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Sample records for hot hydrogen atoms

  1. Hot hydrogen atom reactions moderated by H2 and He

    NASA Technical Reports Server (NTRS)

    Aronowitz, S.; Scattergood, T.; Flores, J.; Chang, S.

    1986-01-01

    Photolysis experiments were performed on the H2-CD4-NH3 and He-CD4-NH3 systems. The photolysis (1849 A) involved only NH3. Mixtures of H2:CD4:NH3 included all combinations of the ratios (200,400,800):(10,20,40):4. Two He:CD4:NH3 mixtures were examined where the ratios equalled the combinations 100:(10,20):4. Abstraction of a D from CD4 by the photolytically produced hot hydrogen from ammonia was monitored by mass spectrometric determination of HD. Both experiment and semiempirical hot-atom theory show that H2 is a very poor thermalizer of hot hydrogens with excess kinetic energy of about 2 eV. Applications of the hard-sphere collision model to the H2-CD4-NH3 system resulted in predicted ratios of net HD production to NH3 decomposition that were two orders of magnitude smaller than the experimental ratios. On the other hand, helium is found to be a very efficient thermalizer; here, the classical model yields reasonable agreement with experiments. Application of a semiempirical hot-atom program gave quantitative agreement with experiment for either system.

  2. Muon transfer from hot muonic hydrogen atoms to neon

    SciTech Connect

    Jacot-Guillarmod, R. . Inst. de Physique); Bailey, J.M. ); Beer, G.A.; Knowles, P.E.; Mason, G.R.; Olin, A. ); Beveridge, J.L.; Marshall, G.M.; Brewer, J.H.; Forster, B.M. ); Huber, T.M. ); Kammel, P.; Zmeskal, J.

    1992-01-01

    A negative muon beam has been directed on adjacent solid layers of hydrogen and neon. Three targets differing by their deuterium concentration were investigated. Muonic hydrogen atoms can drift to the neon layer where the muon is immediately transferred. The time structure of the muonic neon X-rays follows the exponential law with a disappearance rate corresponding to the one of [mu][sup [minus]p] atoms in each target. The rates [lambda][sub pp[mu

  3. Muon transfer from hot muonic hydrogen atoms to neon

    SciTech Connect

    Jacot-Guillarmod, R.; Bailey, J.M.; Beer, G.A.; Knowles, P.E.; Mason, G.R.; Olin, A.; Beveridge, J.L.; Marshall, G.M.; Brewer, J.H.; Forster, B.M.; Huber, T.M.; Kammel, P.; Zmeskal, J.; Kunselman, A.R.; Petitjean, C.

    1992-12-31

    A negative muon beam has been directed on adjacent solid layers of hydrogen and neon. Three targets differing by their deuterium concentration were investigated. Muonic hydrogen atoms can drift to the neon layer where the muon is immediately transferred. The time structure of the muonic neon X-rays follows the exponential law with a disappearance rate corresponding to the one of {mu}{sup {minus}p} atoms in each target. The rates {lambda}{sub pp{mu}} and {lambda}{sub pd} can be extracted.

  4. Dry soldering with hot filament produced atomic hydrogen

    DOEpatents

    Panitz, J.K.G.; Jellison, J.L.; Staley, D.J.

    1995-04-25

    A system is disclosed for chemically transforming metal surface oxides to metal that is especially, but not exclusively, suitable for preparing metal surfaces for dry soldering and solder reflow processes. The system employs one or more hot, refractory metal filaments, grids or surfaces to thermally dissociate molecular species in a low pressure of working gas such as a hydrogen-containing gas to produce reactive species in a reactive plasma that can chemically reduce metal oxides and form volatile compounds that are removed in the working gas flow. Dry soldering and solder reflow processes are especially applicable to the manufacture of printed circuit boards, semiconductor chip lead attachment and packaging multichip modules. The system can be retrofitted onto existing metal treatment ovens, furnaces, welding systems and wave soldering system designs. 1 fig.

  5. Dry soldering with hot filament produced atomic hydrogen

    DOEpatents

    Panitz, Janda K. G.; Jellison, James L.; Staley, David J.

    1995-01-01

    A system for chemically transforming metal surface oxides to metal that is especially, but not exclusively, suitable for preparing metal surfaces for dry soldering and solder reflow processes. The system employs one or more hot, refractory metal filaments, grids or surfaces to thermally dissociate molecular species in a low pressure of working gas such as a hydrogen-containing gas to produce reactive species in a reactive plasma that can chemically reduce metal oxides and form volatile compounds that are removed in the working gas flow. Dry soldering and solder reflow processes are especially applicable to the manufacture of printed circuit boards, semiconductor chip lead attachment and packaging multichip modules. The system can be retrofitted onto existing metal treatment ovens, furnaces, welding systems and wave soldering system designs.

  6. Characterization of hot hydrogen-atom reactions by kinetic spectrography.

    NASA Technical Reports Server (NTRS)

    Tomalesky, R. E.; Sturm, J. E.

    1971-01-01

    The flash photolysis of hydrogen iodide in the presence of nitrous oxide, carbon dioxide, and water has been investigated by kinetic spectroscopy. Although the fraction of hydrogen iodide dissociated was very large, the only observable intermediate was imidogen. It was demonstrated that the rapid removal of imidogen and the apparent absence of hydroxyl radicals in each case is a result of the following two reactions, respectively: (1) NH + HI yields NH2 + I; and (2) OH + HI yields H2O + I.

  7. RAPID COMMUNICATION: High silicon etch rates by hot filament generated atomic hydrogen

    NASA Astrophysics Data System (ADS)

    Wanka, H. N.; Schubert, M. B.

    1997-04-01

    The etching of hydrogenated amorphous silicon (a-Si:H) and microcrystalline silicon by hot tungsten filament generated atomic hydrogen has been investigated. Room-temperature etch rates of 27 Å 0022-3727/30/8/002/img1 for amorphous and 20 Å 0022-3727/30/8/002/img1 for microcrystalline silicon have been achieved. Boron doping decreases the etch rate, whereas phosphorus doping does not affect it. No surface roughening occurs, even for the highest a-Si:H etch rates. In the initial phase of the etch process, however, a bond structure modification arises close to the surface. An increase of microcrystalline silicon etch rates towards the substrate/film interface reflects the coalescence of the microcrystalline nuclei. Hot filament atomic hydrogen etching provides high etch rates of amorphous and polycrystalline silicon with a high selectivity against metals and thermal oxide. Due to its simple setup and control, this kind of hydrogen etching is very interesting for applications in semiconductor technology where F- or Cl-etchants are to be avoided.

  8. Correlation between molecular recoil and molecular orientation in collisions of symmetric top molecules with hot hydrogen atoms

    NASA Astrophysics Data System (ADS)

    Ni, C. K.; Flynn, G. W.

    1992-05-01

    Nascent Doppler profiles are measured for hot H-atom—molecule collisions in numerous rotational sublevels of two symmetric tops. Linewidths for CDF 3 molecules due to hot H-atom collisions increase with the quantum number K. In contrast, linewidths for CD 3F molecules due to hot H-atom collisions decrease with the quantum number K. A simple model is proposed to explain the K dependent linewidths.

  9. Translationally and rotationally resolved excitation of CO2(00 0 2) by collisions with hot hydrogen atoms

    NASA Astrophysics Data System (ADS)

    Khan, Farooq A.; Kreutz, Thomas G.; Flynn, George W.; Weston, Ralph E., Jr.

    1993-04-01

    Time domain tunable diode laser absorption spectroscopy has been used to measure rotationally resolved transient absorption line shapes and nascent rotational populations for CO2 molecules excited into the (00 0 2) vibrational state by collisions with translationally hot hydrogen atoms. The 00 0 2 rotational population distribution and rotationally resolved linewidths are remarkably similar to those previously obtained for 00 0 1. Within the context of a simple physical model used to interpret the data, the similar rotational distributions and translational recoils for 00 0 1 and 00 0 2 suggest that these two states are excited by similar collision trajectories, wherein asymmetric stretching excitation is optimized when H strikes near the end of the O-C-O molecule. The magnitude of population scattered into 00 0 2 is about 21 times smaller than that scattered into 00 0 1.

  10. Hot Hydrogen Test Facility

    SciTech Connect

    W. David Swank

    2007-02-01

    The core in a nuclear thermal rocket will operate at high temperatures and in hydrogen. One of the important parameters in evaluating the performance of a nuclear thermal rocket is specific impulse, ISp. This quantity is proportional to the square root of the propellant’s absolute temperature and inversely proportional to square root of its molecular weight. Therefore, high temperature hydrogen is a favored propellant of nuclear thermal rocket designers. Previous work has shown that one of the life-limiting phenomena for thermal rocket nuclear cores is mass loss of fuel to flowing hydrogen at high temperatures. The hot hydrogen test facility located at the Idaho National Lab (INL) is designed to test suitability of different core materials in 2500°C hydrogen flowing at 1500 liters per minute. The facility is intended to test non-uranium containing materials and therefore is particularly suited for testing potential cladding and coating materials. In this first installment the facility is described. Automated Data acquisition, flow and temperature control, vessel compatibility with various core geometries and overall capabilities are discussed.

  11. Hot Hydrogen Test Facility

    SciTech Connect

    Swank, W. David; Carmack, Jon; Werner, James E.; Pink, Robert J.; Haggard, DeLon C.; Johnson, Ryan

    2007-01-30

    The core in a nuclear thermal rocket will operate at high temperatures and in hydrogen. One of the important parameters in evaluating the performance of a nuclear thermal rocket is specific impulse, ISP. This quantity is proportional to the square root of the propellant's absolute temperature and inversely proportional to square root of its molecular weight. Therefore, high temperature hydrogen is a favored propellant of nuclear thermal rocket designers. Previous work has shown that one of the life-limiting phenomena for thermal rocket nuclear cores is mass loss of fuel to flowing hydrogen at high temperatures. The hot hydrogen test facility located at the Idaho National Lab (INL) is designed to test suitability of different core materials in 2500 deg. C hydrogen flowing at 1500 liters per minute. The facility is intended to test low activity uranium containing materials but is also suited for testing cladding and coating materials. In this first installment the facility is described. Automated data acquisition, flow and temperature control, vessel compatibility with various core geometries and overall capabilities are discussed.

  12. Semiempirical hot atom theory. I - Initialization and application

    NASA Technical Reports Server (NTRS)

    Aronowitz, S.; Chang, S.; Scattergood, T.

    1981-01-01

    A semiempirical approach to the modeling of the kinetics of reaction systems containing both hot and nonhot atoms is proposed. The approach is based on the probabilistic kinetic theory of hot-atom reactions formulated by Wolfgang (1963), with transmission probabilities estimated for a rectangular potential barrier for hot-atom and nonhot-atom reactions. A computational scheme for determining product concentrations following hot and nonhot reactions in a system containing photolytically produced hot atoms is then applied to the DBr + CH4 and HBr + CD4 hot hydrogen atom systems studied by Martin and Willard (1964), and good agreement is obtained between theoretical and experimental results.

  13. Atomic hydrogen rocket engine

    NASA Technical Reports Server (NTRS)

    Etters, R. D.; Flurchick, K.

    1981-01-01

    A rocket using atomic hydrogen propellant is discussed. An essential feature of the proposed engine is that the atomic hydrogen fuel is used as it is produced, thus eliminating the necessity of storage. The atomic hydrogen flows into a combustion chamber and recombines, producing high velocity molecular hydrogen which flows out an exhaust port. Standard thermodynamics, kinetic theory and wall recombination cross-sections are used to predict a thrust of approximately 1.4 N for a RF hydrogen flow rate of 4 x 10 to the 22nd/sec. Specific impulses are nominally from 1000 to 2000 sec. It is predicted that thrusts on the order of one Newton and specific impulses of up to 2200 sec are attainable with nominal RF discharge fluxes on the order of 10 to the 22nd atoms/sec; further refinements will probably not alter these predictions by more than a factor of two.

  14. Hot atom chemistry and radiopharmaceuticals

    SciTech Connect

    Krohn, Kenneth A.; Moerlein, Stephen M.; Link, Jeanne M.; Welch, Michael J.

    2012-12-19

    The chemical products made in a cyclotron target are a combined result of the chemical effects of the nuclear transformation that made the radioactive atom and the bulk radiolysis in the target. This review uses some well-known examples to understand how hot atom chemistry explains the primary products from a nuclear reaction and then how radiation chemistry is exploited to set up the optimal product for radiosynthesis. It also addresses the chemical effects of nuclear decay. There are important principles that are common to hot atom chemistry and radiopharmaceutical chemistry. Both emphasize short-lived radionuclides and manipulation of high specific activity nuclides. Furthermore, they both rely on radiochromatographic separation for identification of no-carrieradded products.

  15. Hot atoms in cosmic chemistry.

    PubMed

    Rossler, K; Jung, H J; Nebeling, B

    1984-01-01

    High energy chemical reactions and atom molecule interactions might be important for cosmic chemistry with respect to the accelerated species in solar wind, cosmic rays, colliding gas and dust clouds and secondary knock-on particles in solids. "Hot" atoms with energies ranging from a few eV to some MeV can be generated via nuclear reactions and consequent recoil processes. The chemical fate of the radioactive atoms can be followed by radiochemical methods (radio GC or HPLC). Hot atom chemistry may serve for laboratory simulation of the reactions of energetic species with gaseous or solid interstellar matter. Due to the effective measurement of 10(8)-10(10) atoms only it covers a low to medium dose regime and may add to the studies of ion implantation which due to the optical methods applied are necessarily in the high dose regime. Experimental results are given for the systems: C/H2O (gas), C/H2O (solid, 77 K), N/CH4 (solid, 77K) and C/NH3 (solid, 77 K). Nuclear reactions used for the generation of 2 to 3 MeV atoms are: N(p,alpha) 11C, 16O(p,alpha pn) 11C and 12C(d,n) 13N with 8 to 45 MeV protons or deuterons from a cyclotron. Typical reactions products are: CO, CO2, CH4, CH2O, CH3OH, HCOOH, NH3, CH3NH2, cyanamide, formamidine, guanidine etc. Products of hot reactions in solids are more complex than in corresponding gaseous systems, which underlines the importance of solid state reactions for the build-up of precursors for biomolecules in space. As one of the major mechanisms for product formation, the simultaneous or fast consecutive reactions of a hot carbon with two target molecules (reaction complex) is discussed.

  16. An Atomic Hydrogen Mushroom

    NASA Astrophysics Data System (ADS)

    English, J.; Taylor, A. R.; Irwin, J. A.; Canadian Galactic Plane Survey Collaboration

    1998-12-01

    Neutral hydrogen ``worms'', which stream vertically from the mid-plane to high latitudes, may be conduits through which hot gas can escape into the halo. Using the Dominion Radio Astrophysical Observatory's (DRAO) Synthesis Telescope, as part of the Canadian Galactic Plane Survey, we have resolved an HI worm candidate. Although simulations have previously made general predictions, these data will constrain, for the first time, detailed numerical models of the dynamical processes generating disk-halo features. After the incorporation of the data from the 26-m DRAO's single-dish telescope, the mosaic data cube has full information on all spatial scales down to a resolution limit of 1 arcmin and a velocity resolution of 0.82 km s(-1) . Thus we delineate Rayleigh-Taylor instability-like structures and can distinguish a 5 km s(-1) line of sight velocity difference between the base and top of the worm. In general morphology, the worm is mushroom-shaped. Although it extends only a few hundred parsecs south of the midplane, the cap appears to be fragmenting. This may allow hot material from the stem's cavity, as well as UV photons, to escape to higher galactic latitudes. The preliminary estimate of the observed minimum HI mass is 1.3 x 10(5) Msolar. Our initial thin-shell model, which assumes supernovae explosions drive this outflow, gives a minimum total energy of about 100 x 10(51) ergs s(-1) .

  17. HOT HYDROGEN IN DIFFUSE CLOUDS

    SciTech Connect

    Cecchi-Pestellini, Cesare; Duley, Walt W.; Williams, David A. E-mail: wwduley@uwaterloo.ca

    2012-08-20

    Laboratory evidence suggests that recombination of adsorbed radicals may cause an abrupt temperature excursion of a dust grain to about 1000 K. One consequence of this is the rapid desorption of adsorbed H{sub 2} molecules with excitation temperatures of this magnitude. We compute the consequences of injection of hot H{sub 2} into cold diffuse interstellar gas at a rate of 1% of the canonical H{sub 2} formation rate. We find that the level populations of H{sub 2} in J = 3, 4, and 5 are close to observed values, and that the abundances of CH{sup +} and OH formed in reactions with hot hydrogen are close to the values obtained from observations of diffuse clouds.

  18. Atomic hydrogen interaction with Ru(1010).

    PubMed

    Vesselli, E; Comelli, G; Rosei, R

    2004-05-01

    The interaction of atomic hydrogen with clean and deuterium precovered Ru(1010) was studied by means of temperature-programmed desorption (TPD) spectroscopy. Compared to molecular hydrogen experiments, after exposure of the clean surface to gas-phase atomic hydrogen at 90 K, two additional peaks grow in the desorption spectra at 115 and 150 K. The surface saturation coverage, determined by equilibrium between abstraction and adsorption reactions, is 2.5 monolayers. Preadsorbed deuterium abstraction experiments with gas-phase atomic hydrogen show that a pure Eley-Rideal mechanism is not involved in the process, while a hot atom (HA) kinetics describes well the reaction. By least-squares fitting of the experimental data, a simplified HA kinetic model yields an abstraction cross section value of 0.5 +/- 0.2 angstroms2. The atomic hydrogen interaction with an oxygen precovered surface was also studied by means of both TPD and x-ray photoelectron spectroscopy: oxygen hydrogenation and water production take place already at very low temperature (90 K).

  19. Thin film atomic hydrogen detectors

    NASA Technical Reports Server (NTRS)

    Gruber, C. L.

    1977-01-01

    Thin film and bead thermistor atomic surface recombination hydrogen detectors were investigated both experimentally and theoretically. Devices were constructed on a thin Mylar film substrate. Using suitable Wheatstone bridge techniques sensitivities of 80 microvolts/2x10 to the 13th power atoms/sec are attainable with response time constants on the order of 5 seconds.

  20. Atomic hydrogen in planetary nebulae

    NASA Technical Reports Server (NTRS)

    Schneider, Stephen E.; Silverglate, Peter R.; Altschuler, Daniel R.; Giovanardi, Carlo

    1987-01-01

    The authors searched for neutral atomic hydrogen associated with 22 planetary nebulae and three evolved stars in the 21 cm line at the Arecibo Observatory. Objects whose radial velocities permitted discrimination from Galactic H I were chosen for observation. Hydrogen was detected in absorption from IC 4997. From the measurements new low limits are derived to the mass of atomic hydrogen associated with the undetected nebulae. Radio continuum observations were also made of several of the nebulae at 12.6 cm. The authors reexamine previous measurements of H I in planetary nebulae, and present the data on a consistent footing. The question of planetary nebula distances is considered at length. Finally, implications of the H I measurements for nebular evolution are discussed and it is suggested that atomic hydrogen seen in absorption was expelled from the progenitor star during the final 1000 yr prior to the onset of ionization.

  1. NLTE in a Hot Hydrogen Star: Auer & Mihalas Revisited

    NASA Astrophysics Data System (ADS)

    Wiersma, J.; Rutten, R. J.; Lanz, T.

    2003-01-01

    We pay tribute to two landmark papers published by Auer & Mihalas in 1969. They modeled hot-star NLTE-RE hydrogen-only atmospheres, using two simplified hydrogen atoms: ApJ 156, 157: H I levels 1, 2 and c, Lyman α the only line ApJ 156, 681: H I levels 1, 2, 3 and c, Balmer α the only line and computed LTE and NLTE models with the single line turned on and off. The results were extensively analyzed in the two papers. Any student of stellar line formation should take these beautiful papers to heart. The final exercise in Rutten's lecture notes ``Radiative Transfer in Stellar Atmospheres'' asks the student to work through five pages of questions concerning diagrams from the first paper alone! That exercise led to the present work in which we recompute the Auer-Mihalas hot-hydrogen-star models with TLUSTY, adding results from a complete hydrogen atom for comparison. Our motivation for this Auer-Mihalas re-visitation is twofold: 1. to add diagnostic diagrams to the ones published by Auer & Mihalas, in particular Bν, Jν, Sν graphs to illustrate the role of the radiation field, and radiative heating & cooling graphs to illustrate the radiative energy budget, 2. to see the effect of adding the rest of the hydrogen atom.

  2. Energy storage possibilities of atomic hydrogen

    NASA Technical Reports Server (NTRS)

    Etters, R. D.; Dugan, J. V., Jr.; Palmer, R.

    1976-01-01

    The possibility of storing large amounts of energy in a free radical system such as atomic hydrogen is analyzed. Attention is focused on theoretical calculations of the ground state properties of spin-aligned atomic triplet hydrogen, deuterium, and tritium. The solid-liquid phase transition in atomic hydrogen is also examined.

  3. Phase boundary of hot dense fluid hydrogen

    PubMed Central

    Ohta, Kenji; Ichimaru, Kota; Einaga, Mari; Kawaguchi, Sho; Shimizu, Katsuya; Matsuoka, Takahiro; Hirao, Naohisa; Ohishi, Yasuo

    2015-01-01

    We investigated the phase transformation of hot dense fluid hydrogen using static high-pressure laser-heating experiments in a laser-heated diamond anvil cell. The results show anomalies in the heating efficiency that are likely to be attributed to the phase transition from a diatomic to monoatomic fluid hydrogen (plasma phase transition) in the pressure range between 82 and 106 GPa. This study imposes tighter constraints on the location of the hydrogen plasma phase transition boundary and suggests higher critical point than that predicted by the theoretical calculations. PMID:26548442

  4. Molecular Beam Studies of Hot Atom Chemical Reactions: Reactive Scattering of Energetic Deuterium Atoms

    DOE R&D Accomplishments Database

    Continetti, R. E.; Balko, B. A.; Lee, Y. T.

    1989-02-01

    A brief review of the application of the crossed molecular beams technique to the study of hot atom chemical reactions in the last twenty years is given. Specific emphasis is placed on recent advances in the use of photolytically produced energetic deuterium atoms in the study of the fundamental elementary reactions D + H{sub 2} -> DH + H and the substitution reaction D + C{sub 2}H{sub 2} -> C{sub 2}HD + H. Recent advances in uv laser and pulsed molecular beam techniques have made the detailed study of hydrogen atom reactions under single collision conditions possible.

  5. NASA atomic hydrogen standards program: An update

    NASA Technical Reports Server (NTRS)

    Reinhardt, V. S.; Kaufmann, D. C.; Adams, W. A.; Deluca, J. J.; Soucy, J. L.

    1976-01-01

    Comparisons are made between the NP series and the NX series of hydrogen masers. A field operable hydrogen maser (NR series) is also described. Atomic hydrogen primary frequency standards are in development stages. Standards are being developed for a hydrogen beam frequency standard and for a concertina hydrogen maser.

  6. Hydrogen-Atom Transfer Reactions.

    PubMed

    Wang, Liang; Xiao, Jian

    2016-04-01

    The cascade [1,n]-hydrogen transfer/cyclization, recognized as the tert-amino effect one century ago, has received considerable interest in recent decades, and great achievements have been made. With the aid of this strategy, the inert C(sp(3))-H bonds can be directly functionalized into C-C, C-N, C-O bonds under catalysis of Lewis acids, Brønsted acids, as well as organocatalysts, and even merely under thermal conditions. Hydrogen can be transferred intramolecularly from hydrogen donor to acceptor in the form of hydride, or proton, followed by cyclization to furnish the cyclic products in processes featuring high atom economy. Methylene/methine adjacent to heteroatoms, e.g., nitrogen, oxygen, sulfur, can be exploited as hydride donor as well as methylene/methine without heteroatom assistance. Miscellaneous electrophilic subunits or intermediates, e.g., alkylidene malonate, carbophilic metal activated alkyne or allene, α,β-unsaturated aldehydes/ketone, saturated aldehydes/iminium, ketenimine/carbodiimide, metal carbenoid, electron-withdrawing groups activated allene/alkyne, in situ generated carbocation, can serve as hydride acceptors. This methodology has shown preeminent power to construct 5-, 6-, or 7-membered heterocyclic as well as carbon rings. In this chapter, various hydrogen donors and acceptors are adequately discussed. PMID:27573142

  7. Experiments with trapped hydrogen atoms and neutrons

    NASA Astrophysics Data System (ADS)

    Ramsey, Norman F.

    1995-01-01

    The earliest trapped atom coherent resonance experiments were with material traps or bottles. In the atomic hydrogen maser the atoms are trapped inside a teflon-coated quartz bulb for about a second. Neutrons have been trapped for hundreds of seconds in suitably coated bottles or in superconducting magnetic traps. Results from experiments with trapped atoms and neutrons are given.

  8. Experiments with trapped hydrogen atoms and neutrons

    NASA Astrophysics Data System (ADS)

    Ramsey, Norman F.

    1993-03-01

    The earliest trapped atom coherent resonance experiments were with material traps or bottles. In the atomic hydrogen maser, the atoms are trapped inside a teflon-coated quartz bulb for about a second. Neutrons have been trapped for hundreds of seconds in suitably coated bottles or in superconducting magnetic traps. Results from experiments with trapped atoms and neutrons are reported.

  9. Effects of hydrogen atom spin exchange collisions on atomic hydrogen maser oscillation frequency

    NASA Technical Reports Server (NTRS)

    Crampton, S. B.

    1979-01-01

    Frequency shifts due to collisions between hydrogen atoms in an atomic hydrogen maser frequency standard are studied. Investigations of frequency shifts proportional to the spin exchange frequency shift cross section and those proportional to the duration of exchange collisions are discussed. The feasibility of operating a hydrogen frequency standard at liquid helium temperatures is examined.

  10. Atomic hydrogen as a launch vehicle propellant

    NASA Technical Reports Server (NTRS)

    Palaszewski, Bryan A.

    1990-01-01

    An analysis of several atomic hydrogen launch vehicles was conducted. A discussion of the facilities and the technologies that would be needed for these vehicles is also presented. The Gross Liftoff Weights (GLOW) for two systems were estimated; their specific impulses (I sub sp) were 750 and 1500 lb (sub f)/s/lb(sub m). The atomic hydrogen launch vehicles were also compared to the currently planned Advanced Launch System design concepts. Very significant GLOW reductions of 52 to 58 percent are possible over the Advanced Launch System designs. Applying atomic hydrogen propellants to upper stages was also considered. Very high I(sub sp) (greater than 750 1b(sub f)/s/lb(sub m) is needed to enable a mass savings over advanced oxygen/hydrogen propulsion. Associated with the potential benefits of high I(sub sp) atomic hydrogen are several challenging problems. Very high magnetic fields are required to maintain the atomic hydrogen in a solid kilogauss (3 Tesla). Also the storage temperature of the propellant is 4 K. This very low temperature will require a large refrigeration facility for the launch vehicle. The design considerations for a very high recombination rate for the propellant are also discussed. A recombination rate of 210 cm/s is predicted for atomic hydrogen. This high recombination rate can produce very high acceleration for the launch vehicle. Unique insulation or segmentation to inhibit the propellant may be needed to reduce its recombination rate.

  11. Diagnostics for hot plasmas using hydrogen neutral beams

    SciTech Connect

    Goldston, R.J.

    1982-12-01

    Beams of neutral hydrogen atoms have found a number of uses in the diagnosis of hot plasmas. In the most straightforward application, neutral beams have been used to determine plasma line density, based on simple attenuation measurements. This technique has been applied most intensively recently to the study of beam-injected mirror plasmas. Neutral beams have also now been used in a number of tokamaks to supply a local increase of the neutral atom target density for charge exchange. By directing a time-modulated neutral beam across the sight-line of a charge-exchange analyzer, and measuring the modulated neutral particle efflux from the plasma, local measurements of the ion energy distribution function can be made. If a modulated diagnostic neutral beam is directed across the sight-line of an ultra-violet spectrometer, one can also make measurements of the local densities and possibly velocity distributions of fully stripped impurities. The fast hydrogen neutrals charge exchange with fully stripped impurities in the plasma, leaving the impurities in excited hydrogen-like states. In their prompt radiative decay the impurity ions emit characteristic uv lines, which can be detected easily.

  12. The Hydrogen Atom: The Rutherford Model

    NASA Astrophysics Data System (ADS)

    Tilton, Homer Benjamin

    1996-06-01

    Early this century Ernest Rutherford established the nuclear model of the hydrogen atom, presently taught as representing the best visual model after modification by Niels Bohr and Arnold Sommerfeld. It replaced the so-called "plum pudding" model of J. J. Thomson which held sway previously. While the Rutherford model represented a large step forward in our understanding of the hydrogen atom, questions remained, and still do.

  13. Atomic hydrogen doping in single-crystal vanadium dioxide

    NASA Astrophysics Data System (ADS)

    Ji, Heng; Hardy, Will; Wei, Jiang; Lin, Jian; Paik, Hanjong; Schlom, Darrell; Natelson, Douglas

    2014-03-01

    Vanadium dioxide is a strongly correlated material with a bulk metal-to-insulator transition (MIT) near 340 K. Previous experiments in single-crystal nanowires (J. Wei et al., Nature Nano. 7, 357-362 (2012)) have shown that catalytic doping with atomic hydrogen can stabilize the high temperature metallic state. In this experiment, we used a hot filament source to split hydrogen molecules and directly dope atomic hydrogen into VO2 material, including epitaxial films and nanowires, without any catalyst. From observations of the wire samples, we infer the relative diffusion rates of H in the monoclinic and rutile crystal structures. Transport measurements of the doped film samples show no temperature-driven transition, but rather a conducting state down to 2K. We present Hall and magnetoresistance measurements on macroscale and mesoscale devices fabricated from the doped films.

  14. Energy storage possibilities of atomic hydrogen

    NASA Technical Reports Server (NTRS)

    Etters, R. D.; Dugan, J. V., Jr.; Palmer, R.

    1976-01-01

    Several recent experiments designed to produce and store macroscopic quantities of atomic hydrogen are discussed. The bulk, ground state properties of atomic hydrogen, deuterium, and tritium systems are calculated assuming that all pair interactions occur via the atomic triplet potential. The conditions required to obtain this system, including inhibition of recombination through the energetically favorable singlet interaction, are discussed. The internal energy, pressure, and compressibility are calculated applying the Monte Carlo technique with a quantum mechanical variational wavefunction. The system studied consisted of 32 atoms in a box with periodic boundary conditions. Results show that atomic triplet hydrogen and deuterium remain gaseous at 0 K; i.e., the internal energy is positive at all molar volumes considered.

  15. Solid Hydrogen Formed for Atomic Propellants

    NASA Technical Reports Server (NTRS)

    Palaszewski, Bryan A.

    2000-01-01

    Several experiments on the formation of solid hydrogen particles in liquid helium were recently conducted at the NASA Glenn Research Center at Lewis Field. The solid hydrogen experiments are the first step toward seeing these particles and determining their shape and size. The particles will ultimately store atoms of boron, carbon, or hydrogen, forming an atomic propellant. Atomic propellants will allow rocket vehicles to carry payloads many times heavier than possible with existing rockets or allow them to be much smaller and lighter. Solid hydrogen particles are preferred for storing atoms. Hydrogen is generally an excellent fuel with a low molecular weight. Very low temperature hydrogen particles (T < 4 K) can prevent the atoms from recombining, making it possible for their lifetime to be controlled. Also, particles that are less than 1 mm in diameter are preferred because they can flow easily into a pipe when suspended in liquid helium. The particles and atoms must remain at this low temperature until the fuel is introduced into the engine combustion (or recombination) chamber. Experiments were, therefore, planned to look at the particles and observe their formation and any changes while in liquid helium.

  16. Hydrogen as an atomic beam standard

    NASA Technical Reports Server (NTRS)

    Peters, H. E.

    1972-01-01

    After a preliminary discussion of feasibility, new experimental work with a hydrogen beam is described. A space focused magnetic resonance technique with separated oscillatory fields is used with a monochromatic beam of cold hydrogen atoms which are selected from a higher temperature source. The first resonance curves and other experimental results are presented. These results are interpreted from the point of view of accuracy potential and frequency stability, and are compared with hydrogen maser and cesium beam capabilities.

  17. Atomic hydrogen as a launch vehicle propellant

    NASA Technical Reports Server (NTRS)

    Palaszewski, Bryan A.

    1990-01-01

    An analysis of several atomic hydrogen launch vehicles was conducted. A discussion of the facilities and the technologies that would be needed for these vehicles is also presented. The Gross Liftoff Weights (GLOW) for two systems were estimated; their specific impulses (I sub sp) were 750 and 1500 lb(sub f)/s/lb(sub m). The atomic hydrogen launch vehicles were also compared to the currently planned Advanced Launch System design concepts. Very significant GLOW reductions of 52 to 58 percent are possible over the Advanced Launch System designs. Applying atomic hydrogen propellants to upper stages was also considered. Very high I(sub sp) (greater than 750 lb(sub f)/s/lb(sub m)) is needed to enable a mass savings over advanced oxygen/hydrogen propulsion. Associated with the potential benefits of high I(sub sp) atomic hydrogen are several challenging problems. Very high magnetic fields are required to maintain the atomic hydrogen in a solid hydrogen matrix. The magnetic field strength was estimated to be 30 kilogauss (3 Tesla). Also the storage temperature of the propellant is 4 K. This very low temperature will require a large refrigeration facility for the launch vehicle. The design considerations for a very high recombination rate for the propellant are also discussed. A recombination rate of 210 cm/s is predicted for atomic hydrogen. This high recombination rate can produce very high acceleration for the launch vehicle. Unique insulation or segmentation to inhibit the propellant may be needed to reduce its recombination rate.

  18. Atomic hydrogen as a launch vehicle propellant

    SciTech Connect

    Palaszewski, B.A.

    1990-01-01

    An analysis of several atomic hydrogen launch vehicles was conducted. A discussion of the facilities and the technologies that would be needed for these vehicles is also presented. The Gross Liftoff Weights (GLOW) for two systems were estimated; their specific impulses (I{sub sp}) were 750 and 1500 lb{sub f}/s/lb{sub m}. The atomic hydrogen launch vehicles were also compared to the currently planned Advanced Launch System design concepts. Very significant GLOW reductions of 52 to 58 percent are possible over the Advanced Launch System designs. Applying atomic hydrogen propellants to upper stages was also considered. Very high I{sub sp} (greater than 750 lb{sub f}/s/lb{sub m}) is needed to enable a mass savings over advanced oxygen/hydrogen propulsion. Associated with the potential benefits of high I(sub sp) atomic hydrogen are several challenging problems. Very high magnetic fields are required to maintain the atomic hydrogen in a solid hydrogen matrix. The magnetic field strength was estimated to be 30 kilogauss (3 Tesla). Also the storage temperature of the propellant is 4 K. This very low temperature will require a large refrigeration facility for the launch vehicle. The design considerations for a very high recombination rate for the propellant are also discussed. A recombination rate of 210 cm/s is predicted for atomic hydrogen. This high recombination rate can produce very high acceleration for the launch vehicle. Unique insulation or segmentation to inhibit the propellant may be needed to reduce its recombination rate.

  19. Novel Infrared Dynamics of Cold Atoms on Hot Graphene

    NASA Astrophysics Data System (ADS)

    Sengupta, Sanghita; Kotov, Valeri; Clougherty, Dennis

    The low-energy dynamics of cold atoms interacting with macroscopic graphene membranes exhibits severe infrared divergences when treated perturbatively. These infrared problems are even more pronounced at finite temperature due to the (infinitely) many flexural phonons excited in graphene. We have devised a technique to take account (resummation) of such processes in the spirit of the well-known exact solution of the independent boson model. Remarkably, there is also similarity to the infrared problems and their treatment (via the Bloch-Nordsieck scheme) in finite temperature ``hot'' quantum electrodynamics and chromodynamics due to the long-range, unscreened nature of gauge interactions. The method takes into account correctly the strong damping provided by the many emitted phonons at finite temperature. In our case, the inverse membrane size plays the role of an effective low-energy scale, and, unlike the above mentioned field theories, there remains an unusual, highly nontrivial dependence on that scale due to the 2D nature of the problem. We present detailed results for the sticking (atomic damping rate) rate of cold atomic hydrogen as a function of the membrane temperature and size. We find that the rate is very strongly dependent on both quantities.

  20. Co-Occurring Atomic Contacts for the Characterization of Protein Binding Hot Spots.

    PubMed

    Liu, Qian; Ren, Jing; Song, Jiangning; Li, Jinyan

    2015-01-01

    A binding hot spot is a small area at a protein-protein interface that can make significant contribution to binding free energy. This work investigates the substantial contribution made by some special co-occurring atomic contacts at a binding hot spot. A co-occurring atomic contact is a pair of atomic contacts that are close to each other with no more than three covalent-bond steps. We found that two kinds of co-occurring atomic contacts can play an important part in the accurate prediction of binding hot spot residues. One is the co-occurrence of two nearby hydrogen bonds. For example, mutations of any residue in a hydrogen bond network consisting of multiple co-occurring hydrogen bonds could disrupt the interaction considerably. The other kind of co-occurring atomic contact is the co-occurrence of a hydrophobic carbon contact and a contact between a hydrophobic carbon atom and a π ring. In fact, this co-occurrence signifies the collective effect of hydrophobic contacts. We also found that the B-factor measurements of several specific groups of amino acids are useful for the prediction of hot spots. Taking the B-factor, individual atomic contacts and the co-occurring contacts as features, we developed a new prediction method and thoroughly assessed its performance via cross-validation and independent dataset test. The results show that our method achieves higher prediction performance than well-known methods such as Robetta, FoldX and Hotpoint. We conclude that these contact descriptors, in particular the novel co-occurring atomic contacts, can be used to facilitate accurate and interpretable characterization of protein binding hot spots.

  1. Location of hydrogen atoms in hydronium jarosite

    NASA Astrophysics Data System (ADS)

    Spratt, Henry J.; Avdeev, Maxim; Pfrunder, Michael C.; McMurtrie, John; Rintoul, Llew; Martens, Wayde N.

    2014-07-01

    Various models for the crystal structure of hydronium jarosite were determined from Rietveld refinements against neutron powder diffraction patterns collected at ambient temperature and also single-crystal X-ray diffraction data. The possibility of a lower symmetry space group for hydronium jarosite that has been suggested by the literature was investigated. It was found the space group is best described as , the same for other jarosite minerals. The hydronium oxygen atom was found to occupy the site (3a Wyckoff site). Inadequately refined hydronium bond angles and bond distances without the use of restraints are due to thermal motion and disorder of the hydronium hydrogen atoms across numerous orientations. However, the acquired data do not permit a precise determination of these orientations; the main feature up/down disorder of hydronium is clear. Thus, the highest symmetry model with the least disorder necessary to explain all data was chosen: The hydronium hydrogen atoms were modeled to occupy an m (18 h Wyckoff site) with 50 % fractional occupancy, leading to disorder across two orientations. A rigid body description of the hydronium ion rotated by 60° with H-O-H bond angles of 112° and O-H distances of 0.96 Å was optimal. This rigid body refinement suggests that hydrogen bonds between hydronium hydrogen atoms and basal sulfate oxygen atoms are not predominant. Instead, hydrogen bonds are formed between hydronium hydrogen atoms and hydroxyl oxygen atoms. The structure of hydronium alunite is expected to be similar given that alunite supergroup minerals are isostructural.

  2. Liquid-metal atomization for hot working preforms

    NASA Technical Reports Server (NTRS)

    Grant, N. J.; Pelloux, R. M.

    1974-01-01

    Rapid quenching of a liquid metal by atomization or splat cooling overcomes the major limitation of most solidification processes, namely, the segregation of alloying elements, impurities, and constituent phases. The cooling rates of different atomizing processes are related to the dendrite arm spacings and to the microstructure of the atomized powders. The increased solubility limits and the formation of metastable compounds in splat-cooled alloys are discussed. Consolidation of the powders by hot isostatic compaction, hot extrusion, or hot forging and rolling processes yields billets with properties equivalent to or better than those of the wrought alloys. The application of this powder processing technology to high-performance alloys is reviewed.

  3. Ionization of polarized hydrogen atoms

    SciTech Connect

    Alessi, J.G.

    1983-01-01

    Methods are discussed for the production of polarized H/sup -/ ions from polarized atoms produced in ground state atomic beam sources. Present day sources use ionizers of two basic types - electron ionizers for H/sup +/ Vector production followed by double charge exchange in a vapor, or direct H/sup -/ Vector production by charge exchange of H/sup 0/ with Cs/sup 0/. Both methods have ionization efficiencies of less than 0.5%. Ionization efficiencies in excess of 10% may be obtained in the future by the use of a plasma ionizer plus charge exchange in Cs or Sr vapor, or ionization by resonant charge exchange with a self-extracted D/sup -/ beam from a ring magnetron or HCD source. 36 references, 4 figures.

  4. Moller Polarimetry with Atomic Hydrogen Targets

    SciTech Connect

    Eugene Chudakov; Vladimir Luppov

    2003-10-19

    A novel proposal of using polarized atomic hydrogen gas, stored in an ultra-cold magnetic trap, as the target for electron beam polarimetry based on Moller scattering is discussed. Such a target of practically 100% polarized electrons could provide a superb systematic accuracy of about 0.5% for beam polarization measurements. The feasibility studies for the CEBAF electron beam have been performed.

  5. Compact microwave cavity for hydrogen atomic clock

    NASA Technical Reports Server (NTRS)

    Zhang, Dejun; Zhang, Yan; Fu, Yigen; Zhang, Yanjun

    1992-01-01

    A summary is presented that introduces the compact microwave cavity used in the hydrogen atomic clock. Special emphasis is placed on derivation of theoretical calculating equations of main parameters of the microwave cavity. A brief description is given of several methods for discriminating the oscillating modes. Experimental data and respective calculated values are also presented.

  6. Atomic line emission analyzer for hydrogen isotopes

    DOEpatents

    Kronberg, J.W.

    1993-03-30

    Apparatus for isotopic analysis of hydrogen comprises a low pressure chamber into which a sample of hydrogen is introduced and then exposed to an electrical discharge to excite the electrons of the hydrogen atoms to higher energy states and thereby cause the emission of light on the return to lower energy states, a Fresnel prism made at least in part of a material anomalously dispersive to the wavelengths of interest for dispersing the emitted light, and a photodiode array for receiving the dispersed light. The light emitted by the sample is filtered to pass only the desired wavelengths, such as one of the lines of the Balmer series for hydrogen, the wavelengths of which differ slightly from one isotope to another. The output of the photodiode array is processed to determine the relative amounts of each isotope present in the sample. Additionally, the sample itself may be recovered using a metal hydride.

  7. Atomic line emission analyzer for hydrogen isotopes

    DOEpatents

    Kronberg, James W.

    1993-01-01

    Apparatus for isotopic analysis of hydrogen comprises a low pressure chamber into which a sample of hydrogen is introduced and then exposed to an electrical discharge to excite the electrons of the hydrogen atoms to higher energy states and thereby cause the emission of light on the return to lower energy states, a Fresnel prism made at least in part of a material anomalously dispersive to the wavelengths of interest for dispersing the emitted light, and a photodiode array for receiving the dispersed light. The light emitted by the sample is filtered to pass only the desired wavelengths, such as one of the lines of the Balmer series for hydrogen, the wavelengths of which differ slightly from one isotope to another. The output of the photodiode array is processed to determine the relative amounts of each isotope present in the sample. Additionally, the sample itself may be recovered using a metal hydride.

  8. Atomic line emission analyzer for hydrogen isotopes

    DOEpatents

    Kronberg, J.W.

    1991-05-08

    Apparatus for isotopic analysis of hydrogen comprises a low pressure chamber into which a sample of hydrogen is introduced and then exposed to an electrical discharge to excite the electrons of the hydrogen atoms to higher energy states and thereby cause the emission of light on the return to lower energy states, a Fresnel prism made at least in part of a material anomalously dispersive to the wavelengths of interest for dispersing the emitted light, and a photodiode array for receiving the dispersed light. The light emitted by the sample is filtered to pass only the desired wavelengths, such as one of the lines of the Balmer series for hydrogen, the wavelengths of which differ slightly from one isotope to another. The output of the photodiode array is processed to determine the relative amounts of each isotope present in the sample. Additionally, the sample itself may be recovered using, a metal hydride.

  9. Bichromatic electromagnetically induced transparency in hot atomic vapors

    NASA Astrophysics Data System (ADS)

    Yan, Hui; Liao, Kai-Yu; Li, Jian-Feng; Du, Yan-Xiong; Zhang, Zhi-Ming; Zhu, Shi-Liang

    2013-05-01

    In a three-level Λ atomic system coupled by a symmetrical bichromatic laser field, a weak probe laser field shows multiple absorption peaks in the case of cold atoms. As for hot atomic vapors, we experimentally observe double symmetrical electromagnetically induced transparency windows instead of multiple absorption peaks. This abnormal spectrum is due to the Doppler averaging. The electromagnetically induced transparency windows observed here are useful for obtaining slow photons at different frequencies.

  10. The atomic hydrogen cloud in the saturnian system

    NASA Astrophysics Data System (ADS)

    Tseng, W.-L.; Johnson, R. E.; Ip, W.-H.

    2013-09-01

    The importance of Titan's H torus shaped by solar radiation pressure and of hydrogen atoms flowing out of Saturn's atmosphere in forming the broad hydrogen cloud in Saturn's magnetosphere is still debated. Since the Saturnian system also contains a water product torus which originates from the Enceladus plumes, the icy ring particles, and the inner icy satellites, as well as Titan's H2 torus, we have carried out a global investigation of the atomic hydrogen cloud taking into account all sources. We show that the velocity and angle distributions of the hot H ejected from Saturn's atmosphere following electron-impact dissociation of H2 are modified by collisions with the ambient atmospheric H2 and H. This in turn affects the morphology of the escaping hydrogen from Saturn, as does the morphology of the ionospheric electron distribution. Although an exact agreement with the Cassini observations is not obtained, our simulations show that H directly escaping from Titan is the dominant contributor in the outer magnetosphere. Of the total number of H observed by Cassini from 1 to 5RS, ∼5.7×1034, our simulations suggest ∼20% is from dissociation in the Enceladus torus, ∼5-10% is from dissociation of H2 in the atmosphere of the main rings, and ∼50% is from Titan's H torus, implying that ∼20% comes from Saturn atmosphere.

  11. Cold Light from Hot Atoms and Molecules

    SciTech Connect

    Lister, Graeme; Curry, John J.

    2011-05-11

    The introduction of rare earth atoms and molecules into lighting discharges led to great advances in efficacy of these lamps. Atoms such as Dy, Ho and Ce provide excellent radiation sources for lighting applications, with rich visible spectra, such that a suitable combination of these elements can provide high quality white light. Rare earth molecules have also proved important in enhancing the radiation spectrum from phosphors in fluorescent lamps. This paper reviews some of the current aspects of lighting research, particularly rare earth chemistry and radiation, and the associated fundamental atomic and molecular data.

  12. Beam transport of low temperature atomic hydrogen

    NASA Astrophysics Data System (ADS)

    Kaufman, W. A.

    1993-12-01

    Analytic calculations and particle tracking simulations are presented for a polarized atomic hydrogen beam produced by extraction from an ultra-cold (T=300 mK) helium film coated cell in a large solenoidal magnetic field (12 T). Initial focusing of states 1 and 2 by the solenoidal field and subsequent focusing by a sextupole are examined within the constraints imposed by the requirements of the polarized jet for the experiments NEPTUN and NEPTUN-A at UNK.

  13. Solid Hydrogen Experiments for Atomic Propellants

    NASA Technical Reports Server (NTRS)

    Palaszewski, Bryan

    2001-01-01

    This paper illustrates experiments that were conducted on the formation of solid hydrogen particles in liquid helium. Solid particles of hydrogen were frozen in liquid helium, and observed with a video camera. The solid hydrogen particle sizes, their molecular structure transitions, and their agglomeration times were estimated. article sizes of 1.8 to 4.6 mm (0.07 to 0. 18 in.) were measured. The particle agglomeration times were 0.5 to 11 min, depending on the loading of particles in the dewar. These experiments are the first step toward visually characterizing these particles, and allow designers to understand what issues must be addressed in atomic propellant feed system designs for future aerospace vehicles.

  14. Reaction of atomic hydrogen with formic acid.

    PubMed

    Cao, Qian; Berski, Slawomir; Latajka, Zdzislaw; Räsänen, Markku; Khriachtchev, Leonid

    2014-04-01

    We study the reaction of atomic hydrogen with formic acid and characterize the radical products using IR spectroscopy in a Kr matrix and quantum chemical calculations. The reaction first leads to the formation of an intermediate radical trans-H2COOH, which converts to the more stable radical trans-cis-HC(OH)2via hydrogen atom tunneling on a timescale of hours at 4.3 K. These open-shell species are observed for the first time as well as a reaction between atomic hydrogen and formic acid. The structural assignment is aided by extensive deuteration experiments and ab initio calculations at the UMP2 and UCCSD(T) levels of theory. The simplest geminal diol radical trans-cis-HC(OH)2 identified in the present work as the final product of the reaction should be very reactive, and further reaction channels are of particular interest. These reactions and species may constitute new channels for the initiation and propagation of more complex organic species in the interstellar clouds.

  15. Fourteen Years of Atomic Hydrogen from SABER

    NASA Astrophysics Data System (ADS)

    Hunt, L. A.; Mlynczak, M. G.

    2015-12-01

    We present results for atomic hydrogen in the mesopause region (80-100 km) derived from measurements made by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the TIMED satellite. SABER has been measuring the vertical distribution of infrared radiation emitted by various atmospheric gases for nearly 14 years, providing important information about chemical species, including atomic oxygen, atomic hydrogen, ozone and hydroxyl; temperature; and the radiation budget in the upper atmosphere. The methodology for the derivation of daytime and nighttime concentrations and volume mixing ratios will be presented. Zonal mean and global average daytime and nighttime concentrations of H, which demonstrate excellent agreement between 87 and 95 km, have been calculated and the results are compared with observations from the Solar Mesosphere Explorer (SME) satellite made nearly 30 years ago. Variability over the course of the SABER mission will be shown, including the apparent inverse dependence on the solar cycle, which stems from the temperature dependence of various reaction rate coefficients for H photochemistry. Results for H near solar max will be compared for Solar Cycles 23 and 24.

  16. Transition Probabilities for Hydrogen-Like Atoms

    NASA Astrophysics Data System (ADS)

    Jitrik, Oliverio; Bunge, Carlos F.

    2004-12-01

    E1, M1, E2, M2, E3, and M3 transition probabilities for hydrogen-like atoms are calculated with point-nucleus Dirac eigenfunctions for Z=1-118 and up to large quantum numbers l=25 and n=26, increasing existing data more than a thousandfold. A critical evaluation of the accuracy shows a higher reliability with respect to previous works. Tables for hydrogen containing a subset of the results are given explicitly, listing the states involved in each transition, wavelength, term energies, statistical weights, transition probabilities, oscillator strengths, and line strengths. The complete results, including 1 863 574 distinct transition probabilities, lifetimes, and branching fractions are available at http://www.fisica.unam.mx/research/tables/spectra/1el

  17. Positron impact ionization of atomic hydrogen

    SciTech Connect

    Acacia, P.; Campeanu, R.I.; Horbatsch, M.

    1993-05-01

    We will present integrated cross sections for ionization of atomic hydrogen by positrons. These have been calculated in a distorted-wave approximation using energy-dependent effective charges in the final channel as well as static and polarization potentials in the initial channel. We present two models for calculating the energy-dependent effective charges both of which produce results in good agreement with the recent experimental measurements of Spicher et al. This is in contrast to previous distorted-wave calculations which used fixed effective charges as well as classical trajectory calculations. Both of these latter methods produced results which were substantially below ours and the experimental data.

  18. ATOMIC HYDROGEN IN A GALACTIC CENTER OUTFLOW

    SciTech Connect

    McClure-Griffiths, N. M.; Green, J. A.; Hill, A. S.; Lockman, F. J.; Dickey, J. M.; Gaensler, B. M.; Green, A. J.

    2013-06-10

    We describe a population of small, high-velocity, atomic hydrogen clouds, loops, and filaments found above and below the disk near the Galactic center. The objects have a mean radius of 15 pc, velocity widths of {approx}14 km s{sup -1}, and are observed at |z| heights up to 700 pc. The velocity distribution of the clouds shows no signature of Galactic rotation. We propose a scenario where the clouds are associated with an outflow from a central star-forming region at the Galactic center. We discuss the clouds as entrained material traveling at {approx}200 km s{sup -1} in a Galactic wind.

  19. Functionalization of Carbon Nanotubes using Atomic Hydrogen

    NASA Technical Reports Server (NTRS)

    Khare, Bishun N.; Cassell, Alan M.; Nguyen, Cattien V.; Meyyappan, M.; Han, Jie; Arnold, Jim (Technical Monitor)

    2001-01-01

    We have investigated the irradiation of multi walled and single walled carbon nanotubes (SWNTs) with atomic hydrogen. After irradiating the SWNT sample, a band at 2940/cm (3.4 microns) that is characteristic of the C-H stretching mode is observed using Fourier transform infrared (FTIR) spectroscopy. Additional confirmation of SWNT functionalization is tested by irradiating with atomic deuterium. A weak band in the region 1940/cm (5.2 micron) to 2450/cm (4.1 micron) corresponding to C-D stretching mode is also observed in the FTIR spectrum. This technique provides a clean gas phase process for the functionalization of SWNTs, which could lead to further chemical manipulation and/or the tuning of the electronic properties of SWNTs for nanodevice applications.

  20. Isotope effects of hydrogen and atom tunnelling

    NASA Astrophysics Data System (ADS)

    Buchachenko, A. L.; Pliss, E. M.

    2016-06-01

    The abnormally high mass-dependent isotope effects in liquid-phase hydrogen (deuterium) atom transfer reactions, which are customarily regarded as quantum effects, are actually the products of two classical effects, namely, kinetic and thermodynamic ones. The former is determined by the rate constants for atom transfer and the latter is caused by nonbonded (or noncovalent) isotope effects in the solvation of protiated and deuterated reacting molecules. This product can mimic the large isotope effects that are usually attributed to tunnelling. In enzymatic reactions, tunnelling is of particular interest; its existence characterizes an enzyme as a rigid molecular machine in which the residence time of reactants on the reaction coordinate exceeds the waiting time for the tunnelling event. The magnitude of isotope effect becomes a characteristic parameter of the internal dynamics of the enzyme catalytic site. The bibliography includes 61 references.

  1. Dynamical Crossover in Hot Dense Water: The Hydrogen Bond Role.

    PubMed

    Ranieri, Umbertoluca; Giura, Paola; Gorelli, Federico A; Santoro, Mario; Klotz, Stefan; Gillet, Philippe; Paolasini, Luigi; Koza, Michael Marek; Bove, Livia E

    2016-09-01

    We investigate the terahertz dynamics of liquid H2O as a function of pressure along the 450 K isotherm, by coupled quasielastic neutron scattering and inelastic X-ray scattering experiments. The pressure dependence of the single-molecule dynamics is anomalous in terms of both microscopic translation and rotation. In particular, the Stokes-Einstein-Debye equations are shown to be violated in hot water compressed to the GPa regime. The dynamics of the hydrogen bond network is only weakly affected by the pressure variation. The time scale of the structural relaxation driving the collective dynamics increases by a mere factor of 2 along the investigated isotherm, and the structural relaxation strength turns out to be almost pressure independent. Our results point at the persistence of the hydrogen bond network in hot dense water up to ice VII crystallization, thus questioning the long-standing perception that hydrogen bonds are broken in liquid water under the effect of compression. PMID:27479235

  2. Hydrogen atom in a laser-plasma

    NASA Astrophysics Data System (ADS)

    Falaye, Babatunde J.; Sun, Guo-Hua; Liman, Muhammed S.; Oyewumi, K. J.; Dong, Shi-Hai

    2016-11-01

    We scrutinize the behaviour of the eigenvalues of a hydrogen atom in a quantum plasma as it interacts with an electric field directed along θ  =  π and is exposed to linearly polarized intense laser field radiation. We refer to the interaction of the plasma with the laser light as laser-plasma. Using the Kramers–Henneberger (KH) unitary transformation, which is the semiclassical counterpart of the Block–Nordsieck transformation in the quantized field formalism, the squared vector potential that appears in the equation of motion is eliminated and the resultant equation is expressed in the KH frame. Within this frame, the resulting potential and the corresponding wavefunction have been expanded in Fourier series, and using Ehlotzky’s approximation we obtain a laser-dressed potential to simulate an intense laser field. By fitting the exponential-cosine-screened Coulomb potential into the laser-dressed potential, and then expanding it in Taylor series up to O≤ft({{r}4},α 09\\right) , we obtain the eigensolution (eigenvalues and wavefunction) of the hydrogen atom in laser-plasma encircled by an electric field, within the framework of perturbation theory formalism. Our numerical results show that for a weak external electric field and a very large Debye screening parameter length, the system is strongly repulsive, in contrast with the case for a strong external electric field and a small Debye screening parameter length, when the system is very attractive. This work has potential applications in the areas of atomic and molecular processes in external fields, including interactions with strong fields and short pulses.

  3. Atomic hydrogen propellants: Historical perspectives and future possibilities

    NASA Astrophysics Data System (ADS)

    Palaszewski, Bryan

    1993-02-01

    Atomic hydrogen, a very high density free-radical propellant, is anticipated to generate a specific impulse of 600-1500 lb-f sec/lb-mass performance; this may facilitate the development of unique launch vehicles. A development status evaluation is presently given for atomic hydrogen investigations. It is noted that breakthroughs are required in the production, storage, and transfer of atomic hydrogen, before this fuel can become a viable rocket propellant.

  4. Atomic hydrogen propellants: Historical perspectives and future possibilities

    NASA Technical Reports Server (NTRS)

    Palaszewski, Bryan

    1993-01-01

    Atomic hydrogen, a very high density free-radical propellant, is anticipated to generate a specific impulse of 600-1500 lb-f sec/lb-mass performance; this may facilitate the development of unique launch vehicles. A development status evaluation is presently given for atomic hydrogen investigations. It is noted that breakthroughs are required in the production, storage, and transfer of atomic hydrogen, before this fuel can become a viable rocket propellant.

  5. In-Vacuum Dissociator for Atomic-Hydrogen Masers

    NASA Technical Reports Server (NTRS)

    Vessot, R. F.

    1987-01-01

    Thermal control and vacuum sealing achieved while contamination avoided. Simple, relatively inexpensive molecular-hydrogen dissociator for atomic-hydrogen masers used on Earth or in vacuum of space. No air cooling required, and absence of elastomeric O-ring seals prevents contamination. In-vacuum dissociator for atomic hydrogen masers, hydrogen gas in glass dissociator dissociated by radio-frequency signal transmitted from surrounding 3-turn coil. Heat in glass conducted away by contacting metal surfaces.

  6. Erosion of graphite surface exposed to hot supersonic hydrogen gas

    NASA Technical Reports Server (NTRS)

    Sharma, O. P.

    1972-01-01

    A theoretical model based on laminar boundary layer flow equations is developed to predict the erosion rate of a graphite (AGCarb-101) surface exposed to a hot supersonic stream of hydrogen gas. The supersonic flow in the nozzle outside the boundary layer formed over the surface of the specimen is determined by assuming one-dimensional isentropic conditions. An overall surface reaction rate expression based on the experimental studies by Clarke and Fox is used to describe the interaction of hydrogen with graphite. A satisfactory agreement is found between the results of the computation, and the available experimental data. Some shortcomings of the model, and further possible improvements are discussed.

  7. Hot hydrogen testing of metallic turbo pump materials

    NASA Technical Reports Server (NTRS)

    Zee, Ralph; Chin, Bryan; Inamdar, Rohit

    1993-01-01

    The objectives of this investigation are to expose heat resistant alloys to hydrogen at elevated temperatures and to use various microstructural and analytical techniques to determine the chemical and rate process involved in degradation of these materials due to hydrogen environment. Inconel 718 and NASA-23 (wrought and cast) are candidate materials. The degradation of these materials in the presence of 1 to 5 atmospheric pressure of hydrogen from 450 C to 1100 C was examined. The hydrogen facility at Auburn University was used for this purpose. Control experiments were also conducted wherein the samples were exposed to vacuum so that a direct comparison of the results would separate the thermal contribution from the hydrogen effects. The samples were analyzed prior to and after exposure. A residual gas collection system was used to determine the gaseous species produced by any chemical reaction that may have occurred during the exposure. Analysis of this gas sample shows only the presence of H2 as expected. Analyses of the samples were conducted using optical microscopy, x-ray diffraction, scanning electron microscopy, and weight change. There appears to be no change in weight of the samples as a result of hydrogen exposure. In addition no visible change on the surface structure was detected. This indicates that the materials of interest do not have strong interaction with hot hydrogen. This is consistent with the microstructure results.

  8. The gravitational analogue to the hydrogen atom

    NASA Astrophysics Data System (ADS)

    Kober, Martin; Koch, Ben; Bleicher, Marcus

    2007-05-01

    This paper reports on a student summer project performed in 2006 at the University of Frankfurt. It is addressed to undergraduate students familiar with the basic principles of relativistic quantum mechanics and general relativity. The aim of the project was to study the Dirac equation in curved spacetime. To obtain the general relativistic Dirac equation we use the formulation of gravity as a gauge theory in the first part. After these general considerations we restrict the further discussion to the special case of the Schwarzschild metric. This setting corresponds to the hydrogen atom, with the electromagnetic field replaced by gravity. Although there is a singularity at the event horizon it turns out that a regular solution of the time-independent Dirac equation exists. Finally the Dirac equation is solved numerically using suitable boundary conditions. A summer study at the borders of quantum mechanics and general relativity.

  9. Hydrogen diffusion and stabilization in single-crystal VO2 micro/nanobeams by direct atomic hydrogenation.

    PubMed

    Lin, Jian; Ji, Heng; Swift, Michael W; Hardy, Will J; Peng, Zhiwei; Fan, Xiujun; Nevidomskyy, Andriy H; Tour, James M; Natelson, Douglas

    2014-09-10

    We report measurements of the diffusion of atomic hydrogen in single crystalline VO2 micro/nanobeams by direct exposure to atomic hydrogen, without catalyst. The atomic hydrogen is generated by a hot filament, and the doping process takes place at moderate temperature (373 K). Undoped VO2 has a metal-to-insulator phase transition at ∼340 K between a high-temperature, rutile, metallic phase and a low-temperature, monoclinic, insulating phase with a resistance exhibiting a semiconductor-like temperature dependence. Atomic hydrogenation results in stabilization of the metallic phase of VO2 micro/nanobeams down to 2 K, the lowest point we could reach in our measurement setup. Optical characterization shows that hydrogen atoms prefer to diffuse along the c axis of rutile (a axis of monoclinic) VO2, along the oxygen "channels". Based on observing the movement of the hydrogen diffusion front in single crystalline VO2 beams, we estimate the diffusion constant for hydrogen along the c axis of the rutile phase to be 6.7 × 10(-10) cm(2)/s at approximately 373 K, exceeding the value in isostructural TiO2 by ∼38×. Moreover, we find that the diffusion constant along the c axis of the rutile phase exceeds that along the equivalent a axis of the monoclinic phase by at least 3 orders of magnitude. This remarkable change in kinetics must originate from the distortion of the "channels" when the unit cell doubles along this direction upon cooling into the monoclinic structure. Ab initio calculation results are in good agreement with the experimental trends in the relative kinetics of the two phases. This raises the possibility of a switchable membrane for hydrogen transport.

