Abstract: The coupled partial differential equations used to describe the behavior of impurity ions in magnetically confined controlled fusion plasmas require numerical solution for cases of practical intere...

Abstract: Experimental and theoretical cross section data for electron impact ionization of light atoms and ions have been assessed. Based on this assessment and, in some cases, on the classical scaling laws, a recommended cross section has been produced for each species. This has been used to evaluate recommended Maxwellian rate coefficients over a wide range of temperatures. Convenient analytic expressions have been obtained for the recommended cross sections and rate coefficients. The data are presented in both graphical and tabular form and estimates of the reliability of the recommended data are given.

Abstract: Copper clusters ranging in size from 1 to 29 atoms have been prepared in a supersonic beam by laser vaporization of a rotating copper target rod within the throat of a pulsed supersonic nozzle using helium for the carrier gas. The clusters were cooled extensively in the supersonic expansion [T(translational) 1 to 4 K, T(rotational)=4 K, T(vibrational)=20 to 70 K]. These clusters were detected in the supersonic beam by laser photoionization with time‐of‐flight mass analysis. Using a number of fixed frequency outputs of an exciplex laser, the threshold behavior of the photoionization cross section was monitored as a function of cluster size. The 7.9 eV photon energy of the F2 excimer laser was found to be above the ionization potential of all clusters, and the photoion mass spectrum thus produced showed the copper cluster concentration in the beam to follow a monotonically decreasing function of cluster size. The 6.4 eV ArF exciplex laser photon energy was found to be above the photoionization threshold of clusters with three or more atoms in the case of odd‐numbered clusters, but only for clusters with eight or more atoms for even‐numbered clusters. Extending out to clusters as large as 29 atoms, laser photoionization at 6.4 eV produced a time‐of‐flight mass distribution with a pronounced even/odd alternation in cluster photoion intensity. This alternation in ionization threshold behavior was attributed to an even/odd alternation in the electronic structure of the copper clusters with the highest occupied molecular orbital (HOMO) of the even clusters being considerably more strongly bonding than it is in the clusters with an odd number of copper atoms. The 4.98 eV photon energy of the KrF exciplex laser was found to lie below the ionization threshold of all clusters in the 1 to 29 atom range. An extensive survey of the ultraviolet absorption spectrum of the copper dimer was also performed with this supersonic beam source. Resonance two‐photon ionization (R2PI) with mass selective detection allowed the detection of five new electronic band systems in the region between 2690 and 3200 A, for each of the three naturally occurring isotopic forms of Cu2. In the process of scanning the R2PI spectrum of these new electronic states, the ionization potential of the copper dimer was determined to be 7.894±0.015 eV.

Abstract: A comprehensive theoretical model of both the auroral and nonauroral atmosphere and ionosphere of Jupiter is presented and used to study particle precipitation effects in the Jovian upper atmosphere, both at middle and high latitudes. The sources of energy in the model include extreme ultraviolet radiation and energetic electrons. The precipitation of monoenergetic beams of both one and ten keV electrons at high Jovian latitudes are treated in detail, and the effects of higher energy electrons and soft electrons at middle and low latitudes are considered. The effects of this precipitation, such as airglow excitation, ionization, dissociation, and heating are examined. Calculations of the densities of hydrogen, hydrocarbons, and the important ions as well as the temperatures of the neutral, electron, and ion species are included.

Abstract: The theory of the staircase avalanche photodiode (APD) is presented and recent results on a new class of APD's with enhanced ratio of ionization coefficients are reviewed. The staircase APD consists of a multistage graded gap structure where only electrons ionize; the entire ionization energy is provided by large conduction band steps (dynodes). A general expression for the excess noise factor F in terms of the number of stages and the multiplication per stage is presented. For high ionization yields per dynode the F factor is near unity independently of the number of stages, implying virtually noise free multiplication at high gain similar to a photomultiplier. This cannot be achieved in a conventional APD at high gain even if one of the ionization coefficients is zero. A comparison between the noise behavior of the staircase APD and that of a phototube is also presented. A microscopic theory of the ionization yield γ is discussed; to obtain a high γ electrons must approach the dynode with an energy in the order of ten times the optical phonon energy. The possible problem of residual hole-initiated ionization is also discussed. Formulas for the electron and hole initiated multiplications are derived; from a measurement of these quantities one can directly obtain the ionization yield and the residual hole ionization coefficient. Experimental and theoretical results on other structures (superlattice, channeling, graded gap APD's) with high \alpha/\beta ratio are also reviewed and design considerations for a long-wavelength multilayer APD are presented.

