14 disposed between an end sputter target 12 and a substrate 19, all of which are contained in a vacuum chamber 20. A plurality of magnets 24 are disposed outside the chamber 24 to create intense, plasma regions 48 near the interior surface of the cylindrical target 14 and thereby causing ionization of sputtered neutrals. Rf power is inductively coupled into the chamber 24 through rf coil 16 to sustain the plasma and substrate 19 is electrically biased to control ion directionality and energy.
TL;DR: In this article, a discussion of experimental and theoretical evidence of the two-centre electron emission (TCEE) is presented. But the use of heavy ions or antiprotons as projectiles allows to unravel these effects by monitoring the two centre potential.
Abstract: When an atom is ionized by ion impact, the electron is ejected into a final continuum state of a two-centre potential due to the Coulomb fields of the projectile and ionized atom. The related effects on the electron yield or energy and angular distributions are referred to as two-centre electron emission (TCEE). The present report is devoted to a discussion of experimental and theoretical evidence of this TCEE. The use of heavy ions or antiprotons as projectiles allows to unravel these effects by monitoring the two centre potential. On the theoretical side, the continuum distorted wave-eikonal initial state theory (CDW-EIS) accounts for the TCEE thus allowing a detailed interpretation of the experimental findings.
TL;DR: In this article, the Mg II 280.270-nm/Mg I 285.213-nm line intensity ratio is used to optimize the atomization and ionization processes in an inductively coupled plasma used as a source in atomic emission spectrometry.
TL;DR: In this paper, several techniques for extending the mass/charge range of the quadrupole ion trap were presented, including the use of smaller electrodes, operation at lower radio frequencies, and resonance ion ejection using a voltage of appropriate frequency, applied symmetrically across the end-cap electrodes during the mass scan.
TL;DR: In this paper, a framework for the theoretical description of two-pulse time-resolved ionization spectroscopy of ultrafast excited-state dynamics of polyatomic molecules is developed.
Abstract: A framework for the theoretical description of two‐pulse time‐resolved ionization spectroscopy of ultrafast excited‐state dynamics of polyatomic molecules is developed. The radiation–matter interaction as well as intramolecular couplings in the excited‐state manifold are treated nonperturbatively by solving the time‐dependent Schrodinger equation. The numerical solution is based on a discretization of the ionization continua which becomes particularly efficient for ultrashort laser pulses. With this method converged computations of ionization signals become possible even for complex molecular systems. Computer simulations are performed for a model system representing three‐dimensional non‐Born–Oppenheimer excited‐state dynamics on conically intersecting potential‐energy surfaces (the S1 and S2 surfaces of pyrazine). The dependence of the observable time‐resolved ionization signals (total ion yield as well as photoelectron spectrum) on the properties of the laser pulses (carrier frequency and pulse duratio...
TL;DR: Femtosecond pump-probe techniques are combined with time-of-flight spectroscopy to measure transient ionization spectra of Na 2 in a molecular-beam experiment and it is reported that incoherent contributions from direct photoionization of a singly excited state and from excitation and autoionization from a bound doubly excited molecular state determine the observed transient Ionization signal.
Abstract: We report here the first experimental study of femtosecond time-resolved molecular multiphoton ionization. Femtosecond pump-probe techniques are combined with time-of-flight spectroscopy to measure transient ionization spectra of ${\mathrm{Na}}_{2}$ in a molecular-beam experiment. The wave-packet motions in different molecular potentials show that incoherent contributions from direct photoionization of a singly excited state and from excitation and autoionization of a bound doubly excited molecular state determine the observed transient ionization signal.
TL;DR: The first direct experimental evidence for clathrate structures of (H2O)nH+ (n=20,21) is reported based on a technique allowing the number of nonhydrogen-bonded surface hydrogens to be counted.
Abstract: First direct experimental evidence for clathrate structures of (H2O)nH+ (n=20,21) is reported based on a technique allowing the number of nonhydrogen‐bonded surface hydrogens to be counted. Neutral clusters (H2O)n⋅((CH3)3N)m, prepared in a pulsed nozzle supersonic expansion, are ionized by multiphoton ionization and investigated with a reflectron time‐of‐flight mass spectrometry technique. The magic numbers (n,m) in the ion intensity distributions of (H2O)n⋅((CH3)3N)m⋅H+ studied under various experimental conditions are well correlated to the stable hydrogen‐bonding structures. For the mixed cluster ion (H2O)20⋅((CH3)3N)m⋅H+, the intensity distribution displays an abrupt intensity drop after the magic number at (20,11), while for (H2O)21⋅((CH3)3N)m⋅H+ the magic number appears at (21,10). The findings provide experimental evidence for a stable clathrate structure of (H2O)20H+, with the proton residing on the surface, while for (H2O)21H+, the H3O+ ion is encaged inside the clathrate structure of (H2O)20; th...