  10. Comparative Study on Hot Atom Coronae of Solar and Extrasolar Planets

    NASA Astrophysics Data System (ADS)

    Shematovich, Valery

    Solar/stellar forcing on the upper atmospheres of the solar and extrasolar planets via both absorption of the XUV (soft X-rays and extreme ultraviolet) radiation and atmospheric sputtering results in the formation of an extended neutral corona populated by the suprathermal (hot) H, C, N, and O atoms (see, e.g., Johnson et al., 2008). The hot corona, in turn, is altered by an inflow of the solar wind/magnetospheric plasma and local pick-up ions onto the planetary exosphere. Such inflow results in the formation of the superthermal atoms (energetic neutral atoms - ENAs) due to the charge exchange with the high-energy precipitating ions and can affect the long-term evolution of the atmosphere due to the atmospheric escape. The origin, kinetics and transport of the suprathermal H, C, N, and O atoms in the transition regions (from thermosphere to exosphere) of the planetary atmospheres are discussed. Reactions of dissociative recombination of the ionospheric ions CO _{2} (+) , CO (+) , O _{2} (+) , and N _{2} (+) with thermal electrons are the main photochemical sources of hot atoms. The dissociation of atmospheric molecules by the solar/stellar XUV radiation and accompanying photoelectron fluxes and the induced exothermic photochemistry are also the important sources of the suprathermal atoms. Such kinetic systems with the non-thermal processes are usually investigated with the different (test particles, DSMC, and hybrid) versions of the kinetic Monte Carlo method. In our studies the kinetic energy distribution functions of suprathermal and superthermal atoms were calculated using the stochastic model of the hot planetary corona (Shematovich, 2004, 2010; Groeller et al., 2014), and the Monte Carlo model (Shematovich et al., 2011, 2013) of the high-energy proton and hydrogen atom precipitation into the atmosphere respectively. These functions allowed us to estimate the space distribution of suprathermals in the planetary transition regions. An application of these

  11. Atomic-scale control of graphene magnetism by using hydrogen atoms.

    PubMed

    González-Herrero, Héctor; Gómez-Rodríguez, José M; Mallet, Pierre; Moaied, Mohamed; Palacios, Juan José; Salgado, Carlos; Ugeda, Miguel M; Veuillen, Jean-Yves; Yndurain, Félix; Brihuega, Iván

    2016-04-22

    Isolated hydrogen atoms absorbed on graphene are predicted to induce magnetic moments. Here we demonstrate that the adsorption of a single hydrogen atom on graphene induces a magnetic moment characterized by a ~20-millielectron volt spin-split state at the Fermi energy. Our scanning tunneling microscopy (STM) experiments, complemented by first-principles calculations, show that such a spin-polarized state is essentially localized on the carbon sublattice opposite to the one where the hydrogen atom is chemisorbed. This atomically modulated spin texture, which extends several nanometers away from the hydrogen atom, drives the direct coupling between the magnetic moments at unusually long distances. By using the STM tip to manipulate hydrogen atoms with atomic precision, it is possible to tailor the magnetism of selected graphene regions.

  12. Infrared dynamics of cold atoms on hot graphene membranes

    NASA Astrophysics Data System (ADS)

    Sengupta, Sanghita; Kotov, Valeri N.; Clougherty, Dennis P.

    2016-06-01

    We study the infrared dynamics of low-energy atoms interacting with a sample of suspended graphene at finite temperature. The dynamics exhibits severe infrared divergences order by order in perturbation theory as a result of the singular nature of low-energy flexural phonon emission. Our model can be viewed as a two-channel generalization of the independent boson model with asymmetric atom-phonon coupling. This allows us to take advantage of the exact nonperturbative solution of the independent boson model in the stronger channel while treating the weaker one perturbatively. In the low-energy limit, the exact solution can be viewed as a resummation (exponentiation) of the most divergent diagrams in the perturbative expansion. As a result of this procedure, we obtain the atom's Green function which we use to calculate the atom damping rate, a quantity equal to the quantum sticking rate. A characteristic feature of our results is that the Green's function retains a weak, infrared cutoff dependence that reflects the reduced dimensionality of the problem. As a consequence, we predict a measurable dependence of the sticking rate on graphene sample size. We provide detailed predictions for the sticking rate of atomic hydrogen as a function of temperature and sample size. The resummation yields an enhanced sticking rate relative to the conventional Fermi golden rule result (equivalent to the one-loop atom self-energy), as higher-order processes increase damping at finite temperature.

  13. Hirshfeld atom refinement for modelling strong hydrogen bonds.

    PubMed

    Woińska, Magdalena; Jayatilaka, Dylan; Spackman, Mark A; Edwards, Alison J; Dominiak, Paulina M; Woźniak, Krzysztof; Nishibori, Eiji; Sugimoto, Kunihisa; Grabowsky, Simon

    2014-09-01

    High-resolution low-temperature synchrotron X-ray diffraction data of the salt L-phenylalaninium hydrogen maleate are used to test the new automated iterative Hirshfeld atom refinement (HAR) procedure for the modelling of strong hydrogen bonds. The HAR models used present the first examples of Z' > 1 treatments in the framework of wavefunction-based refinement methods. L-Phenylalaninium hydrogen maleate exhibits several hydrogen bonds in its crystal structure, of which the shortest and the most challenging to model is the O-H...O intramolecular hydrogen bond present in the hydrogen maleate anion (O...O distance is about 2.41 Å). In particular, the reconstruction of the electron density in the hydrogen maleate moiety and the determination of hydrogen-atom properties [positions, bond distances and anisotropic displacement parameters (ADPs)] are the focus of the study. For comparison to the HAR results, different spherical (independent atom model, IAM) and aspherical (free multipole model, MM; transferable aspherical atom model, TAAM) X-ray refinement techniques as well as results from a low-temperature neutron-diffraction experiment are employed. Hydrogen-atom ADPs are furthermore compared to those derived from a TLS/rigid-body (SHADE) treatment of the X-ray structures. The reference neutron-diffraction experiment reveals a truly symmetric hydrogen bond in the hydrogen maleate anion. Only with HAR is it possible to freely refine hydrogen-atom positions and ADPs from the X-ray data, which leads to the best electron-density model and the closest agreement with the structural parameters derived from the neutron-diffraction experiment, e.g. the symmetric hydrogen position can be reproduced. The multipole-based refinement techniques (MM and TAAM) yield slightly asymmetric positions, whereas the IAM yields a significantly asymmetric position.

  14. Quantum Sticking of Atomic Hydrogen to Graphene

    NASA Astrophysics Data System (ADS)

    Zhang, Yanting; Doherty, Adam; Geragotelis, Andrew; Clougherty, Dennis

    2013-03-01

    We consider the low-energy behavior of the sticking probability of atomic hydrogen to suspended graphene. For energy transfer through the flexural modes of graphene, we find that the inelastic coupling falls in the subOhmic regime. Thus the effects of low-frequency fluctuations of the graphene sheet are crucially important for quantum sticking. We analytically solve for the low-energy asymptotic behavior of the sticking coefficient using a variational mean-field method [D.P. Clougherty and Y. Zhang, Phys. Rev. Lett. 109, 120401 (2012)]. We find that as a result of strong coupling to the low-frequency flexural modes of graphene, a new scaling law results. For suspended graphene at finite temperature, we find that at a critical incident energy, the sticking probability drops discontinuously; below this critical energy, the sticking probability is suppressed by the orthogonality catastrophe. We compare our nonperturbative variational results to those obtained by using Fermi's golden rule. We gratefully acknowledge support by the National Science Foundation under DMR-1062966.

  15. The one-dimensional hydrogen atom revisited

    NASA Astrophysics Data System (ADS)

    Palma, G.; Raff, U.

    2006-09-01

    The one-dimensional Schrodinger hydrogen atom is an interesting mathematical and physical problem for the study of bound states, eigenfunctions, and quantum-degeneracy issues. This one-dimensional physical system has given rise to some intriguing controversy for more than four decades. Presently, still no definite consensus seems to have been reached. We reanalyzed this apparently controversial problem, approaching it from a Fourier-transform representation method combined with some fundamental (basic) ideas found in self-adjoint extensions of symmetric operators. In disagreement with some previous claims, we found that the complete Balmer energy spectrum is obtained together with an odd-parity set of eigenfunctions. Closed-form solutions in both coordinate and momentum spaces were obtained. No twofold degeneracy was observed as predicted by the degeneracy theorem in one dimension, though it does not necessarily have to hold for potentials with singularities. No ground state with infinite energy exists since the corresponding eigenfunction does not satisfy the Schrodinger equation at the origin.

  16. Effects of hydrogen atoms on surface conductivity of diamond film

    SciTech Connect

    Liu, Fengbin Cui, Yan; Qu, Min; Di, Jiejian

    2015-04-15

    To investigate the effects of surface chemisorbed hydrogen atoms and hydrogen atoms in the subsurface region of diamond on surface conductivity, models of hydrogen atoms chemisorbed on diamond with (100) orientation and various concentrations of hydrogen atoms in the subsurface layer of the diamond were built. By using the first-principles method based on density functional theory, the equilibrium geometries and densities of states of the models were studied. The results showed that the surface chemisorbed hydrogen alone could not induce high surface conductivity. In addition, isolated hydrogen atoms in the subsurface layer of the diamond prefer to exist at the bond centre site of the C-C bond. However, such a structure would induce deep localized states, which could not improve the surface conductivity. When the hydrogen concentration increases, the C-H-C-H structure and C-3H{sub bc}-C structure in the subsurface region are more stable than other configurations. The former is not beneficial to the increase of the surface conductivity. However, the latter would induce strong surface states near the Fermi level, which would give rise to high surface conductivity. Thus, a high concentration of subsurface hydrogen atoms in diamond would make significant contributions to surface conductivity.

  17. Use of predissociation to enhance the atomic hydrogen ion fraction in ion sources

    DOEpatents

    Kim, Jinchoon

    1979-01-01

    A duopigatron ion source is modified by replacing the normal oxide-coated wire filament cathode of the ion source with a hot tungsten oven through which hydrogen gas is fed into the arc chamber. The hydrogen gas is predissociated in the hot oven prior to the arc discharge, and the recombination rate is minimized by hot walls inside of the arc chamber. With the use of the above modifications, the atomic H.sub.1.sup.+ ion fraction output can be increased from the normal 50% to greater than 70% with a corresponding decrease in the H.sub.2.sup.+ and H.sub.3.sup.+ molecular ion fraction outputs from the ion source.

  18. Long Duration Hot Hydrogen Exposure of Nuclear Thermal Rocket Materials

    NASA Technical Reports Server (NTRS)

    Litchford, Ron J.; Foote, John P.; Hickman, Robert; Dobson, Chris; Clifton, Scooter

    2007-01-01

    An arc-heater driven hyper-thermal convective environments simulator was recently developed and commissioned for long duration hot hydrogen exposure of nuclear thermal rocket materials. This newly established non-nuclear testing capability uses a high-power, multi-gas, wall-stabilized constricted arc-heater to .produce high-temperature pressurized hydrogen flows representative of nuclear reactor core environments, excepting radiation effects, and is intended to serve as a low cost test facility for the purpose of investigating and characterizing candidate fuel/structural materials and improving associated processing/fabrication techniques. Design and engineering development efforts are fully summarized, and facility operating characteristics are reported as determined from a series of baseline performance mapping runs and long duration capability demonstration tests.

  19. Surface characterization of silica glass substrates treated by atomic hydrogen

    SciTech Connect

    Inoue, Hiroyuki; Masuno, Atsunobu; Ishibashi, Keiji; Tawarayama, Hiromasa; Zhang, Yingjiu; Utsuno, Futoshi; Koya, Kazuo; Fujinoki, Akira; Kawazoe, Hiroshi

    2013-12-15

    Silica glass substrates with very flat surfaces were exposed to atomic hydrogen at different temperatures and durations. An atomic force microscope was used to measure root-mean-square (RMS) roughness and two-dimensional power spectral density (PSD). In the treatment with atomic hydrogen up to 900 °C, there was no significant change in the surface. By the treatment at 1000 °C, the changes in the RMS roughness and the PSD curves were observed. It was suggested that these changes were caused by etching due to reactions of atomic hydrogen with surface silica. By analysis based on the k-correlation model, it was found that the spatial frequency of the asperities became higher with an increase of the treatment time. Furthermore, the data showed that atomic hydrogen can flatten silica glass surfaces by controlling heat-treatment conditions. - Highlights: • Silica glass surface was treated by atomic hydrogen at various temperatures. • Surface roughness was measured by an atomic force microscope. • Roughness data were analyzed by two-dimensional power spectral density. • Atomic hydrogen can flatten silica glass surfaces.

  20. Atomic hydrogen adsorption on lithium-doped graphite surfaces

    SciTech Connect

    Allouche, Alain

    2012-01-01

    The effects of lithium doping of pristine and defective graphite surfaces on hydrogen adsorption are studied by the first-principles Plane-Wave Density Functional Theory. The surface defects are simulated by a single atomic vacancy. The DFT calculation is corrected for long-range effects through semi-empirical London terms for each constituent of the system. The lithium doping of the graphite surfaces notably reinforces hydrogen atom binding. Qualitative comparison with experimental results is given using the lithium 1s energy level shifts induced by the atomic vacancy and/or hydrogen trapping.

  1. Hot-atom synthesis of organic compounds on Jupiter

    NASA Technical Reports Server (NTRS)

    Lewis, J. S.; Fegley, B., Jr.

    1979-01-01

    Results of recent laboratory 'simulations' of photochemical processes on Jupiter are combined with available data on mixing rates and exposure times in the Jovian atmosphere to give quantitative predictions of the rate at which hot-atom reactions produce organic molecules. It is shown that abstraction reactions on methane by hot H atoms from solar UV photolysis of H2S will produce no more than 4 times 10 to the -17th power g/sq cm/sec for a steady-state mole fraction of total organics of approximately 10 to the -16th power. This is roughly 10 to the 7th power times less than the limit of detection of the most sensitive gas analysis experiments ever flown on a spacecraft. By far the most common organic molecule produced by this mechanism is CH3SH, methyl mercaptan, which is produced at a rate at least 600 times smaller than the rate of production of ethane by direct photolysis of CH4 at high altitudes.

  2. Atomic hydrogen and nitrogen distributions from atmosphere explorer measurements

    NASA Technical Reports Server (NTRS)

    Breig, Edward L.

    1992-01-01

    We were selective as to our approach to research activities, and devoted primary attention to two investigations concerning the global behavior of atomic hydrogen in the Earth's upper atmosphere. We derive the thermospheric concentration of H by applying the condition of charge-exchange equilibrium between hydrogen and oxygen atoms and ions to in-situ measurements of F-region composition and temperature from the series of Atmosphere Explorer (AE) aeronomy satellites. Progress and accomplishments on these chosen research projects are summarized.

  3. Ultra-cold methods for polarized atomic hydrogen

    SciTech Connect

    Luppov, V. G.; Arnold, J. D.; Blinov, B. B.; Gladycheva, S. E.; Krisch, A. D.; Lin, A. M. T.; Raymond, R. S.; Bychkov, M. A.; Fimushkin, V. V.; Mochalov, V. V.; Semenov, P. A.

    1998-01-20

    Using the ultra-cold electron-spin-polarized atomic hydrogen technique, one can produce a slow monochromatic beam for use as a polarized jet target. We will first review the development of the ultra-cold technique and then discuss the recent progress on Michigan's Mark-II ultra-cold proton-spin-polarized hydrogen jet target.

  4. Topics in atomic hydrogen standard research and applications

    NASA Technical Reports Server (NTRS)

    Peters, H. E.

    1971-01-01

    Hydrogen maser based frequency and time standards have been in continuous use at NASA tracking stations since February 1970, while laboratory work at Goddard has continued in the further development and improvement of hydrogen masers. Concurrently, experimental work has been in progress with a new frequency standard based upon the hydrogen atom using the molecular beam magnetic resonance method. Much of the hydrogen maser technology is directly applicable to the new hydrogen beam standard, and calculations based upon realistic data indicate that the accuracy potential of the hydrogen atomic beam exceeds that of either the cesium beam tube or the hydrogen maser, possibly by several orders of magnitude. In addition, with successful development, the hydrogen beam standard will have several other performance advantages over other devices, particularly exceptional stability and long continuous operating life. Experimental work with a new laboratory hydrogen beam device has recently resulted in the first resonance transition curves, measurements of relative state populations, beam intensities, etc. The most important aspects of both the hydrogen maser and the hydrogen beam work are covered.

  5. Absolute frequency of an atomic hydrogen maser clock

    NASA Technical Reports Server (NTRS)

    Peters, H. E.; Hall, R. G.; Percival, D. B.

    1972-01-01

    An accurate determination was made of the unperturbed atomic hydrogen ground state hyperfine transition frequency (F=1,m=0 - F=0,m=0) in reference to present world wide realizations of internationally defined time interval. In relation to the international atomic time system, the composite value is 1,420,405,751.7755 plus or minus 0.0031 HZ.

  6. Concerted hydrogen atom exchange between three HF molecules

    NASA Technical Reports Server (NTRS)

    Komornicki, Andrew; Dixon, David A.; Taylor, Peter R.

    1992-01-01

    The termolecular reaction involving concerted hydrogen-atom exchange between three HF molecules was investigated with particular attention given to the effects of correlation at the various stationary points along the reaction. Using large segmented Gaussian basis sets to locate the (HF)3 stationary points at the SCF level, the geometries of the stable hydrogen-bonded trimer, which is of C(3h) symmetry, were located, together with the transition state for hydrogen exchange, which is of D(3h) symmetry. Then, using a large atomic natural orbital basis and correlating all valence electrons, the energetics of the exchange reaction were evaluated at the correlated level.

  7. Bonding changes in hot fluid hydrogen at megabar pressures

    PubMed Central

    Subramanian, Natarajan; Goncharov, Alexander F.; Struzhkin, Viktor V.; Somayazulu, Maddury; Hemley, Russell J.

    2011-01-01

    Raman spectroscopy in laser-heated diamond anvil cells has been employed to probe the bonding state and phase diagram of dense hydrogen up to 140 GPa and 1,500 K. The measurements were made possible as a result of the development of new techniques for containing and probing the hot, dense fluid, which is of fundamental importance in physics, planetary science, and astrophysics. A pronounced discontinuous softening of the molecular vibron was found at elevated temperatures along with a large broadening and decrease in intensity of the roton bands. These phenomena indicate the existence of a state of the fluid having significantly modified intramolecular bonding. The results are consistent with the existence of a pressure-induced transformation in the fluid related to the presence of a temperature maximum in the melting line as a function of pressure. PMID:21447715

  8. Characterization of an atomic hydrogen source for charge exchange experiments

    NASA Astrophysics Data System (ADS)

    Leutenegger, M. A.; Beiersdorfer, P.; Betancourt-Martinez, G. L.; Brown, G. V.; Hell, N.; Kelley, R. L.; Kilbourne, C. A.; Magee, E. W.; Porter, F. S.

    2016-11-01

    We characterized the dissociation fraction of a thermal dissociation atomic hydrogen source by injecting the mixed atomic and molecular output of the source into an electron beam ion trap containing highly charged ions and recording the x-ray spectrum generated by charge exchange using a high-resolution x-ray calorimeter spectrometer. We exploit the fact that the charge exchange state-selective capture cross sections are very different for atomic and molecular hydrogen incident on the same ions, enabling a clear spectroscopic diagnostic of the neutral species.

  9. Precision Spectroscopy of Atomic Hydrogen and the Proton Size Puzzle

    NASA Astrophysics Data System (ADS)

    Udem, Thomas

    2016-05-01

    Precise determination of transition frequencies of simple atomic systems are required for a number of fundamental applications such as tests of quantum electrodynamics (QED), the determination of fundamental constants and nuclear charge radii. The sharpest transition in atomic hydrogen occurs between the metastable 2S state and the 1S ground state. Its transition frequency has now been measured with almost 15 digits accuracy using an optical frequency comb and a cesium atomic clock as a reference. A recent measurement of the Lamb shift in muonic hydrogen is in significant contradiction to the hydrogen data if QED calculations are assumed to be correct. We hope to contribute to the resolution of this so called `proton size puzzle' by providing additional experimental input from the hydrogen side.

  10. The sticking of atomic hydrogen on amorphous water ice

    SciTech Connect

    Veeraghattam, Vijay K.; Manrodt, Katie; Lewis, Steven P.; Stancil, P. C. E-mail: lewis@physast.uga.edu

    2014-07-20

    Using classical molecular dynamics, we have simulated the sticking and scattering process of a hydrogen atom on an amorphous ice film to predict the sticking probability of hydrogen on ice surfaces. A wide range of initial kinetic energies of the incident hydrogen atom (10 K-600 K) and two different ice temperatures (10 K and 70 K) were used to investigate this fundamental process in interstellar chemistry. We report here the sticking probability of atomic hydrogen as a function of incident kinetic energy, gas temperature, and substrate temperature, which can be used in astrophysical models. The current results are compared to previous theoretical and experimental studies that have reported a wide range in the sticking coefficient.

  11. Hydrogen transport diagnostics by atomic and molecular emission line profiles simultaneously measured for large helical device

    SciTech Connect

    Fujii, K.; Shikama, T.; Hasuo, M.; Goto, M.; Morita, S.

    2013-01-15

    We observe the Balmer-{alpha}, -{beta}, and -{gamma} lines of hydrogen atoms and Q branches of the Fulcher-{alpha} band of hydrogen molecules simultaneously with their polarization resolved for large helical device. From the fit including the line splits and the polarization dependences by the Zeeman effect, the emission locations, intensities, and the temperatures of the atoms and molecules are determined. The emission locations of the hydrogen atoms are determined outside but close to the last closed flux surface (LCFS). The results are consistent with a previous work (Phys. Plasmas 12, 042501 (2005)). On the other hand, the emission locations of the molecules are determined to be in the divertor legs, which is farer from those of the atoms. The kinetic energy of the atoms is 1 {approx} 20 eV, while the rotational temperature of molecules is {approx}0.04 eV. Additionally, substantial wings, which originate from high velocity atoms and are not reproduced by the conventional spectral analysis, are observed in the Balmer line profiles. We develop a one-dimensional model to simulate the transport of the atoms and molecules. The model reproduces the differences of the emission locations of the atoms and molecules when their initial temperatures are assumed to be 3 eV and 0.04 eV, respectively. From the model, the wings of the Balmer-{alpha} line is attributed to the high velocity atoms exist deep inside the LCFS, which are generated by the charge exchange collisions with hot protons there.

  12. Cold atomic hydrogen in the inner galaxy

    NASA Technical Reports Server (NTRS)

    Dickey, J. M.; Garwood, R. W.

    1986-01-01

    The VLA is used to measure 21 cm absorption in directions with the absolute value of b less than 1 deg., the absolute value of 1 less than 25 deg. to probe the cool atomic gas in the inner galaxy. Abundant H I absorption is detected; typical lines are deep and narrow, sometimes blending in velocity with adjacent features. Unlike 21 cm emission not all allowed velocities are covered: large portions of the l-v diagram are optically thin. Although not similar to H I emission, the absorption shows a striking correspondence with CO emission in the inner galaxy: essentially every strong feature detected in one survey is seen in the other. The provisional conclusion is that in the inner galaxy most cool atomic gas is associated with molecular cloud complexes. There are few or no cold atomic clouds devoid of molecules in the inner galaxy, although these are common in the outer galaxy.

  13. Thermochemical nonequilibrium in atomic hydrogen at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Scott, R. K.

    1972-01-01

    A numerical study of the nonequilibrium flow of atomic hydrogen in a cascade arc was performed to obtain insight into the physics of the hydrogen cascade arc. A rigorous mathematical model of the flow problem was formulated, incorporating the important nonequilibrium transport phenomena and atomic processes which occur in atomic hydrogen. Realistic boundary conditions, including consideration of the wall electrostatic sheath phenomenon, were included in the model. The governing equations of the asymptotic region of the cascade arc were obtained by writing conservation of mass and energy equations for the electron subgas, an energy conservation equation for heavy particles and an equation of state. Finite-difference operators for variable grid spacing were applied to the governing equations and the resulting system of strongly coupled, stiff equations were solved numerically by the Newton-Raphson method.

  14. Atomic hydrogen on Mars - Measurements at solar minimum

    NASA Technical Reports Server (NTRS)

    Levine, J. S.; Mcdougal, D. S.; Anderson, D. E., Jr.; Barker, E. S.

    1978-01-01

    The Copernicus Orbiting Astronomical Observatory was used to obtain measurements of Mars Lyman-alpha (1215.671-angstrom) emission at the solar minimum, which has resulted in the first information on atomic hydrogen concentrations in the upper atmosphere of Mars at the solar minimum. The Copernicus measurements, coupled with the Viking in situ measurements of the temperature (170 plus or minus 30 K) of the upper atmosphere of Mars, indicate that the atomic hydrogen number density at the exobase of Mars (250 kilometers) is about 60 times greater than that deduced from Mariner 6 and 7 Lyman-alpha measurements obtained during a period of high solar activity. The Copernicus results are consistent with Hunten's hypothesis of the diffusion-limited escape of atomic hydrogen from Mars.

  15. Sensor for measuring the atomic fraction in highly dissociated hydrogen

    SciTech Connect

    Gardner, W.L.

    1994-12-31

    Atomic hydrogen is a very important constituent for processes ranging from cleaning oxide from GaAs and annealing amorphous silicon to the deposition of diamond. Because the usual techniques for measuring atomic fraction are either expensive and cumbersome to use, or unsuitable for application to highly dissociated hydrogen, a specially designed sensor was developed. Sensor design is based on a diffusion tube with noncatalytic walls, having one end open to the atom source and a catalytic closure at the other end. The sensor is simple and inexpensive to fabricate, and determining atom density is straightforward. Sensor design also inhibits thermal runaway, which occurs when atom density is high enough to impart enough recombination energy to the non-catalytic surface to substantially raise its temperature. While recombination coefficients for such surfaces are very low near room temperature, they increase nearly exponentially with temperature unless actively cooled. With the use of a straightforward calibration scheme to determine the variation in species fraction along the diffusion tube, the atomic fraction at the tube opening is determined. Design strategy, implementation considerations, and calibration method are presented. In addition, data obtained from an atomic hydrogen source are compared to relevant published data.

  16. Proton form factor effects in hydrogenic atoms

    SciTech Connect

    Daza, F. Garcia; Kelkar, N. G.; Nowakowski, M.

    2011-10-21

    The proton structure corrections to the hyperfine splittings in electronic and muonic hydrogen are evaluated using the Breit potential with electromagnetic form factors. In contrast to other methods, the Breit equation with q{sup 2} dependent form factors is just an extension of the standard Breit equation which gives the hyperfine splitting Hamiltonian. Precise QED corrections are comparable to the structure corrections which therefore need to be evaluated ab initio.

  17. Atomic hydrogen distribution. [in Titan atmospheric model

    NASA Technical Reports Server (NTRS)

    Tabarie, N.

    1974-01-01

    Several possible H2 vertical distributions in Titan's atmosphere are considered with the constraint of 5 km-A a total quantity. Approximative calculations show that hydrogen distribution is quite sensitive to two other parameters of Titan's atmosphere: the temperature and the presence of other constituents. The escape fluxes of H and H2 are also estimated as well as the consequent distributions trapped in the Saturnian system.

  18. Ultra-cold methods for polarized atomic hydrogen

    SciTech Connect

    Luppov, V.G.; Arnold, J.D.; Blinov, B.B.; Bychkov, M.A.; Gladycheva, S.E.; Krisch, A.D.; Lin, A.M.; Raymond, R.S.; Fimushkin, V.V.; Bychkov, M.A.; Mochalov, V.V.; Semenov, P.A.

    1998-01-01

    Using the ultra-cold electron-spin-polarized atomic hydrogen technique, one can produce a slow monochromatic beam for use as a polarized jet target. We will first review the development of the ultra-cold technique and then discuss the recent progress on Michigan{close_quote}s Mark-II ultra-cold proton-spin-polarized hydrogen jet target. {copyright} {ital 1998 American Institute of Physics.}

  19. Michigan ultra-cold polarized atomic hydrogen jet target

    NASA Astrophysics Data System (ADS)

    Blinov, B. B.; Gladycheva, S. E.; Kageya, T.; Kantsyrev, D. Yu.; Krisch, A. D.; Luppov, V. G.; Morozov, V. S.; Murray, J. R.; Raymond, R. S.; Borisov, N. S.; Fimushkin, V. V.; Grishin, V. N.; Mysnik, A. I.; Kleppner, D.

    2001-06-01

    To study spin effects in high energy collisions, we are developing an ultra-cold high-density jet target of proton-spin-polarized hydrogen atoms. The target uses a 12 Tesla magnetic field and a 0.3 K separation cell coated with superfluid helium-4 to produce a slow monochromatic electron-spin-polarized atomic hydrogen beam, which is then focused by a superconducting sextupole into the interaction region. In recent tests, we studied a polarized beam of hydrogen atoms focused by the superconducting sextupole into a compression tube detector, which measured the polarized atoms' intensity. The Jet produced, at the detector, a spin-polarized atomic hydrogen beam with a measured intensity of about 2.8.1015 H s-1 and a FWHM area of less than 0.13 cm2. This intensity corresponds to a free jet density of about 1.1012 H cm-3 with a proton polarization of about 50%. When the transition RF unit is installed, we expect a proton polarization higher than 90%. .

  20. Slow metastable atomic hydrogen beam by optical pumping

    NASA Astrophysics Data System (ADS)

    Harvey, K. C.

    1982-05-01

    A beam source of atomic hydrogen is described which produces metastable atoms in the 2S1/2 state by optical pumping. A beam flux of 1016 atoms/s is generated in the ground state. The atoms in the beam pass in front of a lamp producing Lyman-β (1026 Å) radiation, where some of them are excited to the 3P level and cascade with a branching ratio of 12% to the 2S1/2 state. The number of metastable atoms produced is measured by quenching them with an electric field and detecting the emitted Lyman-α (1216 Å) radiation. Beams of 106 metastable atoms/s were obtained. Using the Bethe-Lamb theory for the quenching process, a metastable beam effective temperature of 100 K was measured.

  1. Probing the heliosphere with energetic hydrogen atoms

    NASA Technical Reports Server (NTRS)

    Hsieh, K. C.; Shih, K. L.; Jokipii, J. R.; Grzedzielski, S.

    1992-01-01

    The idea of using energetic neutral atoms (ENAs), produced by charge exchange between energetic ions and ambient neutral atoms, as a diagnostic tool to investigate planetary magnetospheres from a distance has been extended to the investigation of the heliosphere. The paper explores what one can reasonably expect of the heliospheric ENA (HSENA) and what criteria would be imposed on HSENA instruments by concentrating on 10-10 exp 3 keV protons in quiet-time interplanetary space, solar-flare events, corotating interaction regions, and populations have distinctive signatures and that the detection of these particles can reveal energy spatial and propagation of ions in 3D interplanetary space, including the solar-wind termination shock. Such breadth of information could not be gained by in situ means.

  2. Hydrogen atom temperature measured with wavelength-modulated laser absorption spectroscopy in large scale filament arc negative hydrogen ion source

    SciTech Connect

    Nakano, H. Goto, M.; Tsumori, K.; Kisaki, M.; Ikeda, K.; Nagaoka, K.; Osakabe, M.; Takeiri, Y.; Kaneko, O.; Nishiyama, S.; Sasaki, K.

    2015-04-08

    The velocity distribution function of hydrogen atoms is one of the useful parameters to understand particle dynamics from negative hydrogen production to extraction in a negative hydrogen ion source. Hydrogen atom temperature is one of the indicators of the velocity distribution function. To find a feasibility of hydrogen atom temperature measurement in large scale filament arc negative hydrogen ion source for fusion, a model calculation of wavelength-modulated laser absorption spectroscopy of the hydrogen Balmer alpha line was performed. By utilizing a wide range tunable diode laser, we successfully obtained the hydrogen atom temperature of ∼3000 K in the vicinity of the plasma grid electrode. The hydrogen atom temperature increases as well as the arc power, and becomes constant after decreasing with the filling of hydrogen gas pressure.

  3. Photoionization of atoms and molecules. [of hydrogen, helium, and xenon

    NASA Technical Reports Server (NTRS)

    Samson, J. A. R.

    1976-01-01

    A literature review on the present state of knowledge in photoionization is presented. Various experimental techniques that have been developed to study photoionization, such as fluorescence and photoelectron spectroscopy, mass spectroscopy, are examined. Various atoms and molecules were chosen to illustrate these techniques, specifically helium and xenon atoms and hydrogen molecules. Specialized photoionization such as in positive and negative ions, excited states, and free radicals is also treated. Absorption cross sections and ionization potentials are also discussed.

  4. Variational Perturbation Treatment of the Confined Hydrogen Atom

    ERIC Educational Resources Information Center

    Montgomery, H. E., Jr.

    2011-01-01

    The Schrodinger equation for the ground state of a hydrogen atom confined at the centre of an impenetrable cavity is treated using variational perturbation theory. Energies calculated from variational perturbation theory are comparable in accuracy to the results from a direct numerical solution. The goal of this exercise is to introduce the…

  5. The Confined Hydrogen Atom with a Moving Nucleus

    ERIC Educational Resources Information Center

    Fernandez, Francisco M.

    2010-01-01

    We study the hydrogen atom confined to a spherical box with impenetrable walls but, unlike earlier pedagogical articles on the subject, we assume that the nucleus also moves. We obtain the ground-state energy approximately by means of first-order perturbation theory and show that it is greater than that for the case in which the nucleus is clamped…

  6. Probability of Locating the Electron in a Hydrogen Atom

    NASA Astrophysics Data System (ADS)

    Mak, Thomas C. W.; Li, Wai-Kee

    2000-04-01

    A variety of numerical problems, along with their solutions, regarding the probability of locating the electron in a hydrogen atom are given. These problems range from simple substitution exercises to graduate-level take-home questions. Comments on the physical meaning of some of the results are also provided. These problems may be easily modified by teachers to suit their purposes.

  7. Quantitative calculation of the absorption spectrum of the hydrogen atom

    NASA Astrophysics Data System (ADS)

    Ogilvie, J. F.; Fee, G. J.

    2014-03-01

    With mathematical software (Maple), we have calculated quantitatively the entire absorption spectrum of the hydrogen atom in its electronic ground state for transitions to both discrete and continuum states, within the purview of non-relativistic wave mechanics. We present plots of wave functions in both coordinate and momentum representations and the calculated spectra.

  8. Quantum-Classical Connection for Hydrogen Atom-Like Systems

    ERIC Educational Resources Information Center

    Syam, Debapriyo; Roy, Arup

    2011-01-01

    The Bohr-Sommerfeld quantum theory specifies the rules of quantization for circular and elliptical orbits for a one-electron hydrogen atom-like system. This article illustrates how a formula connecting the principal quantum number "n" and the length of the major axis of an elliptical orbit may be arrived at starting from the quantum…

  9. Microwave plasma generation of hydrogen atoms for rocket propulsion

    NASA Technical Reports Server (NTRS)

    Chapman, R.; Filpus, J.; Morin, T.; Snellenberger, R.; Asmussen, J.; Hawley, M.; Kerber, R.

    1981-01-01

    A flow microwave plasma reaction system is used to study the conversion of hydrogen to hydrogen atoms as a function of pressure, power density, cavity tuning, cavity mode, and time in the plasma zone. Hydrogen atom concentration is measured down-stream from the plasma by NOCl titration. Extensive modeling of the plasma and recombination zones is performed with the plasma zone treated as a backmix reaction system and the recombination zone treated as a plug flow. The thermodynamics and kinetics of the recombination process are examined in detail to provide an understanding of the conversion of recombination energy to gas kinetic energy. It is found that cavity tuning, discharge stability, and optimum power coupling are critically dependent on the system pressure, but nearly independent of the flow rate.

  10. Transition state geometry in radical hydrogen atom abstraction

    NASA Astrophysics Data System (ADS)

    Denisov, Evgenii T.; Shestakov, Alexander F.; Denisova, Taisa G.

    2012-12-01

    The interatomic distances in the transition states of radical hydrogen atom abstraction reactions X•+HY → XH+Y• determined by quantum chemical calculations are systematized and generalized. It is shown that depending on the reaction centre structure, these reactions can be subdivided into classes with the same X...Y interatomic distance in each class. The transition state geometries found by the methods of intersecting parabolas and intersecting Morse curves are also presented. The X...H...Y fragments are almost linear, the hydrogen atom position being determined by the reaction enthalpy. The effects of triplet repulsion, electronegativities and radii of X and Y atoms, the presence of adjoining π-bonds, and steric effects on the X...Y interatomic distances are analyzed and characterized. The bibliography includes 62 references.

  11. Atomic cobalt on nitrogen-doped graphene for hydrogen generation

    NASA Astrophysics Data System (ADS)

    Fei, Huilong; Dong, Juncai; Arellano-Jiménez, M. Josefina; Ye, Gonglan; Dong Kim, Nam; Samuel, Errol L. G.; Peng, Zhiwei; Zhu, Zhuan; Qin, Fan; Bao, Jiming; Yacaman, Miguel Jose; Ajayan, Pulickel M.; Chen, Dongliang; Tour, James M.

    2015-10-01

    Reduction of water to hydrogen through electrocatalysis holds great promise for clean energy, but its large-scale application relies on the development of inexpensive and efficient catalysts to replace precious platinum catalysts. Here we report an electrocatalyst for hydrogen generation based on very small amounts of cobalt dispersed as individual atoms on nitrogen-doped graphene. This catalyst is robust and highly active in aqueous media with very low overpotentials (30 mV). A variety of analytical techniques and electrochemical measurements suggest that the catalytically active sites are associated with the metal centres coordinated to nitrogen. This unusual atomic constitution of supported metals is suggestive of a new approach to preparing extremely efficient single-atom catalysts.

  12. Atomic hydrogen maser active oscillator cavity and bulb design optimization

    NASA Technical Reports Server (NTRS)

    Peters, H. E.; Washburn, P. J.

    1984-01-01

    The performance characteristics and reliability of the active oscillator atomic hydrogen maser depend upon oscillation parameters which characterize the interaction region of the maser, the resonant cavity and atom storage bulb assembly. With particular attention to use of the cavity frequency switching servo (1) to reduce cavity pulling, it is important to maintain high oscillation level, high atomic beam flux utilization efficiency, small spin exchange parameter and high cavity quality factor. It is also desirable to have a small and rigid cavity and bulb structure and to minimize the cavity temperature sensitivity. Curves for a novel hydrogen maser cavity configuration which is partially loaded with a quartz dielectric cylinder and show the relationships between cavity length, cavity diameter, bulb size, dielectric thickness, cavity quality factor, filling factor and cavity frequency temperature coefficient are presented. The results are discussed in terms of improvement in maser performance resulting from particular design choices.

  13. Atomic cobalt on nitrogen-doped graphene for hydrogen generation

    PubMed Central

    Fei, Huilong; Dong, Juncai; Arellano-Jiménez, M. Josefina; Ye, Gonglan; Dong Kim, Nam; Samuel, Errol L.G.; Peng, Zhiwei; Zhu, Zhuan; Qin, Fan; Bao, Jiming; Yacaman, Miguel Jose; Ajayan, Pulickel M.; Chen, Dongliang; Tour, James M.

    2015-01-01

    Reduction of water to hydrogen through electrocatalysis holds great promise for clean energy, but its large-scale application relies on the development of inexpensive and efficient catalysts to replace precious platinum catalysts. Here we report an electrocatalyst for hydrogen generation based on very small amounts of cobalt dispersed as individual atoms on nitrogen-doped graphene. This catalyst is robust and highly active in aqueous media with very low overpotentials (30 mV). A variety of analytical techniques and electrochemical measurements suggest that the catalytically active sites are associated with the metal centres coordinated to nitrogen. This unusual atomic constitution of supported metals is suggestive of a new approach to preparing extremely efficient single-atom catalysts. PMID:26487368

  14. Atomic cobalt on nitrogen-doped graphene for hydrogen generation.

    PubMed

    Fei, Huilong; Dong, Juncai; Arellano-Jiménez, M Josefina; Ye, Gonglan; Dong Kim, Nam; Samuel, Errol L G; Peng, Zhiwei; Zhu, Zhuan; Qin, Fan; Bao, Jiming; Yacaman, Miguel Jose; Ajayan, Pulickel M; Chen, Dongliang; Tour, James M

    2015-01-01

    Reduction of water to hydrogen through electrocatalysis holds great promise for clean energy, but its large-scale application relies on the development of inexpensive and efficient catalysts to replace precious platinum catalysts. Here we report an electrocatalyst for hydrogen generation based on very small amounts of cobalt dispersed as individual atoms on nitrogen-doped graphene. This catalyst is robust and highly active in aqueous media with very low overpotentials (30 mV). A variety of analytical techniques and electrochemical measurements suggest that the catalytically active sites are associated with the metal centres coordinated to nitrogen. This unusual atomic constitution of supported metals is suggestive of a new approach to preparing extremely efficient single-atom catalysts. PMID:26487368

  15. Reactivity and Catalytic Activity of Hydrogen Atom Chemisorbed Silver Clusters.

    PubMed

    Manzoor, Dar; Pal, Sourav

    2015-06-18

    Metal clusters of silver have attracted recent interest of researchers as a result of their potential in different catalytic applications and low cost. However, due to the completely filled d orbital and very high first ionization potential of the silver atom, the silver-based catalysts interact very weakly with the reacting molecules. In the current work, density functional theory calculations were carried out to investigate the effect of hydrogen atom chemisorption on the reactivity and catalytic properties of inert silver clusters. Our results affirm that the hydrogen atom chemisorption leads to enhancement in the binding energy of the adsorbed O2 molecule on the inert silver clusters. The increase in the binding energy is also characterized by the decrease in the Ag-O and increase in the O-O bond lengths in the case of the AgnH silver clusters. Pertinent to the increase in the O-O bond length, a significant red shift in the O-O stretching frequency is also noted in the case of the AgnH silver clusters. Moreover, the hydrogen atom chemisorbed silver clusters show low reaction barriers and high heat of formation of the final products for the environmentally important CO oxidation reaction as compared to the parent catalytically inactive clusters. The obtained results were compared with those of the corresponding gold and hydrogen atom chemisorbed gold clusters obtained at the same level of theory. It is expected the current computational study will provide key insights for future advances in the design of efficient nanosilver-based catalysts through the adsorption of a small atom or a ligand.

  16. Electron-impact ionization of atomic hydrogen

    SciTech Connect

    Baertschy, Mark D.

    2000-02-14

    Since the invention of quantum mechanics, even the simplest example of collisional breakup in a system of charged particles, e{sup {minus}} + H {r_arrow} H{sup +} + e{sup {minus}} + e{sup {minus}}, has stood as one of the last unsolved fundamental problems in atomic physics. A complete solution requires calculating the energies and directions for a final state in which three charged particles are moving apart. Advances in the formal description of three-body breakup have yet to lead to a viable computational method. Traditional approaches, based on two-body formalisms, have been unable to produce differential cross sections for the three-body final state. Now, by using a mathematical transformation of the Schrodinger equation that makes the final state tractable, a complete solution has finally been achieved, Under this transformation, the scattering wave function can be calculated without imposing explicit scattering boundary conditions. This approach has produced the first triple differential cross sections that agree on an absolute scale with experiment as well as the first ab initio calculations of the single differential cross section.

  17. The role of hydrogen in hot-salt stress corrosion cracking of titanium-aluminum alloys

    NASA Technical Reports Server (NTRS)

    Ondrejcin, R. S.

    1971-01-01

    Additional support is presented for the previously proposed role of hydrogen as an embrittling agent in hot-salt stress corrosion cracking of titanium-aluminum alloys. The main source of hydrogen formed during the reactions of titanium alloys with hot salt was identified as water associated with the salt. Hydrogen is produced by the reaction of an intermediate (hydrogen halide) with the alloy rather than from metal-water reactions. The fracture mode of precracked tensile specimens was ductile when the specimens were tested in air, and brittle when tests were made in high-pressure hydrogen. Stressed titanium-aluminum alloys also were cracked by bombardment with hydrogen ions produced in a proton accelerator. The approximate concentrations of the hydrogen ions in the alloys were calculated.

  18. Hydrogen in hot subdwarfs formed by double helium white dwarf mergers

    NASA Astrophysics Data System (ADS)

    Hall, Philip D.; Jeffery, C. Simon

    2016-09-01

    Isolated hot subdwarfs might be formed by the merging of two helium-core white dwarfs. Before merging, helium-core white dwarfs have hydrogen-rich envelopes and some of this hydrogen may survive the merger. We calculate the mass of hydrogen that is present at the start of such mergers and, with the assumption that hydrogen is mixed throughout the disrupted white dwarf in the merger process, estimate how much can survive. We find a hydrogen mass of up to about 2 × 10-3 M⊙ in merger remnants. We make model merger remnants that include the hydrogen mass appropriate to their total mass and compare their atmospheric parameters with a sample of apparently isolated hot subdwarfs, hydrogen-rich sdBs. The majority of these stars can be explained as the remnants of double helium white dwarf mergers.

  19. Doppler spectroscopy of hydrogen atoms from the photodissociation of saturated hydrocarbons and methyl halides at 157 nm

    SciTech Connect

    Tonokura, K.; Matsumi, Y.; Kawasaki, M. ); Kasatani, K. )

    1991-10-01

    Hydrocarbons (C{sub {ital n}}H{sub 2{ital n}+2}, {ital n}=3, 4, and 6) and methyl halides (CH{sub 3}{ital X}, {ital X}=Cl, Br, I) are photodissociated at 157 nm. The hydrogen atom photofragments are detected by a resonance-enhanced multiphoton ionization technique. The Doppler profiles of the hydrogen atoms from hydrocarbons are well represented by a Gaussian profile, while those from methyl halides by a mixture of a Gaussian and a non-Gaussian profiles. These Doppler profiles are interpreted assuming that (a) hot ethyl photofragments from hydrocarbons result in the formation of hydrogen atoms and (b) methyl halides undergo both direct and indirect photolytic scissions of the C---H bonds at 157 nm.

  20. Analysis of Material Sample Heated by Impinging Hot Hydrogen Jet in a Non-Nuclear Tester

    NASA Technical Reports Server (NTRS)

    Wang, Ten-See; Foote, John; Litchford, Ron

    2006-01-01

    A computational conjugate heat transfer methodology was developed and anchored with data obtained from a hot-hydrogen jet heated, non-nuclear materials tester, as a first step towards developing an efficient and accurate multiphysics, thermo-fluid computational methodology to predict environments for hypothetical solid-core, nuclear thermal engine thrust chamber. The computational methodology is based on a multidimensional, finite-volume, turbulent, chemically reacting, thermally radiating, unstructured-grid, and pressure-based formulation. The multiphysics invoked in this study include hydrogen dissociation kinetics and thermodynamics, turbulent flow, convective and thermal radiative, and conjugate heat transfers. Predicted hot hydrogen jet and material surface temperatures were compared with those of measurement. Predicted solid temperatures were compared with those obtained with a standard heat transfer code. The interrogation of physics revealed that reactions of hydrogen dissociation and recombination are highly correlated with local temperature and are necessary for accurate prediction of the hot-hydrogen jet temperature.

  1. Sudden perturbation of hydrogen atoms by intense ultrashort laser pulses

    SciTech Connect

    Lugovskoy, A. V.; Bray, I.

    2005-12-15

    We study theoretically how hydrogen atoms respond to intense ultrashort laser pulses of duration {tau} shorter than the inverse of the initial-state energy {epsilon}{sub i}{sup -1}. An analytical expression for the evolution operator S is derived up to the first order of the sudden perturbation approximation. This approximation treats the laser-atom interaction beyond the dipole approximation and yields S as a series in the small parameter {epsilon}{sub i}{tau}. It is shown that the effect of realistic laser pulses on atoms begins at the first order of {epsilon}{sub i}{tau}. Transitions between atomic (nlm) states of different m become possible due to the action of the pulse's magnetic field. Transitions between states of same m and arbitrary l become possible if the static Coulomb potential is taken into account during the pulse.

  2. Distinct metallization and atomization transitions in dense liquid hydrogen.

    PubMed

    Mazzola, Guglielmo; Sorella, Sandro

    2015-03-13

    We perform molecular dynamics simulations driven by accurate quantum Monte Carlo forces on dense liquid hydrogen. There is a recent report of a complete atomization transition between a mixed molecular-atomic liquid and a completely dissociated fluid in an almost unaccessible pressure range [Nat. Commun. 5, 3487 (2014)]. Here, instead, we identify a different transition between the fully molecular liquid and the mixed-atomic fluid at ∼400  GPa, i.e., in a much more interesting pressure range. We provide numerical evidence supporting the metallic behavior of this intermediate phase. Therefore, we predict that the metallization at finite temperature occurs in this partially dissociated molecular fluid, well before the complete atomization of the liquid. At high temperature this first-order transition becomes a crossover, in very good agreement with the experimental observation. Several systematic tests supporting the quality of our large scale calculations are also reported.

  3. Unparticle contribution to the hydrogen atom ground state energy

    NASA Astrophysics Data System (ADS)

    Wondrak, Michael F.; Nicolini, Piero; Bleicher, Marcus

    2016-08-01

    In the present work we study the effect of unparticle modified static potentials on the energy levels of the hydrogen atom. By using Rayleigh-Schrödinger perturbation theory, we obtain the energy shift of the ground state and compare it with experimental data. Bounds on the unparticle energy scale ΛU as a function of the scaling dimension dU and the coupling constant λ are derived. We show that there exists a parameter region where bounds on ΛU are stringent, signaling that unparticles could be tested in atomic physics experiments.

  4. Laser stripping of hydrogen atoms by direct ionization

    DOE PAGES

    Brunetti, E.; Becker, W.; Bryant, H. C.; Jaroszynski, D. A.; Chou, W.

    2015-05-08

    Direct ionization of hydrogen atoms by laser irradiation is investigated as a potential new scheme to generate proton beams without stripping foils. The time-dependent Schrödinger equation describing the atom-radiation interaction is numerically solved obtaining accurate ionization cross-sections for a broad range of laser wavelengths, durations and energies. Parameters are identified where the Doppler frequency up-shift of radiation colliding with relativistic particles can lead to efficient ionization over large volumes and broad bandwidths using currently available lasers.

  5. Semirelativistic model for ionization of atomic hydrogen by electron impact

    SciTech Connect

    Attaourti, Y.; Taj, S.; Manaut, B.

    2005-06-15

    We present a semirelativistic model for the description of the ionization process of atomic hydrogen by electron impact in the first Born approximation by using the Darwin wave function to describe the bound state of atomic hydrogen and the Sommerfeld-Maue wave function to describe the ejected electron. This model, accurate to first order in Z/c in the relativistic correction, shows that, even at low kinetic energies of the incident electron, spin effects are small but not negligible. These effects become noticeable with increasing incident electron energies. All analytical calculations are exact and our semirelativistic results are compared with the results obtained in the nonrelativistic Coulomb Born approximation both for the coplanar asymmetric and the binary coplanar geometries.

  6. Fluorescence Quenching of Benzaldehyde in Water by Hydrogen Atom Abstraction.

    PubMed

    Fletcher, Katharyn; Bunz, Uwe H F; Dreuw, Andreas

    2016-09-01

    We computed the mechanism of fluorescence quenching of benzaldehyde in water through relaxed potential energy surface scans. Time-dependent density functional theory calculations along the protonation coordinate from water to benzaldehyde reveal that photoexcitation to the bright ππ* (S3 ) state is immediately followed by ultrafast decay to the nπ* (S1 ) state. Evolving along this state, benzaldehyde (BA) abstracts a hydrogen atom, resulting in a BAH(.) and OH(.) radical pair. Benzaldehyde does not act as photobase in water, but abstracts a hydrogen atom from a nearby solvent molecule. The system finally decays back to the ground state by non-radiative decay and an electron transfers back to the OH(.) radical. Proton transfer from BAH(+) to OH(-) restores the initial situation, BA in water. PMID:27305520

  7. Quadrupole photoionization of hydrogen atoms in Debye plasmas

    SciTech Connect

    Lin, C. Y.; Ho, Y. K.

    2010-09-15

    Although a great deal of effort has been devoted to investigating dipole photoionization of plasma-embedded atoms, far less is known about the corresponding quadrupole transitions. In the present work, quadrupole photoionization processes for the ground and excited states of hydrogen atoms in Debye plasma are explored using the method of complex coordinate rotation. The plasma shielding effects on the quadrupole photoionization cross sections are reported for a variety of Debye screening lengths and compared to the dipole results accordingly. Under the perturbation of plasma screening, shape resonances and Cooper-type minima occurring in both dipole and quadrupole photoionization cross sections are presented and discussed. Comparisons are made to other theoretical calculations for the dipole photoionization with good agreement. The present quadrupole results are the first predictions for hydrogen photoionization in Debye plasmas.

  8. Analytic Solution of a Two-Dimensional Hydrogen Atom

    NASA Astrophysics Data System (ADS)

    Yang, Xiao-Li.

    1990-03-01

    The two dimensional hydrogen atom problem is solved analytically in both the relativistic and non-relativistic cases. In the nonrelativistic case, exact formulae for energy eigenvalues and eigenfunctions for both the discrete and continuous parts of the spectrum, dipole matrix elements, DC Stark effect, single- and two-photon transition rate, fine and hyperfine structures are obtained. The binding energy of the ground state is found to be reduced by a factor of four from that of a three dimensional hydrogen atom. In the relativistic case, exact analytic expressions for discrete eigen energy and normalized eigen wave function are derived. It is shown that the solution to the Dirac equation is disjoint in the spin-coordinate space (four -component spinor) in contrast to the three dimensional counterpart. This surprising result is a consequence of the planar motion of the electron.

  9. Fluorescence Quenching of Benzaldehyde in Water by Hydrogen Atom Abstraction.

    PubMed

    Fletcher, Katharyn; Bunz, Uwe H F; Dreuw, Andreas

    2016-09-01

    We computed the mechanism of fluorescence quenching of benzaldehyde in water through relaxed potential energy surface scans. Time-dependent density functional theory calculations along the protonation coordinate from water to benzaldehyde reveal that photoexcitation to the bright ππ* (S3 ) state is immediately followed by ultrafast decay to the nπ* (S1 ) state. Evolving along this state, benzaldehyde (BA) abstracts a hydrogen atom, resulting in a BAH(.) and OH(.) radical pair. Benzaldehyde does not act as photobase in water, but abstracts a hydrogen atom from a nearby solvent molecule. The system finally decays back to the ground state by non-radiative decay and an electron transfers back to the OH(.) radical. Proton transfer from BAH(+) to OH(-) restores the initial situation, BA in water.

  10. Solid Hydrogen Experiments for Atomic Propellants: Image Analyses

    NASA Technical Reports Server (NTRS)

    Palaszewski, Bryan

    2002-01-01

    This paper presents the results of detailed analyses of the images from experiments that were conducted on the formation of solid hydrogen particles in liquid helium. Solid particles of hydrogen were frozen in liquid helium, and observed with a video camera. The solid hydrogen particle sizes, their agglomerates, and the total mass of hydrogen particles were estimated. Particle sizes of 1.9 to 8 mm (0.075 to 0.315 in.) were measured. The particle agglomerate sizes and areas were measured, and the total mass of solid hydrogen was computed. A total mass of from 0.22 to 7.9 grams of hydrogen was frozen. Compaction and expansion of the agglomerate implied that the particles remain independent particles, and can be separated and controlled. These experiment image analyses are one of the first steps toward visually characterizing these particles, and allow designers to understand what issues must be addressed in atomic propellant feed system designs for future aerospace vehicles.

  11. Hydrogenated fullerenes dimer, peanut and capsule: An atomic comparison

    NASA Astrophysics Data System (ADS)

    EL-Barbary, A. A.

    2016-04-01

    Hydrogenated fullerenes are detected in the Universe in space but their identification is still unsolved task. Therefore, this paper provides useful information about hydrogenated fullerenes (dimer, peanut and capsule) using DFT method at the B3LYP/6-31G(d) level of theory. The stability, geometric structures, hydrogen adsorption energies and NMR chemical shifts are calculated. The results show that the energy of most stable isomer of C118 dimer is lower than the energies sum of C60 and C58 cages by 1.77 eV and the energy per carbon atom of C144 capsule is more stable than C60 cage by 126.98 meV. Also, endohedral Ti-doped C118 dimer and C128 peanut are found to be most stable structures than exohedral Ti-doped C118 dimer and C128 peanut by 2.19 eV/Ti and 3.52 eV/Ti, respectively. The hydrogenation process is found to be enhanced (especially at the caps) for endohedral Ti-doped C118 dimer and C128 peanut through electronic surface modifications. The most active hydrogenation sites are selected and it is found that the most stable hydrogenation sites are Houts1 and Houts3 for fullerenes and endohedral Ti-doped fullerenes, respectively.

  12. Effects of wall coatings and temperature on hydrogen atom surface recombination

    NASA Technical Reports Server (NTRS)

    Wong, E. L.; Baker, C. E.

    1973-01-01

    The efficiency of various surface coatings and materials toward inhibiting hydrogen atom surface recombination was investigated over a temperature range of 77 to 298 K. A flow discharge, mass spectrometer technique was used to make the experimental measurements. Hydrogen atoms were monitored directly, and these measurements were expressed as ratios of mass spectrometer peak heights for atomic and molecular hydrogen. Several of the surface coatings studied were efficient at reducing hydrogen atom surface recombination at room temperature. However, as the temperature was lowered, this efficiency was drastically reduced. Calibration of the mass spectrometer for atomic and molecular hydrogen indicated that mass spectrometer discrimination against hydrogen atoms was severe. Mass spectrometer sensitivity for hydrogen atoms was only about one-sixth of that for molecular hydrogen.

  13. Infrared atomic hydrogen line formation in luminous stars

    NASA Technical Reports Server (NTRS)

    Krolik, J. H.; Smith, H. A.

    1981-01-01

    Infrared atomic hydrogen lines observed in luminous stars, generally attributed to compact circumstellar H II regions, can also be formed in the winds likely to emanate from these stars. Implications are discussed for the class of obscured infrared point sources showing these lines, and an illustrative model is derived for the BN object in Orion. Such stellar winds should also produce weak, but detectable, radio emission.

  14. Lamb shift in the hydrogen atom: Leading logarithmic corrections

    SciTech Connect

    Karshenboim, S.G.

    1995-04-01

    The leading logarithmic correction to the difference of the Lamb shifts of the 1s{sub 1/2} and 2s{sub 1/2} levels is found. The difference {Delta}E{sub L}(1s{sub 1/2}) {minus} 8{Delta}E{sub L}(2s{sub 1/2}) for the hydrogen atom is found to be {minus}187.236(11) MHz. 13 refs., 2 figs.

  15. Continuous coherent Lyman- alpha excitation of atomic hydrogen.

    PubMed

    Eikema, K S; Walz, J; Hänsch, T W

    2001-06-18

    The 1S-2P transition in atomic hydrogen has been observed for the first time with almost natural linewidth. We employ a unique source of continuous coherent Lyman- alpha radiation based on four-wave mixing in mercury. The output of the source has been improved 40-fold to yield 20 nW. This demonstration shows that laser cooling and detection with continuous Lyman- alpha radiation has excellent prospects for future experiments with antihydrogen.

  16. Continuous Coherent Lyman-{alpha} Excitation of Atomic Hydrogen

    SciTech Connect

    Eikema, K. S. E.; Walz, J.; Hansch, T. W.

    2001-06-18

    The 1S{minus}2P transition in atomic hydrogen has been observed for the first time with almost natural linewidth. We employ a unique source of continuous coherent Lyman-{alpha} radiation based on four-wave mixing in mercury. The output of the source has been improved 40-fold to yield 20nW. This demonstration shows that laser cooling and detection with continuous Lyman-{alpha} radiation has excellent prospects for future experiments with antihydrogen.

  17. Amide-Substituted Titanocenes in Hydrogen-Atom Transfer Catalysis.

    PubMed

    Zhang, Yong-Qiang; Jakoby, Verena; Stainer, Katharina; Schmer, Alexander; Klare, Sven; Bauer, Mirko; Grimme, Stefan; Cuerva, Juan Manuel; Gansäuer, Andreas

    2016-01-22

    Two new catalytic systems for hydrogen-atom transfer (HAT) catalysis involving the N-H bonds of titanocene(III) complexes with pendant amide ligands are reported. In a monometallic system, a bifunctional catalyst for radical generation and reduction through HAT catalysis depending on the coordination of the amide ligand is employed. The pendant amide ligand is used to activate Crabtree's catalyst to yield an efficient bimetallic system for radical generation and HAT catalysis. PMID:26636435

  18. Alkane desaturation by concerted double hydrogen atom transfer to benzyne.

    PubMed

    Niu, Dawen; Willoughby, Patrick H; Woods, Brian P; Baire, Beeraiah; Hoye, Thomas R

    2013-09-26

    The removal of two vicinal hydrogen atoms from an alkane to produce an alkene is a challenge for synthetic chemists. In nature, desaturases and acetylenases are adept at achieving this essential oxidative functionalization reaction, for example during the biosynthesis of unsaturated fatty acids, eicosanoids, gibberellins and carotenoids. Alkane-to-alkene conversion almost always involves one or more chemical intermediates in a multistep reaction pathway; these may be either isolable species (such as alcohols or alkyl halides) or reactive intermediates (such as carbocations, alkyl radicals, or σ-alkyl-metal species). Here we report a desaturation reaction of simple, unactivated alkanes that is mechanistically unique. We show that benzynes are capable of the concerted removal of two vicinal hydrogen atoms from a hydrocarbon. The discovery of this exothermic, net redox process was enabled by the simple thermal generation of reactive benzyne intermediates through the hexadehydro-Diels-Alder cycloisomerization reaction of triyne substrates. We are not aware of any single-step, bimolecular reaction in which two hydrogen atoms are simultaneously transferred from a saturated alkane. Computational studies indicate a preferred geometry with eclipsed vicinal C-H bonds in the alkane donor.

  19. Manufacture and deflagration of an atomic hydrogen propellant

    NASA Technical Reports Server (NTRS)

    Rosen, G.

    1974-01-01

    It is observed that the use of very low temperatures (in the range from 0.1 to 1.5 K) produced by advanced cryogenic apparatus and the use of very strong magnetic fields (in the range from 50 to 100 kG) produced by superconducting magnets can yield a significant improvement in the atomic hydrogen trapping effectiveness of an H2 matrix. The use of a radioactive beta-ray emiter isotope may yield H-H2 propellants (with a specific impulse of about 740 sec) by secondary electron impact dissociations of H2 in an impregnated matrix maintained below 1 K in a strong magnetic field. Another method for manufacturing an H-H2 propellant involves bombardment of supercooled solid H2 with a cyclotron-produced beam of 10-MeV hydrogen atoms. The matrix-isolated atomic hydrogen must be used directly without prior melting as a solid propellant, and an analysis of the steady deflagration is presented.

  20. An experimental limit on parity mixing in atomic hydrogen

    SciTech Connect

    Fehrenbach, C.C.W.

