Direct Observation of Double Hydrogen Transfer via Quantum Tunneling in a Single Porphycene Molecule on a Ag(110) Surface.

PubMed

Koch, Matthias; Pagan, Mark; Persson, Mats; Gawinkowski, Sylwester; Waluk, Jacek; Kumagai, Takashi

2017-09-13

Quantum tunneling of hydrogen atoms (or protons) plays a crucial role in many chemical and biological reactions. Although tunneling of a single particle has been examined extensively in various one-dimensional potentials, many-particle tunneling in high-dimensional potential energy surfaces remains poorly understood. Here we present a direct observation of a double hydrogen atom transfer (tautomerization) within a single porphycene molecule on a Ag(110) surface using a cryogenic scanning tunneling microscope (STM). The tautomerization rates are temperature independent below ∼10 K, and a large kinetic isotope effect (KIE) is observed upon substituting the transferred hydrogen atoms by deuterium, indicating that the process is governed by tunneling. The observed KIE for three isotopologues and density functional theory calculations reveal that a stepwise transfer mechanism is dominant in the tautomerization. It is also found that the tautomerization rate is increased by vibrational excitation via an inelastic electron tunneling process. Moreover, the STM tip can be used to manipulate the tunneling dynamics through modification of the potential landscape.

Solar cell structure incorporating a novel single crystal silicon material

DOEpatents

Pankove, Jacques I.; Wu, Chung P.

1983-01-01

A novel hydrogen rich single crystal silicon material having a band gap energy greater than 1.1 eV can be fabricated by forming an amorphous region of graded crystallinity in a body of single crystalline silicon and thereafter contacting the region with atomic hydrogen followed by pulsed laser annealing at a sufficient power and for a sufficient duration to recrystallize the region into single crystal silicon without out-gassing the hydrogen. The new material can be used to fabricate semiconductor devices such as single crystal silicon solar cells with surface window regions having a greater band gap energy than that of single crystal silicon without hydrogen.

Method of making selective crystalline silicon regions containing entrapped hydrogen by laser treatment

DOEpatents

Pankove, J.I.; Wu, C.P.

1982-03-30

A novel hydrogen rich single crystalline silicon material having a band gap energy greater than 1.1 eV can be fabricated by forming an amorphous region of graded crystallinity in a body of single crystalline silicon and thereafter contacting the region with atomic hydrogen followed by pulsed laser annealing at a sufficient power and for a sufficient duration to recrystallize the region into single crystalline silicon without out-gassing the hydrogen. The new material can be used to fabricate semi-conductor devices such as single crystalline silicon solar cells with surface window regions having a greater band gap energy than that of single crystalline silicon without hydrogen. 2 figs.

Method of making selective crystalline silicon regions containing entrapped hydrogen by laser treatment

DOEpatents

Pankove, Jacques I.; Wu, Chung P.

1982-01-01

A novel hydrogen rich single crystalline silicon material having a band gap energy greater than 1.1 eV can be fabricated by forming an amorphous region of graded crystallinity in a body of single crystalline silicon and thereafter contacting the region with atomic hydrogen followed by pulsed laser annealing at a sufficient power and for a sufficient duration to recrystallize the region into single crystalline silicon without out-gasing the hydrogen. The new material can be used to fabricate semi-conductor devices such as single crystalline silicon solar cells with surface window regions having a greater band gap energy than that of single crystalline silicon without hydrogen.

Effects of the molecule-electrode interface on the low-bias conductance of Cu–H{sub 2}–Cu single-molecule junctions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang, Zhuoling; Centre for Nanoscale Science and Technology, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing 100871; Wang, Hao

The atomic structure and electronic transport properties of a single hydrogen molecule connected to both symmetric and asymmetric Cu electrodes are investigated by using the non-equilibrium Green’s function formalism combined with the density functional theory. Our calculations show that in symmetric Cu–H{sub 2}–Cu junctions, the low-bias conductance drops rapidly upon stretching, while asymmetric ones present a low-bias conductance spanning the 0.2–0.3 G{sub 0} interval for a wide range of electrode separations. This is in good agreement with experiments on Cu atomic contacts in a hydrogen environment. Furthermore, the distribution of the calculated vibrational energies of the two hydrogen atoms inmore » the asymmetric Cu–H{sub 2}–Cu junction is also consistent with experiments. These findings provide clear evidence for the formation of asymmetric Cu–H{sub 2}–Cu molecular junctions in breaking Cu atomic contacts in the presence of hydrogen and are also helpful for the design of molecular devices with Cu electrodes.« less

Single Platinum Atoms Electrocatalysts: Oxygen Reduction and Hydrogen Oxidation Reactions

DOE PAGES

Vukmirovic, Miomir B.; Teeluck, Krishani M.; Liu, Ping; ...

2017-08-08

We prepared atomically dispersed catalyst consisting of Pt atoms arranged in a c(2 × 2) array on RuO2(110) substrate. A large interatomic distance of Pt atoms in a c(2 × 2) phase precludes the reactants to interact with more than one Pt atoms. A strong bond of Pt atoms with RuO2 prevents agglomeration of Pt atoms to form 2D-islands or 3D-clusters. The activities of single Pt atom catalyst for the oxygen reduction and hydrogen oxidation reactions were determined and compared with those of bulk Pt. It has lower catalytic activity for the oxygen reduction reaction and similar activity for hydrogenmore » oxidation reaction compared to Pt(111). This was explained by a large calculated up-shift of the dband center of Pt atoms and larger Pt-Pt interatomic distance than that of Pt(111). Our information is of considerable interest for further development of electrocatalysis.« less

Single and double carbon vacancies in pyrene as first models for graphene defects: A survey of the chemical reactivity toward hydrogen

NASA Astrophysics Data System (ADS)

Nieman, Reed; Das, Anita; Aquino, Adélia J. A.; Amorim, Rodrigo G.; Machado, Francisco B. C.; Lischka, Hans

2017-01-01

Graphene is regarded as one of the most promising materials for nanoelectronics applications. Defects play an important role in modulating its electronic properties and also enhance its chemical reactivity. In this work the reactivity of single vacancies (SV) and double vacancies (DV) in reaction with a hydrogen atom Hr is studied. Because of the complicated open shell electronic structures of these defects due to dangling bonds, multireference configuration interaction (MRCI) methods are being used in combination with a previously developed defect model based on pyrene. Comparison of the stability of products derived from Csbnd Hr bond formation with different carbon atoms of the different polyaromatic hydrocarbons is made. In the single vacancy case the most stable structure is the one where the incoming hydrogen is bound to the carbon atom carrying the dangling bond. However, stable Csbnd Hr bonded structures are also observed in the five-membered ring of the single vacancy. In the double vacancy, most stable bonding of the reactant Hr atom is found in the five-membered rings. In total, Csbnd Hr bonds, corresponding to local energy minimum structures, are formed with all carbon atoms in the different defect systems and the pyrene itself. Reaction profiles for the four lowest electronic states show in the case of a single vacancy a complex picture of curve crossings and avoided crossings which will give rise to a complex nonadiabatic reaction dynamics involving several electronic states.

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

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.

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

Hydrogen storage capacity on Ti-decorated porous graphene: First-principles investigation

NASA Astrophysics Data System (ADS)

Yuan, Lihua; Kang, Long; Chen, Yuhong; Wang, Daobin; Gong, Jijun; Wang, Chunni; Zhang, Meiling; Wu, Xiaojuan

2018-03-01

Hydrogen storage capacity on Titanium (Ti) decorated porous graphene (PG) has been investigated using density functional theory simulations with generalized gradient approximation method. The possible adsorption sites of Ti atom on PG and electronic properties of Ti-PG system are also discussed.The results show a Ti atom prefers to strongly adsorb on the center site above the C hexagon with the binding energy of 3.65 eV, and the polarization and the hybridization mechanisms both contribute to the Ti atom adsorption on PG. To avoid a tendency of clustering among Ti atoms, the single side of the PG unit cell should only contain one Ti atom. For the single side of PG, four H2 molecules can be adsorbed around Ti atom, and the adsorption mechanism of H2 molecules come from not only the polarization mechanism between Ti and H atoms but also the orbital hybridization among Ti atom, H2 molecules and C atoms. For the case of double sides of PG, eight H2 molecules can be adsorbed on Ti-decorated PG unit cell with the average adsorption energy of -0.457 eV, and the gravimetric hydrogen storage capacity is 6.11 wt.%. Furthermore, ab inito molecular-dynaics simulation result shows that six H2 molecules can be adsorbed on double sides of unit cell of Ti-PG system and the configuration of Ti-PG is very stable at 300 K and without external pressure, which indicates Ti-decorated PG could be considered as a potential hydrogen storage medium at ambient conditions.

Single-atom gold catalysis in the context of developments in parahydrogen-induced polarization.

PubMed

Corma, Avelino; Salnikov, Oleg G; Barskiy, Danila A; Kovtunov, Kirill V; Koptyug, Igor V

2015-05-04

A highly isolated monoatomic gold catalyst, with single gold atoms dispersed on multiwalled carbon nanotubes (MWCNTs), has been synthesized, characterized, and tested in heterogeneous hydrogenation of 1,3-butadiene and 1-butyne with parahydrogen to maximize the polarization level and the contribution of the pairwise hydrogen addition route. The Au/MWCNTs catalyst was found to be active and efficient in pairwise hydrogen addition and the estimated contributions from the pairwise hydrogen addition route are at least an order of magnitude higher than those for supported metal nanoparticle catalysts. Therefore, the use of the highly isolated monoatomic catalysts is very promising for production of hyperpolarized fluids that can be used for the significant enhancement of NMR signals. A mechanism of 1,3-butadiene hydrogenation with parahydrogen over the highly isolated monoatomic Au/MWCNTs catalyst is also proposed. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Origins of hole traps in hydrogenated nanocrystalline and amorphous silicon revealed through machine learning

NASA Astrophysics Data System (ADS)

Mueller, Tim; Johlin, Eric; Grossman, Jeffrey C.

2014-03-01

Genetic programming is used to identify the structural features most strongly associated with hole traps in hydrogenated nanocrystalline silicon with very low crystalline volume fraction. The genetic programming algorithm reveals that hole traps are most strongly associated with local structures within the amorphous region in which a single hydrogen atom is bound to two silicon atoms (bridge bonds), near fivefold coordinated silicon (floating bonds), or where there is a particularly dense cluster of many silicon atoms. Based on these results, we propose a mechanism by which deep hole traps associated with bridge bonds may contribute to the Staebler-Wronski effect.

Total Born approximation cross sections for single electron loss by atoms and ions colliding with atoms

NASA Technical Reports Server (NTRS)

Rule, D. W.

1977-01-01

The first born approximation (FBA) is applied to the calculation of single electron loss cross sections for various ions and atoms containing from one to seven electrons. Screened hydrogenic wave functions were used for the states of the electron ejected from the projectile, and Hartree-Fock elastic and incoherent scattering factors were used to describe the target. The effect of the target atom on the scaling of projectile ionization cross sections with respect to the projectile nuclear charge was explored in the case of hydrogen-like ions. Scaling of the cross section with respect to the target nuclear charge for electron loss by Fe (+25) in collision with neutral atoms ranging from H to Fe is also examined. These results were compared to those of the binary encounter approximation and to the FBA for the case of ionization by completely stripped target ions.

Sc-Decorated Porous Graphene for High-Capacity Hydrogen Storage: First-Principles Calculations.

PubMed

Chen, Yuhong; Wang, Jing; Yuan, Lihua; Zhang, Meiling; Zhang, Cairong

2017-08-02

The generalized gradient approximation (GGA) function based on density functional theory is adopted to investigate the optimized geometrical structure, electron structure and hydrogen storage performance of Sc modified porous graphene (PG). It is found that the carbon ring center is the most stable adsorbed position for a single Sc atom on PG, and the maximum number of adsorbed H₂ molecules is four with the average adsorption energy of -0.429 eV/H₂. By adding a second Sc atom on the other side of the system, the hydrogen storage capacity of the system can be improved effectively. Two Sc atoms located on opposite sides of the PG carbon ring center hole is the most suitable hydrogen storage structure, and the hydrogen storage capacity reach a maximum 9.09 wt % at the average adsorption energy of -0.296 eV/H₂. The adsorption of H₂ molecules in the PG system is mainly attributed to orbital hybridization among H, Sc, and C atoms, and Coulomb attraction between negatively charged H₂ molecules and positively charged Sc atoms.

Sc-Decorated Porous Graphene for High-Capacity Hydrogen Storage: First-Principles Calculations

PubMed Central

Chen, Yuhong; Wang, Jing; Yuan, Lihua; Zhang, Meiling

2017-01-01

The generalized gradient approximation (GGA) function based on density functional theory is adopted to investigate the optimized geometrical structure, electron structure and hydrogen storage performance of Sc modified porous graphene (PG). It is found that the carbon ring center is the most stable adsorbed position for a single Sc atom on PG, and the maximum number of adsorbed H2 molecules is four with the average adsorption energy of −0.429 eV/H2. By adding a second Sc atom on the other side of the system, the hydrogen storage capacity of the system can be improved effectively. Two Sc atoms located on opposite sides of the PG carbon ring center hole is the most suitable hydrogen storage structure, and the hydrogen storage capacity reach a maximum 9.09 wt % at the average adsorption energy of −0.296 eV/H2. The adsorption of H2 molecules in the PG system is mainly attributed to orbital hybridization among H, Sc, and C atoms, and Coulomb attraction between negatively charged H2 molecules and positively charged Sc atoms. PMID:28767084

Different catalytic effects of a single water molecule: the gas-phase reaction of formic acid with hydroxyl radical in water vapor.

PubMed

Anglada, Josep M; Gonzalez, Javier

2009-12-07

The effect of a single water molecule on the reaction mechanism of the gas-phase reaction between formic acid and the hydroxyl radical was investigated with high-level quantum mechanical calculations using DFT-B3LYP, MP2 and CCSD(T) theoretical approaches in concert with the 6-311+G(2df,2p) and aug-cc-pVTZ basis sets. The reaction between HCOOH and HO has a very complex mechanism involving a proton-coupled electron transfer process (pcet), two hydrogen-atom transfer reactions (hat) and a double proton transfer process (dpt). The hydroxyl radical predominantly abstracts the acidic hydrogen of formic acid through a pcet mechanism. A single water molecule affects each one of these reaction mechanisms in different ways, depending on the way the water interacts. Very interesting is also the fact that our calculations predict that the participation of a single water molecule results in the abstraction of the formyl hydrogen of formic acid through a hydrogen atom transfer process (hat).

Chemisorption and Diffusion of H on a Graphene Sheet and Single-Wall Carbon Nanotubes

NASA Technical Reports Server (NTRS)

Srivastava, Deepak; Dzegilenko, Fedor; Menon, Madhu

2000-01-01

Recent experiments on hydrogen storage in single wall nanotubes and nanotube bundles have reported large fractional weight of stored molecular hydrogen which are not in agreement with theoretical estimates based of simulation of hydrogen storage by physisorption mechanisms. Hydrogen storage in catalytically doped nanotube bundles indicate that atomic H might undergo chemisorption changing the basic nature of the storage mechanism under investigation by many groups. Using a generalized tight-binding molecular dynamics (GTBMD) method for reactive C-H dynamics, we investigate chemisorption and diffusion of atomic H on graphene sheet and C nanotubes. Effective potential energy surfaces (EPS) for chemisorption and diffusion are calculated for graphene sheet and nanotubes of different curvatures. Analysis of the activation barriers and quantum rate constants, computed via wave-packet dynamics method, will be discussed in this presentation.

Handbook of Basic Atomic Spectroscopic Data

National Institute of Standards and Technology Data Gateway

SRD 108 Handbook of Basic Atomic Spectroscopic Data (Web, free access)   This handbook provides a selection of the most important and frequently used atomic spectroscopic data. The compilation includes data for the neutral and singly-ionized atoms of all elements hydrogen through einsteinium (Z = 1-99). The wavelengths, intensities, and spectrum assignments are given for each element, and the data for the approximately 12,000 lines of all elements are also collected into a single table.

Clarifying Atomic Weights: A 2016 Four-Figure Table of Standard and Conventional Atomic Weights

ERIC Educational Resources Information Center

Coplen, Tyler B.; Meyers, Fabienne; Holden, Norman E.

2017-01-01

To indicate that atomic weights of many elements are not constants of nature, in 2009 and 2011 the Commission on Isotopic Abundances and Atomic Weights (CIAAW) of the International Union of Pure and Applied Chemistry (IUPAC) replaced single-value standard atomic weight values with atomic weight intervals for 12 elements (hydrogen, lithium, boron,…

Metallic Hydrogen and Nano-Tube Magnets

NASA Technical Reports Server (NTRS)

Cole, John W.

2004-01-01

When hydrogen is subjected to enough pressure the atoms will be pressed into close enough proximity that each electron is no longer bound to a single proton. The research objectives is to find whether metallic hydrogen can be produced and once produced will the metallic hydrogen be metastable and remain in the metallic form when the pressure is released.

Graphenes in the absence of metals as carbocatalysts for selective acetylene hydrogenation and alkene hydrogenation

NASA Astrophysics Data System (ADS)

Primo, Ana; Neatu, Florentina; Florea, Mihaela; Parvulescu, Vasile; Garcia, Hermenegildo

2014-10-01

Catalysis makes possible a chemical reaction by increasing the transformation rate. Hydrogenation of carbon-carbon multiple bonds is one of the most important examples of catalytic reactions. Currently, this type of reaction is carried out in petrochemistry at very large scale, using noble metals such as platinum and palladium or first row transition metals such as nickel. Catalysis is dominated by metals and in many cases by precious ones. Here we report that graphene (a single layer of one-atom-thick carbon atoms) can replace metals for hydrogenation of carbon-carbon multiple bonds. Besides alkene hydrogenation, we have shown that graphenes also exhibit high selectivity for the hydrogenation of acetylene in the presence of a large excess of ethylene.

Dynamical core-hole screening in the x-ray absorption spectra of hydrogenated carbon nanotubes and graphene

NASA Astrophysics Data System (ADS)

Wessely, O.; Katsnelson, M. I.; Nilsson, A.; Nikitin, A.; Ogasawara, H.; Odelius, M.; Sanyal, B.; Eriksson, O.

2007-10-01

We have calculated the electronic structure and the x-ray absorption (XA) spectrum of a hydrogenated single graphite plane, in order to simulate recent experimental results on hydrogenated single wall carbon nanotubes (SWCNT) as well as hydrogenated graphene. We find that the presence of H induces a substantial component of sp3 bonding and as a result the π and π* components to the electronic structure vanish. We have calculated a theoretical x-ray absorption spectrum using a multiband version of the Mahan-Nozières-De Dominicis theory. By making a fitting of the XA signal of C atoms that have H attached to them and C atoms without H in the vicinity we obtain a good representation of the experimental data and we can draw the conclusion that in the experiments [A. Nikitin , Phys. Rev. Lett. 95, 225507 (2005)] some 35-50 % H have been absorbed in the SWCNT.

Single-Atom Catalyst of Platinum Supported on Titanium Nitride for Selective Electrochemical Reactions.

PubMed

Yang, Sungeun; Kim, Jiwhan; Tak, Young Joo; Soon, Aloysius; Lee, Hyunjoo

2016-02-05

As a catalyst, single-atom platinum may provide an ideal structure for platinum minimization. Herein, a single-atom catalyst of platinum supported on titanium nitride nanoparticles were successfully prepared with the aid of chlorine ligands. Unlike platinum nanoparticles, the single-atom active sites predominantly produced hydrogen peroxide in the electrochemical oxygen reduction with the highest mass activity reported so far. The electrocatalytic oxidation of small organic molecules, such as formic acid and methanol, also exhibited unique selectivity on the single-atom platinum catalyst. A lack of platinum ensemble sites changed the reaction pathway for the oxygen-reduction reaction toward a two-electron pathway and formic acid oxidation toward direct dehydrogenation, and also induced no activity for the methanol oxidation. This work demonstrates that single-atom platinum can be an efficient electrocatalyst with high mass activity and unique selectivity. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nitrogen diffusion in hafnia and the impact of nitridation on oxygen and hydrogen diffusion: A first-principles study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sathiyanarayanan, Rajesh, E-mail: rajessat@in.ibm.com, E-mail: rajesh.sathiyanarayanan@gmail.com; Pandey, R. K.; Murali, K. V. R. M.

2015-01-21

Using first-principles simulations, we have computed incorporation energies and diffusion barriers of ammonia, the nitrogen molecule and atomic nitrogen in monoclinic hafnia (m-HfO{sub 2}). Our calculations show that ammonia is likely to dissociate into an NH{sub 2} molecular unit, whereas the nitrogen molecule remains as a molecule either in the interstitial space or at an oxygen lattice site. The lowest energy pathway for the diffusion of atomic nitrogen interstitials consists of the hopping of the nitrogen interstitial between neighboring three-coordinated lattice oxygen atoms that share a single Hf atom, and the barrier for such hops is determined by a switchingmore » mechanism. The substitutional nitrogen atom shows a preference for diffusion through the doubly positive oxygen vacancy-mediated mechanism. Furthermore, we have investigated the impact of nitrogen atoms on the diffusion barriers of oxygen and hydrogen interstitials in m-HfO{sub 2}. Our results show that nitrogen incorporation has a significant impact on the barriers for oxygen and hydrogen diffusion: nitrogen atoms attract oxygen and hydrogen interstitials diffusing in the vicinity, thereby slowing down (reducing) their diffusion (diffusion length)« less

Tackling CO Poisoning with Single Atom Alloy Catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Jilei; Lucci, Felicia R.; Yang, Ming

2016-05-01

Platinum (Pt) catalysts are extensively used in the chemical industry and as electrocatalysts in fuel cells. Pt is notorious for its sensitivity to poisoning by strong CO adsorption. Here we demonstrate that the single atom alloy (SAA) strat-egy applied to Pt reduces the binding strength of CO while maintaining catalytic performance. By using surface sensi-tive studies, we accurately determined the binding strength of CO to different Pt ensembles, and this in turn guided the preparation of PtCu alloy nanoparticles. The atomic ratio Pt:Cu = 1:120 yielded a SAA which exhibited excellent CO tolerance in H2 activation, the key elementary stepmore » for hy-drogenation and hydrogen electro-oxidation. As a probe reaction, the selective hydrogenation of acetylene to ethene was performed under flow conditions on the SAA nanopar-ticles supported on alumina without activity loss in the pres-ence of CO. The ability to maintain reactivity in the presence of CO is vital to other industrial reactions including fuel reforming and methanol/ethanol fuel cells.« less

Sinter-Resistant Platinum Catalyst Supported by Metal-Organic Framework.

PubMed

Kim, In Soo; Li, Zhanyong; Zheng, Jian; Platero-Prats, Ana E; Mavrandonakis, Andreas; Pellizzeri, Steven; Ferrandon, Magali; Vjunov, Aleksei; Gallington, Leighanne C; Webber, Thomas E; Vermeulen, Nicolaas A; Penn, R Lee; Getman, Rachel B; Cramer, Christopher J; Chapman, Karena W; Camaioni, Donald M; Fulton, John L; Lercher, Johannes A; Farha, Omar K; Hupp, Joseph T; Martinson, Alex B F

2018-01-22

Single atoms and few-atom clusters of platinum are uniformly installed on the zirconia nodes of a metal-organic framework (MOF) NU-1000 via targeted vapor-phase synthesis. The catalytic Pt clusters, site-isolated by organic linkers, are shown to exhibit high catalytic activity for ethylene hydrogenation while exhibiting resistance to sintering up to 200 °C. In situ IR spectroscopy reveals the presence of both single atoms and few-atom clusters that depend upon synthesis conditions. Operando X-ray absorption spectroscopy and X-ray pair distribution analyses reveal unique changes in chemical bonding environment and cluster size stability while on stream. Density functional theory calculations elucidate a favorable reaction pathway for ethylene hydrogenation with the novel catalyst. These results provide evidence that atomic layer deposition (ALD) in MOFs is a versatile approach to the rational synthesis of size-selected clusters, including noble metals, on a high surface area support. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Formic acid decomposition on Pt1/Cu (111) single platinum atom catalyst: Insights from DFT calculations and energetic span model analysis

NASA Astrophysics Data System (ADS)

Wang, Ying-Fan; Li, Kun; Wang, Gui-Chang

2018-04-01

Inspired by the recent surface experimental results that the monatomic Pt catalysts has more excellent hydrogen production that Cu(111) surface, the mechanism of decomposition of formic acid on Cu(111) and single atom Pt1/Cu(111) surface was studied by periodic density functional theory calculations in the present work. The results show that the formic acid tends to undergo dehydrogenation on both surfaces to obtain the hydrogen product of the target product, and the selectivity and catalytic activity of Pt1/Cu (111) surface for formic acid dehydrogenation are better. The reason is that the single atom Pt1/Cu(111) catalyst reduces the reaction energy barrier (i.e., HCOO → CO2 + H) of the critical step of the dehydrogenation reaction due to the fact that the single atom Pt1/Cu(111) catalyst binds formate weakly compared to that of Cu (111) one. Moreover, it was found that the Pt1/Cu (111) binds CO more strongly than that of Cu (111) one and thus leading to the difficult for the formation of CO. These two factors would make the single Pt atom catalyst had the high selectivity for the H2 production. It is hoped that the present work may help people to design the efficient H2 production from HCOOH decomposition by reduce the surface binding strength of HCOO species, for example, using the low coordination number active site like single atom or other related catalytic system.

Chemical Kinetics of Hydrogen Atom Abstraction from Allylic Sites by 3O2; Implications for Combustion Modeling and Simulation.

PubMed

Zhou, Chong-Wen; Simmie, John M; Somers, Kieran P; Goldsmith, C Franklin; Curran, Henry J

2017-03-09

Hydrogen atom abstraction from allylic C-H bonds by molecular oxygen plays a very important role in determining the reactivity of fuel molecules having allylic hydrogen atoms. Rate constants for hydrogen atom abstraction by molecular oxygen from molecules with allylic sites have been calculated. A series of molecules with primary, secondary, tertiary, and super secondary allylic hydrogen atoms of alkene, furan, and alkylbenzene families are taken into consideration. Those molecules include propene, 2-butene, isobutene, 2-methylfuran, and toluene containing the primary allylic hydrogen atom; 1-butene, 1-pentene, 2-ethylfuran, ethylbenzene, and n-propylbenzene containing the secondary allylic hydrogen atom; 3-methyl-1-butene, 2-isopropylfuran, and isopropylbenzene containing tertiary allylic hydrogen atom; and 1-4-pentadiene containing super allylic secondary hydrogen atoms. The M06-2X/6-311++G(d,p) level of theory was used to optimize the geometries of all of the reactants, transition states, products and also the hinder rotation treatments for lower frequency modes. The G4 level of theory was used to calculate the electronic single point energies for those species to determine the 0 K barriers to reaction. Conventional transition state theory with Eckart tunnelling corrections was used to calculate the rate constants. The comparison between our calculated rate constants with the available experimental results from the literature shows good agreement for the reactions of propene and isobutene with molecular oxygen. The rate constant for toluene with O 2 is about an order magnitude slower than that experimentally derived from a comprehensive model proposed by Oehlschlaeger and coauthors. The results clearly indicate the need for a more detailed investigation of the combustion kinetics of toluene oxidation and its key pyrolysis and oxidation intermediates. Despite this, our computed barriers and rate constants retain an important internal consistency. Rate constants calculated in this work have also been used in predicting the reactivity of the target fuels of 1-butene, 2-butene, isobutene, 2-methylfuran, 2,5-dimethylfuran, and toluene, and the results show that the ignition delay times for those fuels have been increased by a factor of 1.5-3. This work provides a first systematic study of one of the key initiation reaction for compounds containing allylic hydrogen atoms.

Vacancy-hydrogen complexes in ammonothermal GaN

NASA Astrophysics Data System (ADS)

Tuomisto, F.; Kuittinen, T.; Zając, M.; Doradziński, R.; Wasik, D.

2014-10-01

We have applied positron annihilation spectroscopy to study in-grown vacancy defects in bulk GaN crystals grown by the ammonothermal method. We observe a high concentration of Ga vacancy related defects in n-type samples with varying free electron and oxygen content. The positron lifetimes found in these samples suggest that the Ga vacancies are complexed with hydrogen impurities. The number of hydrogen atoms in each vacancy decreases with increasing free electron concentration and oxygen and hydrogen content. The local vibrational modes observed in infrared absorption support this conclusion. Growth of high-quality ammonothermal GaN single crystals with varying electron concentrations. Identification of defect complexes containing a Ga vacancy and 1 or more hydrogen atoms, and possibly O. These vacancy complexes provide a likely explanation for electrical compensation in ammonothermal GaN.

Dynamical Core-Hole Screening in the X-Ray Absorption Spectra of Hydrogenated Carbon Nanotubes And Graphene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wessely, O.; /Uppsala U. /Imperial Coll., London; Katsnelson, M.I.

2009-04-30

We have calculated the electronic structure and the x-ray absorption (XA) spectrum of a hydrogenated single graphite plane, in order to simulate recent experimental results on hydrogenated single wall carbon nanotubes (SWCNT) as well as hydrogenated graphene. We find that the presence of H induces a substantial component of sp{sup 3} bonding and as a result the {pi} and {pi}* components to the electronic structure vanish. We have calculated a theoretical x-ray absorption spectrum using a multiband version of the Mahan-Nozieres-De Dominicis theory. By making a fitting of the XA signal of C atoms that have H attached to themmore » and C atoms without H in the vicinity we obtain a good representation of the experimental data and we can draw the conclusion that in the experiments [A. Nikitin et al., Phys. Rev. Lett. 95, 225507 (2005)] some 35-50 % H have been absorbed in the SWCNT.« less

First principles study of hydrogen adsorption on carbon nanowires.