TL;DR: In this paper, a hybrid fluid-particle (Monte Carlo) model to describe the initiation of pseudospark discharges has been developed, where time-dependent fluid equations for the electrons and positive ions are solved self-consistently with Poisson's equation for the electric field in a two-dimensional, cylindrically symmetrical geometry.
Abstract: A hybrid fluid-particle (Monte Carlo) model to describe the initiation of pseudospark discharges has been developed. In this model, time-dependent fluid equations for the electrons and positive ions are solved self-consistently with Poisson's equation for the electric field in a two-dimensional, cylindrically symmetrical geometry. The Monte Carlo simulation is used to determine the ionization source term in the fluid equations. This model has been used to study the evolution of a discharge in helium at 0.5 torr, with an applied voltage of 2 kV and in a typical pseudospark geometry. From the numerical results, the authors have identified a sequence of physical events that lead to the rapid rise in current associated with the onset of the pseudospark discharge mode. They find that there is a maximum in the electron multiplication at the time which corresponds to the onset of the hollow cathode effect, and although the multiplication later decreases, it is always greater than needed for a steady-state discharge. >
TL;DR: An overview of the current understanding of multiphoton ionization of atoms can be found in this article, where a large part of the review is devoted to some nonperturbative theories.
Abstract: Presents an overview of the current understanding of multiphoton ionization of atoms. It begins with an introductory section to explain the background of the subject. Then the article develops the three topics which have been central themes of discussion in multiphoton ionization of atoms these past few years: multiply charged ion production, very high order harmonic generation, and above-threshold ionization, a name given to the absorption of a very large number of photons by an already ionized electron. A large part of the review is devoted to some theoretical aspects of multiphoton ionization of atoms and especially non-perturbative theories. Finally the article considers the very near future prospects of laser-electron interactions and more generally laser-matter interactions at 1018-1019 W cm-2, an intensity range now within reach due to new short pulse laser technology.
TL;DR: The ionization potentials of several large carbon clusters Cn (n ≥ 48), including the enhanced abundance (‘‘magic number’’) clusters C50, C60, and C70, have been determined by Fourier transform ion cyclotron resonance (FTICR) mass spectrometric charge transfer bracketing experiments.
Abstract: The ionization potentials (IPs) of several large carbon clusters Cn (n≥48), including the enhanced abundance (‘‘magic number’’) clusters C50, C60, and C70, have been determined by Fourier transform ion cyclotron resonance (FTICR) mass spectrometric charge transfer bracketing experiments. The IPs of C50, C60, and C70 were bracketed by the same two charge transfer compounds, leading to a common value of 7.61±0.11 eV. The IPs of even numbered clusters adjacent to these magic number clusters were found to be lower by as much as 0.5 eV and all clusters between C50 and C200 were determined to have IPs greater than 6.20 eV. The reaction rates of C+60 and C+70 with metallocenes were anomalously slow in comparison to the other large carbon cluster ions. IP and reactivity results suggest that C50, C60, and C70 may indeed have different or more stable structures than neighboring clusters, which supports the hypothesis of closed‐shell, spherical species. The implications of these results for the mechanism of C+n formation by direct laser vaporization are also discussed.
TL;DR: In this article, the electron avalanche ionization in water was considered experimentally and theoretically, and the effect appeared to be due to electron avalanches ionization due to the dependence of the breakdown probability on the laser field.
Abstract: Dielectric breakdown induced in water by Nd: YAG laser pulses is considered experimentally and theoretically. The effect appears to be due to electron avalanche ionization. The aspects of this process considered here are the following: (i) The dependence of the breakdown probability on the laser field. At high fields, electron interaction with molecular (Raman) vibrations or with collective molecular motions occurs. (ii) Bragg scattering, which contributes to keeping the electron motion in phase with the optical field. (iii) The role of the electron mobility, which contributes to stabilizing the process. (iv) The generation of the electrons that start the avalanche in relation to different laser-pulse durations and irradiances.
TL;DR: In this paper, nighttime ionospheric electrons at 90-95 km altitude were found to be heated by a factor of 100-500 during the upward passage of short (< 100 μs) pulses of intense (5-20 V/m at 100 km distance) electromagnetic radiation from lightning.
