This paper, the third in a series of three, describes work carried in the context of Plasma Data Exchange Project of the Gaseous Electronics Conference (PDEP-GEC) to compare electron collision cross-sections sets from ground-state, noble gases atoms and to check their consistency with measured swarm parameters. Such consistency is a minimum requirement if the cross-section data are to be used for modelling low-temperature plasmas. In this paper, we present intercomparisons of the independently compiled sets of electron cross-sections from ground-state, neutral Kr and Xe atoms presently available on the LXCat open-access website (www.lxcat.laplace.univ-tlse.fr). Swarm parameters (reduced mobility, characteristic energy, reduced longitudinal diffusion coefficient, reduced ionization coefficient) calculated in a Boltzmann solver or Monte Carlo simulation using these cross-sections sets are compared with experimental data, also available online on the LXCat site.

An explanation of the so-called hydrino continuum emissions proposed by Mills and Lu, most recently in [Eur. Phys. J. D 64, 65 (2011)], is presented using conventional atomic, plasma, and discharge physics. It is argued that the observed EUV emissions during their pulsed discharges originate from transitions in ions sputtered or evaporated from the electrodes. Such an interpretation removes their justification for the introduction of hydrino particles.

LXCat is a dynamic, open-access, website for collecting, displaying, and downloading ELECtron SCATtering cross sections and swarm parameters (mobility, diffusion coefficient, reaction rates, etc.) required for modeling low temperature, non-equilibrium plasmas. Contributors set up individual databases, and the available databases, indicated by the contributor’s chosen title, include mainly complete sets of electron-neutral scattering cross sections, although the option for introducing partial sets of cross sections exists. A database for measured swarm parameters is also part of LXCat, and this is a growing activity. On-line tools include options for browsing, plotting, and downloading cross section data. The electron energy distribution functions (edfs) in low temperature plasmas are in general non-Maxwellian, and LXCat provides an option for execution of an on-line Boltzmann equation solver to calculate the edf in homogeneous electric fields. Thus, the user can obtain electron transport and rate coefficients (averages over the edfs) in pure gases or gas mixtures over a range of values of the reduced electric fields strength, E/N, the ratio of the electric field strength to the neutral density, using cross sections from the available databases. New contributors are welcome and anyone wishing to create a database and upload data can request a username and password. LXCat is part of a larger, community-wide effort aimed at collecting, evaluating, and sharing data relevant to modeling low temperature plasmas. To illustrate the utility of LXCat in this context, we compare electron swarm parameters in argon calculated using the different compilations of cross sections presently available on LXCat. These compilations include quite different groupings of excited states, yet lead to swarm parameters in good agreement. LXCat is available at http://www.lxcat.laplace.univ-tlse.fr.

Absolute excitation probabilities from very low to moderate-current hydrogen discharges in parallel-plane geometry are measured and used to test models. Relative emission data are obtained for the Hα line, the H2 (a3Σ → b3Π) near-UV continuum, and the H2 (G1Σ→B1Πu+) band at pressures of 0.5 and 2 Torr, a 1.05 cm gap, and voltages from 300 to 900 V. Electron behavior is traced using the first negative (A2Σg → X2Πu, ν″ = 0 → ν′ = 0) band of N2+ by adding 2% N2. Relative measurements of Hα, H2 near-UV, and N2 1st negative emission are placed on a absolute scale by normalization to published measurements and Boltzmann calculations of electron excitation. Emission probabilities calculated using a multi-beam kinetics model for the electrons, H+, H2+, H3+, H−, H, and H2 are compared with the calibrated experiments. Fast H atoms are calculated to produce Hα excitation that is comparable with that of electrons. The calculated emission intensities for Hα and H2 near-UV continuum are within a factor of three of the absolute measurements for a range of 5000:1 in current and 4:1 in hydrogen pressure. Calculations at 2 Torr show that most of the space charge electric field responsible for the cathode fall is produced by H3+ ions.

A model of the collisional kinetics of energetic hydrogen atoms, molecules and ions in pure H-2 discharges is used to predict H-alpha emission profiles and spatial distributions of emission from the cathode regions of low-pressure, weakly ionized discharges for comparison with a wide variety of experiments. Positive and negative ion-energy distributions are also predicted. The model developed for spatially uniform electric fields and current densities less than 10(-3) Am-2 is extended to non-uniform electric fields, current densities of 10(3) Am-2 and electric field to gas density ratios E/N = 1.3 MTd at 0.002-5 Torr pressure. (1 Td = 10(-21) V m(2) and 1 Torr = 133 Pa.) The observed far-wing Doppler broadening and spatial distribution of the H a emission is consistent with reactions among H+, H-2(+), H-3(+) and H- ions, fast H atoms and fast H-2 molecules, and with reflection, excitation and attachment to fast H atoms at surfaces. The H a excitation and H- formation occur principally by collisions of fast H, fast H-2 and H+ with H-2. Simplifications include using a one-dimensional geometry, a multi-beam transport model, and the average cathode-fall electric field. The H alpha emission is linear with current density over eight orders of magnitude. The calculated ion-energy distributions agree satisfactorily with experiment for H-2(+) and H-3(+), but are only in qualitative agreement for H+ and H-. The experiments successfully modeled range from short-gap, parallel-plane glow discharges to beam-like, electrostatic-confinement discharges.