    1993-12-31

    An experiment was performed to detect the forbidden E1 transition between two hyperfine levels of the 2S state of atomic hydrogen. Such a transition, with {Delta}l = 0, violates parity symmetry. The technique used was to induce an interference between the forbidden transition and a parity-allowed E1 transition polarized by a DC electric field. The two induced transitions were driven coherently in a single microwave cavity. A magnetic field was used to shift the atoms into resonance with the RF radiation and to make the 2S and 2P states degenerate in energy, which would maximize any parity-violating mixing between these states. The measurements were made by passing a beam of hydrogen through the microwave cavity, and monitoring the state of the emerging atoms. To separate the parity-violating component of the transition rate from the parity-conserving part, the change in the transition rate was monitored when the handedness of the interaction region was reversed. From the transition asymmetry it was possible to extract the size of the proton-spin dependent part of a general parity-violating interaction between an electron and a proton. This can be stated in terms of a dimensionless constant C{sub 2}. The result of this experiment is C{sub 2p} = 1.5 {plus_minus} 22. The error bound represents a 95% confidence level and is an improvement of an order of magnitude over previous limits set by similar experiments in hydrogen.

  1. The hydrogen atom in plasmas with an external electric field

    SciTech Connect

    Bahar, M. K.; Soylu, A.

    2014-09-15

    We numerically solve the Schrödinger equation, using a more general exponential cosine screened Coulomb (MGECSC) potential with an electric field, in order to investigate the screening and weak external electric field effects on the hydrogen atom in plasmas. The MGECSC potential is examined for four different cases, corresponding to different screening parameters of the potential and the external electric field. The influences of the different screening parameters and the weak external electric field on the energy eigenvalues are determined by solving the corresponding equations using the asymptotic iteration method (AIM). It is found that the corresponding energy values shift when a weak external electric field is applied to the hydrogen atom in a plasma. This study shows that a more general exponential cosine screened Coulomb potential allows the influence of an applied, weak, external electric field on the hydrogen atom to be investigated in detail, for both Debye and quantum plasmas simultaneously. This suggests that such a potential would be useful in modeling similar effects in other applications of plasma physics, and that AIM is an appropriate method for solving the Schrödinger equation, the solution of which becomes more complex due to the use of the MGECSC potential with an applied external electric field.

  2. Zero-Temperature Structures of Atomic Metallic Hydrogen

    NASA Astrophysics Data System (ADS)

    McMahon, Jeffrey; Ceperley, David

    2011-03-01

    Since the first prediction of an atomic metallic phase of hydrogen by Wigner and Huntington over 75 years ago, there have been many theoretical efforts aimed at determining the crystal structures of the zero-temperature phases. We present results from ab initio random structure searching with density functional theory performed to determine the ground state structures from 500 GPa to 5 TPa. We estimate that molecular hydrogen dissociates into a monatomic body-centered tetragonal structure near 500 GPa (rs = 1.225), which then remains stable to 2.5 TPa (rs = 0.969). At higher pressures, hydrogen stabilizes in an . . . ABCABC . . . planar structure that is remarkably similar to the ground state of lithium, which compresses to the face-centered cubic lattice beyond 5 TPa (rs < 0.86). Our results provide a complete ab initio description of the atomic metallic crystal structures of hydrogen, resolving one of the most fundamental and long outstanding issues concerning the structures of the elements.

  3. Coherent anti-Stokes Raman scattering (CARS) detection or hot atom reaction product internal energy distributions

    SciTech Connect

    Quick, C.R. Jr.; Moore, D.S.

    1983-01-01

    Coherent anti-Stokes Raman spectroscopy (CARS) is being utilized to investigate the rovibrational energy distributions produced by reactive and nonreactive collisions of translationally hot atoms with simple molecules. Translationally hot H atoms are produced by ArF laser photolysis of HBr. Using CARS we have monitored, in a state-specific and time-resolved manner, rotational excitation of HBr (v = 0), vibrational excitation of HBr and H/sub 2/, rovibrational excitation of H/sub 2/ produced by the reaction H + HBr ..-->.. H/sub 2/ + Br, and Br atom production by photolysis of HBr.

  4. Reactions of atomic hydrogen in water : solvent and isotope effects.

    SciTech Connect

    Bartels, D. M.

    1999-06-10

    It has been known for many years that hydrogen atoms can be easily created and studied in water using radiolytic techniques [1]. The use of CW EPR detection coupled with electron radiolysis proved extremely useful in estimating many reaction rates, and revealed the interesting phenomenon of chemically induced dynamic electron polarization (CIDEP) [2]. In recent years, we have made use of pulsed EPR detection to make precision reaction rate measurements which avoid the complications of CIDEP [3]. Activation energies and H/D isotope effects measured in these studies [4-14] will be described below. An interesting aspect of the hydrogen atom reactions is the effect of hydrophobic solvation. EPR evidence--an almost gas-phase hyperfine coupling and extremely narrow linewidth--is quite convincing to show that the H atom is just a minimally perturbed gas phase atom inside a small ''bubble''. In several systems we have found that the hydrophobic free energy of solvation dominates the solvent effect on reaction rates.

  5. Reactions of butadiyne. 1: The reaction with hydrogen atoms

    NASA Technical Reports Server (NTRS)

    Schwanebeck, W.; Warnatz, J.

    1984-01-01

    The reaction of hydrogen (H) atoms with butadiene (C4H2) was studied at room temperature in a pressure range between w mbar and 10 mbar. The primary step was an addition of H to C4H2 which is in its high pressure range at p 1 mbar. Under these conditions the following addition of a second H atom lies in the transition region between low and high pressure range. Vibrationally excited C4H4 can be deactivated to form buten-(1)-yne-(3)(C4H4) or decomposes into two C2H2 molecules. The rate constant at room temperature for primary step is given. The second order rate constant for the consumption of buten-(1)-yne-(3) is an H atom excess at room temperature is given.

  6. Ultrafast effective multilevel atom method for primordial hydrogen recombination

    SciTech Connect

    Ali-Haiemoud, Yacine; Hirata, Christopher M.

    2010-09-15

    Cosmological hydrogen recombination has recently been the subject of renewed attention because of its importance for predicting the power spectrum of cosmic microwave background anisotropies. It has become clear that it is necessary to account for a large number n > or approx. 100 of energy shells of the hydrogen atom, separately following the angular momentum substates in order to obtain sufficiently accurate recombination histories. However, the multilevel atom codes that follow the populations of all these levels are computationally expensive, limiting recent analyses to only a few points in parameter space. In this paper, we present a new method for solving the multilevel atom recombination problem, which splits the problem into a computationally expensive atomic physics component that is independent of the cosmology and an ultrafast cosmological evolution component. The atomic physics component follows the network of bound-bound and bound-free transitions among excited states and computes the resulting effective transition rates for the small set of 'interface' states radiatively connected to the ground state. The cosmological evolution component only follows the populations of the interface states. By pretabulating the effective rates, we can reduce the recurring cost of multilevel atom calculations by more than 5 orders of magnitude. The resulting code is fast enough for inclusion in Markov chain Monte Carlo parameter estimation algorithms. It does not yet include the radiative transfer or high-n two-photon processes considered in some recent papers. Further work on analytic treatments for these effects will be required in order to produce a recombination code usable for Planck data analysis.

  7. Hydrogen atom density in narrow-gap microwave hydrogen plasma determined by calorimetry

    NASA Astrophysics Data System (ADS)

    Yamada, Takahiro; Ohmi, Hiromasa; Kakiuchi, Hiroaki; Yasutake, Kiyoshi

    2016-02-01

    The density of hydrogen (H) atoms in the narrow-gap microwave hydrogen plasma generated under high-pressure conditions is expected to be very high because of the high input power density of the order of 104 W/cm3. For measuring the H atom density in such a high-pressure and high-density plasma, power-balance calorimetry is suited since a sufficient signal to noise ratio is expected. In this study, H atom density in the narrow-gap microwave hydrogen plasma has been determined by the power-balance calorimetry. The effective input power to the plasma is balanced with the sum of the powers related to the out-going energy per unit time from the plasma region via heat conduction, outflow of high-energy particles, and radiation. These powers can be estimated by simple temperature measurements using thermocouples and optical emission spectroscopy. From the power-balance data, the dissociation fraction of H2 molecules is determined, and the obtained maximum H atom density is (1.3 ± 0.2) × 1018 cm-3. It is found that the H atom density increases monotonically with increasing the energy invested per one H2 molecule within a constant plasma volume.

  8. Concerted hydrogen atom exchange between three HF molecules

    NASA Technical Reports Server (NTRS)

    Komornicki, Andrew; Dixon, David A.; Taylor, Peter R.

    1992-01-01

    We have investigated the termolecular reaction involving concerted hydrogen exchange between three HF molecules, with particular emphasis on the effects of correlation at the various stationary points along the reaction. Using an extended basis, we have located the geometries of the stable hydrogen-bonded trimer, which is of C(sub 3h) symmetry, and the transition state for hydrogen exchange, which is of D(sub 3h) symmetry. The energies of the exchange reation were then evaluated at the correlated level, using a large atomic natural orbital basis and correlating all valence electrons. Several correlation treatments were used, namely, configration interaction with single and double excitations, coupled-pair functional, and coupled-cluster methods. We are thus able to measure the effect of accounting for size-extensivity. Zero-point corrections to the correlated level energetics were determined using analytic second derivative techniques at the SCF level. Our best calculations, which include the effects of connected triple excitations in the coupled-cluster procedure, indicate that the trimer is bound by 9 +/- 1 kcal/mol relative to three separate monomers, in excellent agreement with previous estimates. The barrier to concerted hydrogen exchange is 15 kcal/mol above the trimer, or only 4.7 kcal/mol above three separated monomers. Thus the barrier to hydrogen exchange between HF molecules via this termolecular process is very low.

  9. Hydrogen-hydrogen interaction in planar biphenyl: a theoretical study based on the interacting quantum atoms and Hirshfeld atomic energy partitioning methods.

    PubMed

    Eskandari, Kiamars; Van Alsenoy, Christian

    2014-10-01

    The nature of H-H interaction between ortho-hydrogen atoms in planar biphenyl is investigated by two different atomic energy partitioning methods, namely fractional occupation iterative Hirshfeld (FOHI) and interacting quantum atoms (IQA), and compared with the traditional virial-based approach of quantum theory of atoms in molecules (QTAIM). In agreement with Bader's hypothesis of H-H bonding, partitioning the atomic energy into intra-atomic and interatomic terms reveals that there is a net attractive interaction between the ortho-hydrogens in the planar biphenyl. This falsifies the classical view of steric repulsion between the hydrogens. In addition, in contrast to the traditional QTAIM energy analysis, both FOHI and IQA show that the total atomic energy of the ortho-hydrogens remains almost constant when they participate in the H-H interaction. Although, the interatomic part of atomic energy of the hydrogens plays a stabilizing role during the formation of the H-H bond, it is almost compensated by the destabilizing effects of the intra-atomic parts and consequently, the total energy of the hydrogens remains constant. The trends in the changes of intra-atomic and interatomic energy terms of ortho-hydrogens during H-H bond formation are very similar to those observed for the H2 molecule.

  10. Role of Double Hydrogen Atom Transfer Reactions in Atmospheric Chemistry.

    PubMed

    Kumar, Manoj; Sinha, Amitabha; Francisco, Joseph S

    2016-05-17

    Hydrogen atom transfer (HAT) reactions are ubiquitous and play a crucial role in chemistries occurring in the atmosphere, biology, and industry. In the atmosphere, the most common and traditional HAT reaction is that associated with the OH radical abstracting a hydrogen atom from the plethora of organic molecules in the troposphere via R-H + OH → R + H2O. This reaction motif involves a single hydrogen transfer. More recently, in the literature, there is an emerging framework for a new class of HAT reactions that involves double hydrogen transfers. These reactions are broadly classified into four categories: (i) addition, (ii) elimination, (iii) substitution, and (iv) rearrangement. Hydration and dehydration are classic examples of addition and elimination reactions, respectively whereas tautomerization or isomerization belongs to a class of rearrangement reactions. Atmospheric acids and water typically mediate these reactions. Organic and inorganic acids are present in appreciable levels in the atmosphere and are capable of facilitating two-point hydrogen bonding interactions with oxygenates possessing an hydroxyl and/or carbonyl-type functionality. As a result, acids influence the reactivity of oxygenates and, thus, the energetics and kinetics of their HAT-based chemistries. The steric and electronic effects of acids play an important role in determining the efficacy of acid catalysis. Acids that reduce the steric strain of 1:1 substrate···acid complex are generally better catalysts. Among a family of monocarboxylic acids, the electronic effects become important; barrier to the catalyzed reaction correlates strongly with the pKa of the acid. Under acid catalysis, the hydration of carbonyl compounds leads to the barrierless formation of diols, which can serve as seed particles for atmospheric aerosol growth. The hydration of sulfur trioxide, which is the principle mechanism for atmospheric sulfuric acid formation, also becomes barrierless under acid catalysis

  11. Role of Double Hydrogen Atom Transfer Reactions in Atmospheric Chemistry.

    PubMed

    Kumar, Manoj; Sinha, Amitabha; Francisco, Joseph S

    2016-05-17

    Hydrogen atom transfer (HAT) reactions are ubiquitous and play a crucial role in chemistries occurring in the atmosphere, biology, and industry. In the atmosphere, the most common and traditional HAT reaction is that associated with the OH radical abstracting a hydrogen atom from the plethora of organic molecules in the troposphere via R-H + OH → R + H2O. This reaction motif involves a single hydrogen transfer. More recently, in the literature, there is an emerging framework for a new class of HAT reactions that involves double hydrogen transfers. These reactions are broadly classified into four categories: (i) addition, (ii) elimination, (iii) substitution, and (iv) rearrangement. Hydration and dehydration are classic examples of addition and elimination reactions, respectively whereas tautomerization or isomerization belongs to a class of rearrangement reactions. Atmospheric acids and water typically mediate these reactions. Organic and inorganic acids are present in appreciable levels in the atmosphere and are capable of facilitating two-point hydrogen bonding interactions with oxygenates possessing an hydroxyl and/or carbonyl-type functionality. As a result, acids influence the reactivity of oxygenates and, thus, the energetics and kinetics of their HAT-based chemistries. The steric and electronic effects of acids play an important role in determining the efficacy of acid catalysis. Acids that reduce the steric strain of 1:1 substrate···acid complex are generally better catalysts. Among a family of monocarboxylic acids, the electronic effects become important; barrier to the catalyzed reaction correlates strongly with the pKa of the acid. Under acid catalysis, the hydration of carbonyl compounds leads to the barrierless formation of diols, which can serve as seed particles for atmospheric aerosol growth. The hydration of sulfur trioxide, which is the principle mechanism for atmospheric sulfuric acid formation, also becomes barrierless under acid catalysis

  12. Atomically resolved real-space imaging of hot electron dynamics

    PubMed Central

    Lock, D.; Rusimova, K. R.; Pan, T. L.; Palmer, R. E.; Sloan, P. A.

    2015-01-01

    The dynamics of hot electrons are central to understanding the properties of many electronic devices. But their ultra-short lifetime, typically 100 fs or less, and correspondingly short transport length-scale in the nanometre range constrain real-space investigations. Here we report variable temperature and voltage measurements of the nonlocal manipulation of adsorbed molecules on the Si(111)-7 × 7 surface in the scanning tunnelling microscope. The range of the nonlocal effect increases with temperature and, at constant temperature, is invariant over a wide range of electron energies. The measurements probe, in real space, the underlying hot electron dynamics on the 10 nm scale and are well described by a two-dimensional diffusive model with a single decay channel, consistent with 2-photon photo-emission (2PPE) measurements of the real time dynamics. PMID:26387703

  13. Atomically resolved real-space imaging of hot electron dynamics.

    PubMed

    Lock, D; Rusimova, K R; Pan, T L; Palmer, R E; Sloan, P A

    2015-09-21

    The dynamics of hot electrons are central to understanding the properties of many electronic devices. But their ultra-short lifetime, typically 100 fs or less, and correspondingly short transport length-scale in the nanometre range constrain real-space investigations. Here we report variable temperature and voltage measurements of the nonlocal manipulation of adsorbed molecules on the Si(111)-7 × 7 surface in the scanning tunnelling microscope. The range of the nonlocal effect increases with temperature and, at constant temperature, is invariant over a wide range of electron energies. The measurements probe, in real space, the underlying hot electron dynamics on the 10 nm scale and are well described by a two-dimensional diffusive model with a single decay channel, consistent with 2-photon photo-emission (2PPE) measurements of the real time dynamics.

  14. Thermal hydrogen-atom transfer from methane: A mechanistic exercise

    NASA Astrophysics Data System (ADS)

    Schwarz, Helmut

    2015-06-01

    Hydrogen-atom transfer (HAT) constitutes a key process in a broad range of chemical transformations as it covers heterogeneous, homogeneous, and enzymatic reactions. While open-shell metal oxo species [MO]rad are no longer regarded as being involved in the heterogeneously catalyzed oxidative coupling of methane (2CH4 + → C2H6 + H2O), these reagents are rather versatile in bringing about (gas-phase) hydrogen-atom transfer, even from methane at ambient conditions. In this mini-review, various mechanistic scenarios will be presented, and it will be demonstrated how these are affected by the composition of the metal-oxide cluster ions. Examples will be discussed, how 'doping' the clusters permits the control of the charge and spin situation at the active site and, thus, the course of the reaction. Also, the interplay between supposedly inert support material and the active site - the so-called 'aristocratic atoms' - of the gas-phase catalyst will be addressed. Finally, gas-phase HAT from methane will be analyzed in the broader context of thermal activation of inert Csbnd H bonds by metal-oxo species.

  15. Hot Hydrogen Testing of Refractory Metals and Ceramics

    NASA Technical Reports Server (NTRS)

    Zee, Ralph; Chin, Bryan; Cohron, Jon

    1993-01-01

    The objective of this investigation is to develop a technique with which refractory metal carbide samples can be exposed to hydrogen containing gases at high temperatures, and to use various microstructural and analytical techniques to determine the chemical and rate processes involved in hydrogen degradation in these materials. Five types of carbides were examined including WC, NbC, HfC, ZrC, and TaC. The ceramics were purchased and were all monolithic in nature. The temperature range investigated was from 850 to 1600 C with a hydrogen pressure of one atmosphere. Control experiments, in vacuum, were also conducted for comparison so that the net effects due to hydrogen could be isolated. The samples were analyzed prior to and after exposure. Gas samples were collected in selected experiments and analyzed using gas chromography. Characterization of the resulting microstructure after exposure to hydrogen was conducted using optical microscopy, x-ray diffraction, scanning electron microscopy, and weight change. The ceramics were purchased and were all monolithic in nature. It was found that all samples lost weight after exposure, both in hydrogen and vacuum. Results from the microstructure analyses show that the degradation processes are different among the five types of ceramics involved. In addition, the apparent activation energy for the degradation process is a function of temperature even within the same material. This indicates that there are more than one mechanism involved in each material, and that the mechanisms are temperature dependent.

  16. Effect of initial hydrogen content of a titanium alloy on susceptibility to hot salt stress corrosion.

    NASA Technical Reports Server (NTRS)

    Gray, H. R.

    1972-01-01

    The influence of the initial hydrogen content of a titanium alloy on subsequent resistance to hot salt stress corrosion embrittlement and cracking was investigated. A Ti-8Al-1Mo-1V alloy was tested in four conditions: mill annealed (70 ppm H), duplex annealed (70 ppm H), vacuum annealed to an intermediate (36 ppm H) and a low (9 ppm H) hydrogen level. Material annealed at 650 C (duplex condition) exhibited resistance to hot salt stress corrosion superior to that exhibited by material in the mill annealed condition. Reduction of the alloy hydrogen content from 70 to as low as 9 ppm did not influence resistance to hot salt stress corrosion embrittlement or cracking.

  17. Kinetic modeling of α-hydrogen abstractions from unsaturated and saturated oxygenate compounds by hydrogen atoms.

    PubMed

    Paraskevas, Paschalis D; Sabbe, Maarten K; Reyniers, Marie-Françoise; Papayannakos, Nikos G; Marin, Guy B

    2014-10-01

    Hydrogen-abstraction reactions play a significant role in thermal biomass conversion processes, as well as regular gasification, pyrolysis, or combustion. In this work, a group additivity model is constructed that allows prediction of reaction rates and Arrhenius parameters of hydrogen abstractions by hydrogen atoms from alcohols, ethers, esters, peroxides, ketones, aldehydes, acids, and diketones in a broad temperature range (300-2000 K). A training set of 60 reactions was developed with rate coefficients and Arrhenius parameters calculated by the CBS-QB3 method in the high-pressure limit with tunneling corrections using Eckart tunneling coefficients. From this set of reactions, 15 group additive values were derived for the forward and the reverse reaction, 4 referring to primary and 11 to secondary contributions. The accuracy of the model is validated upon an ab initio and an experimental validation set of 19 and 21 reaction rates, respectively, showing that reaction rates can be predicted with a mean factor of deviation of 2 for the ab initio and 3 for the experimental values. Hence, this work illustrates that the developed group additive model can be reliably applied for the accurate prediction of kinetics of α-hydrogen abstractions by hydrogen atoms from a broad range of oxygenates. PMID:25209711

  18. Hydrogen Oxidation-Driven Hot Electron Flow Detected by Catalytic Nanodiodes

    SciTech Connect

    Hervier, Antoine; Renzas, J. Russell; Park, Jeong Y.; Somorjai, Gabor A.

    2009-07-20

    Hydrogen oxidation on platinum is shown to be a surface catalytic chemical reaction that generates a steady state flux of hot (>1 eV) conduction electrons. These hot electrons are detected as a steady-state chemicurrent across Pt/TiO{sub 2} Schottky diodes whose Pt surface is exposed to hydrogen and oxygen. Kinetic studies establish that the chemicurrent is proportional to turnover frequency for temperatures ranging from 298 to 373 K for P{sub H2} between 1 and 8 Torr and P{sub O2} at 760 Torr. Both chemicurrent and turnover frequency exhibit a first order dependence on P{sub H2}.

  19. The confined hydrogen atom: a linear variational approach

    NASA Astrophysics Data System (ADS)

    Aquino, N.; Rojas, R. A.

    2016-01-01

    We study the size effect on the confinement of a hydrogen atom in a spherical box of impenetrable walls. We compute the energy of the ground and a few excited states as a function of the box radius R c . To obtain the energy eigenvalues and eigenfunctions we utilize the linear variational method via a basis set of free-particle-in-a-box wave functions. For small values of R c convergence is attained with a small number of basis set functions, whereas for R c ≥ 5.0 au, it is necessary to use over 100 terms in the expansion.

  20. Electron-impact-ionization cross section for the hydrogen atom

    NASA Astrophysics Data System (ADS)

    Hu, W.; Fang, D.; Wang, Y.; Yang, F.

    1994-02-01

    A distorted-wave Born exchange approximation was used to calculate the cross section for electron-impact ionization of the hydrogen atoms. Both the integral and energy-differential cross section were calculated. The results were compared with the latest experimental data and other theoretical calculations. Comparison shows that the calculations agree with differential cross-section measurements in general. For integral cross sections the calculation shows a better agreement with an earlier measurement [M.B. Shah, D. S. Elliott, and H. B. Gilbody, J. Phys. B 20, 3501 (1987)] in which the cross sections are normalized to the first Born approximation.

  1. Atomic hydrogen cleaning of GaAS Photocathodes

    SciTech Connect

    M. Poelker; J. Price; C. Sinclair

    1997-01-01

    It is well known that surface contaminants on semiconductors can be removed when samples are exposed to atomic hydrogen. Atomic H reacts with oxides and carbides on the surface, forming compounds that are liberated and subsequently pumped away. Experiments at Jefferson lab with bulk GaAs in a low-voltage ultra-high vacuum H cleaning chamber have resulted in the production of photocathodes with high photoelectron yield (i.e., quantum efficiency) and long lifetime. A small, portable H cleaning apparatus also has been constructed to successfully clean GaAs samples that are later removed from the vacuum apparatus, transported through air and installed in a high-voltage laser-driven spin-polarized electron source. These results indicate that this method is a versatile and robust alternative to conventional wet chemical etching procedures usually employed to clean bulk GaAs.

  2. Microwave ionization of hydrogen atoms: Experiment vs classical dynamics

    SciTech Connect

    van Leeuwen, K.A.H.; Oppen, G.V.; Renwick, S.; Bowlin, J.B.; Koch, P.M.; Jensen, R.V.; Rath, O.; Richards, D.; Leopold, J.G.

    1985-11-18

    Ionization of hydrogen atoms with principal quantum number n = 32, 40, and 51--74 by a 9.92-GHz electric field F(t)zF0 cos t was studied with a superimposed static electric field F-bar/sub s/ = 0,2,5,8 V/cm. The measured field strengths F0(10%) at which 10% of the atoms were ionized are in excellent agreement with classical calculations in both one and two spatial dimensions. Covering finer detail as well as gross structure of the n dependence of F0(10%), the agreement supports the application of classical dynamics to the analysis of this strongly perturbed quantum system.

  3. Classical and quantum dynamics of the impulsively driven hydrogen atom

    SciTech Connect

    Melles, M.; Reinhold, C.O.; Burgdoerfer, J. |

    1992-12-01

    We investigate the classical and quantum dynamics of the hydrogen atom in a Rydberg state subject to a sequence of periodic and random pulses. One goal of this study is to test the validity of classical electron transport theories. We analyze the critical momentum transfer for which 10% of the Rydberg atoms are ionized after a large number of pulses as a function of the frequency of the perturbation. The quantum mechanical results for a periodic sequence of pulses exhibit clear structures which are not present in a classical simulation. These structures are shown to vanish for the case of stochastic pulses for which agreement is obtained between the classical and quantum mechanical results. The dynamics of the quantum mechanical periodic system is analyzed in terms of quasi-eigenstates of the period-one time evolution operator.

  4. Classical and quantum dynamics of the impulsively driven hydrogen atom

    SciTech Connect

    Melles, M.; Reinhold, C.O.; Burgdoerfer, J. Oak Ridge National Lab., TN )

    1992-01-01

    We investigate the classical and quantum dynamics of the hydrogen atom in a Rydberg state subject to a sequence of periodic and random pulses. One goal of this study is to test the validity of classical electron transport theories. We analyze the critical momentum transfer for which 10% of the Rydberg atoms are ionized after a large number of pulses as a function of the frequency of the perturbation. The quantum mechanical results for a periodic sequence of pulses exhibit clear structures which are not present in a classical simulation. These structures are shown to vanish for the case of stochastic pulses for which agreement is obtained between the classical and quantum mechanical results. The dynamics of the quantum mechanical periodic system is analyzed in terms of quasi-eigenstates of the period-one time evolution operator.

  5. Ionization of atomic hydrogen by 30 1000 keV antiprotons

    SciTech Connect

    Knudsen, H.; Mikkelsen, U.; Paludan, K.; Kirsebom, K.; Moller, S.P.; Uggerhoj, E.; Slevin, J.; Charlton, M.; Morenzoni, E.

    1995-06-05

    Ionization in collisions between antiprotons and atomic hydrogen is perhaps the least complicated and most fundamental process that can be treated by atomic-collision theory. We present measurements of the ionization cross section for 30--1000 keV antiprotons colliding with atomic hydrogen.

  6. Hot Hydrogen Exposure Degradation of the Strength of Mullite

    NASA Technical Reports Server (NTRS)

    Herbell, Thomas P.; Hull, David R.; Garg, Anita

    1996-01-01

    This study deals with the corrosion of near stoichiometric mullite (3Al2O3-2SiO2) by pure dry hydrogen gas. Exposure of the mullite samples was at temperatures of 1050 and 1250 C for times up to 500 hours. Preferential attack of the alumino-silicate glass present in the grain boundaries of the mullite occurred after 125 hours at 1250 C. Hydrogen scrubbing of the SiO2 from the glassy grain boundaries and the mullite grains yielded a porous alumina-rich surface. The room temperature strength increased after short exposure times at 1250 C (up to 125 hours), then decreased by 53 percent after exposure for 500 hours. At 1050 C, all exposure times (25 to 500 hours) decreased the strength. After 500 hours in hydrogen at 1050 C, the room temperature strength of mullite decreased 22 percent. We also observed a rapid 25 percent strength loss after short exposure times at 1050 C. This is attributed to the calcium/hydrogen assisted crystallization of the glassy, grain-boundary phase.

  7. 1,2-shifts of hydrogen atoms in aryl radicals

    SciTech Connect

    Brooks, M.A.; Scott, L.T.

    1999-06-16

    An energy barrier on the order of 60 kcal/mol is predicted for the 1,2-shift of hydrogen atoms in aryl radicals. Such rearrangements are, therefore, not expected to occur under ordinary laboratory conditions, but they should be prevalent in the aryl radicals formed during combustion, flash vacuum pyrolysis, and other high-temperature gas-phase processes. As a demonstration of this rearrangement, the 2-benzo[c]phenanthryl radical (1) was generated by flash vacuum pyrolysis of the corresponding aryl bromide. A 1,2-shift of hydrogen out of the sterically congested cover region of 1, followed by cyclization and rearomatization of the resulting radical, is proposed to explain the observation of benzo[ghi]fluoranthene as the dominant monomeric product formed. Under the same conditions, [1,3,4,5-{sup 2}H{sub 4}]-2-bromobenzo[c]phenanthrene gives [1,2,3,4-{sup 2}H{sub 4}]-benzo[ghi]fluoranthene as the dominant monomeric product, in accord with the expectation of a deuterium atom 1,2-shift.

  8. Hydrogen-like atom with nonnegative quantum distribution function

    SciTech Connect

    Zorin, A. V. Sevastianov, L. A.

    2007-04-15

    Among numerous approaches to probabilistic interpretation of conventional quantum mechanics (CQM), the closest to N. Bohr's idea of the correspondence principle is the Blokhintzev-Terletsky approach of the quantum distribution function (QDF) on the coordinate-momentum (q, p) phase space. The detailed investigation of this approach has led to the correspondence rule of V.V. Kuryshkin parametrically dependent on a set of auxiliary functions. According to investigations of numerous authors, the existence and the explicit form of QDF depends on the correspondence rule between classical functions A(q, p) and quantum operator A. At the same time, the QDF corresponding to all known quantization rules turns out to be alternating in sign or overly complex valued. Finally nonexistence of nonnegative QDF in CQM was proved. On the other hand, from this follows the possibility to construct quantum mechanics where a nonnegative QDF exists. We consider a certain set of auxiliary functions to construct explicit expressions for operators O(H) for the hydrogen atom. Naturally, these operators differ from the related operator H in CQM, so that spherical coordinates are no longer separable for a hydrogen-like atom in quantum mechanics with nonnegative QDF.

  9. Atomic hydrogen for low temperature atomic hydrogen masers and in-vacuum dissociators for VLG-11 series masers

    NASA Technical Reports Server (NTRS)

    Vessot, R. F. C.

    1984-01-01

    The operation of a cryogenically-cooled hydrogen maser using an RF plasma dissociator operating at liquid nitrogen temperature (77K) in confunction with a state selector magnet whose dimensions are suitable for slow atoms is studied. The focusing characteristics for a hexapole state selector magnet with maximum fields at the pole tips, provide a maximum acceptance angle for atoms at the most probable velocity in the beam. By thermally isolating the RF circuitry from the dissociator glassware, only dielectric losses in the glass and the energy coupled to the plasma will result in the boil-off of liquid nitrogen. It is estimated that this is about one watt and thus a loss rate of approximately .022 liters pr hour is anticipated.

  10. Plasma Effects on the Metastable Neutral HYDROGEN(2S) Atom.

    NASA Astrophysics Data System (ADS)

    Benage, John Ferns, Jr.

    Atomic radiative processes which occur in plasmas have long been of interest of plasma physicists. The process we are investigating is atomic dipole transitions, specifically transitions from the metastable 2s to the 2p in hydrogen, which are induced by processes which occur in the plasma. An experiment was done to measure the rate of transitions from 2s to 2p in hydrogen. This experiment was divided into two sections. The first was to measure the transition rate in a near equilibrium plasma. The second section measured the transition rate when RF oscillations were imposed on the plasma. The results of the first part of the experiment show that microscopic fluctuating electric fields which are produced by the motions of the charged particles induce transitions from 2s to 2p in hydrogen. The magnitude of this effect is compared to predicted transition rates due to collisions with electrons and ions and to rates predicted for an equilibrium plasma. In the second part of the experiment, the plasma was shown to act as a filter, preventing transitions from being caused by the RF unless the RF was in the range where plasma waves could be launched. The interpretation we give for this effect is that when the oscillations are inducing transitions, it is because plasma waves are being launched in the plasma and it is these waves which are inducing the transitions. These results have a couple of important applications. The results for the equilibrium part of the experiment can be used to explain a limit in the current which is produced by the Lamb-shift polarized ion source. The other important application is the possible use of the effect seen in the RF case as a non-perturbing diagnostic for plasma waves. Since dipole transition rates are proportional to E('2) and very sensitive near resonance, this effect could prove to be more accurate and more sensitive than methods currently used.

  11. Electromagnetically induced photonic bandgap in hot Cs atoms

    SciTech Connect

    Li, D. W.; Zhang, L.; Su, X. M.; Zhuo, Z. C.; Kim, J. B

    2010-04-15

    Three-level {Lambda}-type thermal Cs atoms are used to demonstrate the phenomenon of a photonic bandgap induced by quantum coherence with a standing wave (SW). We observed the transmitted signals of probe field driven by several kinds of SW, which are formed by a strong forward-traveling field and a backward-traveling field when a mirror reflects the forward-traveling beam. Considering Doppler inhomogeneous broadenings with a SW drive, we employ Fourier transformation to solve density-matrix equations for simulation results. The simulation results are found to be consistent with the experimental results.

  12. The ground state properties of spin-aligned atomic hydrogen, deuterium, and tritium

    NASA Technical Reports Server (NTRS)

    Etters, R. D.; Dugan, J. V., Jr.; Palmer, R. W.

    1975-01-01

    The internal energy, pressure, and compressibility of ground-state, spin-aligned atomic hydrogen, deuterium, and tritium are calculated assuming that all pair interactions occur via the atomic triplet (spin-aligned) potential. The conditions required to obtain atomic hydrogen and its isotopes in bulk are discussed; such a development would be of value in propulsion systems because of the light mass and energetic recombination of atomic hydrogen. Results show that atomic triplet hydrogen and deuterium remain gaseous at 0 K, and that tritium forms a liquid with a binding energy of approximately -0.75 K per atom at a molar volume of 130 cu cm per mole. The pair distribution function for these systems is calculated, and the predicted superfluid behavior of atomic triplet hydrogen and tritium is briefly discussed.

  13. Atomic interactions and phase transition in hydrogen metal systems

    SciTech Connect

    Shirley, A.I.

    1985-01-01

    The statistical mechanical behavior of H in pure metals and metal alloys is investigated using elasticity theory and lattice-gas models. The interactions between H atoms are separated into elastic and electronic contributions, and only the elastic contributions are evaluated. Three studies are reported: trapping of H by interstitial and substitutional impurities in bbc metals; modeling of H in impure metals; and modeling of H in concentration metal hydrides. The elastic interactions between H and interstitial and substitutional impurities in bbc metals are calculated using the method of lattice statics. Comparison with experimentally-measured trapping energies indicates that trapping by interstitial impurities is due solely to elastic energy, whereas both elastic and electronic interactions contribute to trapping by substitutional impurities. To include the effect of substitutional trapping on the phase transitions of H in metal alloys, the random-field lattice-gas model is developed. Interactions between H atoms are determined using the effective metal atom approximation. Hydrogen-impurity interactions are treated as a random field, in analogy with the random-field Ising model. Phase diagrams of the Nb/sub .95/Mo/sub .05/-H and Nb/sub .85/Mo/sub .15/-H systems are calculated by Monte Carlo simulation using the random-field model. The model gives qualitatively correct predictions of the phase behavior when the random field is included.

  14. On the role of 'hot' atoms in plasma-assisted ignition.

    PubMed

    Starikovskiy, Andrey Yu

    2015-08-13

    This paper discusses the processes leading to the formation of 'hot' atoms and radicals possessing excessive translational energy in high-voltage NS pulse discharges. It is shown that the formation of such 'hot' atoms occurs efficiently both in the dissociation of molecules by direct electron impact, and in the collisional quenching of electronically excited states. Depending on the magnitude of the reduced electric field in the discharge, reactions of these 'hot' atoms increase the initial concentration of radicals in the discharge afterglow two to three times when compared with the values calculated without effects of translational non-equilibrium. The role of thermally non-equilibrium excitation has been demonstrated in the formation of the initial distribution of the chemically active components in the mixture and its influence on the kinetics of ignition initiation at low and high temperatures. It was found that in undiluted mixtures the presence of 'hot' atoms can significantly decrease an ignition threshold and accelerate a low-temperature oxidation.

  15. Hydrogen atom abstraction from organometallic hydrogen sources: First kinetics of H atom abstraction by benzyl radical from `Mo-S-H`

    SciTech Connect

    Birbaum, J.C.; Franz, J.A.; Linehan, J.C.

    1997-12-31

    Hydrogen transfers are very important in catalytic and stoichiometric organometallic reaction schemes, yet few kinetic studies of the transfers from a metal hydride to an organic radical have been performed. To our knowledge there are no kinetic studies of hydrogen atom transfers from atoms attached to metals such as sulfur or oxygen. We present the first study with the extremely fast hydrogen atom transfer from (CpMoSSH){sub 2} to benzyl radical. The rate constant for this reaction was found to be greater than 10{sup 6} M{sup -1}s{sup -1} at room temperature.

  16. Atomic-scale observation of hydrogen-induced crack growth by atom-probe FIM. [Fe-0. 29% Ti

    SciTech Connect

    Kuk, Y.; Pickering, H.W.; Sakurai, T.

    1980-01-01

    Formation and propagation of a microcrack due to hydrogen in a Fe-0.29 wt.% Ti alloy was observed at the atomic scale by field ion microscopy. A microcrack (-20 nm in length) formed and became noticeably large when the tip was heated at 950/sup 0/C in the presence of about 1 torr of Hg. Propagation was reported several times by reheating, until a portion of the tip ruptured and became detached from the tip. Compositional analysis, performed in situ using a high performance atom-probe, identified atomic hydrogen in quantity and some hydrogen molecules and FEH in the crack, but not elsewhere on the surface.

  17. Positron impact excitations of hydrogen atom embedded in weakly coupled plasmas: Formation of Rydberg atoms

    SciTech Connect

    Rej, Pramit; Ghoshal, Arijit

    2014-09-15

    Formation of Rydberg atoms due to 1s→nlm excitations of hydrogen, for arbitrary n, l, m, by positron impact in weakly coupled plasma has been investigated using a distorted-wave theory in the momentum space. The interactions among the charged particles in the plasma have been represented by Debye-Huckel potentials. Making use of a simple variationally determined wave function for the hydrogen atom, it has been possible to obtain the distorted-wave scattering amplitude in a closed analytical form. A detailed study has been made on the effects of plasma screening on the differential and total cross sections in the energy range 20–300 eV of incident positron. For the unscreened case, our results agree nicely with some of the most accurate results available in the literature. To the best of our knowledge, such a study on the differential and total cross sections for 1s→nlm inelastic positron-hydrogen collisions for arbitrary n, l, m in weakly coupled plasmas is the first reported in the literature.

  18. Theory of catalytic dissociation of hydrogen atoms on a metal surface

    SciTech Connect

    Konstantinov, O. V. Dymnikov, V. D.; Mittsev, M. A.

    2008-08-15

    The model of hydrogen atom ionization near a metal surface is discussed on the basis of a comparison between the metal work function and the atom ionization energy. In the theoretical calculation, it is shown that the hydrogen atom ionization energy decreases when the atom approaches the metal surface. The ionization energy vanishes when the distance between proton and the metal surface is somewhat less than the Bohr radius.

  19. Entropy and complexity analysis of hydrogenic Rydberg atoms

    NASA Astrophysics Data System (ADS)

    López-Rosa, S.; Toranzo, I. V.; Sánchez-Moreno, P.; Dehesa, J. S.

    2013-05-01

    The internal disorder of hydrogenic Rydberg atoms as contained in their position and momentum probability densities is examined by means of the following information-theoretic spreading quantities: the radial and logarithmic expectation values, the Shannon entropy, and the Fisher information. As well, the complexity measures of Crámer-Rao, Fisher-Shannon, and López Ruiz-Mancini-Calvet types are investigated in both reciprocal spaces. The leading term of these quantities is rigorously calculated by use of the asymptotic properties of the concomitant entropic functionals of the Laguerre and Gegenbauer orthogonal polynomials which control the wavefunctions of the Rydberg states in both position and momentum spaces. The associated generalized Heisenberg-like, logarithmic and entropic uncertainty relations are also given. Finally, application to linear (l = 0), circular (l = n - 1), and quasicircular (l = n - 2) states is explicitly done.

  20. Phase Space Structures Explain Hydrogen Atom Roaming in Formaldehyde Decomposition.

    PubMed

    Mauguière, Frédéric A L; Collins, Peter; Kramer, Zeb C; Carpenter, Barry K; Ezra, Gregory S; Farantos, Stavros C; Wiggins, Stephen

    2015-10-15

    We re-examine the prototypical roaming reaction--hydrogen atom roaming in formaldehyde decomposition--from a phase space perspective. Specifically, we address the question "why do trajectories roam, rather than dissociate through the radical channel?" We describe and compute the phase space structures that define and control all possible reactive events for this reaction, as well as provide a dynamically exact description of the roaming region in phase space. Using these phase space constructs, we show that in the roaming region, there is an unstable periodic orbit whose stable and unstable manifolds define a conduit that both encompasses all roaming trajectories exiting the formaldehyde well and shepherds them toward the H2···CO well.

  1. Inelastic cross sections for positron scattering from atomic hydrogen

    SciTech Connect

    Weber, M.; Hofmann, A.; Raith, W.; Sperber, W.; Jacobsen, F.; Lynn, K.G.

    1994-12-31

    Positronium formation (Ps) cross sections for positrons impinging on atomic hydrogen were measured in the impact energy range from 13eV to 255eV at the High Intensity Positron (HIP) beam at Brookhaven National Laboratory (BNL). The Ps-formation cross section was found to rise rapidly from the threshold at 6.8eV to a maximum value of (2.98 {plus_minus} 0.18) {times} 10{sup {minus}16} cm{sup 2} for {approx} 15eV positrons. By 75eV it drops below the detection limit of 0.17 {times} 10{sup {minus}16} cm{sup 2} which is the present level of statistical uncertainty. The experiment was modified to enable the measurement of doubly differential scattering cross sections.

  2. Ionization of atomic hydrogen in strong infrared laser fields

    SciTech Connect

    Grum-Grzhimailo, Alexei N.; Abeln, Brant; Bartschat, Klaus; Weflen, Daniel; Urness, Timothy

    2010-04-15

    We have used the matrix iteration method of Nurhuda and Faisal [Phys. Rev. A 60, 3125 (1999)] to treat ionization of atomic hydrogen by a strong laser pulse. After testing our predictions against a variety of previous calculations, we present ejected-electron spectra as well as angular distributions for few-cycle infrared laser pulses with peak intensities of up to 10{sup 15} W/cm{sup 2}. It is shown that the convergence of the results with the number of partial waves is a serious issue, which can be managed in a satisfactory way by using the velocity form of the electric dipole operator in connection with an efficient time-propagation scheme.

  3. Entropy and complexity analysis of hydrogenic Rydberg atoms

    SciTech Connect

    Lopez-Rosa, S.; Toranzo, I. V.; Dehesa, J. S.; Sanchez-Moreno, P.

    2013-05-15

    The internal disorder of hydrogenic Rydberg atoms as contained in their position and momentum probability densities is examined by means of the following information-theoretic spreading quantities: the radial and logarithmic expectation values, the Shannon entropy, and the Fisher information. As well, the complexity measures of Cramer-Rao, Fisher-Shannon, and Lopez Ruiz-Mancini-Calvet types are investigated in both reciprocal spaces. The leading term of these quantities is rigorously calculated by use of the asymptotic properties of the concomitant entropic functionals of the Laguerre and Gegenbauer orthogonal polynomials which control the wavefunctions of the Rydberg states in both position and momentum spaces. The associated generalized Heisenberg-like, logarithmic and entropic uncertainty relations are also given. Finally, application to linear (l= 0), circular (l=n- 1), and quasicircular (l=n- 2) states is explicitly done.

  4. Communication: Test of quantum chemistry in vibrationally hot hydrogen molecules

    NASA Astrophysics Data System (ADS)

    Niu, M. L.; Salumbides, E. J.; Ubachs, W.

    2015-08-01

    Precision measurements are performed on highly excited vibrational quantum states of molecular hydrogen. The v = 12, J = 0 - 3 rovibrational levels of H2 ( X 1 Σg + ), lying only 2000 cm-1 below the first dissociation limit, were populated by photodissociation of H2S and their level energies were accurately determined by two-photon Doppler-free spectroscopy. A comparison between the experimental results on v = 12 level energies with the best ab initio calculations shows a good agreement, where the present experimental accuracy of 3.5 × 10-3 cm-1 is more precise than theory, hence providing a gateway to further test theoretical advances in this benchmark quantum system.

  5. Communication: Test of quantum chemistry in vibrationally hot hydrogen molecules.

    PubMed

    Niu, M L; Salumbides, E J; Ubachs, W

    2015-08-28

    Precision measurements are performed on highly excited vibrational quantum states of molecular hydrogen. The v = 12, J = 0 - 3 rovibrational levels of H2 (X(1)Σg (+)), lying only 2000 cm(-1) below the first dissociation limit, were populated by photodissociation of H2S and their level energies were accurately determined by two-photon Doppler-free spectroscopy. A comparison between the experimental results on v = 12 level energies with the best ab initio calculations shows a good agreement, where the present experimental accuracy of 3.5 × 10(-3) cm(-1) is more precise than theory, hence providing a gateway to further test theoretical advances in this benchmark quantum system.

  6. Cold collisions of atomic hydrogen with antihydrogen atoms: An optical potential approach

    SciTech Connect

    Zygelman, B.; Saenz, Alejandro; Froelich, P.; Jonsell, S.

    2004-04-01

    We present a theory that describes the interaction of hydrogen atoms with antihydrogen at subkelvin temperatures. The formalism includes a nonlocal complex optical potential, whose imaginary component describes the breakup of the H-H-bar complex into positronium and protonium fragments. Using ab inito methods, we construct the imaginary part of the optical potential and calculate the cross sections for fragmentation in ultracold collisions of H and H-bar. We find a 35% reduction in the value of the scattering length from that obtained in the Born-Oppenheimer approximation. We estimate the lifetimes for quasibound states of this complex to fragment into a protonium-positronium pair.

  7. Hot wire deposited hydrogenated amorphous silicon solar cells

    SciTech Connect

    Mahan, A.H.; Iwaniczko, E.; Nelson, B.P.; Reedy, R.C. Jr.; Crandall, R.S.

    1996-05-01

    This paper details the results of a study in which low H content, high deposition rate hot wire (HW) deposited amorphous silicon (a-Si:H) has been incorporated into a substrate solar cell. The authors find that the treatment of the top surface of the HW i layer while it is being cooled from its high deposition temperature is crucial to device performance. They present data concerning these surface treatments, and correlate these treatments with Schottky device performance. The authors also present first generation HW n-i-p solar cell efficiency data, where a glow discharge (GD) {mu}c-Si(p) layer was added to complete the partial devices. No light trapping layer was used to increase the device Jsc. Their preliminary investigations have yielded efficiencies of up to 6.8% for a cell with a 4000 {Angstrom} thick HW i-layer, which degrade less than 10% after a 900 hour light soak. The authors suggest avenues for further improvement of their devices.

  8. Transient absorption spectra of the laser-dressed hydrogen atom

    NASA Astrophysics Data System (ADS)

    Murakami, Mitsuko; Chu, Shih-I.

    2013-10-01

    We present a theoretical study of transient absorption spectra of laser-dressed hydrogen atoms, based on numerical solutions of the time-dependent Schrödinger equation. The timing of absorption is controlled by the delay between an extreme ultra violet (XUV) pulse and an infrared (IR) laser field. The XUV pulse is isolated and several hundred attoseconds in duration, which acts as a pump to drive the ground-state electron to excited p states. The subsequent interaction with the IR field produces dressed states, which manifest as sidebands between the 1s-np absorption spectra separated by one IR-photon energy. We demonstrate that the population of dressed states is maximized when the timing of the XUV pulse coincides with the zero crossing of the IR field, and that their energies can be manipulated in a subcycle time scale by adding a chirp to the IR field. An alternative perspective to the problem is to think of the XUV pulse as a probe to detect the dynamical ac Stark shifts. Our results indicate that the accidental degeneracy of the hydrogen excited states is removed while they are dressed by the IR field, leading to large ac Stark shifts. Furthermore, we observe the Autler-Townes doublets for the n=2 and 3 levels using the 656 nm dressing field, but their separation does not agree with the prediction by the conventional three-level model that neglects the dynamical ac Stark shifts.

  9. Positron scattering from hydrogen atom embedded in dense quantum plasma

    SciTech Connect

    Bhattacharya, Arka; Kamali, M. Z. M.; Ghoshal, Arijit; Ratnavelu, K.

    2013-08-15

    Scattering of positrons from the ground state of hydrogen atoms embedded in dense quantum plasma has been investigated by applying a formulation of the three-body collision problem in the form of coupled multi-channel two-body Lippmann-Schwinger equations. The interactions among the charged particles in dense quantum plasma have been represented by exponential cosine-screened Coulomb potentials. Variationally determined hydrogenic wave function has been employed to calculate the partial-wave scattering amplitude. Plasma screening effects on various possible mode of fragmentation of the system e{sup +}+H(1s) during the collision, such as 1s→1s and 2s→2s elastic collisions, 1s→2s excitation, positronium formation, elastic proton-positronium collisions, have been reported in the energy range 13.6-350 eV. Furthermore, a comparison has been made on the plasma screening effect of a dense quantum plasma with that of a weakly coupled plasma for which the plasma screening effect has been represented by the Debye model. Our results for the unscreened case are in fair agreement with some of the most accurate results available in the literature.

  10. Quantum dynamics of hydrogen atoms on graphene. II. Sticking

    SciTech Connect

    Bonfanti, Matteo; Jackson, Bret; Hughes, Keith H.; Burghardt, Irene

    2015-09-28

    Following our recent system-bath modeling of the interaction between a hydrogen atom and a graphene surface [Bonfanti et al., J. Chem. Phys. 143, 124703 (2015)], we present the results of converged quantum scattering calculations on the activated sticking dynamics. The focus of this study is the collinear scattering on a surface at zero temperature, which is treated with high-dimensional wavepacket propagations with the multi-configuration time-dependent Hartree method. At low collision energies, barrier-crossing dominates the sticking and any projectile that overcomes the barrier gets trapped in the chemisorption well. However, at high collision energies, energy transfer to the surface is a limiting factor, and fast H atoms hardly dissipate their excess energy and stick on the surface. As a consequence, the sticking coefficient is maximum (∼0.65) at an energy which is about one and half larger than the barrier height. Comparison of the results with classical and quasi-classical calculations shows that quantum fluctuations of the lattice play a primary role in the dynamics. A simple impulsive model describing the collision of a classical projectile with a quantum surface is developed which reproduces the quantum results remarkably well for all but the lowest energies, thereby capturing the essential physics of the activated sticking dynamics investigated.

  11. Quantum dynamics of hydrogen atoms on graphene. II. Sticking.

    PubMed

    Bonfanti, Matteo; Jackson, Bret; Hughes, Keith H; Burghardt, Irene; Martinazzo, Rocco

    2015-09-28

    Following our recent system-bath modeling of the interaction between a hydrogen atom and a graphene surface [Bonfanti et al., J. Chem. Phys. 143, 124703 (2015)], we present the results of converged quantum scattering calculations on the activated sticking dynamics. The focus of this study is the collinear scattering on a surface at zero temperature, which is treated with high-dimensional wavepacket propagations with the multi-configuration time-dependent Hartree method. At low collision energies, barrier-crossing dominates the sticking and any projectile that overcomes the barrier gets trapped in the chemisorption well. However, at high collision energies, energy transfer to the surface is a limiting factor, and fast H atoms hardly dissipate their excess energy and stick on the surface. As a consequence, the sticking coefficient is maximum (∼0.65) at an energy which is about one and half larger than the barrier height. Comparison of the results with classical and quasi-classical calculations shows that quantum fluctuations of the lattice play a primary role in the dynamics. A simple impulsive model describing the collision of a classical projectile with a quantum surface is developed which reproduces the quantum results remarkably well for all but the lowest energies, thereby capturing the essential physics of the activated sticking dynamics investigated. PMID:26429029

  12. Evidence of a liquid–liquid phase transition in hot dense hydrogen

    PubMed Central

    Dzyabura, Vasily; Zaghoo, Mohamed; Silvera, Isaac F.

    2013-01-01

    We use pulsed-laser heating of hydrogen at static pressures in the megabar pressure region to search for the plasma phase transition to liquid atomic metallic hydrogen. We heat our samples substantially above the melting line and observe a plateau in a temperature vs. laser power curve that otherwise increases with power. This anomaly in the heating curve appears correlated with theoretical predictions for the plasma phase transition. PMID:23630287

  13. Evidence of a liquid-liquid phase transition in hot dense hydrogen.

    PubMed

    Dzyabura, Vasily; Zaghoo, Mohamed; Silvera, Isaac F

    2013-05-14

    We use pulsed-laser heating of hydrogen at static pressures in the megabar pressure region to search for the plasma phase transition to liquid atomic metallic hydrogen. We heat our samples substantially above the melting line and observe a plateau in a temperature vs. laser power curve that otherwise increases with power. This anomaly in the heating curve appears correlated with theoretical predictions for the plasma phase transition. PMID:23630287

  14. Quantum effects of hydrogen atoms on the dynamical rearrangement of hydrogen-bond networks in liquid water.

    PubMed

    Hyeon-Deuk, Kim; Ando, Koji

    2010-04-28

    Quantum effects such as zero-point energy and delocalization of wave packets (WPs) representing water hydrogen atoms are essential to understand anomalous energetics and dynamics in water. Since quantum calculations of many-body dynamics are highly complicated, no one has yet directly viewed the quantum WP dynamics of hydrogen atoms in liquid water. Our semiquantum molecular dynamics simulation made it possible to observe the hydrogen WP dynamics in liquid water. We demonstrate that the microscopic WP dynamics are closely correlated with and actually play key roles in the dynamical rearrangement in the hydrogen-bond network (HBN) of bulk water. We found the quantum effects of hydrogen atoms on liquid water dynamics such as the rearrangement of HBN and the concomitant fluctuation and relaxation. Our results provide new physical insights on HBN dynamics in water whose significance is not limited to pure liquid dynamics but also a greater understanding of chemical and biological reactions in liquid water.

  15. Scattering of cold-atom coherences by hot atoms: frequency shifts from background-gas collisions.

    PubMed

    Gibble, Kurt

    2013-05-01

    Frequency shifts from background-gas collisions currently contribute significantly to the inaccuracy of atomic clocks. Because nearly all collisions with room-temperature background gases that transfer momentum eject the cold atoms from the clock, the interference between the scattered and unscattered waves in the forward direction dominates these frequency shifts. We show they are ≈ 10 times smaller than in room-temperature clocks and that van der Waals interactions produce the cold-atom background-gas shift. General considerations allow the loss of the Ramsey fringe amplitude to bound this frequency shift. PMID:23683186

  16. Schrodinger Equation Solutions that Lead to the Solution for the Hydrogen Atom

    ERIC Educational Resources Information Center

    Newhouse, Paul F.; McGill, K.C.

    2004-01-01

    Two exercises that would provide beginning quantum theory students with an introduction to more advanced quantum mechanical treatments, especially the hydrogen atom are given. The exercises are stepwise in difficulty, leading naturally to the full hydrogen atom development and greatly extend the pedagogy of most multidimensional Cartesian systems…

  17. Which hydrogen atom of toluene protonates PAH molecules in (+)-mode APPI MS analysis?

    PubMed

    Ahmed, Arif; Ghosh, Manik Kumer; Choi, Myung Chul; Choi, Cheol Ho; Kim, Sunghwan

    2013-03-01

    A previous study (Ahmed, A. et al., Anal. Chem. 84, 1146-1151( 2012) reported that toluene used as a solvent was the proton source for polyaromatic hydrocarbon compounds (PAHs) that were subjected to (+)-mode atmospheric-pressure photoionization. In the current study, the exact position of the hydrogen atom in the toluene molecule (either a methyl hydrogen or an aromatic ring hydrogen) involved in the formation of protonated PAH ions was investigated. Experimental analyses of benzene and anisole demonstrated that although the aromatic hydrogen atom of toluene did not contribute to the formation of protonated anthracene, it did contribute to the formation of protonated acridine. Thermochemical data and quantum mechanical calculations showed that the protonation of anthracene by an aromatic ring hydrogen atom of toluene is endothermic, while protonation by a methyl hydrogen atom is exothermic. However, protonation of acridine by either an aromatic ring hydrogen or a methyl hydrogen atom of toluene is exothermic. The different behavior of acridine and anthracene was attributed to differences in gas-phase basicity. It was concluded that both types of hydrogen in toluene can be used for protonation of PAH compounds, but a methyl hydrogen atom is preferred, especially for non-basic compounds.

  18. Positron impact excitations of hydrogen atom embedded in dense quantum plasmas: Formation of Rydberg atoms

    SciTech Connect

    Rej, Pramit; Ghoshal, Arijit

    2014-11-15

    Formation of Rydberg atoms due to 1 s → nlm excitations of hydrogen by positron impact, for arbitrary n, l, m, in dense quantum plasma has been investigated using a distorted wave theory which includes screened dipole polarization potential. The interactions among the charged particles in the plasma have been represented by exponential cosine-screened Coulomb potentials. Making use of a simple variationally determined hydrogen wave function, it has been possible to obtain the distorted wave scattering amplitude in a closed analytical form. A detailed study has been made to explore the structure of differential and total cross sections in the energy range 20–300 eV of incident positron. For the unscreened case, our results agree nicely with some of the most accurate results available in the literature. To the best of our knowledge, such a study on the differential and total cross sections for 1 s → nlm inelastic positron-hydrogen collisions in dense quantum plasma is the first reported in the literature.

  19. Arc-Heater Facility for Hot Hydrogen Exposure of Nuclear Thermal Rocket Materials

    NASA Technical Reports Server (NTRS)

    Litchford, Ron J.; Foote, John P.; Wang,Ten-See; Hickman, Robert; Panda, Binayak; Dobson, Chris; Osborne, Robin; Clifton, Scooter

    2006-01-01

    A hyper-thermal environment simulator is described for hot hydrogen exposure of nuclear thermal rocket material specimens and component development. This newly established testing capability uses a high-power, multi-gas, segmented arc-heater to produce high-temperature pressurized hydrogen flows representative of practical reactor core environments and is intended to serve. as a low cost test facility for the purpose of investigating and characterizing candidate fueUstructura1 materials and improving associated processing/fabrication techniques. Design and development efforts are thoroughly summarized, including thermal hydraulics analysis and simulation results, and facility operating characteristics are reported, as determined from a series of baseline performance mapping tests.

  20. SPHERICALLY SYMMETRIC NLTE MODEL ATMOSPHERES OF HOT HYDROGEN-HELIUM FIRST STARS

    SciTech Connect

    Kubat, Jiri

    2012-12-15

    We present results of our calculations of NLTE model stellar atmospheres for hot Population III stars composed of hydrogen and helium. We use our own computer code for the calculation of spherically symmetric NLTE model atmospheres in hydrostatic and radiative equilibrium. The model atmospheres are then used for the calculation of emergent fluxes. These fluxes serve to evaluate the flow of high-energy photons for energies higher than ionization energies of hydrogen and helium, the so-called ionizing photon fluxes. We also present the time evolution of the ionizing photon fluxes.

  1. New horizons in chemical propulsion. [processes using free radicals, atomic hydrogen, excited species, etc

    NASA Technical Reports Server (NTRS)

    Cohen, W.

    1973-01-01

    After a review of the work of the late-Fifties on free radicals for propulsion, it is concluded that atomic hydrogen would provide a potentially large increase in specific impulse. Work conducted to find an approach for isolating atomic hydrogen is considered. Other possibilities for obtaining propellants of greatly increased capability might be connected with the technology for the generation of activated states of gases, metallic hydrogen, fuels obtained from other planets, and laser transfer of energy.

  2. Ultra fast cooling of hot steel plate by air atomized spray with salt solution

    NASA Astrophysics Data System (ADS)

    Mohapatra, Soumya S.; Ravikumar, Satya V.; Jha, Jay M.; Singh, Akhilendra K.; Bhattacharya, Chandrima; Pal, Surjya K.; Chakraborty, Sudipto

    2014-05-01

    In the present study, the applicability of air atomized spray with the salt added water has been studied for ultra fast cooling (UFC) of a 6 mm thick AISI-304 hot steel plate. The investigation includes the effect of salt (NaCl and MgSO4) concentration and spray mass flux on the cooling rate. The initial temperature of the steel plate before the commencement of cooling is kept at 900 °C or above, which is usually observed as the "finish rolling temperature" in the hot strip mill of a steel plant. The heat transfer analysis shows that air atomized spray with the MgSO4 salt produces 1.5 times higher cooling rate than atomized spray with the pure water, whereas air atomized spray with NaCl produces only 1.2 times higher cooling rate. In transition boiling regime, the salt deposition occurs which causes enhancement in heat transfer rate by conduction. Moreover, surface tension is the governing parameter behind the vapour film instability and this length scale increases with increase in surface tension of coolant. Overall, the achieved cooling rates produced by both types of salt added air atomized spray are found to be in the UFC regime.

  3. Two-color ghost interference with photon pairs generated in hot atoms

    SciTech Connect

    Ding Dongsheng; Zhou Zhiyuan; Shi Baosen; Zou Xubo; Guo Guangcan

    2012-09-15

    We report on an experimental observation of a two-photon ghost interference experiment. A distinguishing feature of our experiment is that the photons are generated via a non-degenerated spontaneous four-wave mixing process in a hot atomic ensemble; therefore the photon has narrow bandwidth. Besides, there is a large difference in frequency between two photons in a pair. Our works may be important to achieve more secure, large transmission capacity long-distance quantum communication.

  4. Apparatus for trapping and thermal detection of atomic hydrogen in high magnetic fields at low temperatures

    NASA Technical Reports Server (NTRS)

    Woollam, J. A.

    1980-01-01

    An apparatus is described in which hydrogen atoms were trapped at temperatures down to 1.1 K in the 11 T field of a large volume superconducting magnet. A high sensitivity thermal detector was used to study trapping and recombination of atoms on the detector surface. The apparatus permits the application of extremely high steady state magnetic fields to study the potential effects of electron spin polarization on the stabilization of hydrogen atoms.

  5. Hydrogen abstraction from the hydrazine molecule by an oxygen atom.

    PubMed

    Spada, Rene F K; Ferrão, Luiz F A; Rocha, Roberta J; Iha, Koshun; Rocco, José A F F; Roberto-Neto, Orlando; Lischka, Hans; Machado, Francisco B C

    2015-03-01

    Thermochemical and kinetics properties of the hydrogen abstraction from the hydrazine molecule (N2H4) by an oxygen atom were computed using high-level ab initio methods and the M06-2X DFT functional with aug-cc-pVXZ (X = T, Q) and maug-cc-pVTZ basis sets, respectively. The properties along the reaction path were obtained using the dual-level methodology to build the minimum energy path with the potential energy surface obtained with the M06-2X method and thermochemical properties corrected with the CCSD(T)/CBS//M06-2X/maug-cc-pVTZ results. The thermal rate constants were calculated in the framework of variational transition-state theory. Wells on both sides of the reaction (reactants and products) were found and considered in the chemical kinetics calculations. Additionally, the product yields were investigated by means of a study of the triplet and singlet surfaces of the N2H4 + O → N2H2 + H2O reaction.