Abstract: Gas phase spectroscopic studies of copper trimer are reported. A band system in the 5430–5225 A region has been assigned to Cu3 and has been studied by resonant two‐photon ionization spectroscopy, spectroscopy by depletion through predissociation, and by radiation repopulation of excited vibrational states in a cold supersonic molecular beam. The spectrum fits well to a 2E″←2E′ transition of a D3h molecule with both states undergoing Jahn–Teller distortions. In this interpretation, the excited state is well described by a weak Jahn–Teller effect, stabilizing the molecule at a configuration in which one Cu–Cu bond length differs from the others by 0.03 A, with a Jahn–Teller stabilization energy of 9 cm−1. The ground electronic state corresponds to a deep Jahn–Teller situation with the lowest vibronic levels trapped in the distorted configuration. The spectra indicate the tunneling splitting of the lowest vibrational levels in the ground state is 12±7 cm−1. These assignments are based on measured vibrationa...

Abstract: Monte Carlo simulations of electron impact ionization in silicon are presented which include the pseudopotential band structure as well as collision broadening and higher order effects in the electron phonon interaction. Conduction in the two lowest conduction bands of silicon is considered. We also present new results for the impact ionization probability and deformation potential constants which are obtained by comparing our theory with a variety of experimental results.

Abstract: A simple analytic expression for the ionisation coefficient for impact ionisation is derived on the basis of a new approach which exploits the difference between momentum- and energy-relaxation rates for hot electrons. The basic mechanism whereby an electron gains sufficient energy to ionise is lucky to drift in which the electrons relax momentum but not energy. The electrons gain energy by drift and not by ballistic motion, and a few lucky ones reach the threshold. Those which thermalise may also contribute through the lucky-drift mechanism, starting from the average hot-electron energy. Good agreement with Baraff's theory is obtained. It is shown that neither the Schockley lucky electron nor the Wolff thermalised electron contribute significantly, in agreement with Baraff. However, the concept of Schockley's lucky electron is an essential part of the lucky-drift mechanism. The theory is simply extended to accommodate electrons injected at energies above zero, and some calculations are presented on this topic. A discussion is given of the effect of real band structure and it is concluded that the theory based on parabolic bands remains good provided the mean free path is taken as an average quantity over the relevant energy range. It is argued that the theory has wide application to semiconductors with moderate-to-large energy gaps because of the predominance of nonpolar scattering at high energies. A specific model of a nonparabolic band structure is discussed in which the electron distribution function has a Gaussian form, rather than the Maxwellian form associated with parabolic bands, and a weak negative differential resistance is exhibited.

Abstract: Soft-x-ray excitation involving C $1s$ electrons in CO and acetone, ${(\mathrm{C}{\mathrm{H}}_{3})}_{2}$CO, is found to result in ionic fragmentation of the original molecule. The fragmentation pattern changes whether the C $1s$ electron gets ionized or excited into a Rydberg-line orbital or into an antibonding ${\ensuremath{\pi}}^{*}$ molecular orbital. Moreover, the fragmentation occurs specifically around the site of the carbon atom where the optical excitation takes place. Based on these observations one might consider the use of tunable soft x rays to stimulate chemical reactions or to selectively break large organic molecules.

Abstract: Available data on the electron transport properties and electron swarm coefficients are discussed for the following electronegative gases: SF6, CF4, C2F6, C3F8, C4F10, CCl2F2, O2, air, H2O, CO2, F2, NF3, Cl2, Br2, I2, N2O, NO, HCl, NH3. Graphical presentations comparing measured and calculated data are given for the electron drift velocity, the ratio of diffusion to mobility, the electron attachment and ionization coefficients, and the electron growth constant as functions of E/N, the reduced field strength, for each gas. Graphs of the detachment and excitation coefficients are presented where these data are available. Data originally reported in terms of rate coefficients as functions of mean electron energy are graphically presented in that form. Recommendations concerning reliability are made.