NASA Astrophysics Data System (ADS)

Tapia, Alejandro; Aguilera, Luis; Murrieta, Gabriel; de Coss, Romeo

2007-03-01

Recently has been reported a new type of one-dimensional carbon structures. Carbon nanowires formed by a linear carbon-atom chain inside an armchair (5,5) carbon nanotube has been observed using high-resolution transmission electron microscopy. In the present work we have studied the changes in the electronic structure of a carbon nanowires and (5,5) single-walled carbon nanotubes (SWCN) when a hydrogen atom is adsorbed. We used the Density Functional Theory and the calculations where performed by the pseudopotentials LCAO method (SIESTA code) and the Generalized Gradient Approximation (GGA) for the exchange-correlation potential. We have analyzed the changes in the atomic structure, density of states (LDOS), and the local orbital population. We found charge transfer from the nanotube to the linear chain and the hydrogen atom, the electronic character of the chain and nanotube sub-systems in chain@SWCN is the same that in the corresponding isolated systems, chain or SWCN. But the hydrogen adsorption produced changes in the atomic estructure and the electronic properties. This research was supported by PRIORI-UADY under Grant No. FING-05-004 and Consejo Nacional de Ciencia y Tecnolog'ia (Conacyt) under Grants No. 43830-F and 49985-J.

Ganoderma-Like MoS2 /NiS2 with Single Platinum Atoms Doping as an Efficient and Stable Hydrogen Evolution Reaction Catalyst.

PubMed

Guan, Yongxin; Feng, Yangyang; Wan, Jing; Yang, Xiaohui; Fang, Ling; Gu, Xiao; Liu, Ruirui; Huang, Zhengyong; Li, Jian; Luo, Jun; Li, Changming; Wang, Yu

2018-05-27

Herein, a unique ganoderma-like MoS 2 /NiS 2 hetero-nanostructure with isolated Pt atoms anchored is reported. This novel ganoderma-like heterostructure can not only efficiently disperse and confine the few-layer MoS 2 nanosheets to fully expose the edge sites of MoS 2 , and provide more opportunity to capture the Pt atoms, but also tune the electronic structure to modify the catalytic activity. Because of the favorable dispersibility and exposed large specific surface area, single Pt atoms can be easily anchored on MoS 2 nanosheets with ultrahigh loading of 1.8 at% (the highest is 1.3 at% to date). Owing to the ganoderma-like structure and platinum atoms doping, this catalyst shows Pt-like catalytic activity for the hydrogen evolution reaction with an ultralow overpotential of 34 mV and excellent durability of only 2% increase in overpotential for 72 h under the constant current density of 10 mA cm -2 . © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hydrogen Atomic Positions of O-H···O Hydrogen Bonds in Solution and in the Solid State: The Synergy of Quantum Chemical Calculations with ¹H-NMR Chemical Shifts and X-ray Diffraction Methods.

PubMed

Siskos, Michael G; Choudhary, M Iqbal; Gerothanassis, Ioannis P

2017-03-07

The exact knowledge of hydrogen atomic positions of O-H···O hydrogen bonds in solution and in the solid state has been a major challenge in structural and physical organic chemistry. The objective of this review article is to summarize recent developments in the refinement of labile hydrogen positions with the use of: (i) density functional theory (DFT) calculations after a structure has been determined by X-ray from single crystals or from powders; (ii) ¹H-NMR chemical shifts as constraints in DFT calculations, and (iii) use of root-mean-square deviation between experimentally determined and DFT calculated ¹H-NMR chemical shifts considering the great sensitivity of ¹H-NMR shielding to hydrogen bonding properties.

ALMA Shows that Gas Reservoirs of Star-forming Disks over the Past 3 Billion Years Are Not Predominantly Molecular

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cortese, Luca; Catinella, Barbara; Janowiecki, Steven, E-mail: luca.cortese@uwa.edu.au

Cold hydrogen gas is the raw fuel for star formation in galaxies, and its partition into atomic and molecular phases is a key quantity for galaxy evolution. In this Letter, we combine Atacama Large Millimeter/submillimeter Array and Arecibo single-dish observations to estimate the molecular-to-atomic hydrogen mass ratio for massive star-forming galaxies at z ∼ 0.2 extracted from the HIGHz survey, i.e., some of the most massive gas-rich systems currently known. We show that the balance between atomic and molecular hydrogen in these galaxies is similar to that of local main-sequence disks, implying that atomic hydrogen has been dominating the coldmore » gas mass budget of star-forming galaxies for at least the past three billion years. In addition, despite harboring gas reservoirs that are more typical of objects at the cosmic noon, HIGHz galaxies host regular rotating disks with low gas velocity dispersions suggesting that high total gas fractions do not necessarily drive high turbulence in the interstellar medium.« less

Ortho and para hydrogen dimers on G/SiC(0001): combined STM and DFT study.

PubMed

Merino, P; Švec, M; Martínez, J I; Mutombo, P; Gonzalez, C; Martín-Gago, J A; de Andres, P L; Jelinek, P

2015-01-01

The hydrogen (H) dimer structures formed upon room-temperature H adsorption on single layer graphene (SLG) grown on SiC(0001) are addressed using a combined theoretical-experimental approach. Our study includes density functional theory (DFT) calculations for the full (6√3 × 6√3)R30° unit cell of the SLG/SiC(0001) substrate and atomically resolved scanning tunneling microscopy images determining simultaneously the graphene lattice and the internal structure of the H adsorbates. We show that H atoms normally group in chemisorbed coupled structures of different sizes and orientations. We make an atomic scale determination of the most stable experimental geometries, the small dimers and ellipsoid-shaped features, and we assign them to hydrogen adsorbed in para dimers and ortho dimers configuration, respectively, through comparison with the theory.

Site-specific binding of a water molecule to the sulfa drugs sulfamethoxazole and sulfisoxazole: a laser-desorption isomer-specific UV and IR study.

PubMed

Uhlemann, Thomas; Seidel, Sebastian; Müller, Christian W

2018-03-07

To determine the preferred water molecule binding sites of the polybasic sulfa drugs sulfamethoxazole (SMX) and sulfisoxazole (SIX), we have studied their monomers and monohydrated complexes through laser-desorption conformer-specific UV and IR spectroscopy. Both the SMX and SIX monomer adopt a single conformer in the molecular beam. On the basis of their conformer-specific IR spectra in the NH stretch region, these conformers were assigned to the SMX and SIX global minimum structures, both exhibiting a staggered sulfonamide group and an intramolecular C-HO[double bond, length as m-dash]S hydrogen bond. The SMX-H 2 O and SIX-H 2 O complexes each adopt a single isomer in the molecular beam. Their isomeric structures were determined based on their isomer-specific IR spectra in the NH/OH stretch region. Quantum Theory of Atoms in Molecules analysis of the calculated electron densities revealed that in the SMX-H 2 O complex the water molecule donates an O-HN hydrogen bond to the heterocycle nitrogen atom and accepts an N-HO hydrogen bond from the sulfonamide NH group. In the SIX-H 2 O complex, however, the water molecule does not bind to the heterocycle but instead donates an O-HO[double bond, length as m-dash]S hydrogen bond to the sulfonamide group and accepts an N-HO hydrogen bond from the sulfonamide NH group. Both water complexes are additionally stabilized by a C ph -HOH 2 hydrogen bond. Interacting Quantum Atoms analysis suggests that all intermolecular hydrogen bonds are dominated by the short-range exchange-correlation contribution.

First-principles study of Li decorated coronene graphene

NASA Astrophysics Data System (ADS)

Zhang, Yafei; Cheng, Xinlu

2017-11-01

We use the first-principles calculation based on density functional theory (DFT) to investigate the hydrogen storage of Li decorated coronene graphene. Our result indicates that single Li atom can adsorb three H2 molecules and the adsorption energy per H2 is -0.224 eV. When four Li atoms doped, the largest hydrogen gravimetric density is 6.82 wt.% and this is higher than the 2017 target by the US department of energy (DOE). Meanwhile, the adsorption energy per H2 is -0.220 eV, which is suitable for H2 molecules to store. Therefore, Li decorated coronene graphene will be a candidate for hydrogen storage materials in the future.

The Halogen Bond in the Design of Functional Supramolecular Materials: Recent Advances

PubMed Central

2013-01-01

Halogen bonding is an emerging noncovalent interaction for constructing supramolecular assemblies. Though similar to the more familiar hydrogen bonding, four primary differences between these two interactions make halogen bonding a unique tool for molecular recognition and the design of functional materials. First, halogen bonds tend to be much more directional than (single) hydrogen bonds. Second, the interaction strength scales with the polarizability of the bond-donor atom, a feature that researchers can tune through single-atom mutation. In addition, halogen bonds are hydrophobic whereas hydrogen bonds are hydrophilic. Lastly, the size of the bond-donor atom (halogen) is significantly larger than hydrogen. As a result, halogen bonding provides supramolecular chemists with design tools that cannot be easily met with other types of noncovalent interactions and opens up unprecedented possibilities in the design of smart functional materials. This Account highlights the recent advances in the design of halogen-bond-based functional materials. Each of the unique features of halogen bonding, directionality, tunable interaction strength, hydrophobicity, and large donor atom size, makes a difference. Taking advantage of the hydrophobicity, researchers have designed small-size ion transporters. The large halogen atom size provided a platform for constructing all-organic light-emitting crystals that efficiently generate triplet electrons and have a high phosphorescence quantum yield. The tunable interaction strengths provide tools for understanding light-induced macroscopic motions in photoresponsive azobenzene-containing polymers, and the directionality renders halogen bonding useful in the design on functional supramolecular liquid crystals and gel-phase materials. Although halogen bond based functional materials design is still in its infancy, we foresee a bright future for this field. We expect that materials designed based on halogen bonding could lead to applications in biomimetics, optics/photonics, functional surfaces, and photoswitchable supramolecules. PMID:23805801

Single step synthesis of gold-amino acid composite, with the evidence of the catalytic hydrogen atom transfer (HAT) reaction, for the electrochemical recognition of Serotonin

NASA Astrophysics Data System (ADS)

Choudhary, Meenakshi; Siwal, Samarjeet; Nandi, Debkumar; Mallick, Kaushik

2016-03-01

A composite architecture of amino acid and gold nanoparticles has been synthesized using a generic route of 'in-situ polymerization and composite formation (IPCF)' [1,2]. The formation mechanism of the composite has been supported by a model hydrogen atom (H•≡H++e-) transfer (HAT) type of reaction which belongs to the proton coupled electron transfer (PCET) mechanism. The 'gold-amino acid composite' was used as a catalyst for the electrochemical recognition of Serotonin.

Calculated Properties of Fully Hydrogenated Single Layers of BN, BC2N, and Graphene: Graphane and Its BN-Containing Analogues

DOE Office of Scientific and Technical Information (OSTI.GOV)

Averill, Frank; Morris, James R; Cooper, Valentino R

2009-01-01

Carbon is an attractive material for hydrogen adsorption, due to its light weight, variety of structures, and ability to both physisorb and chemisorb hydrogen. Recently, fully hydrogenated graphene layers ( graphane ) have been predicted to exist [J.O. Sofo et al., Phys. Rev. B 75, 15340 (2007)], and experimentally observed [D.C. Elias et al., Science 323, 610 (2009)]. In this work, we examine analogues of graphane, in particular BNH2 and BC2NH4. Unlike graphene, these materials have a band gap without hydrogenation. Our results indicate that the hydrogenation product of BN is metastable: the fully hydrogenated compound BNH2 is higher inmore » energy than hexagonal BN sheets plus H2 molecules, in sharp contrast with graphane. We find that BC2NH4 is energetically very close to hexagonal BC2N+2H2 molecules. Furthermore our examination of the relative binding strengths of rows of symmetry related hydrogen atoms on BC2NH4shows that this compound is marginally higher in energy than BC2NH2 plus an H2 molecule, with the hydrogen atoms in BC2NH2 absorbed on the carbon sites. These remaining hydrogen atoms are not as strongly bound as in graphane, indicating that the average hydrogen chemisorption energy is controllable by changing the carbon content in the B-C-N layer.« less

Nanosheet Supported Single-Metal Atom Bifunctional Catalyst for Overall Water Splitting.

PubMed

Ling, Chongyi; Shi, Li; Ouyang, Yixin; Zeng, Xiao Cheng; Wang, Jinlan

2017-08-09

Nanosheet supported single-atom catalysts (SACs) can make full use of metal atoms and yet entail high selectivity and activity, and bifunctional catalysts can enable higher performance while lowering the cost than two separate unifunctional catalysts. Supported single-atom bifunctional catalysts are therefore of great economic interest and scientific importance. Here, on the basis of first-principles computations, we report a design of the first single-atom bifunctional eletrocatalyst, namely, isolated nickel atom supported on β 12 boron monolayer (Ni 1 /β 12 -BM), to achieve overall water splitting. This nanosheet supported SAC exhibits remarkable electrocatalytic performance with the computed overpotential for oxygen/hydrogen evolution reaction being just 0.40/0.06 V. The ab initio molecular dynamics simulation shows that the SAC can survive up to 800 K elevated temperature, while enacting a high energy barrier of 1.68 eV to prevent isolated Ni atoms from clustering. A viable experimental route for the synthesis of Ni 1 /β 12 -BM SAC is demonstrated from computer simulation. The desired nanosheet supported single-atom bifunctional catalysts not only show great potential for achieving overall water splitting but also offer cost-effective opportunities for advancing clean energy technology.

An Electron Density Source-Function Study of DNA Base Pairs in Their Neutral and Ionized Ground States†.

PubMed

Gatti, Carlo; Macetti, Giovanni; Boyd, Russell J; Matta, Chérif F

2018-07-05

The source function (SF) decomposes the electron density at any point into contributions from all other points in the molecule, complex, or crystal. The SF "illuminates" those regions in a molecule that most contribute to the electron density at a point of reference. When this point of reference is the bond critical point (BCP), a commonly used surrogate of chemical bonding, then the SF analysis at an atomic resolution within the framework of Bader's Quantum Theory of Atoms in Molecules returns the contribution of each atom in the system to the electron density at that BCP. The SF is used to locate the important regions that control the hydrogen bonds in both Watson-Crick (WC) DNA dimers (adenine:thymine (AT) and guanine:cytosine (GC)) which are studied in their neutral and their singly ionized (radical cationic and anionic) ground states. The atomic contributions to the electron density at the BCPs of the hydrogen bonds in the two dimers are found to be delocalized to various extents. Surprisingly, gaining or loosing an electron has similar net effects on some hydrogen bonds concealing subtle compensations traced to atomic sources contributions. Coarser levels of resolutions (groups, rings, and/or monomers-in-dimers) reveal that distant groups and rings often have non-negligible effects especially on the weaker hydrogen bonds such as the third weak CH⋅⋅⋅O hydrogen bond in AT. Interestingly, neither the purine nor the pyrimidine in the neutral or ionized forms dominate any given hydrogen bond despite that the former has more atoms that can act as source or sink for the density at its BCP. © 2018 Wiley Periodicals, Inc. © 2018 Wiley Periodicals, Inc.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Samskog, P.; Kispert, L.D.; Lund, A.

Three different radicals were identified by EPR in x-ray irradiated single crystals of trehalose at 3 K. The species are the trapped electron, a hydroxy alkyl radical, and an alkoxy radical. The electron is trapped in an intermolecular site formed by two hydroxyl groups, one on the carbohydrate and the other on a water molecule as evidenced by the anisotropic proton hyperfine couplings. A geometric model for the trapping site is presented. The trapped electron decays by cleavage of an OH bond and the liberated hydrogen atom abstracts another hydrogen atom from an adjacent carbon atom forming a hydroxy alkylmore » radical. The site of the alkoxy radical has been identified. The primary reaction mechanism is discussed.« less

Getting the chemistry right: protonation, tautomers and the importance of H atoms in biological chemistry.

PubMed

Bax, Ben; Chung, Chun Wa; Edge, Colin

2017-02-01

There are more H atoms than any other type of atom in an X-ray crystal structure of a protein-ligand complex, but as H atoms only have one electron they diffract X-rays weakly and are `hard to see'. The positions of many H atoms can be inferred by our chemical knowledge, and such H atoms can be added with confidence in `riding positions'. For some chemical groups, however, there is more ambiguity over the possible hydrogen placements, for example hydroxyls and groups that can exist in multiple protonation states or tautomeric forms. This ambiguity is far from rare, since about 25% of drugs have more than one tautomeric form. This paper focuses on the most common, `prototropic', tautomers, which are isomers that readily interconvert by the exchange of an H atom accompanied by the switch of a single and an adjacent double bond. Hydrogen-exchange rates and different protonation states of compounds (e.g. buffers) are also briefly discussed. The difference in heavy (non-H) atom positions between two tautomers can be small, and careful refinement of all possible tautomers may single out the likely bound ligand tautomer. Experimental methods to determine H-atom positions, such as neutron crystallography, are often technically challenging. Therefore, chemical knowledge and computational approaches are frequently used in conjugation with experimental data to deduce the bound tautomer state. Proton movement is a key feature of many enzymatic reactions, so understanding the orchestration of hydrogen/proton motion is of critical importance to biological chemistry. For example, structural studies have suggested that, just as a chemist may use heat, some enzymes use directional movement to protonate specific O atoms on phosphates to catalyse phosphotransferase reactions. To inhibit `wriggly' enzymes that use movement to effect catalysis, it may be advantageous to have inhibitors that can maintain favourable contacts by adopting different tautomers as the enzyme `wriggles'.

Single and double acceptor-levels of a carbon-hydrogen defect in n-type silicon

NASA Astrophysics Data System (ADS)

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

2016-05-01

In the present study, we discuss the origin of two dominant deep levels (E42 and E262) observed in n-type Si, which is subjected to hydrogenation by wet chemical etching or a dc H-plasma treatment. Their activation enthalpies determined from Laplace deep level transient spectroscopy measurements are EC-0.06 eV (E42) and EC-0.51 eV (E262). The similar annealing behavior and identical depth profiles of E42 and E262 correlate them with two different charge states of the same defect. E262 is attributed to a single acceptor state due to the absence of the Poole-Frenkel effect and the lack of a capture barrier for electrons. The emission rate of E42 shows a characteristic enhancement with the electric field, which is consistent with the assignment to a double acceptor state. In samples with different carbon and hydrogen content, the depth profiles of E262 can be explained by a defect with one H-atom and one C-atom. From a comparison with earlier calculations [Andersen et al., Phys. Rev. B 66, 235205 (2002)], we attribute E42 to the double acceptor and E262 to the single acceptor state of the CH1AB configuration, where one H atom is directly bound to carbon in the anti-bonding position.

Single and double acceptor-levels of a carbon-hydrogen defect in n-type silicon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stübner, R.; Scheffler, L.; Kolkovsky, Vl., E-mail: kolkov@ifpan.edu.pl

In the present study, we discuss the origin of two dominant deep levels (E42 and E262) observed in n-type Si, which is subjected to hydrogenation by wet chemical etching or a dc H-plasma treatment. Their activation enthalpies determined from Laplace deep level transient spectroscopy measurements are E{sub C}-0.06 eV (E42) and E{sub C}-0.51 eV (E262). The similar annealing behavior and identical depth profiles of E42 and E262 correlate them with two different charge states of the same defect. E262 is attributed to a single acceptor state due to the absence of the Poole-Frenkel effect and the lack of a capture barrier formore » electrons. The emission rate of E42 shows a characteristic enhancement with the electric field, which is consistent with the assignment to a double acceptor state. In samples with different carbon and hydrogen content, the depth profiles of E262 can be explained by a defect with one H-atom and one C-atom. From a comparison with earlier calculations [Andersen et al., Phys. Rev. B 66, 235205 (2002)], we attribute E42 to the double acceptor and E262 to the single acceptor state of the CH{sub 1AB} configuration, where one H atom is directly bound to carbon in the anti-bonding position.« less

Rational Design of Single Molybdenum Atoms Anchored on N-Doped Carbon for Effective Hydrogen Evolution Reaction.

PubMed

Chen, Wenxing; Pei, Jiajing; He, Chun-Ting; Wan, Jiawei; Ren, Hanlin; Zhu, Youqi; Wang, Yu; Dong, Juncai; Tian, Shubo; Cheong, Weng-Chon; Lu, Siqi; Zheng, Lirong; Zheng, Xusheng; Yan, Wensheng; Zhuang, Zhongbin; Chen, Chen; Peng, Qing; Wang, Dingsheng; Li, Yadong

2017-12-11

The highly efficient electrochemical hydrogen evolution reaction (HER) provides a promising pathway to resolve energy and environment problems. An electrocatalyst was designed with single Mo atoms (Mo-SAs) supported on N-doped carbon having outstanding HER performance. The structure of the catalyst was probed by aberration-corrected scanning transmission electron microscopy (AC-STEM) and X-ray absorption fine structure (XAFS) spectroscopy, indicating the formation of Mo-SAs anchored with one nitrogen atom and two carbon atoms (Mo 1 N 1 C 2 ). Importantly, the Mo 1 N 1 C 2 catalyst displayed much more excellent activity compared with Mo 2 C and MoN, and better stability than commercial Pt/C. Density functional theory (DFT) calculation revealed that the unique structure of Mo 1 N 1 C 2 moiety played a crucial effect to improve the HER performance. This work opens up new opportunities for the preparation and application of highly active and stable Mo-based HER catalysts. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electron Localization States in Asymmetric Shape Carbon Nanotubes Caused by Hydrogen Adsorption

NASA Astrophysics Data System (ADS)

Pan, L. J.; Chen, W. G.

2017-12-01

In this paper, we presented pseudopotential-based density functional theory studies on energy, structure, energy band structure of hydrogenated single-walled carbon nanotube. The stability of the configuration mainly depends on hydrogen coverage. According to the adsorption energies, the stability deteriorates with the increase of the hydrogen adsorption. The cross section of configurations become various shapes such as “beetle” or “lip” appearance without the balanced effects of hydrogen atoms. We also explored the energy band structures of configurations in three typical adsorption patterns, showing that the disparate trends of energy band gap as the hydrogen atoms concentrate. For C32H24, the band gap may reach the large value of 2.79 eV for the adsorption pattern A configuration and reduce to be zero for the adsorption pattern C case, the values of band gap for pattern A configurations decrease, which is opposite of the pattern B configurations as the adsorption hydrogen becomes more disperse. It is deduced that the hydrogen adsorption has significant effect on the electrical properties of the carbon nanotube.

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.

Measurements of the electrical resistance and the hydrogen depth distribution for Ni 60Nb 20Zr 20 amorphous alloy before and after hydrogen charging

NASA Astrophysics Data System (ADS)

Nakano, Sumiaki; Ohtsu, Naofumi; Nagata, Shinji; Yamaura, Shin-ichi; Uchinashi, Sakae; Kimura, Hisamichi; Shikama, Tatsuo; Inoue, Akihisa

2005-02-01

A Ni 60Nb 20Zr 20 amorphous alloy was prepared by the single-roller melt-spinning technique. The change in the electrical resistance of the alloy after electrochemical hydrogen charging in 6 N KOH solution was investigated. The change in the hydrogen depth distribution in the alloy was also investigated by elastic recoil detection. As a result, we found that the electrical resistance of the alloy increases with increasing the hydrogen content in the alloy and that a large number of hydrogen atoms are remained in the surface area of the hydrogen-charged alloy.

Stability investigation of a high number density Pt1/Fe2O3 single-atom catalyst under different gas environments by HAADF-STEM

NASA Astrophysics Data System (ADS)

Duan, Sibin; Wang, Rongming; Liu, Jingyue

2018-05-01

Catalysis by supported single metal atoms has demonstrated tremendous potential for practical applications due to their unique catalytic properties. Unless they are strongly anchored to the support surfaces, supported single atoms, however, are thermodynamically unstable, which poses a major obstacle for broad applications of single-atom catalysts (SACs). In order to develop strategies to improve the stability of SACs, we need to understand the intrinsic nature of the sintering processes of supported single metal atoms, especially under various gas environments that are relevant to important catalytic reactions. We report on the synthesis of high number density Pt1/Fe2O3 SACs using a facial strong adsorption method and the study of the mobility of these supported Pt single atoms at 250 °C under various gas environments that are relevant to CO oxidation, water–gas shift, and hydrogenation reactions. Under the oxidative gas environment, Fe2O3 supported Pt single atoms are stable even at high temperatures. The presence of either CO or H2 molecules in the gas environment, however, facilitates the movement of the Pt atoms. The strong interaction between CO and Pt weakens the binding between the Pt atoms and the support, facilitating the movement of the Pt single atoms. The dissociation of H2 molecules on the Pt atoms and their subsequent interaction with the oxygen species of the support surfaces dislodge the surface oxygen anchored Pt atoms, resulting in the formation of Pt clusters. The addition of H2O molecules to the CO or H2 significantly accelerates the sintering of the Fe2O3 supported Pt single atoms. An anchoring-site determined sintering mechanism is further proposed, which is related to the metal–support interaction.

Stability investigation of a high number density Pt1/Fe2O3 single-atom catalyst under different gas environments by HAADF-STEM.

PubMed

Duan, Sibin; Wang, Rongming; Liu, Jingyue

2018-05-18

Catalysis by supported single metal atoms has demonstrated tremendous potential for practical applications due to their unique catalytic properties. Unless they are strongly anchored to the support surfaces, supported single atoms, however, are thermodynamically unstable, which poses a major obstacle for broad applications of single-atom catalysts (SACs). In order to develop strategies to improve the stability of SACs, we need to understand the intrinsic nature of the sintering processes of supported single metal atoms, especially under various gas environments that are relevant to important catalytic reactions. We report on the synthesis of high number density Pt 1 /Fe 2 O 3 SACs using a facial strong adsorption method and the study of the mobility of these supported Pt single atoms at 250 °C under various gas environments that are relevant to CO oxidation, water-gas shift, and hydrogenation reactions. Under the oxidative gas environment, Fe 2 O 3 supported Pt single atoms are stable even at high temperatures. The presence of either CO or H 2 molecules in the gas environment, however, facilitates the movement of the Pt atoms. The strong interaction between CO and Pt weakens the binding between the Pt atoms and the support, facilitating the movement of the Pt single atoms. The dissociation of H 2 molecules on the Pt atoms and their subsequent interaction with the oxygen species of the support surfaces dislodge the surface oxygen anchored Pt atoms, resulting in the formation of Pt clusters. The addition of H 2 O molecules to the CO or H 2 significantly accelerates the sintering of the Fe 2 O 3 supported Pt single atoms. An anchoring-site determined sintering mechanism is further proposed, which is related to the metal-support interaction.

Direct observation and control of hydrogen-bond dynamics using low-temperature scanning tunneling microscopy

NASA Astrophysics Data System (ADS)

Kumagai, Takashi

2015-08-01

Hydrogen(H)-bond dynamics are involved in many elementary processes in chemistry and biology. Because of its fundamental importance, a variety of experimental and theoretical approaches have been employed to study the dynamics in gas, liquid, solid phases, and their interfaces. This review describes the recent progress of direct observation and control of H-bond dynamics in several model systems on a metal surface by using low-temperature scanning tunneling microscopy (STM). General aspects of H-bond dynamics and the experimental methods are briefly described in chapter 1 and 2. In the subsequent four chapters, I present direct observation of an H-bond exchange reaction within a single water dimer (chapter 3), a symmetric H bond (chapter 4) and H-atom relay reactions (chapter 5) within water-hydroxyl complexes, and an intramolecular H-atom transfer reaction (tautomerization) within a single porphycene molecule (chapter 6). These results provide novel microscopic insights into H-bond dynamics at the single-molecule level, and highlight significant impact on the process from quantum effects, namely tunneling and zero-point vibration, resulting from the small mass of H atom. Additionally, local environmental effect on H-bond dynamics is also examined by using atom/molecule manipulation with the STM.

Single-Atom Electrocatalysts.

PubMed

Zhu, Chengzhou; Fu, Shaofang; Shi, Qiurong; Du, Dan; Lin, Yuehe

2017-11-06

Recent years have witnessed a dramatic increase in the production of sustainable and renewable energy. However, the electrochemical performances of the various systems are limited, and there is an intensive search for highly efficient electrocatalysts by more rational control over the size, shape, composition, and structure. Of particular interest are the studies on single-atom catalysts (SACs), which have sparked new interests in electrocatalysis because of their high catalytic activity, stability, selectivity, and 100 % atom utilization. In this Review, we introduce innovative syntheses and characterization techniques for SACs, with a focus on their electrochemical applications in the oxygen reduction/evolution reaction, hydrogen evolution reaction, and hydrocarbon conversion reactions for fuel cells (electrooxidation of methanol, ethanol, and formic acid). The electrocatalytic performance is further considered at an atomic level and the underlying mechanisms are discussed. The ultimate goal is the tailoring of single atoms for electrochemical applications. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hirshfeld atom refinement.