  6. Charge exchange and ionization in hydrogen atom-fully stripped ion collisions in Debye plasmas

    SciTech Connect

    Zhang, H.; Wang, J. G.; He, B.; Qiu, Y. B.; Janev, R. K.

    2007-05-15

    The processes of charge exchange and ionization in collisions of ground state hydrogen atom with fully stripped ions in a weakly coupled plasma are studied by the classical trajectory Monte Carlo method in the collision energy range 10-900 keV/amu. The interparticle interactions are described by the Debye-Hueckel model with inclusion of dynamical effects associated with the projectile velocity. The microcanonical distribution of initial state electronic coordinates and momenta has been determined by inclusion of plasma screening effects. The cross section dependencies on plasma parameters and ion charge and velocity are investigated. It is shown that plasma effects on charge exchange and ionization cross sections are significant and particularly pronounced at low collision velocities. The results of systematic cross section calculations for different values of Debye screening length (in the range 1-50a{sub 0}) and ion charges (in the range 1-14) are presented.

  7. Subnatural-linewidth biphotons from a Doppler-broadened hot atomic vapour cell

    PubMed Central

    Shu, Chi; Chen, Peng; Chow, Tsz Kiu Aaron; Zhu, Lingbang; Xiao, Yanhong; Loy, M.M.T.; Du, Shengwang

    2016-01-01

    Entangled photon pairs, termed as biphotons, have been the benchmark tool for experimental quantum optics. The quantum-network protocols based on photon–atom interfaces have stimulated a great demand for single photons with bandwidth comparable to or narrower than the atomic natural linewidth. In the past decade, laser-cooled atoms have often been used for producing such biphotons, but the apparatus is too large and complicated for engineering. Here we report the generation of subnatural-linewidth (<6 MHz) biphotons from a Doppler-broadened (530 MHz) hot atomic vapour cell. We use on-resonance spontaneous four-wave mixing in a hot paraffin-coated 87Rb vapour cell at 63 °C to produce biphotons with controllable bandwidth (1.9–3.2 MHz) and coherence time (47–94 ns). Our backward phase-matching scheme with spatially separated optical pumping is the key to suppress uncorrelated photons from resonance fluorescence. The result may lead towards miniature narrowband biphoton sources. PMID:27658721

  8. Application of KrCI excilamp for cleaning GaAs surfaces using atomic hydrogen

    NASA Astrophysics Data System (ADS)

    Tarasenko, Victor F.; Kagadei, Valerii A.; Lomaev, Mikhail I.; Panchenko, Alexei N.; Proskurovsky, Dmitrii I.

    1998-06-01

    Novel single block process facility including UV excilamp and sources of atomic hydrogen is described. Circular sealed-off KrCl* excilamp emitting two intensive bands at 195 and 222 nm was used. The source of atomic hydrogen on the base of reflecting Penning arc discharge was placed in line with the lamp. Semiconducting structures were treated in an expanding effusion jet of atomic hydrogen. The possibility to realize the process of cleaning GaAs surface under joint action of atomic hydrogen and UV radiation has been investigated. Effect of UV radiation on the rate of removing oxide layer is found at low temperature (18 - 100 degree(s)C). The mechanism providing an explanation for this event is suggested. The possibility to realize GaAs surface cleaning using successive performing the procedures of the surface treatment by atomic hydrogen, its oxidation with UV- stimulation and additional treatment by atomic hydrogen was also studied. The sources of atomic hydrogen and UV radiation developed allows to improve cleaning control and provides a way of producing the surface with specified properties.

  9. HAAD: A quick algorithm for accurate prediction of hydrogen atoms in protein structures.

    PubMed

    Li, Yunqi; Roy, Ambrish; Zhang, Yang

    2009-08-20

    Hydrogen constitutes nearly half of all atoms in proteins and their positions are essential for analyzing hydrogen-bonding interactions and refining atomic-level structures. However, most protein structures determined by experiments or computer prediction lack hydrogen coordinates. We present a new algorithm, HAAD, to predict the positions of hydrogen atoms based on the positions of heavy atoms. The algorithm is built on the basic rules of orbital hybridization followed by the optimization of steric repulsion and electrostatic interactions. We tested the algorithm using three independent data sets: ultra-high-resolution X-ray structures, structures determined by neutron diffraction, and NOE proton-proton distances. Compared with the widely used programs CHARMM and REDUCE, HAAD has a significantly higher accuracy, with the average RMSD of the predicted hydrogen atoms to the X-ray and neutron diffraction structures decreased by 26% and 11%, respectively. Furthermore, hydrogen atoms placed by HAAD have more matches with the NOE restraints and fewer clashes with heavy atoms. The average CPU cost by HAAD is 18 and 8 times lower than that of CHARMM and REDUCE, respectively. The significant advantage of HAAD in both the accuracy and the speed of the hydrogen additions should make HAAD a useful tool for the detailed study of protein structure and function. Both an executable and the source code of HAAD are freely available at http://zhang.bioinformatics.ku.edu/HAAD.

  10. Ab initio calculations on etching of graphite and diamond surfaces by atomic hydrogen

    SciTech Connect

    Kanai, C.; Watanabe, K.; Takakuwa, Y.

    2001-06-15

    Etching of graphite and hydrogenated diamond C(100) 2{times}1 surfaces by irradiating atomic hydrogen, which is one of the key reactions to promote epitaxial diamond growth by chemical vapor deposition, has been investigated by ab initio pseudopotential calculations. We demonstrate the reaction pathways and determine the activation energies for breaking C-C bonds on the surfaces by irradiating hydrogen atoms. The activation energy for C-C bond breaking on graphite is found to be only one-half of that on the hydrogenated diamond surface. This indicates that graphite, which is a typical nondiamond phase unnecessarily generated on the diamond surface during epitaxial growth, can be selectively eliminated by atomic hydrogen, resulting in methane desorption. Our result supports the growth rate enhancement in diamond epitaxy observed in a recent experiment by gas-source molecular beam epitaxy under hydrogen beam irradiation.

  11. The adsorption of a hydrogen atom on the two types of boron sheets surface

    NASA Astrophysics Data System (ADS)

    Boroznina, E. V.; Borkhoeva, N. N.; Boroznin, S. V.

    2015-01-01

    The possible connection between the atom of hydrogen and the surface of twodimensional boron sheets have been investigated. The calculations were carried out within the model of molecular cluster with the use of quantum chemical MNDO scheme. Two types of BS were studied: triangular BS (TBS) and α-sheet of boron atoms (αBS). The hydrogen atoms attacking BS have been simulated by a step-by-step approach for all atom locations. The surface patterns of potential energy for these processes were built. The analysis of curves showed that the active atom of hydrogen is adsorbed on the surface of BS. The adsorption distances (Rad) and the adsorption energy (Ead) were calculated. We have proved that αBS has a greater sorption capacity than hydrogen TBS.

  12. On-board hydrogen generation for transport applications: the HotSpot™ methanol processor

    NASA Astrophysics Data System (ADS)

    Edwards, Neil; Ellis, Suzanne R.; Frost, Jonathan C.; Golunski, Stanislaw E.; van Keulen, Arjan N. J.; Lindewald, Nicklas G.; Reinkingh, Jessica G.

    In the absence of a hydrogen infrastructure, development of effective on-board fuel processors is likely to be critical to the commercialisation of fuel-cell cars. The HotSpot™ reactor converts methanol, water and air in a single compact catalyst bed into a reformate containing mainly CO2 and hydrogen (and unreacted nitrogen). The process occurs by a combination of exothermic partial oxidation and endothermic steam reforming of methanol, to produce 750 l of hydrogen per hour from a 245-cm3 reactor. The relative contribution of each reaction can be tuned to match the system requirements at a given time. Scale-up is achieved by the parallel combination of the required number of individual HotSpot reactors, which are fed from a central manifold. Using this modular design, the start-up and transient characteristics of a large fuel-processor are identical to that of a single reactor. When vaporised liquid feed and air are introduced into cold reactors, 100% output is achieved in 50 s; subsequent changes in throughput result in instantaneous changes in output. Surplus energy within the fuel-cell powertrain can be directed to the manifold, where it can be used to vaporise the liquid feeds and so promote steam reforming, resulting in high system efficiency. The small amount of CO that is produced by the HotSpot reactions is attenuated to <10 ppm by a catalytic clean-up unit. The HotSpot concept and CO clean-up strategy are not limited to the processing of methanol, but are being applied to other organic fuels.

  13. Using Hydrogen Isotopes to Distinguish Allochthony and Autochthony in Hot Springs Ecosystems

    NASA Astrophysics Data System (ADS)

    Hungate, J.; DeSousa, T. M.; Ong, J. C.; Caron, M. M.; Brown, J. R.; Patel, N.; Dijkstra, P.; Hedlund, B. P.; Hungate, B. A.

    2013-12-01

    Hot springs are hosts to abundant and diverse microbial communities. Above the temperature threshold for photosynthesis (~73 degrees C), a variety of chemosynthetic organisms support autochthonous primary production in hot springs ecosystems. These organisms are thought to drive the carbon and energy budgets of these ecosystems, but the importance of energy inputs from the surrounding terrestrial environments - allochthonous inputs - is not well known. Here, we tested the efficacy of stable isotopes of hydrogen in distinguishing autochthonous from allochthonous sources of organic matter in hot springs ecosystems. Under laboratory conditions and in pure culture, we grew autotrophic, mixotrophic, and heterotrophic organisms from the Great Boiling Springs in northern Nevada as well as organisms typical of other hot springs environments. We measured the δ2H composition of biomass, water and organic matter sources used by the organisms to produce that biomass. We also surveyed organic matter in and around hot springs in Nevada and in the Tengchong geothermal region in China, sampling terrestrial plants at the hot springs margin, microorganisms (either scraped from surfaces or in the water column), and organic matter in the sediment accruing in the spring itself as an integrative measure of the relative importance of organic matter sources to the spring ecosystem. We found that autotrophic production in culture results in strongly depleted δ2H signatures, presumably because of fractionation against 2H-H2O during chemosynthesis. The observed difference between microbial biomass and water was larger than that typically found for terrestrial plants during photosynthesis, setting the stage for using δ2H to distinguish allochthonous from autochthonous sources of productivity in hot springs. In surveys of natural hot springs, microbial biomass sampled from the water column or from surfaces was often strongly depleted in δ2H, consistent with in situ chemosynthesis. Organic

  14. Trapping of hydrogen atoms in X-irradiated salts at room temperature and the decay kinetics

    NASA Technical Reports Server (NTRS)

    May, C. E.; Philipp, W. H.; Marsik, S. J.

    1974-01-01

    The salts (hypophosphites, formates, a phosphite, a phosphate, and an oxalate) were X-irradiated, whereby hydrogen formed chemically by a radiolytic process becomes trapped in the solid. By room temperature vacuum extraction, the kinetics for the evolution of this trapped hydrogen was studied mass spectrometrically. All salts except two exhibited second-order kinetics. The two exceptions (NaH2PO2(H2O) and K2HPO4) showed first-order kinetics. Based on experimental results, the escape of hydrogen involves three steps: the diffusion of hydrogen atoms from the bulk to the surface, association of these atoms on the surface (rate controlling step for second-order hydrogen evolution), and the desorption of molecular hydrogen from the surface. The hydrogen does not escape if the irradiated salt is stored in air, apparently because adsorbed air molecules occupy surface sites required in the escape mechanism.

  15. The adsorption of atomic hydrogen on tellurium and formation of H 2Te

    NASA Astrophysics Data System (ADS)

    Outka, Duane A.

    1990-09-01

    The adsorption of hydrogen on a polycrystalline tellurium surface has been studied with temperature programmed desorption. Atomic hydrogen adsorbs on a tellurium surface and reacts to form H 2Te. Molecular hydrogen, in contrast, does not adsorb or react with tellurium at temperatures down to 80 K. When a tellurium surface which has been exposed to atomic hydrogen is heated, two desorption products are observed, H 2 and H 2Te. The H 2Te desorbs in three peaks at 130, 150, and 270 K. The H 2 desorbs in two peaks at 150 and 270 K. The desorption peaks at 270 K for both H 2 and H 2Te are unusually broad with a half-width of 80 K, and standard kinetic analysis of these peaks yields unusual desorption parameters. Overall, the adsorption of hydrogen on tellurium is similar to hydrogen adsorption on other covalent solids and differs in several respects from hydrogen adsorbed on metal surfaces.

  16. Infrared light emission from nano hot electron gas created in atomic point contacts

    NASA Astrophysics Data System (ADS)

    Malinowski, T.; Klein, H. R.; Iazykov, M.; Dumas, Ph.

    2016-06-01

    Gold atomic point contacts are prototype systems to evidence ballistic electron transport. The typical dimension of the nanojunction being smaller than the electron-phonon interaction length, even at room temperature, electrons transfer their excess energy to the lattice only far from the contact. At the contact however, favored by huge current densities, electron-electron interactions result in a nano hot electron gas acting as a source of photons. Using a home built Mechanically Controlled Break Junction, it is reported here, for the first time, that this nano hot electron gas also radiates in the infrared range (0.2 eV to 1.2 eV). Moreover, following the description introduced by Tomchuk et al. (Sov. Phys.-Solid State, 8 (1966) 2510), we show that this radiation is compatible with a black-body-like spectrum emitted from an electron gas at temperatures of several thousands of kelvins.

  17. Infrared light emission from nano hot electron gas created in atomic point contacts

    NASA Astrophysics Data System (ADS)

    Malinowski, T.; Klein, H. R.; Iazykov, M.; Dumas, Ph.

    2016-06-01

    Gold atomic point contacts are prototype systems to evidence ballistic electron transport. The typical dimension of the nanojunction being smaller than the electron-phonon interaction length, even at room temperature, electrons transfer their excess energy to the lattice only far from the contact. At the contact however, favored by huge current densities, electron-electron interactions result in a nano hot electron gas acting as a source of photons. Using a home built Mechanically Controlled Break Junction, it is reported here, for the first time, that this nano hot electron gas also radiates in the infrared range (0.2 eV to 1.2 eV). Moreover, following the description introduced by Tomchuk et al. (Sov. Phys.-Solid State, 8 (1966) 2510), we show that this radiation is compatible with a black-body–like spectrum emitted from an electron gas at temperatures of several thousands of kelvins.

  18. Ab Initio Vibrational Levels For HO2 and Vibrational Splittings for Hydrogen Atom Transfer

    NASA Technical Reports Server (NTRS)

    Barclay, V. J.; Dateo, Christopher E.; Hamilton, I. P.; Arnold, James O. (Technical Monitor)

    1994-01-01

    We calculate vibrational levels and wave functions for HO2 using the recently reported ab initio potential energy surface of Walch and Duchovic. There is intramolecular hydrogen atom transfer when the hydrogen atom tunnels through a T-shaped saddle point separating two equivalent equilibrium geometries, and correspondingly, the energy levels are split. We focus on vibrational levels and wave functions with significant splitting. The first three vibrational levels with splitting greater than 2/cm are (15 0), (0 7 1) and (0 8 0) where V(sub 2) is the O-O-H bend quantum number. We discuss the dynamics of hydrogen atom transfer; in particular, the O-O distances at which hydrogen atom transfer is most probable for these vibrational levels. The material of the proposed presentation was reviewed and the technical content will not reveal any information not already in the public domain and will not give any foreign industry or government a competitive advantage.

  19. Simulation of diffusion of hydrogen atoms in the lattice of tungsten

    NASA Astrophysics Data System (ADS)

    Degtyarenko, N. N.; Pisarev, A. A.

    2016-09-01

    Results of DFT calculations of the activation energy for diffusion and vibrational spectra of interstitial hydrogen atoms in the lattice of tungsten are presented. The temperature dependences of the diffusion coefficient are calculated and compared with experimental data.

  20. Direct observation of hydrogen atom dynamics and interactions by ultrahigh resolution neutron protein crystallography.

    PubMed

    Chen, Julian C-H; Hanson, B Leif; Fisher, S Zoë; Langan, Paul; Kovalevsky, Andrey Y

    2012-09-18

    The 1.1 Å, ultrahigh resolution neutron structure of hydrogen/deuterium (H/D) exchanged crambin is reported. Two hundred ninety-nine out of 315, or 94.9%, of the hydrogen atom positions in the protein have been experimentally derived and resolved through nuclear density maps. A number of unconventional interactions are clearly defined, including a potential O─H…π interaction between a water molecule and the aromatic ring of residue Y44, as well as a number of potential C─H…O hydrogen bonds. Hydrogen bonding networks that are ambiguous in the 0.85 Å ultrahigh resolution X-ray structure can be resolved by accurate orientation of water molecules. Furthermore, the high resolution of the reported structure has allowed for the anisotropic description of 36 deuterium atoms in the protein. The visibility of hydrogen and deuterium atoms in the nuclear density maps is discussed in relation to the resolution of the neutron data.

  1. Distribution of hot stars and hydrogen in the Large Magellanic Cloud

    NASA Technical Reports Server (NTRS)

    Page, T.; Carruthers, G. R.

    1981-01-01

    Far-UV brightness distribution data for the face of the Large Magellanic Cloud (LMC) are derived from calibrated electrographic imagery in the 1050-1600 and 1250-1600 A ranges, and far-UV fluxes for individual hot-star groupings in the LMC are compared with H-alpha measurements and with a 21-cm survey. It is found that large clouds of interstellar hydrogen contain smaller concentrations revealed by H-alpha emission and other clear regions where hot O-B stars excite no H II regions. Either (1) four of these associations lie behind the large interstellar clouds, or (2) the clouds may be very diffuse and extended in the line of sight. Six other peaks in far-UV flux not previously cataloged are also indicated.

  2. Global Dynamics of Hot Atomic Oxygen in Mars' Upper Atmosphere and Comparison with Recent Observation

    NASA Astrophysics Data System (ADS)

    Lee, Y.; Combi, M. R.; Tenishev, V.; Bougher, S. W.

    2012-12-01

    The production of energetic particles in Mars's upper thermosphere and exosphere results in the formation of hot atom coronae. Dissociative recombination (DR) of O2+ ion is the dominant source of the production of hot atomic oxygen and the most important reaction for the exosphere on Mars, which occurs mostly deep in the dayside thermosphere of Mars. In this investigation, we have carried out the study of the global dynamics of energetic particles in Mars' upper atmosphere using our newly developed self-consistent Monte-Carlo model. The calculated total global escapes of hot oxygen are presented for different solar activities (solar maximum and minimum) and Martian seasons (aphelion, equinox, and perihelion). To describe self-consistently the exosphere and the upper thermosphere, a combination of our 3D Direct Simulation Monte Carlo (DSMC) model [Valeille, A., Combi, M., Bougher, S., Tenishev, V., Nagy, A., 2009. J. Geophys. Res. 114, E11006. doi:10.1029/2009JE003389] and the 3D Mars Thermosphere General Circulation Model (MTGCM) [Bougher, S.W., Bell, J.M., Murphy, J.R., Lopez-Valverde, M.A., Withers, P.G., 2006. Geophys. Res. Lett. 32, doi: 10.1029/2005GL024059. L02203] is used. Profiles of density and temperature, atmospheric loss rates, and return fluxes are studied using the model for the cases considered. Progress in updating the model physics is also described. Along with comparisons of our DSMC model outputs with those from other recent exosphere model studies, we present a comparison of our model results with the derived neutral oxygen density from atomic oxygen emission at 1304Å that was detected by Alice instrument on board European Space Agency's Rosetta spacecraft [Feldman, P., Steffl, A., Parker, J, A'Hearn, M., Bertaux, J., Stern, S., Weaver, H., Slater, D., Versteeg, M., Throop, H., Cunningham, N., Feaga, L., 2011. Icarus. 214, 2, 394-399, doi:10.1016/j.icarus.2011.06.013].

  3. Quantum beats in hydrogen and antihydrogen atoms in an external electric field.

    PubMed

    Labzowsky, L; Sharipov, V

    2004-04-01

    An effect of quantum beats that arises due to the coherent excitation of 2s and 2p states of hydrogen and antihydrogen atoms in an external electric field is described. It is shown that the quantum beat signal contains terms linear in electric field, i.e., is of opposite sign for the hydrogen and antihydrogen atoms. The conditions for the observation of this effect are discussed.

  4. Erwin Schrödinger, Wave Mechanics, and the Hydrogen Atom

    NASA Astrophysics Data System (ADS)

    de Lange, Owen L.

    1996-06-01

    A brief account is given of some of the main events in Erwin Schrödinger's life, the circumstances leading to his discovery of wave mechanics in 1925-1926, and the application of this mechanics to a model of the hydrogen atom. Two methods of solving this model are outlined, namely, Sommerfeld's polynomial method and Schrödinger's shift operator method. The relation to Pauli's analysis of the quantum-mechanical hydrogen atom is also discussed.

  5. Evidence of wave-particle duality for single fast hydrogen atoms.

    PubMed

    Schmidt, H T; Fischer, D; Berenyi, Z; Cocke, C L; Gudmundsson, M; Haag, N; Johansson, H A B; Källberg, A; Levin, S B; Reinhed, P; Sassenberg, U; Schuch, R; Simonsson, A; Støchkel, K; Cederquist, H

    2008-08-22

    We report the direct observation of interference effects in a Young's double-slit experiment where the interfering waves are two spatially separated components of the de Broglie wave of single 1.3 MeV hydrogen atoms formed close to either target nucleus in H++H2 electron-transfer collisions. Quantum interference strongly influences the results even though the hydrogen atoms have a de Broglie wavelength, lambda_{dB}, as small as 25 fm.

  6. Enhancement of electrical conductivity and electrochemical activity of hydrogenated amorphous carbon by incorporating boron atoms

    NASA Astrophysics Data System (ADS)

    Naragino, Hiroshi; Yoshinaga, Kohsuke; Nakahara, Akira; Tanaka, Sakuya; Honda, Kensuke

    2013-06-01

    Conductive boron-doped hydrogenated amorphous carbon (B-DLC) thin films were successfully synthesized with RF plasma-enhanced CVD method. By incorporating boron atoms in amorphous carbon, conduction types were changed from n- to p-type, and volume resistivity was decreased from 30.4 (non-doped) to 6.36 × 10-2 Ω cm (B/C = 2.500 atom%). B-DLC film with sp2/(sp2 + sp3) carbons of 75 atom% exhibited high resistance to electrochemically-induced corrosion in strong acid solution. Furthermore, it was clarified that boron atoms in DLC could enhance kinetics of hydrogen evolution during water electrolysis at B-DLC surface. B-DLC is, therefore, a promising electrode material for hydrogen production by increasing the concentration of boron atoms in B-DLC and enhancing the reactivity of H2 evolution.

  7. Atomic-Scale Mechanism for Hydrogenation of o-Cresol on Pt Catalysis

    NASA Astrophysics Data System (ADS)

    Li, Yaping; Liu, Zhimin; Xue, Wenhua; Crossley, Steven; Jentoft, Friederike; Wang, Sanwu

    Biofuels derived from lignocellulosic biomass have received significant attention lately due to increasing environmental concerns. With first-principles density-functional theory and ab initio molecular dynamic simulations, we investigated the atomic-scale mechanism of o-cresol hydrogenation on the Pt(111) surface. The formation of 2-methyl-cyclohexanone (the intermediate product) was found to involve two steps. The first step is the dehydrogenation, that is, the H atom in the hydroxyl group moves to the Pt surface. The second step is the hydrogenation, that is, the H atoms on Pt react with the carbon atoms in the aromatic ring. The first step involves a smaller barrier, suggesting that dehydrogenation occurs first, followed by hydrogenation of the ring. In particular, tautomerization is found to occur via a two-step process over the catalyst. On the other hand, 2-methyl-cyclohexanol (the final product) is produced through two paths. One is direct hydrogenation of the aromatic ring. Another pathway includes partial hydrogenation of the ring, dehydrogenation of -OH group, finally hydrogenation of remaining C atoms and the O atom. Our theoretical results agree well with the experimental observations. Supported by DOE (DE-SC0004600). This research used the supercomputer resources of NERSC, XSEDE, TACC.

  8. Fluorescence (TALIF) measurement of atomic hydrogen concentration in a coplanar surface dielectric barrier discharge

    NASA Astrophysics Data System (ADS)

    Mrkvičková, M.; Ráheľ, J.; Dvořák, P.; Trunec, D.; Morávek, T.

    2016-10-01

    Spatially and temporally resolved measurements of atomic hydrogen concentration above the dielectric of coplanar barrier discharge are presented for atmospheric pressure in 2.2% H2/Ar. The measurements were carried out in the afterglow phase by means of two-photon absorption laser-induced fluorescence (TALIF). The difficulties of employing the TALIF technique in close proximity to the dielectric surface wall were successfully addressed by taking measurements on a suitable convexly curved dielectric barrier, and by proper mathematical treatment of parasitic signals from laser-surface interactions. It was found that the maximum atomic hydrogen concentration is situated closest to the dielectric wall from which it gradually decays. The maximum absolute concentration was more than 1022 m-3. In the afterglow phase, the concentration of atomic hydrogen above the dielectric surface stays constant for a considerable time (10 μs-1 ms), with longer times for areas situated farther from the dielectric surface. The existence of such a temporal plateau was explained by the presented 1D model: the recombination losses of atomic hydrogen farther from the dielectric surface are compensated by the diffusion of atomic hydrogen from regions close to the dielectric surface. The fact that a temporal plateau exists even closest to the dielectric surface suggests that the dielectric surface acts as a source of atomic hydrogen in the afterglow phase.

  9. Generating Molecular Rovibrational Coherence by Two-Photon Femtosecond Photoassociation of Thermally Hot Atoms

    SciTech Connect

    Rybak, Leonid; Levin, Liat; Amitay, Zohar; Amaran, Saieswari; Kosloff, Ronnie; Tomza, Michal; Moszynski, Robert; Koch, Christiane P.

    2011-12-30

    The formation of diatomic molecules with rotational and vibrational coherence is demonstrated experimentally in free-to-bound two-photon femtosecond photoassociation of hot atoms. In a thermal gas at a temperature of 1000 K, pairs of magnesium atoms, colliding in their electronic ground state, are excited into coherent superpositions of bound rovibrational levels in an electronically excited state. The rovibrational coherence is probed by a time-delayed third photon, resulting in quantum beats in the UV fluorescence. A comprehensive theoretical model based on ab initio calculations rationalizes the generation of coherence by Franck-Condon filtering of collision energies and partial waves, quantifying it in terms of an increase in quantum purity of the thermal ensemble. Our results open the way to coherent control of a binary reaction.

  10. Generating Molecular Rovibrational Coherence by Two-Photon Femtosecond Photoassociation of Thermally Hot Atoms

    NASA Astrophysics Data System (ADS)

    Rybak, Leonid; Amaran, Saieswari; Levin, Liat; Tomza, Michał; Moszynski, Robert; Kosloff, Ronnie; Koch, Christiane P.; Amitay, Zohar

    2011-12-01

    The formation of diatomic molecules with rotational and vibrational coherence is demonstrated experimentally in free-to-bound two-photon femtosecond photoassociation of hot atoms. In a thermal gas at a temperature of 1000 K, pairs of magnesium atoms, colliding in their electronic ground state, are excited into coherent superpositions of bound rovibrational levels in an electronically excited state. The rovibrational coherence is probed by a time-delayed third photon, resulting in quantum beats in the UV fluorescence. A comprehensive theoretical model based on ab initio calculations rationalizes the generation of coherence by Franck-Condon filtering of collision energies and partial waves, quantifying it in terms of an increase in quantum purity of the thermal ensemble. Our results open the way to coherent control of a binary reaction.

  11. The simplicity of perfect atoms: Degeneracies in supersymmetric hydrogen

    DOE PAGES

    Rube, Tomas; Wacker, Jay G.

    2011-06-07

    In this study, supersymmetric QED hydrogen-like bound states are remarkably similar to nonsupersymmetric hydrogen, including an accidental degeneracy of the fine structure and is broken by the Lamb shift. This article classifies the states, calculates the leading order spectrum, and illustrates the results in several limits. The relation to other nonrelativistic bound states is explored.

  12. The simplicity of perfect atoms: Degeneracies in supersymmetric hydrogen

    SciTech Connect

    Rube, Tomas; Wacker, Jay G.

    2011-06-15

    Supersymmetric QED hydrogen-like bound states are remarkably similar to nonsupersymmetric hydrogen, including an accidental degeneracy of the fine structure and is broken by the Lamb shift. This article classifies the states, calculates the leading order spectrum, and illustrates the results in several limits. The relation to other nonrelativistic bound states is explored.

  13. Femtosecond two-photon photoassociation of hot magnesium atoms: A quantum dynamical study using thermal random phase wavefunctions

    SciTech Connect

    Amaran, Saieswari; Kosloff, Ronnie; Tomza, Michał; Skomorowski, Wojciech; Pawłowski, Filip; Moszynski, Robert; Rybak, Leonid; Levin, Liat; Amitay, Zohar; Berglund, J. Martin; Reich, Daniel M.; Koch, Christiane P.

    2013-10-28

    Two-photon photoassociation of hot magnesium atoms by femtosecond laser pulses, creating electronically excited magnesium dimer molecules, is studied from first principles, combining ab initio quantum chemistry and molecular quantum dynamics. This theoretical framework allows for rationalizing the generation of molecular rovibrational coherence from thermally hot atoms [L. Rybak, S. Amaran, L. Levin, M. Tomza, R. Moszynski, R. Kosloff, C. P. Koch, and Z. Amitay, Phys. Rev. Lett. 107, 273001 (2011)]. Random phase thermal wavefunctions are employed to model the thermal ensemble of hot colliding atoms. Comparing two different choices of basis functions, random phase wavefunctions built from eigenstates are found to have the fastest convergence for the photoassociation yield. The interaction of the colliding atoms with a femtosecond laser pulse is modeled non-perturbatively to account for strong-field effects.

  14. ATOMIC AND MOLECULAR PHYSICS: Multiphoton ionization of the hydrogen atom exposed to circularly or linearly polarized laser pulses

    NASA Astrophysics Data System (ADS)

    Wang, Pei-Jie; He, Feng

    2009-12-01

    This paper studies the multiphoton ionization of the hydrogen atom exposed to the linearly or circularly polarized laser pulses by solving the time-dependent Schrödinger equation. It finds that the ratio of the ionization probabilities by linearly and circularly polarized laser pulses varies with the numbers of absorbing photons. With the same laser intensity, the circularly polarized laser pulse favors to ionize the atom with more ease than the linearly polarized laser pulse if only two or three photons are necessary to be absorbed. For the higher order multiphoton ionization, the linearly polarized laser pulse has the advantage over circularly polarized laser pulse to ionize the atom.

  15. Hydrogen atoms can be located accurately and precisely by x-ray crystallography

    PubMed Central

    Woińska, Magdalena; Grabowsky, Simon; Dominiak, Paulina M.; Woźniak, Krzysztof; Jayatilaka, Dylan

    2016-01-01

    Precise and accurate structural information on hydrogen atoms is crucial to the study of energies of interactions important for crystal engineering, materials science, medicine, and pharmacy, and to the estimation of physical and chemical properties in solids. However, hydrogen atoms only scatter x-radiation weakly, so x-rays have not been used routinely to locate them accurately. Textbooks and teaching classes still emphasize that hydrogen atoms cannot be located with x-rays close to heavy elements; instead, neutron diffraction is needed. We show that, contrary to widespread expectation, hydrogen atoms can be located very accurately using x-ray diffraction, yielding bond lengths involving hydrogen atoms (A–H) that are in agreement with results from neutron diffraction mostly within a single standard deviation. The precision of the determination is also comparable between x-ray and neutron diffraction results. This has been achieved at resolutions as low as 0.8 Å using Hirshfeld atom refinement (HAR). We have applied HAR to 81 crystal structures of organic molecules and compared the A–H bond lengths with those from neutron measurements for A–H bonds sorted into bonds of the same class. We further show in a selection of inorganic compounds that hydrogen atoms can be located in bridging positions and close to heavy transition metals accurately and precisely. We anticipate that, in the future, conventional x-radiation sources at in-house diffractometers can be used routinely for locating hydrogen atoms in small molecules accurately instead of large-scale facilities such as spallation sources or nuclear reactors. PMID:27386545

  16. Hydrogen atoms can be located accurately and precisely by x-ray crystallography.

    PubMed

    Woińska, Magdalena; Grabowsky, Simon; Dominiak, Paulina M; Woźniak, Krzysztof; Jayatilaka, Dylan

    2016-05-01

    Precise and accurate structural information on hydrogen atoms is crucial to the study of energies of interactions important for crystal engineering, materials science, medicine, and pharmacy, and to the estimation of physical and chemical properties in solids. However, hydrogen atoms only scatter x-radiation weakly, so x-rays have not been used routinely to locate them accurately. Textbooks and teaching classes still emphasize that hydrogen atoms cannot be located with x-rays close to heavy elements; instead, neutron diffraction is needed. We show that, contrary to widespread expectation, hydrogen atoms can be located very accurately using x-ray diffraction, yielding bond lengths involving hydrogen atoms (A-H) that are in agreement with results from neutron diffraction mostly within a single standard deviation. The precision of the determination is also comparable between x-ray and neutron diffraction results. This has been achieved at resolutions as low as 0.8 Å using Hirshfeld atom refinement (HAR). We have applied HAR to 81 crystal structures of organic molecules and compared the A-H bond lengths with those from neutron measurements for A-H bonds sorted into bonds of the same class. We further show in a selection of inorganic compounds that hydrogen atoms can be located in bridging positions and close to heavy transition metals accurately and precisely. We anticipate that, in the future, conventional x-radiation sources at in-house diffractometers can be used routinely for locating hydrogen atoms in small molecules accurately instead of large-scale facilities such as spallation sources or nuclear reactors. PMID:27386545

  17. Hydrogen atoms can be located accurately and precisely by x-ray crystallography.

    PubMed

    Woińska, Magdalena; Grabowsky, Simon; Dominiak, Paulina M; Woźniak, Krzysztof; Jayatilaka, Dylan

    2016-05-01

    Precise and accurate structural information on hydrogen atoms is crucial to the study of energies of interactions important for crystal engineering, materials science, medicine, and pharmacy, and to the estimation of physical and chemical properties in solids. However, hydrogen atoms only scatter x-radiation weakly, so x-rays have not been used routinely to locate them accurately. Textbooks and teaching classes still emphasize that hydrogen atoms cannot be located with x-rays close to heavy elements; instead, neutron diffraction is needed. We show that, contrary to widespread expectation, hydrogen atoms can be located very accurately using x-ray diffraction, yielding bond lengths involving hydrogen atoms (A-H) that are in agreement with results from neutron diffraction mostly within a single standard deviation. The precision of the determination is also comparable between x-ray and neutron diffraction results. This has been achieved at resolutions as low as 0.8 Å using Hirshfeld atom refinement (HAR). We have applied HAR to 81 crystal structures of organic molecules and compared the A-H bond lengths with those from neutron measurements for A-H bonds sorted into bonds of the same class. We further show in a selection of inorganic compounds that hydrogen atoms can be located in bridging positions and close to heavy transition metals accurately and precisely. We anticipate that, in the future, conventional x-radiation sources at in-house diffractometers can be used routinely for locating hydrogen atoms in small molecules accurately instead of large-scale facilities such as spallation sources or nuclear reactors.

  18. A spectroscopic study of hydrogen atom and molecule collision. Final report

    SciTech Connect

    Kielkopf, John F.

    2002-07-01

    The fundamental processes which occur in low-energy collisions of excited states of the hydrogen atom with other neutral atoms, protons, and electrons in dense plasmas were investigated in this project. Theoretical and experimental results for the Lyman and Balmer series are described here, including references to recent publications resulting from this project.

  19. In situ study of erosion and deposition of amorphous hydrogenated carbon films by exposure to a hydrogen atom beam

    SciTech Connect

    Markelj, Sabina; Pelicon, Primoz; Cadez, Iztok; Schwarz-Selinger, Thomas; Jacob, Wolfgang

    2012-07-15

    This paper reports on the first dual-beam experiment employing a hydrogen atom beam for sample exposure and an ion beam for analysis, enabling in situ and real-time studies of hydrogen atom interaction with materials. The erosion of an amorphous hydrogenated carbon (a-C:H) layer by deuterium atoms at 580 K sample temperature was studied and the uptake of deuterium during the erosion process was measured in real time. The deuterium areal density increased at the beginning to 7.3 Multiplication-Sign 10{sup 15} D cm{sup -2}, but then stabilized at a constant value of 5.5 Multiplication-Sign 10{sup 15} D cm{sup -2}. Formation of a polymer-like deposit on an a-C:H layer held at room temperature and subjected to the deuterium atom beam was observed and also studied in situ. For both erosion and deposition studies an a-{sup 13}C:H layer on top of an Si substrate was used as a sample, making the experiments isotopically fully specified and thereby differentiating the deposited from the original layer and the interacting D atoms from H atoms present in the layer and in the residual vacuum. From the deposition study it was shown that carbon in the deposited layer originates from carbon-carrying species in the background vacuum that interact with hydrogen atoms. The areal density of the carbon at the surface was determined from the energy shift of the Si edge in the Rutherford backscattering spectrum. The cross section for {sup 7}Li on D at 4.3 MeV Li ion energy and at a recoil angle of 30 Degree-Sign was also determined to be (236 {+-} 16) Multiplication-Sign 10{sup -27} cm{sup 2}/sr. This is a factor of 3 {+-} 0.2 times higher than the Rutherford elastic cross section.

  20. Trapping of hydrogen atoms inside small beryllium clusters and their ions

    NASA Astrophysics Data System (ADS)

    Naumkin, F. Y.; Wales, D. J.

    2016-08-01

    Structure, stability and electronic properties are evaluated computationally for small Ben (n = 5-9) cluster cages accommodating atomic H inside and forming core-shell species. These parameters are predicted to vary significantly upon insertion of H, for ionic derivatives, and with the system size. In particular, the energy barrier for H-atom exit from the cage changes significantly for ions compared to the neutral counterparts. The corresponding effects predicted for cage assemblies suggest the possibility of efficient charge-control of hydrogen release. This, together with a high capacity for storing hydrogen in extended such assemblies might indicate a possible way towards feasible hydrogen-storage solutions.

  1. Hydrogen atom scrambling in ion-molecule reactions of methane and ethylene.

    NASA Technical Reports Server (NTRS)

    Huntress, W. T., Jr.

    1972-01-01

    The extent of hydrogen atom exchange in the reaction, CH3(+) + CH4 yields C2H5(+) + H2, is determined by examining the product distribution for the reactions CH3(+) + CD4 and CD3(+) + CH4 as a function of relative kinetic energy from thermal energies to 10 eV. It is found that the reaction of CH4(+) with the parent neutral proceeds both via proton transfer and hydrogen abstraction accompanied by approximately 10% hydrogen atom exchange during the reaction.

  2. Kinetic study on hot-wire-assisted atomic layer deposition of nickel thin films

    SciTech Connect

    Yuan, Guangjie Shimizu, Hideharu; Momose, Takeshi; Shimogaki, Yukihiro

    2014-01-15

    High-purity Ni films were deposited using hot-wire-assisted atomic layer deposition (HW-ALD) at deposition temperatures of 175, 250, and 350 °C. Negligible amount of nitrogen or carbon contamination was detected, even though the authors used NH{sub 2} radical as the reducing agent and nickelocene as the precursor. NH{sub 2} radicals were generated by the thermal decomposition of NH{sub 3} with the assist of HW and used to reduce the adsorbed metal growth precursors. To understand and improve the deposition process, the kinetics of HW-ALD were analyzed using a Langmuir-type model. Unlike remote-plasma-enhanced atomic layer deposition, HW-ALD does not lead to plasma-induced damage. This is a significant advantage, because the authors can supply sufficient NH{sub 2} radicals to deposit high-purity metallic films by adjusting the distance between the hot wire and the substrate. NH{sub 2} radicals have a short lifetime, and it was important to use a short distance between the radical generation site and substrate. Furthermore, the impurity content of the nickel films was independent of the deposition temperature, which is evidence of the temperature-independent nature of the NH{sub 2} radical flux and the reactivity of the NH{sub 2} radicals.

  3. Identification of titanium-hydrogen complexes with up to four hydrogen atoms in silicon

    SciTech Connect

    Scheffler, L.; Kolkovsky, Vl. Weber, J.

    2015-02-28

    Using high-resolution Laplace deep level transient spectroscopy studies, several TiH-related complexes (E40′, E170, E170′, and E260) were observed in wet-chemically etched and H-plasma treated n-type Si. We assign E40′ and E170 to two different configurations of Ti with one H atom. Both of them are shown to behave as single donor states with an activation enthalpy of E{sub C} − 0.07 eV (E40′) and E{sub C} − 0.34 eV (E170) in the upper half of Si. E170′ with an activation energy of E{sub C} − 0.37 eV is correlated with the donor state of the Ti{sub i}H{sub 2} defect, whereas E260 is attributed to the donor state of Ti{sub i}H{sub 3}. Besides the TiH defects, the presence of electrically inactive TiH{sub 4} is reported. No titanium-hydrogen-related levels were observed in p-type Si.

  4. Studies of mixing and combustion in hypervelocity flows with hot hydrogen injection

    NASA Astrophysics Data System (ADS)

    Belanger, Jacques Jean

    1993-01-01

    The ability to build an air-breathing single-stage-to-orbit propulsion system requires the examination of key elements such as turbulent mixing rates, especially at the 'zero shear' fuel-air mixing condition, and combustion efficiency. The required data can only be obtained in experiments which simultaneously match the flight total pressure and total enthalpy as well as the fuel conditions. GALCIT, with its new free piston shock tunnel T5, has the capability to do some of these combustion experiments. But prior to these tests, it was felt that there was a need to simulate the gas dynamical processes in the free piston shock tunnel and also in a new combustion driven shock tunnel built for these experiments so that both systems could be used as efficiently as possible. The numerical code helped explain the piston motion in the free piston shock tunnel. The code was also very useful for the design of the combustion driven shock tunnel. Because hydrogen has to be injected into the combustion chamber of the propulsion system after being used as a cooling fluid, a combustion driven shock tunnel was built to reproduce this 'hot' hydrogen at up to 1500 K for the experiments. To reduce the complexity of the problem, a very basic configuration for the hydrogen injection system was tested. This was first done with an injection system mounted flush with the surface of a flat plate in the test section of T5. Different test conditions as well as Mach 2 and 5 nozzle injectors at angles of 15 or 30 degrees were tested to determine criteria for significant combustion. Lower limits in pressure and enthalpy were found where hydrogen combustion becomes very limited using this 'hot' hydrogen fuel. The second set of experiments still used an injection system mounted slush with the surface but involved a small combustor model previously tested in the hypervelocity HYPULSE facility. Low pressure experiments were performed to reproduce some of the HYPULSE tests and excellent agreement was

  5. The signature of hot hydrogen in the atmosphere of the extrasolar planet HD 209458b.

    PubMed

    Ballester, Gilda E; Sing, David K; Herbert, Floyd

    2007-02-01

    About ten per cent of the known extrasolar planets are gas giants that orbit very close to their parent stars. The atmospheres of these 'hot Jupiters' are heated by the immense stellar irradiation. In the case of the planet HD 209458b, this energy deposition results in a hydrodynamic state in the upper atmosphere, allowing for sizeable expansion and escape of neutral hydrogen gas. HD 209458b was the first extrasolar planet discovered that transits in front of its parent star. The size of the planet can be measured using the total optical obscuration of the stellar disk during an observed transit, and the structure and composition of the planetary atmosphere can be studied using additional planetary absorption signatures in the stellar spectrum. Here we report the detection of absorption by hot hydrogen in the atmosphere of HD 209458b. Previously, the lower atmosphere and the full extended upper atmosphere of HD 209458b have been observed, whereas here we probe a layer where the escaping gas forms in the upper atmosphere of HD 209458b.

  6. The signature of hot hydrogen in the atmosphere of the extrasolar planet HD 209458b.

    PubMed

    Ballester, Gilda E; Sing, David K; Herbert, Floyd

    2007-02-01

    About ten per cent of the known extrasolar planets are gas giants that orbit very close to their parent stars. The atmospheres of these 'hot Jupiters' are heated by the immense stellar irradiation. In the case of the planet HD 209458b, this energy deposition results in a hydrodynamic state in the upper atmosphere, allowing for sizeable expansion and escape of neutral hydrogen gas. HD 209458b was the first extrasolar planet discovered that transits in front of its parent star. The size of the planet can be measured using the total optical obscuration of the stellar disk during an observed transit, and the structure and composition of the planetary atmosphere can be studied using additional planetary absorption signatures in the stellar spectrum. Here we report the detection of absorption by hot hydrogen in the atmosphere of HD 209458b. Previously, the lower atmosphere and the full extended upper atmosphere of HD 209458b have been observed, whereas here we probe a layer where the escaping gas forms in the upper atmosphere of HD 209458b. PMID:17268463

  7. Optical radiation and ionization of hydrogen atoms in heterogeneous exothermal reactions proceeding in an electric field

    NASA Astrophysics Data System (ADS)

    Blashenkov, N. M.; Lavrent'ev, G. Ya.

    2009-09-01

    Optical radiation related to the Balmer series (Hα, Hβ, Hγ) of hydrogen atoms is discovered when studying the isothermal reaction of trimeric acetone peroxide decomposition on the surface of oxidized tungsten in a static electric field with a strength of up to 4 × 106 V/cm at T = 300 K. The distance from the surface over which desorbing excited hydrogen atoms radiate is determined from the Stark splitting of the lines. Electronically excited atoms remaining on the surface ionize according to the surface ionization mechanism.

  8. 2s Hyperfine splitting in light hydrogen-like atoms: Theory and experiment

    SciTech Connect

    Karshenboim, S. G. Kolachevsky, N. N.; Ivanov, V. G.; Fischer, M.; Fendel, P.; Haensch, T. W.

    2006-03-15

    Since the combination D{sub 21} = 8f{sub HFS}(2s)-f{sub HFS}(1s) of hyperfine intervals in hydrogen and light two-body hydrogen-like atomic systems weakly depends on the nuclear structure, comparison between theory and experiment can be sensitive to high order QED corrections. New theoretical and experimental results are presented. Calculations have been performed for the hydrogen and deuterium atoms and for the helium-3 ion. Experiments on the 2s hyperfine splitting (responsible for the dominant contribution to the error in D{sub 21}) have been conducted for hydrogen and deuterium. The theory and experiment are in good agreement, and their accuracy is comparable to that attained in verifying the QED theory of the hyperfine splitting in leptonic atoms (muonium and positronium)

  9. Hydrogen trapped in Ben cluster cages: The atomic encapsulation option

    NASA Astrophysics Data System (ADS)

    Naumkin, Fedor Y.; Wales, David J.

    2012-08-01

    Core-shell (kH)@Ben (k = 1-3, n = 6-11) systems are studied computationally. The smallest system with endohedral hydrogen is H@Be6 with a central H anion, thermodynamically stable to dissociation into H + Be6. Larger structures are constructed by merging a few such units and have reduced stability. Potential energy barriers to hydrogen exit from the cage assemblies are estimated. Face- and edge-sharing combinations of the structural units are considered. The extrapolated upper bound for the potential 'nanofoam' material storage capacity is 10 weight-% of hydrogen. The changes in shape and electronic properties of the Ben cages upon insertion of hydrogen are also analyzed.

  10. An improved atomic hydrogen frequency and time standard

    NASA Technical Reports Server (NTRS)

    Mc Gunigal, T. E.; Peters, H. E.

    1969-01-01

    Use of a large bulb, long-multipole magnet, automatic tuner and aluminum cavity provides an improved hydrogen maser which is accurate over long periods of time and suitable for tracking station environments.

  11. Basic study on hot-wire flow meter in forced flow of liquid hydrogen

    NASA Astrophysics Data System (ADS)

    Oura, Y.; Shirai, Y.; Shiotsu, M.; Murakami, K.; Tatsumoto, H.; Naruo, Y.; Nonaka, S.; Kobayashi, H.; Inatani, Y.; Narita, N.

    2014-01-01

    Liquid hydrogen (LH2) is a key issue in a carbon-free energy infrastructure at the energy storage and transportation stage. The typical features of LH2 are low viscosity, large latent heat and small density, compared with other general liquids. It is necessary to measure a mass flow of liquid hydrogen with a simple and compact method, especially in a two phase separate flow condition. We have proposed applying a hot-wire type flow meter, which is usually used a for gas flow meter, to LH2 flow due to the quite low viscosity and density. A test model of a compact LH2 hot-wire flow meter to measure local flow velocities near and around an inside perimeter of a horizontal tube by resistance thermometry was designed and made. The model flow meter consists of two thin heater wires made of manganin fixed in a 10 mm-diameter and 40 mm-length tube flow path made of GFRP. Each rigid heater wire was set twisted by 90 degrees from the inlet to the outlet along the inner wall. In other words, the wires were aslant with regard to the LH2 stream line. The heated wire was cooled by flowing LH2, and the flow velocity was obtained by means of the difference of the cooling characteristic in response to the flow velocity. In this report, we show results on the basic experiments with the model LH2 hot-wire flow meter. First, the heat transfer characteristics of the two heater wires for several LH2 flow velocities were measured. Second, the heating current was controlled to keep the wire temperature constant for various flow velocities. The relations between the flow velocity and the heating current were measured. The feasibility of the proposed model was confirmed.

  12. Electron-hole pair excitation determines the mechanism of hydrogen atom adsorption.

    PubMed

    Bünermann, Oliver; Jiang, Hongyan; Dorenkamp, Yvonne; Kandratsenka, Alexander; Janke, Svenja M; Auerbach, Daniel J; Wodtke, Alec M

    2015-12-11

    How much translational energy atoms and molecules lose in collisions at surfaces determines whether they adsorb or scatter. The fact that hydrogen (H) atoms stick to metal surfaces poses a basic question. Momentum and energy conservation demands that the light H atom cannot efficiently transfer its energy to the heavier atoms of the solid in a binary collision. How then do H atoms efficiently stick to metal surfaces? We show through experiments that H-atom collisions at an insulating surface (an adsorbed xenon layer on a gold single-crystal surface) are indeed nearly elastic, following the predictions of energy and momentum conservation. In contrast, H-atom collisions with the bare gold surface exhibit a large loss of translational energy that can be reproduced by an atomic-level simulation describing electron-hole pair excitation. PMID:26612832

  13. Adsorption of atomic hydrogen on ZnO(1010): STM study.

    PubMed

    Yin, Xiu-Li; Birkner, Alexander; Hänel, Kathrin; Löber, Thomas; Köhler, Ulrich; Wöll, Christof

    2006-04-01

    The adsorption of atomic hydrogen on a single crystal ZnO(1010) surface has been studied by scanning tunneling microscopy (STM) under ultrahigh vacuum conditions at room temperature and at elevated temperatures. High resolution STM images indicate that a well-ordered (1x1) H adlayer is formed on the ZnO(1010) surface. The STM data strongly indicate that the hydrogen adsorbs on top of the oxygen atoms forming hydroxyl species. Scanning tunneling spectroscopy (STS) studies reveal a H atom induced metallization at room temperature. In contrast to the clean surface for the hydrogen-covered surface distinct defects structures consisting of missing O and Zn atoms could be identified.

  14. Reconstructing a Hot and High Eocene Sierra Nevada Using Oxygen and Hydrogen Isotopes in Kaolinite

    NASA Astrophysics Data System (ADS)

    Mix, H.; Ibarra, D. E.; Mulch, A.; Graham, S. A.; Chamberlain, C. P.

    2014-12-01

    Despite the broad interest in determining the topographic and climatic histories of mountain ranges, the evolution of California's Sierra Nevada remains actively debated. Prior stable isotope-based studies of Sierra Nevada have relied exclusively on hydrogen isotopes in kaolinite, hydrated volcanic glass and leaf n-alkanes. Additional constraints from the oxygen isotope composition of phyllosilicates increase the robustness of findings from a single isotope system and allow for the reconstruction of paleotemperatures. Here, we reconstruct the temperature and elevation of the Early Eocene Sierra Nevada using the oxygen isotope composition of kaolinitized granite clasts from the ancestral Yuba and American Rivers. We evaluate the possible contributions of hydrogen isotope exchange by direct comparison with more robust oxygen isotope measurements. Next, we utilize differences in the hydrogen and oxygen isotope fractionation in kaolinite to constrain paleotemperature. Oxygen isotope geochemistry of in-situ kaolinites indicates upstream (eastward) depletion of 18O in the northern Sierra Nevada. δ18O values ranging from 11.4 - 14.4 ‰ at the easternmost localities correspond to paleoelevations as high as 2400 m when simulating the orographic precipitation of moisture from a Pacific source using Eocene boundary conditions. This finding is consistent with stable isotope studies of the northern Sierra, but oxygen isotope based paleoelevation estimates are systematically ~500 - 1000 m higher than those from hydrogen-based estimates from the same samples. Kaolinite geothermometry from 16 samples measured in duplicate or triplicate produce an average Early Eocene temperature of 24.2 ± 2.0 °C (1s). This kaolinite temperature reconstruction is in agreement with paleofloral and geochemical constraints and general circulation model simulations from Eocene California. Our results confirm prior hydrogen isotope-based paleoelevations and further substantiate the existence of a

  15. Atomically isolated nickel species anchored on graphitized carbon for efficient hydrogen evolution electrocatalysis.

    PubMed

    Fan, Lili; Liu, Peng Fei; Yan, Xuecheng; Gu, Lin; Yang, Zhen Zhong; Yang, Hua Gui; Qiu, Shilun; Yao, Xiangdong

    2016-01-01

    Hydrogen production through electrochemical process is at the heart of key renewable energy technologies including water splitting and hydrogen fuel cells. Despite tremendous efforts, exploring cheap, efficient and durable electrocatalysts for hydrogen evolution still remains as a great challenge. Here we synthesize a nickel-carbon-based catalyst, from carbonization of metal-organic frameworks, to replace currently best-known platinum-based materials for electrocatalytic hydrogen evolution. This nickel-carbon-based catalyst can be activated to obtain isolated nickel atoms on the graphitic carbon support when applying electrochemical potential, exhibiting highly efficient hydrogen evolution performance with high exchange current density of 1.2 mA cm(-2) and impressive durability. This work may enable new opportunities for designing and tuning properties of electrocatalysts at atomic scale for large-scale water electrolysis. PMID:26861684

  16. Atomically isolated nickel species anchored on graphitized carbon for efficient hydrogen evolution electrocatalysis

    PubMed Central

    Fan, Lili; Liu, Peng Fei; Yan, Xuecheng; Gu, Lin; Yang, Zhen Zhong; Yang, Hua Gui; Qiu, Shilun; Yao, Xiangdong

    2016-01-01

    Hydrogen production through electrochemical process is at the heart of key renewable energy technologies including water splitting and hydrogen fuel cells. Despite tremendous efforts, exploring cheap, efficient and durable electrocatalysts for hydrogen evolution still remains as a great challenge. Here we synthesize a nickel–carbon-based catalyst, from carbonization of metal-organic frameworks, to replace currently best-known platinum-based materials for electrocatalytic hydrogen evolution. This nickel-carbon-based catalyst can be activated to obtain isolated nickel atoms on the graphitic carbon support when applying electrochemical potential, exhibiting highly efficient hydrogen evolution performance with high exchange current density of 1.2 mA cm−2 and impressive durability. This work may enable new opportunities for designing and tuning properties of electrocatalysts at atomic scale for large-scale water electrolysis. PMID:26861684

  17. Symmetry in chemistry from the hydrogen atom to proteins

    PubMed Central

    Kellman, Michael E.

    1996-01-01

    The last 2 decades have seen discoveries in highly excited states of atoms and molecules of phenomena that are qualitatively different from the “planetary” model of the atom, and the near-rigid model of molecules, characteristic of these systems in their low-energy states. A unified view is emerging in terms of approximate dynamical symmetry principles. Highly excited states of two-electron atoms display “molecular” behavior of a nonrigid linear structure undergoing collective rotation and vibration. Highly excited states of molecules described in the “standard molecular model” display normal mode couplings, which induce bifurcations on the route to molecular chaos. New approaches such as rigid–nonrigid correlation, vibrons, and quantum groups suggest a unified view of collective electronic motion in atoms and nuclear motion in molecules. PMID:8962040

  18. Evidence of a Liquid-Liquid Phase Transition Hot Dense Hydrogen

    NASA Astrophysics Data System (ADS)

    Silvera, Isaac; Dzyabura, Vasily; Zaghoo, Mohamed

    2013-03-01

    We use pulsed laser heating of hydrogen at static pressures in the megabar pressure region generated in a diamond anvil cell to search for the plasma phase transition (PPT) to liquid atomic metallic hydrogen. Heating the sample substantially above the melting line we observe a plateau in a temperature vs laser power curve that otherwise increases with power. This anomaly in the heating curve is closely correlated with theoretical predictions for the PPT, falling within the theoretically predicted range and having a negative slope with increasing pressure. Details will be presented. The NSF, grant DMR-0804378 and the DOE Stockpile Stewardship Academic Alliance program, grant DE-FG52-10NA29656 supported this research.

  19. Effect of initial hydrogen content of a titanium alloy on susceptibility to hot-salt stress-corrosion

    NASA Technical Reports Server (NTRS)

    Gray, H. R.

    1971-01-01

    The Ti-8Al-1Mo-1V alloy was tested in four conditions: mill annealed (70 ppM H), duplex annealed (70 ppM H), vacuum annealed to an intermediate (36 ppM) and a low (9 ppM H) hydrogen level. Material annealed at 650 C (duplex condition) exhibited resistance to hot-salt stress corrosion superior to that exhibited by material in the mill-annealed condition. Reduction of the alloy hydrogen content from 70 to as low as 9 ppM did not influence resistance to hot-salt stress corrosion embrittlement or cracking.

  20. Positron scattering from hydrogen atom with screened Coulomb potentials

    SciTech Connect

    Ghoshal, Arijit; Nayek, Sujay; Kamali, M. Z. M.; Ratnavelu, K.

    2014-03-05

    Elastic positron-hydrogen collisions with screened Coulomb potentials have been investigated using a second-order distorted wave Born approximation in the momentum space. Two types of potentials have been considered, namely, static screened Coulomb potential and exponential cosine-screened Coulomb potential. Using a simple variationally determined hydrogenic wave function it has been possible to obtain the scattering amplitude in a closed form. A detailed study has been made on the differential and total cross sections in the energy range 20–300 eV.

  1. Hydrogen bond cooperativity in water hexamers: atomic energy perspective of local stabilities.

    PubMed

    Albrecht, Laura; Chowdhury, Saptarshi; Boyd, Russell J

    2013-10-17

    Atomic energies are used to describe local stability in eight low-lying water hexamers: prism, cage, boat 1, boat 2, bag, chair, book 1, and book 2. The energies are evaluated using the quantum theory of atoms in molecules (QTAIM) at MP2/aug-cc-pVTZ geometries. It is found that the simple, stabilizing cooperativity observed in linear hydrogen-bonded water systems is diminished as clusters move from nearly planar to three-dimensional structures. The prism, cage, and bag clusters can have local water stabilities differing up to 5 kcal mol(-1) as a result of mixed cooperative and anticooperative interactions. At the atomic level, in many cases a water may have a largely stabilized oxygen atom but the net water stability will be diminished due to strong destabilization of the water's hydrogen atoms. Analysis of bond critical point (BCP) electron densities shows that the reduced cooperativity results in a decrease in hydrogen bond strength and an increase in covalent bond strength, most evident in the prism. The chair, with the greatest cooperativity, has the largest average electron density at the BCP per hydrogen bond, whereas the cage has the largest total value for BCP density at all hydrogen bonds. The cage also has the second largest value (after the prism) for covalent bond critical point densities and an oxygen-oxygen BCP which may factor into the experimentally observed stability of the structure.

  2. Hydrogen-induced atomic rearrangement in MgPd{sub 3}

    SciTech Connect

    Kohlmann, H. . E-mail: h.kohlmann@mx.uni-saarland.de; Renaudin, G.; Yvon, K.; Wannek, C.; Harbrecht, B.

    2005-04-15

    The hydrogenation behavior of MgPd{sub 3} has been studied by in situ X-ray powder diffraction and by neutron powder diffraction. At room temperature and p {approx}500kPa hydrogen pressure its structure is capable of incorporating up to one hydrogen atom per formula unit ({alpha}-MgPd{sub 3}H{sub {approx}}{sub 1}), thereby retaining a tetragonal ZrAl{sub 3}-type metal atom arrangement. Upon heating to 750K in a hydrogen atmosphere of 610kPa it transforms into a cubic modification with AuCu{sub 3}-type metal atom arrangement ({beta}-MgPd{sub 3}H{sub {approx}}{sub 0.7}). Neutron diffraction on the deuteride reveals an anion deficient anti-perovskite-type structure ({beta}-MgPd{sub 3}D{sub 0.67}, a=398.200(7)pm) in which octahedral sites surrounded exclusively by palladium atoms are occupied by deuterium. Complete removal of hydrogen (480K, 1Pa) stabilizes a new binary modification ({beta}-MgPd{sub 3}, a=391.78(2)pm) crystallizing with a primitive cubic AuCu{sub 3}-type structure. Mechanical treatment (grinding) transforms both {alpha} and {beta} modifications of MgPd{sub 3} into a cubic face-centered solid solution Mg{sub 0.25}Pd{sub 0.75} showing a random distribution of magnesium and palladium atoms.

  3. Hydrogen Atom Reactivity toward Aqueous tert-Butyl Alcohol

    SciTech Connect

    Lymar S. V.; Schwarz, H.A.

    2012-02-09

    Through a combination of pulse radiolysis, purification, and analysis techniques, the rate constant for the H + (CH{sub 3}){sub 3}COH {yields} H{sub 2} + {sm_bullet}CH{sub 2}C(CH{sub 3}){sub 2}OH reaction in aqueous solution is definitively determined to be (1.0 {+-} 0.15) x 10{sup 5} M{sup -1} s{sup -1}, which is about half of the tabulated number and 10 times lower than the more recently suggested revision. Our value fits on the Polanyi-type, rate-enthalpy linear correlation ln(k/n) = (0.80 {+-} 0.05){Delta}H + (3.2 {+-} 0.8) that is found for the analogous reactions of other aqueous aliphatic alcohols with n equivalent abstractable H atoms. The existence of such a correlation and its large slope are interpreted as an indication of the mechanistic similarity of the H atom abstraction from {alpha}- and {beta}-carbon atoms in alcohols occurring through the late, product-like transition state. tert-Butyl alcohol is commonly contaminated by much more reactive secondary and primary alcohols (2-propanol, 2-butanol, ethanol, and methanol), whose content can be sufficient for nearly quantitative scavenging of the H atoms, skewing the H atom reactivity pattern, and explaining the disparity of the literature data on the H + (CH{sub 3}){sub 3}COH rate constant. The ubiquitous use of tert-butyl alcohol in pulse radiolysis for investigating H atom reactivity and the results of this work suggest that many other previously reported rate constants for the H atom, particularly the smaller ones, may be in jeopardy.

  4. A New Time-Dependent Scattering Theory: Application to the Capture of Antiprotons by Hydrogen Atoms and Helium Atoms

    SciTech Connect

    Tong, X. M.; Hino, K.; Toshima, N.