Abstract: Nighttime ionospheric electrons at 90–95 km altitude are found to be heated by a factor of 100–500 during the upward passage of short (< 100 μs) pulses of intense (5–20 V/m at 100 km distance) electromagnetic radiation from lightning. Heated electrons with average energy of 4–20 eV in turn produce secondary ionization, of up to 400 cm−3 at ∼95 km altitude in a single ionization cycle (∼3 μs). With the time constant of heating being 5–10 μs, a number of such ionization cycles can occur during a 50 μs, radiation pulse, leading to even higher density enhancements. This effect can account for previously reported observations of ‘early’ or ‘fast’ subionospheric VLF perturbations.
TL;DR: In this paper, a stable triangular structure for the neutral benzene trimer was established and a sandwich-like structure for trimer ion was shown to have high binding energy in the presence of a delocalized charge.
TL;DR: The above threshold ionization (ATI) phenomenon was discovered in 1979 and is now expected to be a universal phenomenon observable in all atomic species as discussed by the authors, at intensities above 1 TW/cm 2.
TL;DR: In this paper, the latest most important developments in (e, 2e) studies are reviewed from an experimental point of view, including ionization processes near threshold, symmetric energy sharing collisions involving double scattering mechanisms, core states ionization, measurements for autoionizing states and for the simultaneous excitation and ionization of the target.
Abstract: The latest, most important developments in (e,2e) studies are reviewed from an experimental point of view. These include ionization processes near threshold, the symmetric energy sharing collisions involving double scattering mechanisms, core states ionization, (e,2e) measurements for autoionizing states and for the simultaneous excitation and ionization of the target. Double ionizing processes with coincidence detection of two or three electrons in the final state are also reviewed, including (e,e'-Auger) experiments and the new born (e,(3-1)e) and (e,3e) domain.
TL;DR: The new plasma diagnostic technique of spectral blueshifting of femtosecond pulses is used for the first time to analyze quantitatively the ionization of noble gases under the influence of intense, femTosecond illumination.
Abstract: The new plasma diagnostic technique of spectral blueshifting of femtosecond pulses is used for the first time to analyze quantitatively the ionization of noble gases under the influence of intense, femtosecond illumination. The two processes of strong-field tunneling ionization and electron impact ionization are found to play competing roles on these time scales
TL;DR: In this article, radioastronomical measurements are synthesized to derive a large-scale Galactic model for the distribution of free electrons and for microstructure in the distribution that seems to be caused by turbulence in the ISM.
Abstract: Various radioastronomical measurements are synthesized here to derive a large-scale Galactic model for the distribution of free electrons and for microstructure in the distribution that seems to be caused by turbulence in the ISM. A two-component axisymmetric model fitted on all scales from 100 km to a few pc, accounts for most of the data. A population of dense, discrete clouds is also needed, and there is some evidence for spiral structure. The model allows better distance estimates for pulsars to be made. The implications of the model for the structure and ionization of the ISM and for the distribution of interstellar turbulence and the diffusion of cosmic rays are discussed.
TL;DR: The above threshold ionization (ATI) phenomenon was first investigated in this paper, where the electron energy spectrum changes from a single, well defined threshold peak into multiple peaks, separated from one another by the photon energy.
Abstract: At very high light intensities, the electron energy spectrum in multiphoton ionization (MPI) spectroscopy of even the simplest atoms changes from a single, well defined threshold peak into multiple peaks, separated from one another by the photon energy. This phenomenon is generally referred to as 'above-threshold ionization' (ATI). The original experiments investigating ATI used relatively long laser pulses, with the result that amplitudes, energy widths and angular distributions of the individual photoelectron peaks depended on the laser intensity. In addition, the widths of the peaks, as well as their absolute energy positions, changed according to the temporal width of the laser pulse. These dependencies were not intrinsic to the ionization process, but rather were all eventually ascribed to ponderomotive forces exerted on free photoelectrons by the laser focus. The ponderomotive effects frustrated comparisons between theoretical calculations and experimental data.
TL;DR: In this paper, the lifetime of the lowest triplet state of the two most stable fullerenes, C 60 and C 70, was measured in a supersonic beam by two-color resonant two-photon ionization.
TL;DR: Delayed ionization with average lifetimes on the order of several \ensuremath{mu}sec has been observed for two-photon 308-mn excimer laser ionization of ${\mathrm{C}}_{60}$ and ${ \mathrm{\mu}_{70}$ as mentioned in this paper.
Abstract: Delayed ionization with average lifetimes on the order of several \ensuremath{\mu}sec has been observed for two-photon 308-mn excimer laser ionization of ${\mathrm{C}}_{60}$ and ${\mathrm{C}}_{70}$.