PubMed

Capelli, Silvia C; Bürgi, Hans-Beat; Dittrich, Birger; Grabowsky, Simon; Jayatilaka, Dylan

2014-09-01

Hirshfeld atom refinement (HAR) is a method which determines structural parameters from single-crystal X-ray diffraction data by using an aspherical atom partitioning of tailor-made ab initio quantum mechanical molecular electron densities without any further approximation. Here the original HAR method is extended by implementing an iterative procedure of successive cycles of electron density calculations, Hirshfeld atom scattering factor calculations and structural least-squares refinements, repeated until convergence. The importance of this iterative procedure is illustrated via the example of crystalline ammonia. The new HAR method is then applied to X-ray diffraction data of the dipeptide Gly-l-Ala measured at 12, 50, 100, 150, 220 and 295 K, using Hartree-Fock and BLYP density functional theory electron densities and three different basis sets. All positions and anisotropic displacement parameters (ADPs) are freely refined without constraints or restraints - even those for hydrogen atoms. The results are systematically compared with those from neutron diffraction experiments at the temperatures 12, 50, 150 and 295 K. Although non-hydrogen-atom ADPs differ by up to three combined standard uncertainties (csu's), all other structural parameters agree within less than 2 csu's. Using our best calculations (BLYP/cc-pVTZ, recommended for organic molecules), the accuracy of determining bond lengths involving hydrogen atoms from HAR is better than 0.009 Å for temperatures of 150 K or below; for hydrogen-atom ADPs it is better than 0.006 Å(2) as judged from the mean absolute X-ray minus neutron differences. These results are among the best ever obtained. Remarkably, the precision of determining bond lengths and ADPs for the hydrogen atoms from the HAR procedure is comparable with that from the neutron measurements - an outcome which is obtained with a routinely achievable resolution of the X-ray data of 0.65 Å.

Hirshfeld atom refinement

PubMed Central

Capelli, Silvia C.; Bürgi, Hans-Beat; Dittrich, Birger; Grabowsky, Simon; Jayatilaka, Dylan

2014-01-01

Hirshfeld atom refinement (HAR) is a method which determines structural parameters from single-crystal X-ray diffraction data by using an aspherical atom partitioning of tailor-made ab initio quantum mechanical molecular electron densities without any further approximation. Here the original HAR method is extended by implementing an iterative procedure of successive cycles of electron density calculations, Hirshfeld atom scattering factor calculations and structural least-squares refinements, repeated until convergence. The importance of this iterative procedure is illustrated via the example of crystalline ammonia. The new HAR method is then applied to X-ray diffraction data of the dipeptide Gly–l-Ala measured at 12, 50, 100, 150, 220 and 295 K, using Hartree–Fock and BLYP density functional theory electron densities and three different basis sets. All positions and anisotropic displacement parameters (ADPs) are freely refined without constraints or restraints – even those for hydrogen atoms. The results are systematically compared with those from neutron diffraction experiments at the temperatures 12, 50, 150 and 295 K. Although non-hydrogen-atom ADPs differ by up to three combined standard uncertainties (csu’s), all other structural parameters agree within less than 2 csu’s. Using our best calculations (BLYP/cc-pVTZ, recommended for organic molecules), the accuracy of determining bond lengths involving hydrogen atoms from HAR is better than 0.009 Å for temperatures of 150 K or below; for hydrogen-atom ADPs it is better than 0.006 Å2 as judged from the mean absolute X-ray minus neutron differences. These results are among the best ever obtained. Remarkably, the precision of determining bond lengths and ADPs for the hydrogen atoms from the HAR procedure is comparable with that from the neutron measurements – an outcome which is obtained with a routinely achievable resolution of the X-ray data of 0.65 Å. PMID:25295177

Positron annihilation lifetime and photoluminescence studies on single crystalline ZnO

NASA Astrophysics Data System (ADS)

Sarkar, A.; Chakrabarti, Mahuya; Ray, S. K.; Bhowmick, D.; Sanyal, D.

2011-04-01

The room temperature positron annihilation lifetime for single crystalline ZnO has been measured as 164 ± 1 ps. The single component lifetime value is very close to but higher than the theoretically predicted value of ~ 154 ps. Photoluminescence study (at 10 K) indicates the presence of hydrogen and other defects, mainly acceptor related, in the crystal. Defects related to a lower open volume than zinc vacancies, presumably a complex with two hydrogen atoms, are the major trapping sites in the sample. The bulk positron lifetime in ZnO is expected to be a little less than 164 ps.

Positron annihilation lifetime and photoluminescence studies on single crystalline ZnO.

PubMed

Sarkar, A; Chakrabarti, Mahuya; Ray, S K; Bhowmick, D; Sanyal, D

2011-04-20

The room temperature positron annihilation lifetime for single crystalline ZnO has been measured as 164 ± 1 ps. The single component lifetime value is very close to but higher than the theoretically predicted value of ~154 ps. Photoluminescence study (at 10 K) indicates the presence of hydrogen and other defects, mainly acceptor related, in the crystal. Defects related to a lower open volume than zinc vacancies, presumably a complex with two hydrogen atoms, are the major trapping sites in the sample. The bulk positron lifetime in ZnO is expected to be a little less than 164 ps.

Electrodeposition of Isolated Platinum Atoms and Clusters on Bismuth-Characterization and Electrocatalysis.

PubMed

Zhou, Min; Dick, Jeffrey E; Bard, Allen J

2017-12-06

We describe a method for the electrodeposition of an isolated single Pt atom or small cluster, up to 9 atoms, on a bismuth ultramicroelectrode (UME). This deposition was immediately followed by electrochemical characterization via the hydrogen evolution reaction (HER) that occurs readily on the electrodeposited Pt but not on Bi. The observed voltammetric current plateau, even for a single atom, which behaves as an electrode, allows the estimation of deposit size. Pt was plated from solutions of femtomolar PtCl 6 2- , which allowed precise control of the arrival of ions and thus the plating rate on the Bi UME, to one ion every few seconds. This allowed the atom-by-atom fabrication of isolated platinum deposits, ranging from single atoms to 9-atom clusters. The limiting currents in voltammetry gave the size and number of atoms of the clusters. Given the stochasticity of the plating process, we show that the number of atoms plated over a given time (10 and 20 s) follows a Poisson distribution. Taking the potential at a certain current density as a measure of the relative rate of the HER, we found that the potential shifted positively as the size increased, with single atoms showing the largest overpotentials compared to bulk Pt.

Activation energy for diamond growth from the carbon-hydrogen gas system at low substrate temperatures

NASA Astrophysics Data System (ADS)

Stiegler, J.; Lang, T.; von Kaenel, Y.; Michler, J.; Blank, E.

1997-01-01

The growth kinetics of diamond films deposited at low substrate temperatures (600-400 °C) from the carbon-hydrogen gas system have been studied. When the substrate temperature alone was varied, independently of all other process parameters in the microwave plasma reactor, an activation energy in the order of 7 kcal/mol was observed. This value did not change with different carbon concentrations in hydrogen. It is supposed that growth kinetics in this temperature range are controlled by a single chemical reaction, probably the abstraction of surface bonded hydrogen by gas phase atomic hydrogen.

From Artificial Atoms to Nanocrystal Molecules: Preparation and Properties of More Complex Nanostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Choi, Charina L; Alivisatos, A Paul

2009-10-20

Quantum dots, which have found widespread use in fields such as biomedicine, photovoltaics, and electronics, are often called artificial atoms due to their size-dependent physical properties. Here this analogy is extended to consider artificial nanocrystal molecules, formed from well-defined groupings of plasmonically or electronically coupled single nanocrystals. Just as a hydrogen molecule has properties distinct from two uncoupled hydrogen atoms, a key feature of nanocrystal molecules is that they exhibit properties altered from those of the component nanoparticles due to coupling. The nature of the coupling between nanocrystal atoms and its response to vibrations and deformations of the nanocrystal moleculemore » bonds are of particular interest. We discuss synthetic approaches, predicted and observed physical properties, and prospects and challenges toward this new class of materials.« less

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.

Metal Catalysts for Heterogeneous Catalysis: From Single Atoms to Nanoclusters and Nanoparticles.

PubMed

Liu, Lichen; Corma, Avelino

2018-05-23

Metal species with different size (single atoms, nanoclusters, and nanoparticles) show different catalytic behavior for various heterogeneous catalytic reactions. It has been shown in the literature that many factors including the particle size, shape, chemical composition, metal-support interaction, and metal-reactant/solvent interaction can have significant influences on the catalytic properties of metal catalysts. The recent developments of well-controlled synthesis methodologies and advanced characterization tools allow one to correlate the relationships at the molecular level. In this Review, the electronic and geometric structures of single atoms, nanoclusters, and nanoparticles will be discussed. Furthermore, we will summarize the catalytic applications of single atoms, nanoclusters, and nanoparticles for different types of reactions, including CO oxidation, selective oxidation, selective hydrogenation, organic reactions, electrocatalytic, and photocatalytic reactions. We will compare the results obtained from different systems and try to give a picture on how different types of metal species work in different reactions and give perspectives on the future directions toward better understanding of the catalytic behavior of different metal entities (single atoms, nanoclusters, and nanoparticles) in a unifying manner.

Adsorbate-induced reconstruction in the phase 1 × 2-3H/Rh(110)

NASA Astrophysics Data System (ADS)

Michl, M.; Nichtl-Pecher, W.; Oed, W.; Landskron, H.; Heinz, K.; Müller, K.

1989-10-01

The 1 × 2-3H superstructure of hydrogen on Rh(110) at coverage θ = {3}/{2} is analysed by low energy electron diffraction at 90 K. The spectra of eight beams are recorded with a computer-controlled TV measurement technique which yields low noise data even for weak superstructure spots by multiple averaging. Comparison to full dynamical calculations shows that a kinematic treatment of the hydrogen layer diffraction coupled to the full dynamical diffraction of the substrate is a very good approximation. Spectra computed in this way are compared with experimental data by R-factor evaluation. The three non-equivalent hydrogen atoms are found to adsorb in quasi-three-fold coordinated adsorption sites with slightly different local configurations and with H-Rh bond lengths between 1.87 and 1.93 Å to the first-layer rhodium atoms. Interaction between the adatoms seems to weaken the bonding to the adjacent atom in the second layer, so that H-Rh bond lengths larger than 2.17 Å result. A slight reconstruction of the substrate is necessary to bring superstructure spot intensities near the experimentally observed level. Rhodium atoms bonded to two hydrogen atoms are moved out of the surface by 0.03 ± 0.02 Å relative to Rh atoms bonded to only a single H atom. The relaxation of the first Rh layer spacing is determined to be {d 12}/{d 0} = -3.8 ± 1% and {d 22}/{d 0} = 0 ± 1% . The best fit Pendry R-factor is 0.33.

Adsorption, hydrogenation and dehydrogenation of C2H on a CoCu bimetallic layer

NASA Astrophysics Data System (ADS)

Wu, Donghai; Yuan, Jinyun; Yang, Baocheng; Chen, Houyang

2018-05-01

In this paper, adsorption, hydrogenation and dehydrogenation of C2H on a single atomic layer of bimetallic CoCu were investigated using first-principles calculations. The CoCu bimetallic layer is formed by Cu replacement of partial Co atoms on the top layer of a Co(111) surface. Our adsorption and reaction results showed those sites, which have stronger adsorption energy of C2H, possess higher reactivity. The bimetallic layer possesses higher reactivity than either of the pure monometallic layer. A mechanism of higher reactivity of the bimetallic layer is proposed and identified, i.e. in the bimetallic catalyst, the catalytic performance of one component is promoted by the second component, and in our work, the catalytic performance of Co atoms in the bimetallic layer are improved by introducing Cu atoms, lowing the activation barrier of the reaction of C2H. The bimetallic layer could tune adsorption and reaction of C2H by modulating the ratio of Co and Cu. Results of adsorption energies and adsorption configurations reveal that C2H prefers to be adsorbed in parallel on both the pure Co metallic and CoCu bimetallic layers, and Co atoms in subsurface which support the metallic or bimetallic layer have little effect on C2H adsorption. For hydrogenation reactions, the products greatly depend on the concentration and initial positions of hydrogen atoms, and the C2H hydrogenation forming acetylene is more favorable than forming vinylidene in both thermodynamics and kinetics. This study would provide fundamental guidance for hydrocarbon reactions on Co-based and/or Cu-based bimetallic surface chemistry and for development of new bimetallic catalysts.

Correlation of Hydrogen-Atom Abstraction Reaction Efficiencies for Aryl Radicals with their Vertical Electron Affinities and the Vertical Ionization Energies of the Hydrogen Atom Donors

PubMed Central

Jing, Linhong; Nash, John J.

2009-01-01

The factors that control the reactivities of aryl radicals toward hydrogen-atom donors were studied by using a dual-cell Fourier-transform ion cyclotron resonance mass spectrometer (FT – ICR). Hydrogen-atom abstraction reaction efficiencies for two substrates, cyclohexane and isopropanol, were measured for twenty-three structurally different, positively-charged aryl radicals, which included dehydrobenzenes, dehydronaphthalenes, dehydropyridines, and dehydro(iso)quinolines. A logarithmic correlation was found between the hydrogen-atom abstraction reaction efficiencies and the (calculated) vertical electron affinities (EA) of the aryl radicals. Transition state energies calculated for three of the aryl radicals with isopropanol were found to correlate linearly with their (calculated) EAs. No correlation was found between the hydrogen-atom abstraction reaction efficiencies and the (calculated) enthalpy changes for the reactions. Measurement of the reaction efficiencies for the reactions of several different hydrogen-atom donors with a few selected aryl radicals revealed a logarithmic correlation between the hydrogen-atom abstraction reaction efficiencies and the vertical ionization energies (IE) of the hydrogen-atom donors, but not the lowest homolytic X – H (X = heavy atom) bond dissociation energies of the hydrogen-atom donors. Examination of the hydrogen-atom abstraction reactions of twenty-nine different aryl radicals and eighteen different hydrogen-atom donors showed that the reaction efficiency increases (logarithmically) as the difference between the IE of the hydrogen-atom donor and the EA of the aryl radical decreases. This dependence is likely to result from the increasing polarization, and concomitant stabilization, of the transition state as the energy difference between the neutral and ionic reactants decreases. Thus, the hydrogen-atom abstraction reaction efficiency for an aryl radical can be “tuned” by structural changes that influence either the vertical EA of the aryl radical or the vertical IE of the hydrogen atom donor. PMID:19061320

Effective and Durable Co Single Atomic Cocatalysts for Photocatalytic Hydrogen Production.

PubMed

Zhao, Qi; Yao, Weifeng; Huang, Cunping; Wu, Qiang; Xu, Qunjie

2017-12-13

This research reports for the first time that single cobalt atoms anchored in nitrogen-doped graphene (Co-NG) can serve as a highly effective and durable cocatalyst for visible light photocatalytic hydrogen production from water. Results show that, under identical conditions, the hydrogen production rate (1382 μmol/h) for 0.25 wt % Co-NG-loaded CdS photocatalyst (0.25 wt % Co-NG/CdS) is 3.42 times greater than that of nitrogen-doped graphene (NG) loaded CdS photocatalyst (NG/CdS) and about 1.3 times greater than the greatest hydrogen production rate (1077 μmol/h) for 1.5 wt % Pt nanoparticle loaded CdS photocatalyst (1.5 wt % Pt-NPs/CdS). At 420 nm irradiation, the quantum efficiency of the 0.25 wt % Co-NG/CdS photocatalyst is 50.5%, the highest efficiency among those literature-reported non-noble metal cocatalysts. The Co-NG/CdS nanocomposite-based photocatalyst also has an extended durability. No activity decline was detected during three cyclic photocatalytic life span tests. The very low cocatalyst loading, along with the facile preparation technology for this non-noble metal cocatalyst, will significantly reduce the hydrogen production costs and finally lead to the commercialization of the solar catalytic hydrogen production process. Based on experimental results, we conclude that Co-NG can successfully replace noble metal cocatalysts as a highly effective and durable cocatalyst for renewable solar hydrogen production. This finding will point to a new way for the development of highly effective, long life span, non-noble metal-based cocatalysts for renewable and cost-effective hydrogen production.

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.

Two different carbon-hydrogen complexes in silicon with closely spaced energy levels

NASA Astrophysics Data System (ADS)

Stübner, R.; Kolkovsky, Vl.; Weber, J.

2015-08-01

An acceptor and a single donor state of carbon-hydrogen defects (CHA and CHB) are observed by Laplace deep level transient spectroscopy at 90 K. CHA appears directly after hydrogenation by wet chemical etching or hydrogen plasma treatment, whereas CHB can be observed only after a successive annealing under reverse bias at about 320 K. The activation enthalpies of these states are 0.16 eV for CHA and 0.14 eV for CHB. Our results reconcile previous controversial experimental results. We attribute CHA to the configuration where substitutional carbon binds a hydrogen atom on a bond centered position between carbon and the neighboring silicon and CHB to another carbon-hydrogen defect.

Two-probe STM experiments at the atomic level.

PubMed

Kolmer, Marek; Olszowski, Piotr; Zuzak, Rafal; Godlewski, Szymon; Joachim, Christian; Szymonski, Marek

2017-11-08

Direct characterization of planar atomic or molecular scale devices and circuits on a supporting surface by multi-probe measurements requires unprecedented stability of single atom contacts and manipulation of scanning probes over large, nanometer scale area with atomic precision. In this work, we describe the full methodology behind atomically defined two-probe scanning tunneling microscopy (STM) experiments performed on a model system: dangling bond dimer wire supported on a hydrogenated germanium (0 0 1) surface. We show that 70 nm long atomic wire can be simultaneously approached by two independent STM scanners with exact probe to probe distance reaching down to 30 nm. This allows direct wire characterization by two-probe I-V characteristics at distances below 50 nm. Our technical results presented in this work open a new area for multi-probe research, which can be now performed with precision so far accessible only by single-probe scanning probe microscopy (SPM) experiments.

Defect studies of ZnO single crystals electrochemically doped with hydrogen

NASA Astrophysics Data System (ADS)

Čížek, J.; Žaludová, N.; Vlach, M.; Daniš, S.; Kuriplach, J.; Procházka, I.; Brauer, G.; Anwand, W.; Grambole, D.; Skorupa, W.; Gemma, R.; Kirchheim, R.; Pundt, A.

2008-03-01

Various defect studies of hydrothermally grown (0001) oriented ZnO crystals electrochemically doped with hydrogen are presented. The hydrogen content in the crystals is determined by nuclear reaction analysis and it is found that already 0.3at.% H exists in chemically bound form in the virgin ZnO crystals. A single positron lifetime of 182ps is detected in the virgin crystals and attributed to saturated positron trapping at Zn vacancies surrounded by hydrogen atoms. It is demonstrated that a very high amount of hydrogen (up to ˜30at.%) can be introduced into the crystals by electrochemical doping. More than half of this amount is chemically bound, i.e., incorporated into the ZnO crystal lattice. This drastic increase of the hydrogen concentration is of marginal impact on the measured positron lifetime, whereas a contribution of positrons annihilated by electrons belonging to O-H bonds formed in the hydrogen doped crystal is found in coincidence Doppler broadening spectra. The formation of hexagonal shape pyramids on the surface of the hydrogen doped crystals by optical microscopy is observed and discussed.

Attosecond Optics and Technology: Progress to Date and Future Prospects [Invited

DTIC Science & Technology

2016-06-01

1s electron in the hydrogen atom experiences is 5.14 × 109 V∕cm. In such a strong external field, an electron can be freed from an atom via tunneling ...been replaced by laser diodes , which leads to user-friendly products that deliver either single-longitudinal mode beams for pumping laser oscillators...steps. First, an electron is released by tunneling through the potential barrier formed by the atomic Coulomb field and the driving laser field. Then

Single-ring magnetic cusp low gas pressure ion source

DOEpatents

Bacon, Frank M.; Brainard, John P.; O'Hagan, James B.; Walko, Robert J.

1985-01-01

A single-ring magnetic cusp low gas pressure ion source designed for use in a sealed, nonpumped neutron generator utilizes a cathode and an anode, three electrically floating electrodes (a reflector behind the cathode, a heat shield around the anode, and an aperture plate), together with a single ring-cusp magnetic field, to establish and energy-filtering mechanism for producing atomic-hydrogen ions.

Analytic model of a multi-electron atom

NASA Astrophysics Data System (ADS)

Skoromnik, O. D.; Feranchuk, I. D.; Leonau, A. U.; Keitel, C. H.

2017-12-01

A fully analytical approximation for the observable characteristics of many-electron atoms is developed via a complete and orthonormal hydrogen-like basis with a single-effective charge parameter for all electrons of a given atom. The basis completeness allows us to employ the secondary-quantized representation for the construction of regular perturbation theory, which includes in a natural way correlation effects, converges fast and enables an effective calculation of the subsequent corrections. The hydrogen-like basis set provides a possibility to perform all summations over intermediate states in closed form, including both the discrete and continuous spectra. This is achieved with the help of the decomposition of the multi-particle Green function in a convolution of single-electronic Coulomb Green functions. We demonstrate that our fully analytical zeroth-order approximation describes the whole spectrum of the system, provides accuracy, which is independent of the number of electrons and is important for applications where the Thomas-Fermi model is still utilized. In addition already in second-order perturbation theory our results become comparable with those via a multi-configuration Hartree-Fock approach.

Signatures of the atomic nucleus in laser-assisted single ionization of one-electron atoms

NASA Astrophysics Data System (ADS)

Ajana, Imane; Khalil, Driss; Makhoute, Abdelkader

2018-03-01

The dynamics of the electron-impact single ionization of hydrogenic targets in the presence of a laser field (e, 2e) has been studied for different residual ion charges Z = 1, 2, 3 and 4. The state of fast electron in the laser field is described by the Volkov state, while the dressed state of the ejected slow electron and atomic target is treated perturbatively to the first-order perturbation theory. We calculate the triple differential cross section in the Ehrhardt asymmetric coplanar geometry. We have compared and analyzed the triple differential cross sections from one-electron atoms by varying the charge state of the residual ion, and evaluating the interplay between the laser influence and the role of scattering from the residual ion.

An important rule for realizing metal → half-metal → semiconductor transition in single-molecule junctions

NASA Astrophysics Data System (ADS)

Zeng, Jing; Chen, Ke-Qiu; Long, Mengqiu

2017-06-01

Recently, Zhong et al (2015 Nano Lett. 15 8091) found that two additional hydrogen atoms can be adsorbed to the opposite aza-bridging nitrogen atoms of the manganese phthalocyanine (MnPc) macrocycle when exposed to H2. Thus the symmetry of the MnPc molecule is changed from 4-fold to 2-fold. Motivated by this recent experiment, we theoretically investigate a MnPc-based single-molecule junction in this work and propose a simple and reliable way to realize the transition of its electronic properties. On the basis of spin-polarized density-functional theory calculations combined with the Keldysh nonequilibrium Green’s technique, we find that the gradual hydrogenation in MnPc molecules gives rise to the changes of the hardness of the electron density and spin-selective orbital decoupling, which eventually leads to the realization of the first ever metal  →  half-metal  →  semiconductor transition behavior in single-molecule junctions. Analysis of molecular projected self-consistent Hamiltonian, Mulliken population, and local density of states also reveals an important rule for realizing this transition behavior. Our research confirms that the hydrogenation of MnPc molecules can realize various molecular functionalities in unitary material background.

Reaction Kinetics of Hydrogen Atom Abstraction from C4-C6 Alkenes by the Hydrogen Atom and Methyl Radical.

PubMed

Wang, Quan-De; Liu, Zi-Wu

2018-06-14

Alkenes are important ingredients of realistic fuels and are also critical intermediates during the combustion of a series of other fuels including alkanes, cycloalkanes, and biofuels. To provide insights into the combustion behavior of alkenes, detailed quantum chemical studies for crucial reactions are desired. Hydrogen abstractions of alkenes play a very important role in determining the reactivity of fuel molecules. This work is motivated by previous experimental and modeling evidence that current literature rate coefficients for the abstraction reactions of alkenes are still in need of refinement and/or redetermination. In light of this, this work reports a theoretical and kinetic study of hydrogen atom abstraction reactions from C4-C6 alkenes by the hydrogen (H) atom and methyl (CH 3 ) radical. A series of C4-C6 alkene molecules with enough structural diversity are taken into consideration. Geometry and vibrational properties are determined at the B3LYP/6-31G(2df,p) level implemented in the Gaussian-4 (G4) composite method. The G4 level of theory is used to calculate the electronic single point energies for all species to determine the energy barriers. Conventional transition state theory with Eckart tunneling corrections is used to determine the high-pressure-limit rate constants for 47 elementary reaction rate coefficients. To faciliate their applications in kinetic modeling, the obtained rate constants are given in the Arrhenius expression and rate coefficients for typical reaction classes are recommended. The overall rate coefficients for the reaction of H atom and CH 3 radical with all the studied alkenes are also compared. Branching ratios of these reaction channels for certain alkenes have also been analyzed.

Ethylene hydrogenation catalysis on Pt(111) single-crystal surfaces studied by using mass spectrometry and in situ infrared absorption spectroscopy

NASA Astrophysics Data System (ADS)

Tillekaratne, Aashani; Simonovis, Juan Pablo; Zaera, Francisco

2016-10-01

The catalytic hydrogenation of ethylene promoted by a Pt(111) single crystal was studied by using a ultrahigh-vacuum surface-science instrument equipped with a so-called high-pressure cell. Kinetic data were acquired continuously during the catalytic conversion of atmospheric-pressure mixtures of ethylene and hydrogen by using mass spectrometry while simultaneously characterizing the surface species in operando mode by reflection-absorption infrared spectroscopy (RAIRS). Many observations reported in previous studies of this system were corroborated, including the presence of adsorbed alkylidyne intermediates during the reaction and the zero-order dependence of the rate of hydrogenation on the pressure of ethylene. In addition, the high quality of the kinetic data, which could be recorded continuously versus time and processed to calculate time-dependent turnover frequencies (TOFs), afforded a more detailed analysis of the mechanism. Specifically, deuterium labeling could be used to estimate the extent of isotope scrambling reached with mixed-isotope-substituted reactants (C2H4 + D2 and C2D4 + H2). Perhaps the most important new observation from this work is that, although extensive H-D exchange takes place on ethylene before being fully converted to ethane, the average stoichiometry of the final product retains the expected stoichiometry of the gas mixture, that is, four regular hydrogen atoms and two deuteriums per ethane molecule in the case of the experiments with C2H4 + D2. This means that no hydrogen atoms are removed from the surface via their inter-recombination to produce X2 (X = H or D). It is concluded that, under catalytic conditions, hydrogen surface recombination is much slower than ethylene hydrogenation and H-D exchange.

Using light transmission to watch hydrogen diffuse

PubMed Central

Pálsson, Gunnar K.; Bliersbach, Andreas; Wolff, Max; Zamani, Atieh; Hjörvarsson, Björgvin

2012-01-01

Because of its light weight and small size, hydrogen exhibits one of the fastest diffusion rates in solid materials, comparable to the diffusion rate of liquid water molecules at room temperature. The diffusion rate is determined by an intricate combination of quantum effects and dynamic interplay with the displacement of host atoms that is still only partially understood. Here we present direct observations of the spatial and temporal changes in the diffusion-induced concentration profiles in a vanadium single crystal and we show that the results represent the experimental counterpart of the full time and spatial solution of Fick's diffusion equation. We validate the approach by determining the diffusion rate of hydrogen in a single crystal vanadium (001) film, with net diffusion in the [110] direction. PMID:22692535

Using light transmission to watch hydrogen diffuse

NASA Astrophysics Data System (ADS)

Pálsson, Gunnar K.; Bliersbach, Andreas; Wolff, Max; Zamani, Atieh; Hjörvarsson, Björgvin

2012-06-01

Because of its light weight and small size, hydrogen exhibits one of the fastest diffusion rates in solid materials, comparable to the diffusion rate of liquid water molecules at room temperature. The diffusion rate is determined by an intricate combination of quantum effects and dynamic interplay with the displacement of host atoms that is still only partially understood. Here we present direct observations of the spatial and temporal changes in the diffusion-induced concentration profiles in a vanadium single crystal and we show that the results represent the experimental counterpart of the full time and spatial solution of Fick's diffusion equation. We validate the approach by determining the diffusion rate of hydrogen in a single crystal vanadium (001) film, with net diffusion in the [110] direction.

Name that compound: The numbers game for CFCs, HFCs, HCFCs, and Halons

DOE Data Explorer

Blasing, T. J.; Jones, Sonja

2012-02-01

Chlorofluorocarbons (CFCs) contain Carbon and some combination of Fluorine and Chlorine atoms. Hydrofluorocarbons (HFCs) contain Hydrogen, Fluorine, and Carbon (no chlorine). Hydrochlorofluorocarbons (HCFCs) contain Hydrogen, Chlorine, Fluorine, and Carbon atoms. Hydrobromofluorocarbons (HBFCs) contain Hydrogen, Bromine, Fluorine, and Carbon atoms. Perfluorocarbons contain Fluorine, Carbon, and Bromine atoms, and some contain Chlorine and/or Hydrogen atoms. These compounds are often designated by a combination of letters and numbers (e.g., CFC-11, HCFC-142b). In the latter example, the lower-case b refers to an isomer, which has no relationship to the chemical formula (C2H3F2Cl), but designates a particular structural arrangement of the atoms included. For example, HCFC-142b identifies the isomer in which all three hydrogen atoms are attached to the same carbon atom, and the structural formula is written as CH3CF2Cl. By contrast, HCFC-142 (without the b) refers to an arrangement in which one carbon atom is attached to two hydrogen atoms and one chlorine atom, while the other carbon atom is attached to the third hydrogen atom and two fluorine atoms. Hence, it has a different structural formula (CH2ClCHF2).