    2008-08-08

    We present a theoretical method for Coulomb three-body rearrangement collisions solving a Chew-Goldberger-type integral equation directly. The scattering boundary condition is automatically satisfied by adiabatically switching on the interaction between the projectile and target. Hence the outgoing wave function is obtained without the tedious procedure of adjusting the total wave function in the asymptotic region. All the dynamical information can be derived from the scattering wave function obtained on pseudo-spectral grids numerically. Using this method, we obtained the state-specified capture cross sections when antiprotons collide with hydrogen atoms or helium atoms. Differing from the capture processes of antiprotons by hydrogen atoms, the anomalous bumpy structures are revealed in the total angular momentum dependent capture cross sections by helium atoms. Further analysis shows that the bumps arise from the partial channel closing due to the removal of the energy degeneracy in the antiprotonic helium atom. The ejected electron energy distributions are also provided for the comparison with future experiments.

  5. Study on a negative hydrogen ion source with hot cathode arc discharge

    SciTech Connect

    Lin, S. H. Fang, X.; Zhang, H. J.; Qian, C.; Ma, B. H.; Wang, H.; Li, X. X.; Zhang, X. Z.; Sun, L. T.; Zhang, Z. M.; Yuan, P.; Zhao, H. W.

    2014-02-15

    A negative hydrogen (H{sup −}) ion source with hot cathode arc discharge was designed and fabricated as a primary injector for a 10 MeV PET cyclotron at IMP. 1 mA dc H{sup −} beam with ε {sub N,} {sub RMS} = 0.08 π mm mrad was extracted at 25 kV. Halbach hexapole was adopted to confine the plasma. The state of arc discharge, the parameters including filament current, arc current, gas pressure, plasma electrode bias, and the ratio of I{sub e{sup −}}/I{sub H{sup −}} were experimentally studied. The discussion on the result, and opinions to improve the source were given.

  6. (F)UV Spectral Analysis of Hot, Hydrogen-Rich Central Stars of Planetary Nebulae

    NASA Astrophysics Data System (ADS)

    Ziegler, M.; Rauch, T.; Werner, K.; Kruk, J. W.

    2010-11-01

    Metal abundances of CSPNe are not well known although they provide important constraints on AGB nucleosynthesis. We aim to determine metal abundances of two hot, hydrogen-rich CSPNe (namely of A35 and NGC3587, the latter also known as M97 or the Owl Nebula) and to derive Teff and log g precisely from high-resolution, high-S/N (far-) ultraviolet observations obtained with FUSE and HST/STIS. For this purpose, we utilize NLTE model atmospheres calculated with TMAP, the Tübingen Model Atmosphere Package. Due to strong line absorption of the ISM, simultaneous modeling of interstellar features has become a standard tool in our analyses. We present preliminary results, demonstrating the importance of combining stellar and interstellar models, in order to clearly identify and measure the strengths of strategic photospheric lines.

  7. Experimental investigations of electron capture from atomic hydrogen and deuterium by alpha particles

    SciTech Connect

    Gay, T.J.; Park, J.T.

    1992-01-01

    We report progress made during the period 15 September 1991--14 September 1992 on the project Experimental Investigations of Electron Capture from Atomic Hydrogen and Deuterium by Alpha Particles''. In the past year we have developed reliable, narrow energy spread, high-current sources of He[sup ++] based on direct-current magentron and electron-cyclotron resonance discharges. These sources have been proven on our test bench accelerator which has been upgraded to also allow us to test atomic hydrogen effusive targets. We have thus made substantial progress toward our goal of studying single electron capture from atomic hydrogen by doubly-ionized helium. A research plan for the upcoming year is also presented.

  8. Hydrogen atom wave function and eigen energy in the Rindler space

    NASA Astrophysics Data System (ADS)

    Dai, De-Chang

    2016-10-01

    We study the hydrogen atom eigenstate energy and wave function in the Rindler space. The probability distribution is tilted because the electric field of the nucleus is no longer spherically symmetric. The hydrogen atom therefore cannot be treated exactly in the same way as what it is in an inertial frame. We also find that if the external force accelerates only the nucleus and then the nucleus accelerates its surrounding electrons through electromagnetic force, the electrons can tunnel through the local energy gap and split the hydrogen atom into an ion. This is similar to what one expects from the Stark effect. However, the critical acceleration is about 3 ×1022 m /s2. It is well beyond the gravitational acceleration on a regular star surface.

  9. Hydrogen bond donors accelerate vibrational cooling of hot purine derivatives in heavy water.

    PubMed

    Zhang, Yuyuan; Chen, Jinquan; Kohler, Bern

    2013-08-01

    Natural nucleobases and many of their derivatives have ultrashort excited state lifetimes that make them excellent model systems for studying intermolecular energy flow from a hot solute molecule to the solvent. UV-pump/broadband-mid-IR-probe transient absorption spectra of canonical purine nucleobases and several xanthine derivatives were acquired in D2O and acetonitrile in the probe frequency range of 1500-1750 cm(-1). The spectra reveal that vibrationally hot ground state molecules created by ultrafast internal conversion return to thermal equilibrium in several picoseconds by dissipating their excess energy to solvent molecules. In acetonitrile solution, where hydrogen bonding is minimal, vibrational cooling (VC) occurs with the same time constant of 10 ± 3 ps for paraxanthine, theophylline, and caffeine within experimental uncertainty. In D2O, VC by these molecules occurs more rapidly and at different rates that are correlated with the number of N-D bonds. Hypoxanthine has a VC time constant of 3 ± 1 ps, while similar lifetimes of 2.3 ± 0.8 ps and 3.1 ± 0.3 ps are seen for 5'-adenosine monophosphate and 5'-guanosine monophosphate, respectively. All three molecules have at least two N-D bonds. Slightly slower VC time constants are measured for paraxanthine (4 ± 1 ps) and theophylline (5.1 ± 0.8 ps), dimethylated xanthines that have only one N-D bond. Caffeine, a trimethylated xanthine with no N-D bonds, has a VC time constant of 7.7 ± 0.9 ps, the longest ever observed for any nucleobase in aqueous solution. Hydrogen bond donation by solute molecules is proposed to enable rapid energy disposal to water via direct coupling of high frequency solute-solvent modes.

  10. A massive cloud of cold atomic hydrogen in the outer Galaxy.

    PubMed

    Knee, L B; Brunt, C M

    2001-07-19

    A large fraction of the mass of the interstellar medium in our Galaxy is in the form of warm (103-104 K) and cool (50-100 K) atomic hydrogen (H i) gas. Cold (10-30 K) regions are thought to be dominated by dense clouds of molecular hydrogen. Cold H i is difficult to observe, and therefore our knowledge of its abundance and distribution in the interstellar medium is poor. The few known clouds of cold H i are much smaller in size and mass than typical molecular clouds. Here we report the discovery that the H i supershell GSH139-03-69 is very cold (10 K). It is about 2 kiloparsecs in size and as massive as the largest molecular complexes. The existence of such an immense structure composed of cold atomic hydrogen in the interstellar medium runs counter to the prevailing view that cold gas resides almost exclusively in clouds dominated by molecular hydrogen.

  11. Lewis acid-water/alcohol complexes as hydrogen atom donors in radical reactions.

    PubMed

    Povie, Guillaume; Renaud, Philippe

    2013-01-01

    Water or low molecular weight alcohols are, due to their availability, low price and low toxicity ideal reagents for organic synthesis. Recently, it was reported that, despite the very strong BDE of the O-H bond, they can be used as hydrogen atom donors in place of expensive and/or toxic group 14 metal hydrides when boron and titanium(III) Lewis acids are present. This finding represents a considerable innovation and uncovers a new perspective on the paradigm of hydrogen atom transfers to radicals. We discuss here the influence of complex formation and other association processes on the efficacy of the hydrogen transfer step. A delicate balance between activation by complex formation and deactivation by further hydrogen bonding is operative.

  12. Performance evaluation of the SAO VLG-11 atomic hydrogen masers

    NASA Technical Reports Server (NTRS)

    Levine, M. W.; Vessot, R. F.; Mattison, E. M.

    1978-01-01

    A new generation of frequency standards, the VLG-11 hydrogen maser, has been designed and built at the Smithsonian Astrophysical Observatory (SAO). A comprehensive series of environmental and short-term stability tests on three VLG-11 masers has been completed and evaluated. The test results reported here show substantial improvements over previous hydrogen masers in measured sensitivity to variations in ambient temperature, barometric pressure, and magnetic fields. The maser frequency stability, as represented by the two-sample (Allan) variance, has been measured for averaging times ranging from 1 to 100,00 seconds. The variance is lower than 1 x 10 to the -15th for averaging intervals between 1400 and 20,000 seconds. For times shorter than 4000 seconds, the measured stability data agree remarkably well with theoretical values calculated from thermal noise mechanisms and the 'noise within the linewidth' regime is clearly discernable in the data.

  13. Atomic Hydrogen Measurements in a Fusion-Relevant Plasma

    NASA Astrophysics Data System (ADS)

    Samuell, Cameron; Corr, Cormac

    2012-10-01

    Critical to the success of large-scale fusion reactors is the development of new materials that can withstand the extreme conditions at the plasma-surface boundary. The materials required for plasma-facing components will need to withstand a very aggressive environment that is characterized by both a high heat load and high ion flux produced by the hydrogen isotope plasma. As such, investigating the ways in which hydrogen plasmas interact with a range of materials is an important area for research and development and is vital to the future success of fusion. A new experimental reactor, the MAGnetized Plasma Interaction Experiment (MAGPIE), has been constructed at the Australian National University to help resolve some of the critical issues surrounding the choice of fusion reactor materials. MAGPIE is a linear system with a 2.5kW, 13.56MHz helicon source that operates in a magnetic hill configuration with field strengths up to 0.19T. Densities up to 10^19m-3 at temperatures < 5eV have been achieved. The focus of this presentation is the interaction between a magnetized hydrogen plasma and tungsten and graphite targets in MAGPIE. Results from two-photon absorption laser induced fluorescence (TALIF), optical emission spectroscopy (OES) and probe diagnostics will be presented.

  14. Cooper-type minima in multipole cross sections of atomic hydrogen

    SciTech Connect

    Fazio, P.M.; Copeland, G.E.

    1984-07-09

    The quadrupole photoionization cross sections for hydrogen are shown to contain minima at kinetic energies of the free electron that are less than 2 eV. These minima are the result of zeros that occur in some of the quadrupole transition strengths between bound excited (Vertical Barn,l>) and continuum (Vertical BarW,l+2>) states for atomic hydrogen. These minima are compared with Cooper minima which occur in the photoionization cross sections for some multielectron systems.

  15. Resonant Coherent Excitation of Fast Hydrogen Atoms in Front of a LiF(001) Surface

    SciTech Connect

    Auth, C.; Mertens, A.; Winter, H.; Borisov, A.G.; Garcia de Abajo, F.J.

    1997-12-01

    We have scattered protons and hydrogen atoms with energies of some keV from a LiF(001) surface under a grazing angle of incidence. From the intensity of Lyman-{alpha} radiation (transition from n=2 to n=1, {lambda}=121.6 nm ) as a function of projectile energy for different azimuthal orientations of the crystal surface, we find clear evidence for a resonant coherent excitation of n=2 states of hydrogen atoms in the oscillating electric field in front of the insulator surface. {copyright} {ital 1997} {ital The American Physical Society}

  16. Deformylation Reaction by a Nonheme Manganese(III)-Peroxo Complex via Initial Hydrogen-Atom Abstraction.

    PubMed

    Barman, Prasenjit; Upadhyay, Pranav; Faponle, Abayomi S; Kumar, Jitendra; Nag, Sayanta Sekhar; Kumar, Devesh; Sastri, Chivukula V; de Visser, Sam P

    2016-09-01

    Metal-peroxo intermediates are key species in the catalytic cycles of nonheme metalloenzymes, but their chemical properties and reactivity patterns are still poorly understood. The synthesis and characterization of a manganese(III)-peroxo complex with a pentadentate bispidine ligand system and its reactivity with aldehydes was studied. Manganese(III)-peroxo can react through hydrogen-atom abstraction reactions instead of the commonly proposed nucleophilic addition reaction. Evidence of the mechanism comes from experiments which identify a primary kinetic isotope effect of 5.4 for the deformylation reaction. Computational modeling supports the established mechanism and identifies the origin of the reactivity preference of hydrogen-atom abstraction over nucleophilic addition.

  17. Deuterium removal from radiation damage in tungsten by isotopic exchange with hydrogen atomic beam

    NASA Astrophysics Data System (ADS)

    Ogorodnikova, O. V.; Markelj, S.; Efimov, V. S.; Gasparyan, Yu M.

    2016-09-01

    The tungsten samples were pre-irradiated with self-ions to create radiation-induced defects and then exposed to the deuterium atomic beam. The deuterium removal was studied by isotopic exchange with atomic hydrogen beam. Modification of the deuterium depth profile in self-ion irradiated tungsten under isotopic exchange up to a depth of 6 μm was measured in- situ by nuclear reaction analysis. The total deuterium retention after isotopic exchange was measured by thermal desorption spectroscopy. It is shown that the efficiency of the deuterium removal increases with increasing of the hydrogen incident flux, incident energy and temperature of the tungsten sample.

  18. Reduction of uranium hexafluoride to tetrafluoride by using the hydrogen atoms

    NASA Astrophysics Data System (ADS)

    Aleksandrov, B. P.; Gordon, E. B.; Ivanov, A. V.; Kotov, A. A.; Smirnov, V. E.

    2016-09-01

    We consider the reduction of UF6 to UF4 by chemical reaction with hydrogen atoms originated in the powerful chemical generator. The principal design of such a chemical convertor is described. The results of the mathematical modeling of the thermodynamics and kinetics of the UF6 to UF4 reduction process are analyzed. The few options for the hydrogen atom generator design are proposed. A layout of the experimental setup with the chemical reactor is presented. The high efficiency together with the ability of the process scaling without loss of its efficiency makes this approach to the uranium hexafluoride depletion into tetrafluoride promising for its application in the industry.

  19. Production and consumption of hydrogen in hot spring microbial mats dominated by a filamentous anoxygenic photosynthetic bacterium.

    PubMed

    Otaki, Hiroyo; Everroad, R Craig; Matsuura, Katsumi; Haruta, Shin

    2012-01-01

    Microbial mats containing the filamentous anoxygenic photosynthetic bacterium Chloroflexus aggregans develop at Nakabusa hot spring in Japan. Under anaerobic conditions in these mats, interspecies interaction between sulfate-reducing bacteria as sulfide producers and C. aggregans as a sulfide consumer has been proposed to constitute a sulfur cycle; however, the electron donor utilized for microbial sulfide production at Nakabusa remains to be identified. In order to determine this electron donor and its source, ex situ experimental incubation of mats was explored. In the presence of molybdate, which inhibits biological sulfate reduction, hydrogen gas was released from mat samples, indicating that this hydrogen is normally consumed as an electron donor by sulfate-reducing bacteria. Hydrogen production decreased under illumination, indicating that C. aggregans also functions as a hydrogen consumer. Small amounts of hydrogen may have also been consumed for sulfur reduction. Clone library analysis of 16S rRNA genes amplified from the mats indicated the existence of several species of hydrogen-producing fermentative bacteria. Among them, the most dominant fermenter, Fervidobacterium sp., was successfully isolated. This isolate produced hydrogen through the fermentation of organic carbon. Dispersion of microbial cells in the mats resulted in hydrogen production without the addition of molybdate, suggesting that simultaneous production and consumption of hydrogen in the mats requires dense packing of cells. We propose a cyclic electron flow within the microbial mats, i.e., electron flow occurs through three elements: S (elemental sulfur, sulfide, sulfate), C (carbon dioxide, organic carbon) and H (di-hydrogen, protons).

  20. Atomic hydrogen beam source: a convenient, extended cavity, microwave discharge design.

    PubMed

    Murphy, E J; Brophy, J H

    1979-05-01

    An extended cavity design of a microwave discharge source for production of intense beams of atomic, radical, and metastable species in vacuo is described. The extended cavity enables the discharge to be run at the beam source nozzle while the power connection and tuning elements remain conveniently outside the apparatus. This design minimizes wall recombination losses to produce intense atomic hydrogen beams with considerably less engineering than previous discharge sources.

  1. Ground state properties of solid and liquid spin-aligned atomic hydrogen

    NASA Technical Reports Server (NTRS)

    Danilowicz, R. L.; Dugan, J. V., Jr.; Etters, R. D.

    1976-01-01

    Calculations of the ground state energy in the solid phase were performed with the aid of a variational approach. The Morse potential form of the atomic triple potential computed by Kolos and Wolniewicz (1965) was employed for the calculations. The ground state energies of both the liquid and solid phases of spin-aligned atomic hydrogen around the volume of the transition are presented in a graph.

  2. Role of hydrogen in the chemical vapor deposition growth of MoS2 atomic layers

    NASA Astrophysics Data System (ADS)

    Li, Xiao; Li, Xinming; Zang, Xiaobei; Zhu, Miao; He, Yijia; Wang, Kunlin; Xie, Dan; Zhu, Hongwei

    2015-04-01

    Hydrogen plays a crucial role in the chemical vapor deposition (CVD) growth of graphene. Here, we have revealed the roles of hydrogen in the two-step CVD growth of MoS2. Our study demonstrates that hydrogen acts as the following: (i) an inhibitor of the thermal-induced etching effect in the continuous film growth process; and (ii) a promoter of the desulfurization reaction by decreasing the S/Mo atomic ratio and the oxidation reaction of the obtained MoSx (0 < x < 2) films. A high hydrogen content of more than 100% in argon forms nano-sized circle-like defects and damages the continuity and uniformity of the film. Continuous MoS2 films with a high crystallinity and a nearly perfect S/Mo atomic ratio were finally obtained after sulfurization annealing with a hydrogen content in the range of 20%-80%. This insightful understanding reveals the crucial roles of hydrogen in the CVD growth of MoS2 and paves the way for the controllable synthesis of two-dimensional materials.Hydrogen plays a crucial role in the chemical vapor deposition (CVD) growth of graphene. Here, we have revealed the roles of hydrogen in the two-step CVD growth of MoS2. Our study demonstrates that hydrogen acts as the following: (i) an inhibitor of the thermal-induced etching effect in the continuous film growth process; and (ii) a promoter of the desulfurization reaction by decreasing the S/Mo atomic ratio and the oxidation reaction of the obtained MoSx (0 < x < 2) films. A high hydrogen content of more than 100% in argon forms nano-sized circle-like defects and damages the continuity and uniformity of the film. Continuous MoS2 films with a high crystallinity and a nearly perfect S/Mo atomic ratio were finally obtained after sulfurization annealing with a hydrogen content in the range of 20%-80%. This insightful understanding reveals the crucial roles of hydrogen in the CVD growth of MoS2 and paves the way for the controllable synthesis of two-dimensional materials. Electronic supplementary

  3. Coupled Electron-Ion Monte Carlo calculations of atomic hydrogen

    NASA Astrophysics Data System (ADS)

    Holzmann, Markus; Pierleoni, Carlo; Ceperley, David M.

    2005-07-01

    We present a new Monte Carlo method which couples Path Integral for finite temperature protons with Quantum Monte Carlo for ground state electrons, and we apply it to metallic hydrogen for pressures beyond molecular dissociation. This method fills the gap between high temperature electron-proton Path Integral and ground state Diffusion Monte Carlo methods. Our data exhibit more structure and higher melting temperatures of the proton crystal than Car-Parrinello Molecular Dynamics results using LDA. We further discuss the quantum motion of the protons and the zero temperature limit.

  4. Multiphysics Thermal-Fluid Design Analysis of a Non-Nuclear Tester for Hot-Hydrogen Materials and Component Development

    NASA Technical Reports Server (NTRS)

    Wang, Ten-See; Foote, John; Litchford, Ron

    2006-01-01

    The objective of this effort is to perform design analyses for a non-nuclear hot-hydrogen materials tester, as a first step towards developing efficient and accurate multiphysics, thermo-fluid computational methodology to predict environments for hypothetical solid-core, nuclear thermal engine thrust chamber design and analysis. The computational methodology is based on a multidimensional, finite-volume, turbulent, chemically reacting, thermally radiating, unstructured-grid, and pressure-based formulation. The multiphysics invoked in this study include hydrogen dissociation kinetics and thermodynamics, turbulent flow, convective, and thermal radiative heat transfers. The goals of the design analyses are to maintain maximum hot-hydrogen jet impingement energy and to minimize chamber wall heating. The results of analyses on three test fixture configurations and the rationale for final selection are presented. The interrogation of physics revealed that reactions of hydrogen dissociation and recombination are highly correlated with local temperature and are necessary for accurate prediction of the hot-hydrogen jet temperature.

  5. Multiphysics Thermal-Fluid Design Analysis of a Non-Nuclear Tester for Hot-Hydrogen Materials and Component Development

    SciTech Connect

    Wang, T.-S.; Foote, John; Litchford, Ron

    2006-01-20

    The objective of this effort is to perform design analyses for a non-nuclear hot-hydrogen materials tester, as a first step towards developing efficient and accurate multiphysics, thermo-fluid computational methodology to predict environments for hypothetical solid-core, nuclear thermal engine thrust chamber design and analysis. The computational methodology is based on a multidimensional, finite-volume, turbulent, chemically reacting, thermally radiating, unstructured-grid, and pressure-based formulation. The multiphysics invoked in this study include hydrogen dissociation kinetics and thermodynamics, turbulent flow, convective, and thermal radiative heat transfers. The goals of the design analyses are to maintain maximum hot-hydrogen jet impingement energy and to minimize chamber wall heating. The results of analyses on three test fixture configurations and the rationale for final selection are presented. The interrogation of physics revealed that reactions of hydrogen dissociation and recombination are highly correlated with local temperature and are necessary for accurate prediction of the hot-hydrogen jet temperature.

  6. Nucleon polarizabilities: From Compton scattering to hydrogen atom

    NASA Astrophysics Data System (ADS)

    Hagelstein, Franziska; Miskimen, Rory; Pascalutsa, Vladimir

    2016-05-01

    We review the current state of knowledge of the nucleon polarizabilities and of their role in nucleon Compton scattering and in hydrogen spectrum. We discuss the basic concepts, the recent lattice QCD calculations and advances in chiral effective-field theory. On the experimental side, we review the ongoing programs aimed to measure the nucleon (scalar and spin) polarizabilities via the Compton scattering processes, with real and virtual photons. A great part of the review is devoted to the general constraints based on unitarity, causality, discrete and continuous symmetries, which result in model-independent relations involving nucleon polarizabilities. We (re-)derive a variety of such relations and discuss their empirical value. The proton polarizability effects are presently the major sources of uncertainty in the assessment of the muonic hydrogen Lamb shift and hyperfine structure. Recent calculations of these effects are reviewed here in the context of the "proton-radius puzzle". We conclude with summary plots of the recent results and prospects for the near-future work.

  7. Linear quadratic stochastic control of atomic hydrogen masers.

    PubMed

    Koppang, P; Leland, R

    1999-01-01

    Data are given showing the results of using the linear quadratic Gaussian (LQG) technique to steer remote hydrogen masers to Coordinated Universal Time (UTC) as given by the United States Naval Observatory (USNO) via two-way satellite time transfer and the Global Positioning System (GPS). Data also are shown from the results of steering a hydrogen maser to the real-time USNO mean. A general overview of the theory behind the LQG technique also is given. The LQG control is a technique that uses Kalman filtering to estimate time and frequency errors used as input into a control calculation. A discrete frequency steer is calculated by minimizing a quadratic cost function that is dependent on both the time and frequency errors and the control effort. Different penalties, chosen by the designer, are assessed by the controller as the time and frequency errors and control effort vary from zero. With this feature, controllers can be designed to force the time and frequency differences between two standards to zero, either more or less aggressively depending on the application.

  8. Zirconium-nickel crystals—hydrogen accumulators: Dissolution and penetration of hydrogen atoms in alloys

    NASA Astrophysics Data System (ADS)

    Matysina, Z. A.; Zaginaichenko, S. Yu.; Shchur, D. V.; Gabdullin, M. T.; Kamenetskaya, E. A.

    2016-07-01

    The calculation of the free energy, thermodynamic equilibrium equations, and kinetic equations of the intermetallic compound Zr2NiH x has been carried out based on molecular-kinetic concepts. The equilibrium hydrogen concentration depending on the temperature, pressure, and energy parameters has been calculated. The absorption-desorption of hydrogen has been studied, and the possibility of the realization of the hysteresis effect has been revealed. The kinetics of the dissolution and permeability of hydrogen is considered, the time dependence of these values has been found, and conditions for the extremum character of their time dependence have been determined. Relaxation times of the dissolution and permeability of hydrogen into the alloy have been calculated. The calculation results are compared with the experimental data available in the literature.

  9. STEM Imaging of Single Pd Atoms in Activated Carbon Fibers Considered for Hydrogen Storage

    SciTech Connect

    Van Benthem, Klaus; Bonifacio, Cecile S; Contescu, Cristian I; Pennycook, Stephen J; Gallego, Nidia C

    2011-01-01

    Aberration corrected scanning transmission electron microscopy was used to demonstrate the feasibility of imaging individual Pd atoms that are highly dispersed throughout the volume of activated carbon fibers. Simultaneous acquisition of high-angle annular dark-field and bright-field images allows correlation of the location of single Pd atoms with microstructural features of the carbon host material. Sub-Angstrom imaging conditions revealed that 18 wt% of the total Pd content is dispersed as single Pd atoms in three re-occurring local structural arrangements. The identified structural configurations may represent effective storage sites for molecular hydrogen through Kubas complex formation as discussed in detail in the preceding article.

  10. Continuous spectra of atomic hydrogen in a strong magnetic field

    NASA Astrophysics Data System (ADS)

    Zhao, L. B.; Zatsarinny, O.; Bartschat, K.

    2016-09-01

    We describe a theoretical method, developed in the coupled-channel formalism, to study photoionization of H atoms in a strong magnetic field of a size that is typical for magnetic white dwarfs. The coupled Schrödinger equations are solved numerically using the renormalized Numerov method proposed by Johnson [B. R. Johnson, J. Chem. Phys. 67, 4086 (1977), 10.1063/1.435384; B. R. Johnson, J. Chem. Phys. 69, 4678 (1978), 10.1063/1.436421]. The distinct advantage of this method is the fact that no overflow problems are encountered in the classically forbidden region, and hence the method exhibits excellent numerical stability. Photoionization cross sections are presented for magnetized H atoms in the ground and 2 p excited states. The calculated results are compared with those obtained by other theories. The present method is particularly useful for explaining the complex features of continuous spectra in a strong magnetic field and hence provides an efficient tool for modeling photoionization spectra observed in the atmosphere of magnetic white dwarfs.

  11. Detecting Hydrogen Atoms in Solid Parahydrogen Using FTIR Spectroscopy

    NASA Astrophysics Data System (ADS)

    Anderson, David T.; Ruzi, Mahmut

    2012-06-01

    Our group is currently studying the 193.3 nm photochemistry of a number of precursor molecules isolated in solid parahydrogen (pH_2) using high-resolution FTIR spectroscopy. In photochemical studies of formic acid and ammonia, right after the photolysis laser is turned off, we observe metastable satellite peaks in close proximity to the strong rovibrational transition out of the ground state of the respective monomer photoproducts H_2O and NH_3. In both cases, there are two satellite peaks near the R(0) monomer transition. We have assigned these satellite features to H-H_2O and H-NH_3 radical clusters that form via reactions of the photoproduct with the pH_2 host. We will present IR spectroscopic studies of these two H-atom cluster systems that we hope to use in future photochemical studies to measure the concentration of H-atoms in our sample using FTIR spectroscopy. K. A. Kufeld, W. R. Wonderly, L. O. Paulson, S. C. Kettwich, and D. T. Anderson, J. Phys. Chem. Lett. 3, 342-347 (2012).

  12. The distribution of atomic hydrogen in the magnetosphere of Saturn

    NASA Technical Reports Server (NTRS)

    Shemansky, D. E.; Hall, D. T.

    1992-01-01

    Three sets of previously unpublished Voyager ultraviolet spectrometer observations of the Saturn system conducted by Voyager 1 and 2 are presented. Voyager 1 observations during the postencounter period provided a map of the distribution looking down on the equatorial plane. The reduced data show a nonuniform distribution in local time with a preponderance of emission on the duskside. The emission extends radially inward to the top of the Saturn atmosphere with stronger signals appearing close to the planet, strongly suggesting that the principal source is the sunlit Saturn atmosphere. In the subsolar sector of the magnetosphere no excess emission in the vicinity of Titan's orbit is detectable. Voyager 1 and 2 preencounter observations also show H Ly-alpha emissions increasing monotonically toward the planet but with a distinctive dawnside excess. It is concluded that the preliminary results reporting a toroidal hydrogen distribution with a cavity inside 8 RS are invalid because of limited spatial resolution and poor statistics.

  13. The distribution of atomic hydrogen in the Jovian atmosphere

    NASA Technical Reports Server (NTRS)

    Killen, R. M.; Chamberlain, J. W.

    1986-01-01

    An analysis is presented of the Voyager and IUE lyman alpha spectra of the Jovian equatorial emission in which was derived a zonal asymmetry in the hydrogen column abundance. Using two estimates of the fraction of Lyman alpha which is due to direct excitation by charged particle precipitation from the ionosphere, upper and lower limits were derived to the H column abundance within and without the perturbed region. That the asymmetry in H abundance may be due to localized heating near the homopause with a consequent rise in scale height is shown. The derived exospheric temperature remains fairly constant with longitude. The required additional heat input over the bulge region, 0.02 erg/cm/s, is supplied by an additional flux of magnetospheric electrons due to Jupiter's magnetic anomaly.

  14. Compression experiments with spin-polarized atomic hydrogen

    NASA Astrophysics Data System (ADS)

    Sprik, R.; Walraven, J. T. M.; Silvera, Isaac F.

    1985-11-01

    Doubly polarized hydrogen has been produced up to densities of 2×1018 cm-3 with the use of a compression technique. Samples were compressed up to five orders of magnitude into small bubblelike volumes under a column of liquid helium. This technique enabled us to study the volume decay of a bubble at almost constant gas density for minutes. The analysis of the volume decay of such a bubble is discussed. A bulk three-body recombination process was observed with rate constant C3=[7(2)]×10-39 cm6 s-1, as well as bulk electronic b-->c relaxation with rate constant Gvbc↓=[12(4)]×10-16 cm3 s-1. The nature of the three-body process is analyzed with a set of extended rate equations. The samples were very delicate and rapid compressions could result in explosions.

  15. Continuous vs. discrete models for the quantum harmonic oscillator and the hydrogen atom

    NASA Astrophysics Data System (ADS)

    Lorente, Miguel

    2001-07-01

    The Kravchuk and Meixner polynomials of discrete variable are introduced for the discrete models of the harmonic oscillator and hydrogen atom. Starting from Rodrigues formula we construct raising and lowering operators, commutation and anticommutation relations. The physical properties of discrete models are figured out through the equivalence with the continuous models obtained by limit process.

  16. Compensation of logarithmic corrections in calculating the fine structure of levels in hydrogen-like atoms

    SciTech Connect

    Boikova, N. A. Tyukhtyaev, Yu. N.; Faustov, R. N.

    2011-01-15

    Special features of the quasipotential approach to calculating logarithmic (in the fine-structure constant) contributions to the fine splitting of energy levels in hydrogen-like atoms are analyzed. The boundaries of the region of applicability of the Fell technique are indicated, and the order of corrections beyond this region is estimated.

  17. Moøller polarimetry with polarized atomic hydrogen at MESA

    SciTech Connect

    Bartolomé, P. Aguar; Aulenbacher, K.; Tyukin, V.

    2013-11-07

    A new generation of parity violation (PV) electron scattering experiments are planned to be carried out at the Institut für Kernphysik in Mainz. These experiments will be performed at low energies of 100-200 MeV using the new accelerator MESA (Mainz Energy recovering Superconducting Accelerator). One of the main challenges of such experiments is to achieve an accuracy in beam polarization measurements that must be below 0.5%. This very high accuracy can be reached using polarized atomic hydrogen gas, stored in an ultra-cold magnetic trap, as the target for electron beam polarimetry based on Mo/ller scattering. Electron spin-polarized atomic hydrogen can be stored at high densities of 10{sup 16} cm{sup −2}, over relatively long time periods, in a high magnetic field (8T) and at low temperatures (0.3K). The gradient force splits the ground state of the hydrogen into four states with different energies. Atoms in the low energy states are trapped in the strong magnetic field region whereas the high energy states are repelled and pumped away. The physics of ultra-cold atomic hydrogen in magnetic traps and the status of the Mainz Hydro-Mo/ller project will be presented.

  18. The Lamb shift in the hydrogen atom: Shift of s states

    SciTech Connect

    Karshenboim, S.G.

    1995-02-01

    A theoretical expression for the difference of the Lamb shifts of the 1s{sub 1/2} and 2s{sub 1/2} levels is obtained. The Lamb shift of the ground state in the hydrogen atom is recalculated and found to be 8172.898(26) MHz. 22 refs.

  19. Determination of the Relative Atomic Masses of Metals by Liberation of Molecular Hydrogen

    ERIC Educational Resources Information Center

    Waghorne, W. Earle; Rous, Andrew J.

    2009-01-01

    Students determine the relative atomic masses of calcium, magnesium, and aluminum by reaction with hydrochloric acid and measurement of the volume of hydrogen gas liberated. The experiment demonstrates stoichiometry and illustrates clearly that mass of the reagent is not the determinant of the amounts in chemical reactions. The experiment is…

  20. Learning about Regiochemistry from a Hydrogen-Atom Abstraction Reaction in Water

    ERIC Educational Resources Information Center

    Sears-Dundes, Christopher; Huon, Yoeup; Hotz, Richard P.; Pinhas, Allan R.

    2011-01-01

    An experiment has been developed in which the hydrogen-atom abstraction and the coupling of propionitrile, using Fenton's reagent, are investigated. Students learn about the regiochemistry of radical formation, the stereochemistry of product formation, and the interpretation of GC-MS data, in a safe reaction that can be easily completed in one…

  1. Effects of laser radiation field on energies of hydrogen atom in plasmas

    SciTech Connect

    Bahar, M. K.

    2015-09-15

    In this study, for the first time, the Schrödinger equation with more general exponential cosine screened Coulomb (MGECSC) potential is solved numerically in the presence of laser radiation field within the Ehlotzky approximation using the asymptotic iteration method. The MGECSC potential includes four different potential forms in consideration of different sets of the parameters in the potential. By applying laser field, the total interaction potential of hydrogen atom embedded in plasmas converts to double well-type potential. The plasma screening effects under the influence of laser field as well as confinement effects of laser field on hydrogen atom in Debye and quantum plasmas are investigated by solving the Schrödinger equation with the laser-dressed MGECSC potential. It is resulted that since applying a monochromatic laser field on hydrogen atom embedded in a Debye and quantum plasma causes to shift in the profile of the total interaction potential, the confinement effects of laser field on hydrogen atom in plasmas modeled by the MGECSC potential change localizations of energy states.

  2. Quantum dynamics of hydrogen atoms on graphene. I. System-bath modeling

    SciTech Connect

    Bonfanti, Matteo; Jackson, Bret; Hughes, Keith H.; Burghardt, Irene

    2015-09-28

    An accurate system-bath model to investigate the quantum dynamics of hydrogen atoms chemisorbed on graphene is presented. The system comprises a hydrogen atom and the carbon atom from graphene that forms the covalent bond, and it is described by a previously developed 4D potential energy surface based on density functional theory ab initio data. The bath describes the rest of the carbon lattice and is obtained from an empirical force field through inversion of a classical equilibrium correlation function describing the hydrogen motion. By construction, model building easily accommodates improvements coming from the use of higher level electronic structure theory for the system. Further, it is well suited to a determination of the system-environment coupling by means of ab initio molecular dynamics. This paper details the system-bath modeling and shows its application to the quantum dynamics of vibrational relaxation of a chemisorbed hydrogen atom, which is here investigated at T = 0 K with the help of the multi-configuration time-dependent Hartree method. Paper II deals with the sticking dynamics.

  3. Laboratory Measurements of Charge Transfer on Atomic Hydrogen at Thermal Energies

    NASA Technical Reports Server (NTRS)

    Havener, C. C.; Vane, C. R.; Krause, H. F.; Stancil, P. C.; Mroczkowski, T.; Savin, D. W.

    2002-01-01

    We describe our ongoing program to measure velocity dependent charge transfer (CT) cross sections for selected ions on atomic hydrogen using the ion-aloin merged-beams apparatus at Oak Ridge Natioiial Laboralory. Our focus is on those ions for which CT plays an important role in determining the ionization structure, line emis sion, and thermal structure of observed cosmic photoionized plasmas.

  4. Moøller polarimetry with polarized atomic hydrogen at MESA

    NASA Astrophysics Data System (ADS)

    Bartolomé, P. Aguar; Aulenbacher, K.; Tyukin, V.

    2013-11-01

    A new generation of parity violation (PV) electron scattering experiments are planned to be carried out at the Institut für Kernphysik in Mainz. These experiments will be performed at low energies of 100-200 MeV using the new accelerator MESA (Mainz Energy recovering Superconducting Accelerator). One of the main challenges of such experiments is to achieve an accuracy in beam polarization measurements that must be below 0.5%. This very high accuracy can be reached using polarized atomic hydrogen gas, stored in an ultra-cold magnetic trap, as the target for electron beam polarimetry based on Mo/ller scattering. Electron spin-polarized atomic hydrogen can be stored at high densities of 1016 cm-2, over relatively long time periods, in a high magnetic field (8T) and at low temperatures (0.3K). The gradient force splits the ground state of the hydrogen into four states with different energies. Atoms in the low energy states are trapped in the strong magnetic field region whereas the high energy states are repelled and pumped away. The physics of ultra-cold atomic hydrogen in magnetic traps and the status of the Mainz Hydro-Mo/ller project will be presented.

  5. Hydrogen atom formation from the photodissociation of water ice at 193 nm.

    PubMed

    Yabushita, Akihiro; Hashikawa, Yuichi; Ikeda, Atsushi; Kawasaki, Masahiro; Tachikawa, Hiroto

    2004-03-15

    The TOF spectra of photofragment hydrogen atoms from the 193 nm photodissociation of amorphous ice at 90-140 K have been measured. The spectra consist of both a fast and a slow components that are characterized by average translational energies of 2k(B)T(trans)=0.39+/-0.04 eV (2300+/-200 K) and 0.02 eV (120+/-20 K), respectively. The incident laser power dependency of the hydrogen atom production suggests one-photon process. The electronic excitation energy of a branched cluster, (H(2)O)(6+1), has been theoretically calculated, where (H(2)O)(6+1) is a (H(2)O)(6) cyclic cluster attached by a water molecule with the hydrogen bond. The photoabsorption of this branched cluster is expected to appear at around 200 nm. The source of the hydrogen atoms is attributed to the photodissociation of the ice surface that is attached by water molecules with the hydrogen bond. Atmospheric implications are estimated for the photodissociation of the ice particles (Noctilucent clouds) at 190-230 nm in the region between 80 and 85 km altitude.

  6. Quantum states of hydrogen atom on Pd(1 1 0) surface

    NASA Astrophysics Data System (ADS)

    Padama, Allan Abraham B.; Nakanishi, Hiroshi; Kasai, Hideaki

    2015-12-01

    The quantum states of adsorbed hydrogen atom on Pd(1 1 0) surface are investigated in this work. From the calculated potential energy surface (PES) of hydrogen atom on Pd(1 1 0), the wave functions and eigenenergies in the ground and few excited states of protium (H) and deuterium (D) are calculated. Localized wave functions of hydrogen atom exist on pseudo-threefold and long bridge sites of Pd(1 1 0). The short bridge site is a local minimum from the result of PES, however, quantum behavior of hydrogen revealed that its vibration would allow it to hop to other pseudo-threefold site (that crosses the short bridge site) than to stay on the short bridge site. Exchange of ordering of the wave functions between H and D is attributed to the difference in their masses. The calculated eigenenergies are found to be in fair agreement with experimental data based from the identified vibrations of hydrogen with component perpendicular to the surface. The activation barriers measured from the eigenenergies are in better agreement with experimental findings in comparison to the data gathered from PES.

  7. Self-interaction in Green's-function theory of the hydrogen atom

    SciTech Connect

    Nelson, W.; Bokes, P.; Rinke, Patrick; Godby, R. W.

    2007-03-15

    Atomic hydrogen provides a unique test case for computational electronic structure methods, since its electronic excitation energies are known analytically. With only one electron, hydrogen contains no electronic correlation and is therefore particularly susceptible to spurious self-interaction errors introduced by certain computational methods. In this paper we focus on many-body perturbation theory (MBPT) in Hedin's GW approximation. While the Hartree-Fock and the exact MBPT self-energy are free of self-interaction, the correlation part of the GW self-energy does not have this property. Here we use atomic hydrogen as a benchmark system for GW and show that the self-interaction part of the GW self-energy, while nonzero, is small. The effect of calculating the GW self-energy from exact wave functions and eigenvalues, as distinct from those from the local-density approximation, is also illuminating.

  8. The possibility of constructing the hydrogen scale of the absolute atomic masses of the elements

    NASA Astrophysics Data System (ADS)

    Kuz'min, I. I.

    2009-12-01

    The paper presents a scheme for the experimental-empirical construction of the existing chemical, physical, and carbon scales of the relative nonintegral atomic masses of the elements. The quantitative interrelation between the nonintegral relative atomic masses, their minimized fractional positive and negative natural deviations from integral numbers, and their integral parts are reproduced mathematically. Nonisotopic fractional deviations are shown to be a consequence of methodological side effects of the scheme for theoretical processing of the data of thorough physical and chemical measurements performed by Stas and Aston in constructing scales of relative atomic masses. In conformity with the Prout hypothesis, the absolute atomic mass unit and the corresponding Avogadro’s number value are suggested for the construction of the hydrogen scale of absolute atomic masses of nonisotopic elements, individual isotopes, and isotope-containing elements.

  9. Loss of hydrogen atoms in H{sub 2} plasma on the surfaces of materials used in EUV lithography

    SciTech Connect

    Zyryanov, S. M.; Kovalev, A. S.; Lopaev, D. V.; Malykhin, E. M.; Rakhimov, A. T.; Rakhimova, T. V.; Koshelev, K. N.; Krivtsun, V. M.

    2011-10-15

    Low-pressure hydrogen is an important component of the working medium in extreme ultraviolet (EUV) projection lithography. Under the action of EUV photons and fast secondary electrons on the gas medium, plasma and atomic hydrogen, actively interacting with the surface, are produced. This interaction is very important, because it largely determines the lifetime of the multilayered EUV optics. In this study, the loss of atomic hydrogen under the conditions of a low pressure (<10 Torr) RF plasma discharge on the surfaces of materials used in EUV lithography is investigated. The surface loss probabilities of H atoms on these materials are measured. It is shown that surface recombination of atomic hydrogen goes according to the Eley-Rideal mechanism via direct recombination of H atoms from the gas phase with chemically and physically adsorbed atoms. In this case, the surface recombination probability is mainly determined by the density of chemical adsorption sites. The density of adsorption sites and the desorption energy of H atoms are estimated. The desorption energy of physically adsorbed H atoms on pure metal surfaces (or surfaces exposed to plasma) is about 0.5 eV, and the density of sorption sites is close to the surface density of atoms. This results in a high loss probability of H atoms on metals ({approx}0.1). Therefore, to provide efficient transportation of hydrogen atoms, it is necessary to use materials with the lowest loss probability of H atoms, i.e., dielectrics.

  10. Insights into the Electronic Structure of Ozone and Sulfur Dioxide from Generalized Valence Bond Theory: Addition of Hydrogen Atoms.

    PubMed

    Lindquist, Beth A; Takeshita, Tyler Y; Dunning, Thom H

    2016-05-01

    Ozone (O3) and sulfur dioxide (SO2) are valence isoelectronic species, yet their properties and reactivities differ dramatically. In particular, O3 is highly reactive, whereas SO2 is chemically relatively stable. In this paper, we investigate serial addition of hydrogen atoms to both the terminal atoms of O3 and SO2 and to the central atom of these species. It is well-known that the terminal atoms of O3 are much more amenable to bond formation than those of SO2. We show that the differences in the electronic structure of the π systems in the parent triatomic species account for the differences in the addition of hydrogen atoms to the terminal atoms of O3 and SO2. Further, we find that the π system in SO2, which is a recoupled pair bond dyad, facilitates the addition of hydrogen atoms to the sulfur atom, resulting in stable HSO2 and H2SO2 species.

  11. Production of Excited Atomic Hydrogen and Deuterium from HD Photodissociation

    NASA Astrophysics Data System (ADS)

    Machacek, J. R.; Bozek, J. D.; Furst, J. E.; Gay, T. J.; Gould, H.; Kilcoyne, A. L. D.; McLaughlin, K. W.

    2008-05-01

    We have measured the production of Lyα, Hα, and Hβ fluorescence from atomic H and D for the photodissociation of HD by linearly-polarized photons with energies between 20 and 66 eV. In this energy range, excited photofragments result primarily from the production of doubly-excited molecular species which promptly autoionize or dissociate into two neutrals. Theoretical calculation are not yet available for HD, but comparison between the relative cross sections for H2, D2 and HD targets and the available theory for H2 and D2 [1] allow for an estimate of the relative strength of each dissociation channel in this energy range. [1] J. D. Bozek et al., J. Phys. B 39, 4871 (2006). Support provided by the NSF (Grant PHY-0653379), DOE (LBNL/ALS) and ANSTO (Access to Major Research Facilities Programme).

  12. Hydrogen atom initiated chemistry. [chemical evolution in planetary atmospheres

    NASA Technical Reports Server (NTRS)

    Hong, J. H.; Becker, R. S.

    1979-01-01

    H Atoms have been created by the photolysis of H2S. These then initiated reactions in mixtures involving acetylene-ammonia-water and ethylene-ammonia-water. In the case of the acetylene system, the products consisted of two amino acids, ethylene and a group of primarily cyclic thio-compounds, but no free sulfur. In the case of the ethylene systems, seven amino acids, including an aromatic one, ethane, free sulfur, and a group of solely linear thio-compounds were produced. Total quantum yields for the production of amino acids were about 3 x 10 to the -5th and about 2 x 10 to the -4th with ethylene and acetylene respectively as carbon substrates. Consideration is given of the mechanism for the formation of some of the products and implications regarding planetary atmosphere chemistry, particularly that of Jupiter, are explored.

  13. Optical Hydrogen Absorption Consistent with a Bow Shock Leading the Hot Jupiter HD 189733b

    NASA Astrophysics Data System (ADS)

    Cauley, Paul Wilson; Redfield, Seth; Jensen, Adam

    2015-08-01

    Bow shocks are ubiquitous astrophysical phenomena resulting from the supersonic passage of an object through a gas. Recently, pre-transit absorption in UV metal transitions of the hot Jupiter exoplanets HD 189733b and WASP12-b have been interpreted as being caused by material compressed in a planetary bow shock. Here we present a robust detection of a time-resolved pre-transit, as well as in-transit, absorption signature around the hot Jupiter exoplanet HD 189733b using high spectral resolution observations of several hydrogen Balmer lines. The line shape of the pre-transit feature and the shape of the time series absorption provide the strongest constraints on the morphology and physical characteristics of extended structures around an exoplanet. The in-transit measurements confirm the exospheric Hα detection of Jensen et al. (2012) although the absorption depth measured here is ~50% lower. The pre-transit absorption feature occurs 125 minutes before the predicted optical transit, a projected linear distance to the stellar disk of 7.2 Rp. The absorption strength observed in the Balmer lines indicates an optically thick, but physically small, geometry. We model this signal as the early ingress of a planetary bow shock. If the bow shock is mediated by a planetary magnetosphere, the large standoff distance derived from the model suggests a large planetary magnetic field strength. Better knowledge of exoplanet magnetic field strengths is crucial to understanding the role these fields play in star-planet interactions and protecting planets in the habitable zone from dangerous stellar flares.

  14. Graphene oxide/metal nanocrystal multilaminates as the atomic limit for safe and selective hydrogen storage

    DOE PAGES

    Cho, Eun Seon; Ruminski, Anne M.; Aloni, Shaul; Liu, Yi-Sheng; Guo, Jinghua; Urban, Jeffrey J.

    2016-02-23

    Interest in hydrogen fuel is growing for automotive applications; however, safe, dense, solid-state hydrogen storage remains a formidable scientific challenge. Metal hydrides offer ample storage capacity and do not require cryogens or exceedingly high pressures for operation. However, hydrides have largely been abandoned because of oxidative instability and sluggish kinetics. We report a new, environmentally stable hydrogen storage material constructed of Mg nanocrystals encapsulated by atomically thin and gas-selective reduced graphene oxide (rGO) sheets. This material, protected from oxygen and moisture by the rGO layers, exhibits exceptionally dense hydrogen storage (6.5 wt% and 0.105 kg H2 per litre in themore » total composite). As rGO is atomically thin, this approach minimizes inactive mass in the composite, while also providing a kinetic enhancement to hydrogen sorption performance. In conclusion, these multilaminates of rGO-Mg are able to deliver exceptionally dense hydrogen storage and provide a material platform for harnessing the attributes of sensitive nanomaterials in demanding environments.« less

  15. Graphene oxide/metal nanocrystal multilaminates as the atomic limit for safe and selective hydrogen storage

    PubMed Central

    Cho, Eun Seon; Ruminski, Anne M.; Aloni, Shaul; Liu, Yi-Sheng; Guo, Jinghua; Urban, Jeffrey J.

    2016-01-01

    Interest in hydrogen fuel is growing for automotive applications; however, safe, dense, solid-state hydrogen storage remains a formidable scientific challenge. Metal hydrides offer ample storage capacity and do not require cryogens or exceedingly high pressures for operation. However, hydrides have largely been abandoned because of oxidative instability and sluggish kinetics. We report a new, environmentally stable hydrogen storage material constructed of Mg nanocrystals encapsulated by atomically thin and gas-selective reduced graphene oxide (rGO) sheets. This material, protected from oxygen and moisture by the rGO layers, exhibits exceptionally dense hydrogen storage (6.5 wt% and 0.105 kg H2 per litre in the total composite). As rGO is atomically thin, this approach minimizes inactive mass in the composite, while also providing a kinetic enhancement to hydrogen sorption performance. These multilaminates of rGO-Mg are able to deliver exceptionally dense hydrogen storage and provide a material platform for harnessing the attributes of sensitive nanomaterials in demanding environments. PMID:26902901

  16. Electrochemical removal of hydrogen atoms in Mg-doped GaN epitaxial layers

    SciTech Connect

    Lee, June Key E-mail: hskim7@jbnu.ac.kr; Hyeon, Gil Yong; Tawfik, Wael Z.; Choi, Hee Seok; Ryu, Sang-Wan; Jeong, Tak; Jung, Eunjin; Kim, Hyunsoo E-mail: hskim7@jbnu.ac.kr

    2015-05-14

    Hydrogen atoms inside of an Mg-doped GaN epitaxial layer were effectively removed by the electrochemical potentiostatic activation (EPA) method. The role of hydrogen was investigated in terms of the device performance of light-emitting diodes (LEDs). The effect of the main process parameters for EPA such as solution type, voltage, and time was studied and optimized for application to LED fabrication. In optimized conditions, the light output of 385-nm LEDs was improved by about 26% at 30 mA, which was caused by the reduction of the hydrogen concentration by ∼35%. Further removal of hydrogen seems to be involved in the breaking of Ga-H bonds that passivate the nitrogen vacancies. An EPA process with high voltage breaks not only Mg-H bonds that generate hole carriers but also Ga-H bonds that generate electron carriers, thus causing compensation that impedes the practical increase of hole concentration, regardless of the drastic removal of hydrogen atoms. A decrease in hydrogen concentration affects the current-voltage characteristics, reducing the reverse current by about one order and altering the forward current behavior in the low voltage region.

  17. Graphene oxide/metal nanocrystal multilaminates as the atomic limit for safe and selective hydrogen storage.

    PubMed

    Cho, Eun Seon; Ruminski, Anne M; Aloni, Shaul; Liu, Yi-Sheng; Guo, Jinghua; Urban, Jeffrey J

    2016-02-23

    Interest in hydrogen fuel is growing for automotive applications; however, safe, dense, solid-state hydrogen storage remains a formidable scientific challenge. Metal hydrides offer ample storage capacity and do not require cryogens or exceedingly high pressures for operation. However, hydrides have largely been abandoned because of oxidative instability and sluggish kinetics. We report a new, environmentally stable hydrogen storage material constructed of Mg nanocrystals encapsulated by atomically thin and gas-selective reduced graphene oxide (rGO) sheets. This material, protected from oxygen and moisture by the rGO layers, exhibits exceptionally dense hydrogen storage (6.5 wt% and 0.105 kg H2 per litre in the total composite). As rGO is atomically thin, this approach minimizes inactive mass in the composite, while also providing a kinetic enhancement to hydrogen sorption performance. These multilaminates of rGO-Mg are able to deliver exceptionally dense hydrogen storage and provide a material platform for harnessing the attributes of sensitive nanomaterials in demanding environments.

  18. Femtosecond real-time probing of reactions. IX. Hydrogen-atom transfer

    NASA Astrophysics Data System (ADS)

    Herek, J. L.; Pedersen, S.; Bañares, L.; Zewail, A. H.

    1992-12-01

    The real-time dynamics of hydrogen-atom-transfer processes under collisionless conditions are studied using femtosecond depletion techniques. The experiments focus on the methyl salicylate system, which exhibits ultrafast hydrogen motion between two oxygen atoms due to molecular tautomerization, loosely referred to as intramolecular ``proton'' transfer. To test for tunneling and mass effects on the excited potential surface, we also studied deuterium and methyl-group substitutions. We observe that the motion of the hydrogen, under collisionless conditions, takes place within 60 fs. At longer times, on the picosecond time scale, the hydrogen-transferred form decays with a threshold of 15.5 kJ/mol; this decay behavior was observed up to a total vibrational energy of ˜7200 cm-1. The observed dynamics provide the global nature of the motion, which takes into account bonding before and after the motion, and the evolution of the wave packet from the initial nonequilibrium state to the transferred form along the O-H—O reaction coordinate. The vibrational periods (2π/ω) of the relevant modes range from 13 fs (the OH stretch) to 190 fs (the low-frequency distortion) and the motion involves (in part) these coordinates. The intramolecular vibrational-energy redistribution dynamics at longer times are important to the hydrogen-bond dissociation and to the nonradiative decay of the hydrogen-transferred form.

  19. Graphene oxide/metal nanocrystal multilaminates as the atomic limit for safe and selective hydrogen storage

    NASA Astrophysics Data System (ADS)

    Cho, Eun Seon; Ruminski, Anne M.; Aloni, Shaul; Liu, Yi-Sheng; Guo, Jinghua; Urban, Jeffrey J.

    2016-02-01

    Interest in hydrogen fuel is growing for automotive applications; however, safe, dense, solid-state hydrogen storage remains a formidable scientific challenge. Metal hydrides offer ample storage capacity and do not require cryogens or exceedingly high pressures for operation. However, hydrides have largely been abandoned because of oxidative instability and sluggish kinetics. We report a new, environmentally stable hydrogen storage material constructed of Mg nanocrystals encapsulated by atomically thin and gas-selective reduced graphene oxide (rGO) sheets. This material, protected from oxygen and moisture by the rGO layers, exhibits exceptionally dense hydrogen storage (6.5 wt% and 0.105 kg H2 per litre in the total composite). As rGO is atomically thin, this approach minimizes inactive mass in the composite, while also providing a kinetic enhancement to hydrogen sorption performance. These multilaminates of rGO-Mg are able to deliver exceptionally dense hydrogen storage and provide a material platform for harnessing the attributes of sensitive nanomaterials in demanding environments.

  20. Stabilizing a Platinum1 Single-Atom Catalyst on Supported Phosphomolybdic Acid without Compromising Hydrogenation Activity.

    PubMed

    Zhang, Bin; Asakura, Hiroyuki; Zhang, Jia; Zhang, Jiaguang; De, Sudipta; Yan, Ning

    2016-07-11

    In coordination chemistry, catalytically active metal complexes in a zero- or low-valent state often adopt four-coordinate square-planar or tetrahedral geometry. By applying this principle, we have developed a stable Pt1 single-atom catalyst with a high Pt loading (close to 1 wt %) on phosphomolybdic acid(PMA)-modified active carbon. This was achieved by anchoring Pt on the four-fold hollow sites on PMA. Each Pt atom is stabilized by four oxygen atoms in a distorted square-planar geometry, with Pt slightly protruding from the oxygen planar surface. Pt is positively charged, absorbs hydrogen easily, and exhibits excellent performance in the hydrogenation of nitrobenzene and cyclohexanone. It is likely that the system described here can be extended to a number of stable SACs with superior catalytic activities.

  1. Local atomic structure modulations activate metal oxide as electrocatalyst for hydrogen evolution in acidic water.

    PubMed

    Li, Yu Hang; Liu, Peng Fei; Pan, Lin Feng; Wang, Hai Feng; Yang, Zhen Zhong; Zheng, Li Rong; Hu, P; Zhao, Hui Jun; Gu, Lin; Yang, Hua Gui

    2015-08-19

    Modifications of local structure at atomic level could precisely and effectively tune the capacity of materials, enabling enhancement in the catalytic activity. Here we modulate the local atomic structure of a classical but inert transition metal oxide, tungsten trioxide, to be an efficient electrocatalyst for hydrogen evolution in acidic water, which has shown promise as an alternative to platinum. Structural analyses and theoretical calculations together indicate that the origin of the enhanced activity could be attributed to the tailored electronic structure by means of the local atomic structure modulations. We anticipate that suitable structure modulations might be applied on other transition metal oxides to meet the optimal thermodynamic and kinetic requirements, which may pave the way to unlock the potential of other promising candidates as cost-effective electrocatalysts for hydrogen evolution in industry.

  2. Local atomic structure modulations activate metal oxide as electrocatalyst for hydrogen evolution in acidic water

    PubMed Central

    Li, Yu Hang; Liu, Peng Fei; Pan, Lin Feng; Wang, Hai Feng; Yang, Zhen Zhong; Zheng, Li Rong; Hu, P.; Zhao, Hui Jun; Gu, Lin; Yang, Hua Gui

    2015-01-01

    Modifications of local structure at atomic level could precisely and effectively tune the capacity of materials, enabling enhancement in the catalytic activity. Here we modulate the local atomic structure of a classical but inert transition metal oxide, tungsten trioxide, to be an efficient electrocatalyst for hydrogen evolution in acidic water, which has shown promise as an alternative to platinum. Structural analyses and theoretical calculations together indicate that the origin of the enhanced activity could be attributed to the tailored electronic structure by means of the local atomic structure modulations. We anticipate that suitable structure modulations might be applied on other transition metal oxides to meet the optimal thermodynamic and kinetic requirements, which may pave the way to unlock the potential of other promising candidates as cost-effective electrocatalysts for hydrogen evolution in industry. PMID:26286479

  3. Benchmarking all-atom simulations using hydrogen exchange

    PubMed Central

    Skinner, John J.; Yu, Wookyung; Gichana, Elizabeth K.; Baxa, Michael C.; Hinshaw, James R.; Freed, Karl F.; Sosnick, Tobin R.

    2014-01-01

    Long-time molecular dynamics (MD) simulations are now able to fold small proteins reversibly to their native structures [Lindorff-Larsen K, Piana S, Dror RO, Shaw DE (2011) Science 334(6055):517–520]. These results indicate that modern force fields can reproduce the energy surface near the native structure. To test how well the force fields recapitulate the other regions of the energy surface, MD trajectories for a variant of protein G are compared with data from site-resolved hydrogen exchange (HX) and other biophysical measurements. Because HX monitors the breaking of individual H-bonds, this experimental technique identifies the stability and H-bond content of excited states, thus enabling quantitative comparison with the simulations. Contrary to experimental findings of a cooperative, all-or-none unfolding process, the simulated denatured state ensemble, on average, is highly collapsed with some transient or persistent native 2° structure. The MD trajectories of this protein G variant and other small proteins exhibit excessive intramolecular H-bonding even for the most expanded conformations, suggesting that the force fields require improvements in describing H-bonding and backbone hydration. Moreover, these comparisons provide a general protocol for validating the ability of simulations to accurately capture rare structural fluctuations. PMID:25349413

  4. Semiclassical study of the quenching of excited-state fluorine atom by hydrogen molecule - Comparison between reactive and nonreactive processes

    NASA Technical Reports Server (NTRS)

    Yuan, J.-M.; Skuse, B. M.; Jaffe, R. L.; Komornicki, A.; Morokuma, K.; George, T. F.

    1980-01-01

    Semiclassical calculations are carried out for the quenching of excited-state fluorine atom by collinear collisions with hydrogen molecule. The overall quenching probability is the sum of two contributions: the reactive quenching probability associated with the formation of hydrogen fluoride and the nonreactive quenching probability leading to ground-state fluorine atom and hydrogen molecule. The reactive probability is greater in the threshold region of the collision energy, whereas the nonreactive probability dominates for energies above the threshold region.

  5. Breakdown into nanoscale of graphene oxide: Confined hot spot atomic reduction and fragmentation

    NASA Astrophysics Data System (ADS)

    Gonçalves, Gil; Vila, Mercedes; Bdikin, Igor; de Andrés, Alicia; Emami, Nazanin; Ferreira, Rute A. S.; Carlos, Luís D.; Grácio, José; Marques, Paula A. A. P.

    2014-10-01

    Nano-graphene oxide (nano-GO) is a new class of carbon based materials being proposed for biomedical applications due to its small size, intrinsic optical properties, large specific surface area, and easy to functionalize. To fully exploit nano-GO properties, a reproducible method for its production is of utmost importance. Herein we report, the study of the sequential fracture of GO sheets onto nano-GO with controllable lateral width, by a simple, and reproducible method based on a mechanism that we describe as a confined hot spot atomic fragmentation/reduction of GO promoted by ultrasonication. The chemical and structural changes on GO structure during the breakage were monitored by XPS, FTIR, Raman and HRTEM. We found that GO sheets starts breaking from the defects region and in a second phase through the disruption of carbon bonds while still maintaining crystalline carbon domains. The breaking of GO is accompanied by its own reduction, essentially by the elimination of carboxylic and carbonyl functional groups. Photoluminescence and photothermal studies using this nano-GO are also presented highlighting the potential of this nanomaterial as a unique imaging/therapy platform.

  6. Solid Hydrogen Experiments for Atomic Propellants: Particle Formation Energy and Imaging Analyses

    NASA Technical Reports Server (NTRS)

    Palaszewski, Bryan

    2002-01-01

    This paper presents particle formation energy balances and detailed analyses of the images from experiments that were conducted on the formation of solid hydrogen particles in liquid helium during the Phase II testing in 2001. Solid particles of hydrogen were frozen in liquid helium and observed with a video camera. The solid hydrogen particle sizes and the total mass of hydrogen particles were estimated. The particle formation efficiency is also estimated. Particle sizes from the Phase I testing in 1999 and the Phase II testing in 2001 were similar. Though the 2001 testing created similar particles sizes, many new particle formation phenomena were observed. These experiment image analyses are one of the first steps toward visually characterizing these particles and it allows designers to understand what issues must be addressed in atomic propellant feed system designs for future aerospace vehicles.

  7. Solid Hydrogen Experiments for Atomic Propellants: Particle Formation, Imaging, Observations, and Analyses

    NASA Technical Reports Server (NTRS)

    Palaszewski, Bryan

    2005-01-01

    This report presents particle formation observations and detailed analyses of the images from experiments that were conducted on the formation of solid hydrogen particles in liquid helium. Hydrogen was frozen into particles in liquid helium, and observed with a video camera. The solid hydrogen particle sizes and the total mass of hydrogen particles were estimated. These newly analyzed data are from the test series held on February 28, 2001. Particle sizes from previous testing in 1999 and the testing in 2001 were similar. Though the 2001 testing created similar particles sizes, many new particle formation phenomena were observed: microparticles and delayed particle formation. These experiment image analyses are some of the first steps toward visually characterizing these particles, and they allow designers to understand what issues must be addressed in atomic propellant feed system designs for future aerospace vehicles.