Absolute spectral emissivities for Doppler broadened H(alpha) profiles are measured and compared with predictions of energetic hydrogen ion, atom, and molecule behavior in low-current electrical discharges in H2 at very high electric field E to gas density N ratios E/N and low values of Nd , where d is the parallel-plate electrode separation. These observations reflect the energy and angular distributions for the excited atoms and quantitatively test features of multiple-scattering kinetic models in weakly ionized hydrogen in the presence of an electric field that are not tested by the spatial distributions of H(alpha) emission. Absolute spectral intensities agree well with predictions. Asymmetries in Doppler profiles observed parallel to the electric field at 4<or=E/N<or=20 kTd result primarily from excitation by fast H atoms directed toward the cathode and diffusely reflected from the cathode. (1 Td=10(-21) V m(2)) The effects of reflection of hydrogen particles and of changes with cathode material are modeled accurately without adjustable parameters. Maximum measured wavelength shifts result from acceleration of H+ ions and charge transfer to fast H atoms. The Doppler profiles are consistent with models of reactions among H+, H2+, H3 , H, and H2 leading to fast H atoms and then fast excited H(n=3) atoms.

Spatial distributions of H alpha , H beta , and the near-uv continuum emission from the H2 a ;{3}Sigma g;+ state are measured and compared with a model for low-current electrical discharges in H2 at high E/N and low Nd , where E is the spatially uniform electric field, N is the gas density, and d is the electrode separation. Data are analyzed for 300 Td<E/N<45 kTd , d=0.04 m , and 2 x 10;{21}<N<2.6 x 10;{22} m;{-3} . (1 Td=10;{-21} V m;{2}) The excitation is produced by electrons and by hydrogen atoms and molecules with mean energies from 5 to 1500 eV. Electron-induced emission, dominant at low E/N and low pressures, is distinguished by its buildup toward the anode. Excitation of H alpha by fast H atoms dominates at high E/N and increases toward the cathode. The observed H alpha emission at low E/N is normalized to previous experiments to yield absolute experimental excitation coefficients for all E/N and Nd . Small adjustments of model parameters yield good agreement with H alpha data. Cross sections are derived for excitation of the H2 near-uv continuum by H atoms. Spatial and pressure dependencies of H alpha and H2 near-uv emissions agree well with a model in which reactions of H2+ , H3+ , and H+ ions with H2 lead to fast H atoms and H2 molecules, which then excite H atoms or H2 molecules.

The objective of this work is to evaluate the influence of an external electric field on the ioninduced secondary electron emission coefficient, γ, from metal surfaces. This work is an extension of the classical theory of Hagstrum ([1]-[2]) which is based on the idea of Auger neutralisation of an incoming ion followed by possible ejection of an electron from the surface. It is shown that, among the various effects due to the presence of the field, the Schottky effect is the dominant one and leads an approximate square root dependence of γ on the electric field strength at the cathode.

Models of the elastic, inelastic, and reactive collisions of energetic hydrogen ions, atoms, and molecules are developed for predicting H_{alpha} and H2 near-uv emission, H_{alpha} Doppler profiles, and ion energy distributions for low-pressure, low-current discharges in H2 . The model is applied to spatially uniform electric field E to gas density N ratios of 350 Td< or =E/N< or =45 kTd and 8 x10;{19}< or =Nd< or =10 x10;{21} m;{-2} , where d is the electrode separation and 1 Td=10;{-21} V m;{2} . Mean ion energies at the cathode are 5-1500 eV. Cross sections for H+ , H2+ , H3+ , H, H2 , and excited H(n=3) collisions with H2 and reflection probabilities from electrodes are updated and summarized. Spatial and energy distributions of ions and fast neutrals are calculated using a "multibeam" technique. At the lower E/N and Nd , electron excitation of H_{alpha} dominates near the anode. Excitation of H_{alpha} by fast H atoms near the cathode increases rapidly with pressure through a multistep reaction sequence. At higher E/N , fast H atoms produced at the cathode surface excite much of the H_{alpha} . The model agrees with experimental spatial distributions of H_{alpha} emission and Doppler profiles. Ion energy distributions agree with experiments only for H2+ . Cross sections are derived for excitation of the near-uv continuum of H2 by H atoms.