Synthesis of SWNT/Pt nanocomposites for their effective role in hydrogen storage applications

NASA Astrophysics Data System (ADS)

Sharma, Anshu; Andreas, Rossos; Nehra, S. P.

2018-05-01

Single Wall Carbon Nanotubes (SWNTs) decorated with platinum were synthesized for hydrogen storage applications. Platinum was deposited on the nanotubes using hexachloroplatinic acid (H2PtCl6.6H2O) as a precursor. Commercial SWNTs were also used to compare the results. The obtained SWNTs/Pt nanocomposite was characterized by various techniques such as powder X-ray diffractrometry (XRD), Raman Spectroscopy and Scanning Electron Microscopy (SEM). Furthermore, in the case of SWNTs/Pt, Pt nanoparticles are found to be uniformly dispersed and bound to the SWNTs acting like a single atom catalyst.

Probing the Structure and Dynamics of Interfacial Water with Scanning Tunneling Microscopy and Spectroscopy.

PubMed

Guo, Jing; You, Sifan; Wang, Zhichang; Peng, Jinbo; Ma, Runze; Jiang, Ying

2018-05-27

Water/solid interfaces are ubiquitous and play a key role in many environmental, biophysical, and technological processes. Resolving the internal structure and probing the hydrogen-bond (H-bond) dynamics of the water molecules adsorbed on solid surfaces are fundamental issues of water science, which remains a great challenge owing to the light mass and small size of hydrogen. Scanning tunneling microscopy (STM) is a promising tool for attacking these problems, thanks to its capabilities of sub-Ångström spatial resolution, single-bond vibrational sensitivity, and atomic/molecular manipulation. The designed experimental system consists of a Cl-terminated tip and a sample fabricated by dosing water molecules in situ onto the Au(111)-supported NaCl(001) surfaces. The insulating NaCl films electronically decouple the water from the metal substrates, so the intrinsic frontier orbitals of water molecules are preserved. The Cl-tip facilitates the manipulation of the single water molecules, as well as gating the orbitals of water to the proximity of Fermi level (EF) via tip-water coupling. This paper outlines the detailed methods of submolecular resolution imaging, molecular/atomic manipulation, and single-bond vibrational spectroscopy of interfacial water. These studies open up a new route for investigating the H-bonded systems at the atomic scale.

Non-thermal hydrogen atoms in the terrestrial upper thermosphere.

PubMed

Qin, Jianqi; Waldrop, Lara

2016-12-06

Model predictions of the distribution and dynamical transport of hydrogen atoms in the terrestrial atmosphere have long-standing discrepancies with ultraviolet remote sensing measurements, indicating likely deficiencies in conventional theories regarding this crucial atmospheric constituent. Here we report the existence of non-thermal hydrogen atoms that are much hotter than the ambient oxygen atoms in the upper thermosphere. Analysis of satellite measurements indicates that the upper thermospheric hydrogen temperature, more precisely the mean kinetic energy of the atomic hydrogen population, increases significantly with declining solar activity, contrary to contemporary understanding of thermospheric behaviour. The existence of hot hydrogen atoms in the upper thermosphere, which is the key to reconciling model predictions and observations, is likely a consequence of low atomic oxygen density leading to incomplete collisional thermalization of the hydrogen population following its kinetic energization through interactions with hot atomic or ionized constituents in the ionosphere, plasmasphere or magnetosphere.

Non-thermal hydrogen atoms in the terrestrial upper thermosphere

PubMed Central

Qin, Jianqi; Waldrop, Lara

2016-01-01

Model predictions of the distribution and dynamical transport of hydrogen atoms in the terrestrial atmosphere have long-standing discrepancies with ultraviolet remote sensing measurements, indicating likely deficiencies in conventional theories regarding this crucial atmospheric constituent. Here we report the existence of non-thermal hydrogen atoms that are much hotter than the ambient oxygen atoms in the upper thermosphere. Analysis of satellite measurements indicates that the upper thermospheric hydrogen temperature, more precisely the mean kinetic energy of the atomic hydrogen population, increases significantly with declining solar activity, contrary to contemporary understanding of thermospheric behaviour. The existence of hot hydrogen atoms in the upper thermosphere, which is the key to reconciling model predictions and observations, is likely a consequence of low atomic oxygen density leading to incomplete collisional thermalization of the hydrogen population following its kinetic energization through interactions with hot atomic or ionized constituents in the ionosphere, plasmasphere or magnetosphere. PMID:27922018

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.

First principles study of hydrogen behaviors in hexagonal tungsten carbide

NASA Astrophysics Data System (ADS)

Kong, Xiang-Shan; You, Yu-Wei; Liu, C. S.; Fang, Q. F.; Chen, Jun-Ling; Luo, G.-N.

2011-11-01

Understanding the behaviors of hydrogen in hexagonal tungsten carbide (WC) is of particular interest for fusion reactor design due to the presence of WC in the divertor of fusion reactors. Here, we have used first principles calculations to study the hydrogen behavior in WC. It is found that the most stable interstitial site for the hydrogen atom is the projection of the octahedral interstitial site on tungsten basal plane, followed by the site near the projection of the octahedral interstitial site on carbon basal plane. The binding energy between two interstitial hydrogen atoms is negative, suggesting that hydrogen itself is not capable of trapping another hydrogen atoms to form hydrogen molecule. The calculated results on the interaction between hydrogen and vacancy indicate that hydrogen atom is preferably trapped by vacancy defects and hydrogen molecule can not be formed in mono-vacancy. In addition, the hydrogen atom bound to carbon is only found in tungsten vacancy. We also study the migrations of hydrogen in WC and find that the interstitial hydrogen atom prefers to diffuse along the c-axis. Our studies provide some explanations for the results of the thermal desorption process of energetic hydrogen ion implanted into WC.

Tailoring Thermal Conductivity of Single-stranded Carbon-chain Polymers through Atomic Mass Modification

PubMed Central

Liao, Quanwen; Zeng, Lingping; Liu, Zhichun; Liu, Wei

2016-01-01

Tailoring the thermal conductivity of polymers is central to enlarge their applications in the thermal management of flexible integrated circuits. Progress has been made over the past decade by fabricating materials with various nanostructures, but a clear relationship between various functional groups and thermal properties of polymers remains to be established. Here, we numerically study the thermal conductivity of single-stranded carbon-chain polymers with multiple substituents of hydrogen atoms through atomic mass modification. We find that their thermal conductivity can be tuned by atomic mass modifications as revealed through molecular dynamics simulations. The simulation results suggest that heavy homogeneous substituents do not assist heat transport and trace amounts of heavy substituents can in fact hinder heat transport substantially. Our analysis indicates that carbon chain has the biggest contribution (over 80%) to the thermal conduction in single-stranded carbon-chain polymers. We further demonstrate that atomic mass modifications influence the phonon bands of bonding carbon atoms, and the discrepancies of phonon bands between carbon atoms are responsible for the remarkable drops in thermal conductivity and large thermal resistances in carbon chains. Our study provides fundamental insight into how to tailor the thermal conductivity of polymers through variable substituents. PMID:27713563

Alkali (Li, K and Na) and alkali-earth (Be, Ca and Mg) adatoms on SiC single layer

NASA Astrophysics Data System (ADS)

Baierle, Rogério J.; Rupp, Caroline J.; Anversa, Jonas

2018-03-01

First-principles calculations within the density functional theory (DFT) have been addressed to study the energetic stability, and electronic properties of alkali and alkali-earth atoms adsorbed on a silicon carbide (SiC) single layer. We observe that all atoms are most stable (higher binding energy) on the top of a Si atom, which moves out of the plane (in the opposite direction to the adsorbed atom). Alkali atoms adsorbed give raise to two spin unpaired electronic levels inside the band gap leading the SiC single layer to exhibit n-type semiconductor properties. For alkaline atoms adsorbed there is a deep occupied spin paired electronic level inside the band gap. These finding suggest that the adsorption of alkaline and alkali-earth atoms on SiC layer is a powerful feature to functionalize two dimensional SiC structures, which can be used to produce new electronic, magnetic and optical devices as well for hydrogen and oxygen evolution reaction (HER and OER, respectively). Furthermore, we observe that the adsorption of H2 is ruled by dispersive forces (van der Waals interactions) while the O2 molecule is strongly adsorbed on the functionalized system.

Laser desorption single-conformation UV and IR spectroscopy of the sulfonamide drug sulfanilamide, the sulfanilamide-water complex, and the sulfanilamide dimer.

PubMed

Uhlemann, Thomas; Seidel, Sebastian; Müller, Christian W

2017-06-07

We have studied the conformational preferences of the sulfonamide drug sulfanilamide, its dimer, and its monohydrated complex through laser desorption single-conformation UV and IR spectroscopy in a molecular beam. Based on potential energy curves for the inversion of the anilinic and the sulfonamide NH 2 groups calculated at DFT level, we suggest that the zero-point level wave function of the sulfanilamide monomer is appreciably delocalized over all four conformer wells. The sulfanilamide dimer, and the monohydrated complex each exhibit a single isomer in the molecular beam. The isomeric structures of the sulfanilamide dimer and the monohydrated sulfanilamide complex were assigned based on their conformer-specific IR spectra in the NH and OH stretch region. Quantum Theory of Atoms in Molecules (QTAIM) analysis of the calculated electron density in the water complex suggests that the water molecule is bound side-on in a hydrogen bonding pocket, donating one O-HO[double bond, length as m-dash]S hydrogen bond and accepting two hydrogen bonds, a NHO and a CHO hydrogen bond. QTAIM analysis of the dimer electron density suggests that the C i symmetry dimer structure exhibits two dominating N-HO[double bond, length as m-dash]S hydrogen bonds, and three weaker types of interactions: two CHO bonds, two CHN bonds, and a chalcogen OO interaction. Most interestingly, the molecular beam dimer structure closely resembles the R dimer unit - the dimer unit with the greatest interaction energy - of the α, γ, and δ crystal polymorphs. Interacting Quantum Atoms analysis provides evidence that the total intermolecular interaction in the dimer is dominated by the short-range exchange-correlation contribution.

Photoionization microscopy: Hydrogenic theory in semiparabolic coordinates and comparison with experimental results

NASA Astrophysics Data System (ADS)

Kalaitzis, P.; Danakas, S.; Lépine, F.; Bordas, C.; Cohen, S.

2018-05-01

Photoionization microscopy (PM) is an experimental method allowing for high-resolution measurements of the electron current probability density in the case of photoionization of an atom in an external uniform static electric field. PM is based on high-resolution velocity-map imaging and offers the unique opportunity to observe the quantum oscillatory spatial structure of the outgoing electron flux. We present the basic elements of the quantum-mechanical theoretical framework of PM for hydrogenic systems near threshold. Our development is based on the computationally more convenient semiparabolic coordinate system. Theoretical results are first subjected to a quantitative comparison with hydrogenic images corresponding to quasibound states and a qualitative comparison with nonresonant images of multielectron atoms. Subsequently, particular attention is paid on the structure of the electron's momentum distribution transversely to the static field (i.e., of the angularly integrated differential cross-section as a function of electron energy and radius of impact on the detector). Such 2D maps provide at a glance a complete picture of the peculiarities of the differential cross-section over the entire near-threshold energy range. Hydrogenic transverse momentum distributions are computed for the cases of the ground and excited initial states and single- and two-photon ionization schemes. Their characteristics of general nature are identified by comparing the hydrogenic distributions among themselves, as well as with a presently recorded experimental distribution concerning the magnesium atom. Finally, specificities attributed to different target atoms, initial states, and excitation scenarios are also discussed, along with directions of further work.

Carbon-hydrogen defects with a neighboring oxygen atom in n-type Si

NASA Astrophysics Data System (ADS)

Gwozdz, K.; Stübner, R.; Kolkovsky, Vl.; Weber, J.

2017-07-01

We report on the electrical activation of neutral carbon-oxygen complexes in Si by wet-chemical etching at room temperature. Two deep levels, E65 and E75, are observed by deep level transient spectroscopy in n-type Czochralski Si. The activation enthalpies of E65 and E75 are obtained as EC-0.11 eV (E65) and EC-0.13 eV (E75). The electric field dependence of their emission rates relates both levels to single acceptor states. From the analysis of the depth profiles, we conclude that the levels belong to two different defects, which contain only one hydrogen atom. A configuration is proposed, where the CH1BC defect, with hydrogen in the bond-centered position between neighboring C and Si atoms, is disturbed by interstitial oxygen in the second nearest neighbor position to substitutional carbon. The significant reduction of the CH1BC concentration in samples with high oxygen concentrations limits the use of this defect for the determination of low concentrations of substitutional carbon in Si samples.

STM observation of the chemical reaction of atomic hydrogen on the N-adsorbed Cu(001) surface

NASA Astrophysics Data System (ADS)

Hattori, Takuma; Yamada, Masamichi; Komori, Fumio

2017-01-01

Chemical reaction of atomic hydrogen with the N-adsorbed Cu(001) surfaces was investigated at room temperature by scanning tunnel microscopy. At the low exposure of atomic hydrogen, it reacted with the N atoms and turned to be the NH species on the surface. The reaction rate is proportional to the amount of the unreacted N atoms. By increasing the exposure of atomic hydrogen from this condition, the amount of nitrogen species on the surface decreased. This is attributed to the formation of ammonia and its desorption from the surface. The NH species on the surface turn to NH3 through the surface NH2 species by atomic hydrogen. Coexistence of the clean Cu surface enhances the rate of ammonia formation owing to atomic hydrogen migrating on the clean surface.

Sinter-Resistant Platinum Catalyst Supported by Metal-Organic Framework

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, In Soo; Li, Zhanyong; Zheng, Jian

Installed on the zirconia nodes of a metal-organic framework (MOF) NU-1000 via targeted vapor-phase synthesis. The catalytic Pt clusters, site-isolated by organic linkers, are shown to exhibit high catalytic activity for ethylene hydrogenation while exhibiting resistance to sintering up to 200 degrees C. In situ IR spectroscopy reveals the presence of both single atoms and few-atom clusters that depend upon synthesis conditions. Operando X-ray absorption spectroscopy and Xray pair distribution analyses reveal unique changes in chemical bonding environment and cluster size stability while on stream. Density functional theory calculations elucidate a favorable reaction pathway for ethylene hydrogenation with the novelmore » catalyst. These results provide evidence that atomic layer deposition (ALD) in MOFs is a versatile approach to the rational synthesis of size-selected clusters, including noble metals, on a high surface area support.« less

Atomically Thin Mesoporous Nanomesh of Graphitic C₃N₄ for High-Efficiency Photocatalytic Hydrogen Evolution.

PubMed

Han, Qing; Wang, Bing; Gao, Jian; Cheng, Zhihua; Zhao, Yang; Zhang, Zhipan; Qu, Liangti

2016-02-23

Delamination of layer materials into two-dimensional single-atom sheets has induced exceptional physical properties, including large surface area, ultrahigh intrinsic carrier mobility, pronounced changes in the energy band structure, and other properties. Here, atomically thin mesoporous nanomesh of graphitic carbon nitride (g-C3N4) is fabricated by solvothermal exfoliation of mesoporous g-C3N4 bulk made from thermal polymerization of freeze-drying assembled Dicyandiamide nanostructure precursor. With the unique structural advantages for aligned energy levels, electron transfer, light harvesting, and the richly available reaction sites, the as-prepared monolayer of mesoporous g-C3N4 nanomesh exhibits a superior photocatalytic hydrogen evolution rate of 8510 μmol h(-1) g(-1) under λ > 420 nm and an apparent quantum efficiency of 5.1% at 420 nm, the highest of all the metal-free g-C3N4 nanosheets photocatalysts.

Electron impact ionization of metastable 2P-state hydrogen atoms in the coplanar geometry

NASA Astrophysics Data System (ADS)

Dhar, S.; Nahar, N.

Triple differential cross sections (TDCS) for the ionization of metastable 2P-state hydrogen atoms by electrons are calculated for various kinematic conditions in the asymmetric coplanar geometry. In this calculation, the final state is described by a multiple-scattering theory for ionization of hydrogen atoms by electrons. Results show qualitative agreement with the available experimental data and those of other theoretical computational results for ionization of hydrogen atoms from ground state, and our first Born results. There is no available other theoretical results and experimental data for ionization of hydrogen atoms from the 2P state. The present study offers a wide scope for the experimental study for ionization of hydrogen atoms from the metastable 2P state.

Carbon-hydrogen-related complexes in Si

NASA Astrophysics Data System (ADS)

Kolkovsky, Vl.; Stübner, R.; Gwozdz, K.; Weber, J.

2018-04-01

Several deep level transient spectroscopy (DLTS) peaks (E42, E65, E75, E90, E262, and H180) are observed in n- and p-type Czochralski-grown Si samples subjected to hydrogenation by a dc H plasma treatment. The concentration of the defects is found to be proportional to the carbon and hydrogen content in our samples. The analysis of the depth profiles performed in Si samples hydrogenated by wet chemically etching shows that all these defects contain a single H atom. E65 and E75 appear only in samples with a high oxygen content which shows that oxygen is a constituent of these defects. The analysis of the enhancement of the emission rate of the defects with electric field shows that E65, E75, E90, and E262 are single acceptors whereas E42 is a double acceptor. The presence of a barrier for hole capture (about 53 meV) can explain the absence of the enhancement of the emission rate of H180, which can be attributed to a single acceptor state. From a comparison with theory, we assign E90 to CH1BC, E42 (E262) to CH1AB, and H180 to CH1Td. The similarity of the electrical properties of E65 and E75 to those of E90 suggest that E65 and E75 may originate from the CH1BC defect with an oxygen atom in its nearest neighborhood. Our results on the CH-related complexes give a conclusive explanation of some previously reported controversial experimental data.

Insight into conformational changes of a single α-helix peptide molecule through stiffness measurements

NASA Astrophysics Data System (ADS)

Kageshima, Masami; Lantz, Mark A.; Jarvis, Suzanne P.; Tokumoto, Hiroshi; Takeda, Seiji; Ptak, Arkadiusz; Nakamura, Chikashi; Miyake, Jun

2001-07-01

Stiffness variations during the conformational change of a single α-helix polylysine peptide molecule were measured in a liquid environment using atomic force microscopy (AFM) with magnetic cantilever modulation. At the initial stage of the stretching process the stiffness decreased due to the breaking of hydrogen bonds and then increased due to the stretching of the helix backbone. These changes were reversible on reversal of the stretching motion. Below p K, the stiffness did not show increase on reversal, indicating that the reforming of hydrogen bonds did not take place. Conformational changes in the molecule were examined via these changes in stiffness.

Phosphorus Nitride Imide Nanotube as Carbon-free Support to Anchor Single Ru Sites for Efficient and Robust Hydrogen Evolution.

PubMed

Yang, Jian; Chen, Bingxu; Liu, Xiaokang; Liu, Wei; Li, Zhijun; Dong, Juncai; Chen, Wenxing; Yan, Wensheng; Yao, Tao; Duan, Xuezhi; Wu, Yuen; Li, Yadong

2018-06-13

Herein, we report amorphous phosphorus nitride imide nanotubes (HPN) as a novel substrate to stabilize single metal sites materials by its abundant dangling unsaturated P vacancies. The Ru single atom can be successfully anchored by the strong coordination interaction between the d orbitals of Ru and the lone pair electrons of nitrogen at the skeleton of the HPN matrix. The atomic dispersion of Ru atoms can be distinguished by the X-ray absorption fine structure measurement and spherical aberration correction electron microscopy. Importantly, we find that the Ru SAs@PN can serve as an excellent electrocatalyst for hydrogen evolution reaction (HER) in 0.5 M H2SO4, delivering a low overpotential of 24 mV at 10 mA/cm2 and a Tafel slope of 38 mV/dec. Most importantly, it exhibits robust stability towards a constant current test at large current density of 162 mA/cm2 for more than 24 h and a cyclic voltammetry for more than 5,000 cycles. Additionally, it shows a turnover frequency (TOF) of 1.67 H2 s-1 at 25 mV and 4.29 H2 s-1 at 50 mV in 0.5 M H2SO4 solution, respectively, outperforming most of the reported hydrogen evolution catalyst. Density functional theory (DFT) calculations further demonstrate the Gibbs free-energy of adsorbed H* over the Ru SAs on PN is much closer to zero compared with the Ru/C and Ru SAs supported on carbon and C3N4, thus considerably facilitating the overall HER performance. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Depopulation of Single-Phthalocyanine Molecular Orbitals upon Pyrrolic-Hydrogen Abstraction on Graphene.

PubMed

Néel, Nicolas; Lattelais, Marie; Bocquet, Marie-Laure; Kröger, Jörg

2016-02-23

Single-molecule chemistry with a scanning tunneling microscope has preponderantly been performed on metal surfaces. The molecule-metal hybridization, however, is often detrimental to genuine molecular properties and obscures their changes upon chemical reactions. We used graphene on Ir(111) to reduce the coupling between Ir(111) and adsorbed phthalocyanine molecules. By local electron injection from the tip of a scanning tunneling microscope the two pyrrolic H atoms were removed from single phthalocyanines. The detachment of the H atom pair induced a strong modification of the molecular electronic structure, albeit with no change in the adsorption geometry. Spectra and maps of the differential conductance combined with density functional calculations unveiled the entire depopulation of the highest occupied molecular orbital upon H abstraction. Occupied π states of intact molecules are proposed to be emptied via intramolecular electron transfer to dangling σ states of H-free N atoms.

High-energy accelerator for beams of heavy ions

DOEpatents

Martin, Ronald L.; Arnold, Richard C.

1978-01-01

An apparatus for accelerating heavy ions to high energies and directing the accelerated ions at a target comprises a source of singly ionized heavy ions of an element or compound of greater than 100 atomic mass units, means for accelerating the heavy ions, a storage ring for accumulating the accelerated heavy ions and switching means for switching the heavy ions from the storage ring to strike a target substantially simultaneously from a plurality of directions. In a particular embodiment the heavy ion that is accelerated is singly ionized hydrogen iodide. After acceleration, if the beam is of molecular ions, the ions are dissociated to leave an accelerated singly ionized atomic ion in a beam. Extraction of the beam may be accomplished by stripping all the electrons from the atomic ion to switch the beam from the storage ring by bending it in magnetic field of the storage ring.

On the activation of molecular hydrogen by gold: a theoretical approximation to the nature of potential active sites.

PubMed

Corma, Avelino; Boronat, Mercedes; González, Silvia; Illas, Francesc

2007-08-28

The study of adsorption and dissociation of molecular hydrogen on single crystal Au(111) and Au(001) surfaces, monoatomic rows in an extended line defect and different Au nanoparticles by means of DF calculations allows us to firmly conclude that the necessary and sufficient condition for H2 dissociation is the existence of low coordinated Au atoms, regardless if they are in nanoparticles or at extended line defects.

Detector and energy analyzer for energetic-hydrogen in beams and plasmas

DOEpatents

Bastasz, Robert J.; Hughes, Robert C.; Wampler, William R.

1988-01-01

A detector for detecting energetic hydrogen ions and atoms ranging in energy from about 1 eV up to 1 keV in an evacuated environment includes a Schottky diode with a palladium or palladium-alloy gate metal applied to a silicondioxide layer on an n-silicon substrate. An array of the energetic-hydrogen detectors having a range of energy sensitivities form a plasma energy analyzer having a rapid response time and a sensitivity for measuring fluxes of energetic hydrogen. The detector is sensitive to hydrogen and its isotopes but is insensitive to non-hydrogenic particles. The array of energetic-hydrogen detectors can be formed on a single silicon chip, with thin-film layers of gold metal applied in various thicknesses to successive detectors in the array. The gold layers serve as particle energy-filters so that each detector is sensitive to a different range of hydrogen energies.

Detector and energy analyzer for energetic-hydrogen in beams and plasmas

DOEpatents

Bastasz, R.J.; Hughes, R.C.; Wampler, W.R.

1988-11-01

A detector for detecting energetic hydrogen ions and atoms ranging in energy from about 1 eV up to 1 keV in an evacuated environment includes a Schottky diode with a palladium or palladium-alloy gate metal applied to a silicon-dioxide layer on an n-silicon substrate. An array of the energetic-hydrogen detectors having a range of energy sensitivities form a plasma energy analyzer having a rapid response time and a sensitivity for measuring fluxes of energetic hydrogen. The detector is sensitive to hydrogen and its isotopes but is insensitive to non-hydrogenic particles. The array of energetic-hydrogen detectors can be formed on a single silicon chip, with thin-film layers of gold metal applied in various thicknesses to successive detectors in the array. The gold layers serve as particle energy-filters so that each detector is sensitive to a different range of hydrogen energies. 4 figs.

Hydrogenated pyrene: Statistical single-carbon loss below the knockout threshold

NASA Astrophysics Data System (ADS)

Wolf, Michael; Giacomozzi, Linda; Gatchell, Michael; de Ruette, Nathalie; Stockett, Mark H.; Schmidt, Henning T.; Cederquist, Henrik; Zettergren, Henning

2016-04-01

An ongoing discussion revolves around the question of what effect hydrogenation has on carbon backbone fragmentation in polycyclic aromatic hydrocarbons (PAHs). In order to shed more light on this issue, we have measured absolute single carbon loss cross sections in collisions between native or hydrogenated pyrene cations (C16H+10+m, m = 0, 6, 16) and He as functions of center-of-mass energies down to 20 eV. Classical molecular dynamics (MD) simulations give further insight into energy transfer processes and also yield m-dependent threshold energies for prompt (femtoseconds) carbon knockout. Such fast, non-statistical fragmentation processes dominate CHx-loss for native pyrene (m = 0), while much slower statistical fragmentation processes contribute significantly to single-carbon loss for the hydrogenated molecules (m = 6 and m = 16). The latter is shown by measurements of large CHx-loss cross sections far below the MD knockout thresholds for C16H+16 and C16H+26. Contribution to the "Atomic Cluster Collisions (7th International Symposium)", edited by Gerardo Delgado Barrio, Andrey Solov'Yov, Pablo Villarreal, Rita Prosmiti.

Atomic Beam Scattering Methods to Study Overlayer Structures and H-Surface Interaction Relevant to Astrophysics

NASA Astrophysics Data System (ADS)

Lin, Jingsu

In this thesis we present results of experimental methods for studying surface structures of ultra-thin films and describe a new apparatus to study the recombination of atomic hydrogen on well characterized low temperature surface using atomic and molecular beam methods. We have used atomic beam scattering (ABS) to characterize the growth of mercury and lead overlayers on Cu(001) surface. The structures of ordered phases have been identified using ABS and low-energy electron diffraction (LEED). A model to analyze diffraction data from these phases is presented. The new apparatus we are going to describe includes a high performance atomic hydrogen source using radio-frequency (RF) dissociation. The dissociation efficiency can be as high as 90% in the optimized pressure range. An atomic hydrogen beam line has been added to our ultra-high vacuum (UHV) scattering apparatus. We have also designed and constructed a low temperature sample manipulator for experiments at liquid helium temperatures. The manipulator has one degree of freedom of rotation and the capability of heating the sample to 700K and cooling down to 12K. The first sample studied was a single graphite surface. We have used a He beam to characterize the sample surface and to monitor deposition of H on the sample surface in real time. A series of "adsorption curves" have been obtained at different temperature and doses. We found that at temperatures below 16K, both H and H_2 have formed a partial layer on the surface. From adsorption curve, we deduce that the initial sticking coefficient for H is about 0.06 when surface at 16K. When the H beam is interrupted, the He specularly reflected beam recovers partially, indicating that hydrogen atoms desorb, while others remain on the surface. The residual coverage of H is estimated to be about 2% of a monolayer.

Depolarizing collisions with hydrogen: Neutral and singly ionized alkaline earths

DOE Office of Scientific and Technical Information (OSTI.GOV)

Manso Sainz, Rafael; Ramos, Andrés Asensio; Bueno, Javier Trujillo

2014-06-20

Depolarizing collisions are elastic or quasielastic collisions that equalize the populations and destroy the coherence between the magnetic sublevels of atomic levels. In astrophysical plasmas, the main depolarizing collider is neutral hydrogen. We consider depolarizing rates on the lowest levels of neutral and singly ionized alkali earths Mg I, Sr I, Ba I, Mg II, Ca II, and Ba II, due to collisions with H°. We compute ab initio potential curves of the atom-H° system and solve the quantum mechanical dynamics. From the scattering amplitudes, we calculate the depolarizing rates for Maxwellian distributions of colliders at temperatures T ≤ 10,000more » K. A comparative analysis of our results and previous calculations in the literature is completed. We discuss the effect of these rates on the formation of scattering polarization patterns of resonant lines of alkali earths in the solar atmosphere, and their effect on Hanle effect diagnostics of solar magnetic fields.« less

Prediction of a new graphenelike Si2BN solid

NASA Astrophysics Data System (ADS)

Andriotis, Antonis N.; Richter, Ernst; Menon, Madhu

2016-02-01

While the possibility to create a single-atom-thick two-dimensional layer from any material remains, only a few such structures have been obtained other than graphene and a monolayer of boron nitride. Here, based upon ab initio theoretical simulations, we propose a new stable graphenelike single-atomic-layer Si2BN structure that has all of its atoms with s p2 bonding with no out-of-plane buckling. The structure is found to be metallic with a finite density of states at the Fermi level. This structure can be rolled into nanotubes in a manner similar to graphene. Combining first- and second-row elements in the Periodic Table to form a one-atom-thick material that is also flat opens up the possibility for studying new physics beyond graphene. The presence of Si will make the surface more reactive and therefore a promising candidate for hydrogen storage.

