Abstract: Velocity spectra of electrons emitted into the forward direction have been measured for 0.7--8.5-MeV/u projectile ions traversing He, Ne, and Ar targets, polycrystalline solids (C, Al, Ag, Au), and axial channels in gold. Spectral shapes and yields are compared and contrasted with one another and with theories which seek to account for the cusp-shaped peaks observed in terms of electron capture and loss to low-lying projectile-centered continuum states. We report the results of both singles and coincidence measurements, where the dependence of cusp shapes and yields on the emergent-ion charge state are examined. For electron capture to the continuum (ECC), variance is noted with respect to the simple, first-order theory of Dettmann, Harrison, and Lucas. The ECC yields are compared to experimental and theoretical studies of bound-state capture, especially to high Rydberg states. For electron loss to low-lying continuum states (ELC), variance is noted with respect to the corresponding theories of Briggs, Drepper, and Day, and ELC cross sections are compared to total electron-loss cross sections. For convoy electron production in solids, no known theory accounts for the results. As in ELC processes, convoy cusp widths are observed to be velocity independent. Convoy electron yields are also observed to bemore » independent of emergent-ion charge state.« less

Abstract: The electron and hole ionization coefficients α and β in (100) InP have been determined through analysis of photomultiplication data on p+‐n and n+‐p junctions grown by liquid phase epitaxy (LPE). A special device structure is described which allows reproducible thinning of the substrate in order to achieve pure carrier injection from either side of the p‐n junction. By fabricating wafers with depletion layer doping levels from 1.2×1015 to 1.2×1017 cm−3, α and β have been determined over a wider range of electric fields than previously reported. The ratio of β/α decreases from 4.0 to 1.3 as the electric field is increased from 2.4 to 7.7×105 V/cm.

Abstract: A sensitive method is demonstrated for determining (v'',J'') populations of H/sub 2/. Single rotational levels of the E,F /sup 1/..sigma../sup +//sub g/ state are prepared by two-photon excitation; absorption of a third quantum causes ionization. Detection of J'' levels of v'' = 0, 1, and 2 is possible while scanning the dye laser fundamental over just 5 nm. Measured rotational populations at different temperatures (295--750 K) agree well with the corresponding Boltzmann distributions. Rotational line strengths show almost no J'' dependence for this process.

Abstract: Fundamental Mechanisms of Laser-Enhanced Ionization: The Production of Ions (O Axner & H Rubinsztein-Dunlop) Fundamental Mechanisms of Laser-Enhanced Ionization: Signal Detection (J Travis & G Turk) Analytical Performance of Laser-Enhanced Ionization in Flames (G Turk) Applications of Laser-Enhanced Ionization Spectrometry (R Green) Non Flame Reservoirs for Laser-Enhanced Ionization Spectrometry (N Zorov) Ions and Photons: Interplay of Laser-Induced Ionization and Fluorescence Techniques in Different Atomic and Molecular Reservoirs (N Omenetto & P Farnsworth) Index

Abstract: Argon clusters were produced in a free supersonic molecular beam expansion of pure argon at room temperature and the photoionization efficiency curves of the trimer through hexamer were measured in the wavelength regions from threshold to 700 A. A study of the Ar+3 photoionization efficiency curve as a function of nozzle stagnation pressure shows that fragmentation of heavier clusters can dominate the spectrum, even near threshold, and even when the nozzle conditions are such that the Ar+4 intensity is only a small fraction of the Ar+3 intensity. The Ar+3 photoionization efficiency curve, obtained using nozzle stagnation conditions such that no heavier ions were detected, exhibits several broad peaks near threshold which show similarities to bands of the dimer. At high nozzle stagnation pressures, the photoionization efficiency curves for Ar+3 to Ar+6 are nearly identical due to the effects of fragmentation. These spectra exhibit two very broad features which are similar to features observed in the solid....