Abstract: Presentation des differentes techniques d'ionisation pour la spectrometrie de masse. Mecanismes

Abstract: SiHn radical densities at the surface of discharges in Ar‐SiH4 mixtures have been measured by low‐energy, electron‐collisional ionization and mass spectrometer detection of SiH+n. The principal radical seen at the substrate surface of a dc proximity discharge is SiH3.

Abstract: Recent developments in laser and molecular beam technology have now made it possible to produce supersonic beams of virtually any element in the periodic table. Using laser vaporization of the appropriate target, the beam source conditions may be adjusted to produce either the cold free atoms alone, or clusters of these atoms with each other—or with another element. Since the vaporization laser heats only a small spot on the target, extremely high local temperatures can be obtained without heating any other part of the apparatus; and beams of even the highest boiling element (tungsten) are readily obtained both in atomic and cluster form. The physics and chemistry of these exotic cluster species is almost completely unknown on the fundamental level. Even for clusters containing 100 atoms, most of these atoms lie on the surface, and the chemical and physical properties will be predominately surface phenomena. Initial studies of these clusters have entailed the use of one- and two- photon laser ionization with time-of-flight mass selective detection. Using a variety of fixed frequency lasers, the work function of copper clusters has been examined as a function of cluster size in the range from 2 to 29 atoms per cluster. Considerable detailed information has also been obtained for the electronic structure and bond lengths of a number of transition metal dimers and trimers (including Cu2, Cr2, V2, Mo2, and Cu3) through the use of high resolution laser spectroscopy with mass-selective photoionization detection.

Abstract: Metastable He(2 1S) and Ne(3P2,0) beams were used to probe the electronic properties of Ni(111) and CO/Ni(111) surfaces. The metastable atoms collide with the surface and transfer their electronic excitation energy, causing electron ejection. With the Ni(111) surface, the metastable is first resonantly ionized and the ion is subsequently Auger neutralized, giving an electron energy spectrum which is similar to the corresponding low kinetic energy ion neutralization spectrum (INS). Differences between the metastable quenching spectrum and the INS spectrum were observed, and are discussed in terms of the differences in the mechanisms and the ion kinetic energies. With a CO/Ni(111) surface, the CO eliminates direct interaction of the metastable atom with the metal and the surface Penning ionization electron spectrum (SPIES) is obtained. The SPIES spectrum is much more surface sensitive than the corresponding UPS spectrum, since there is no background due to primary electron emission from the metal which domi...

Abstract: The 'frozen' solar wind ionization state within a few solar radii of the photosphere suggests that ion measurements at 1 AU may yield information on the electron temperature conditions at the base of the coronal expansion. The freezing-in process is examined in light of traditional assumptions as to coronal expansion, where electron temperature decreases monotonically with height, the bulk flow of all charge states of a given ion species are equal to the proton speed, and the ion outflow is spherically symmetric. The consequences of the relaxation of these assumptions include the underestimation of the magnitude of a temperature maximum occurring near the freezing-in radius. Because it is associated with high speed, low density flow, an areal divergence that is faster than that in a spherical outflow lowers the ionization state freezing-in level relative to that which is typical in spherically symmetric expansion.

Abstract: The dual fluorescence in polar solvents of 9,9′-bianthryl (BA) and of the electronically perturbed BA-derivatives 10-chloro-BA (BACl), BA-10-carboxaldehyde (BAA) and N-(9-anthryl)-carbazole (C9A) as well as of N-(4-cyanophenyl)-carbazole (CBN) is analysed and interpreted in terms of a simplified microstructural solvent interaction model. Dipole moments μT relative to μT (CBN) of the fluorescent charge transfer state have been derived from the solvatochromic band shifts in nitrile and alcohol homologous solvent series and are similar for BA, BACl and C9A. This implies that the charge transfer in the excited state occurs to a maximum degree even in the symmetric molecule BA. – QCFF/PI-potential energy curves have been calculated and are used to discuss these findings. BAA fluoresces in alcohols only, μT-compared to the other compounds studied being somewhat smaller probably because of specific H-bond interactions with the solvent. – Using relative fluorescence quantum yields and energetic considerations the dependence of the excited states equilibrium on both solvent polarity and solute perturbation is discussed.