Raman Scattered He II 4332 and Photoionization Model in the Symbiotic Star V1016 Cygni

NASA Astrophysics Data System (ADS)

Lee, H.-W.; Heo, J.-E.; Lee, B.-C.

2014-08-01

Symbiotic stars are wide binary systems of a white dwarf and a mass losing giant. They exhibit unique Raman scattered features as a result of inelastic scattering of far UV line photons by atomic hydrogen. Co-existence of a far UV He II emission region and a thick H I region in symbiotic stars is necessary for the formation of Raman-scattered features blueward of hydrogen Balmer emission lines. Being a single electron atom, He II has the same atomic structure as the hydrogen atom and hence emits far UV emission lines that are slightly blueward of hydrogen Lyman lines. These far UV He II emission lines can be Raman scattered to appear blueward of hydrogen Balmer lines. In particular, the symbiotic star V1016 Cyg is found to exhibit Raman scattered He II 4332 feature in the BOES high resolution spectrum. Our profile fitting of Raman scattered He II 4332 is consistent with the mass loss geometry proposed by Jung & Lee (2004). We use the photoionization code ‘ CLOUDY' to estimate the far UV He II emission lines and make comparisons with the observed Raman scattered He II 4332 blueward of Hγ in the high resolution echelle V1016 Cyg. The emission nebula is assumed to be of uniform density of 108 cm-3 that is illuminated by a black body characterized by its temperature and total luminosity. With our comparisons we conclude that the Raman scattered He II features are consistent with the existence of a photoionized nebula by a hot black body source with temperature 7-8× 104 K with a luminosity 1038erg s-1.

Molecular weight growth in Titan's atmosphere: Branching pathways for the reaction of 1-propynyl radical (H 3CC≡C˙) with small alkenes and alkynes

DOE PAGES

Kirk, Benjamin B.; Savee, John D.; Trevitt, Adam J.; ...

2015-07-16

The reaction of small hydrocarbon radicals (i.e. ˙CN, ˙C 2H) with trace alkenes and alkynes is believed to play an important role in molecular weight growth and ultimately the formation of Titan's characteristic haze. Current photochemical models of Titan's atmosphere largely assume hydrogen atom abstraction or unimolecular hydrogen elimination reactions dominate the mechanism, in contrast to recent experiments that reveal significant alkyl radical loss pathways during reaction of ethynyl radical (˙C 2H) with alkenes and alkynes. In this study, the trend is explored for the case of a larger ethynyl radical analogue, the 1-propynyl radical (H3CC≡C˙), a likely product frommore » the high-energy photolysis of propyne in Titan's atmosphere. Using synchrotron vacuum ultraviolet photoionization mass spectrometry, product branching ratios are measured for the reactions of 1-propynyl radical with a suite of small alkenes (ethylene and propene) and alkynes (acetylene and d 4-propyne) at 4 Torr and 300 K. Reactions of 1-propynyl radical with acetylene and ethylene form single products, identified as penta-1,3-diyne and pent-1-en-3-yne, respectively. These products form by hydrogen atom loss from the radical-adduct intermediates. The reactions of 1-propynyl radical with d4-propyne and propene form products from both hydrogen atom and methyl loss, (–H = 27%, –CH 3 = 73%) and (–H = 14%, –CH 3 = 86%), respectively. Altogether, these results indicate that reactions of ethynyl radical analogues with alkenes and alkynes form significant quantities of products by alkyl loss channels, suggesting that current photochemical models of Titan over predict both hydrogen atom production as well as the efficiency of molecular weight growth in these reactions.« less

Molecular weight growth in Titan's atmosphere: branching pathways for the reaction of 1-propynyl radical (H3CC≡C˙) with small alkenes and alkynes.

PubMed

Kirk, Benjamin B; Savee, John D; Trevitt, Adam J; Osborn, David L; Wilson, Kevin R

2015-08-28

The reaction of small hydrocarbon radicals (i.e.˙CN, ˙C2H) with trace alkenes and alkynes is believed to play an important role in molecular weight growth and ultimately the formation of Titan's characteristic haze. Current photochemical models of Titan's atmosphere largely assume hydrogen atom abstraction or unimolecular hydrogen elimination reactions dominate the mechanism, in contrast to recent experiments that reveal significant alkyl radical loss pathways during reaction of ethynyl radical (˙C2H) with alkenes and alkynes. In this study, the trend is explored for the case of a larger ethynyl radical analogue, the 1-propynyl radical (H3CC[triple bond, length as m-dash]C˙), a likely product from the high-energy photolysis of propyne in Titan's atmosphere. Using synchrotron vacuum ultraviolet photoionization mass spectrometry, product branching ratios are measured for the reactions of 1-propynyl radical with a suite of small alkenes (ethylene and propene) and alkynes (acetylene and d4-propyne) at 4 Torr and 300 K. Reactions of 1-propynyl radical with acetylene and ethylene form single products, identified as penta-1,3-diyne and pent-1-en-3-yne, respectively. These products form by hydrogen atom loss from the radical-adduct intermediates. The reactions of 1-propynyl radical with d4-propyne and propene form products from both hydrogen atom and methyl loss, (-H = 27%, -CH3 = 73%) and (-H = 14%, -CH3 = 86%), respectively. Together, these results indicate that reactions of ethynyl radical analogues with alkenes and alkynes form significant quantities of products by alkyl loss channels, suggesting that current photochemical models of Titan over predict both hydrogen atom production as well as the efficiency of molecular weight growth in these reactions.

Molecular weight growth in Titan's atmosphere: Branching pathways for the reaction of 1-propynyl radical (H 3CC≡C˙) with small alkenes and alkynes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kirk, Benjamin B.; Savee, John D.; Trevitt, Adam J.

The reaction of small hydrocarbon radicals (i.e. ˙CN, ˙C 2H) with trace alkenes and alkynes is believed to play an important role in molecular weight growth and ultimately the formation of Titan's characteristic haze. Current photochemical models of Titan's atmosphere largely assume hydrogen atom abstraction or unimolecular hydrogen elimination reactions dominate the mechanism, in contrast to recent experiments that reveal significant alkyl radical loss pathways during reaction of ethynyl radical (˙C 2H) with alkenes and alkynes. In this study, the trend is explored for the case of a larger ethynyl radical analogue, the 1-propynyl radical (H3CC≡C˙), a likely product frommore » the high-energy photolysis of propyne in Titan's atmosphere. Using synchrotron vacuum ultraviolet photoionization mass spectrometry, product branching ratios are measured for the reactions of 1-propynyl radical with a suite of small alkenes (ethylene and propene) and alkynes (acetylene and d 4-propyne) at 4 Torr and 300 K. Reactions of 1-propynyl radical with acetylene and ethylene form single products, identified as penta-1,3-diyne and pent-1-en-3-yne, respectively. These products form by hydrogen atom loss from the radical-adduct intermediates. The reactions of 1-propynyl radical with d4-propyne and propene form products from both hydrogen atom and methyl loss, (–H = 27%, –CH 3 = 73%) and (–H = 14%, –CH 3 = 86%), respectively. Altogether, these results indicate that reactions of ethynyl radical analogues with alkenes and alkynes form significant quantities of products by alkyl loss channels, suggesting that current photochemical models of Titan over predict both hydrogen atom production as well as the efficiency of molecular weight growth in these reactions.« less

Lithium doping on covalent organic framework-320 for enhancing hydrogen storage at ambient temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xia, Liangzhi, E-mail: 15004110853@163.com; Liu, Qing

2016-12-15

Density Functional Theory (DFT) combines with grand canonical Monte Carlo (GCMC) simulations are performed to explore the effect of Li doping on the hydrogen storage capability of COF-320. The results show that the interaction energy between the H{sub 2} and the Li-doped COF-320 is about three times higher than that of pristine COF-320. GCMC simulations are employed to study the hydrogen uptake of Li-doped COF-320 at ambient temperature, further confirm that the lithium doping can improve the hydrogen uptake at ambient temperature. Our results demonstrate that Li-doped COFs have good potential in the field of hydrogen storage. - Graphical abstract:more » Fig. 1. The optimized cluster model used here to represent the COF-320 and possible adsorption sites (A, B, C) for adsorption of metals in the COF-320. The dangling bonds are terminated by H atoms. C, H, and N atoms are shown as gray, white, and blue colors, respectively. Fig. 2. The adsorption isotherm of H{sub 2} in the pristine and Li-doped COF-320 at 298 K. - Highlights: • The binding sites of single and two lithium atoms in COF-320 were studied. • The interaction energy between the H{sub 2} and the Li-doped COF-320 is about three times higher than that of pristine COF-320. • H{sub 2} uptakes on the Li-doped COFs obtain significant improvement at ambient temperature. • Lithium-doping is a successful strategy for improving hydrogen uptake.« less

Hydrogen-Bonding Network and OH Stretch Vibration of Cellulose: Comparison of Computational Modeling with Polarized IR and SFG Spectra.

PubMed

Lee, Christopher M; Kubicki, James D; Fan, Bingxin; Zhong, Linghao; Jarvis, Michael C; Kim, Seong H

2015-12-10

Hydrogen bonds play critical roles in noncovalent directional interactions determining the crystal structure of cellulose. Although diffraction studies accurately determined the coordinates of carbon and oxygen atoms in crystalline cellulose, the structural information on hydrogen atoms involved in hydrogen-bonding is still elusive. This could be complemented by vibrational spectroscopy; but the assignment of the OH stretch peaks has been controversial. In this study, we performed calculations using density functional theory with dispersion corrections (DFT-D2) for the cellulose Iβ crystal lattices with the experimentally determined carbon and oxygen coordinates. DFT-D2 calculations revealed that the OH stretch vibrations of cellulose are highly coupled and delocalized through intra- and interchain hydrogen bonds involving all OH groups in the crystal. Additionally, molecular dynamics (MD) simulations of a single cellulose microfibril showed that the conformations of OH groups exposed at the microfibril surface are not well-defined. Comparison of the computation results with the experimentally determined IR dichroism of uniaxially aligned cellulose microfibrils and the peak positions of various cellulose crystals allowed unambiguous identification of OH stretch modes observed in the vibrational spectra of cellulose.

Photoelectron spectroscopy and density functional theory studies of (FeS)mH- (m = 2-4) cluster anions: effects of the single hydrogen.

PubMed

Yin, Shi; Bernstein, Elliot R

2017-12-20

Single hydrogen containing iron hydrosulfide cluster anions (FeS) m H - (m = 2-4) are studied by photoelectron spectroscopy (PES) at 3.492 eV (355 nm) and 4.661 eV (266 nm) photon energies, and by Density Functional Theory (DFT) calculations. The structural properties, relative energies of different spin states and isomers, and the first calculated vertical detachment energies (VDEs) of different spin states for these (FeS) m H - (m = 2-4) cluster anions are investigated at various reasonable theory levels. Two types of structural isomers are found for these (FeS) m H - (m = 2-4) clusters: (1) the single hydrogen atom bonds to a sulfur site (SH-type); and (2) the single hydrogen atom bonds to an iron site (FeH-type). Experimental and theoretical results suggest such available different SH- and FeH-type structural isomers should be considered when evaluating the properties and behavior of these single hydrogen containing iron sulfide clusters in real chemical and biological systems. Compared to their related, respective pure iron sulfur (FeS) m - clusters, the first VDE trend of the diverse type (FeS) m H 0,1 - (m = 1-4) clusters can be understood through (1) the different electron distribution properties of their highest singly occupied molecular orbital employing natural bond orbital analysis (NBO/HSOMO), and (2) the partial charge distribution on the NBO/HSOMO localized sites of each cluster anion. Generally, the properties of the NBO/HSOMOs play the principal role with regard to the physical and chemical properties of all the anions. The change of cluster VDE from low to high is associated with the change in nature of their NBO/HSOMO from a dipole bound and valence electron mixed character, to a valence p orbital on S, to a valence d orbital on Fe, and to a valence p orbital on Fe or an Fe-Fe delocalized valence bonding orbital. For clusters having the same properties for NBO/HSOMOs, the partial charge distributions at the NBO/HSOMO localized sites additionally affect their VDEs: a more negative or less positive localized charge distribution is correlated with a lower first VDE. The single hydrogen in these (FeS) m H - (m = 2-4) cluster anions is suggested to affect their first VDEs through the different structure types (SH- or FeH-), the nature of the NBO/HSOMOs at the local site, and the value of partial charge number at the local site of the NBO/HSOMO.

Ab initio EPR parameters for dangling-bond defect complexes in silicon: Effect of Jahn-Teller distortion

NASA Astrophysics Data System (ADS)

Pfanner, Gernot; Freysoldt, Christoph; Neugebauer, Jörg; Gerstmann, Uwe

2012-05-01

A dangling bond (db) is an important point defect in silicon. It is realized in crystalline silicon by defect complexes of the monovacancy V with impurities. In this work, we present spin-polarized density-functional theory calculations of EPR parameters (g and hyperfine tensors) within the GIPAW formalism for two kinds of db defect complexes. The first class characterizes chemically saturated db systems, where three of the four dangling bonds of the isolated vacancy are saturated by hydrogen (VH3) or hydrogen and oxygen (hydrogen-oxygen complex, VOH). The second kind of db consists of systems with a Jahn-Teller distortion, where the vacancy includes either a substitutional phosphorus atom (the E center, VP) or a single hydrogen atom (VH). For all systems we obtain excellent agreement with available experimental data, and we are therefore able to quantify the effect of the Jahn-Teller distortion on the EPR parameters. Furthermore we study the influence of strain to obtain further insights into the structural and electronic characteristics of the considered defects.

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.

Two photon absorption laser induced fluorescence measurements of neutral density in a helicon plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Galante, M. E.; Magee, R. M.; Scime, E. E.

2014-05-15

We have developed a new diagnostic based on two-photon absorption laser induced fluorescence (TALIF). We use a high intensity (5 MW/cm{sup 2}), narrow bandwidth (0.1 cm{sup −1}) laser to probe the ground state of neutral hydrogen, deuterium and krypton with spatial resolution better than 0.2 cm, a time resolution of 10 ns, and a measurement cadence of 20 Hz. Here, we describe proof-of-principle measurements in a helicon plasma source that demonstrate the TALIF diagnostic is capable of measuring neutral densities spanning four orders of magnitude; comparable to the edge neutral gradients predicted in the DIII-D tokamak pedestal. The measurements are performed in hydrogen and deuteriummore » plasmas and absolute calibration is accomplished through TALIF measurements in neutral krypton. The optical configuration employed is confocal, i.e., both light injection and collection are accomplished with a single lens through a single optical port in the vacuum vessel. The wavelength resolution of the diagnostic is sufficient to separate hydrogen and deuterium spectra and we present measurements from mixed hydrogen and deuterium plasmas that demonstrate isotopic abundance measurements are feasible. Time resolved measurements also allow us to explore the evolution of the neutral hydrogen density and temperature and effects of wall recycling. We find that the atomic neutral density grows rapidly at the initiation of the discharge, reaching the steady-state value within 1 ms. Additionally, we find that neutral hydrogen atoms are born with 0.08 eV temperatures, not 2 eV as is typically assumed.« less

Spin switch in iron phthalocyanine on Au(111) surface by hydrogen adsorption

NASA Astrophysics Data System (ADS)

Wang, Yu; Li, Xiaoguang; Zheng, Xiao; Yang, Jinlong

2017-10-01

The manipulation of spin states at the molecular scale is of fundamental importance for the development of molecular spintronic devices. One of the feasible approaches for the modification of a molecular spin state is through the adsorption of certain specific atoms or molecules including H, NO, CO, NH3, and O2. In this paper, we demonstrate that the local spin state of an individual iron phthalocyanine (FePc) molecule adsorbed on an Au(111) surface exhibits controllable switching by hydrogen adsorption, as evidenced by using first-principles calculations based on density functional theory. Our theoretical calculations indicate that different numbers of hydrogen adsorbed at the pyridinic N sites of the FePc molecule largely modify the structural and electronic properties of the FePc/Au(111) composite by forming extra N-H bonds. In particular, the adsorption of one or up to three hydrogen atoms induces a redistribution of charge (spin) density within the FePc molecule, and hence a switching to a low spin state (S = 1/2) from an intermediate spin state (S = 1) is achieved, while the adsorption of four hydrogen atoms distorts the molecular conformation by increasing Fe-N bond lengths in FePc and thus breaks the ligand field exerted on the Fe 3d orbitals via stronger hybridization with the substrate, leading to an opposite switching to a high-spin state (S = 2). These findings obtained from the theoretical simulations could be useful for experimental manipulation or design of single-molecule spintronic devices.

Two different carbon-hydrogen complexes in silicon with closely spaced energy levels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stübner, R., E-mail: ronald.stuebner@physik.tu-dresden.de, E-mail: kolkov@ifpan.edu.pl; Kolkovsky, Vl., E-mail: ronald.stuebner@physik.tu-dresden.de, E-mail: kolkov@ifpan.edu.pl; Weber, J.

An acceptor and a single donor state of carbon-hydrogen defects (CH{sub A} and CH{sub B}) are observed by Laplace deep level transient spectroscopy at 90 K. CH{sub A} appears directly after hydrogenation by wet chemical etching or hydrogen plasma treatment, whereas CH{sub B} can be observed only after a successive annealing under reverse bias at about 320 K. The activation enthalpies of these states are 0.16 eV for CH{sub A} and 0.14 eV for CH{sub B}. Our results reconcile previous controversial experimental results. We attribute CH{sub A} to the configuration where substitutional carbon binds a hydrogen atom on a bond centered position between carbonmore » and the neighboring silicon and CH{sub B} to another carbon-hydrogen defect.« less

Ultrafine hydrogen storage powders

DOEpatents

Anderson, Iver E.; Ellis, Timothy W.; Pecharsky, Vitalij K.; Ting, Jason; Terpstra, Robert; Bowman, Robert C.; Witham, Charles K.; Fultz, Brent T.; Bugga, Ratnakumar V.

2000-06-13

A method of making hydrogen storage powder resistant to fracture in service involves forming a melt having the appropriate composition for the hydrogen storage material, such, for example, LaNi.sub.5 and other AB.sub.5 type materials and AB.sub.5+x materials, where x is from about -2.5 to about +2.5, including x=0, and the melt is gas atomized under conditions of melt temperature and atomizing gas pressure to form generally spherical powder particles. The hydrogen storage powder exhibits improved chemcial homogeneity as a result of rapid solidfication from the melt and small particle size that is more resistant to microcracking during hydrogen absorption/desorption cycling. A hydrogen storage component, such as an electrode for a battery or electrochemical fuel cell, made from the gas atomized hydrogen storage material is resistant to hydrogen degradation upon hydrogen absorption/desorption that occurs for example, during charging/discharging of a battery. Such hydrogen storage components can be made by consolidating and optionally sintering the gas atomized hydrogen storage powder or alternately by shaping the gas atomized powder and a suitable binder to a desired configuration in a mold or die.

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.

Surface Modification of Plastic Substrates Using Atomic Hydrogen

NASA Astrophysics Data System (ADS)

Heya, Akira; Matsuo, Naoto

The surface properties of a plastic substrate were changed by a novel surface treatment called atomic hydrogen annealing (AHA). In this method, a plastic substrate was exposed to atomic hydrogen generated by cracking of hydrogen molecules on heated tungsten wire. Surface roughness was increased and halogen elements (F and Cl) were selectively etched by AHA. In addition, plastic surface was reduced by AHA. The surface can be modified by the recombination reaction of atomic hydrogen, the reduction reaction and selective etching of halogen atom. It is concluded that this method is a promising technique for improvement of adhesion between inorganic films and plastic substrates at low temperatures.

Information-theoretic measures of hydrogen-like ions in weakly coupled Debye plasmas

NASA Astrophysics Data System (ADS)

Zan, Li Rong; Jiao, Li Guang; Ma, Jia; Ho, Yew Kam

2017-12-01

Recent development of information theory provides researchers an alternative and useful tool to quantitatively investigate the variation of the electronic structure when atoms interact with the external environment. In this work, we make systematic studies on the information-theoretic measures for hydrogen-like ions immersed in weakly coupled plasmas modeled by Debye-Hückel potential. Shannon entropy, Fisher information, and Fisher-Shannon complexity in both position and momentum spaces are quantified in high accuracy for the hydrogen atom in a large number of stationary states. The plasma screening effect on embedded atoms can significantly affect the electronic density distributions, in both conjugate spaces, and it is quantified by the variation of information quantities. It is shown that the composite quantities (the Shannon entropy sum and the Fisher information product in combined spaces and Fisher-Shannon complexity in individual space) give a more comprehensive description of the atomic structure information than single ones. The nodes of wave functions play a significant role in the changes of composite information quantities caused by plasmas. With the continuously increasing screening strength, all composite quantities in circular states increase monotonously, while in higher-lying excited states where nodal structures exist, they first decrease to a minimum and then increase rapidly before the bound state approaches the continuum limit. The minimum represents the most reduction of uncertainty properties of the atom in plasmas. The lower bounds for the uncertainty product of the system based on composite information quantities are discussed. Our research presents a comprehensive survey in the investigation of information-theoretic measures for simple atoms embedded in Debye model plasmas.

PCTDSE: A parallel Cartesian-grid-based TDSE solver for modeling laser-atom interactions

NASA Astrophysics Data System (ADS)

Fu, Yongsheng; Zeng, Jiaolong; Yuan, Jianmin

2017-01-01

We present a parallel Cartesian-grid-based time-dependent Schrödinger equation (TDSE) solver for modeling laser-atom interactions. It can simulate the single-electron dynamics of atoms in arbitrary time-dependent vector potentials. We use a split-operator method combined with fast Fourier transforms (FFT), on a three-dimensional (3D) Cartesian grid. Parallelization is realized using a 2D decomposition strategy based on the Message Passing Interface (MPI) library, which results in a good parallel scaling on modern supercomputers. We give simple applications for the hydrogen atom using the benchmark problems coming from the references and obtain repeatable results. The extensions to other laser-atom systems are straightforward with minimal modifications of the source code.

Imaging the Hydrogen Absorption Dynamics of Individual Grains in Polycrystalline Palladium Thin Films in 3D

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yau, Allison; Harder, Ross J.; Kanan, Matthew W.

Defects such as dislocations and grain boundaries often control the properties of polycrystalline materials. In nanocrystalline materials, investigating this structure-function relationship while preserving the sample remains challenging because of the short length scales and buried interfaces involved. Here we use Bragg coherent diffractive imaging to investigate the role of structural inhomogeneity on the hydriding phase transformation dynamics of individual Pd grains in polycrystalline films in three-dimensional detail. In contrast to previous reports on single- and polycrystalline nanoparticles, we observe no evidence of a hydrogen-rich surface layer and consequently no size dependence in the hydriding phase transformation pressure over a 125-325more » nm size range. We do observe interesting grain boundary dynamics, including reversible rotations of grain lattices while the material remains in the hydrogen-poor phase. The mobility of the grain boundaries, combined with the lack of a hydrogen-rich surface layer, suggests that the grain boundaries are acting as fast diffusion sites for the hydrogen atoms. Such hydrogen-enhanced plasticity in the hydrogen poor phase provides insight into the switch from the size-dependent behavior of single-crystal nanoparticles to the lower transformation pressures of polycrystalline materials and may play a role in hydrogen embrittlement.« less

Nanomedicine photoluminescence crystal-inspired brain sensing approach

NASA Astrophysics Data System (ADS)

Fang, Yan; Wang, Fangzhen; Wu, Rong

2018-02-01

Precision sensing needs to overcome a gap of a single atomic step height standard. In response to the cutting-edge challenge, a heterosingle molecular nanomedicine crystal was developed wherein a nanomedicine crystal height less than 1 nm was designed and selfassembled on a substrate of either a highly ordered and freshly separated graphite or a N-doped silicon with hydrogen bonding by a home-made hybrid system of interacting single bioelectron donor-acceptor and a single biophoton donor-acceptor according to orthogonal mathematical optimization scheme, and an atomic spatial resolution conducting atomic force microscopy (C-AFM) with MHz signal processing by a special transformation of an atomic force microscopy (AFM) and a scanning tunneling microscopy (STM) were employed, wherein a z axis direction UV-VIS laser interferometer and a feedback circuit were used to achieve the minimized uncertainty of a micro-regional structure height and its corresponding local differential conductance quantization (spin state) process was repeatedly measured with a highly time resolution, as well as a pulsed UV-VIS laser micro-photoluminescence (PL) spectrum with a single photon resolution was set up by traceable quantum sensing and metrology relied up a quantum electrical triangle principle. The coupling of a single bioelectron conducting, a single biophoton photoluminescence, a frequency domain temporal spin phase in nanomedicine crystal-inspired sensing methods and sensor technologies were revealed by a combination of C-AFM and PL measurement data-based mathematic analyses1-3, as depicted in Figure 1 and repeated in nanomedicine crystals with a single atomic height. It is concluded that height-current-phase uncertainty correlation pave a way to develop a brain imaging and a single atomic height standard, quantum sensing, national security, worldwide impact1-3 technology and beyond.

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.

Unraveling the formation of HCPH(X2A') molecules in extraterrestrial environments: crossed molecular beam study of the reaction of carbon atoms, C(3Pj), with phosphine, PH3(X1A1).

PubMed

Guo, Y; Gu, X; Zhang, F; Sun, B J; Tsai, M F; Chang, A H H; Kaiser, R I

2007-05-03

The reaction between ground state carbon atoms, C(3P(j)), and phosphine, PH3(X(1)A1), was investigated at two collision energies of 21.1 and 42.5 kJ mol(-1) using the crossed molecular beam technique. The chemical dynamics extracted from the time-of-flight spectra and laboratory angular distributions combined with ab initio calculations propose that the reaction proceeds on the triplet surface via an addition of atomic carbon to the phosphorus atom. This leads to a triplet CPH3 complex. A successive hydrogen shift forms an HCPH2 intermediate. The latter was found to decompose through atomic hydrogen emission leading to the cis/trans-HCPH(X(2)A') reaction products. The identification of cis/trans-HCPH(X(2)A') molecules under single collision conditions presents a potential pathway to form the very first carbon-phosphorus bond in extraterrestrial environments like molecular clouds and circumstellar envelopes, and even in the postplume chemistry of the collision of comet Shoemaker-Levy 9 with Jupiter.

A quantum chemistry study on surface reactivity of pristine and carbon-substituted AlN nanotubes

NASA Astrophysics Data System (ADS)

Mahdaviani, Amir; Esrafili, Mehdi D.; Esrafili, Ali; Behzadi, Hadi

2013-09-01

A density functional theory investigation was performed to predict the surface reactivity of pristine and carbon-substituted (6,0) single-walled aluminum nitride nanotubes (AlNNTs). The properties determined include the electrostatic potentials VS(r) and average local ionization energies ĪS(r) on the surfaces of the investigated tubes. According to computed VS(r) results, the Al/N atoms in edge or cap regions show a different reactivity pattern than those at the middle portion of the tubes. Due to the carbon-substitution at the either Al or N sites of the tubes, the negative regions associated with nitrogen atoms are stronger than before. The prediction of surface reactivity and regioselectivity using average local ionization energies has been verified by atomic hydrogen chemisorption energies calculated for AlNNTs at the B3LYP/6-31 G* level. There is an acceptable correlation between the minima of ĪS(r) and the atomic hydrogen chemisorption energies, demonstrating that ĪS(r) provides an effective means for rapidly and economically assessing the relative reactivities of finite sized AlNNTs.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang, Zhuoling; Wang, Hao; Sanvito, Stefano

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 ofmore » 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.« less

Trapping hydrogen atoms from a neon-gas matrix: a theoretical simulation.

PubMed

Bovino, S; Zhang, P; Kharchenko, V; Dalgarno, A

2009-08-07

Hydrogen is of critical importance in atomic and molecular physics and the development of a simple and efficient technique for trapping cold and ultracold hydrogen atoms would be a significant advance. In this study we simulate a recently proposed trap-loading mechanism for trapping hydrogen atoms released from a neon matrix. Accurate ab initio quantum calculations are reported of the neon-hydrogen interaction potential and the energy- and angular-dependent elastic scattering cross sections that control the energy transfer of initially cold atoms are obtained. They are then used to construct the Boltzmann kinetic equation, describing the energy relaxation process. Numerical solutions of the Boltzmann equation predict the time evolution of the hydrogen energy distribution function. Based on the simulations we discuss the prospects of the technique.