Abstract: Dual sets of Monte Carlo computations were made for electrons in water to assess differences due to the state of condensation. The GSF computer code was used for the vapor and the ORNL code for the liquid. The underlying physical differences specifically incorporated into the liquid code are discussed. At electron energies greater than or equal to 50 eV, ionization is considerably more efficient in the liquid than in the vapor, the high-energy W values for the two phases being 24.6 and 30.0 eV/ip. Above 50 eV, the Fano factor is about half as large in the liquid as in the vapor. The single-collision spectrum in the liquid is harder, giving a greater stopping power in the range 50 to 10/sup 4/ eV, beyond which the liquid and vapor stopping powers merge. Slowing down spectra for 10/sup 3/- and 10/sup 4/-eV electrons and depth-dose curves for 1-keV electrons are calculated. In addition, the radial dose distributions around electron paths in liquid and vapor are compared.

Abstract: ing's vector it follows that the light amplitude at the focal spot would reach 108 volts per centimeter, comparable to the electric field internal to the atoms and molecules responsible for the binding of valence electrons. These are literally pulled out of their orbits in multiphoton tunneling processes, and any material will be converted to a highly ionized dense plasma at these flux densities. It is clear that the familiar notion of a linear optical response with a constant index of refraction, that is, an induced polarization proportional to the amplitude of the light field, should be dropped at much less extreme intensities. There is a nonlinearity in the constitutive relationship which may be expanded in terms of a power series in the electric field components

Abstract: In this work, we report the study of bimolecular and termolecular charge transfer and Penning ionization reactions in He–N2 mixtures excited by repetitive 3 kA, 7 ns duration discharges. He(2 3S) destruction frequencies have been determined from measurements of the optical absorption of the 2 3S→3 3P helium transition and were found to correlate with the late‐time decay rate of the N2+(B 2Σu→X 2Σg) fluorescence. The much more intense early‐time fluorescence was ascribed to charge transfer from He2+. The values found for the bimolecular and termolecular charge transfer reactions were, respectively, (1.1±0.1)×10−9 cm3 s−1 and (1.36±0.20)×10−29 cm6 s−1, while the corresponding values for the Penning reactions were (7.6±0.4)×10−11 cm3 s−1 and (3.3±0.3)×10−30 cm6 s−1. Branching ratios for producing the N2+(B 2Σu) state in these reactions are discussed. A comprehensive kinetic model of the He–N2 afterglow has been formulated which was able to reproduce all the experimental data obtained as functions of helium p...

Abstract: Calculations have been performed which demonstrate the possibility of operating poloidal divertors at high densities and low temperatures. Ionization of recycling neutral gas near the divertor neutralizer plate amplifies the input particle flux thereby raising the plasma density and lowering the plasma temperature. Low-temperature, high-density operation should reduce the erosion rate of the divertor walls and plate, and ease the pumping requirements in future large tokamaks.

Abstract: Molecular multiphoton ionization experiments are reported for the first time in a flame environment. The resonantly enhanced two‐photon photoionization spectrum of NO from 270 to 317 nm in an atmospheric pressure H2/air/N2O flame is essentially identical with respect to both line position and intensity to that which is predicted for the one‐photon absorption to the intermediate A state. A model is developed here which accounts for this result by including rates for collisional repopulation of the laser depleted state. Based on this model, the rotational transfer rate constant for NO is estimated to be ⩾4×109 s−1 in the flame, corresponding to a cross section of ∼70 A2. It is found that the photoionization spectra obtained in this work have far better signal‐to‐noise and resolution than those reported for NO in flames using laser‐induced fluorescence methods and that the estimated detection limit for NO is 1 ppm.

Abstract: The excitation of electronic transitions in matter by a group of swift ions traveling close together and at nearly the same velocity may depend on the spatial configuration of ions making up the cluster. We have studied theoretically the effect of configuration on the interactions of clusters with an electron gas and in collisions with single atoms (vicinage effect). The latter case is explored using a classical harmonic-oscillator model and with quantum-mechanical perturbation theory. We discuss similarities between the vicinage function for energy loss of a swift cluster in the electron gas and that for the same cluster colliding with a system of noninteracting atoms at condensed-matter density. The aligning effect of the wake potential on the trailing ion of a dicluster penetrating a solid target, as first observed by Gemmell et al., is not expected to occur in cluster collision with single atoms, and does not occur in collision with gases at ordinary pressures. Aligning forces comparable with those in solids require target densities of the same order of magnitude as those occurring in condensed matter. The data of Lurio, Anderson, and Feldman taken in a search for vicinage effects in inner-shell excitation are discussed. The effect of wakemore » fluctuations on cluster energy loss is shown to be negligible under ordinary conditions. We evaluate the effect of residual molecular ionic structure on cluster energy loss.« less