Abstract: In this paper, we present the theory of photoelectron angular distributions in resonant multiphoton ionization that rigorously takes into account the saturation, ac Stark-shift, and the laser-linewidth effects. The influence of these effects on the distribution is incorporated through the coupling equations between the angle-resolved ionization probabilities and the (time-dependent) bound-state density-matrix elements. General expressions for the angular distributions are derived and several properties of these distributions are arrived at from these expressions. Finally, numerical results are presented to illustrate the effects of saturation, of ac Stark shifts, and of the laser line shape.

Abstract: Range type spread F indices in the post sunset hours, determined from ionograms, are compared with F layer vertical velocities, also deduced from ionograms, for a period of one year, over the magnetic equatorial station Fortaleza (geographic coordinates: 4/sup 0/S, 38/sup 0/W; dip latitude: 1.8/sup 0/S), Brazil. Besides good correlation between the two parameters, the results suggest the presence of a certain threshold value for the vertical ionization velocity and a corresponding threshold height for the base of the evening F layer, as one of the necessary conditions for the occurrence of spread F irregularities valid for southern solstice (summer) and equinoctial months. The nature of the possible variabilities in the amplitude of the initial perturbation in the ionization (seeding mechanism), which is another prerequisite for the generation of irregularities, is discussed briefly.

Abstract: Coupled-state calculations based upon a two-center expansion in atomic orbitals and pseudostates have been performed for H/sup +/ + H in the 1--75-keV region. Cross sections for excitation and charge transfer to n = 2 states as well as total ionization cross sections are reported. It is shown that the calculated cross sections are not sensitive to the specific set of pseudostates included if the low-energy continuum states are reasonably well represented. The present results compare favorably with several sets of experimental data and with some large-scale calculations. The need for further experimental data in some areas is discussed.

Abstract: Potential Energy Surfaces and Theory of Unimolecular Dissociation.- Scanning Methods for Double-Focussing Mass Spectrometers.- Charge Exchange Mass Spectrometry.- Isotope Exchange in Ion-Molecule Reactions.- Energetics and Dynamics of Ion-Molecule Reactions at Thermal Energies.- Recent Studies of Gas-Phase Reactions of Anions with Organic Molecules.- Gas-Phase Studies of the Influence of Solvation on Ion Reactivity.- Exothermic Bimolecular Ion Molecule Reactions with Negative Temperature Dependence.- Spectroscopic Structure and Radiationless Decay of Open-Shell Organic Cations.- Gas-Phase Ion Photodissociation.- Dissociation Dynamics of Energy Selected Ions Studied by one and Multiphoton Ionization.- Sift-Drift Studies of Anions.- Determinations of Gas-Phase Organic Ion Structures.- Carbon Skeletal Rearrangements Via Pyramidal Carbocations.- Low Rate Fragmentation Reactions of Gaseous Ions.- Applications of the Franck-Condon Factors to Polyatomic Molecules.- Ion Clusters: Summary of The Panel Discussion.- Ion Thermochemistry: Summary of the Panel Discussion.- Instrumentation: Summary of the Panel Discussion.

Abstract: We report measurements of photoelectron spectra of an electronically excited state of H2 (B 1Σ+u) in selected vibrational and rotational levels The excited state was prepared by resonant three photon excitation of H2 X 1Σ+g, v=0, J=3 and subsequently was ionized by a single additional photon Partially resolved rotational structure is observed in the photoelectron spectra and is discussed in terms of the selection rules for direct photoionization and the partial wave composition of the ejected photoelectrons An additional peak is observed in the spectra, which is tentatively interpreted as arising from photoionization of H*(n=2) formed by photodissociation of H2 in the B 1Σ+u state