Theoretical analysis of hydrogen spillover mechanism on carbon nanotubes

PubMed Central

Juarez-Mosqueda, Rosalba; Mavrandonakis, Andreas; Kuc, Agnieszka B.; Pettersson, Lars G. M.; Heine, Thomas

2015-01-01

The spillover mechanism of molecular hydrogen on carbon nanotubes in the presence of catalytically active platinum clusters was critically and systematically investigated by using density-functional theory. Our simulation model includes a Pt4 cluster for the catalyst nanoparticle and curved and planar circumcoronene for two exemplary single-walled carbon nanotubes (CNT), the (10,10) CNT and one of large diameter, respectively. Our results show that the H2 molecule dissociates spontaneously on the Pt4 cluster. However, the dissociated H atoms have to overcome a barrier of more than 2 eV to migrate from the catalyst to the CNT, even if the Pt4 cluster is at full saturation with six adsorbed and dissociated hydrogen molecules. Previous investigations have shown that the mobility of hydrogen atoms on the CNT surface is hindered by a barrier. We find that instead the Pt4 catalyst may move along the outer surface of the CNT with activation energy of only 0.16 eV, and that this effect offers the possibility of full hydrogenation of the CNT. Thus, although we have not found a low-energy pathway to spillover onto the CNT, we suggest, based on our calculations and calculated data reported in the literature, that in the hydrogen-spillover process the observed saturation of the CNT at hydrogen background pressure occurs through mobile Pt nanoclusters, which move on the substrate more easily than the substrate-chemisorbed hydrogens, and deposit or reattach hydrogens in the process. Initial hydrogenation of the carbon substrate, however, is thermodynamically unfavoured, suggesting that defects should play a significant role. PMID:25699250

Applications of Quantum Theory of Atomic and Molecular Scattering to Problems in Hypersonic Flow

NASA Technical Reports Server (NTRS)

Malik, F. Bary

1995-01-01

The general status of a grant to investigate the applications of quantum theory in atomic and molecular scattering problems in hypersonic flow is summarized. Abstracts of five articles and eleven full-length articles published or submitted for publication are included as attachments. The following topics are addressed in these articles: fragmentation of heavy ions (HZE particles); parameterization of absorption cross sections; light ion transport; emission of light fragments as an indicator of equilibrated populations; quantum mechanical, optical model methods for calculating cross sections for particle fragmentation by hydrogen; evaluation of NUCFRG2, the semi-empirical nuclear fragmentation database; investigation of the single- and double-ionization of He by proton and anti-proton collisions; Bose-Einstein condensation of nuclei; and a liquid drop model in HZE particle fragmentation by hydrogen.

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.

Electron capture in collisions of N^+ with H and H^+ with N

NASA Astrophysics Data System (ADS)

Lin, C. Y.; Stancil, P. C.; Gu, J. P.; Buenker, R. J.; Kimura, M.

2004-05-01

Charge transfer processes due to collisions of N^+ with atomic hydrogen and H^+ with atomic nitrogen are investigated using the quantum-mechanical molecular-orbital close-coupling (MOCC) method. The MOCC calculations utilize ab initio adiabatic potential curves and nonadiabatic radial and rotational coupling matrix elements obtained with the multireference single- and double-excitation configuration interaction approach. Total and state-selective cross sections for the energy range 0.1-500 eV/u will be presented and compared with existing experimental and theoretical data.

First Evidence of Vibrationally Driven Bimolecular Reactions in Solution: Reactions of Br Atoms with Dimethylsulfoxide and Methanol.

PubMed

Shin, Jae Yoon; Shaloski, Michael A; Crim, F Fleming; Case, Amanda S

2017-03-23

We present evidence for vibrational enhancement of the rate of bimolecular reactions of Br atoms with dimethylsulfoxide (DMSO) and methanol (CH 3 OH) in the condensed phase. The abstraction of a hydrogen atom from either of these solvents by a Br atom is highly endoergic: 3269 cm -1 for DMSO and 1416 or 4414 cm -1 for CH 3 OH, depending on the hydrogen atom abstracted. Thus, there is no thermal abstraction reaction at room temperature. Broadband electronic transient absorption shows that following photolysis of bromine precursors Br atoms form van der Waals complexes with the solvent molecules in about 5 ps and this Br • -solvent complex undergoes recombination. To explore the influence of vibrational energy on the abstraction reactions, we introduce a near-infrared (NIR) pump pulse following the photolysis pulse to excite the first overtone of the C-H (or O-H) stretch of the solvent molecules. Using single-wavelength detection, we observe a loss of the Br • -solvent complex that requires the presence of both photolysis and NIR pump pulses. Moreover, the magnitude of this loss depends on the NIR wavelength. Although this loss of reactive Br supports the notion of vibrationally driven chemistry, it is not concrete evidence of the hydrogen-abstraction reaction. To verify that the loss of reactive Br results from the vibrationally driven bimolecular reaction, we examine the pH dependence of the solution (as a measure of the formation of the HBr product) following long-time irradiation of the sample with both photolysis and NIR pump beams. We observe that when the NIR beam is on-resonance, the hydronium ion concentration increases fourfold as compared to that when it is off-resonance, suggesting the formation of HBr via a vibrationally driven hydrogen-abstraction reaction in solution.

Sequential desorption energy of hydrogen from nickel clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deepika,; Kumar, Rakesh, E-mail: rakesh@iitrpr.ac.in; R, Kamal Raj.

2015-06-24

We report reversible Hydrogen adsorption on Nickel clusters, which act as a catalyst for solid state storage of Hydrogen on a substrate. First-principles technique is employed to investigate the maximum number of chemically adsorbed Hydrogen molecules on Nickel cluster. We observe a maximum of four Hydrogen molecules adsorbed per Nickel atom, but the average Hydrogen molecules adsorbed per Nickel atom decrease with cluster size. The dissociative chemisorption energy per Hydrogen molecule and sequential desorption energy per Hydrogen atom on Nickel cluster is found to decrease with number of adsorbed Hydrogen molecules, which on optimization may help in economical storage andmore » regeneration of Hydrogen as a clean energy carrier.« less

Ionisation of atomic hydrogen by positron impact

NASA Technical Reports Server (NTRS)

Spicher, Gottfried; Olsson, Bjorn; Raith, Wilhelm; Sinapius, Guenther; Sperber, Wolfgang

1990-01-01

With the crossed beam apparatus the relative impact-ionization cross section of atomic hydrogen by positron impact was measured. A layout of the scattering region is given. The first measurements on the ionization of atomic hydrogen by positron impact are also given.

Two-photon laser-induced fluorescence of atomic hydrogen in a diamond-depositing dc arcjet.

PubMed

Juchmann, Wolfgang; Luque, Jorge; Jeffries, Jay B

2005-11-01

Atomic hydrogen in the plume of a dc-arcjet plasma is monitored by use of two-photon excited laser-induced fluorescence (LIF) during the deposition of diamond film. The effluent of a dc-arc discharge in hydrogen and argon forms a luminous plume as it flows through a converging-diverging nozzle into a reactor. When a trace of methane (< 2%) is added to the flow in the diverging part of the nozzle, diamond thin film grows on a water-cooled molybdenum substrate from the reactive mixture. LIF of atomic hydrogen in the arcjet plume is excited to the 3S and 3D levels with two photons near 205 nm, and the subsequent fluorescence is observed at Balmer-alpha near 656 nm. Spatially resolved LIF measurements of atomic hydrogen are made as a function of the ratio of hydrogen to argon feedstock gas, methane addition, and reactor pressure. At lower reactor pressures, time-resolved LIF measurements are used to verify our collisional quenching correction algorithm. The quenching rate coefficients for collisions with the major species in the arcjet (Ar, H, and H2) do not change with gas temperature variations in the plume (T < 2300 K). Corrections of the LIF intensity measurements for the spatial variation of collisional quenching are important to determine relative distributions of the atomic hydrogen concentration. The relative atomic hydrogen concentrations measured here are calibrated with an earlier calorimetric determination of the feedstock hydrogen dissociation to provide quantitative hydrogen-atom concentration distributions.

LIFS atomic hydrogen density measurements at the URAGAN-3M facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Volkov, E.D.; Zhmurin, P.N.; Letuchii, A.N.

1994-12-31

Molecular and atomic hydrogen behavior within a plasma column of the URAGAN-3M facility was numerically simulated for a low density regime ({bar n}{sub e} {approx_equal} 2 x 10{sup 12} cm{sup {minus}3}). Local density of hydrogen atoms in the axial region was measured by Laser-Induced Fluorescence Spectroscopy technique. A good agreement of the measurements and simulations was observed. In the regime under investigation the results of hydrogen density spectroscopic measurements were found to be greatly affected by dissociative population of hydrogen atom excited states. 2 refs., 3 figs.

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.

History of Hubble Space Telescope (HST)

NASA Image and Video Library

1995-01-01

These eerie, dark, pillar-like structures are actually columns of cool interstellar hydrogen gas and dust that are also incubators for new stars. The pillars protrude from the interior wall of a dark molecular cloud like stalagmites from the floor of a cavern. They are part of the Eagle Nebula (also called M16), a nearby star-forming region 7,000 light-years away, in the constellation Serpens. The ultraviolet light from hot, massive, newborn stars is responsible for illuminating the convoluted surfaces of the columns and the ghostly streamers of gas boiling away from their surfaces, producing the dramatic visual effects that highlight the three-dimensional nature of the clouds. This image was taken on April 1, 1995 with the Hubble Space Telescope Wide Field Planetary Camera 2. The color image is constructed from three separate images taken in the light of emission from different types of atoms. Red shows emissions from singly-ionized sulfur atoms, green shows emissions from hydrogen, and blue shows light emitted by doubly-ionized oxygen atoms.

New Propellants and Cryofuels

NASA Technical Reports Server (NTRS)

Palasezski, Bryan; Sullivan, Neil S.; Hamida, Jaha; Kokshenev, V.

2006-01-01

The proposed research will investigate the stability and cryogenic properties of solid propellants that are critical to NASA s goal of realizing practical propellant designs for future spacecraft. We will determine the stability and thermal properties of a solid hydrogen-liquid helium stabilizer in a laboratory environment in order to design a practical propellant. In particular, we will explore methods of embedding atomic species and metallic nano-particulates in hydrogen matrices suspended in liquid helium. We will also measure the characteristic lifetimes and diffusion of atomic species in these candidate cryofuels. The most promising large-scale advance in rocket propulsion is the use of atomic propellants; most notably atomic hydrogen stabilized in cryogenic environments, and metallized-gelled liquid hydrogen (MGH) or densified gelled hydrogen (DGH). The new propellants offer very significant improvements over classic liquid oxygen/hydrogen fuels because of two factors: (1) the high energy-release, and (ii) the density increase per unit energy release. These two changes can lead to significant reduced mission costs and increased payload to orbit weight ratios. An achievable 5 to 10 percent improvement in specific impulse for the atomic propellants or MGH fuels can result in a doubling or tripling of system payloads. The high-energy atomic propellants must be stored in a stabilizing medium such as solid hydrogen to inhibit or delay their recombination into molecules. The goal of the proposed research is to determine the stability and thermal properties of the solid hydrogen-liquid helium stabilizer. Magnetic resonance techniques will be used to measure the thermal lifetimes and the diffusive motions of atomic species stored in solid hydrogen grains. The properties of metallic nano-particulates embedded in hydrogen matrices will also be studied and analyzed. Dynamic polarization techniques will be developed to enhance signal/noise ratios in order to be able to detect low concentrations of the introduced species. The required lifetimes for atomic hydrogen and other species can only be realized at low temperatures to avoid recombination of atoms before use as a fuel.

Atomic hydrogen storage method and apparatus

NASA Technical Reports Server (NTRS)

Woollam, J. A. (Inventor)

1978-01-01

Atomic hydrogen, for use as a fuel or as an explosive, is stored in the presence of a strong magnetic field in exfoliated layered compounds such as molybdenum disulfide or an elemental layer material such as graphite. The compound is maintained at liquid helium temperatures and the atomic hydrogen is collected on the surfaces of the layered compound which are exposed during delamination (exfoliation). The strong magnetic field and the low temperature combine to prevent the atoms of hydrogen from recombining to form molecules.

Atomic hydrogen storage method and apparatus

NASA Technical Reports Server (NTRS)

Woollam, J. A. (Inventor)

1980-01-01

Atomic hydrogen, for use as a fuel or as an explosive, is stored in the presence of a strong magnetic field in exfoliated layered compounds such as molybdenum disulfide or an elemental layer material such as graphite. The compounds maintained at liquid helium temperatures and the atomic hydrogen is collected on the surfaces of the layered compound which are exposed during delamination (exfoliation). The strong magnetic field and the low temperature combine to prevent the atoms of hydrogen from recombining to form molecules.

Atomic hydrogen storage. [cryotrapping and magnetic field strength

NASA Technical Reports Server (NTRS)

Woollam, J. A. (Inventor)

1980-01-01

Atomic hydrogen, for use as a fuel or as an explosive, is stored in the presence of a strong magnetic field in exfoliated layered compounds such as molybdenum disulfide or an elemental layer material such as graphite. The compound is maintained at liquid temperatures and the atomic hydrogen is collected on the surfaces of the layered compound which are exposed during delamination (exfoliation). The strong magnetic field and the low temperature combine to prevent the atoms of hydrogen from recombining to form molecules.

Hydrogen-induced structural transition in single layer ReS2

NASA Astrophysics Data System (ADS)

Yagmurcukardes, M.; Bacaksiz, C.; Senger, R. T.; Sahin, H.

2017-09-01

By performing density functional theory-based calculations, we investigate how structural, electronic and mechanical properties of single layer ReS2 can be tuned upon hydrogenation of its surfaces. It is found that a stable, fully hydrogenated structure can be obtained by formation of strong S-H bonds. The optimized atomic structure of ReS2H2 is considerably different than that of the monolayer ReS2 which has a distorted-1T phase. By performing phonon dispersion calculations, we also predict that the Re2-dimerized 1T structure (called 1T {{}\\text{R{{\\text{e}}2}}} ) of the ReS2H2 is dynamically stable. Unlike the bare ReS2 the 1T {{}\\text{R{{\\text{e}}2}}} -ReS2H2 structure which is formed by breaking the Re4 clusters into separated Re2 dimers, is an indirect-gap semiconductor. Furthermore, mechanical properties of the 1T {{}\\text{R{{\\text{e}}2}}} phase in terms of elastic constants, in-plane stiffness (C) and Poisson ratio (ν) are investigated. It is found that full hydrogenation not only enhances the flexibility of the single layer ReS2 crystal but also increases anisotropy of the elastic constants.

Generation of subnanometric platinum with high stability during transformation of a 2D zeolite into 3D.

PubMed

Liu, Lichen; Díaz, Urbano; Arenal, Raul; Agostini, Giovanni; Concepción, Patricia; Corma, Avelino

2017-01-01

Single metal atoms and metal clusters have attracted much attention thanks to their advantageous capabilities as heterogeneous catalysts. However, the generation of stable single atoms and clusters on a solid support is still challenging. Herein, we report a new strategy for the generation of single Pt atoms and Pt clusters with exceptionally high thermal stability, formed within purely siliceous MCM-22 during the growth of a two-dimensional zeolite into three dimensions. These subnanometric Pt species are stabilized by MCM-22, even after treatment in air up to 540 °C. Furthermore, these stable Pt species confined within internal framework cavities show size-selective catalysis for the hydrogenation of alkenes. High-temperature oxidation-reduction treatments result in the growth of encapsulated Pt species to small nanoparticles in the approximate size range of 1 to 2 nm. The stability and catalytic activity of encapsulated Pt species is also reflected in the dehydrogenation of propane to propylene.

Hydrogen bond and halogen bond inside the carbon nanotube

NASA Astrophysics Data System (ADS)

Wang, Weizhou; Wang, Donglai; Zhang, Yu; Ji, Baoming; Tian, Anmin

2011-02-01

The hydrogen bond and halogen bond inside the open-ended single-walled carbon nanotubes have been investigated theoretically employing the newly developed density functional M06 with the suitable basis set and the natural bond orbital analysis. Comparing with the hydrogen or halogen bond in the gas phase, we find that the strength of the hydrogen or halogen bond inside the carbon nanotube will become weaker if there is a larger intramolecular electron-density transfer from the electron-rich region of the hydrogen or halogen atom donor to the antibonding orbital of the X-H or X-Hal bond involved in the formation of the hydrogen or halogen bond and will become stronger if there is a larger intermolecular electron-density transfer from the electron-rich region of the hydrogen or halogen atom acceptor to the antibonding orbital of the X-H or X-Hal bond. According to the analysis of the molecular electrostatic potential of the carbon nanotube, the driving force for the electron-density transfer is found to be the negative electric field formed in the carbon nanotube inner phase. Our results also show that the X-H bond involved in the formation of the hydrogen bond and the X-Hal bond involved in the formation of the halogen bond are all elongated when encapsulating the hydrogen bond and halogen bond within the carbon nanotube, so the carbon nanotube confinement may change the blue-shifting hydrogen bond and the blue-shifting halogen bond into the red-shifting hydrogen bond and the red-shifting halogen bond. The possibility to replace the all electron nanotube-confined calculation by the simple polarizable continuum model is also evaluated.

Launch Vehicle Performance for Bipropellant Propulsion Using Atomic Propellants With Oxygen

NASA Technical Reports Server (NTRS)

Palaszewski, Bryan

2000-01-01

Atomic propellants for bipropellant launch vehicles using atomic boron, carbon, and hydrogen were analyzed. The gross liftoff weights (GLOW) and dry masses of the vehicles were estimated, and the 'best' design points for atomic propellants were identified. Engine performance was estimated for a wide range of oxidizer to fuel (O/F) ratios, atom loadings in the solid hydrogen particles, and amounts of helium carrier fluid. Rocket vehicle GLOW was minimized by operating at an O/F ratio of 1.0 to 3.0 for the atomic boron and carbon cases. For the atomic hydrogen cases, a minimum GLOW occurred when using the fuel as a monopropellant (O/F = 0.0). The atomic vehicle dry masses are also presented, and these data exhibit minimum values at the same or similar O/F ratios as those for the vehicle GLOW. A technology assessment of atomic propellants has shown that atomic boron and carbon rocket analyses are considered to be much more near term options than the atomic hydrogen rockets. The technology for storing atomic boron and carbon has shown significant progress, while atomic hydrogen is not able to be stored at the high densities needed for effective propulsion. The GLOW and dry mass data can be used to estimate the cost of future vehicles and their atomic propellant production facilities. The lower the propellant's mass, the lower the overall investment for the specially manufactured atomic propellants.

Characteristics of a Two-Dimensional Hydrogenlike Atom

NASA Astrophysics Data System (ADS)

Skobelev, V. V.

2018-06-01

Using the customary and well-known representation of the radiation probability of a hydrogen-like atom in the three-dimensional case, a general expression for the probability of single-photon emission of a twodimensional atom has been obtained along with an expression for the particular case of the transition from the first excited state to the ground state, in the latter case in comparison with corresponding expressions for the three-dimensional atom and the one-dimensional atom. Arguments are presented in support of the claim that this method of calculation gives a value of the probability that is identical to the value given by exact methods of QED extended to the subspace {0, 1, 2}. Relativistic corrections (Zα)4 to the usual Schrödinger value of the energy ( (Zα)2) are also discussed.

Emirates Mars Ultraviolet Spectrometer (EMUS) Overview from the Emirates Mars Mission

NASA Astrophysics Data System (ADS)

Lootah, F. H.; Almatroushi, H. R.; AlMheiri, S.; Holsclaw, G.; Deighan, J.; Chaffin, M.; Reed, H.; Lillis, R. J.; Fillingim, M. O.; England, S.

2017-12-01

The Emirates Mars Ultraviolet Spectrometer (EMUS) instrument is one of three science instruments on board the "Hope Probe" of the Emirates Mars Mission (EMM). EMM is a United Arab Emirates' (UAE) mission to Mars, launching in 2020, to explore the global dynamics of the Martian atmosphere, while sampling on both diurnal and seasonal timescales. The EMUS instrument is a far-ultraviolet imaging spectrograph that measures emissions in the spectral range 100-170 nm. Using a combination of its one-dimensional imaging and spacecraft motion, it will build up two-dimensional far-ultraviolet images of the Martian disk and near-space environment at several important wavelengths: the Lyman beta atomic hydrogen emission (102.6 nm), the Lyman alpha atomic hydrogen emission (121.6 nm), two atomic oxygen emissions (130.4 nm and 135.6 nm), and the carbon monoxide fourth positive group band emission (140 nm-170 nm). Radiances at these wavelengths will be used to derive the column abundance of atomic oxygen, and carbon monoxide in the Martian thermosphere, and the density of atomic oxygen and atomic hydrogen in the Martian exosphere both with spatial and sub-seasonal variability. The EMUS instrument consists of a single telescope mirror feeding a Rowland circle imaging spectrograph with selectable spectral resolution (1.3 nm, 1.8 nm, or 5 nm), and a photon-counting and locating detector (provided by the Space Sciences Laboratory at the University of California, Berkeley). The EMUS spatial resolution of less than 300 km on the disk is sufficient to characterize spatial variability in the Martian thermosphere (100-200 km altitude) and exosphere (>200 km altitude). The instrument is jointly developed by the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado Boulder and Mohammed Bin Rashid Space Centre (MBRSC) in Dubai, UAE.

Emirates Mars Ultraviolet Spectrometer (EMUS) Overview from the Emirates Mars Mission

NASA Astrophysics Data System (ADS)

Almatroushi, Hessa; Lootah, Fatma; Holsclaw, Greg; Deighan, Justin; Chaffin, Michael; Lillis, Robert; Fillingim, Matthew; England, Scott; AlMheiri, Suhail; Reed, Heather

2017-04-01

The Emirates Mars Ultraviolet Spectrometer (EMUS) instrument is one of three science instruments to be carried on board the Emirate Mars Mission (EMM), the "Hope Probe". EMM is a United Arab Emirates' (UAE) mission to Mars launching in 2020 to explore the dynamics in the Martian atmosphere globally, while sampling on both diurnal and seasonal timescales. The EMUS instrument is a far-ultraviolet imaging spectrograph that measures emissions in the spectral range 100-170 nm. Using spacecraft motion, it will build up two-dimensional far-ultraviolet images of the Martian disk and near-space environment at several important wavelengths: Lyman beta atomic hydrogen emission (102.6 nm), Lyman alpha atomic hydrogen emission (121.6 nm), atomic oxygen emission (130.4 nm and 135.6 nm), and carbon monoxide fourth positive group band emission (140 nm-170 nm). Radiances at these wavelengths will be used to derive the column abundance of atomic oxygen, and carbon monoxide in the Martian thermosphere, and the density of atomic oxygen and atomic hydrogen in the Martian exosphere both with spatial and sub-seasonal variability. EMUS consists of a single telescope mirror feeding a Rowland circle imaging spectrograph capable of selectable spectral resolution (1.3 nm, 1.8 nm, or 5 nm) with a photon-counting and locating detector (provided by the Space Sciences Laboratory at the University of California, Berkeley). The EMUS spatial resolution of less than 300km on the disk is sufficient to characterize spatial variability in the Martian thermosphere (100-200 km altitude) and exosphere (>200 km altitude). The instrument is jointly developed by the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado Boulder and Mohammed Bin Rashid Space Centre (MBRSC) in Dubai, UAE

Method for the hydrogenation of poly-si

DOEpatents

Wang, Qi

2013-11-12

A method for hydrogenating poly-si. Poly-si is placed into the interior of a chamber. A filament is placed into the interior of a chamber. The base pressure of the interior of the chamber is evacuated, preferably to 10.sup.-6 Torr or less. The poly-si is heated for a predetermined poly-si heating time. The filament is heated by providing an electrical power to the filament. Hydrogen is supplied into the pressurized interior of the chamber comprising the heated poly-si and the heated filament. Atomic hydrogen is produced by the filament at a rate whereby the atomic hydrogen surface density at the poly-si is less than the poly-si surface density. Preferably, the poly-si is covered from the atomic hydrogen produced by the heated filament for a first predetermined covering time. Preferably, the poly-si is then uncovered from the atomic hydrogen produced by the heated filament for a first hydrogenation time.

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.

Hot-atom versus Eley-Rideal dynamics in hydrogen recombination on Ni(100). I. The single-adsorbate case.

PubMed

Martinazzo, R; Assoni, S; Marinoni, G; Tantardini, G F

2004-05-08

We compare the efficiency of the Eley-Rideal (ER) reaction with the formation of hot-atom (HA) species in the simplest case, i.e., the scattering of a projectile off a single adsorbate, considering the Hydrogen and Hydrogen-on-Ni(100) system. We use classical mechanics and the accurate embedded diatomics-in-molecules potential to study the collision system over a wide range of collision energies (0.10-1.50 eV), both with a rigid and a nonrigid Ni substrate and for impact on the occupied and neighboring empty cells. In the rigid model metastable and truly bound hot-atoms occur and we find that the cross section for the formation of bound hot-atoms is considerably higher than that for the ER reaction over the whole range of collision energies examined. Metastable hot-atoms form because of the inefficient energy transfer to the adsorbate and have lifetimes of the order 0.1-0.7 ps, depending on the collision energy. When considering the effects of lattice vibrations we find, on average, a consistent energy transfer to the substrate, say 0.1-0.2 eV, which forced us to devise a two-step dynamical model to get rid of the problems associated with the use of periodic boundary conditions. Results for long-lived HA formation due to scattering on the occupied cell at a surface temperature of 120 K agree well with those of the rigid model, suggesting that in the above process the substrate plays only a secondary role and further calculations at surface temperatures of 50 and 300 K are in line with these findings. However, considerably high cross sections for formation of long-lived hot-atoms result also from scattering off the neighboring cells where the energy transfer to the lattice cannot be neglected. Metastable hot-atoms are reduced in number and have usually lifetimes shorter than those of the rigid-model, say less than 0.3 ps. In addition, ER cross sections are only slightly affected by the lattice motion and show a little temperature dependence. Finally, we find also that absorption and reflection strongly depend on the correct consideration of lattice vibrations and the occurrence of trapping. (c) 2004 American Institute of Physics.

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.

First-principles study of the solid solution of hydrogen in lanthanum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schoellhammer, Gunther; Herzig, Peter; Wolf, Walter

2011-09-01

Results from first-principles investigations of the energetical, structural, electronic, and vibrational properties of model structures probing the metal-rich region of the lanthanum-hydrogen system, i.e., the region of the solid solution of hydrogen in lanthanum, are presented. We have studied the site preference and the ordering tendency of hydrogen atoms interstitially bonded in close-packed lanthanum. Spatially separated hydrogen atoms have turned out to exhibit an energetical preference for the occupation of octahedral interstitial sites at low temperature. Indications for a reversal of the site preference in favor of the occupation of tetrahedral interstitial sites at elevated temperature have been found. Linearmore » arrangements consisting of pairs of octahedrally and/or tetrahedrally coordinated hydrogen atoms collinearly bonded to a central lanthanum atom have turned out to be energetically favorable structure elements. Further stabilization is achieved if such hydrogen pairs are in turn linked together so that extended chains of La-H bonds are formed. Pair formation and chain linking counteract the energetical preference for octahedral coordination observed for separated hydrogen atoms.« less

Synthesis and Stability of Lanthanum Superhydrides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Geballe, Zachary M.; Liu, Hanyu; Mishra, Ajay K.

Recent theoretical calculations predict that megabar pressure stabilizes very hydrogen-rich simple compounds having new clathrate-like structures and remarkable electronic properties including room-temperature superconductivity. X-ray diffraction and optical studies demonstrate that superhydrides of lanthanum can be synthesized with La atoms in an fcc lattice at 170 GPa upon heating to about 1000 K. The results match the predicted cubic metallic phase of LaH10 having cages of thirty-two hydrogen atoms surrounding each La atom. Upon decompression, the fcc-based structure undergoes a rhombohedral distortion of the La sublattice. The superhydride phases consist of an atomic hydrogen sublattice with H-H distances of about 1.1more » Å, which are close to predictions for solid atomic metallic hydrogen at these pressures. With stability below 200 GPa, the superhydride is thus the closest analogue to solid atomic metallic hydrogen yet to be synthesized and characterized.« less

Hydrogenation and hydrogen intercalation of hexagonal boron nitride on Ni(1 1 1): reactivity and electronic structure

NASA Astrophysics Data System (ADS)

Späth, F.; Gebhardt, J.; Düll, F.; Bauer, U.; Bachmann, P.; Gleichweit, C.; Görling, A.; Steinrück, H.-P.; Papp, C.

2017-09-01

We investigate the reactivity of hexagonal boron nitride (h-BN) on a Ni(1 1 1) single crystal towards atomic hydrogen over a wide exposure range. Near edge x-ray absorption fine structure and x-ray photoelectron spectroscopy (XPS) show that for low hydrogen exposures hydrogenation of the h-BN sheet is found. In contrast, intercalation of hydrogen between h-BN and the Ni(1 1 1) substrate occurs for high exposures. For intermediate regimes, a mixture of intercalation and hydrogenation is observed. From temperature-programmed desorption and temperature-programmed XPS experiments, we conclude that the hydrogen covalently bound to h-BN is rather stable with a desorption temperature of 600 K, while intercalated hydrogen is desorbing already at 390 K. Further insight into the structural arrangements and the thermodynamics of the system is obtained by comparing our experimental results with extensive density-functional theory calculations. Together with ultraviolet photoelectron spectroscopy measurements, the calculations provide detailed insight into the influence of hydrogenation on the electronic structure of h-BN.

Atomic hydrogen in. gamma. -irradiated hydroxides of alkaline-earth elements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spitsyn, V.I.; Yurik, T.K.; Barsova, L.I.