  8. Hydrogen-isotopic variability in fatty acids from Yellowstone National Park hot spring microbial communities

    NASA Astrophysics Data System (ADS)

    Osburn, Magdalena R.; Sessions, Alex L.; Pepe-Ranney, Charles; Spear, John R.

    2011-09-01

    We report the abundances and hydrogen-isotopic compositions (D/H ratios) of fatty acids extracted from hot-spring microbial mats in Yellowstone National Park. The terrestrial hydrothermal environment provides a useful system for studying D/H fractionations because the numerous microbial communities in and around the springs are visually distinct, separable, and less complex than those in many other aquatic environments. D/H fractionations between lipids and water ranged from -374‰ to +41‰ and showed systematic variations between different types of microbial communities. Lipids produced by chemoautotrophic hyperthermophilic bacteria, such as icosenoic acid (20:1), generally exhibited the largest and most variable fractionations from water (-374‰ to -165‰). This was in contrast to lipids characteristic of heterotrophs, such as branched, odd chain-length fatty acids, which had the smallest fractionations (-163‰ to +41‰). Mats dominated by photoautotrophs exhibited intermediate fractionations similar in magnitude to those expressed by higher plants. These data support the hypothesis that variations in lipid D/H are strongly influenced by central metabolic pathways. Shifts in the isotopic compositions of individual fatty acids across known ecological boundaries show that the isotopic signature of specific metabolisms can be recognized in modern environmental samples, and potentially recorded in ancient ones. Considering all sampled springs, the total range in D/H ratios is similar to that observed in marine sediments, suggesting that the trends observed here are not exclusive to the hydrothermal environment.

  9. Analysis of a Cylindrical Specimen Heated by an Impinging Hot Hydrogen Jet

    NASA Technical Reports Server (NTRS)

    Wang, Ten-See; Luong, Van; Foote, John; Litchford, Ron; Chen, Yen-Sen

    2006-01-01

    A computational conjugate heat transfer methodology was developed, as a first step towards an efficient and accurate multiphysics, thermo-fluid computational methodology to predict environments for hypothetical solid-core, nuclear thermal engine thrust chamber and components. A solid conduction heat transfer procedure was implemented onto a pressure-based, multidimensional, finite-volume, turbulent, chemically reacting, thermally radiating, and unstructured grid computational fluid dynamics formulation. The conjugate heat transfer of a cylindrical material specimen heated by an impinging hot hydrogen jet inside an enclosed test fixture was simulated and analyzed. The solid conduction heat transfer procedure was anchored with a standard solid heat transfer code. Transient analyses were then performed with ,variable thermal conductivities representing three composites of a material utilized as flow element in a legacy engine test. It was found that material thermal conductivity strongly influences the transient heat conduction characteristics. In addition, it was observed that high thermal gradient occur inside the cylindrical specimen during an impulsive or a 10 s ramp start sequence, but not during steady-state operations.

  10. Electrical and Surface Properties of InAs/InSb Nanowires Cleaned by Atomic Hydrogen.

    PubMed

    Webb, James L; Knutsson, Johan; Hjort, Martin; Gorji Ghalamestani, Sepideh; Dick, Kimberly A; Timm, Rainer; Mikkelsen, Anders

    2015-08-12

    We present a study of InAs/InSb heterostructured nanowires by X-ray photoemission spectroscopy (XPS), scanning tunneling microscopy (STM), and in-vacuum electrical measurements. Starting with pristine nanowires covered only by the native oxide formed through exposure to ambient air, we investigate the effect of atomic hydrogen cleaning on the surface chemistry and electrical performance. We find that clean and unreconstructed nanowire surfaces can be obtained simultaneously for both InSb and InAs by heating to 380 ± 20 °C under an H2 pressure 2 × 10(-6) mbar. Through electrical measurement of individual nanowires, we observe an increase in conductivity of 2 orders of magnitude by atomic hydrogen cleaning, which we relate through theoretical simulation to the contact-nanowire junction and nanowire surface Fermi level pinning. Our study demonstrates the significant potential of atomic hydrogen cleaning regarding device fabrication when high quality contacts or complete control of the surface structure is required. As hydrogen cleaning has recently been shown to work for many different types of III-V nanowires, our findings should be applicable far beyond the present materials system.

  11. Single Pd atoms in activated carbon fibers and their contribution to hydrogen storage

    SciTech Connect

    Contescu, Cristian I; van Benthem, Klaus; Li, Sa; Bonifacio, Cecile S; Pennycook, Stephen J; Jena, Puru; Gallego, Nidia C

    2011-01-01

    Palladium-modified activated carbon fibers (Pd-ACF) were synthesized by meltspinning, carbonization and activation of an isotropic pitch carbon precursor premixed with an organometallic Pd compound. The hydrogen uptake at 25 oC and 20 bar on Pd- ACF exceeded the expected capacity based solely on Pd hydride formation and hydrogen physisorption on the microporous carbon support. Aberration-corrected scanning transmission electron microscopy (STEM) with sub- ngstrom spatial resolution provided unambiguous identification of isolated Pd atoms occurring in the carbon matrix that coexist with larger Pd particles. First principles calculations revealed that each single Pd atom can form Kubas-type complexes by binding up to three H2 molecules in the pressure range of adsorption measurements. Based on Pd atom concentration determined from STEM images, the contribution of various mechanisms to the excess hydrogen uptake measured experimentally was evaluated. With consideration of Kubas binding as a viable mechanism (along with hydride formation and physisorption to carbon support) the role of hydrogen spillover in this system may be smaller than previously thought.

  12. Atomic hydrogen adsorption and incipient hydrogenation of the Mg(0001) surface: a density-functional theory study.

    PubMed

    Li, Yanfang; Zhang, Ping; Sun, Bo; Yang, Yu; Wei, Yinghui

    2009-07-21

    We investigate the atomic hydrogen adsorption on Mg(0001) by using density-functional theory within the generalized gradient approximation and a supercell approach. The coverage dependence of the adsorption structures and energetics is systematically studied for a wide range of coverage Theta [from 0.11 to 2.0 monolayers (ML)] and adsorption sites. In the coverage range 0 < Theta < 1.0, the most stable among all possible adsorption sites is the on-surface fcc site followed by the hcp site, and the binding energy increases with the coverage, thus indicating the higher stability of on-surface adsorption and a tendency to the formation of H islands (clusters) when increasing the coverage within the region 0 < Theta < 1.0. The on-surface diffusion path energetics of atomic hydrogen as well as the activation barriers for hydrogen penetration from the on-surface to the subsurface sites are also presented at low coverage. At high coverage of 1.0 < Theta < or = 2.0, it is found that the coadsorption configuration with 1.0 monolayer of H residing on the surface fcc sites and the remaining (Theta-1.0) monolayer of H occupying the subsurface tetra-I sites is most energetically favorable. The resultant H-Mg-H sandwich structure for this most stable coadsorption configuration displays similar spectral features to the bulk hydride MgH(2) in the density of states. The other properties of the H/Mg(0001) system including the charge distribution, the lattice relaxation, the work function, and the electronic density of states are also studied and discussed in detail. It is pointed out that the H-Mg chemical bonding during surface hydrogenation displays a mixed ionic/covalent character.

  13. Analytical transition-matrix treatment of electric multipole polarizabilities of hydrogen-like atoms

    SciTech Connect

    Kharchenko, V.F.

    2015-04-15

    The direct transition-matrix approach to the description of the electric polarization of the quantum bound system of particles is used to determine the electric multipole polarizabilities of the hydrogen-like atoms. It is shown that in the case of the bound system formed by the Coulomb interaction the corresponding inhomogeneous integral equation determining an off-shell scattering function, which consistently describes virtual multiple scattering, can be solved exactly analytically for all electric multipole polarizabilities. Our method allows to reproduce the known Dalgarno–Lewis formula for electric multipole polarizabilities of the hydrogen atom in the ground state and can also be applied to determine the polarizability of the atom in excited bound states. - Highlights: • A new description for electric polarization of hydrogen-like atoms. • Expression for multipole polarizabilities in terms of off-shell scattering functions. • Derivation of integral equation determining the off-shell scattering function. • Rigorous analytic solving the integral equations both for ground and excited states. • Study of contributions of virtual multiple scattering to electric polarizabilities.

  14. Selective adsorption of atomic hydrogen on a h-BN thin film

    SciTech Connect

    Koswattage, Kaveenga Rasika; Shimoyama, Iwao; Baba, Yuji; Sekiguchi, Tetsuhiro; Nakagawa, Kazumichi

    2011-07-07

    The adsorption of atomic hydrogen on hexagonal boron nitride (h-BN) is studied using two element-specific spectroscopies, i.e., near-edge x-ray absorption fine structure (NEXAFS) spectroscopy and x-ray photoelectron spectroscopy (XPS). B K-edge NEXAFS spectra show a clear change in the energy region of the {pi}{sup *} band before and after reaction with atomic deuterium. On the other hand, N K-edge NEXAFS spectra show only a little change. B 1s XPS spectra show a distinct component at the low binding energy side of a main component, while N 1s XPS spectra show peak broadening at the high binding energy side. These experimental results are analyzed by the discrete variational X{alpha} method with a core-hole effect and are explained by a model in which hydrogen atoms are preferentially adsorbed on the B sites of h-BN. Based on the experimental and theoretical results, we propose a site-selective property of BN material on adsorption of atomic hydrogen.

  15. Selective adsorption of atomic hydrogen on a h-BN thin film.

    PubMed

    Koswattage, Kaveenga Rasika; Shimoyama, Iwao; Baba, Yuji; Sekiguchi, Tetsuhiro; Nakagawa, Kazumichi

    2011-07-01

    The adsorption of atomic hydrogen on hexagonal boron nitride (h-BN) is studied using two element-specific spectroscopies, i.e., near-edge x-ray absorption fine structure (NEXAFS) spectroscopy and x-ray photoelectron spectroscopy (XPS). B K-edge NEXAFS spectra show a clear change in the energy region of the π* band before and after reaction with atomic deuterium. On the other hand, N K-edge NEXAFS spectra show only a little change. B 1s XPS spectra show a distinct component at the low binding energy side of a main component, while N 1s XPS spectra show peak broadening at the high binding energy side. These experimental results are analyzed by the discrete variational Xα method with a core-hole effect and are explained by a model in which hydrogen atoms are preferentially adsorbed on the B sites of h-BN. Based on the experimental and theoretical results, we propose a site-selective property of BN material on adsorption of atomic hydrogen. PMID:21744913

  16. Nanochemistry at the atomic scale revealed in hydrogen-induced semiconductor surface metallization

    NASA Astrophysics Data System (ADS)

    Derycke, Vincent; Soukiassian, Patrick G.; Amy, Fabrice; Chabal, Yves J.; D'Angelo, Marie D.; Enriquez, Hanna B.; Silly, Mathieu G.

    2003-04-01

    Passivation of semiconductor surfaces against chemical attack can be achieved by terminating the surface-dangling bonds with a monovalent atom such as hydrogen. Such passivation invariably leads to the removal of all surface states in the bandgap, and thus to the termination of non-metallic surfaces. Here we report the first observation of semiconductor surface metallization induced by atomic hydrogen. This result, established by using photo-electron and photo-absorption spectroscopies and scanning tunnelling techniques, is achieved on a Si-terminated cubic silicon carbide (SiC) surface. It results from competition between hydrogen termination of surface-dangling bonds and hydrogen-generated steric hindrance below the surface. Understanding the ingredient for hydrogen-stabilized metallization directly impacts the ability to eliminate electronic defects at semiconductor interfaces critical for microelectronics, provides a means to develop electrical contacts on high-bandgap chemically passive materials, particularly for interfacing with biological systems, and gives control of surfaces for lubrication, for example of nanomechanical devices.

  17. Nanochemistry at the atomic scale revealed in hydrogen-induced semiconductor surface metallization.

    PubMed

    Derycke, Vincent; Soukiassian, Patrick G; Amy, Fabrice; Chabal, Yves J; D'angelo, Marie D; Enriquez, Hanna B; Silly, Mathieu G

    2003-04-01

    Passivation of semiconductor surfaces against chemical attack can be achieved by terminating the surface-dangling bonds with a monovalent atom such as hydrogen. Such passivation invariably leads to the removal of all surface states in the bandgap, and thus to the termination of non-metallic surfaces. Here we report the first observation of semiconductor surface metallization induced by atomic hydrogen. This result, established by using photo-electron and photo-absorption spectroscopies and scanning tunnelling techniques, is achieved on a Si-terminated cubic silicon carbide (SiC) surface. It results from competition between hydrogen termination of surface-dangling bonds and hydrogen-generated steric hindrance below the surface. Understanding the ingredient for hydrogen-stabilized metallization directly impacts the ability to eliminate electronic defects at semiconductor interfaces critical for microelectronics, provides a means to develop electrical contacts on high-bandgap chemically passive materials, particularly for interfacing with biological systems, and gives control of surfaces for lubrication, for example of nanomechanical devices.

  18. Theoretical realization of cluster-assembled hydrogen storage materials based on terminated carbon atomic chains.

    PubMed

    Liu, Chun-Sheng; An, Hui; Guo, Ling-Ju; Zeng, Zhi; Ju, Xin

    2011-01-14

    The capacity of carbon atomic chains with different terminations for hydrogen storage is studied using first-principles density functional theory calculations. Unlike the physisorption of H(2) on the H-terminated chain, we show that two Li (Na) atoms each capping one end of the odd- or even-numbered carbon chain can hold ten H(2) molecules with optimal binding energies for room temperature storage. The hybridization of the Li 2p states with the H(2)σ orbitals contributes to the H(2) adsorption. However, the binding mechanism of the H(2) molecules on Na arises only from the polarization interaction between the charged Na atom and the H(2). Interestingly, additional H(2) molecules can be bound to the carbon atoms at the chain ends due to the charge transfer between Li 2s2p (Na 3s) and C 2p states. More importantly, dimerization of these isolated metal-capped chains does not affect the hydrogen binding energy significantly. In addition, a single chain can be stabilized effectively by the C(60) fullerenes termination. With a hydrogen uptake of ∼10 wt.% on Li-coated C(60)-C(n)-C(60) (n = 5, 8), the Li(12)C(60)-C(n)-Li(12)C(60) complex, keeping the number of adsorbed H(2) molecules per Li and stabilizing the dispersion of individual Li atoms, can serve as better building blocks of polymers than the (Li(12)C(60))(2) dimer. These findings suggest a new route to design cluster-assembled hydrogen storage materials based on terminated sp carbon chains.

  19. Rydberg hydrogen atom near a metallic surface: Stark regime and ionization dynamics

    SciTech Connect

    Inarrea, Manuel; Salas, J. Pablo; Lanchares, Victor; Pascual, Ana Isabel; Palacian, Jesus F.; Yanguas, Patricia

    2007-11-15

    We investigate the classical dynamics of a hydrogen atom near a metallic surface in the presence of a uniform electric field. To describe the atom-surface interaction we use a simple electrostatic image model. Owing to the axial symmetry of the system, the z-component of the canonical angular momentum P{sub {phi}} is an integral and the electronic dynamics is modeled by a two degrees of freedom Hamiltonian in cylindrical coordinates. The structure and evolution of the phase space as a function of the electric field strength is explored extensively by means of numerical techniques of continuation of families of periodic orbits and Poincare surfaces of section. We find that, due to the presence of the electric field, the atom is strongly polarized through two consecutive pitchfork bifurcations that strongly change the phase space structure. Finally, by means of the phase space transition state theory and the classical spectral theorem, the ionization dynamics of the atom is studied.

  20. Relativistic spectrum of hydrogen atom in the space-time non-commutativity

    SciTech Connect

    Moumni, Mustafa; BenSlama, Achour; Zaim, Slimane

    2012-06-27

    We study space-time non-commutativity applied to the hydrogen atom and its phenomenological effects. We find that it modifies the Coulomb potential in the Hamiltonian and add an r{sup -3} part. By calculating the energies from Dirac equation using perturbation theory, we study the modifications to the hydrogen spectrum. We find that it removes the degeneracy with respect to the total angular momentum quantum number and acts like a Lamb shift. Comparing the results with experimental values from spectroscopy, we get a new bound for the space-time non-commutative parameter.

  1. The contribution of dissociative processes to the production of atomic lines in hydrogen plasmas

    NASA Technical Reports Server (NTRS)

    Kunc, J. A.

    1985-01-01

    The contribution of molecular dissociative processes to the production of atomic lines is considered for a steady-state hydrogen plasma. If the contribution of dissociative processes is dominant, a substantial simplification in plasma diagnostics can be achieved. Numerical calculations have been performed for the production of Balmer alpha, beta, and gamma lines in hydrogen plasmas with medium and large degrees of ionization (x greater than about 0.0001) and for electron temperatures of 5000-45,000 K and electron densities of 10 to the 10th to 10 to the 16th/cu cm.

  2. Production and Consumption of Hydrogen in Hot Spring Microbial Mats Dominated by a Filamentous Anoxygenic Photosynthetic Bacterium

    PubMed Central

    Otaki, Hiroyo; Everroad, R. Craig; Matsuura, Katsumi; Haruta, Shin

    2012-01-01

    Microbial mats containing the filamentous anoxygenic photosynthetic bacterium Chloroflexus aggregans develop at Nakabusa hot spring in Japan. Under anaerobic conditions in these mats, interspecies interaction between sulfate-reducing bacteria as sulfide producers and C. aggregans as a sulfide consumer has been proposed to constitute a sulfur cycle; however, the electron donor utilized for microbial sulfide production at Nakabusa remains to be identified. In order to determine this electron donor and its source, ex situ experimental incubation of mats was explored. In the presence of molybdate, which inhibits biological sulfate reduction, hydrogen gas was released from mat samples, indicating that this hydrogen is normally consumed as an electron donor by sulfate-reducing bacteria. Hydrogen production decreased under illumination, indicating that C. aggregans also functions as a hydrogen consumer. Small amounts of hydrogen may have also been consumed for sulfur reduction. Clone library analysis of 16S rRNA genes amplified from the mats indicated the existence of several species of hydrogen-producing fermentative bacteria. Among them, the most dominant fermenter, Fervidobacterium sp., was successfully isolated. This isolate produced hydrogen through the fermentation of organic carbon. Dispersion of microbial cells in the mats resulted in hydrogen production without the addition of molybdate, suggesting that simultaneous production and consumption of hydrogen in the mats requires dense packing of cells. We propose a cyclic electron flow within the microbial mats, i.e., electron flow occurs through three elements: S (elemental sulfur, sulfide, sulfate), C (carbon dioxide, organic carbon) and H (di-hydrogen, protons). PMID:22446313

  3. Magnetic state selection in atomic frequency and time standards. [hydrogen masers

    NASA Technical Reports Server (NTRS)

    Peters, H. E.

    1982-01-01

    Atomic standards such as those based upon cesium and hydrogen rely upon magnetic state selection to obtain population inversion in the hyperfine transition levels. Use of new design approaches and improved magnetic materials has made it possible to fabricate improved state selectors of small size, and thus the efficiency of utilization of beam flux is greatly improved and the size and weight of the standard is reduced. The sensitivity to magnetic perturbations is also decreased, so that the accuracy and stability of the standard is improved. Several new state selector designs are illustrated and the application to standards utilizing different atomic species is analyzed.

  4. Nonadiabatic coupling in cold collisions of spin-polarized metastable hydrogen atoms

    SciTech Connect

    Forrey, Robert C.; Dalgarno, Alex; Vanne, Yulian V.; Saenz, Alejandro; Froelich, Piotr

    2007-11-15

    Previous calculations of low-temperature cross sections for collisions between spin-polarized metastable hydrogen atoms are improved to include nonadiabatic radial and angular coupling at large interatomic separations. The electrostatic dipole-quadrupole interaction produces nonadiabatic radial coupling between (2s,2p) and (2p,2p) states, while the Coriolis interaction produces nonadiabatic angular coupling. Both of these long-range contributions are handled in a space-fixed atomic gauge that is particularly convenient for a spin-polarized system. The improved theoretical results are compared with an existing experiment.

  5. Measurement of the absolute cross section for multiphoton ionization of atomic hydrogen at 248 nm

    SciTech Connect

    Kyrala, G.A.; Nichols, T.D.

    1990-01-01

    We present measurements of the absolute rates for multiphoton ionization of the ground state from atomic hydrogen by a linearly polarized, subpicosecond KrF laser pulse at a wavelength of 248 nm. A laser crossed atomic beam technique is used. The irradiance was varied from 3{times}10{sup 12} w/cm{sup 2} to 2{times}10{sup 14} w/cm{sup 2} and three above threshold ionization peaks were observed. The measured rate for total electron production is less than predicted by the numerical and perturbation calculations, but significantly higher than calculated by the Reiss and Keldysh methods. 21 refs., 7 figs.

  6. CHEMI-IONIZATION IN SOLAR PHOTOSPHERE: INFLUENCE ON THE HYDROGEN ATOM EXCITED STATES POPULATION

    SciTech Connect

    Mihajlov, Anatolij A.; Ignjatovic, Ljubinko M.; Sreckovic, Vladimir A.; Dimitrijevic, Milan S. E-mail: mihajlov@ipb.ac.rs

    2011-03-15

    In this paper, the influence of chemi-ionization processes in H*(n {>=} 2) + H(1s) collisions, as well as the influence of inverse chemi-recombination processes on hydrogen atom excited-state populations in solar photosphere, are compared with the influence of concurrent electron-atom and electron-ion ionization and recombination processes. It has been found that the considered chemi-ionization/recombination processes dominate over the relevant concurrent processes in almost the whole solar photosphere. Thus, it is shown that these processes and their importance for the non-local thermodynamic equilibrium modeling of the solar atmosphere should be investigated further.

  7. Calculation of harmonic generation during the multiphoton ionization of the hydrogen atom

    SciTech Connect

    DeVries, P.L. )

    1990-04-01

    The response of a hydrogen atom to an intense nonresonant laser field is investigated by direct numerical solution of the time-dependent Schroedinger equation. This calculation is nonperturbative and does not involve the eigenstates of the field-free atom. An ionization rate for three-photon ionization is calculated and found to be in excellent agreement with previous values. The time-dependent electric dipole moment is calculated; its Fourier transform yields the spectrum of scattered light. Odd-order harmonic peaks through at least the 25th order are present in the spectrum.

  8. Hydrogen atom abstraction from aldehydes - OH + H2CO and O + H2CO

    NASA Technical Reports Server (NTRS)

    Dupuis, M.; Lester, W. A., Jr.

    1984-01-01

    The essential features of the potential energy surfaces governing hydrogen abstraction from formaldehyde by oxygen atom and hydroxyl radical have been characterized with ab inito multiconfiguration Hartree-Fock (MCHF) and configuration interaction (CI) wave functions. The results are consistent with a very small activation energy for the OH + H2CO reaction, and an activation energy of a few kcal/mol for the O + H2CO reaction. In the transition state structure of both systems, the attacking oxygen atom is nearly collinear with the attacked CH bond.

  9. Nonadiabatic couplings in low-energy collisions of hydrogen ground-state atoms

    SciTech Connect

    Wolniewicz, L.

    2003-10-01

    The effect of nonadiabatic couplings on low-energy s-wave scattering of two hydrogen atoms is investigated. Coupling matrix elements are computed in a wide range of internuclear distances. The resulting scattering equations are numerically unstable and therefore are integrated only approximately. Computations are performed for H, D, and T atoms. The phase shifts in the zero velocity limit are inversely proportional to the nuclear reduced mass {delta}{sub 0}{approx_equal}0.392/{mu}. This leads to infinite scattering lengths.

  10. A fuzzy-atom analysis of electron delocalization on hydrogen bonds.

    PubMed

    Guillaumes, L; Salvador, P; Simon, S

    2014-02-13

    The extent of electron delocalization is quantified for set of cyclic complexes exhibiting two or more hydrogen bonds (HBs). In particular, the delocalization index (DI) between the atoms directly involved in the HB, and the ING (a normalized n-center delocalization index) have been evaluated using several fuzzy-atom schemes, namely Becke, Becke-ρ, Hirshfeld, and Hirshfeld-Iterative. The results have been compared with the widely used Quantum Theory of Atoms in Molecules (QTAIM) atomic definition. The DI values are found to correlate very well with geometrical or topological descriptors widely used in the literature to characterize HB systems. Among all fuzzy-atom methods, the ones that can better accommodate the different partial ionic character of the bonds perform particularly well. The best performing fuzzy-atom scheme for both pairwise and n-center electron delocalization is found to be the Becke-ρ method, for which similar results to QTAIM model are obtained with a much reduced computational cost. These results open up a wide range of applications of such electron delocalization descriptors based on fuzzy-atoms for noncovalent interactions in more complex and larger systems.

  11. A fuzzy-atom analysis of electron delocalization on hydrogen bonds.

    PubMed

    Guillaumes, L; Salvador, P; Simon, S

    2014-02-13

    The extent of electron delocalization is quantified for set of cyclic complexes exhibiting two or more hydrogen bonds (HBs). In particular, the delocalization index (DI) between the atoms directly involved in the HB, and the ING (a normalized n-center delocalization index) have been evaluated using several fuzzy-atom schemes, namely Becke, Becke-ρ, Hirshfeld, and Hirshfeld-Iterative. The results have been compared with the widely used Quantum Theory of Atoms in Molecules (QTAIM) atomic definition. The DI values are found to correlate very well with geometrical or topological descriptors widely used in the literature to characterize HB systems. Among all fuzzy-atom methods, the ones that can better accommodate the different partial ionic character of the bonds perform particularly well. The best performing fuzzy-atom scheme for both pairwise and n-center electron delocalization is found to be the Becke-ρ method, for which similar results to QTAIM model are obtained with a much reduced computational cost. These results open up a wide range of applications of such electron delocalization descriptors based on fuzzy-atoms for noncovalent interactions in more complex and larger systems. PMID:24444143

  12. Interstitial modification of palladium nanoparticles with boron atoms as a green catalyst for selective hydrogenation.

    PubMed

    Chan, Chun Wong Aaron; Mahadi, Abdul Hanif; Li, Molly Meng-Jung; Corbos, Elena Cristina; Tang, Chiu; Jones, Glenn; Kuo, Winson Chun Hsin; Cookson, James; Brown, Christopher Michael; Bishop, Peter Trenton; Tsang, Shik Chi Edman

    2014-01-01

    Lindlar catalysts comprising of palladium/calcium carbonate modified with lead acetate and quinoline are widely employed industrially for the partial hydrogenation of alkynes. However, their use is restricted, particularly for food, cosmetic and drug manufacture, due to the extremely toxic nature of lead, and the risk of its leaching from catalyst surface. In addition, the catalysts also exhibit poor selectivities in a number of cases. Here we report that a non-surface modification of palladium gives rise to the formation of an ultra-selective nanocatalyst. Boron atoms are found to take residence in palladium interstitial lattice sites with good chemical and thermal stability. This is favoured due to a strong host-guest electronic interaction when supported palladium nanoparticles are treated with a borane tetrahydrofuran solution. The adsorptive properties of palladium are modified by the subsurface boron atoms and display ultra-selectivity in a number of challenging alkyne hydrogenation reactions, which outclass the performance of Lindlar catalysts. PMID:25523894

  13. Oxygen atom kinetics in silane-hydrogen-nitrous oxide mixtures behind reflected shock waves

    NASA Astrophysics Data System (ADS)

    Javoy, S.; Mével, R.; Dupré, G.

    2010-11-01

    Resonance Absorption Spectroscopy has been used to study the O-atom dynamics behind reflected shock waves in highly argon diluted silane-hydrogen-nitrous oxide mixtures in the temperature range 1606-2528 K and at total pressures from 234 to 584 kPa. The absorptions at 130.5 nm of N 2O, SiH 4 and Si have been taken into account to compare simulated and experimental absorption profiles. A detailed kinetic model has been also used to interpret the results and reaction pathway and sensitivity analyses have been performed to underline important elementary reactions. A comparison with the O-atom kinetic in silane-nitrous oxide and hydrogen-nitrous oxide mixtures is also proposed.

  14. K-series X-ray yield measurement of kaonic hydrogen atoms in a gaseous target

    NASA Astrophysics Data System (ADS)

    Bazzi, M.; Beer, G.; Bellotti, G.; Berucci, C.; Bragadireanu, A. M.; Bosnar, D.; Cargnelli, M.; Curceanu, C.; Butt, A. D.; d'Uffizi, A.; Fiorini, C.; Ghio, F.; Guaraldo, C.; Hayano, R. S.; Iliescu, M.; Ishiwatari, T.; Iwasaki, M.; Levi Sandri, P.; Marton, J.; Okada, S.; Pietreanu, D.; Piscicchia, K.; Romero Vidal, A.; Sbardella, E.; Scordo, A.; Shi, H.; Sirghi, D. L.; Sirghi, F.; Tatsuno, H.; Vazquez Doce, O.; Widmann, E.; Zmeskal, J.

    2016-10-01

    We measured the K-series X-rays of the K- p exotic atom in the SIDDHARTA experiment with a gaseous hydrogen target of 1.3 g /l, which is about 15 times the ρSTP of hydrogen gas. At this density, the absolute yields of kaonic X-rays, when a negatively charged kaon stopped inside the target, were determined to be 0.012-0.003+0.004 for Kα and 0.043-0.011+0.012 for all the K-series transitions Ktot. These results, together with the KEK E228 experiment results, confirm for the first time a target density dependence of the yield predicted by the cascade models, and provide valuable information to refine the parameters used in the cascade models for the kaonic atoms.

  15. Catechols as Sources of Hydrogen Atoms in Radical Deiodination and Related Reactions.

    PubMed

    Povie, Guillaume; Ford, Leigh; Pozzi, Davide; Soulard, Valentin; Villa, Giorgio; Renaud, Philippe

    2016-09-01

    When used with trialkylboranes, catechol derivatives, which are low-cost and low toxicity, are valuable hydrogen atom donors for radical chain reactions involving alkyl iodides and related radical precursors. The system 4-tert-butylcatechol/triethylborane has been used to reduce a series of secondary and tertiary iodides, a xanthate, and a thiohydroxamate ester. Catechol derivatives are right in the optimal kinetic window for synthetic applications, as demonstrated by highly efficient radical cyclizations. Cyclizations leading to the formation of quaternary centers can be performed in an all-at-once process (no slow addition of the hydrogen atom donor) at standard concentrations. The H-donor properties of catechol derivatives can be fine-tuned by changing their substitution pattern. In slow radical cyclization processes, an enhanced ratio of cyclized/uncyclized products was obtained by using 3-methoxycatechol instead of 4-tert-butylcatechol.

  16. Interstitial modification of palladium nanoparticles with boron atoms as a green catalyst for selective hydrogenation

    NASA Astrophysics Data System (ADS)

    Chan, Chun Wong Aaron; Mahadi, Abdul Hanif; Li, Molly Meng-Jung; Corbos, Elena Cristina; Tang, Chiu; Jones, Glenn; Kuo, Winson Chun Hsin; Cookson, James; Brown, Christopher Michael; Bishop, Peter Trenton; Tsang, Shik Chi Edman

    2014-12-01

    Lindlar catalysts comprising of palladium/calcium carbonate modified with lead acetate and quinoline are widely employed industrially for the partial hydrogenation of alkynes. However, their use is restricted, particularly for food, cosmetic and drug manufacture, due to the extremely toxic nature of lead, and the risk of its leaching from catalyst surface. In addition, the catalysts also exhibit poor selectivities in a number of cases. Here we report that a non-surface modification of palladium gives rise to the formation of an ultra-selective nanocatalyst. Boron atoms are found to take residence in palladium interstitial lattice sites with good chemical and thermal stability. This is favoured due to a strong host-guest electronic interaction when supported palladium nanoparticles are treated with a borane tetrahydrofuran solution. The adsorptive properties of palladium are modified by the subsurface boron atoms and display ultra-selectivity in a number of challenging alkyne hydrogenation reactions, which outclass the performance of Lindlar catalysts.

  17. Proton scattering by a hydrogen atom in an effectively two-body model

    SciTech Connect

    Pupyshev, V. V.

    2013-02-15

    It is assumed that the total potential of proton interaction with a hydrogen atom is the sum of the short-range nuclear soft-core Reid potential and the long-range Thomas-Fermi potential. A quantum mechanical analysis of low-energy features of the phase shift and cross section for elastic proton scattering on a hydrogen atom is given for the case of zero total angular momentum. The calculations performed in the present study within a nonlinear version of the variable-phase approach ultimately revealed that, because of a long-range character of the asymptotic behavior of the Thomas-Fermi potential, the respective cross section at low energies oscillates but has a finite number of zeros.

  18. Deposition of device quality, low hydrogen content, hydrogenated amorphous silicon at high deposition rates with increased stability using the hot wire filament technique

    DOEpatents

    Molenbroek, Edith C.; Mahan, Archie Harvin; Gallagher, Alan C.

    2000-09-26

    A method or producing hydrogenated amorphous silicon on a substrate, comprising the steps of: positioning the substrate in a deposition chamber at a distance of about 0.5 to 3.0 cm from a heatable filament in the deposition chamber; maintaining a pressure in said deposition chamber in the range of about 10 to 100 millitorr and pressure times substrate-filament spacing in the range of about 10 to 100 millitorr-cm, heating the filament to a temperature in the range of about 1,500 to 2,000.degree. C., and heating the substrate to a surface temperature in the range of about 280 to 475.degree. C.; and flowing silicohydride gas into the deposition chamber with said heated filament, decomposing said silicohydride gas into silicon and hydrogen atomic species and allowing products of gas reactions between said atomic species and the silicohydride gas to migrate to and deposit on said substrate while adjusting and maintaining said pressure times substrate-filament spacing in said deposition chamber at a value in said 10 to 100 millitorr range to produce statistically about 3 to 50 atomic collisions between the silicon and hydrogen atomic species migrating to said substrate and undecomposed molecules of the silane or other silicohydride gas in the deposition chamber.

  19. Spectrum of the hydrogen atom in Snyder space in a semiclassical approximation

    NASA Astrophysics Data System (ADS)

    Ivetić, B.; Mignemi, S.; Samsarov, A.

    2016-03-01

    We study the spectrum of the hydrogen atom in Snyder space in a semiclassical approximation based on a generalization of the Born-Sommerfeld quantization rule. While the corrections to the standard quantum mechanical spectrum arise at first order in the Snyder parameter for the l =0 states, they are of second order for l ≠0 . This can be understood as due to the different topology of the regions of integration in phase space.

  20. Hydrogen atom donor compounds as contrast enhancers for black-and-white photothermographic and thermographic elements

    DOEpatents

    Harring, Lori S.; Simpson, Sharon M.; Sansbury, Francis H.

    1997-01-01

    Hydrogen atom donor compounds are useful as contrast enhancers when used in combination with (i) hindered phenol developers, and (ii) trityl hydrazide and/or formyl-phenyl hydrazine co-developers, to produce ultra-high contrast black-and-white photothermographic and thermographic elements. The photothermographic and thermographic elements may be used as a photomask in a process where there is a subsequent exposure of an ultraviolet or short wavelength visible radiation-sensitive imageable medium.

  1. Lamb shift in the hydrogen atom: Lifetime of the 2p{1/2}level

    SciTech Connect

    Karshenboim, S.G.

    1995-05-01

    Corrections of order {alpha}(Z{alpha}){sup 2} to the width of the 2p{1/2} level in the hydrogen atom are considered in the logarithmic approximation. The ratio of this width to the splitting of n=2 states can be measured to high accuracy. With the aid of the experimental data available for this ratio, the new value for the Lamb splitting is found to be 1057.8576(21) MHz. 17 refs.

  2. Distortion effects in electron excitation of hydrogen atoms by impact of heavy ions

    SciTech Connect

    Ramirez, C.A.; Rivarola, R.D.

    1995-12-01

    Electron excitation from the fundamental state of hydrogen atoms by impact of bare ions is studied at intermediate and high collision velocities. Total cross sections for final {ital np} states by impact of protons, alpha particles, and He{sup +} ions are calculated using the symmetric eikonal approximation and compared with experimental data. This comparison supports the existence of distortion effects recently predicted by Bugacov and co-workers [Phys. Rev. A {bold 47}, 1052 (1993)]. The validity of scaling laws is analyzed.

  3. Absolute rate of the reaction of hydrogen atoms with ozone from 219-360 K

    NASA Technical Reports Server (NTRS)

    Lee, J. H.; Michael, J. V.; Payne, W. A.; Stief, L. J.

    1978-01-01

    Absolute rate constants for the reaction of atomic hydrogen with ozone were obtained over the temperature range 219-360 K by the flash photolysis-resonance fluorescence technique. The results can be expressed in Arrhenius form by K = (1.33 plus or minus 0.32)x10 to the minus 10 power exp (-449 plus or minus 58/T) cu cm/molecule/s (two standard deviations). The present work is compared to two previous determinations and is discussed theoretically.

  4. Lower bounds to energies for cusped-gaussian wavefunctions. [hydrogen atom ground state

    NASA Technical Reports Server (NTRS)

    Eaves, J. O.; Walsh, B. C.; Steiner, E.

    1974-01-01

    Calculations for the ground states of H, He, and Be, conducted by Steiner and Sykes (1972), show that the inclusion of a very small number of cusp functions can lead to a substantial enhancement of the quality of the Gaussian basis used in molecular wavefunction computations. The properties of the cusped-Gaussian basis are investigated by a calculation of lower bounds concerning the ground state energy of the hydrogen atom.

  5. Effects of disorder on the correlation energy of rings of hydrogen atoms

    NASA Astrophysics Data System (ADS)

    Liegener, C.-M.; Ladik, J.

    1985-01-01

    The correlation energy of disordered systems has been calculated by means of second-order Rayleigh-Schrödinger perturbation theory in the M∅ller-Plesset partitioning. Rings of hydrogen atoms have been chosen as model systems and the degree of disorder has been varied from complete delocalization to complete localization of the one-particle states. The correlation energy was found to have an extremum at an intermediate degree of disorder, corresponding to incomplete localization.

  6. Tables of branching ratios for electric dipole transitions between arbitrary levels of hydrogen-like atoms

    NASA Technical Reports Server (NTRS)

    Omidvar, K.

    1977-01-01

    The branching ratios in hydrogen-like atoms due to the electric-dipole transitions are tabulated for the initial principal and azimuthal quantum numbers n prime l prime, and final principal and azimuthal quantum numbers n l. Average values with respect to l prime are given. The branching ratios not tabulated, including the initial states n prime yields infinity l prime corresponding to the threshold of the continuum, could be obtained by extrapolation.

  7. THE INFRARED SPECTRA OF POLYCYCLIC AROMATIC HYDROCARBONS WITH SOME OR ALL HYDROGEN ATOMS REMOVED

    SciTech Connect

    Bauschlicher, Charles W. Jr.; Ricca, Alessandra E-mail: Alessandra.Ricca-1@nasa.gov

    2013-10-20

    The loss of one hydrogen from C{sub 96}H{sub 24} does not significantly affect the infrared spectra of the neutral, cation, or anion. Excluding a very weak C-C stretching band at 5.1 μm, the loss of two adjacent duo hydrogens does not significantly affect the spectra compared with the parent. Removing all of the hydrogen atoms significantly increases the intensity of the new C-C stretching band, and, for the cation, shifts it to a longer (5.2 μm) wavelength. Observations show a feature near 5.25 μm, which has been attributed to overtone and combination bands from polycyclic aromatic hydrocarbons (PAHs). This current work suggests that dehydrogenated PAHs might also contribute to this band, but its weakness implies that fully dehydrogenated cationic or dicationic species are very rare.

  8. Absolute rate calculations: atom and proton transfers in hydrogen-bonded systems.

    PubMed

    Barroso, Mónica; Arnaut, Luis G; Formosinho, Sebastião J

    2005-02-01

    We calculate energy barriers of atom- and proton-transfer reactions in hydrogen-bonded complexes in the gas phase. Our calculations do not involve adjustable parameters and are based on bond-dissociation energies, ionization potentials, electron affinities, bond lengths, and vibration frequencies of the reactive bonds. The calculated barriers are in agreement with experimental data and high-level ab initio calculations. We relate the height of the barrier with the molecular properties of the reactants and complexes. The structure of complexes with strong hydrogen bonds approaches that of the transition state, and substantially reduces the barrier height. We calculate the hydrogen-abstraction rates in H-bonded systems using the transition-state theory with the semiclassical correction for tunneling, and show that they are in excellent agreement with the experimental data. H-bonding leads to an increase in tunneling corrections at room temperature. PMID:15751360

  9. Europa - Ultraviolet emissions and the possibility of atomic oxygen and hydrogen clouds

    NASA Technical Reports Server (NTRS)

    Wu, F.-M.; Judge, D. L.; Carlson, R. W.

    1978-01-01

    Emission signals from Europa with wavelength below 800 A were detected by the Pioneer 10 ultraviolet photometer. In the present paper, improved procedures for data reduction are used to determine the spatial region as well as the intensity of the suggested emission sources. The observations indicate a cloud with a radius of about 1.5 Jupiter radii and an apparent brightness of approximately 10 rayleighs for a wavelength of 500 A. It is argued that neutral oxygen atoms, along with neutral hydrogen, are produced through dissociation of water ice on the surface of Europa by particle impact. Electron impact ionization excitation of oxygen atoms in the resulting cloud then gives rise to the observed emission. The present source brightness and cloud radius results are used to estimate an oxygen column density of the order of 10 trillion per sq cm, while the density of atomic hydrogen is at most 100 billion per sq cm and 1 trillion per sq cm for molecular hydrogen.

  10. Polarized Atomic Hydrogen Beam Tests in the Michigan Ultra-Cold Jet Target

    NASA Astrophysics Data System (ADS)

    Kageya, T.; Blinov, B. B.; Denbow, J. M.; Kandes, M. C.; Krisch, A. D.; Kulkarni, D. A.; Lehman, M. A.; Luppov, V. G.; Morozov, V. S.; Murray, J. R.; Peters, C. C.; Raymond, R. S.; Ross, M. R.; Yonehara, K.; Borisov, N. S.; Fimushkin, V. V.; Kleppner, D.; Grishin, V. N.; Mysnik, A. L.

    2001-04-01

    To study spin effects in high energy collisions, we are developing an ultra-cold high-density jet target of proton-spin-polarized hydrogen atoms (Michigan Jet Target). The target uses a 12 Tesla magnetic field and a 0.3 K separation cell coated with superfluid helium-4 to produce a slow monochromatic electron-spin-polarized atomic hydrogen beam; an rf transition unit then converts this into a proton-spin-polarized beam, which is focused by a superconducting sextupole into the interaction region. The Jet produced, at the detector, a spin-polarized atomic hydrogen beam with a measured intensity of about 1.7 10^15 H s-1 and a FWHM area of less than 0.13 cm^2. This intensity corresponds to a free jet density of about 1.3 10^12 H cm-3 with a proton polarization of about 50%. When the transition RF unit is installed, we expect a proton polarization higher than 90%.

  11. Polarized Atomic Hydrogen Beam Tests in the Mark-II Ultra-Cold Jet Target.

    NASA Astrophysics Data System (ADS)

    Luppov, V. G.; Blinov, B. B.; Gladycheva, S. E.; Kageya, T.; Kantsyrev, D. Yu.; Krisch, A. D.; Murray, J. R.; Neumann, J. J.; Raymond, R. S.; Borisov, N. S.; Kleppner, D.; Davidenko, A. M.; Grishin, V. N.

    2000-04-01

    To study spin effects in high energy collisions, we are developing an ultra-cold high-density jet target of proton-spin-polarized hydrogen atoms (Mark-II). The target uses a 12 Tesla magnetic field and a 0.3 K separation cell coated with superfluid helium-4 to produce a slow monochromatic electron-spin-polarized atomic hydrogen beam; an rf transition unit then converts this into a proton-spin-polarized beam, which is focused by a superconducting sextupole into the interaction region. Recently, the Jet produced a measured electron-spin-polarized atomic hydrogen beam of about 10^15 H s-1 into a 0.3 cm^2 area at the detector. This intensity corresponds to the free jet density of about 10^11 H cm-3 with a proton polarization of about 50%. So far, the intensity is limited by the high insulation vacuum pressure due to the evaporation of the separation cell's helium film. The beam's angular and radial distributions were measured. A test of a new superfluid-^4He-coated parabolic mirror, attached to the separation cell, appeared to increase the beam intensity by a factor of about 3, as expected.

  12. Confinement effects of magnetic field on two-dimensional hydrogen atom in plasmas

    SciTech Connect

    Bahar, M. K.; Soylu, A.

    2015-05-15

    In this study, for the first time, the Schrödinger equation with more general exponential cosine screened Coulomb (MGECSC) potential is solved numerically in the presence and in the absence of an external magnetic field within two-dimensional formalism using the asymptotic iteration method. The MGECSC potential includes four different potential forms when considering different sets of the parameters in the potential. The plasma screening effects in the weak and strong magnetic field regimes as well as the confinement effects of magnetic field on the two-dimensional hydrogen atom in Debye and quantum plasmas are investigated by solving the corresponding equations. It is found that applying a uniform magnetic field on the hydrogen atom embedded in a plasma leads to change in the profile of the total interaction potential. Thus, confinement effects of magnetic field on hydrogen atom embedded in Debye and quantum plasmas modeled by a MGECSC potential lead to shift bound state energies. This effect would be important to isolate the plasma from the external environment in the experimental applications of plasma physics.

  13. Transport of atomic hydrogen through graphite and its reaction with azoaromatic compounds.

    PubMed

    Ye, Jianchang; Chiu, Pei C

    2006-06-15

    Graphite is a major non-iron component in commercial iron granules that are typically used for groundwater remediation. Recent studies suggest graphite inclusions in commercial iron may serve as both adsorption and reaction sites for nitrogenous pollutants such as nitroaromatics, nitrate esters, and heterocyclic nitramines. In this study, we investigated graphite-mediated reduction of azoaromatic compounds with elemental iron in dialysis cells, where azo compounds and iron were physically separated by graphite foil. Both the nonpolar azobenzene and the water-soluble orange G were reduced to aniline, suggesting that exposed graphite in granular iron may mediate reduction of both polar and nonpolar compounds. Orange G reduction was zero-order and commenced after a long initial lag. Both the lag time and the zero-order rate constant varied with graphite thickness, consistent with the explanation that orange G reduction was limited by atomic hydrogen, which was formed via anaerobic iron corrosion and spilled over to graphite. Involvement of atomic hydrogen was confirmed by detection of deuterated aniline when iron was placed in a D2O-based buffer. Our results indicate that atomic hydrogen is mobile in graphite at room temperature, is reactive toward azoaromatic compounds, and may be consumed during transport in graphite.

  14. Isotope Dependence and Quantum Effects on Atomic Hydrogen Diffusion in Liquid Water.

    PubMed

    Walker, J A; Mezyk, S P; Roduner, E; Bartels, D M

    2016-03-01

    Relative diffusion coefficients were determined in water for the D, H, and Mu isotopes of atomic hydrogen by measuring their diffusion-limited spin-exchange rate constants with Ni(2+) as a function of temperature. H and D atoms were generated by pulse radiolysis of water and measured by time-resolved pulsed EPR. Mu atoms are detected by muonium spin resonance. To isolate the atomic mass effect from solvent isotope effect, we measured all three spin-exchange rates in 90% D2O. The diffusion depends on the atomic mass, demonstrating breakdown of Stokes-Einstein behavior. The diffusion can be understood using a combination of water "cavity diffusion" and "hopping" mechanisms, as has been proposed in the literature. The H/D isotope effect agrees with previous modeling using ring polymer molecular dynamics. The "quantum swelling" effect on muonium due to its larger de Broglie wavelength does not seem to slow its "hopping" diffusion as much as predicted in previous work. Quantum effects of both the atom mass and the water librations have been modeled using RPMD and a qTIP4P/f quantized flexible water model. These results suggest that the muonium diffusion is very sensitive to the Mu versus water potential used.

  15. Revisiting the inelastic electron tunneling spectroscopy of single hydrogen atom adsorbed on the Cu(100) surface.

    PubMed

    Jiang, Zhuoling; Wang, Hao; Sanvito, Stefano; Hou, Shimin

    2015-12-21

    Inelastic electron tunneling spectroscopy (IETS) of a single hydrogen atom on the Cu(100) surface in a scanning tunneling microscopy (STM) configuration has been investigated by employing the non-equilibrium Green's function formalism combined with density functional theory. The electron-vibration interaction is treated at the level of lowest order expansion. Our calculations show that the single peak observed in the previous STM-IETS experiments is dominated by the perpendicular mode of the adsorbed H atom, while the parallel one only makes a negligible contribution even when the STM tip is laterally displaced from the top position of the H atom. This propensity of the IETS is deeply rooted in the symmetry of the vibrational modes and the characteristics of the conduction channel of the Cu-H-Cu tunneling junction, which is mainly composed of the 4s and 4pz atomic orbitals of the Cu apex atom and the 1s orbital of the adsorbed H atom. These findings are helpful for deepening our understanding of the propensity rules for IETS and promoting IETS as a more popular spectroscopic tool for molecular devices.

  16. Revisiting the inelastic electron tunneling spectroscopy of single hydrogen atom adsorbed on the Cu(100) surface

    SciTech Connect

    Jiang, Zhuoling; Wang, Hao; Sanvito, Stefano; Hou, Shimin

    2015-12-21

    Inelastic electron tunneling spectroscopy (IETS) of a single hydrogen atom on the Cu(100) surface in a scanning tunneling microscopy (STM) configuration has been investigated by employing the non-equilibrium Green’s function formalism combined with density functional theory. The electron-vibration interaction is treated at the level of lowest order expansion. Our calculations show that the single peak observed in the previous STM-IETS experiments is dominated by the perpendicular mode of the adsorbed H atom, while the parallel one only makes a negligible contribution even when the STM tip is laterally displaced from the top position of the H atom. This propensity of the IETS is deeply rooted in the symmetry of the vibrational modes and the characteristics of the conduction channel of the Cu-H-Cu tunneling junction, which is mainly composed of the 4s and 4p{sub z} atomic orbitals of the Cu apex atom and the 1s orbital of the adsorbed H atom. These findings are helpful for deepening our understanding of the propensity rules for IETS and promoting IETS as a more popular spectroscopic tool for molecular devices.

  17. Nonperturbative treatments of nonresonant multiphoton ionization of the hydrogen atom: weak field limit

    SciTech Connect

    Trombetta, F.; Basile, S.; Ferrante, G.

    1989-04-01

    A nonperturbative treatment of the multiphoton ionization of the hydrogen atom based on the S matrix and devised for nonresonant strong-field situations is analyzed in the weak-field limit. Comparisons are presented with other S matrices as well as other nonperturbative approaches. Our treatment is found to perform generally better than similar S-matrix treatments. The usual perturbative results are recovered provided that the photon wavelengths are sufficiently short and are off resonance with the atomic transitions. Important indications are obtained as to the role of the atomic structure, the relevance of the gauge consistency, and the reliability and improvement of the present nonperturbative treatment. The results represent a significant step toward an assessment of the S-matrix-based treatments of multiphoton ionization.

  18. Excited-state hydrogen-atom transfer along solvent wires: water molecules stop the transfer.

    PubMed

    Tanner, Christian; Thut, Markus; Steinlin, Andreas; Manca, Carine; Leutwyler, Samuel

    2006-02-01

    Excited-state hydrogen-atom transfer (ESHAT) along a hydrogen-bonded solvent wire occurs for the supersonically cooled n = 3 ammonia-wire cluster attached to the scaffold molecule 7-hydroxyquinoline (7HQ) [Tanner, C.; et al. Science 2003, 302, 1736]. Here, we study the analogous three-membered solvent-wire clusters 7HQ.(NH3)n.(H2O)m, n + m = 3, using resonant two-photon ionization (R2PI) and UV-UV hole-burning spectroscopies. Substitution of H2O for NH3 has a dramatic effect on the excited-state H-atom transfer: The threshold for the ESHAT reaction is approximately 200 cm(-1) for 7HQ.(NH3)3, approximately 350 cm(-1) for both isomers of the 7HQ.(NH3)2.H2O cluster, and approximately 600 cm(-1) for 7HQ.NH3.(H2O)2 but increases to approximately 2000 cm(-1) for the pure 7HQ.(H2O)3 water-wire cluster. To understand the effect of the chemical composition of the solvent wire on the H-atom transfer, the reaction profiles of the low-lying electronic excited states of the n = 3 pure and mixed solvent-wire clusters are calculated with the configuration interaction singles (CIS) method. For those solvent wires with an NH3 molecule at the first position, injection of the H atom into the wire can occur by tunneling. However, further H-atom transfer is blocked by a high barrier at the first (and second) H2O molecule along the solvent wire. H-atom transfer along the entire length of the solvent wire, leading to formation of the 7-ketoquinoline (7KQ) tautomer, cannot occur for any of the H2O-containing clusters, in agreement with experimentally observed absence of 7KQ fluorescence.

  19. Surface atomic relaxation and magnetism on hydrogen-adsorbed Fe(110) surfaces from first principles

    NASA Astrophysics Data System (ADS)

    Chohan, Urslaan K.; Jimenez-Melero, Enrique; Koehler, Sven P. K.

    2016-11-01

    We have computed adsorption energies, vibrational frequencies, surface relaxation and buckling for hydrogen adsorbed on a body-centred-cubic Fe(110) surface as a function of the degree of H coverage. This adsorption system is important in a variety of technological processes such as the hydrogen embrittlement in ferritic steels, which motivated this work, and the Haber-Bosch process. We employed spin-polarised density functional theory to optimise geometries of a six-layer Fe slab, followed by frozen mode finite displacement phonon calculations to compute Fe-H vibrational frequencies. We have found that the quasi-threefold (3f) site is the most stable adsorption site, with adsorption energies of ∼3.0 eV/H for all coverages studied. The long-bridge (lb) site, which is close in energy to the 3f site, is actually a transition state leading to the stable 3f site. The calculated harmonic vibrational frequencies collectively span from 730 to 1220 cm-1, for a range of coverages. The increased first-to-second layer spacing in the presence of adsorbed hydrogen, and the pronounced buckling observed in the Fe surface layer, may facilitate the diffusion of hydrogen atoms into the bulk, and therefore impact the early stages of hydrogen embrittlement in steels.

  20. Synthetic use of the primary kinetic isotope effect in hydrogen atom transfer: generation of α-aminoalkyl radicals.

    PubMed

    Wood, Mark E; Bissiriou, Sabine; Lowe, Christopher; Norrish, Andrew M; Sénéchal, Katell; Windeatt, Kim M; Coles, Simon J; Hursthouse, Michael B

    2010-10-21

    The extent to which deuterium can act as a protecting group to prevent unwanted 1,5-hydrogen atom transfer to aryl and vinyl radical intermediates was examined in the context of the generation of α-aminoalkyl radicals in a pyrrolidine ring. Intra- and intermolecular radical trapping following hydrogen atom transfer provides an illustration of the use of the primary kinetic isotope effect in directing the outcome of synthetic C-C bond-forming processes.

  1. The constitution of the atmospheric layers and the extreme ultraviolet spectrum of hot hydrogen-rich white dwarfs

    NASA Technical Reports Server (NTRS)

    Vennes, Stephane

    1992-01-01

    An analysis is presented of the atmospheric properties of hot, H-rich, DA white dwarfs that is based on optical, UV, and X-ray observations aimed at predicting detailed spectral properties of these stars in the range 80-800 A. The divergences between observations from a sample of 15 hot DA white dwarfs emitting in the EUV/soft X-ray range and pure H synthetic spectra calculated from a grid of model atmospheres characterized by Teff and g are examined. Seven out of 15 DA stars are found to consistently exhibit pure hydrogen atmospheres, the remaining seven stars showing inconsistency between FUV and EUV/soft X-ray data that can be explained by the presence of trace EUV/soft X-ray absorbers. Synthetic data are computed assuming two other possible chemical structures: photospheric traces of radiatively levitated heavy elements and a stratified hydrogen/helium distribution. Predictions about forthcoming medium-resolution observations of the EUV spectrum of selected hot H-rich white dwarfs are made.

  2. Selective hydrogenation of 1,3-butadiene on platinum–copper alloys at the single-atom limit

    PubMed Central

    Lucci, Felicia R.; Liu, Jilei; Marcinkowski, Matthew D.; Yang, Ming; Allard, Lawrence F.; Flytzani-Stephanopoulos, Maria; Sykes, E. Charles H.

    2015-01-01

    Platinum is ubiquitous in the production sectors of chemicals and fuels; however, its scarcity in nature and high price will limit future proliferation of platinum-catalysed reactions. One promising approach to conserve platinum involves understanding the smallest number of platinum atoms needed to catalyse a reaction, then designing catalysts with the minimal platinum ensembles. Here we design and test a new generation of platinum–copper nanoparticle catalysts for the selective hydrogenation of 1,3-butadiene,, an industrially important reaction. Isolated platinum atom geometries enable hydrogen activation and spillover but are incapable of C–C bond scission that leads to loss of selectivity and catalyst deactivation. γ-Alumina-supported single-atom alloy nanoparticle catalysts with <1 platinum atom per 100 copper atoms are found to exhibit high activity and selectivity for butadiene hydrogenation to butenes under mild conditions, demonstrating transferability from the model study to the catalytic reaction under practical conditions. PMID:26449766

  3. Selective hydrogenation of 1,3-butadiene on platinum–copper alloys at the single-atom limit

    SciTech Connect

    Lucci, Felicia R.; Liu, Jilei; Marcinkowski, Matthew D.; Yang, Ming; Allard, Lawrence F.; Flytzani-Stephanopoulos, Maria; Sykes, E. Charles H.

    2015-10-09

    Platinum is ubiquitous in the production sectors of chemicals and fuels; however, its scarcity in nature and high price will limit future proliferation of platinum-catalysed reactions. One definite approach to conserve platinum involves understanding the smallest number of platinum atoms needed to catalyse a reaction, then designing catalysts with the minimal platinum ensembles. Here we design and test a new generation of platinum–copper nanoparticle catalysts for the selective hydrogenation of 1,3-butadiene,, an industrially important reaction. Isolated platinum atom geometries enable hydrogen activation and spillover but are incapable of C–C bond scission that leads to loss of selectivity and catalyst deactivation. γ-Alumina-supported single-atom alloy nanoparticle catalysts with <1 platinum atom per 100 copper atoms are found to exhibit high activity and selectivity for butadiene hydrogenation to butenes under mild conditions, demonstrating transferability from the model study to the catalytic reaction under practical conditions.

  4. Selective hydrogenation of 1,3-butadiene on platinum-copper alloys at the single-atom limit

    NASA Astrophysics Data System (ADS)

    Lucci, Felicia R.; Liu, Jilei; Marcinkowski, Matthew D.; Yang, Ming; Allard, Lawrence F.; Flytzani-Stephanopoulos, Maria; Sykes, E. Charles H.

    2015-10-01

    Platinum is ubiquitous in the production sectors of chemicals and fuels; however, its scarcity in nature and high price will limit future proliferation of platinum-catalysed reactions. One promising approach to conserve platinum involves understanding the smallest number of platinum atoms needed to catalyse a reaction, then designing catalysts with the minimal platinum ensembles. Here we design and test a new generation of platinum-copper nanoparticle catalysts for the selective hydrogenation of 1,3-butadiene,, an industrially important reaction. Isolated platinum atom geometries enable hydrogen activation and spillover but are incapable of C-C bond scission that leads to loss of selectivity and catalyst deactivation. γ-Alumina-supported single-atom alloy nanoparticle catalysts with <1 platinum atom per 100 copper atoms are found to exhibit high activity and selectivity for butadiene hydrogenation to butenes under mild conditions, demonstrating transferability from the model study to the catalytic reaction under practical conditions.

  5. Selective hydrogenation of 1,3-butadiene on platinum-copper alloys at the single-atom limit.

    PubMed

    Lucci, Felicia R; Liu, Jilei; Marcinkowski, Matthew D; Yang, Ming; Allard, Lawrence F; Flytzani-Stephanopoulos, Maria; Sykes, E Charles H

    2015-01-01

    Platinum is ubiquitous in the production sectors of chemicals and fuels; however, its scarcity in nature and high price will limit future proliferation of platinum-catalysed reactions. One promising approach to conserve platinum involves understanding the smallest number of platinum atoms needed to catalyse a reaction, then designing catalysts with the minimal platinum ensembles. Here we design and test a new generation of platinum-copper nanoparticle catalysts for the selective hydrogenation of 1,3-butadiene,, an industrially important reaction. Isolated platinum atom geometries enable hydrogen activation and spillover but are incapable of C-C bond scission that leads to loss of selectivity and catalyst deactivation. γ-Alumina-supported single-atom alloy nanoparticle catalysts with <1 platinum atom per 100 copper atoms are found to exhibit high activity and selectivity for butadiene hydrogenation to butenes under mild conditions, demonstrating transferability from the model study to the catalytic reaction under practical conditions. PMID:26449766

  6. Formation of metastable atomic hydrogen in the 2s state from symmetry-resolved doubly excited states of molecular hydrogen

    SciTech Connect

    Odagiri, Takeshi; Kumagai, Yoshiaki; Nakano, Motoyoshi; Tanabe, Takehiko; Kitajima, Masashi; Kouchi, Noriyuki; Suzuki, Isao H.

    2011-11-15

    The cross sections for the formation of the metastable atomic hydrogen in the 2s state in photoexcitation of H{sub 2} and D{sub 2} were measured as a function of the incident photon energy in the range of the doubly excited states with their symmetries of the electronic states, {sup 1}{Sigma}{sub u}{sup +} or {sup 1}{Pi}{sub u}, being resolved. It has turned out from the comparison with the cross-section curves for other dissociation processes and the theoretical calculation [J. D. Bozek et al., J. Phys. B 39, 4871 (2006)] that the Q{sub 2}{sup 1}{Pi}{sub u}(1) doubly excited state of H{sub 2} dissociates into both H(2s) + H(2p) and H(2p) + H(2p). The dissociation dynamics of this state has been discussed in terms of the nonadiabatic transition during neutral dissociations.

  7. A Guided-Inquiry Lab for the Analysis of the Balmer Series of the Hydrogen Atomic Spectrum

    ERIC Educational Resources Information Center

    Bopegedera, A. M. R. P.

    2011-01-01

    A guided-inquiry lab was developed to analyze the Balmer series of the hydrogen atomic spectrum. The emission spectrum of hydrogen was recorded with a homemade benchtop spectrophotometer. By drawing graphs and a trial-and-error approach, students discover the linear relationship presented in the Rydberg formula and connect it with the Bohr model…

  8. Efficient epoxidation of a terminal alkene containing allylic hydrogen atoms: trans-methylstyrene on Cu{111}.

    PubMed

    Cropley, Rachael L; Williams, Federico J; Urquhart, Andrew J; Vaughan, Owain P H; Tikhov, Mintcho S; Lambert, Richard M

    2005-04-27

    The selective oxidation of trans-methylstyrene, a phenyl-substituted propene that contains labile allylic hydrogen atoms, has been studied on Cu{111}. Mass spectrometry and synchrotron fast XPS were used to detect, respectively, desorbing gaseous products and the evolution of surface species as a function of temperature and time. Efficient partial oxidation occurs yielding principally the epoxide, and the behavior of the system is sensitive to the order in which reactants are adsorbed. The latter is understandable in terms of differences in the spatial distribution of oxygen adatoms; isolated adatoms lead to epoxidation, while islands of "oxidic" oxygen do not. NEXAFS data taken over a range of coverages and in the presence and absence of coadsorbed oxygen indicate that the adsorbed alkene lies essentially flat with the allylic hydrogen atoms close to the surface. The photoemission results and comparison with the corresponding behavior of styrene on Cu{111} strongly suggest that allylic hydrogen abstraction is indeed a critical factor that limits epoxidation selectivity. An overall mechanism consistent with the structural and reactive properties is proposed.