Abstract: In previous model calculations for multiphoton dissociation (MPD) either no assumption is made about the dynamics of the MPD process or it is assumed that first energy is deposited by the laser solely in parent ions which then, depending on their energy, partition into products. No products are produced during the laser pulse. In the present approach competition between the unimolecular reaction and photon-absorption during the light pulse was taken as a new ansatz in modelling multiphoton dissociation mass spectra. We treat the case that the unimolecuiar reaction rates will become so fast with increasing excitation energy that the competition for further photon-absorption stops at a certain amount of excitation energy thus leading to a cut-off in the excitation ladder and to a switch to a new ladder of product ions for further photon-absorption. The effectiveness of primary to secondary ion conversion and the influence on fragmentation pathways are discussed qualitatively in comparison with other statistical models which involve a separate treatment of excitation and fragmentation. The model is applied to calculate the light intensity dependence of the benzene (MPD) mass spectrum at 2590 A laser wavelength. RRKM calculations for benzene and its products are performed in order to check the ladder switching assumption. Theoretically computed MPD mass spectra agree well with the experimental ones.

Abstract: Photoejection of both electrons from the H/sup -/ ion by a single incident photon has been observed with use of a crossed relativistic beam technique. The dipole selection rules for a single-photon pick out the /sup 1/P/sup 0/ final state. The relative cross section was measured over a 0.30 eV range of photon energies near threshold in steps of 0.007 eV with a resolution of 0.007 eV full width at half maximum. The energy dependence of the cross section in this region was consistent with a Wannier threshold law.

Abstract: A derivation of the explicit form of the threshold law for electron impact ionization of atoms is presented, based on the Coulomb-dipole theory. The important generalization is made of using a dipole function whose moment is the dipole moment formed by an inner electron and the nucleus. The result is a modulated quasi-linear law for the yield of positive ions which applies to positron-atom impact ionization.

Abstract: The vibration and rotational state distributions of a supersonic nitric oxide beam, scattered from a Pt(111) single crystal surface, were investigated. A two-photon ionization technique was applied to monitor the internal energy content of the scattered molecules. Vibrational distributions were found to be colder than that corresponding to the crystal temperature between 450--1100 K. Rotational temperatures were also found to be colder than expected for thermal equilibrium with the platinum surface.

Abstract: An instrument developed in the author's laboratory and incorporating a capillary column supercritical fluid chromatography (SFC), a direct fluid injection (DFI) interface, and a tandem quadrupole mass spectrometer equipped with a dual electron impact-chemical ionization ion source is described. Initial results of separations suggest excellent separations and sensitivities using the described instrument. Advantages of the capillary SFC-DFI interface are due to the low flow rates, high mobile phase volatility, and the capability for mixed chemical ionization reagents. (BLM)

Abstract: Using synchrotron radiation in the energy range 60< or =h..nu..< or =130 eV, we have measured h..nu..-dependent photoemission energy distribution curves and constant-initial-state spectra from single crystals of U/sub x/,Th/sub 1-x/Sb, UTe, UO/sub 2/, and UPd/sub 3/. The U 5f and U and Th 6d conduction bands, as well as the Sb and Te 5p valence band emission, all exhibit Fano-like resonance behavior at the 5d core ionization thresholds. The 5f emission shows the strongest intensity variation, which can be explained by the super-Coster-Kronig character of the decay of the autoionizing core excited state. Thus f and d emission features in the photoemission spectra are unambiguously identified by their different resonance behavior. It is concluded that the spectra are dominated by localized 5f states in all of these compounds.