1982-04-01

Atomic hydrogen is an important intermediate product formed in the radiolysis of compounds containing X-H bonds. H atoms have been detected in irradiated matrices of H/sub 2/ and inert gases at 4/sup 0/K, in irradiated ice and frozen solutions of acids in irradiated salts and in other systems. Here results are presented from a study of the ESR spectra of H atoms generated in polycrystalline hydroxides of alkaline-earth elements that have been ..gamma..-irradiated at 77/sup 0/K, after preliminary treatment at various temperatures. For the first time stabilization of atomic hydrogen in ..gamma..-irradiated polycrystalline alkaline-earth element hydroxides has been detected. Dependingmore » on the degree of dehydroxylation, several types of hydrogen atoms may be stabilized in the hydroxides, these hydrogen atoms having different radiospectroscopic parameters. In the magnesium-calcium-strontium-barium hydroxide series, a regular decrease has been found in the hfi constants for H atoms with the cations in the immediate surroundings. A direct proportionality has been found between the parameters ..delta..A/A/sub 0/ and the polarizability of the cation.« less

Crystal structure of tetra­wickmanite, Mn2+Sn4+(OH)6

PubMed Central

Lafuente, Barbara; Yang, Hexiong; Downs, Robert T.

2015-01-01

The crystal structure of tetra­wickmanite, ideally Mn2+Sn4+(OH)6 [mangan­ese(II) tin(IV) hexa­hydroxide], has been determined based on single-crystal X-ray diffraction data collected from a natural sample from Långban, Sweden. Tetra­wickmanite belongs to the octa­hedral-framework group of hydroxide-perovskite minerals, described by the general formula BB’(OH)6 with a perovskite derivative structure. The structure differs from that of an ABO3 perovskite in that the A site is empty while each O atom is bonded to an H atom. The perovskite B-type cations split into ordered B and B′ sites, which are occupied by Mn2+ and Sn4+, respectively. Tetra­wickmanite exhibits tetra­gonal symmetry and is topologically similar to its cubic polymorph, wickmanite. The tetra­wickmanite structure is characterized by a framework of alternating corner-linked [Mn2+(OH)6] and [Sn4+(OH)6] octa­hedra, both with point-group symmetry -1. Four of the five distinct H atoms in the structure are statistically disordered. The vacant A site is in a cavity in the centre of a distorted cube formed by eight octa­hedra at the corners. However, the hydrogen-atom positions and their hydrogen bonds are not equivalent in every cavity, resulting in two distinct environments. One of the cavities contains a ring of four hydrogen bonds, similar to that found in wickmanite, while the other cavity is more distorted and forms crankshaft-type chains of hydrogen bonds, as previously proposed for tetra­gonal stottite, Fe2+Ge4+(OH)6. PMID:25878828

Quantitative structure-activity relationship for the oxidation of aromatic organic contaminants in water by TAML/H2O2.

PubMed

Su, Hanrui; Yu, Chunyang; Zhou, Yongfeng; Gong, Lidong; Li, Qilin; Alvarez, Pedro J J; Long, Mingce

2018-05-02

Tetra-amido macrocyclic ligand (TAML) activator is a functional analog of peroxidase enzymes, which activates hydrogen peroxide (H 2 O 2 ) to form high valence iron-oxo complexes that selectively degrade persistent aromatic organic contaminants (ACs) in water. Here, we develop quantitative structure-activity relationship (QSAR) models based on measured pseudo first-order kinetic rate coefficients (k obs ) of 29 ACs (e.g., phenols and pharmaceuticals) oxidized by TAML/H 2 O 2 at neutral and basic pH values to gain mechanistic insight on the selectivity and pH dependence of TAML/H 2 O 2 systems. These QSAR models infer that electron donating ability (E HOMO ) is the most important AC characteristic for TAML/H 2 O 2 oxidation, pointing to a rate-limiting single-electron transfer (SET) mechanism. Oxidation rates at pH 7 also depend on AC reactive indices such as f min - and qH + , which respectively represent propensity for electrophilic attack and the most positive net atomic charge on hydrogen atoms. At pH 10, TAML/H 2 O 2 is more reactive towards ACs with a lower hydrogen to carbon atoms ratio (#H:C), suggesting the significance of hydrogen atom abstraction. In addition, lnk obs of 14 monosubstituted phenols is negatively correlated with Hammett constants (σ) and exhibits similar sensitivity to substituent effects as horseradish peroxidase. Although accurately predicting degradation rates of specific ACs in complex wastewater matrices could be difficult, these QSAR models are statistically robust and help predict both relative degradability and reaction mechanism for TAML/H 2 O 2 -based treatment processes. Copyright © 2018 Elsevier Ltd. All rights reserved.

Measurements of atomic splittings in atomic hydrogen and the proton charge radius

NASA Astrophysics Data System (ADS)

Hessels, E. A.

2016-09-01

The proton charge radius can be determined from precise measurements of atomic hydrogen spectroscopy. A review of the relevant measurements will be given, including an update on our measurement of the n=2 Lamb shift. The values obtained from hydrogen will be compared to those obtained from muonic hydrogen and from electron-proton elastic scattering measurements. This work is funded by NSERC, CRC and CFI.

Quantum nature of protons in water probed by scanning tunneling microscopy and spectroscopy

NASA Astrophysics Data System (ADS)

Guo, Jing; Lü, Jing-Tao; Feng, Yexin; Chen, Ji; Peng, Jinbo; Lin, Zeren; Meng, Xiangzhi; Wang, Zhichang; Li, Xin-Zheng; Wang, En-Ge; Jiang, Ying; Jing-Tao Lü Team; Xin-Zheng Li Team

The complexity of hydrogen-bonding interaction largely arises from the quantum nature of light hydrogen nuclei, which has remained elusive for decades. Here we report the direct assessment of nuclear quantum effects on the strength of a single hydrogen bond formed at a water-salt interface, using tip-enhanced inelastic electron tunneling spectroscopy (IETS) based on a low-temperature scanning tunneling microscope (STM). The IETS signals are resonantly enhanced by gating the frontier orbitals of water via a chlorine-terminated STM tip, such that the hydrogen-bonding strength can be determined with unprecedentedly high accuracy from the redshift in the O-H stretching frequency of water. Isotopic substitution experiments combined with quantum simulations reveal that the anharmonic quantum fluctuations of hydrogen nuclei weaken the weak hydrogen bonds and strengthen the relatively strong ones. However, this trend can be completely reversed when the hydrogen bond is strongly coupled to the polar atomic sites of the surface.

2-Acetyl-1,1,3,3-tetra­methyl­guanidine

PubMed Central

Tiritiris, Ioannis

2012-01-01

In the mol­ecule of the title compound, C7H15N3O, the central C atom is surrounded in a nearly ideal trigonal–planar geometry by three N atoms. The C—N bond lengths in the CN3 unit are 1.3353 (13), 1.3463 (12) and 1.3541 (13) Å, indicating an inter­mediate character between a single and a double bond for each C—N bond. The bonds between the N atoms and the terminal C-methyl groups all have values close to that of a typical single bond [1.4526 (13)–1.4614 (14) Å]. In the crystal, the guanidine mol­ecules are connected by weak C—H⋯O and C—H⋯N hydrogen bonds, generating layers parallel to the ab plane. PMID:23125768

The formation of molecules in interstellar clouds from singly and multiply ionized atoms

NASA Technical Reports Server (NTRS)

Langer, W. D.

1978-01-01

The suggestion is considered that multiply ionized atoms produced by K- and L-shell X-ray ionization and cosmic-ray ionization can undergo ion-molecule reactions and also initiate molecule production. The role of X-rays in molecule production in general is discussed, and the contribution to molecule production of the C(+) radiative association with hydrogen is examined. Such gas-phase reactions of singly and multiply ionized atoms are used to calculate molecular abundances of carbon-, nitrogen-, and oxygen-bearing species. The column densities of the molecules are evaluated on the basis of a modified version of previously developed isobaric cloud models. It is found that reactions of multiply ionized carbon with H2 can contribute a significant fraction of the observed CH in diffuse interstellar clouds in the presence of diffuse X-ray structures or discrete X-ray sources and that substantial amounts of CH(+) can be produced under certain conditions.

Transferable Pseudo-Classical Electrons for Aufbau of Atomic Ions

PubMed Central

Ekesan, Solen; Kale, Seyit; Herzfeld, Judith

2014-01-01

Generalizing the LEWIS reactive force field from electron pairs to single electrons, we present LEWIS• in which explicit valence electrons interact with each other and with nuclear cores via pairwise interactions. The valence electrons are independently mobile particles, following classical equations of motion according to potentials modified from Coulombic as required to capture quantum characteristics. As proof of principle, the aufbau of atomic ions is described for diverse main group elements from the first three rows of the periodic table, using a single potential for interactions between electrons of like spin and another for electrons of unlike spin. The electrons of each spin are found to distribute themselves in a fashion akin to the major lobes of the hybrid atomic orbitals, suggesting a pointillist description of the electron density. The broader validity of the LEWIS• force field is illustrated by predicting the vibrational frequencies of diatomic and triatomic hydrogen species. PMID:24752384

Transferable pseudoclassical electrons for aufbau of atomic ions.

PubMed

Ekesan, Solen; Kale, Seyit; Herzfeld, Judith

2014-06-05

Generalizing the LEWIS reactive force field from electron pairs to single electrons, we present LEWIS• in which explicit valence electrons interact with each other and with nuclear cores via pairwise interactions. The valence electrons are independently mobile particles, following classical equations of motion according to potentials modified from Coulombic as required to capture quantum characteristics. As proof of principle, the aufbau of atomic ions is described for diverse main group elements from the first three rows of the periodic table, using a single potential for interactions between electrons of like spin and another for electrons of unlike spin. The electrons of each spin are found to distribute themselves in a fashion akin to the major lobes of the hybrid atomic orbitals, suggesting a pointillist description of the electron density. The broader validity of the LEWIS• force field is illustrated by predicting the vibrational frequencies of diatomic and triatomic hydrogen species. Copyright © 2014 Wiley Periodicals, Inc.

Quantum study of Eley-Rideal reaction and collision induced desorption of hydrogen atoms on a graphite surface. II. H-physisorbed case.

PubMed

Martinazzo, Rocco; Tantardini, Gian Franco

2006-03-28

Following previous investigation of collision induced (CI) processes involving hydrogen atoms chemisorbed on graphite [R. Martinazzo and G. F. Tantardini, J. Chem. Phys. 124, 124702 (2006)], the case in which the target hydrogen atom is initially physisorbed on the surface is considered here. Several adsorbate-substrate initial states of the target H atom in the physisorption well are considered, and CI processes are studied for projectile energies up to 1 eV. Results show that (i) Eley-Rideal cross sections at low collision energies may be larger than those found in the H-chemisorbed case but they rapidly decrease as the collision energy increases; (ii) product hydrogen molecules are vibrationally very excited; (iii) collision induced desorption cross sections rapidly increase, reaching saturation values greater than 10 A2; (iv) trapping of the incident atoms is found to be as efficient as the Eley-Rideal reaction at low energies and remains sizable (3-4 A2) at high energies. The latter adsorbate-induced trapping results mainly in formation of metastable hot hydrogen atoms, i.e., atoms with an excess energy channeled in the motion parallel to the surface. These atoms might contribute in explaining hydrogen formation on graphite.

Polymeric Materials With Additives for Durability and Radiation Shielding in Space

NASA Technical Reports Server (NTRS)

Kiefer, Richard

2011-01-01

Polymeric materials are attractive for use in space structures because of their light weight and high strength In addition, polymers are made of elements with low atomic numbers (Z), primarily carbon (C), hydrogen (H), oxygen (0), and nitrogen (N) which provide the best shielding from galactic cosmic rays (GCR) (ref. 1). Galactic cosmic rays are composed primarily of nuclei (i.e., fully ionized atoms) plus a contribution of about 2% from electrons and positrons. There is a small but significant component of GCR particles with high charge (Z > 10) and high energy (E >100 GeV) (ref. 2). These so-called HZE particles comprise only 1 to 2% of the cosmic ray fluence but they interact with very high specific ionization and contribute 50% of the long- term dose to humans. The best shield for this radiation would be liquid hydrogen, which is not feasible. For this reason, hydrogen-containing polymers make the most effective practical shields. Moreover, neutrons are formed in the interactions of GCR particles with materials. Neutrons can only lose energy by collisions or reactions with a nucleus since they are uncharged. This is a process that is much less probable than the Coulombic interactions of charged particles. Thus, neutrons migrate far from the site of the reaction in which they were formed. This increases the probability of neutrons reaching humans or electronic equipment. Fast neutrons (> 1 MeV) can interact with silicon chips in electronic equipment resulting in the production of recoil ions which can cause single event upsets (SEU) in sensitive components (ref. 3). Neutrons lose energy most effectively by elastic collisions with light atoms, particularly hydrogen atoms. Therefore, hydrogen-containing polymers are not only effective in interacting with GCR particles; they are also effective in reducing the energy of the neutrons formed in the interactions.

NiCu single atom alloys catalyze the C—H bond activation in the selective non- oxidative ethanol dehydrogenation reaction

DOE PAGES

Shan, Junjun; Liu, Jilei; Li, Mengwei; ...

2017-12-29

Here, NiCu single atom alloy (SAA) nanoparticles supported on silica are reported to catalyze the non-oxidative dehydrogenation of ethanol, selectively to acetaldehyde and hydrogen products by facilitating the C—H bond cleavage. The activity and selectivity of the NiCu SAA catalysts were compared to monometallic copper and to PtCu and PdCu single atom alloys, in a flow reactor at moderate temperatures. In-situ DRIFTS showed that the silica support facilitates the O—H bond cleavage of ethanol to form ethoxy intermediates over all the supported alloy catalysts. However, these remain unreactive up to 250°C for the Cu/SiO 2 monometallic nanoparticles, while in themore » NiCu SAA, acetaldehyde is formed at much lower temperatures, below 150°C. In situ DRIFTS was also used to identify the C—H activation step as the rate determining step of this reaction on all the copper catalysts we examined. The presence of atomically dispersed Ni in Cu significantly lowers the C—H bond activation barrier, whereas Pt and Pd atoms were found less effective. This work provides direct evidence that the C—H bond cleavage is the rate determining step in ethanol dehydrogenation over this type catalyst.« less

NiCu single atom alloys catalyze the C—H bond activation in the selective non- oxidative ethanol dehydrogenation reaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shan, Junjun; Liu, Jilei; Li, Mengwei

Here, NiCu single atom alloy (SAA) nanoparticles supported on silica are reported to catalyze the non-oxidative dehydrogenation of ethanol, selectively to acetaldehyde and hydrogen products by facilitating the C—H bond cleavage. The activity and selectivity of the NiCu SAA catalysts were compared to monometallic copper and to PtCu and PdCu single atom alloys, in a flow reactor at moderate temperatures. In-situ DRIFTS showed that the silica support facilitates the O—H bond cleavage of ethanol to form ethoxy intermediates over all the supported alloy catalysts. However, these remain unreactive up to 250°C for the Cu/SiO 2 monometallic nanoparticles, while in themore » NiCu SAA, acetaldehyde is formed at much lower temperatures, below 150°C. In situ DRIFTS was also used to identify the C—H activation step as the rate determining step of this reaction on all the copper catalysts we examined. The presence of atomically dispersed Ni in Cu significantly lowers the C—H bond activation barrier, whereas Pt and Pd atoms were found less effective. This work provides direct evidence that the C—H bond cleavage is the rate determining step in ethanol dehydrogenation over this type catalyst.« less

Database of non-canonical base pairs found in known RNA structures

NASA Technical Reports Server (NTRS)

Nagaswamy, U.; Voss, N.; Zhang, Z.; Fox, G. E.

2000-01-01

Atomic resolution RNA structures are being published at an increasing rate. It is common to find a modest number of non-canonical base pairs in these structures in addition to the usual Watson-Crick pairs. This database summarizes the occurrence of these rare base pairs in accordance with standard nomenclature. The database, http://prion.bchs.uh.edu/, contains information such as sequence context, sugar pucker conformation, anti / syn base conformations, chemical shift, p K (a)values, melting temperature and free energy. Of the 29 anticipated pairs with two or more hydrogen bonds, 20 have been encountered to date. In addition, four unexpected pairs with two hydrogen bonds have been reported bringing the total to 24. Single hydrogen bond versions of five of the expected geometries have been encountered among the single hydrogen bond interactions. In addition, 18 different types of base triplets have been encountered, each of which involves three to six hydrogen bonds. The vast majority of the rare base pairs are antiparallel with the bases in the anti configuration relative to the ribose. The most common are the GU wobble, the Sheared GA pair, the Reverse Hoogsteen pair and the GA imino pair.

Charge transfer between O6+ and atomic hydrogen

NASA Astrophysics Data System (ADS)

Wu, Y.; Stancil, P. C.; Liebermann, H. P.; Buenker, R. J.; Schultz, D. R.; Hui, Y.

2011-05-01

The charge exchange process has been found to play a dominant role in the production of X-rays and/or EUV photons observed in cometary and planetary atmospheres and from the heliosphere. Charge transfer cross sections, especially state-selective cross sections, are necessary parameters in simulations of X-ray emission. In the present work, charge transfer due to collisions of ground state O6+(1s2 1 S) with atomic hydrogen has been investigated theoretically using the quantum-mechanical molecular-orbital close-coupling method (QMOCC). The multi-reference single- and double-excitation configuration interaction approach (MRDCI) has been applied to compute the adiabatic potential and nonadiabatic couplings, and the atomic basis sets used have been optimized with the method proposed previously to obtain precise potential data. Total and state-selective cross sections are calculated for energies between 10 meV/u and 10 keV/u. The QMOCC results are compared to available experimental and theoretical data as well as to new atomic-orbital close-coupling (AOCC) and classical trajectory Monte Carlo (CTMC) calculations. A recommended set of cross sections, based on the MOCC, AOCC, and CTMC calculations, is deduced which should aid in X-ray modeling studies.

The cluster Ir4 and its interaction with a hydrogen impurity. A density functional study.

PubMed

Bussai, Chuenchit; Krüger, Sven; Vayssilov, Georgi N; Rösch, Notker

2005-07-07

To contribute to the understanding of how iridium particles act as catalysts for hydrogenation and dehydrogenation of hydrocarbons, we have determined structures and binding energies of various isomers of Ir(4) as well as HIr(4) on the basis of relativistic density functional theory. The most stable isomer of Ir(4) showed a square planar structure with eight unpaired electrons. The tetrahedral structure, experimentally suggested for supported species, was calculated 49 kJ mol(-1) less stable. Hydrogen coordinates preferentially to a single Ir center of the planar cluster with a binding energy of up to 88 kJ mol(-1) with respect to the atom in the H(2) molecule. Terminal interaction of hydrogen with an Ir(4) tetrahedron causes the cluster to open to a butterfly structure. We calculated terminal binding of hydrogen at different Ir(4) isomers to be more stable than bridge coordination, at variance with earlier studies.

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

2016-05-05

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.

Single Crystalline Film of Hexagonal Boron Nitride Atomic Monolayer by Controlling Nucleation Seeds and Domains

PubMed Central

Wu, Qinke; Park, Ji-Hoon; Park, Sangwoo; Jung, Seong Jun; Suh, Hwansoo; Park, Noejung; Wongwiriyapan, Winadda; Lee, Sungjoo; Lee, Young Hee; Song, Young Jae

2015-01-01

A monolayer hexagonal boron nitride (h-BN) film with controllable domain morphology and domain size (varying from less than 1 μm to more than 100 μm) with uniform crystalline orientation was successfully synthesized by chemical vapor deposition (CVD). The key for this extremely large single crystalline domain size of a h-BN monolayer is a decrease in the density of nucleation seeds by increasing the hydrogen gas flow during the h-BN growth. Moreover, the well-defined shape of h-BN flakes can be selectively grown by controlling Cu-annealing time under argon atmosphere prior to h-BN growth, which provides the h-BN shape varies in triangular, trapezoidal, hexagonal and complex shapes. The uniform crystalline orientation of h-BN from different nucleation seeds can be easily confirmed by polarized optical microscopy (POM) with a liquid crystal coating. Furthermore, seamlessly merged h-BN flakes without structural domain boundaries were evidence by a selective hydrogen etching after a full coverage of a h-BN film was achieved. This seamless large-area and atomic monolayer of single crystalline h-BN film can offer as an ideal and practical template of graphene-based devices or alternative two-dimensional materials for industrial applications with scalability. PMID:26537788

Single Crystalline Film of Hexagonal Boron Nitride Atomic Monolayer by Controlling Nucleation Seeds and Domains

NASA Astrophysics Data System (ADS)

Wu, Qinke; Park, Ji-Hoon; Park, Sangwoo; Jung, Seong Jun; Suh, Hwansoo; Park, Noejung; Wongwiriyapan, Winadda; Lee, Sungjoo; Lee, Young Hee; Song, Young Jae

2015-11-01

A monolayer hexagonal boron nitride (h-BN) film with controllable domain morphology and domain size (varying from less than 1 μm to more than 100 μm) with uniform crystalline orientation was successfully synthesized by chemical vapor deposition (CVD). The key for this extremely large single crystalline domain size of a h-BN monolayer is a decrease in the density of nucleation seeds by increasing the hydrogen gas flow during the h-BN growth. Moreover, the well-defined shape of h-BN flakes can be selectively grown by controlling Cu-annealing time under argon atmosphere prior to h-BN growth, which provides the h-BN shape varies in triangular, trapezoidal, hexagonal and complex shapes. The uniform crystalline orientation of h-BN from different nucleation seeds can be easily confirmed by polarized optical microscopy (POM) with a liquid crystal coating. Furthermore, seamlessly merged h-BN flakes without structural domain boundaries were evidence by a selective hydrogen etching after a full coverage of a h-BN film was achieved. This seamless large-area and atomic monolayer of single crystalline h-BN film can offer as an ideal and practical template of graphene-based devices or alternative two-dimensional materials for industrial applications with scalability.

Porphyrins and their synthesis from dipyrromethanes and aldehydes

DOEpatents

Wijesekera, Tilak; Lyons, James E.; Ellis, Jr., Paul E.

1998-01-01

The invention comprises new compositions of matter, which are iron, manganese, cobalt or ruthenium complexes of porphyrins having hydrogen, haloalkyl or haloaryl groups in meso positions, two of the opposed meso atoms or groups being hydrogen or haloaryl, and two of the opposed meso atoms or groups being hydrogen or haloalkyl, but not all four of the meso atoms or groups being hydrogen. The invention also comprises new compositions of matter in which all four of the meso positions are substituted with haloalkyl groups and the beta positions are substituted with halogen atoms. A new method of synthesizing porphyrinogens is also provided.

Porphyrins and their synthesis from dipyrromethanes and aldehydes

DOEpatents

Wijesekera, T.; Lyons, J.E.; Ellis, P.E. Jr.

1998-06-02

The invention comprises new compositions of matter, which are iron, manganese, cobalt or ruthenium complexes of porphyrins having hydrogen, haloalkyl or haloaryl groups in meso positions, two of the opposed meso atoms or groups being hydrogen or haloaryl, and two of the opposed meso atoms or groups being hydrogen or haloalkyl, but not all four of the meso atoms or groups being hydrogen. The invention also comprises new compositions of matter in which all four of the meso positions are substituted with haloalkyl groups and the beta positions are substituted with halogen atoms. A new method of synthesizing porphyrinogens is also provided.

Investigating single molecule adhesion by atomic force spectroscopy.

PubMed

Stetter, Frank W S; Kienle, Sandra; Krysiak, Stefanie; Hugel, Thorsten

2015-02-27

Atomic force spectroscopy is an ideal tool to study molecules at surfaces and interfaces. An experimental protocol to couple a large variety of single molecules covalently onto an AFM tip is presented. At the same time the AFM tip is passivated to prevent unspecific interactions between the tip and the substrate, which is a prerequisite to study single molecules attached to the AFM tip. Analyses to determine the adhesion force, the adhesion length, and the free energy of these molecules on solid surfaces and bio-interfaces are shortly presented and external references for further reading are provided. Example molecules are the poly(amino acid) polytyrosine, the graft polymer PI-g-PS and the phospholipid POPE (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine). These molecules are desorbed from different surfaces like CH3-SAMs, hydrogen terminated diamond and supported lipid bilayers under various solvent conditions. Finally, the advantages of force spectroscopic single molecule experiments are discussed including means to decide if truly a single molecule has been studied in the experiment.

Investigating Single Molecule Adhesion by Atomic Force Spectroscopy

PubMed Central

Stetter, Frank W. S.; Kienle, Sandra; Krysiak, Stefanie; Hugel, Thorsten

2015-01-01

Atomic force spectroscopy is an ideal tool to study molecules at surfaces and interfaces. An experimental protocol to couple a large variety of single molecules covalently onto an AFM tip is presented. At the same time the AFM tip is passivated to prevent unspecific interactions between the tip and the substrate, which is a prerequisite to study single molecules attached to the AFM tip. Analyses to determine the adhesion force, the adhesion length, and the free energy of these molecules on solid surfaces and bio-interfaces are shortly presented and external references for further reading are provided. Example molecules are the poly(amino acid) polytyrosine, the graft polymer PI-g-PS and the phospholipid POPE (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine). These molecules are desorbed from different surfaces like CH3-SAMs, hydrogen terminated diamond and supported lipid bilayers under various solvent conditions. Finally, the advantages of force spectroscopic single molecule experiments are discussed including means to decide if truly a single molecule has been studied in the experiment. PMID:25867282

Interactions of atomic hydrogen with amorphous SiO2

NASA Astrophysics Data System (ADS)

Yue, Yunliang; Wang, Jianwei; Zhang, Yuqi; Song, Yu; Zuo, Xu

2018-03-01

Dozens of models are investigated by the first-principles calculations to simulate the interactions of an atomic hydrogen with a defect-free random network of amorphous SiO2 (a-SiO2) and oxygen vacancies. A wide variety of stable configurations are discovered due to the disorder of a-SiO2, and their structures, charges, magnetic moments, spin densities, and density of states are calculated. The atomic hydrogen interacts with the defect-free a-SiO2 in positively or negatively charged state, and produces the structures absent in crystalline SiO2. It passivates the neutral oxygen vacancies and generates two neutral hydrogenated E‧ centers with different Si dangling bond projections. Electron spin resonance parameters, including Fermi contacts, and g-tensors, are calculated for these centers. The atomic hydrogen interacts with the positive oxygen vacancies in dimer configuration, and generate four different positive hydrogenated defects, two of which are puckered like the Eγ‧ centers. This research helps to understand the interactions between an atomic hydrogen, and defect-free a-SiO2 and oxygen vacancies, which may generate the hydrogen-complexed defects that play a key role in the degeneration of silicon/silica-based microelectronic devices.

Measurements of the Activation Energies for Atomic Hydrogen Diffusion on Pure Solid CO

NASA Astrophysics Data System (ADS)

Kimura, Y.; Tsuge, M.; Pirronello, V.; Kouchi, A.; Watanabe, N.

2018-05-01

The diffusion of hydrogen atoms on dust grains is a key process in the formation of interstellar H2 and some hydrogenated molecules such as formaldehyde and methanol. We investigate the adsorption and diffusion of H atoms on pure solid CO as an analog of dust surfaces observed toward some cold interstellar regions. Using a combination of photostimulated desorption and resonance-enhanced multiphoton ionization methods to detect H atoms directly, the relative adsorption probabilities and diffusion coefficients of the H atoms are measured on pure solid CO at 8, 12, and 15 K. There is little difference between the diffusion coefficients of the hydrogen and deuterium atoms, indicating that the diffusion is limited by thermal hopping. The activation energies controlling the H-atom diffusion depend on the surface temperature, and values of 22, 30, and ∼37 meV were obtained for 8, 12, and 15 K, respectively.

Assessing the concept of structure sensitivity or insensitivity for sub-nanometer catalyst materials

NASA Astrophysics Data System (ADS)

Crampton, Andrew S.; Rötzer, Marian D.; Ridge, Claron J.; Yoon, Bokwon; Schweinberger, Florian F.; Landman, Uzi; Heiz, Ueli

2016-10-01

The nature of the nano-catalyzed hydrogenation of ethylene, yielding benchmark information pertaining to the concept of structure sensitivity/insensitivity and its applicability at the bottom of the catalyst particle size-range, is explored with experiments on size-selected Ptn (n = 7-40) clusters soft-landed on MgO, in conjunction with first-principles simulations. As in the case of larger particles both the direct ethylene hydrogenation channel and the parallel hydrogenation-dehydrogenation ethylidyne-producing route must be considered, with the fundamental uncovering that at the < 1 nm size-scale the reaction exhibits characteristics consistent with structure sensitivity, in contrast to the structure insensitivity found for larger particles. In this size-regime, the chemical properties can be modulated and tuned by a single atom, reflected by the onset of low temperature hydrogenation at T > 150 K catalyzed by Ptn (n ≥ 10) clusters, with maximum room temperature reactivity observed for Pt13 using a pulsed molecular beam technique. Structure insensitive behavior, inherent for specific cluster sizes at ambient temperatures, can be induced in the more active sizes, e.g. Pt13, by a temperature increase, up to 400 K, which opens dehydrogenation channels leading to ethylidyne formation. This reaction channel was, however found to be attenuated on Pt20, as catalyst activity remained elevated after the 400 K step. Pt30 displayed behavior which can be understood from extrapolating bulk properties to this size range; in particular the calculated d-band center. In the non-scalable sub-nanometer size regime, however, precise control of particle size may be used for atom-by-atom tuning and manipulation of catalyzed hydrogenation activity and selectivity.