  9. Stable isolated metal atoms as active sites for photocatalytic hydrogen evolution.

    PubMed

    Xing, Jun; Chen, Jian Fu; Li, Yu Hang; Yuan, Wen Tao; Zhou, Ying; Zheng, Li Rong; Wang, Hai Feng; Hu, P; Wang, Yun; Zhao, Hui Jun; Wang, Yong; Yang, Hua Gui

    2014-02-17

    The process of using solar energy to split water to produce hydrogen assisted by an inorganic semiconductor is crucial for solving our energy crisis and environmental problems in the future. However, most semiconductor photocatalysts would not exhibit excellent photocatalytic activity without loading suitable co-catalysts. Generally, the noble metals have been widely applied as co-catalysts, but always agglomerate during the loading process or photocatalytic reaction. Therefore, the utilization efficiency of the noble co-catalysts is still very low on a per metal atom basis if no obvious size effect exists, because heterogeneous catalytic reactions occur on the surface active atoms. Here, for the first time, we have synthesized isolated metal atoms (Pt, Pd, Rh, or Ru) stably by anchoring on TiO2 , a model photocatalystic system, by a facile one-step method. The isolated metal atom based photocatalysts show excellent stability for H2 evolution and can lead to a 6-13-fold increase in photocatalytic activity over the metal clusters loaded on TiO2 by the traditional method. Furthermore, the configurations of isolated atoms as well as the originality of their unusual stability were analyzed by a collaborative work from both experiments and theoretical calculations.

  10. Density functional study of manganese atom adsorption on hydrogen-terminated armchair boron nitride nanoribbons

    NASA Astrophysics Data System (ADS)

    Abdullahi, Yusuf Zuntu; Rahman, Md. Mahmudur; Shuaibu, Alhassan; Abubakar, Shamsu; Zainuddin, Hishamuddin; Muhida, Rifki; Setiyanto, Henry

    2014-08-01

    In this paper, we have investigated stable structural, electric and magnetic properties of manganese (Mn) atom adsorption on armchair hydrogen edge-terminated boron nitride nanoribbon (A-BNNRs) using first principles method based on density-functional theory with the generalized gradient approximation. Calculation shows that Mn atom situated on the ribbons of A-BNNRs is the most stable configuration, where the bonding is more pronounced. The projected density of states (PDOS) of the favored configuration has also been computed. It has been found that the covalent bonding of boron (B), nitrogen (N) and Mn is mainly contributed by s, d like-orbitals of Mn and partially occupied by the 2p like-orbital of N. The difference in energy between the inner and the edge adsorption sites of A-BNNRs shows that Mn atoms prefer to concentrate at the edge sites. The electronic structures of the various configurations are wide, narrow-gap semiconducting and half-metallic, and the magnetic moment of Mn atoms are well preserved in all considered configurations. This has shown that the boron nitride (BN) sheet covered with Mn atoms demonstrates additional information on its usefulness in future spintronics, molecular magnet and nanoelectronics devices.

  11. The Absolute Rates of the Solution Phase Addition of Atomic Hydrogen to a Vinyl Ether and a Vinyl Ester. The Effect of Oxygen Substitution on Hydrogen Atom Reactivity with Olefins

    SciTech Connect

    Tanner, D. D.; Kandanarachchi, P.; Das, N. C.; Franz, James A.

    2003-04-08

    The reactions of vinyl butyl ether and vinyl butyrate with atomic hydrogen and deuterium lead to addition of atomic hydrogen to the terminal position of the olefins. This observation is consistent with the reactions carried out earlier with other olefins. Both the absolute rates of addition to vinylbutyl ether and vinyl butyrate in acetone and hexane were carried out at several temperatures. The relative rates are consistent with only modest stabilization of the transition state of the radical adduct by the ??-o substituent compared with hydrogen atom addition to 1-octene. The relative rates measured in acetone and hexane indicate no significant differential solvation of ground state relative to the transition structures of the hydrogen atom addition. The kinetics reveal that the early transition states of hydrogen atom addition exhibit little selectivity (vinyl ether versus simple olefin) in either abstraction of hydrogen ??- to the oxygen or by terminal addition to the olefinic ether, reflecting the modest influence of the increased enthalpy of reaction associated with resonance stabilization by the oxygen substituent at the developing radical site.

  12. Hot Electrons at Solid-Liquid Interfaces: A Large Chemoelectric Effect during the Catalytic Decomposition of Hydrogen Peroxide.

    PubMed

    Nedrygailov, Ievgen I; Lee, Changhwan; Moon, Song Yi; Lee, Hyosun; Park, Jeong Young

    2016-08-26

    The study of energy and charge transfer during chemical reactions on metals is of great importance for understanding the phenomena involved in heterogeneous catalysis. Despite extensive studies, very little is known about the nature of hot electrons generated at solid-liquid interfaces. Herein, we report remarkable results showing the detection of hot electrons as a chemicurrent generated at the solid-liquid interface during decomposition of hydrogen peroxide (H2 O2 ) catalyzed on Schottky nanodiodes. The chemicurrent reflects the activity of the catalytic reaction and the state of the catalyst in real time. We show that the chemicurrent yield can reach values up to 10(-1) electrons/O2 molecule, which is notably higher than that for solid-gas reactions on similar nanodiodes.

  13. Exposure of GaAs to atomic hydrogen for cleaning prior to NEA photocathode activation

    SciTech Connect

    Sinclair, C.K.; Poelker, B.M.; Price, J.S.

    1998-12-31

    Creating an atomically clean semiconductor surface is an essential step in preparing negative electron affinity (NEA) photoemission cathodes. While bulk GaAs can be satisfactorily cleaned by chemical etching and in situ heat cleaning, many high polarization electron source materials are either much too thin, or have oxides and carbides which are too tightly bound, to be cleaned by these methods. Some polarized source candidate materials may be degraded during the heat cleaning step. It is well established that the exposure of many III-V, II-VI, and elemental semiconductors to atomic hydrogen, typically at elevated temperatures, produces semiconductor surfaces free of contamination. Furthermore, this cleaning, possibly followed by thermal annealing, leaves surfaces which show sharp LEED patterns, indicating good stoichiometry and surface order. Atomic hydrogen cleaning should eliminate the chemical etching step, and might reduce the temperature and/or temperature-time product presently used in forming NEA cathodes. The process is readily adaptable to in situ use in ultrahigh vaccum.

  14. Antiradical power of carotenoids and vitamin E: testing the hydrogen atom transfer mechanism.

    PubMed

    Martínez, Ana; Barbosa, Andrés

    2008-12-25

    The antiradical capacities of 13 carotenoids (CAR) and vitamin E are explored, by assessing CAR-H bond dissociation energy. Density functional theory (DFT) calculations were performed, in order to evaluate the hydrogen atom transfer (HAT) antiradical mechanism. Results indicate that C4 or C4' is not always the reactive position when it is unsubstituted and also that CAR without H atoms in the 4 position may be as effective against free radicals as other CAR with H atoms in C4 and C4'. Lutein is the most effective antiradical for the purpose of hydrogen abstraction, whereas the least effective antiradical for this process is canthaxanthin, which is one of the reddest CAR. Vitamin E is not as effective as most of the yellow CAR but may be a better antiradical than canthaxanthin. In addition to the CAR-H bond dissociation energy, the number of reactive positions as we report in this paper represents another important aspect for consideration, when analyzing capacity for scavenging free radicals. Many additional aspects exist, which we do not consider here; thus we cannot attempt to reflect all the factors seen in vivo. However, our results provide comparative information on the relative ability of CAR to protect against free radicals, using the CAR-H bond dissociation energy, as one useful parameter. We hope that our theoretical results will contribute to the advancement of this complex research field.

  15. Hydrogen atom transfer reactions in thiophenol: photogeneration of two new thione isomers.

    PubMed

    Reva, Igor; Nowak, Maciej J; Lapinski, Leszek; Fausto, Rui

    2015-02-21

    Photoisomerization reactions of monomeric thiophenol have been investigated for the compound isolated in low-temperature argon matrices. The initial thiophenol population consists exclusively of the thermodynamically most stable thiol form. Phototransformations were induced by irradiation of the matrices with narrowband tunable UV light. Irradiation at λ > 290 nm did not induce any changes in isolated thiophenol molecules. Upon irradiation at 290-285 nm, the initial thiol form of thiophenol converted into its thione isomer, cyclohexa-2,4-diene-1-thione. This conversion occurs by transfer of an H atom from the SH group to a carbon atom at the ortho position of the ring. Subsequent irradiation at longer wavelengths (300-427 nm) demonstrated that this UV-induced hydrogen-atom transfer is photoreversible. Moreover, upon irradiation at 400-425 nm, the cyclohexa-2,4-diene-1-thione product converts, by transfer of a hydrogen atom from the ortho to para position, into another thione isomer, cyclohexa-2,5-diene-1-thione. The latter thione isomer is also photoreactive and is consumed if irradiated at λ < 332 nm. The obtained results clearly show that H-atom-transfer isomerization reactions dominate the unimolecular photochemistry of thiophenol confined in a solid argon matrix. A set of low-intensity infrared bands, observed in the spectra of UV irradiated thiophenol, indicates the presence of a phenylthiyl radical with an H- atom detached from the SH group. Alongside the H-atom-transfer and H-atom-detachment processes, the ring-opening photoreaction occurred in cyclohexa-2,4-diene-1-thione by the cleavage of the C-C bond at the alpha position with respect to the thiocarbonyl C[double bond, length as m-dash]S group. The resulting open-ring conjugated thioketene adopts several isomeric forms, differing by orientations around single and double bonds. The species photogenerated upon UV irradiation of thiophenol were identified by comparison of their experimental infrared

  16. Multiply Confined Nickel Nanocatalysts Produced by Atomic Layer Deposition for Hydrogenation Reactions.

    PubMed

    Gao, Zhe; Dong, Mei; Wang, Guizhen; Sheng, Pei; Wu, Zhiwei; Yang, Huimin; Zhang, Bin; Wang, Guofu; Wang, Jianguo; Qin, Yong

    2015-07-27

    To design highly efficient catalysts, new concepts for optimizing the metal-support interactions are desirable. Here we introduce a facile and general template approach assisted by atomic layer deposition (ALD), to fabricate a multiply confined Ni-based nanocatalyst. The Ni nanoparticles are not only confined in Al2 O3 nanotubes, but also embedded in the cavities of Al2 O3 interior wall. The cavities create more Ni-Al2 O3 interfacial sites, which facilitate hydrogenation reactions. The nanotubes inhibit the leaching and detachment of Ni nanoparticles. Compared with the Ni-based catalyst supported on the outer surface of Al2 O3 nanotubes, the multiply confined catalyst shows a striking improvement of catalytic activity and stability in hydrogenation reactions. Our ALD-assisted template method is general and can be extended for other multiply confined nanoreactors, which may have potential applications in many heterogeneous reactions.

  17. Compact solid-state laser source for 1S-2S spectroscopy in atomic hydrogen

    SciTech Connect

    Kolachevsky, N.; Alnis, J.; Bergeson, S. D.; Haensch, T. W.

    2006-02-15

    We demonstrate a compact solid-state laser source for high-resolution two-photon spectroscopy of the 1S-2S transition in atomic hydrogen. The source emits up to 20 mW at 243 nm and consists of a 972 nm diode laser, a tapered amplifier, and two doubling stages. The diode laser is actively stabilized to a high-finesse cavity. We compare the new source to the stable 486 nm dye laser used in previous experiments and record 1S-2S spectra using both systems. With the solid-state laser system, we demonstrate a resolution of the hydrogen spectrometer of 6x10{sup 11}, which is promising for a number of high-precision measurements in hydrogenlike systems.

  18. Atom-economical synthesis of γ-valerolactone with self-supplied hydrogen from methanol.

    PubMed

    Li, Zheng; Tang, Xing; Jiang, Yetao; Wang, Yanjun; Zuo, Miao; Chen, Wei; Zeng, Xianhai; Sun, Yong; Lin, Lu

    2015-11-25

    γ-Valerolactone (GVL), a versatile biomass derived platform molecule, was synthesized with a highest yield of 89.8% from methyl levulinate (ML) using self-supplied H2 coming from the decomposition of MeOH derived partially from ML. Cu-Cr acted as a bi-functional catalyst for both H2 production from MeOH and carbonyl hydrogenation. An extremely low amount of MeOH (29 mol% relative to ML) was initially necessary to start up the hydrocyclization of ML to GVL and MeOH, which is in turn employed as an in situ H2 source for ML hydrogenation, providing an atom-economical pathway for GVL production. PMID:26403664

  19. Exact nonrelativistic polarizabilities of the hydrogen atom with the Lagrange-mesh method

    NASA Astrophysics Data System (ADS)

    Baye, Daniel

    2012-12-01

    Exact analytical expressions of the dipole polarizabilities of the nonrelativistic hydrogen atom in spherical coordinates are derived with the help of the Lagrange-mesh numerical method. This method can provide exact energies and wave functions for well-chosen conditions of calculation. Exact dipole polarizabilities are obtained after an unambiguous rounding up to at least principal quantum numbers around n=30. The scalar polarizability of any nl level is given by n4[4n2+14+7l(l+1)]/4 and its tensor polarizability is given by -n4[3n2-9+11l(l+1)]l/4(2l+3), which allows the calculation of the polarizability of any hydrogen state nlm.

  20. A Hydrogen Peroxide Hot-Jet Simulator for Wind-Tunnel Tests of Turbojet-Exit Models

    NASA Technical Reports Server (NTRS)

    Runckel, Jack F.; Swihart, John M.

    1959-01-01

    A turbojet-engine-exhaust simulator which utilizes a hydrogen peroxide gas generator has been developed for powered-model testing in wind tunnels with air exchange. Catalytic decomposition of concentrated hydrogen peroxide provides a convenient and easily controlled method of providing a hot jet with characteristics that correspond closely to the jet of a gas turbine engine. The problems associated with simulation of jet exhausts in a transonic wind tunnel which led to the selection of a liquid monopropellant are discussed. The operation of the jet simulator consisting of a thrust balance, gas generator, exit nozzle, and auxiliary control system is described. Static-test data obtained with convergent nozzles are presented and shown to be in good agreement with ideal calculated values.

  1. Activation of extended red emission photoluminescence in carbon solids by exposure to atomic hydrogen and UV radiation

    NASA Technical Reports Server (NTRS)

    Furton, Douglas G.; Witt, Adolf N.

    1993-01-01

    We report on new laboratory results which relate directly to the observation of strongly enhanced extended red emission (ERE) by interstellar dust in H2 photodissociation zones. The ERE has been attributed to photoluminescence by hydrogenated amorphous carbon (HAC). We are demonstrating that exposure to thermally dissociated atomic hydrogen will restore the photoluminescence efficiency of previously annealed HAC. Also, pure amorphous carbon (AC), not previously photoluminescent, can be induced to photoluminesce by exposure to atomic hydrogen. This conversion of AC into HAC is greatly enhanced by the presence of UV irradiation. The presence of dense, warm atomic hydrogen and a strong UV radiation field are characteristic environmental properties of H2 dissociation zones. Our results lend strong support to the HAC photoluminescence explanation for ERE.

  2. Interaction of atomic hydrogen with anthracene and polyacene from density functional theory

    NASA Astrophysics Data System (ADS)

    Ferullo, Ricardo M.; Castellani, Norberto J.; Belelli, Patricia G.

    2016-03-01

    The interaction of atomic hydrogen with two linear polycyclic aromatic hydrocarbons (PAHs), anthracene and polyacene (the polymer of benzene), was studied within the density functional theory (DFT). Using a proper dispersion-corrected method (DFT-D) the preferential physisorption sites were explored. The activation barrier for the bond formation between a peripheral C and the incoming H was calculated to be 58.5 and 34.1 meV with pure DFT on anthracene and polyacene at its antiferromagnetic ground state, respectively. DFT-D, although improves the description of the physisorbed state, tends to underestimate the chemisorption barriers due an artifact arising from the dispersion correction.

  3. Reaction of O/sup +/, CO/sup +/, and CH/sup +/ ions with atomic hydrogen

    SciTech Connect

    Federer, W.; Villinger, H.; Howorka, F.; Lindinger, W.; Tosis, P.; Bassi, D.; Ferguson, E.

    1984-06-04

    Rate coefficients for reactions of the ions O/sup +/, CO/sup +/, and CH/sup +/ with atomic hydrogen have been measured for the first time at 300 K. This provides basic data for the ion chemistry of planetary atmospheres, cometary atmospheres, and interstellar molecular clouds. The O/sup +/+H measurement supports quantal calculations of this reaction. The CO/sup +/+H reaction provides an example of partial spin nonconservation in a charge-transfer reaction occurring in a deep potential well. Reactions of the same ions with H/sub 2/ that have been measured elsewhere are also reported.

  4. Traces of Lorentz symmetry breaking in a hydrogen atom at ground state

    NASA Astrophysics Data System (ADS)

    Borges, L. H. C.; Barone, F. A.

    2016-02-01

    Some traces of a specific Lorentz symmetry breaking scenario in the ground state of the hydrogen atom are investigated. We use standard Rayleigh-Schrödinger perturbation theory in order to obtain the corrections to the ground state energy and the wave function. It is shown that an induced four-pole moment arises, due to the Lorentz symmetry breaking. The model considered is the one studied in Borges et al. (Eur Phys J C 74:2937, 2014), where the Lorentz symmetry is broken in the electromagnetic sector.

  5. Hydrogen Gas Sensors Fabricated on Atomically Flat 4H-SiC Webbed Cantilevers

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Spry, David J.; Trunek, Andrew J.; Evans, Laura J.; Chen, Liang-Yu; Hunter, Gary W.; Androjna, Drago

    2007-01-01

    This paper reports on initial results from the first device tested of a "second generation" Pt-SiC Schottky diode hydrogen gas sensor that: 1) resides on the top of atomically flat 4H-SiC webbed cantilevers, 2) has integrated heater resistor, and 3) is bonded and packaged. With proper selection of heater resistor and sensor diode biases, rapid detection of H2 down to concentrations of 20 ppm was achieved. A stable sensor current gain of 125 +/- 11 standard deviation was demonstrated during 250 hours of cyclic test exposures to 0.5% H2 and N2/air.

  6. Relativistic corrections for screening effects on the energies of hydrogen-like atoms embedded in plasmas

    SciTech Connect

    Poszwa, A.; Bahar, M. K.

    2015-01-15

    The influence of relativistic and plasma screening effects on energies of hydrogen-like atoms embedded in plasmas has been studied. The Dirac equation with a more general exponential cosine screened potential has been solved numerically and perturbatively, by employing the direct perturbation theory. Properties of spectra corresponding to bound states and to different sets of the potential parameters have been studied both in nonrelativistic and relativistic approximations. Binding energies, fine-structure splittings, and relativistic energy shifts have been determined as functions of parameters of the potential. The results have been compared with the ones known from the literature.

  7. The Anomalous Zeeman Effect for the Hydrogen Atom in Noncommutative Space

    NASA Astrophysics Data System (ADS)

    Santos, Willien O.; Souza, Andre M. C.

    2012-12-01

    The Hamiltonian describing an anomalous Zeeman effect for the hydrogen atom on noncommutative space is studied using a Bopp's shift. Using first order perturbation theory, the correction to the energy is calculated for the case of a weak external magnetic field. We also obtained the orbital and spin g-factors in noncommutative space. We show that the experimental values for the orbital and spin g-factors put an upper bound on the magnitude of the parameter of noncommutativity of the order of, respectively, Θ≤(8 GeV)-2 and Θ≤(0.01 GeV)-2.

  8. Phase transition into the metallic state in hypothetical (without molecules) dense atomic hydrogen

    SciTech Connect

    Khomkin, A. L. Shumikhin, A. S.

    2013-10-15

    A simple physical model of the metal-dielectric (vapor-liquid) phase transition in hypothetical (without molecules) atomic hydrogen is proposed. The reason for such a transition is the quantum collective cohesive energy occurring due to quantum electron-electron exchange similar to the cohesive energy in the liquid-metal phase of alkali metals. It is found that the critical parameters of the transition are P{sub c} ∼ 41000 atm, ρ{sub c} ∼ 0.1 g/cm{sup 3}, and T{sub c} ∼ 9750 K.

  9. Exposure of epitaxial graphene on SiC(0001) to atomic hydrogen.

    PubMed

    Guisinger, Nathan P; Rutter, Gregory M; Crain, Jason N; First, Phillip N; Stroscio, Joseph A

    2009-04-01

    Graphene films on SiC exhibit coherent transport properties that suggest the potential for novel carbon-based nanoelectronics applications. Recent studies suggest that the role of the interface between single layer graphene and silicon-terminated SiC can strongly influence the electronic properties of the graphene overlayer. In this study, we have exposed the graphitized SiC to atomic hydrogen in an effort to passivate dangling bonds at the interface, while investigating the results utilizing room temperature scanning tunneling microscopy.

  10. Atomic and ionic spectrum lines below 2000A: hydrogen through argon

    SciTech Connect

    Kelly, R.L.

    1982-10-01

    A critical tabulation of observed spectral lines below 2000 angstroms has been prepared from the published literature up to July 1978. It is intended principally as an aid to those physicists and astronomers who deal with the spectra of highly stripped atoms. This report includes the first 18 elements, from hydrogen (including deuterium) through argon. The tabulation is divided into two main sections: the spectrum lines by spectrum, and a finding list. The entries for each element give the ionization species, ground state term, and ionization potential, as well as the best values of vacuum wavelength, intensity, and classification. A list of the pertinent references is appended at the end.

  11. Dichotomy of the hydrogen atom in superintense, high-frequency laser fields

    SciTech Connect

    Pont, M.; Walet, N.R.; Gavrila, M.; McCurdy, C.W.

    1988-08-22

    We study the behavior of atomic hydrogen in a monochromatic radiation field of high frequency ..omega.. and high-intensity I, when its structure depends only on the parameter ..cap alpha../sub 0/ = I/sup 1/2/..omega../sup -2/ a.u., and multiphoton ionization is quenched. At large ..cap alpha../sub 0/ the ground-state binding energy undergoes a drastic reduction. This is coupled to an unprecedented stretching of the (oscillating) electron wave function, culminating in its separation into two parts (dichotomy) for ..cap alpha../sub 0/>50 a.u.

  12. Absorption of infrared radiation by electrons in the field of a neutral hydrogen atom

    NASA Technical Reports Server (NTRS)

    Stallcop, J. R.

    1974-01-01

    An analytical expression for the absorption coefficient is developed from a relationship between the cross-section for inverse bremsstrahlung absorption and the cross-section for electron-atom momentum transfer; it is accurate for those photon frequencies v and temperatures such that hv/kT is small. The determination of the absorption of infrared radiation by free-free transitions of the negative hydrogen ion has been extended to higher temperatures. A simple analytical expression for the absorption coefficient has been derived.

  13. Absolute differential cross sections for electron capture and loss by kilo-electron-volt hydrogen atoms

    NASA Technical Reports Server (NTRS)

    Smith, G. J.; Johnson, L. K.; Gao, R. S.; Smith, K. A.; Stebbings, R. F.

    1991-01-01

    This paper reports measurements of absolute differential cross sections for electron capture and loss for fast hydrogen atoms incident on H2, N2, O2, Ar, and He. Cross sections have been determined in the 2.0- to 5.0-keV energy range over the laboratory angular range 0.02-2 deg, with an angular, resolution of 0.02 deg. The high angular resolution allows observation of the structure at small angles in some of the cross sections. Comparison of the present results with those of other authors generally shows very good agreement.

  14. Experimentally attainable example of chaotic tunneling: The hydrogen atom in parallel static electric and magnetic fields

    SciTech Connect

    Delande, Dominique; Zakrzewski, Jakub

    2003-12-01

    Statistics of tunneling rates in the presence of chaotic classical dynamics is discussed on a realistic example: a hydrogen atom placed in parallel, uniform, static electric, and magnetic fields, where tunneling is followed by ionization along the fields direction. Depending on the magnetic quantum number, one may observe either a standard Porter-Thomas distribution of tunneling rates or, for strong scarring by a periodic orbit parallel to the external fields, strong deviations from it. For the latter case, a simple model based on random matrix theory gives the correct distribution.

  15. A correlational analysis of the effects of changing environmental conditions on the NR atomic hydrogen maser

    NASA Technical Reports Server (NTRS)

    Dragonette, Richard A.; Suter, Joseph J.

    1992-01-01

    An extensive statistical analysis has been undertaken to determine if a correlation exists between changes in an NR atomic hydrogen maser's frequency offset and changes in environmental conditions. Correlation analyses have been performed comparing barometric pressure, humidity, and temperature with maser frequency offset as a function of time for periods ranging from 5.5 to 17 days. Semipartial correlation coefficients as large as -0.9 have been found between barometric pressure and maser frequency offset. Correlation between maser frequency offset and humidity was small compared to barometric pressure and unpredictable. Analysis of temperature data indicates that in the most current design, temperature does not significantly affect maser frequency offset.

  16. Controlling the spin of co atoms on pt(111) by hydrogen adsorption.

    PubMed

    Dubout, Q; Donati, F; Wäckerlin, C; Calleja, F; Etzkorn, M; Lehnert, A; Claude, L; Gambardella, P; Brune, H

    2015-03-13

    We investigate the effect of H adsorption on the magnetic properties of individual Co atoms on Pt(111) with scanning tunneling microscopy. For pristine Co atoms, we detect no inelastic features in the tunnel spectra. Conversely, CoH and CoH2 show a number of low-energy vibrational features in their differential conductance identified by isotope substitution. Only the fcc-adsorbed species present conductance steps of magnetic origin, with a field splitting identifying their effective spin as Seff=2 for CoH and 3/2 for CoH2. The exposure to H2 and desorption through tunnel electrons allow the reversible control of the spin in half-integer steps. Because of the presence of the surface, the hydrogen-induced spin increase is opposite to the spin sequence of CoHn molecules in the gas phase.

  17. Low Energy Charge Transfer between C5+ and Atomic Hydrogen

    SciTech Connect

    Draganic, Ilija N; Seely, D. G.; Havener, Charles C

    2011-01-01

    Charge transfer (CT) with carbon ions has been identified for a long time as important in both magnetic fusion plasma devices and more recently in solar wind interactions with comets, planets, or neutrals in the heliosphere. A merged-beams technique is used to measure the absolute total charge transfer cross section for C5+ and atomic H over four orders of magnitude in collision energy, from 12,000 eV/u to 0.64 eV/u. The present measurements are compared with previous measurements using an atomic hydrogen target and benchmark available classical trajectory Monte-Carlo and molecular-orbital close-coupling calculations. An increasing cross section below 10 eV/u is attributed to trajectory effects due to the ion-induced dipole attraction between reactants.

  18. Low-energy charge transfer between C5+ and atomic hydrogen

    SciTech Connect

    Draganic, Ilija N; Havener, Charles C; Seely, D. G.

    2011-01-01

    Charge transfer with carbon ions has been identified as important in both magnetic fusion plasma devices and, more recently, in solar wind interactions with comets, planets, or neutrals in the heliosphere. A merged-beams technique is used to measure the absolute total charge-transfer cross section for C{sup 5+} and atomic H over four orders of magnitude in collision energy, from 12,000 to 0.64 eV/u. The present measurements are compared with previous measurements using an atomic hydrogen target and benchmark available classical trajectory Monte Carlo and molecular-orbital close-coupling calculations. An observed increasing cross section below 10 eV/u is attributed to trajectory effects due to the ion-induced dipole attraction between reactants.

  19. Hidden momentum in a hydrogen atom and the Lorentz-force law

    NASA Astrophysics Data System (ADS)

    Filho, J. S. Oliveira; Saldanha, Pablo L.

    2015-11-01

    By using perturbation theory, we show that a hydrogen atom with magnetic moment due to the orbital angular momentum of the electron has so-called hidden momentum in the presence of an external electric field. This means that the atomic electronic cloud has a nonzero linear momentum in its center-of-mass rest frame due to a relativistic effect. This is completely analogous to the hidden momentum that a classical current loop has in the presence of an external electric field. We discuss how this effect is essential for the validity of the Lorentz-force law in quantum systems. We also connect our results to the long-standing Abraham-Minkowski debate about the momentum of light in material media.

  20. Low-energy charge transfer between C{sup 5+} and atomic hydrogen

    SciTech Connect

    Draganic, I. N.; Havener, C. C.; Seely, D. G.

    2011-05-15

    Charge transfer with carbon ions has been identified as important in both magnetic fusion plasma devices and, more recently, in solar wind interactions with comets, planets, or neutrals in the heliosphere. A merged-beams technique is used to measure the absolute total charge-transfer cross section for C{sup 5+} and atomic H over four orders of magnitude in collision energy, from 12 000 to 0.64 eV/u. The present measurements are compared with previous measurements using an atomic hydrogen target and benchmark available classical trajectory Monte Carlo and molecular-orbital close-coupling calculations. An observed increasing cross section below 10 eV/u is attributed to trajectory effects due to the ion-induced dipole attraction between reactants.

  1. State of the art and future directions for the atomic hydrogen maser

    NASA Technical Reports Server (NTRS)

    Vessot, Robert F. C.

    1990-01-01

    The present status of technology development for atomic hydrogen masers (H-masers) is reviewed. The limitations to frequency stability and accuracy are discussed with emphasis on the problems associated with cavity resonator instability and the lack of reproducibility and stability of the storage volume wall coating frequency shift. New types of coating developed in the Soviet Union and better, cavity resonator materials, are expected to make possible frequency at the 10(exp -16) level at 10(exp 4) sec. Better control of systematic effects should extend the long-term stability to levels better than 10(exp -15) for intervals beyond one day. Present use of H-masers as flywheel oscillators in timekeeping systems is discussed as is the outlook for the future cryogenic and room temperature H-masers as flywheel oscillators to operate very high resolution frequency discriminators based on the newly evolving technology of trapped and cooled ions and atoms.

  2. Resonant charge transfer of hydrogen Rydberg atoms incident at a metallic sphere

    NASA Astrophysics Data System (ADS)

    Gibbard, J. A.; Softley, T. P.

    2016-06-01

    A wavepacket propagation study is reported for the charge transfer of low principal quantum number (n = 2) hydrogen Rydberg atoms incident at an isolated metallic sphere. Such a sphere acts as a model for a nanoparticle. The three-dimensional confinement of the sphere yields discrete surface-localized ‘well-image’ states, the energies of which vary with sphere radius. When the Rydberg atom energy is degenerate with one of the quantized nanoparticle states, charge transfer is enhanced, whereas for off-resonant cases little to no charge transfer is observed. Greater variation in charge-transfer probability is seen between the resonant and off-resonant examples in this system than for any other Rydberg-surface system theoretically investigated thus far. The results presented here indicate that it may be possible to use Rydberg-surface ionization as a probe of the surface electronic structure of a nanoparticle, and nanostructures in general.

  3. Spontaneous light emission by atomic hydrogen: Fermi's golden rule without cheating

    NASA Astrophysics Data System (ADS)

    Debierre, V.; Durt, T.; Nicolet, A.; Zolla, F.

    2015-10-01

    Focusing on the 2 p- 1 s transition in atomic hydrogen, we investigate through first order perturbation theory the time evolution of the survival probability of an electron initially taken to be in the excited (2 p) state. We examine both the results yielded by the standard dipole approximation for the coupling between the atom and the electromagnetic field - for which we propose a cutoff-independent regularisation - and those yielded by the exact coupling function. In both cases, Fermi's golden rule is shown to be an excellent approximation for the system at hand: we found its maximal deviation from the exact behaviour of the system to be of order 10-8 /10-7. Our treatment also yields a rigorous prescription for the choice of the optimal cutoff frequency in the dipole approximation. With our cutoff, the predictions of the dipole approximation are almost indistinguishable at all times from the exact dynamics of the system.

  4. On the role of atomic metastability in the production of Balmer line radiation from ‘cold’ atomic hydrogen, deuterium and hydrogenic ion impurities in fusion edge plasmas

    NASA Astrophysics Data System (ADS)

    Hey, J. D.

    2012-03-01

    Published arguments, which assign an important role to atomic metastability in the production of ‘narrow’ Zeeman component radiation from the boundary region of fusion plasmas, are examined critically in relation to l-redistribution by proton and electron collisions, and mixing of unperturbed atomic states by the ion microfield and microfield gradient. It is concluded that these important processes indeed severely constrain the contribution from ‘metastable’ states to the generation of the hydrogen Balmer spectra, for electron concentrations above 1012 cm-3, as pointed out before by the present author (Hey et al 1999 J. Phys. B: At. Mol. Opt. Phys. 32 3555). The analysis of collision-induced l-redistribution represents an extension of that used previously (Hey et al 1996 Contrib. Plasma Phys. 36 583), applicable up to higher electron densities. For comparison purposes, we also consider the question of metastability of ionized helium in a low-temperature plasma, and that of some common hydrogenic impurities (C5+ and Ne9+) in a hydrogen (deuterium) fusion plasma. While for low nuclear charge Z the metastability of 2s1/2 levels is quenched by the plasma environment, it is much reduced in high-Z ions owing to the rapid increase with Z of the two-photon electric dipole (2E1) and magnetic dipole (M1) spontaneous transition rates to the ground state, whereas the role of the plasma in these cases is less important. The main new principle elaborated in this work is the sensitivity of atomic line strengths, and hence collision strengths, to perturbation by the plasma environment for transitions between fine-structure sublevels of the same principal quantum number. As the plasma microfield strength grows, ‘allowed’ transitions diminish in strength, while ‘forbidden’ transitions grow. However, owing to violation of the parity selection rule, there is an overall loss of collision strength available to transitions, resulting from the appearance of significant

  5. Ion-atom charge-transfer reactions and a hot intercloud medium. [in interstellar space

    NASA Technical Reports Server (NTRS)

    Steigman, G.

    1975-01-01

    An investigation is conducted concerning the ionization equilibrium of carbon in a hot intercloud medium (ICM), taking into account various charge-transfer reactions. Attention is given to problems related to observations of carbon along the lines of sight to several unreddened stars. It is pointed out that the observed underabundance of C III and overabundance of C I can be consistent with the presence of a hot, partially ionized ICM, provided that two of the charge-transfer reactions considered are rapid at thermal energies.

  6. Quantitative analysis of hydrogen in SiO2/SiN/SiO2 stacks using atom probe tomography

    NASA Astrophysics Data System (ADS)

    Kunimune, Yorinobu; Shimada, Yasuhiro; Sakurai, Yusuke; Inoue, Masao; Nishida, Akio; Han, Bin; Tu, Yuan; Takamizawa, Hisashi; Shimizu, Yasuo; Inoue, Koji; Yano, Fumiko; Nagai, Yasuyoshi; Katayama, Toshiharu; Ide, Takashi

    2016-04-01

    We have demonstrated that it is possible to reproducibly quantify hydrogen concentration in the SiN layer of a SiO2/SiN/SiO2 (ONO) stack structure using ultraviolet laser-assisted atom probe tomography (APT). The concentration of hydrogen atoms detected using APT increased gradually during the analysis, which could be explained by the effect of hydrogen adsorption from residual gas in the vacuum chamber onto the specimen surface. The amount of adsorbed hydrogen in the SiN layer was estimated by analyzing another SiN layer with an extremely low hydrogen concentration (<0.2 at. %). Thus, by subtracting the concentration of adsorbed hydrogen, the actual hydrogen concentration in the SiN layer was quantified as approximately 1.0 at. %. This result was consistent with that obtained by elastic recoil detection analysis (ERDA), which confirmed the accuracy of the APT quantification. The present results indicate that APT enables the imaging of the three-dimensional distribution of hydrogen atoms in actual devices at a sub-nanometer scale.

  7. Reduction of FeO/Pt(1 1 1) Thin Films by Exposure to Atomic Hydrogen

    SciTech Connect

    Knudsen, Jan; Merte, L. R.; Grabow, Lars C.; Eichhorn, Falk M.; Porsgaard, Soeren; Zeuthen, Helene; Vang, Ronnie T.; Laegsgaard, E.; Mavrikakis, Manos; Besenbacher, Fleming

    2010-01-01

    Using scanning tunneling microscopy (STM), X-ray photoemission spectroscopy (XPS) and density functional theory (DFT) calculations we have studied the reduction of ultra-thin films of FeO(1 1 1) grown on Pt(1 1 1) after exposure to atomic hydrogen at room temperature. A number of new ordered, partlyreduced FeOx structures are identified and as a general trend we reveal that all the reduced FeOx structures incorporate 2-fold coordinated Fe atoms as opposed to the original 3-fold coordinated Fe atoms in the FeO film. We find that when all the Fe atoms are 2-fold O-coordinated the FeOx surface structure is resistant to further reduction at room temperature. We observe that water easily dissociates on the most heavily reduced FeOx, structure in contrast to the initially inert FeO film, and reveal that it is possible to partially re-oxidize the FeOx film by heating the surface slightly in the presence of water.

  8. Time-resolved Absorption Spectra of the Laser-dressed Hydrogen Atom

    NASA Astrophysics Data System (ADS)

    Murakami, Mitsuko; Chu, Shih-I.

    2013-05-01

    A theoretical study of the transient absorption spectra for the laser-dressed hydrogen atom based on the accurate numerical solution of the time-dependent Schrödinger equation is presented. The timing of absorption is controlled by the time delay between an isolated extreme ultraviolet (XUV) pulse and a dressing infrared (IR) field. We identify two different kinds of physical processes in the spectra. One is the formation of dressed states, signified by the appearance of sidebands between the XUV absorption lines separated by one IR-photon energy. We show that their population is maximized when the XUV pulse coincides with the zero-crossing of the IR field, and that their energy can be manipulated by using a chirped IR field. The other process is the dynamical AC Stark shift induced by the IR field and probed by the XUV pulse. Our calculations indicate that the accidental degeneracy of the hydrogen atom leads to the multiple splittings of each XUV absorption line whose separations change in response to a slowly-varying IR envelope. Furthermore, we observe the Autler-Townes doublets for the n=2 and 3 states using the 656 nm dressing field, but their separation does not agree with the prediction by the conventional 3-level model that neglects the dynamical AC Stark effects.

  9. First-principles calculations of the interaction between hydrogen and 3d alloying atom in nickel

    NASA Astrophysics Data System (ADS)

    Liu, Wenguan; Qian, Yuan; Zhang, Dongxun; Liu, Wei; Han, Han

    2015-10-01

    Knowledge of the behavior of hydrogen (H) in Ni-based alloy is essential for the prediction of Tritium behavior in Molten Salt Reactor. First-principles calculations were performed to investigate the interaction between H and 3d transition metal (TM) alloying atom in Ni-based alloy. H prefers the octahedral interstitial site to the tetrahedral interstitial site energetically. Most of the 3d TM elements (except Zn) attract H. The attraction to H in the Ni-TM-H system can be mainly attributed to the differences in electronegativity. With the large electronegativity, H and Ni gain electrons from the other TM elements, resulting in the enhanced Ni-H bonds which are the source of the attraction to H in the Ni-TM-H system. The obviously covalent-like Cr-H and Co-H bindings are also beneficial to the attraction to H. On the other hand, the repulsion to H in the Ni-Zn-H system is due to the stable electronic configuration of Zn. We mainly utilize the results calculated in 32-atom supercell which corresponds to the case of a relatively high concentration of hydrogen. Our results are in good agreement with the experimental ones.

  10. Three-dimensional atomic mapping of hydrogenated polymorphous silicon solar cells

    NASA Astrophysics Data System (ADS)

    Chen, Wanghua; Pareige, Philippe; Roca i Cabarrocas, Pere

    2016-06-01

    Hydrogenated polymorphous silicon (pm-Si:H) is a nanostructured material consisting of silicon nanocrystals embedded in an amorphous silicon matrix. Its use as the intrinsic layer in thin film p-i-n solar cells has led to good cell properties in terms of stability and efficiency. Here, we have been able to assess directly the concentration and distribution of nanocrystals and impurities (dopants) in p-i-n solar cells, by using femtosecond laser-assisted atom probe tomography (APT). An effective sample preparation method for APT characterization is developed. Based on the difference in atomic density between hydrogenated amorphous and crystalline silicon, we are able to distinguish the nanocrystals from the amorphous matrix by using APT. Moreover, thanks to the three-dimensional reconstruction, we demonstrate that Si nanocrystals are homogeneously distributed in the entire intrinsic layer of the solar cell. The influence of the process pressure on the incorporation of nanocrystals and their distribution is also investigated. Thanks to APT we could determine crystalline fractions as low as 4.2% in the pm-Si:H films, which is very difficult to determine by standard techniques, such as X-ray diffraction, Raman spectroscopy, and spectroscopic ellipsometry. Moreover, we also demonstrate a sharp p/i interface in our solar cells.

  11. Observation and Interpretation of Energetic Neutral Hydrogen Atoms from the December 5, 2006 Solar Flare

    NASA Technical Reports Server (NTRS)

    Barghouty, A. F.; Mewaldt, R. A.; Leske, R. A.; Shih, A. Y.; Stone, E. C.; Cohen, C. M. S.; Cummings, A. C.; Labrador, A. W.; vonRosenvinge, T. T.; Wiedenbeck, M. E.

    2009-01-01

    We discuss observations of energetic neutral hydrogen atoms (ENAs) from a solar flare/coronal mass ejection event reported by Mewaldt et al. (2009). The observations were made during the 5 December 2006 X9 solar flare, located at E79, by the Low Energy Telescopes (LETs) on STEREO A and B. Prior to the arrival of the main solar energetic particle (SEP) event at Earth, both LETs observed a sudden burst of 1.6 to 15 MeV particles arriving from the Sun. The derived solar emission profile, arrival directions, and energy spectrum all show that the <5 MeV particles were due to energetic neutral hydrogen atoms produced by either flare or shock-accelerated protons. RHESSI measurements of the 2.2-MeV gamma-ray line provide an estimate of the number of interacting flare-accelerated protons in this event, which leads to an improved estimate of ENA production by flare-accelerated protons. CME-driven shock acceleration is also considered. Taking into account ENA losses, we conclude that the observed ENAs must have been produced in the high corona at heliocentric distances .2 solar radii.

  12. Observations and Interpretations of Energetic Neutral Hydrogen Atoms from the December 5, 2006 Solar Event

    NASA Technical Reports Server (NTRS)

    Mewaldt, R. A.; Leske, R. A.; Shih, A. Y.; Stone, E. C.; Barghouty, A. f.; Cohen, C. M. S.; Cummings, A. c.; Labrador, A. W.; vonRosenvinge, T. T.

    2009-01-01

    We discuss recently reported observations of energetic neutral hydrogen atoms (ENAs) from an X9 solar flare/coronal mass ejection event on 5 December 2006, located at E79. The observations were made by the Low Energy Telescopes (LETs) on STEREO A and B. Prior to the arrival of the main solar energetic particle (SEP) event at Earth, both LETs observed a sudden burst of 1.6 to 15 MeV energetic neutral hydrogen atoms produced by either flare or shock-accelerated protons. RHESSI measurements of the 2.2-MeV gamma-ray line provide an estimate of the number of interacting flare-accelerated protons in this event, which leads to an improved estimate of ENA production by flare-accelerated protons. Taking into account ENA losses, we find that the observed ENAs must have been produced in the high corona at heliocentric distances > or equal to 2 solar radii. Although there are no CME images from this event, it is shown that CME-shock-accelerated protons can, in principle, produce a time-history consistent with the observations.

  13. STEREO Observations of Energetic Neutral Hydrogen Atoms during the 5 December 2006 Solar Flare

    NASA Technical Reports Server (NTRS)

    Mewaldt, R. A.; Leske, R. A.; Stone, E. C.; Barghouty, A. F.; Labrador, A. W.; Cohen, C. M. S.; Cummings, A. C.; Davis, A. J.; vonRosenvinge, T. T.; Wiedenbeck, M. E.

    2009-01-01

    We report the discovery of energetic neutral hydrogen atoms emitted during the X9 solar event of December 5, 2006. Beginning 1 hour following the onset of this E79 flare, the Low Energy Telescopes (LETs) on both the STEREO A and B spacecraft observed a sudden burst of 1.6 to 15 MeV protons beginning hours before the onset of the main solar energetic particle (SEP) event at Earth. More than 70% of these particles arrived from a longitude within 10 of the Sun, consistent with the measurement resolution. The derived emission profile at the Sun had onset and peak times remarkably similar to the GOES soft X-ray profile and continued for more than an hour. The observed arrival directions and energy spectrum argue strongly that the particle events less than 5 MeV were due to energetic neutral hydrogen atoms (ENAs). To our knowledge, this is the first reported observation of ENA emission from a solar flare/coronal mass ejection. Possible origins for the production of ENAs in a large solar event are considered. We conclude that the observed ENAs were most likely produced in the high corona and that charge-transfer reactions between accelerated protons and partially-stripped coronal ions are an important source of ENAs in solar events.

  14. Neutron diffraction determination of hydrogen atom locations in the α(TiCrSiO) 1/1 crystal approximant

    NASA Astrophysics Data System (ADS)

    Kim, J. Y.; Kim, W. J.; Gibbons, P. C.; Kelton, K. F.; Yelon, W. B.

    1999-08-01

    Titanium/zirconium-based quasicrystals and their related crystal approximants have been identified as potential new materials for hydrogen storage applications. To better understand the local chemistry and atomic ordering in these phases, preferential interstitial sites for hydrogen/deuterium were determined for α(TiCrSiO). This is a bcc 1/1 crystal approximant to the icosahedral quasicrystal phase that contains a two-shell, Mackay-icosahedral cluster of atoms at each bcc site. It absorbs hydrogen or deuterium, without formation of other hydride phases, to a maximum hydrogen to metal atom ratio (H/M) of 0.26. For fully deuterated samples, both tetrahedral and octahedral interstitial sites are occupied with fractions of 0.14 and 0.12, respectively. Here, the hydrogen/deuterium sites are determined from a Rietveld analysis of x-ray and neutron powder diffraction data taken from samples of α(TiCrSiO) loaded with deuterium. Only the octahedral sites are occupied in the partially deuterated samples (D/M=0.11). A decrease in the oxygen concentration below the stoichiometric value for α(TiCrSiO) leads to an increase in the total amount of hydrogen that can be absorbed, suggesting that these interstitial atoms are competing for the same octahedral interstitial sites.

  15. Low resistance Cu3Ge compounds formation by the low temperature treatment of Cu/Ge system in atomic hydrogen

    NASA Astrophysics Data System (ADS)

    Kazimirov, A. I.; Erofeev, E. V.; Fedin, I. V.; Kagadei, V. A.; Yurjev, Y. N.

    2016-06-01

    The research deals with the regularities for Cu3Ge compound formation under the low temperature treatment of a double-layer Cu/Ge system deposited on i-GaAs substrate in atomic hydrogen flow. The treatment of a Cu/Ge/i-GaAs system with layer thicknesses, respectively, of 122 and 78 nm, in atomic hydrogen with a flow rate of 1015 at.cm-2s-1 for a duration of 2.5-10 min at room temperature, leads to an interdiffusion of Cu and Ge and formation of a polycrystalline film containing stoichiometric phase Cu3Ge. The film consists of vertically oriented grains of dimensions 100-150 nm and has a minimum specific resistance of 4.5 μΩ cm. Variation in the treatment duration of Cu/Ge/i-GaAs samples in atomic hydrogen affects Cu and Ge distribution profiles, the phase composition of films formed, and the specific resistance of the latter. As observed, Cu3Ge compound synthesis at room temperature demonstrates the stimulative effects characteristic of atomic hydrogen treatment for both Cu and Ge diffusion and for the chemical reaction of Cu3Ge compound generation. Activation of these processes can be conditioned by the energy released during recombination of hydrogen atoms adsorbed on the surface of a Cu/Ge/i-GaAs sample.

  16. Emission of hydrogen energetic neutral atoms from the Martian subsolar magnetosheath

    NASA Astrophysics Data System (ADS)

    Wang, X.-D.; Alho, M.; Jarvinen, R.; Kallio, E.; Barabash, S.; Futaana, Y.

    2016-01-01

    We have simulated the hydrogen energetic neutral atom (ENA) emissions from the subsolar magnetosheath of Mars using a hybrid model of the proton plasma charge exchanging with the Martian exosphere to study statistical features revealed from the observations of the Neutral Particle Detectors on Mars Express. The simulations reproduce well the observed enhancement of the hydrogen ENA emissions from the dayside magnetosheath in directions perpendicular to the Sun-Mars line. Our results show that the neutralized protons from the shocked solar wind are the dominant ENA population rather than those originating from the pickup planetary ions. The simulation also suggests that the observed stronger ENA emissions in the direction opposite to the solar wind convective electric field result from a stronger proton flux in the same direction at the lower magnetosheath; i.e., the proton fluxes in the magnetosheath are not cylindrically symmetric. We also confirm the observed increasing of the ENA fluxes with the solar wind dynamical pressure in the simulations. This feature is associated with a low altitude of the induced magnetic boundary when the dynamic pressure is high and the magnetosheath protons can reach to a denser exosphere, and thus, the charge exchange rate becomes higher. Overall, the analysis suggests that kinetic effects play an important and pronounced role in the morphology of the hydrogen ENA distribution and the plasma environment at Mars, in general.

  17. Hot bubbles of planetary nebulae with hydrogen-deficient winds. I. Heat conduction in a chemically stratified plasma

    NASA Astrophysics Data System (ADS)

    Sandin, C.; Steffen, M.; Schönberner, D.; Rühling, U.

    2016-02-01

    Heat conduction has been found a plausible solution to explain discrepancies between expected and measured temperatures in hot bubbles of planetary nebulae (PNe). While the heat conduction process depends on the chemical composition, to date it has been exclusively studied for pure hydrogen plasmas in PNe. A smaller population of PNe show hydrogen-deficient and helium- and carbon-enriched surfaces surrounded by bubbles of the same composition; considerable differences are expected in physical properties of these objects in comparison to the pure hydrogen case. The aim of this study is to explore how a chemistry-dependent formulation of the heat conduction affects physical properties and how it affects the X-ray emission from PN bubbles of hydrogen-deficient stars. We extend the description of heat conduction in our radiation hydrodynamics code to work with any chemical composition. We then compare the bubble-formation process with a representative PN model using both the new and the old descriptions. We also compare differences in the resulting X-ray temperature and luminosity observables of the two descriptions. The improved equations show that the heat conduction in our representative model of a hydrogen-deficient PN is nearly as efficient with the chemistry-dependent description; a lower value on the diffusion coefficient is compensated by a slightly steeper temperature gradient. The bubble becomes somewhat hotter with the improved equations, but differences are otherwise minute. The observable properties of the bubble in terms of the X-ray temperature and luminosity are seemingly unaffected.

  18. Hot Hydrogen Testing of Tungsten-Uranium Dioxide (W-UO2) CERMET Fuel Materials for Nuclear Thermal Propulsion

    NASA Technical Reports Server (NTRS)

    Hickman, Robert; Broadway, Jeramie

    2014-01-01

    CERMET fuel materials are being developed at the NASA Marshall Space Flight Center for a Nuclear Cryogenic Propulsion Stage. Recent work has resulted in the development and demonstration of a Compact Fuel Element Environmental Test (CFEET) System that is capable of subjecting depleted uranium fuel material samples to hot hydrogen. A critical obstacle to the development of an NCPS engine is the high-cost and safety concerns associated with developmental testing in nuclear environments. The purpose of this testing capability is to enable low-cost screening of candidate materials, fabrication processes, and further validation of concepts. The CERMET samples consist of depleted uranium dioxide (UO2) fuel particles in a tungsten metal matrix, which has been demonstrated on previous programs to provide improved performance and retention of fission products1. Numerous past programs have utilized hot hydrogen furnace testing to develop and evaluate fuel materials. The testing provides a reasonable simulation of temperature and thermal stress effects in a flowing hydrogen environment. Though no information is gained about radiation damage, the furnace testing is extremely valuable for development and verification of fuel element materials and processes. The current work includes testing of subscale W-UO2 slugs to evaluate fuel loss and stability. The materials are then fabricated into samples with seven cooling channels to test a more representative section of a fuel element. Several iterations of testing are being performed to evaluate fuel mass loss impacts from density, microstructure, fuel particle size and shape, chemistry, claddings, particle coatings, and stabilizers. The fuel materials and forms being evaluated on this effort have all been demonstrated to control fuel migration and loss. The objective is to verify performance improvements of the various materials and process options prior to expensive full scale fabrication and testing. Post test analysis will

  19. Absolute Rates of the Solution-Phase Addition of Atomic Hydrogen to a Vinyl Ether and a Vinyl Ester: Effect of Oxygen Substitution on Hydrogen Atom Reactivity with Olefins

    SciTech Connect

    Tanner, D D.; Kandanarachchi, P; Das, N. C.; Franz, James A.

    2003-04-08

    The reactions of vinyl butyl ether and vinyl butyrate with atomic hydrogen and deuterium lead to addition at the terminal position of the olefins. This observation is consistent with the reactions carried out earlier with other olefins. Both of the absolute rates of addition to vinylbutyl ether and vinyl butyrate, in acetone and hexane, were measured at several temperatures. The relative rates are consistent with only modest stabilization of the transition state of the radical adduct by the R-O substituent compared with that of hydrogen atom addition to 1-octene. The relative rates measured in acetone and hexane indicate no significant differential solvation of the ground state relative to the transition structures of the hydrogen atom addition. The kinetics reveal that the early transition states for hydrogen atom addition exhibit little selectivity (vinyl ether versus simple olefin) in either the abstraction of hydrogen R to the oxygen or by terminal addition to the olefinic ether and reflects the modest influence of the increased enthalpy of reaction associated with resonance stabilization by the oxygen substituent at the developing radical site.

  20. Radiative cascade of highly excited hydrogen atoms in strong magnetic fields

    SciTech Connect

    Topcu, Tuerker; Robicheaux, Francis

    2006-04-15

    We have studied the radiative decay of atomic hydrogen in strong magnetic fields of up to 4 T. We have followed the radiative cascade from completely l,m mixed distributions of highly excited states as well as from distributions that involve highly excited states with |m|{approx}n. We have found that the time it takes to populate the ground state is not affected by the magnetic field for the initial states with n < or approx. 20. For higher n manifolds, the electrons in the most negative m states are substantially slowed down by the magnetic field resulting in a much longer lifetime. We show that less than 10% of the antihydrogen atoms with n{approx}35 generated in antihydrogen experiments at 4 K will decay to their ground states before they hit the wall of the vacuum container unless they are trapped. We have also found that the decay time is mainly determined by the fraction of atoms that were initially in highest negative m states due to the fact that only {delta}m+{delta}{pi}=1 transitions are allowed in the magnetic field. We give a semiclassical method for calculating the decay rates for circular states and show that when the initial states have high-m, semiclassical rates agree with the full quantum mechanical rates within a couple of percent for states with effective n > or approx. 20.

  1. Concerted Hydrogen Atom and Electron Transfer Mechanism for Catalysis by Lysine-Specific Demethylase

    PubMed Central

    Yu, Tao; Higashi, Masahiro; Cembran, Alessandro; Gao, Jiali; Truhlar, Donald G.

    2015-01-01

    We calculate the free energy profile for the postulated hydride transfer reaction mechanism for the catalysis of lysine demethylation by lysine-specific demethylase LSD1. The potential energy surface is obtained by using combined electrostatically embedded multi-configuration molecular mechanics (EE-MCMM) and single-configuration molecular mechanics (MM). We employ a constant valence bond coupling term to obtain analytical energies and gradients of the EE-MCMM subsystem, which contains 45 QM atoms and which is parametrized with a density functional calculations employing specific reaction parameters obtained by matching high-level wave function calculations. In the MM region, we employ the Amber ff03 and TIP3P force fields. The free energy of activation at 300 K is calculated by molecular dynamics (MD) umbrella sampling on a system with 102090 atoms as the maximum of the free energy profile along the reaction coordinate as obtained by the weighted histogram analysis method with 17 umbrella sampling windows. This yields a free energy of activation of only 10 kcal/mol, showing that the previously postulated direct hydride transfer reaction mechanism is plausible, although we find that it is better interpreted as a concerted transfer of a hydrogen atom and an electron. PMID:23725223

  2. Imaging the South Pole-Aitken basin in backscattered neutral hydrogen atoms

    NASA Astrophysics Data System (ADS)

    Vorburger, A.; Wurz, P.; Barabash, S.; Wieser, M.; Futaana, Y.; Bhardwaj, A.; Asamura, K.

    2015-09-01

    The lunar surface is very efficient in reflecting impinging solar wind ions as energetic neutral atoms (ENAs). A global analysis of lunar hydrogen ENAs showed that on average 16% of the solar wind protons are reflected, and that the reflected fraction can range from less than 8% to more than 24%, depending on location. It is established that magnetic anomalies reduce the flux of backscattered hydrogen ENAs by screening-off a fraction of the impinging solar wind. The effects of the surface properties, such as porosity, roughness, chemical composition, and extent of weathering, were not known. In this paper, we conduct an in-depth analysis of ENA observations of the South Pole-Aitken basin to determine which of the surface properties might be responsible for the observed variation in the integral ENA flux. The South Pole-Aitken basin with its highly variable surface properties is an ideal object for such studies. It is very deep, possesses strikingly elevated concentrations in iron and thorium, has a low albedo and coincides with a cluster of strong magnetic anomalies located on the northern rim of the basin. Our analysis shows that whereas, as expected, the magnetic anomalies can account well for the observed ENA depletion at the South Pole-Aitken basin, none of the other surface properties seem to influence the ENA reflection efficiency. Therefore, the integral flux of backscattered hydrogen ENAs is mainly determined by the impinging plasma flux and ENA imaging of backscattered hydrogen captures the electrodynamics of the plasma at the surface. We cannot exclude minor effects by surface features. We create two maps of surface reflected ENAs at the South Pole-Aitken basin. We compare these ENA maps to elevation, albedo, composition and magnetic field maps. The ENA maps only significantly correlate with the magnetic field map. ENA imaging captures solely the electrodynamics of the plasma at the surface.

  3. Production of high brightness H- beam by charge exchange of hydrogen atom beam in sodium jet

    SciTech Connect

    Davydenko, V.; Zelenski, A.; Ivanov, A.; Kolmogorov, A.

    2010-11-16

    Production of H{sup -} beam for accelerators applications by charge exchange of high brightness hydrogen neutral beam in a sodium jet cell is experimentally studied in joint BNL-BINP experiment. In the experiment, a hydrogen-neutral beam with 3-6 keV energy, equivalent current up to 5 A and 200 microsecond pulse duration is used. The atomic beam is produced by charge exchange of a proton beam in a pulsed hydrogen target. Formation of the proton beam is performed in an ion source by four-electrode multiaperture ion-optical system. To achieve small beam emittance, the apertures in the ion-optical system have small enough size, and the extraction of ions is carried out from the surface of plasma emitter with a low transverse ion temperature of {approx}0.2 eV formed as a result of plasma jet expansion from the arc plasma generator. Developed for the BNL optically pumped polarized ion source, the sodium jet target with recirculation and aperture diameter of 2 cm is used in the experiment. At the first stage of the experiment H{sup -} beam with 36 mA current, 5 keV energy and {approx}0.15 cm {center_dot} mrad normalized emittance was obtained. To increase H{sup -} beam current ballistically focused hydrogen neutral beam will be applied. The effects of H{sup -} beam space-charge and sodium-jet stability will be studied to determine the basic limitations of this approach.

  4. Electron-stimulated reactions in layered CO/H2O films: Hydrogen atom diffusion and the sequential hydrogenation of CO to methanol

    SciTech Connect

    Petrik, Nikolay G.; Monckton, Rhiannon J.; Koehler, Sven; Kimmel, Gregory A.

    2014-05-28

    Low-energy (100 eV) electron-stimulated reactions in layered H2O/CO/H2O ices are investigated. For CO trapped within approximately 50 ML of the vacuum interface in the amorphous solid water (ASW) films, both oxidation and reduction reactions are observed. However for CO buried more deeply in the film, only the reduction of CO to methanol is observed. Experiments with layered films of H2O and D2O show that the hydrogen atoms participating in the reduction of the buried CO originate in region from ~10 – 40 ML below the surface of the ASW films and subsequently diffuse through the film. For deeply buried CO layers, the CO reduction reactions quickly increase with temperature above ~60 K. We present a simple chemical kinetic model that treats the diffusion of hydrogen atoms in the ASW and sequential hydrogenation of the CO to methanol that accounts for the observations.

  5. The distribution of atomic hydrogen and oxygen in the magnetosphere of Saturn

    NASA Astrophysics Data System (ADS)

    Melin, Henrik; Shemansky, Don E.; Liu, Xianming

    2009-12-01

    The intensity of H Ly α1216A˚ ( 2P- 1S) and OI 1304A˚ ( 2p33s3S-2p4P) is mapped in the magnetosphere of Saturn using the ultraviolet imaging spectrograph (UVIS) [Esposito, L.W., Barth, C.A., Colwell, J.E., Lawrence, G.M., McClintock, W.E., Stewart, A.I.F., Keller, H.U., Korth, A., Lauche, H., Festou, M.C., Lane, A.L., Hansen, C.J., Maki, J.N., West, R.A., Jahn, H., Reulke, R., Warlich, K., Shemansky, D.E., Yung, Y.L., 2004. The Cassini ultraviolet imaging spectrograph investigation. Space Science Reviews 115, 299-361] onboard Cassini. Spatial coverage is built up by stepping the slit sequentially across the system (system scan). Data are obtained at a large range of space-craft-Saturn distances. The observed atomic hydrogen distribution is very broad, extending beyond 40RS in the equatorial plane, with the intensity increasing with decreasing distances to Saturn. The distribution displays persistent local-time asymmetries, and is seen connecting continuously to the upper atmosphere of the planet at sub-solar latitudes located well outside of the equatorial (ring) plane. This is consistent with the source of the atomic hydrogen being located at the top of the atmosphere on the sun-lit side of the planet on the southern hemisphere. In addition there are a number of temporally persistent features in the intensity distribution, indicating a complex hydrogen energy distribution. The emission from OI 1304A˚ is generally distributed as a broad torus centered around ˜4RS although the position of the peak intensity can vary by as much as ±1RS. There is significant intensity present out to ±10RS. HST observations of hydroxyl (OH) are re-analyzed and display a distribution half as broad as that of oxygen, also centered at 4RS. The observed atomic oxygen distribution requires a sourcing of 1.3×1028atomss-1 against loss due to charge capture with the plasma. Using the ion partitioning of Schippers et al. [2008. Multi-instrument analysis of electron populations in Saturn

  6. Effect of hydrogen atoms on the structures of trinuclear metal carbonyl clusters: trinuclear manganese carbonyl hydrides.

    PubMed

    Liu, Xian-mei; Wang, Chao-yang; Li, Qian-shu; Xie, Yaoming; King, R Bruce; Schaefer, Henry F

    2009-05-18

    The structures of the trinuclear manganese carbonyl hydrides H(3)Mn(3)(CO)(n) (n = 12, 11, 10, 9) have been investigated by density functional theory (DFT). Optimization of H(3)Mn(3)(CO)(12) gives the experimentally known structure in which all carbonyl groups are terminal and each edge of a central Mn(3) equilateral triangle is bridged by a single hydrogen atom. This structure establishes the canonical distance 3.11 A for the Mn-Mn single bond satisfying the 18-electron rule. The central triangular (mu-H)(3)Mn(3) unit is retained in the lowest energy structure of H(3)Mn(3)(CO)(11), which may thus be derived from the H(3)Mn(3)(CO)(12) structure by removal of a carbonyl group with concurrent conversion of one of the remaining carbonyl groups into a semibridging carbonyl group to fill the resulting hole. The potential energy surface of H(3)Mn(3)(CO)(10) is relatively complicated with six singlet and five triplet structures. One of the lower energy H(3)Mn(3)(CO)(10) structures has one of the hydrogen atoms bridging the entire Mn(3) triangle and the other two hydrogen atoms bridging Mn-Mn edges. This H(3)Mn(3)(CO)(10) structure achieves the favored 18-electron configuration with a very short MnMn triple bond of 2.36 A. The other low energy H(3)Mn(3)(CO)(10) structure retains the (mu-H)(3)Mn(3) core of H(3)Mn(3)(CO)(12) but has a unique six-electron donor eta(2)-mu(3) carbonyl group bridging the entire Mn(3) triangle similar to the unique carbonyl group in the known compound Cp(3)Nb(3)(CO)(6)(eta(2)-mu(3)-CO). For H(3)Mn(3)(CO)(9) a structure with a central (mu(3)-H)(2)Mn(3) trigonal bipyramid lies >20 kcal/mol below any of the other structures. Triplet structures were found for the unsaturated H(3)Mn(3)(CO)(n) (n = 11, 10, 9) systems but at significantly higher energies than the lowest lying singlet structures.

  7. The distribution of atomic hydrogen in EAGLE galaxies: morphologies, profiles, and H I holes

    NASA Astrophysics Data System (ADS)

    Bahé, Yannick M.; Crain, Robert A.; Kauffmann, Guinevere; Bower, Richard G.; Schaye, Joop; Furlong, Michelle; Lagos, Claudia; Schaller, Matthieu; Trayford, James W.; Dalla Vecchia, Claudio; Theuns, Tom

    2016-02-01

    We compare the mass and internal distribution of atomic hydrogen (H I) in 2200 present-day central galaxies with Mstar > 1010 M⊙ from the 100 Mpc EAGLE `Reference' simulation to observational data. Atomic hydrogen fractions are corrected for self-shielding using a fitting formula from radiative transfer simulations and for the presence of molecular hydrogen using an empirical or a theoretical prescription from the literature. The resulting neutral hydrogen fractions, M_{H_I+H_2} / M_star, agree with observations to better than 0.1 dex for galaxies with Mstar between 1010 and 1011 M⊙. Our fiducial, empirical H2 model based on gas pressure results in galactic H I mass fractions, M_{H I/ M_star, that agree with observations from the GASS survey to better than 0.3 dex, but the alternative theoretical H2 formula from high-resolution simulations leads to a negative offset in M_{H I}/ M_star of up to 0.5 dex. Visual inspection of mock H I images reveals that most H I discs in simulated H I-rich galaxies are vertically disturbed, plausibly due to recent accretion events. Many galaxies (up to 80 per cent) contain spuriously large H I holes, which are likely formed as a consequence of the feedback implementation in EAGLE. The H I mass-size relation of all simulated galaxies is close to (but 16 per cent steeper than) observed, and when only galaxies without large holes in the H I disc are considered, the agreement becomes excellent (better than 0.1 dex). The presence of large H I holes also makes the radial H I surface density profiles somewhat too low in the centre, at Σ _{H I} > 1 M_{⊙} pc^{-2} (by a factor of ≲ 2 compared to data from the Bluedisk survey). In the outer region (Σ _{H I} < 1 M_{⊙} pc^{-2}), the simulated profiles agree quantitatively with observations. Scaled by H I size, the simulated profiles of H I-rich (M_{H I}> 10^{9.8} M_{⊙}) and control galaxies (10^{9.1} M_{⊙}> M_{H I} > 10^{9.8} M_{⊙}) follow each other closely, as observed.

  8. Environmental Assessment for decontaminating and decommissioning the General Atomics Hot Cell Facility. Final [report

    SciTech Connect

    1995-08-01

    This EA evaluates the proposed action to decontaminate and decommission GA`s hot cell facility in northern San Diego, CA. This facility has been used for DOE and commercial nuclear R&D for > 30 years. About 30,000 cubic feet of decontamination debris and up to 50,000 cubic feet of contaminated soil are to be removed. Low-level radioactive waste would be shipped for disposal. It was determined that the proposal does not constitute a major federal action significantly affecting the human environment according to NEPA; therefore, a finding of no significant impact is made, and an environmental impact statement is not required.

  9. Changes in the morphology of interstellar ice analogues after hydrogen atom exposure.

    PubMed

    Accolla, Mario; Congiu, Emanuele; Dulieu, François; Manicò, Giulio; Chaabouni, Henda; Matar, Elie; Mokrane, Hakima; Lemaire, Jean Louis; Pirronello, Valerio

    2011-05-01

    The morphology of water ice in the interstellar medium is still an open question. Although accretion of gaseous water could not be the only possible origin of the observed icy mantles covering dust grains in cold molecular clouds, it is well known that water accreted from the gas phase on surfaces kept at 10 K forms ice films that exhibit a very high porosity. It is also known that in the dark clouds H(2) formation occurs on the icy surface of dust grains and that part of the energy (4.48 eV) released when adsorbed atoms react to form H(2) is deposited in the ice. The experimental study described in the present work focuses on how relevant changes of the ice morphology result from atomic hydrogen exposure and subsequent recombination. Using the temperature-programmed desorption (TPD) technique and a method of inversion analysis of TPD spectra, we show that there is an exponential decrease in the porosity of the amorphous water ice sample following D-atom irradiation. This decrease is inversely proportional to the thickness of the ice and has a value of ϕ(0) = 2 × 10(16) D-atoms cm(-2) per layer of H(2)O. We also use a model which confirms that the binding sites on the porous ice are destroyed regardless of their energy depth, and that the reduction of the porosity corresponds in fact to a reduction of the effective area. This reduction appears to be compatible with the fraction of D(2) formation energy transferred to the porous ice network. Under interstellar conditions, this effect is likely to be efficient and, together with other compaction processes, provides a good argument to believe that interstellar ice is amorphous and non-porous.

  10. Surface loss probability of atomic hydrogen for different electrode cover materials investigated in H₂-Ar low-pressure plasmas

    SciTech Connect

    Sode, M. Schwarz-Selinger, T.; Jacob, W.; Kersten, H.

    2014-07-07

    In an inductively coupled H₂-Ar plasma at a total pressure of 1.5 Pa, the influence of the electrode cover material on selected line intensities of H, H₂, and Ar are determined by optical emission spectroscopy and actinometry for the electrode cover materials stainless steel, copper, tungsten, Macor{sup ®}, and aluminum. Hydrogen dissociation degrees for the considered conditions are determined experimentally from the measured emission intensity ratios. The surface loss probability β{sub H} of atomic hydrogen is correlated with the measured line intensities, and β{sub H} values are determined for the considered materials. Without the knowledge of the atomic hydrogen temperature, β{sub H} cannot be determined exactly. However, ratios of β{sub H} values for different surface materials are in first order approximation independent of the atomic hydrogen temperature. Our results show that β{sub H} of copper is equal to the value of stainless steel, β{sub H} of Macor{sup ®} and tungsten is about 2 times smaller and β{sub H} of aluminum about 5 times smaller compared with stainless steel. The latter ratio is in reasonable agreement with literature. The influence of the atomic hydrogen temperature T{sub H} on the absolute value is thoroughly discussed. For our assumption of T{sub H}=600 K, we determine a β{sub H} for stainless steel of 0.39±0.13.

  11. Excitation and charge transfer in low-energy hydrogen-atom collisions with neutral atoms: Theory, comparisons, and application to Ca

    NASA Astrophysics Data System (ADS)

    Barklem, Paul S.

    2016-04-01

    A theoretical method is presented for the estimation of cross sections and rates for excitation and charge-transfer processes in low-energy hydrogen-atom collisions with neutral atoms, based on an asymptotic two-electron model of ionic-covalent interactions in the neutral atom-hydrogen-atom system. The calculation of potentials and nonadiabatic radial couplings using the method is demonstrated. The potentials are used together with the multichannel Landau-Zener model to calculate cross sections and rate coefficients. The main feature of the method is that it employs asymptotically exact atomic wave functions, which can be determined from known atomic parameters. The method is applied to Li+H , Na+H , and Mg+H collisions, and the results compare well with existing detailed full-quantum calculations. The method is applied to the astrophysically important problem of Ca+H collisions, and rate coefficients are calculated for temperatures in the range 1000-20 000 K.

  12. The influence of hydrogen dilution and substrate temperature in hot-wire deposition of amorphous and microcrystalline silicon with filament temperatures between 1900 and 2500 C

    SciTech Connect

    Conde, J.P.; Brogueira, P.; Castanha, R.; Chu, V.

    1996-12-31

    The effect of hydrogen dilution and substrate temperature on the optoelectronic and structural properties of thin films deposited by hot-wire chemical vapor deposition with filament temperatures between 1,900 and 2,500 C from silane and hydrogen are studied. Amorphous silicon films are obtained at high deposition rates for hydrogen dilutions below 90%. The deposition rate scales approximately linearly with the filament temperature in this regime. Microcrystalline films are obtained for hydrogen dilution above 90%, independently of the filament temperature and substrate temperature, with much lower growth rates. The Raman spectrum of these films shows high crystalline fraction and small grain size. High conductivity films, typical of microcrystalline silicon, with high growth rates were achieved by either increasing the substrate temperature at low hydrogen dilution, or by using a hydrogen dilution just at the amorphous to microcrystalline transition point.

  13. Catalytic activity of Pd-doped Cu nanoparticles for hydrogenation as a single-atom-alloy catalyst.

    PubMed

    Cao, Xinrui; Fu, Qiang; Luo, Yi

    2014-05-14

    The single atom alloy of extended surfaces is known to provide remarkably enhanced catalytic performance toward heterogeneous hydrogenation. Here we demonstrate from first principles calculations that this approach can be extended to nanostructures, such as bimetallic nanoparticles. The catalytic properties of the single-Pd-doped Cu55 nanoparticles have been systemically examined for H2 dissociation as well as H atom adsorption and diffusion, following the concept of single atom alloy. It is found that doping a single Pd atom at the edge site of the Cu55 shell can considerably reduce the activation energy of H2 dissociation, while the single Pd atom doped at the top site or in the inner layers is much less effective. The H atom adsorption on Cu55 is slightly stronger than that on the Cu(111) surface; however, a larger nanoparticle that contains 147 atoms could effectively recover the weak binding of the H atoms. We have also investigated the H atom diffusion on the 55-atom nanoparticle and found that spillover of the produced H atoms could be a feasible process due to the low diffusion barriers. Our results have demonstrated that facile H2 dissociation and weak H atom adsorption could be combined at the nanoscale. Moreover, the effects of doping one more Pd atom on the H2 dissociation and H atom adsorption have also been investigated. We have found that both the doping Pd atoms in the most stable configuration could independently exhibit their catalytic activity, behaving as two single-atom-alloy catalysts.

  14. A comprehensive study on atomic layer deposition of molybdenum sulfide for electrochemical hydrogen evolution

    NASA Astrophysics Data System (ADS)

    Kwon, Do Hyun; Jin, Zhenyu; Shin, Seokhee; Lee, Wook-Seong; Min, Yo-Sep

    2016-03-01

    Atomic layer deposition (ALD) has emerged as an efficient method to design and prepare catalysts with atomic precision. Here, we report a comprehensive study on ALD of molybdenum sulfide (MoSx) for an electrocatalytic hydrogen evolution reaction. By using molybdenum hexacarbonyl and dimethyldisulfide as the precursors of Mo and S, respectively, the MoSx catalysts are grown at 100 °C on porous carbon fiber papers (CFPs). The ALD process results in the growth of particle-like MoSx on the CFP due to the lack of adsorption sites, and its crystallographic structure is a mixture of amorphous and nano-crystalline phases. In order to unveil the intrinsic activity of the ALD-MoSx, the exchange current densities, Tafel slopes, and turnover frequencies of the catalysts grown under various ALD conditions have been investigated by considering the fractional surface coverage of MoSx on the CFP and catalytically-active surface area. In addition, the ALD-MoSx/CFP catalysts exhibit excellent catalytic stability due to the strong adhesion of MoSx on the CFP and the mixed phase.Atomic layer deposition (ALD) has emerged as an efficient method to design and prepare catalysts with atomic precision. Here, we report a comprehensive study on ALD of molybdenum sulfide (MoSx) for an electrocatalytic hydrogen evolution reaction. By using molybdenum hexacarbonyl and dimethyldisulfide as the precursors of Mo and S, respectively, the MoSx catalysts are grown at 100 °C on porous carbon fiber papers (CFPs). The ALD process results in the growth of particle-like MoSx on the CFP due to the lack of adsorption sites, and its crystallographic structure is a mixture of amorphous and nano-crystalline phases. In order to unveil the intrinsic activity of the ALD-MoSx, the exchange current densities, Tafel slopes, and turnover frequencies of the catalysts grown under various ALD conditions have been investigated by considering the fractional surface coverage of MoSx on the CFP and catalytically

  15. In situ observation of thermomigration of Sn atoms to the hot end of 96.5Sn-3Ag-0.5Cu flip chip solder joints

    NASA Astrophysics Data System (ADS)

    Ouyang, Fan-Yi; Kao, C.-L.

    2011-12-01

    In this study, we investigated the phenomenon of thermomigration in 96.5Sn-3Ag-0.5Cu flip chip solder joints at an ambient temperature of 150 °C. We observed mass protrusion on the chip side (hot end), indicating that Sn atoms moved to the hot end, and void formation on the substrate side (cold end). The diffusion markers also moved to the substrate side, in the same direction of the vacancy flux, indicating that the latter played a dominant role during the thermomigration process. The molar heat of transport (Q*) of the Sn atoms was 3.38 kJ/mol.

  16. Characterization of atomic-layer MoS2 synthesized using a hot filament chemical vapor deposition method

    NASA Astrophysics Data System (ADS)

    Ying-Zi, Peng; Yang, Song; Xiao-Qiang, Xie; Yuan, Li; Zheng-Hong, Qian; Ru, Bai

    2016-05-01

    Atomic-layer MoS2 ultrathin films are synthesized using a hot filament chemical vapor deposition method. A combination of atomic force microscopy (AFM), x-ray diffraction (XRD), high-resolution transition electron microscopy (HRTEM), photoluminescence (PL), and x-ray photoelectron spectroscopy (XPS) characterization methods is applied to investigate the crystal structures, valence states, and compositions of the ultrathin film areas. The nucleation particles show irregular morphology, while for a larger size somewhere, the films are granular and the grains have a triangle shape. The films grow in a preferred orientation (002). The HRTEM images present the graphene-like structure of stacked layers with low density of stacking fault, and the interlayer distance of plane is measured to be about 0.63 nm. It shows a clear quasi-honeycomb-like structure and 6-fold coordination symmetry. Room-temperature PL spectra for the atomic layer MoS2 under the condition of right and left circular light show that for both cases, the A1 and B1 direct excitonic transitions can be observed. In the meantime, valley polarization resolved PL spectra are obtained. XPS measurements provide high-purity samples aside from some contaminations from the air, and confirm the presence of pure MoS2. The stoichiometric mole ratio of S/Mo is about 2.0–2.1, suggesting that sulfur is abundant rather than deficient in the atomic layer MoS2 under our experimental conditions. Project supported by the Natural Science Foundation of Zhejiang Province, China (Grant Nos. LY16F040003 and LY16A040007) and the National Natural Science Foundation of China (Grant Nos. 51401069 and 11574067).

  17. Relativistic electronic dressing in laser-assisted ionization of atomic hydrogen by electron impact

    SciTech Connect

    Attaourti, Y.; Taj, S.

    2004-06-01

    Within the framework of the coplanar binary geometry where it is justified to use plane wave solutions for the study of the (e,2e) reaction and in the presence of a circularly polarized laser field, we introduce as a first step the Dirac-Volkov plane wave Born approximation 1 where we take into account only the relativistic dressing of the incident and scattered electrons. Then, we introduce the Dirac-Volkov plane wave Born approximation 2 where we take totally into account the relativistic dressing of the incident, scattered, and ejected electrons. We then compare the corresponding triple differential cross sections for laser-assisted ionization of atomic hydrogen by electron impact both for the nonrelativistic and the relativistic regime.

  18. Atomic layer deposition of aluminum sulfide thin films using trimethylaluminum and hydrogen sulfide

    SciTech Connect

    Sinha, Soumyadeep; Sarkar, Shaibal K.; Mahuli, Neha

    2015-01-15

    Sequential exposures of trimethylaluminum and hydrogen sulfide are used to deposit aluminum sulfide thin films by atomic layer deposition (ALD) in the temperature ranging from 100 to 200 °C. Growth rate of 1.3 Å per ALD cycle is achieved by in-situ quartz crystal microbalance measurements. It is found that the growth rate per ALD cycle is highly dependent on the purging time between the two precursors. Increased purge time results in higher growth rate. Surface limited chemistry during each ALD half cycle is studied by in-situ Fourier transformed infrared vibration spectroscopy. Time of flight secondary ion-mass spectroscopy measurement is used to confirm elemental composition of the deposited films.

  19. Bose-Einstein condensation and heat capacity of two-dimensional spin-polarized atomic hydrogen

    SciTech Connect

    Al-Sugheir, M. K.; Ghassib, H. B.; Awawdeh, M.

    2011-07-15

    The static fluctuation approximation (SFA) is used to study the condensate fraction and the specific heat capacity of finite two-dimensional spin-polarized atomic hydrogen. It is found that Bose-Einstein condensation occurs in this system. The transition temperature at different densities decreases as the number of particles of the system increases. At low density, a sharp peak in the specific heat capacity is observed at the transition temperature. On the other hand, as the density of the system increases, the transition temperature becomes no longer well-defined, and a hump is observed in the specific heat capacity around the transition temperature. A qualitative comparison of our results to published results for finite Bose systems shows good agreement.

  20. Method of producing a storage bulb for an atomic hydrogen maser

    NASA Technical Reports Server (NTRS)

    Erpenbach, H. (Inventor)

    1975-01-01

    A storage bulb for an atomic hydrogen maser is produced by coating its internal surface with an emulsion containing both TFE and FEP particles. The emulsion is produced by mixing a first quantity of TFE in an aqueous dispersion with a second quantity of FEP in an aqueous dispersion, with a third quantity of distilled water. The emulsion is poured into the bulb to coat it uniformly so as to form a thin film of emulsion on the bulb's internal surface. After excess emulsion is drained out of the bulb the emulsion in the bulb is dried to remove the water and most of the aqueous matter therefrom. The remaining emulsion is then cured by heating the bulb to a temperature of at least 380 C.

  1. Circular Rydberg States of the Hydrogen Atom in a Magnetic Field

    SciTech Connect

    Germann, T.C.; Herschbach, D.R. ); Dunn, M.; Watson, D.K. )

    1995-01-30

    Dimensional perturbation theory is used to study circular Rydberg states ([vert bar][ital m][vert bar]=[ital n][minus]1[much gt]1) and other large [vert bar][ital m][vert bar] states of the hydrogen atom in a uniform magnetic field. Because of a degeneracy between states of increased angular momentum and states of increased Cartesian dimensionality, the accuracy of the zeroth-order [ital D][r arrow][infinity] limit and a dimensional perturbation expansion improves significantly for states with larger [vert bar][ital m][vert bar]. In contrast to other approaches, this method is applicable to the entire range of magnetic field strengths. Energies and expectation values are presented as functions of the field strength.

  2. Reaction of an Iron(IV) Nitrido Complex with Cyclohexadienes: Cycloaddition and Hydrogen-Atom Abstraction

    PubMed Central

    2015-01-01

    The iron(IV) nitrido complex PhB(MesIm)3Fe≡N reacts with 1,3-cyclohexadiene to yield the iron(II) pyrrolide complex PhB(MesIm)3Fe(η5-C4H4N) in high yield. The mechanism of product formation is proposed to involve sequential [4 + 1] cycloaddition and retro Diels–Alder reactions. Surprisingly, reaction with 1,4-cyclohexadiene yields the same iron-containing product, albeit in substantially lower yield. The proposed reaction mechanism, supported by electronic structure calculations, involves hydrogen-atom abstraction from 1,4-cyclohexadiene to provide the cyclohexadienyl radical. This radical is an intermediate in substrate isomerization to 1,3-cyclohexadiene, leading to formation of the pyrrolide product. PMID:25068927

  3. Positronium formation in the n = 2 level in positron scattering from hydrogen and helium atoms

    SciTech Connect

    Khan, P.; Mazumdar, P.S.; Ghosh, A.S.

    1985-03-01

    A distorted-wave model (Phys. Rev. A 27, 1904 (1983); 28, 2180 (1983)) is applied to calculate the formation of positronium in the n = 2 states in e/sup +/ scattering from hydrogen and helium atoms. The incident wave is represented by a polarized-orbital method. The first-Born-approximation results of the 2p-excited-state capture cross section in the case of helium is reported for the first time. The first Born approximation is found to be unsuitable for prediction of the rearrangement processes. The present total (ground- and excited-state) positronium-formation cross sections have been compared with the corresponding observed values of Fornari et al. (Phys. Rev. Lett. 51, 2276 (1983)) and of Charlton et al. (J. Phys. B 16, L465 (1983)).

  4. Long term variations and solar variability of atomic oxygen and hydrogen in the mesosphere / lower thermosphere

    NASA Astrophysics Data System (ADS)

    Ern, Manfred; Kaufmann, Martin; Lehmann, Catrin; Riese, Martin; Smith, Anne; Marsh, Daniel

    Global measurements of the hydroxyl mesospheric airglow as observed by the SCIAMACHY satellite instrument are presented. SCIAMACHY is mounted on ESA's Envisat launched in March 2002 into a polar, sun-synchronous orbit with an inclination of 98.7deg and an ascending node at 22:00 local solar time. Limb observations on the night side cover about 70 degrees in terms of latitude during each orbit, covering 30S-70N, depending on season. Based on these measurements altitude profiles of atomic oxygen and hydrogen are retrieved by means of an OH non-LTE model. These data are analyzed with respect to solar illumination conditions and global wave activity. A windowed space-time Fourier analysis is carried out to investigate seasonal changes in mesopause wave activity. First comparisons with simulations of the NCAR ROSE model are shown.

  5. Chemical reactivity of hydrogen, nitrogen, and oxygen atoms at temperatures below 100 k

    NASA Technical Reports Server (NTRS)

    Mcgee, H. A., Jr.

    1973-01-01

    The synthesis of unusual compounds by techniques employing cryogenic cooling to retard their very extreme reactivity was investigated. Examples of such species that were studied are diimide (N2H2), cyclobutadiene (C4H4), cyclopropanone (C3H4O), oxirene (C2H2O), and many others. Special purpose cryogenically cooled inlet arrangements were designed such that the analyses incurred no warm-up of the cold, and frequently explosively unstable, compounds. Controlled energy electron impact techniques were used to measure critical potentials and to develop the molecular energetics and thermodynamics of these molecules and to gain some insight into their kinetic characteristics as well. Three and four carbon strained ring molecules were studied. Several reactions of oxygen and hydrogen atoms with simple molecules of H, N, C, and O in hard quench configurations were studied. And the quench stabilization of BH3 was explored as a model system in cryochemistry.

  6. Calculation of the total and total ionization cross sections for positron scattering on atomic hydrogen

    SciTech Connect

    Bray, I. ); Stelbovics, A.T. )

    1994-04-01

    The total and total ionization cross sections for positron scattering on atomic hydrogen are calculated by applying the convergent-close-coupling method to the model where positronium-formation channels are omitted. This model accurately describes the physics of the scattering whenever the positronium formation cross section is negligible, in particular, above 100 eV for this system. The total ionization cross section results in this energy region are in excellent agreement with the recent measurements of Jones [ital et] [ital al]. [J. Phys. B 26, L483 (1993)], and so lie below the earlier measurements of Spicher [Phys. Rev. Lett. 64, 1019 (1990)], and the recent calculations of Acacia [ital et] [ital al]. [Phys. Rev. Lett. (to be published)]. The total cross section is in very good agreement with the recent measurements of Zhou [ital et] [ital al]. (unpublished) down to 30 eV.

  7. Experiments on continuum electron capture in atomic hydrogen and collisional interaction of trapped ions. Progress report

    SciTech Connect

    Sellin, I.A.; Elston, S.B.

    1981-01-01

    This section describes the background and scope of as well as progress made on experiments designed to test the present theory of charge exchange to continuum for the case of bare nuclei on atomic hydrogen. The charge transfer process is well known to be an essential ingredient of any attempt to understand the ionization of gaseous media traversed by highly-charged energetic ions. Surprisingly, a sometimes dominant contribution to such ionization remained undiscovered until the past decade. This process, known as charge transfer to the continuum, involves the ionization of electrons from the target species into unbound states closely matched in exit direction and speed to the charged particles which generate them. Subsequent measurements of the resultant forward electron production, performed by University of Tennessee searchers at Oak Ridge and Brookhaven National Laboratories, were unique in employing more highly charged projectiles than previously.

  8. Design of an atomic layer deposition reactor for hydrogen sulfide compatibility

    NASA Astrophysics Data System (ADS)

    Dasgupta, Neil P.; Mack, James F.; Langston, Michael C.; Bousetta, Al; Prinz, Fritz B.

    2010-04-01

    A customized atomic layer deposition (ALD) reactor was designed with components compatible with hydrogen sulfide (H2S) chemistry. H2S is used as a reactant for the ALD of metal sulfides. The use of H2S in an ALD reactor requires special attention to safety issues due to its highly toxic, flammable, and corrosive nature. The reactor was designed with respect to materials compatibility of all wetted components with H2S. A customized safety interlock system was developed to shut down the system in the event of toxic gas leakage, power outage, loss of building ventilation or compressed air pressure. ALD of lead sulfide (PbS) and zinc sulfide (ZnS) were demonstrated with no chemical contamination or detectable release of H2S.

  9. Rate of reaction of the hydrogen atom with nitrous oxide in ambient water

    NASA Astrophysics Data System (ADS)

    Kazmierczak, Lukasz; Swiatla-Wojcik, Dorota; Szala-Bilnik, Joanna; Wolszczak, Marian

    2016-08-01

    The reaction of the hydrogen atom with nitrous oxide has been investigated by pulse radiolysis of N2O-saturated 0.1 M HCl solution at room temperature (24±1 °C). The value of (9±2)×104 M-1 s-1 obtained for the reaction rate constant is between the early estimates 1×104 M-1 s-1 by Czapski and Jortner (1960) and 4.3×105 M-1 s-1 by Thomas (1969), and is much lower than 2×106 M-1 s-1 used recently (Janik et al., 2007; Ismail et al., 2013; Liu et al., 2015; Meesungnoen et al., 2015).

  10. Atomic Hydrogen as High-Precision Field Standard for High-Field EPR

    PubMed Central

    Stoll, Stefan; Ozarowski, Andrew; Britt, R. David; Angerhofer, Alexander

    2010-01-01

    We introduce atomic hydrogen trapped in an octaisobutylsilsesquioxane nanocage (H@iBuT8) as a new molecular high-precision magnetic field standard for high-field EPR spectroscopy of organic radicals and other systems with signals around g = 2. Its solid-state EPR spectrum consists of two narrow lines separated by about 51 mT and centered at g ≈ 2. The isotropic g factor is 2.00294(3) and essentially temperature independent. The isotopic 1H hyperfine coupling constant is 1416.8(2) MHz below 70 K and decreases slightly with increasing temperature to 1413.7(1) MHz at room temperature. The spectrum of the standard does not overlap with those of most organic radicals, and it can be easily prepared and is stable at room temperature. PMID:20813570

  11. Absolute rate constants for the reaction of atomic hydrogen with ketene from 298 to 500 K

    NASA Technical Reports Server (NTRS)

    Michael, J. V.; Nava, D. F.; Payne, W. A.; Stief, L. J.

    1979-01-01

    Rate constants for the reaction of atomic hydrogen with ketene have been measured at room temperature by two techniques, flash photolysis-resonance fluorescence and discharge flow-resonance fluorescence. The measured values are (6.19 + or - 1.68) x 10 to the -14th and (7.3 + or - 1.3) x 10 to the -14th cu cm/molecule/s, respectively. In addition, rate constants as a function of temperature have been measured over the range 298-500 K using the FP-RF technique. The results are best represented by the Arrhenius expression k = (1.88 + or - 1.12) x 10 to the -11th exp(-1725 + or - 190/T) cu cm/molecule/s, where the indicated errors are at the two standard deviation level.

  12. A supramolecular structure insight for conversion property of cellulose in hot compressed water: Polymorphs and hydrogen bonds changes.

    PubMed

    Wang, Yan; Lian, Jie; Wan, Jinquan; Ma, Yongwen; Zhang, Yingshi

    2015-11-20

    Waste paper samples with different cellulose supramolecular structure were treated in hot compressed water (HCW) at 375°C and 22.5MPa within 200s to evaluate the specific effect mechanism of cellulose supramolecular structure on the conversion of waste paper to reusable resource. Although the distribution of liquid products and the oligosaccharides were related to reaction time, depolymerization and decrystallization of the cellulose, the characteristics absorption peak of cellulose from FTIR analysis and crystal structure of the cellulose detected in the residues with hydrolysis rate up 96.5% indicated crystal structure was the dominant factor that affect conversion behavior of waste paper. The conversion of cellulose Iβ to cellulose Iα or cellulose I(α+β) in HCW demonstrated that the recrystallization occurred during the decrystallization of cellulose through the rearrangement of hydrogen bonds.

  13. Absolute rate constant of the reaction between chlorine /2P/ atoms and hydrogen peroxide from 298 to 424 K

    NASA Technical Reports Server (NTRS)

    Keyser, L. F.

    1980-01-01

    The absolute rate constant of the reaction between chlorine (2P) atoms and hydrogen peroxide was determined from 298 to 424 K, using the discharge flow resonance fluorescence technique. Pseudo-first-order conditions were used with hydrogen peroxide in large excess. A fast flow-sampling procedure limited hydrogen peroxide decomposition to less than 5% over the temperature range studied. At 298 K, the rate constant is (4.1 plus or minus 0.2) x 10 to the minus 13th cu cm/molecule-sec.

  14. Interaction of hot swirling air and liquid film flow in airblast atomizers

    NASA Astrophysics Data System (ADS)

    Baumann, Wolfgang W.; Bendisch, Holger; Eickhoff, Heinrich; Thiele, Frank

    The flowfield in an airblast atomizer of the prefilming type is studied numerically. Special attention is drawn to the flow near the liquid film surface, which is calculated using a boundary-layer method. Thereby near-wall effects (e.g., evaporation) are exactly accounted for. The main nozzle flow is calculated using the Navier-Stokes equations. Both systems are linked by the boundary conditions. The results for an airblast atomizer with adjacent combustion chamber show significant differences between coupled and uncoupled calculations. It is shown that the detailed modeling of the film and the coupled calculation, which accounts exactly for boundary-layer effects including evaporation, is essential for accurate simulations.

  15. GHz Rabi Flopping to Rydberg States in Hot Atomic Vapor Cells

    SciTech Connect

    Huber, B.; Baluktsian, T.; Schlagmueller, M.; Koelle, A.; Kuebler, H.; Loew, R.; Pfau, T.

    2011-12-09

    We report on the observation of Rabi oscillations to a Rydberg state on a time scale below 1 ns in thermal rubidium vapor. We use a bandwidth-limited pulsed excitation and observe up to 6 full Rabi cycles within a pulse duration of {approx}4 ns. We find good agreement between the experiment and numerical simulations based on a surprisingly simple model. This result shows that fully coherent dynamics with Rydberg states can be achieved even in thermal atomic vapor, thus suggesting small vapor cells as a platform for room-temperature quantum devices. Furthermore, the result implies that previous coherent dynamics in single-atom Rydberg gates can be accelerated by 3 orders of magnitude.

  16. Low temperature removal of surface oxides and hydrocarbons from Ge(100) using atomic hydrogen

    NASA Astrophysics Data System (ADS)

    Walker, M.; Tedder, M. S.; Palmer, J. D.; Mudd, J. J.; McConville, C. F.

    2016-08-01

    Germanium is a group IV semiconductor with many current and potential applications in the modern semiconductor industry. Key to expanding the use of Ge is a reliable method for the removal of surface contamination, including oxides which are naturally formed during the exposure of Ge thin films to atmospheric conditions. A process for achieving this task at lower temperatures would be highly advantageous, where the underlying device architecture will not diffuse through the Ge film while also avoiding electronic damage induced by ion irradiation. Atomic hydrogen cleaning (AHC) offers a low-temperature, damage-free alternative to the common ion bombardment and annealing (IBA) technique which is widely employed. In this work, we demonstrate with X-ray photoelectron spectroscopy (XPS) that the AHC method is effective in removing surface oxides and hydrocarbons, yielding an almost completely clean surface when the AHC is conducted at a temperature of 250 °C. We compare the post-AHC cleanliness and (2 × 1) low energy electron diffraction (LEED) pattern to that obtained via IBA, where the sample is annealed at 600 °C. We also demonstrate that the combination of a sample temperature of 250 °C and atomic H dosing is required to clean the surface. Lower temperatures prove less effective in removal of the oxide layer and hydrocarbons, whilst annealing in ultra-high vacuum conditions only removes weakly bound hydrocarbons. Finally, we examine the subsequent H-termination of an IBA-cleaned sample using XPS, LEED and ultraviolet photoelectron spectroscopy (UPS) in order to examine changes in the work function of Ge(100) upon hydrogenation.

  17. Atomic hydrogen in the mesopause region derived from SABER: Algorithm theoretical basis, measurement uncertainty, and results

    NASA Astrophysics Data System (ADS)

    Mlynczak, Martin G.; Hunt, Linda A.; Marshall, B. Thomas; Mertens, Christopher J.; Marsh, Daniel R.; Smith, Anne K.; Russell, James M.; Siskind, David E.; Gordley, Larry L.

    2014-03-01

    Atomic hydrogen (H) is a fundamental component in the photochemistry and energy balance of the terrestrial mesopause region (80-100 km). H is generated primarily by photolysis of water vapor and participates in a highly exothermic reaction with ozone. This reaction is a significant source of heat in the mesopause region and also creates highly vibrationally excited hydroxyl (OH) from which the Meinel band radiative emission features originate. Concentrations (cm-3) and volume mixing ratios of H are derived from observations of infrared emission from the OH (υ = 9 + 8, Δυ = 2) vibration-rotation bands near 2.0 µm made by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite. The algorithms for deriving day and night H are described herein. Day and night concentrations exhibit excellent agreement between 87 and 95 km. SABER H results also exhibit good agreement with observations from the Solar Mesosphere Explorer made nearly 30 years ago. An apparent inverse dependence on the solar cycle is observed in the SABER H concentrations, with the H increasing as solar activity decreases. This increase is shown to be primarily due to the temperature dependence of various reaction rate coefficients for H photochemistry. The SABER H data, coupled with SABER atomic oxygen, ozone, and temperature, enable tests of mesospheric photochemistry and energetics in atmospheric models, studies of formation of polar mesospheric clouds, and studies of atmospheric evolution via escape of hydrogen. These data and studies are made possible by the wide range of parameters measured simultaneously by the SABER instrument.

  18. Carbon Dioxide in Exoplanetary Atmospheres: Rarely Dominant Compared to Carbon Monoxide and Water in Hot, Hydrogen-dominated Atmospheres

    NASA Astrophysics Data System (ADS)

    Heng, Kevin; Lyons, James R.

    2016-02-01

    We present a comprehensive study of the abundance of carbon dioxide in exoplanetary atmospheres in hot, hydrogen-dominated atmospheres. We construct novel analytical models of systems in chemical equilibrium that include carbon monoxide, carbon dioxide, water, methane and acetylene and relate the equilibrium constants of the chemical reactions to temperature and pressure via the tabulated Gibbs free energies. We prove that such chemical systems may be described by a quintic equation for the mixing ratio of methane. By examining the abundances of these molecules across a broad range of temperatures (spanning equilibrium temperatures from 600 to 2500 K), pressures (via temperature-pressure profiles that explore albedo and opacity variations) and carbon-to-oxygen ratios, we conclude that carbon dioxide is subdominant compared to carbon monoxide and water. Atmospheric mixing does not alter this conclusion if carbon dioxide is subdominant everywhere in the atmosphere. Carbon dioxide and carbon monoxide may attain comparable abundances if the metallicity is greatly enhanced, but this property is negated by temperatures above 1000 K. For hydrogen-dominated atmospheres, our generic result has the implication that retrieval studies may wish to set the subdominance of carbon dioxide as a prior of the calculation and not let its abundance completely roam free as a fitting parameter, because it directly affects the inferred value of the carbon-to-oxygen ratio and may produce unphysical conclusions. We discuss the relevance of these implications for the hot Jupiter WASP-12b and suggest that some of the previous results are chemically impossible. The relative abundance of carbon dioxide to acetylene is potentially a sensitive diagnostic of the carbon-to-oxygen ratio.

  19. Predicting organic hydrogen atom transfer rate constants using the Marcus cross relation

    PubMed Central

    Warren, Jeffrey J.; Mayer, James M.

    2010-01-01

    Chemical reactions that involve net hydrogen atom transfer (HAT) are ubiquitous in chemistry and biology, from the action of antioxidants to industrial and metalloenzyme catalysis. This report develops and validates a procedure to predict rate constants for HAT reactions of oxyl radicals (RO•) in various media. Our procedure uses the Marcus cross relation (CR) and includes adjustments for solvent hydrogen-bonding effects on both the kinetics and thermodynamics of the reactions. Kinetic solvent effects (KSEs) are included by using Ingold’s model, and thermodynamic solvent effects are accounted for by using an empirical model developed by Abraham. These adjustments are shown to be critical to the success of our combined model, referred to as the CR/KSE model. As an initial test of the CR/KSE model we measured self-exchange and cross rate constants in different solvents for reactions of the 2,4,6-tri-tert-butylphenoxyl radical and the hydroxylamine 2,2′-6,6′-tetramethyl-piperidin-1-ol. Excellent agreement is observed between the calculated and directly determined cross rate constants. We then extend the model to over 30 known HAT reactions of oxyl radicals with OH or CH bonds, including biologically relevant reactions of ascorbate, peroxyl radicals, and α-tocopherol. The CR/KSE model shows remarkable predictive power, predicting rate constants to within a factor of 5 for almost all of the surveyed HAT reactions. PMID:20215463

  20. Hybrid Modeling of Hydrogen Energetic Neutral Atoms from Mars: Emission from Subsolar Magnetosheath

    NASA Astrophysics Data System (ADS)

    Wang, Xiao-Dong; Kallio, Esa; Barabash, Stas; Futaana, Yoshifumi

    2015-04-01

    We simulated the hydrogen energetic neutral atom (ENA) emission from the subsolar magnetosheath of Mars using a hybrid scheme in order to reproduce multiple features of the statistical features obtained from statistical observations of the Neutral Particle Detectors on the Mars Express spacecraft. We track the charge exchange reaction between the ions produced by the hybrid plasma model under a Martian neutral exosphere model. The simulation exhibits a directional emission of hydrogen ENAs from dayside magnetosheath. Particularly, the stronger ENA emission in the opposite direction of the solar wind convection electric field is reproduced, being consistent with the observations, by a corresponding asymmetry in the proton flux at the lower magnetosheath. This proton flux asymmetry is caused by the mass loading of ionospheric heavy ions in the direction of the convection electric field. We also investigate the influences of the upstream solar wind dynamic pressure. We demonstrate that higher dynamic pressure causes stronger and more anisotropic ENA emission, besides the influence of the proton flux. This dependence suggests that the induced magnetic boundary is lower during higher dynamic pressure, where the sheath protons can access to a denser exosphere and thus the charge exchange rate is higher.

  1. Intermolecular and intramolecular hydrogen bonds involving fluorine atoms: implications for recognition, selectivity, and chemical properties.

    PubMed

    Dalvit, Claudio; Vulpetti, Anna

    2012-02-01

    A correlation between 19F NMR isotropic chemical shift and close intermolecular F⋅⋅⋅H-X contacts (with X=N or O) has been identified upon analysis of the X-ray crystal structures of fluorinated molecules listed in the Cambridge Structural Database (CSD). An optimal F⋅⋅⋅X distance involving primary and shielded secondary fluorine atoms in hydrogen-bond formation along with a correlation between F⋅⋅⋅H distance and F⋅⋅⋅H-X angle were also derived from the analysis. The hydrogen bonds involving fluorine are relevant, not only for the recognition mechanism and stabilization of a preferred conformation, but also for improvement in the permeability of the molecules, as shown with examples taken from a proprietary database. Results of an analysis of the small number of fluorine-containing natural products listed in the Protein Data Bank (PDB) appear to strengthen the derived correlation between 19F NMR isotropic chemical shift and interactions involving fluorine (also known as the "rule of shielding") and provides a hypothesis for the recognition mechanism and catalytic activity of specific enzymes. Novel chemical scaffolds, based on the rule of shielding, have been designed for recognizing distinct structural motifs present in proteins. It is envisaged that this approach could find useful applications in drug design for the efficient optimization of chemical fragments or promising compounds by increasing potency and selectivity against the desired biomolecular target.

  2. Formation of hydrogen atom in 2s state in proton-sodium inelastic scattering

    NASA Astrophysics Data System (ADS)

    Sabbah, A. Elkilany

    2015-03-01

    The inelastic collision of protons with sodium atoms are treated for the first time within the framework of the coupled-static and frozen core approximations. The method is used for calculating partial and total cross-sections with the assumption that only two channels (elastic and hydrogen formation in 2s state) are open. In each case, the calculations are carried out for seven values of the total angular momentum ℓ(0 ≤ ℓ ≤ 6). The target is described using the Clementi Roetti wave functions within the framework of the one valence electron model. We use Lipmann-Swinger equation to solve the derived equations of the problem, then apply an iterative numerical method to obtain the code of computer to calculate iterative partial cross-sections. This can be done through calculating the reactance matrix at different values of considered energies to obtain the transition matrix that gives partial and total cross sections. The present results for total hydrogen (2s state) formation cross sections are in agreement with results of other available ones in wide range of incident energy.

  3. The elimination of a hydrogen atom in Na(H2O)n

    NASA Astrophysics Data System (ADS)

    Chan, Ka Wai; Siu, Chi-Kit; Wong, S. Y.; Liu, Zhi-Feng

    2005-09-01

    By a systematic examination on Na(H2O)n, with n =4-7, 9, 10, and 15, we demonstrate that a hydrogen loss reaction can be initiated by a single sodium atom with water molecules. This reaction is similar to the well-known size-dependent intracluster hydrogen loss in Mg+(H2O)n, which is isoelectronic to Na(H2O)n. However, with one less charge on Na(H2O)n than that on Mg+(H2O)n, the hydrogen loss for Na(H2O)n is characterized by a higher barrier and a more flexible solvation shell around the metal ion, although the reaction should be accessible, as the lowest barrier is around 8kcal/mol. Interestingly, the hydroxide ion OH- produced in the process is stabilized by the solvation of H2O molecules and the formation of an ion pair Na+(H2O)4(H2O)n-l-4[OH-(H2O)l]. The activation barrier is reduced as the unpaired electron in Na(H2O)n moves to higher solvation shells with increasing cluster size, and the reaction is not switched off for larger clusters. This is in sharp contrast to the reaction for Mg+(H2O)n, in which the OH- ion is stabilized by direct coordination with Mg2+ and the reaction is switched off for n >17, as the unpaired electron moved to higher solvation shells. Such a contrast illustrates the important link between microsolvation environment and chemical reactivity in solvation clusters.

  4. Partial redistribution in multilevel atoms. I. Method and application to the solar hydrogen line formation

    SciTech Connect

    Hubeny, I.

    1995-12-01

    We present a robust method for solution of multilevel non-LTE line transfer problems including the effects of partial frequency redistribution (PRD). This method allows the self-consistent solution for redistribution of scattered line photons simultaneously in multiple transitions of a model atom, including the effects of resonant Raman scattering ({open_quote}{open_quote}cross-redistribution{close_quote}{close_quote}) among lines sharing common upper levels. The method is incorporated into the framework of the widely used non-LTE complete redistribution code MULTI. We have applied this method to the problem of transfer in hydrogen lines in a plane-parallel solar model atmosphere, including cross-redistribution between the H{alpha} and L{beta}, using general redistribution functions for the L{alpha} and L{beta} lines which are not restricted by the impact approximation. The convergence properties of this method are demonstrated to be comparable to that of the equivalent complete redistribution problem. In this solar model, PRD in the L{alpha} line produces the dominant influence on the level populations. It changes considerably the populations of the excited states of hydrogen, as well as the proton number density, in the middle and upper chromosphere, owing to modification of the L{alpha} wing radiation. The population of the hydrogen ground state undergoes only modest changes, however. The influence of cross-redistribution and PRD in L{beta} has a much smaller influence on the level populations but a considerable influence on the wing intensity of the L{beta} line. {copyright} {ital 1995 The American Astronomical Society.}

  5. A comprehensive study on atomic layer deposition of molybdenum sulfide for electrochemical hydrogen evolution.

    PubMed

    Kwon, Do Hyun; Jin, Zhenyu; Shin, Seokhee; Lee, Wook-Seong; Min, Yo-Sep

    2016-04-01

    Atomic layer deposition (ALD) has emerged as an efficient method to design and prepare catalysts with atomic precision. Here, we report a comprehensive study on ALD of molybdenum sulfide (MoSx) for an electrocatalytic hydrogen evolution reaction. By using molybdenum hexacarbonyl and dimethyldisulfide as the precursors of Mo and S, respectively, the MoSx catalysts are grown at 100 °C on porous carbon fiber papers (CFPs). The ALD process results in the growth of particle-like MoSx on the CFP due to the lack of adsorption sites, and its crystallographic structure is a mixture of amorphous and nano-crystalline phases. In order to unveil the intrinsic activity of the ALD-MoSx, the exchange current densities, Tafel slopes, and turnover frequencies of the catalysts grown under various ALD conditions have been investigated by considering the fractional surface coverage of MoSx on the CFP and catalytically-active surface area. In addition, the ALD-MoSx/CFP catalysts exhibit excellent catalytic stability due to the strong adhesion of MoSx on the CFP and the mixed phase. PMID:26973254

  6. Atomic layer deposition of magnesium fluoride via bis(ethylcyclopentadienyl)magnesium and anhydrous hydrogen fluoride

    SciTech Connect

    Hennessy, John Jewell, April D.; Greer, Frank; Lee, Michael C.; Nikzad, Shouleh

    2015-01-15

    A new process has been developed to deposit magnesium fluoride (MgF{sub 2}) thin films via atomic layer deposition (ALD) for use as optical coatings in the ultraviolet. MgF{sub 2} was deposited in a showerhead style ALD reactor using bis(ethylcyclopentadienyl)magnesium and anhydrous hydrogen fluoride (HF) as precursors at substrate temperatures from 100 to 250 °C. The use of HF was observed to result in improved morphology and reduced impurity content compared to other reported MgF{sub 2} ALD approaches that use metal fluoride precursors as the fluorine-containing chemistry. Characterization of these films has been performed using spectroscopic ellipsometry, atomic force microscopy, and x-ray photoelectron spectroscopy for material deposited on silicon substrates. Films at all substrate temperatures were transparent at wavelengths down to 190 nm and the low deposition temperature combined with low surface roughness makes these coatings good candidates for a variety of optical applications in the far ultraviolet.

  7. Nonresonant corrections for the optical resonance frequency measurements in the hydrogen atom

    SciTech Connect

    Labzowsky, Leonti; Schedrin, Gavriil; Solovyev, Dmitrii; Chernovskaya, Evgenia; Plunien, Guenter; Karshenboim, Savely

    2009-05-15

    The deviation of the natural spectral line profile from the Lorentz shape for the optical resonant frequency measurements is considered. This deviation leads to an asymmetry, which is mainly due to nonresonant correction to the resonant Lorentz profile. The nonresonant corrections are studied for the different types of the atomic resonant experiments. The most accurate recent optical resonance experiments are analyzed, i.e., the two-photon 1s-2s resonance excitation of the hydrogen atom with the delayed decay in the external electric field. The description of the nonresonant correction in the latter case requires the employment of QED with different in and out Hamiltonians. The nonresonant corrections for this experiment are investigated and found to be about 10{sup -5} Hz, while the recent experimental uncertainty is 34 Hz and in the near feature is expected to be a few hertz. The projected 1s-2s resonance excitation experiment with the three-photon ionization detection (which is now in progress) is also considered.

  8. Photoionization microscopy of Rydberg hydrogen atom in a non-uniform electrical field

    NASA Astrophysics Data System (ADS)

    Shao-Hao, Cheng; De-Hua, Wang; Zhao-Hang, Chen; Qiang, Chen

    2016-06-01

    In this paper, we investigate the photoionization microscopy of the Rydberg hydrogen atom in a gradient electric field for the first time. The observed oscillatory patterns in the photoionization microscopy are explained within the framework of the semiclassical theory, which can be considered as a manifestation of interference between various electron trajectories arriving at a given point on the detector plane. In contrast with the photoionization microscopy in the uniform electric field, the trajectories of the ionized electron in the gradient electric field will become chaotic. An infinite set of different electron trajectories can arrive at a given point on the detector plane, which makes the interference pattern of the electron probability density distribution extremely complicated. Our calculation results suggest that the oscillatory pattern in the electron probability density distribution depends sensitively on the electric field gradient, the scaled energy and the position of the detector plane. Through our research, we predict that the interference pattern in the electron probability density distribution can be observed in an actual photoionization microscopy experiment once the external electric field strength and the position of the electron detector plane are reasonable. This study provides some references for the future experimental research on the photoionization microscopy of the Rydberg atom in the non-uniform external fields. Project supported by the National Natural Science Foundation of China (Grant No. 11374133) and the Project of Shandong Provincial Higher Educational Science and Technology Program, China (Grant No. J13LJ04).

  9. An optimized intermolecular force field for hydrogen-bonded organic molecular crystals using atomic multipole electrostatics

    PubMed Central

    Pyzer-Knapp, Edward O.; Thompson, Hugh P. G.; Day, Graeme M.

    2016-01-01

    We present a re-parameterization of a popular intermolecular force field for describing intermolecular interactions in the organic solid state. Specifically we optimize the performance of the exp-6 force field when used in conjunction with atomic multipole electrostatics. We also parameterize force fields that are optimized for use with multipoles derived from polarized molecular electron densities, to account for induction effects in molecular crystals. Parameterization is performed against a set of 186 experimentally determined, low-temperature crystal structures and 53 measured sublimation enthalpies of hydrogen-bonding organic molecules. The resulting force fields are tested on a validation set of 129 crystal structures and show improved reproduction of the structures and lattice energies of a range of organic molecular crystals compared with the original force field with atomic partial charge electrostatics. Unit-cell dimensions of the validation set are typically reproduced to within 3% with the re-parameterized force fields. Lattice energies, which were all included during parameterization, are systematically underestimated when compared with measured sublimation enthalpies, with mean absolute errors of between 7.4 and 9.0%. PMID:27484370

  10. An optimized intermolecular force field for hydrogen-bonded organic molecular crystals using atomic multipole electrostatics.

    PubMed

    Pyzer-Knapp, Edward O; Thompson, Hugh P G; Day, Graeme M

    2016-08-01

    We present a re-parameterization of a popular intermolecular force field for describing intermolecular interactions in the organic solid state. Specifically we optimize the performance of the exp-6 force field when used in conjunction with atomic multipole electrostatics. We also parameterize force fields that are optimized for use with multipoles derived from polarized molecular electron densities, to account for induction effects in molecular crystals. Parameterization is performed against a set of 186 experimentally determined, low-temperature crystal structures and 53 measured sublimation enthalpies of hydrogen-bonding organic molecules. The resulting force fields are tested on a validation set of 129 crystal structures and show improved reproduction of the structures and lattice energies of a range of organic molecular crystals compared with the original force field with atomic partial charge electrostatics. Unit-cell dimensions of the validation set are typically reproduced to within 3% with the re-parameterized force fields. Lattice energies, which were all included during parameterization, are systematically underestimated when compared with measured sublimation enthalpies, with mean absolute errors of between 7.4 and 9.0%. PMID:27484370

  11. Status of Charge Exchange Cross Section Measurements for Highly Charged Ions on Atomic Hydrogen

    NASA Astrophysics Data System (ADS)

    Draganic, I. N.; Havener, C. C.; Schultz, D. R.; Seely, D. G.; Schultz, P. C.

    2011-05-01

    Total cross sections of charge exchange (CX) for C5+, N6+, and O7+ ions on ground state atomic hydrogen are measured in an extended collision energy range of 1 - 20,000 eV/u. Absolute CX measurements are performed using an improved merged-beams technique with intense highly charged ion beams extracted from a 14.5 GHz ECR ion source mounted on a high voltage platform. In order to improve the problematic H+ signal collection for these exoergic CX collisions at low relative energies, a new double focusing electrostatic analyzer was installed. Experimental CX data are in good agreement with all previous H-oven relative measurements at higher collision energies. We compare our results with the most recent molecular orbital close-coupling (MOCC) and atomic orbital close-coupling (AOCC) theoretical calculations. Work supported by the NASA Solar & Heliospheric Physics Program NNH07ZDA001N, the Office of Fusion Energy Sciences and the Division of Chemical Sciences, Geosciences, and Biosciences, and the Office of Basic Energy Sciences of the U.S. DoE.

  12. Solar Wind Charge Exchange Studies Of Highly Charged Ions On Atomic Hydrogen

    SciTech Connect

    Draganic, I. N.; Havener, C. C.; Seely, D. G.; McCammon, D.

    2011-06-01

    Accurate studies of low-energy charge exchange (CX) are critical to understanding underlying soft X-ray radiation processes in the interaction of highly charged ions from the solar wind with the neutral atoms and molecules in the heliosphere, cometary comas, planetary atmospheres, interstellar winds, etc.. Particularly important are the CX cross sections for bare, H-like, and He-like ions of C, N, O and Ne, which are the dominant charge states for these heavier elements in the solar wind. Absolute total cross sections for single electron capture by H-like ions of C, N, O and fully-stripped O ions from atomic hydrogen have been measured in an expanded range of relative collision energies (5 eV/u-20 keV/u) and compared to previous H-oven measurements. The present measurements are performed using a merged-beams technique with intense highly charged ion beams extracted from a 14.5 GHz ECR ion source installed on a high voltage platform at the Oak Ridge National Laboratory. For the collision energy range of 0.3 keV/u-3.3 keV/u, which corresponds to typical ion velocities in the solar wind, the new measurements are in good agreement with previous H-oven measurements. The experimental results are discussed in detail and compared with theoretical calculations where available.

  13. Solar Wind Charge Exchange Studies of Highly Charged Ions on Atomic Hydrogen

    SciTech Connect

    Draganic, Ilija N; Seely, D. G.; McCammon, D; Havener, Charles C

    2011-01-01

    Accurate studies of low energy charge exchange (CX) are critical to understanding underlying soft X ray radiation processes in the interaction of highly charged ions from the solar wind with the neutral atoms and molecules in the heliosphere, cometary comas, planetary atmospheres, interstellar winds, etc.. Particularly important are the CX cross sections for bare, H like, and He like ions of C, N, O and Ne, which are the dominant charge states for these heavier elements in the solar wind. Absolute total cross sections for single electron capture by H like ions of C, N, O and fully stripped O ions from atomic hydrogen have been measured in an expanded range of relative collision energies (5 eV u 20 keV u) and compared to previous H oven measurements. The present measurements are performed using a merged beams technique with intense highly charged ion beams extracted from a 14.5 GHz ECR ion source installed on a high voltage platform at the Oak Ridge National Laboratory. For the collision energy range of 0.3 keV u 3.3 keV u, which corresponds to typical ion velocities in the solar wind, the new measurements are in good agreement with previous H oven measurements. The experimental results are discussed in detail and compared with theoretical calculations where available.

  14. The influence hydrogen atom addition has on charge switching during motion of the metal atom in endohedral Ca@C60H4 isomers.

    PubMed

    Raggi, G; Besley, E; Stace, A J

    2016-09-13

    Density functional theory has been applied in a study of charge transfer between an endohedral calcium atom and the fullerene cage in Ca@C60H4 and [Ca@C60H4](+) isomers. Previous calculations on Ca@C60 have shown that the motion of calcium within a fullerene is accompanied by large changes in electron density on the carbon cage. Based on this observation, it has been proposed that a tethered endohedral fullerene might form the bases of a nanoswitch. Through the addition of hydrogen atoms to one hemisphere of the cage it is shown that, when compared with Ca@C60, asymmetric and significantly reduced energy barriers can be generated with respect to motion of the calcium atom. It is proposed that hydrogen atom addition to a fullerene might offer a route for creating a bi-stable nanoswitch that can be fine-tuned through the selection of an appropriate isomer and number of atoms attached to the cage of an endohedral fullerene.This article is part of the themed issue 'Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene'.

  15. Direct atomic-scale imaging of hydrogen and oxygen interstitials in pure niobium using atom-probe tomography and aberration-corrected scanning transmission electron microscopy.

    PubMed

    Kim, Yoon-Jun; Tao, Runzhe; Klie, Robert F; Seidman, David N

    2013-01-22

    Imaging the three-dimensional atomic-scale structure of complex interfaces has been the goal of many recent studies, due to its importance to technologically relevant areas. Combining atom-probe tomography and aberration-corrected scanning transmission electron microscopy (STEM), we present an atomic-scale study of ultrathin (~5 nm) native oxide layers on niobium (Nb) and the formation of ordered niobium hydride phases near the oxide/Nb interface. Nb, an elemental type-II superconductor with the highest critical temperature (T(c) = 9.2 K), is the preferred material for superconducting radio frequency (SRF) cavities in next-generation particle accelerators. Nb exhibits high solubilities for oxygen and hydrogen, especially within the RF-field penetration depth, which is believed to result in SRF quality factor losses. STEM imaging and electron energy-loss spectroscopy followed by ultraviolet laser-assisted local-electrode atom-probe tomography on the same needle-like sample reveals the NbO(2), Nb(2)O(5), NbO, Nb stacking sequence; annular bright-field imaging is used to visualize directly hydrogen atoms in bulk β-NbH.

  16. The influence hydrogen atom addition has on charge switching during motion of the metal atom in endohedral Ca@C60H4 isomers.

    PubMed

    Raggi, G; Besley, E; Stace, A J

    2016-09-13

    Density functional theory has been applied in a study of charge transfer between an endohedral calcium atom and the fullerene cage in Ca@C60H4 and [Ca@C60H4](+) isomers. Previous calculations on Ca@C60 have shown that the motion of calcium within a fullerene is accompanied by large changes in electron density on the carbon cage. Based on this observation, it has been proposed that a tethered endohedral fullerene might form the bases of a nanoswitch. Through the addition of hydrogen atoms to one hemisphere of the cage it is shown that, when compared with Ca@C60, asymmetric and significantly reduced energy barriers can be generated with respect to motion of the calcium atom. It is proposed that hydrogen atom addition to a fullerene might offer a route for creating a bi-stable nanoswitch that can be fine-tuned through the selection of an appropriate isomer and number of atoms attached to the cage of an endohedral fullerene.This article is part of the themed issue 'Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene'. PMID:27501967

  17. Gas phase recombination of hydrogen and deuterium atoms. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Trainor, D. W.; Ham, D. O.; Kaufman, F.

    1973-01-01

    Rate constants for the reaction H + H + M - H2 + M, with M = H2, He, and Ar were measured over the temperature range 77 to 298 K. Hydrogen atoms were produced by thermal dissociation and absolute atom concentrations were measured through use of self-balancing, isothermal catalytic probe detector. The specific rate constants were 8.1 + or - 0.4 x 10 to the minus 33rd power, 7.0 + or - 0.4 x 10 to the minus 33rd power, and 9.2 + or - 0.6 x at 298 K for M = H2, He, and Ar respectively; these values rising to 18.5 + or - 2.2 x 10 to the minus 33rd power, 12.0 + or - 1.5 x 10 to the minus 33rd power, and 27.4 + or - 4.6 x 10 to the minus 33rd power cm to the 6th power/molecules sq/sec at 77 K. for the equivalent deuterium atom process with D2 as the third body, the rate constants are 6.1 + or - 0.3 x 10 to the minus 33rd power cm to the 6th power/molecules sq/sec at 298 K and 15.1 + or - 1.0 x 10 to the minus 33rd power cm to the 6th power/molecules sq/sec at 77 K. These values are compared with previous experimental measurements and with recent theoretical calculations.

  18. Photon pair production from a hot atomic ensemble in the diamond configuration

    NASA Astrophysics Data System (ADS)

    Willis, Richard Thomas

    This thesis discusses four-wave mixing (4WM) in a warm ensemble of rubidium using the diamond configuration level structure. Both classical 4WM and nonclassical photon-pair production are investigated. Quantum information science has spawned a great amount of experimental work on the interaction of light with collective modes of excitation in atomic ensembles. Plans to build quantum networks and quantum repeaters with atom ensembles take advantage of nonlinear interactions to produce and store non-classical states of light. These technologies will require photon sources that not only generate nonclassical light, but also resonant, narrow band light. Here we investigate a system which could be used as such a source. We take advantage of the 4WM interaction in a warm ensemble of Rubidium atoms. Our scheme utilizes the diamond energy level configuration which, in rubidium, allows for correlated pairs at telecommunications wavelengths. We start by examining the properties of classical 4WM in the system. We measure the resonance structure and see that it can be understood in terms of velocity class selective resonant enhancement and power splitting effects. The efficiency of the process is low and limited by linear absorption of the pumps. Our observations agree with a semi-classical Maxwell-Bloch theoretical treatment. Next we observe pair generation by spontaneous 4WM from the warm ensemble. The temporal profile of the cross-correlation function (CCF) for the photons depends on pump-laser power and detuning. This allows us to produce biphotons with controllable spectra. A simple quantum optical theoretical treatment based on linear filtering gives qualitative agreement with the data. We show that the photon pairs are polarization entangled, clearly violating Bell's Inequality. A perturbative quantum optical treatment predicts the polarization state of the pairs and agrees with our measurements. We analyze the photon statistics of the source and find the largest

  19. Use of a PhET Interactive Simulation in General Chemistry Laboratory: Models of the Hydrogen Atom

    ERIC Educational Resources Information Center

    Clark, Ted M.; Chamberlain, Julia M.

    2014-01-01

    An activity supporting the PhET interactive simulation, Models of the Hydrogen Atom, has been designed and used in the laboratory portion of a general chemistry course. This article describes the framework used to successfully accomplish implementation on a large scale. The activity guides students through a comparison and analysis of the six…

  20. Visualization of a Large Set of Hydrogen Atomic Orbital Contours Using New and Expanded Sets of Parametric Equations

    ERIC Educational Resources Information Center

    Rhile, Ian J.

    2014-01-01

    Atomic orbitals are a theme throughout the undergraduate chemistry curriculum, and visualizing them has been a theme in this journal. Contour plots as isosurfaces or contour lines in a plane are the most familiar representations of the hydrogen wave functions. In these representations, a surface of a fixed value of the wave function ? is plotted…