Diaqua­bis[1-hydroxy-2-(imidazol-3-ium-1-yl)-1,1′-ethyl­idenediphophonato-κ2 O,O′]zinc(II)

PubMed Central

Freire, Eleonora; Vega, Daniel R.

2009-01-01

In the title complex, [Zn(C5H9NO7P2)2(H2O)2], the zinc atom is coordinated by two bidentate zoledronate [zoledronate = (2-(1-imidazole)-1-hydr­oxy-1,1′-ethyl­idenediphophonate)] ligands and two water mol­ecules. The coordination number is 6. There is one half-mol­ecule in the asymmetric unit with the zinc atom located on a crystallographic inversion centre. The anion exists as a zwitterion with an overall charge of −1; the protonated nitro­gen in the ring has a positive charge and the two phospho­nates groups each have a single negative charge. There are two intra­molecular O—H⋯O hydrogen bonds. The mol­ecules are linked into a chain by inter­molecular O—H⋯O hydrogen bonds. Adjacent chains are further linked by O—H⋯O hydrogen bonds involving the aqua ligands. An N—H⋯O inter­action is also observed. PMID:21578164

Neutron Nucleic Acid Crystallography.

PubMed

Chatake, Toshiyuki

2016-01-01

The hydration shells surrounding nucleic acids and hydrogen-bonding networks involving water molecules and nucleic acids are essential interactions for the structural stability and function of nucleic acids. Water molecules in the hydration shells influence various conformations of DNA and RNA by specific hydrogen-bonding networks, which often contribute to the chemical reactivity and molecular recognition of nucleic acids. However, X-ray crystallography could not provide a complete description of structural information with respect to hydrogen bonds. Indeed, X-ray crystallography is a powerful tool for determining the locations of water molecules, i.e., the location of the oxygen atom of H2O; however, it is very difficult to determine the orientation of the water molecules, i.e., the orientation of the two hydrogen atoms of H2O, because X-ray scattering from the hydrogen atom is very small.Neutron crystallography is a specialized tool for determining the positions of hydrogen atoms. Neutrons are not diffracted by electrons, but are diffracted by atomic nuclei; accordingly, neutron scattering lengths of hydrogen and its isotopes are comparable to those of non-hydrogen atoms. Therefore, neutron crystallography can determine both of the locations and orientations of water molecules. This chapter describes the current status of neutron nucleic acid crystallographic research as well as the basic principles of neutron diffraction experiments performed on nucleic acid crystals: materials, crystallization, diffraction experiments, and structure determination.

Surface Modification of Poly(ethylene naphthalate) Substrate and Its Effect on SiNx Film Deposition by Atomic Hydrogen Annealing

NASA Astrophysics Data System (ADS)

Heya, Akira; Matsuo, Naoto

2007-07-01

The surface modification of a plastic substrate by atomic hydrogen annealing (AHA) was investigated for flexible displays. In this method, the plastic substrate was exposed to atomic hydrogen generated by cracking hydrogen molecules on heated tungsten wire. Both surface roughness and contact angle of water droplet on poly(ethylene naphthalate) (PEN) substrates were increased by AHA. The surface of a PEN substrate was reduced by atomic hydrogen without optical transmittance degradation. In addition, the properties of a silicon nitride (SiNx) film deposited on a PEN substrate were changed by AHA, and the adhesion between the SiNx film and the PEN substrate was excellent for application to flexible displays.

Quantitative analysis of hydrogen in SiO{sub 2}/SiN/SiO{sub 2} stacks using atom probe tomography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kunimune, Yorinobu, E-mail: yorinobu.kunimune.vz@renesas.com; Shimada, Yasuhiro; Sakurai, Yusuke

2016-04-15

We have demonstrated that it is possible to reproducibly quantify hydrogen concentration in the SiN layer of a SiO{sub 2}/SiN/SiO{sub 2} (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 actualmore » 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.« less

Atomic hydrogen cleaning of EUV multilayer optics

NASA Astrophysics Data System (ADS)

Graham, Samuel, Jr.; Steinhaus, Charles A.; Clift, W. Miles; Klebanoff, Leonard E.; Bajt, Sasa

2003-06-01

Recent studies have been conducted to investigate the use of atomic hydrogen as an in-situ contamination removal method for EUV optics. In these experiments, a commercial source was used to produce atomic hydrogen by thermal dissociation of molecular hydrogen using a hot filament. Samples for these experiments consisted of silicon wafers coated with sputtered carbon, Mo/Si optics with EUV-induced carbon, and bare Si-capped and Ru-B4C-capped Mo/Si optics. Samples were exposed to an atomic hydrogen source at a distance of 200 - 500 mm downstream and angles between 0-90° with respect to the source. Carbon removal rates and optic oxidation rates were measured using Auger electron spectroscopy depth profiling. In addition, at-wavelength peak reflectance (13.4 nm) was measured using the EUV reflectometer at the Advanced Light Source. Data from these experiments show carbon removal rates up to 20 Ê/hr for sputtered carbon and 40 Ê/hr for EUV deposited carbon at a distance of 200 mm downstream. The cleaning rate was also observed to be a strong function of distance and angular position. Experiments have also shown that the carbon etch rate can be increased by a factor of 4 by channeling atomic hydrogen through quartz tubes in order to direct the atomic hydrogen to the optic surface. Atomic hydrogen exposures of bare optic samples show a small risk in reflectivity degradation after extended periods. Extended exposures (up to 20 hours) of bare Si-capped Mo/Si optics show a 1.2% loss (absolute) in reflectivity while the Ru-B4C-capped Mo/Si optics show a loss on the order of 0.5%. In order to investigate the source of this reflectivity degradation, optic samples were exposed to atomic deuterium and analyzed using low energy ion scattering direct recoil spectroscopy to determine any reactions of the hydrogen with the multilayer stack. Overall, the results show that the risk of over-etching with atomic hydrogen is much less than previous studies using RF discharge cleaning while providing cleaning rates suitable for EUV lithography operations.

Atomic hydrogen cleaning of EUV multilayer optics

NASA Astrophysics Data System (ADS)

Graham, Samuel, Jr.; Steinhaus, Charles A.; Clift, W. Miles; Klebanoff, Leonard E.; Bajt, Sasa

2003-06-01

Recent studies have been conducted to investigate the use of atomic hydrogen as an in-situ contamination removal method for EUV optics. In these experiments, a commercial source was used to produce atomic hydrogen by thermal dissociation of molecular hydrogen using a hot filament. Samples for these experiments consisted of silicon wafers coated with sputtered carbon, Mo/Si optics with EUV-induced carbon, and bare Si-capped and Ru-B4C-capped Mo/Si optics. Samples were exposed to an atomic hydrogen source at a distance of 200 - 500 mm downstream and angles between 0-90° with respect to the source. Carbon removal rates and optic oxidation rates were measured using Auger electron spectroscopy depth profiling. In addition, at-wavelength peak reflectance (13.4 nm) was measured using the EUV reflectometer at the Advanced Light Source. Data from these experiments show carbon removal rates up to 20 Å/hr for sputtered carbon and 40 Å/hr for EUV deposited carbon at a distance of 200 mm downstream. The cleaning rate was also observed to be a strong function of distance and angular position. Experiments have also shown that the carbon etch rate can be increased by a factor of 4 by channeling atomic hydrogen through quartz tubes in order to direct the atomic hydrogen to the optic surface. Atomic hydrogen exposures of bare optic samples show a small risk in reflectivity degradation after extended periods. Extended exposures (up to 20 hours) of bare Si-capped Mo/Si optics show a 1.2% loss (absolute) in reflectivity while the Ru-B4C-capped Mo/Si optics show a loss on the order of 0.5%. In order to investigate the source of this reflectivity degradation, optic samples were exposed to atomic deuterium and analyzed using low energy ion scattering direct recoil spectroscopy to determine any reactions of the hydrogen with the multilayer stack. Overall, the results show that the risk of over-etching with atomic hydrogen is much less than previous studies using RF discharge cleaning while providing cleaning rates suitable for EUV lithography operations.

Molecular mechanism of H+ conduction in the single-file water chain of the gramicidin channel.

PubMed

Pomès, Régis; Roux, Benoît

2002-05-01

The conduction of protons in the hydrogen-bonded chain of water molecules (or "proton wire") embedded in the lumen of gramicidin A is studied with molecular dynamics free energy simulations. The process may be described as a "hop-and-turn" or Grotthuss mechanism involving the chemical exchange (hop) of hydrogen nuclei between hydrogen-bonded water molecules arranged in single file in the lumen of the pore, and the subsequent reorganization (turn) of the hydrogen-bonded network. Accordingly, the conduction cycle is modeled by two complementary steps corresponding respectively to the translocation 1) of an ionic defect (H+) and 2) of a bonding defect along the hydrogen-bonded chain of water molecules in the pore interior. The molecular mechanism and the potential of mean force are analyzed for each of these two translocation steps. It is found that the mobility of protons in gramicidin A is essentially determined by the fine structure and the dynamic fluctuations of the hydrogen-bonded network. The translocation of H+ is mediated by spontaneous (thermal) fluctuations in the relative positions of oxygen atoms in the wire. In this diffusive mechanism, a shallow free-energy well slightly favors the presence of the excess proton near the middle of the channel. In the absence of H+, the water chain adopts either one of two polarized configurations, each of which corresponds to an oriented donor-acceptor hydrogen-bond pattern along the channel axis. Interconversion between these two conformations is an activated process that occurs through the sequential and directional reorientation of water molecules of the wire. The effect of hydrogen-bonding interactions between channel and water on proton translocation is analyzed from a comparison to the results obtained previously in a study of model nonpolar channels, in which such interactions were missing. Hydrogen-bond donation from water to the backbone carbonyl oxygen atoms lining the pore interior has a dual effect: it provides a coordination of water molecules well suited both to proton hydration and to high proton mobility, and it facilitates the slower reorientation or turn step of the Grotthuss mechanism by stabilizing intermediate configurations of the hydrogen-bonded network in which water molecules are in the process of flipping between their two preferred, polarized states. This mechanism offers a detailed molecular model for the rapid transport of protons in channels, in energy-transducing membrane proteins, and in enzymes.

Stability of surface and subsurface hydrogen on and in Au/Ni near-surface alloys

DOE PAGES

Celik, Fuat E.; Mavrikakis, Manos

2015-01-12

Periodic, self-consistent DFT-GGA (PW91) calculations were used to study the interaction of hydrogen atoms with the (111) surfaces of substitutional near-surface alloys (NSAs) of Au and Ni with different surface layer compositions and different arrangements of Au atoms in the surface layer. The effect of hydrogen adsorption on the surface and in the first and second subsurface layers of the NSAs was studied. Increasing the Au content in the surface layer weakens hydrogen binding on the surface, but strengthens subsurface binding, suggesting that the distribution of surface and subsurface hydrogen will be different than that on pure Ni(111). While themore » metal composition of the surface layer has an effect on the binding energy of hydrogen on NSA surfaces, the local composition of the binding site has a stronger effect. For example, fcc hollow sites consisting of three Ni atoms bind H nearly as strongly as on Ni(111), and fcc sites consisting of three Au atoms bind H nearly as weakly as on Au(111). Sites with one or two Au atoms show intermediate binding energies. The preference of hydrogen for three-fold Ni hollow sites alters the relative stabilities of different surface metal atom arrangements, and may provide a driving force for adsorbate-induced surface rearrangement.« less

Stability of Surface and Subsurface Hydrogen on and in Au/Ni Near-Surface Alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Celik, Fuat E.; Mavrikakis, Manos

2015-10-01

Periodic, self-consistent DFT-GGA (PW91) calculations were used to study the interaction of hydrogen atoms with the (111) surfaces of substitutional near-surface alloys (NSAs) of Au and Ni with different surface layer compositions and different arrangements of Au atoms in the surface layer. The effect of hydrogen adsorption on the surface and in the first and second subsurface layers of the NSAs was studied. Increasing the Au content in the surface layer weakens hydrogen binding on the surface, but strengthens subsurface binding, suggesting that the distribution of surface and subsurface hydrogen will be different than that on pure Ni(111). While themore » metal composition of the surface layer has an effect on the binding energy of hydrogen on NSA surfaces, the local composition of the binding site has a stronger effect. For example, fcc hollow sites consisting of three Ni atoms bind H nearly as strongly as on Ni(111), and fcc sites consisting of three Au atoms bind H nearly as weakly as on Au(111). Sites with one or two Au atoms show intermediate binding energies. The preference of hydrogen for three-fold Ni hollow sites alters the relative stabilities of different surface metal atom arrangements, and may provide a driving force for adsorbate-induced surface rearrangement.« less

Stability of surface and subsurface hydrogen on and in Au/Ni near-surface alloys

NASA Astrophysics Data System (ADS)

Celik, Fuat E.; Mavrikakis, Manos

2015-10-01

Periodic, self-consistent DFT-GGA (PW91) calculations were used to study the interaction of hydrogen atoms with the (111) surfaces of substitutional near-surface alloys (NSAs) of Au and Ni with different surface layer compositions and different arrangements of Au atoms in the surface layer. The effect of hydrogen adsorption on the surface and in the first and second subsurface layers of the NSAs was studied. Increasing the Au content in the surface layer weakens hydrogen binding on the surface, but strengthens subsurface binding, suggesting that the distribution of surface and subsurface hydrogen will be different than that on pure Ni(111). While the metal composition of the surface layer has an effect on the binding energy of hydrogen on NSA surfaces, the local composition of the binding site has a stronger effect. For example, fcc hollow sites consisting of three Ni atoms bind H nearly as strongly as on Ni(111), and fcc sites consisting of three Au atoms bind H nearly as weakly as on Au(111). Sites with one or two Au atoms show intermediate binding energies. The preference of hydrogen for three-fold Ni hollow sites alters the relative stabilities of different surface metal atom arrangements, and may provide a driving force for adsorbate-induced surface rearrangement.

Inner hydrogen atom transfer in benzo-fused low symmetrical metal-free tetraazaporphyrin and phthalocyanine analogues: density functional theory studies.

PubMed

Qi, Dongdong; Zhang, Yuexing; Cai, Xue; Jiang, Jianzhuang; Bai, Ming

2009-02-01

Density functional theory (DFT) calculations were carried out to study the inner hydrogen atom transfer in low symmetrical metal-free tetrapyrrole analogues ranging from tetraazaporphyrin H(2)TAP (A(0)B(0)C(0)D(0)) to naphthalocyanine H(2)Nc (A(2)B(2)C(2)D(2)) via phthalocyanine H(2)Pc (A(1)B(1)C(1)D(1)). All the transition paths of sixteen different compounds (A(0)B(0)C(0)D(0)-A(2)B(2)C(2)D(2) and A(0)B(0)C(m)D(n), m

Copernicus observations of interstellar absorption at Lyman alpha

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bohlin, R C

1975-09-01

Column densities N/sub H/ of atomic hydrogen have been derived for 40 OB stars from spectral scans at L$alpha$ obtained by the Copernicus (OAO-3) satellite. The stars are all between 60 and 1100 pc away with a range of mean densities n/sub H/ of 0.01 to 2.5 atoms cm $sup -3$. For 27 stars without significant amounts of molecular hydrogen, the mean ratio of gas to color excess is =3.6times10$sup 21$ atoms cm$sup -2$ mag$sup -1$, and the mean density is =0.12 atoms cm$sup -3$. For 10 stars where the molecular hydrogen is at least 5 percent of the totalmore » hydrogen, is 5.4times10$sup 21$ atoms cm $sup -2$ mag$sup -1$ and is 0.7 atoms cm$sup -3$. In this limited set of data, the ratio of gas to color excess in clouds varies from 1 to 3 times the mean outside of clouds. The presence of molecular hydrogen correlates with E (B-V), but the best tracer for H$sub 2$ is atomic hydrogen. The mean density of the gas for all 40 stars is much smaller than the mean of 0.7 atoms cm$sup -3$ obtained from 21-cm observations, because the brightest stars with less than average amounts of matter in the line of sight were selected for observation. (AIP)« less

Compact hydrogenator

NASA Technical Reports Server (NTRS)

Simmonds, P. G. (Inventor)

1974-01-01

The development and characteristics of a hydrogenating apparatus are described. The device consists of a reaction chamber which is selectively permeable to atomic hydrogen and catalytically active to a hydrogenating reaction. In one device, hydrogen is pumped out of the reaction chamber while the reactant remains inside to remove molecular hydrogen so that more atomic hydrogen can pass through the walls. In another device, the reactant is pumped through the reaction chamber, and the hydrogen is removed from the material leaving the chamber. The reactant is then cycled through the chamber.

Candidate chemical systems for air cooled solar powered, absorption air conditioner design. Part I. Organic absorbent systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Biermann, W. J.

1978-01-01

All the available experimental evidence suggests that the optimum ''organic'' absorbent/refrigerant combination would be a methane derivative with a single hydrogen atom with chlorine and fluorine atoms in the other sites, as refrigerant. This would be hydrogen bonded to an absorbent molecule containing the group =NC/sup -/O, with the substituent groups being such that no steric hindrance took place. Cycle analyses showed that the ratio of internal heat transfer to cooling would be large, probably impractically so in view of the high coefficient of performance needed for solar driven cooling and the additional handicap of heat rejection to the atmosphere.more » A more promising approach would be to reduce the internal heat transfer per unit of space cooling by selecting a refrigerant with a high latent heat of vaporization and selecting an absorbent with suitable properties.« less

Food Antioxidants: Chemical Insights at the Molecular Level.

PubMed

Galano, Annia; Mazzone, Gloria; Alvarez-Diduk, Ruslán; Marino, Tiziana; Alvarez-Idaboy, J Raúl; Russo, Nino

2016-01-01

In this review, we briefly summarize the reliability of the density functional theory (DFT)-based methods to accurately predict the main antioxidant properties and the reaction mechanisms involved in the free radical-scavenging reactions of chemical compounds present in food. The analyzed properties are the bond dissociation energies, in particular those involving OH bonds, electron transfer enthalpies, adiabatic ionization potentials, and proton affinities. The reaction mechanisms are hydrogen-atom transfer, proton-coupled electron transfer, radical adduct formation, single electron transfer, sequential electron proton transfer, proton-loss electron transfer, and proton-loss hydrogen-atom transfer. Furthermore, the chelating ability of these compounds and its role in decreasing or inhibiting the oxidative stress induced by Fe(III) and Cu(II) are considered. Comparisons between theoretical and experimental data confirm that modern theoretical tools are not only able to explain controversial experimental facts but also to predict chemical behavior.

Mechanical design of proteins studied by single-molecule force spectroscopy and protein engineering.

PubMed

Carrion-Vazquez, M; Oberhauser, A F; Fisher, T E; Marszalek, P E; Li, H; Fernandez, J M

2000-01-01

Mechanical unfolding and refolding may regulate the molecular elasticity of modular proteins with mechanical functions. The development of the atomic force microscopy (AFM) has recently enabled the dynamic measurement of these processes at the single-molecule level. Protein engineering techniques allow the construction of homomeric polyproteins for the precise analysis of the mechanical unfolding of single domains. alpha-Helical domains are mechanically compliant, whereas beta-sandwich domains, particularly those that resist unfolding with backbone hydrogen bonds between strands perpendicular to the applied force, are more stable and appear frequently in proteins subject to mechanical forces. The mechanical stability of a domain seems to be determined by its hydrogen bonding pattern and is correlated with its kinetic stability rather than its thermodynamic stability. Force spectroscopy using AFM promises to elucidate the dynamic mechanical properties of a wide variety of proteins at the single molecule level and provide an important complement to other structural and dynamic techniques (e.g., X-ray crystallography, NMR spectroscopy, patch-clamp).

Ultrafast atomic layer-by-layer oxygen vacancy-exchange diffusion in double-perovskite LnBaCo2O5.5+δ thin films.

PubMed

Bao, Shanyong; Ma, Chunrui; Chen, Garry; Xu, Xing; Enriquez, Erik; Chen, Chonglin; Zhang, Yamei; Bettis, Jerry L; Whangbo, Myung-Hwan; Dong, Chuang; Zhang, Qingyu

2014-04-22

Surface exchange and oxygen vacancy diffusion dynamics were studied in double-perovskites LnBaCo2O5.5+δ (LnBCO) single-crystalline thin films (Ln = Er, Pr; -0.5 < δ < 0.5) by carefully monitoring the resistance changes under a switching flow of oxidizing gas (O2) and reducing gas (H2) in the temperature range of 250 ~ 800 °C. A giant resistance change ΔR by three to four orders of magnitude in less than 0.1 s was found with a fast oscillation behavior in the resistance change rates in the ΔR vs. t plots, suggesting that the oxygen vacancy exchange diffusion with oxygen/hydrogen atoms in the LnBCO thin films is taking the layer by layer oxygen-vacancy-exchange mechanism. The first principles density functional theory calculations indicate that hydrogen atoms are present in LnBCO as bound to oxygen forming O-H bonds. This unprecedented oscillation phenomenon provides the first direct experimental evidence of the layer by layer oxygen vacancy exchange diffusion mechanism.

Synthesis and structural characterization of lithium, sodium and potassium complexes supported by a tridentate amino-bisphenolate ligand

NASA Astrophysics Data System (ADS)

Durango-García, Clara J.; Rufino-Felipe, Ernesto; López-Cardoso, Marcela; Muñoz-Hernández, Miguel-Ángel; Montiel-Palma, Virginia

2018-07-01

Reactions of methylamino-N,N-bis(2-methylene-4,6-di-tert-butylphenol) (1) with one or two equivalents of bulk Li, Na or K metals in THF or DMSO render mono or dialkali metal complexes depending on the stoichiometric ratio of the reactants. The metal-methylamino-N-(2-methylene-4,6-tert-butylphenol)sbnd N-(2-methylene-4,6-tert-butylphenolate) complexes, 2Li, 2Na and 2K, are generated upon the substitution of a single phenol hydrogen of 1. In the solid state, complex 2Na is a dimer due to the establishment of two symmetric hydrogen bonds between two adjacent molecules. The Na center also engages into the formation of a ten-membered metallacycle ring with a butterfly-like structure. Due to dimerization, an intermolecular six-membered core is formed involving two sodium and four oxygen atoms. The weakly coordinated nitrogen atom from the ligand is nearly perpendicular to the hexagonal core. The dimetal-methylamino-N,N‧-bis(2-methylene-4,6-di-tert-butylphenolate) complexes, 3Li, 3Na and 3K result from metal substitution of the two phenol hydrogens from ligand 1. The SC-XRD structures of 3Li and 3Na are discreet, each incorporating two metal atoms in different coordination environments. Ten-membered rings with boat-boat conformations are also observed as are rhombic central M2O2 cores. The molecular structure of 3K in DMSO shows a higher degree of aggregation. It effectively comprises four K atoms, two ligand backbones and seven solvent molecules forming a central four-membered K2O2 ring perpendicular to an eight-membered structure formed also by K and O atoms spanning over the two ligand moieties.

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.

Comet Kohoutek - Ultraviolet images and spectrograms

NASA Technical Reports Server (NTRS)

Opal, C. B.; Carruthers, G. R.; Prinz, D. K.; Meier, R. R.

1974-01-01

Emissions of atomic oxygen (1304 A), atomic carbon (1657 A), and atomic hydrogen (1216 A) from Comet Kohoutek were observed with ultraviolet cameras carried on a sounding rocket on Jan. 8, 1974. Analysis of the Lyman alpha halo at 1216 A gave an atomic hydrogen production rate of 4.5 x 10 to the 29th atoms per second.

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 spectra with the spectra theoretically calculated for the candidate structures at the B3LYP/aug-cc-pVTZ level.

Single element injector testing for STME injector technology

NASA Technical Reports Server (NTRS)

Hulka, J.; Schneider, J. A.; Davis, J.

1992-01-01

An oxidizer-swirled coaxial element injector is being developed for application in the liquid oxygen/gaseous hydrogen Space Transportation Main Engine (STME) for the National Launch System (NLS) vehicle. This paper reports on the first two parts of a four part single injector element study for optimization of the STME injector design. Measurements of Rupe mixing efficiency and atomization characteristics are reported for single element versions of injection elements from two multielement injectors that have been recently hot fire tested. Rather than attempting to measure a definitive mixing efficiency or droplet size parameters of these injector elements, the purpose of these experiments was to provide a baseline comparison for evaluating future injector element design modifications. Hence, all the experiments reported here were conducted with cold flow simulants to nonflowing, ambient conditions. Mixing experiments were conducted with liquid/liquid simulants to provide economical trend data. Atomization experiments were conducted with liquid/gas simulants without backpressure. The results, despite significant differences from hot fire conditions, were found to relate to mixing and atomization parameters deduced from the hot fire testing, suggesting that these experiments are valid for trend analyses. Single element and subscale multielement hot fire testing will verify optimized designs before committing to fullscale fabrication.

Characterization of an Atomic Hydrogen Source for Charge Exchange Experiments

NASA Technical Reports Server (NTRS)

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

2016-01-01

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

Probing microbubble targeting with atomic force microscopy.

PubMed

Sboros, V; Glynos, E; Ross, J A; Moran, C M; Pye, S D; Butler, M; McDicken, W N; Brown, S B; Koutsos, V

2010-10-01

Microbubble science is expanding beyond ultrasound imaging applications to biological targeting and drug/gene delivery. The characteristics of molecular targeting should be tested by a measurement system that can assess targeting efficacy and strength. Atomic force microscopy (AFM) is capable of piconewton force resolution, and is reported to measure the strength of single hydrogen bonds. An in-house targeted microbubble modified using the biotin-avidin chemistry and the CD31 antibody was used to probe cultures of Sk-Hep1 hepatic endothelial cells. We report that the targeted microbubbles provide a single distribution of adhesion forces with a median of 93pN. This interaction is assigned to the CD31 antibody-antigen unbinding event. Information on the distances between the interaction forces was obtained and could be important for future microbubble fabrication. In conclusion, the capability of single microbubbles to target cell lines was shown to be feasible with AFM.

Hydrogen atom addition to the surface of graphene nanoflakes: A density functional theory study

NASA Astrophysics Data System (ADS)

Tachikawa, Hiroto

2017-02-01

Polycyclic aromatic hydrocarbons (PAHs) provide a 2-dimensional (2D) reaction surface in 3-dimensional (3D) interstellar space and have been utilized as a model of graphene surfaces. In the present study, the reaction of PAHs with atomic hydrogen was investigated by means of density functional theory (DFT) to systematically elucidate the binding nature of atomic hydrogen to graphene nanoflakes. PAHs with n = 4-37 were chosen, where n indicates the number of benzene rings. Activation energies of hydrogen addition to the graphene surface were calculated to be 5.2-7.0 kcal/mol at the CAM-B3LYP/6-311G(d,p) level, which is almost constant for all PAHs. The binding energies of hydrogen atom were slightly dependent on the size (n): 14.8-28.5 kcal/mol. The absorption spectra showed that a long tail is generated at the low-energy region after hydrogen addition to the graphene surface. The electronic states of hydrogenated graphenes were discussed on the basis of theoretical results.

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.

Mechanistic aspects of hydrogen abstraction for phenolic antioxidants. Electronic structure and topological electron density analysis.

PubMed

Singh, Nakul; O'Malley, Patrick J; Popelier, Paul L A

2005-02-21

Density functional calculations using the B3LYP functional are used to provide insight into the hydrogen abstraction mechanism of phenolic antioxidants. The energy profiles for 13 ortho, meta, para and di-methyl substituted phenols with hydroperoxyl radical have been determined. An excellent correlation between the enthalpy (DeltaH) and activation energy (DeltaEa) was found, obeying the Evans-Polanyi rule. The effects of hydrogen bonding on DeltaEa are also discussed. Electron donating groups at the ortho and para positions are able to lower the activation energy for hydrogen abstraction. The highly electron withdrawing fluoro substituent increases the activation energies relative to phenol at the meta position but not at the para position. The electron density is studied using the atoms in molecules (AIM) approach. Atomic and bond properties are extracted to describe the hydrogen atom abstraction mechanism. It is found that on going from reactants to transition state, the hydrogen atom experiences a loss in volume, electronic population and dipole moment. These features suggest that the phenol hydroperoxyl reactions proceed according to a proton coupled electron transfer (PCET) as opposed to a hydrogen atom transfer (HAT) mechanism.

Hydrogen bonds in PC{sub 61}BM solids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sheng, Chun-Qi; Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou Normal University, Hangzhou 311121; Li, Wen-Jie

2015-09-15

We have studied the hydrogen bonds in PC{sub 61}BM solids. Inter-molecular interaction is analyzed theoretically for the well-defined monoclinic (P2{sub 1}/n) structure. The results indicate that PC{sub 61}BM combines into C–H⋯O{sub d} bonded molecular chains, where O{sub d} denotes the doubly-bonded O atom of PC{sub 61}BM. The molecular chains are linked together by C–H⋯O{sub s} bonds, where O{sub s} denotes the singly-bonded O atom of PC{sub 61}BM. To reveal the consequences of hydrogen bond formation on the structural properties of PC{sub 61}BM solids (not limited to the monoclinic structure), we design and perform some experiments for annealed samples with themore » monoclinic (P2{sub 1}/n) PC{sub 61}BM as starting material. The experiments include differential scanning calorimetry, X-ray diffraction and infrared absorption measurements. Structural phase transitions are observed below the melting point. The C–H⋯O{sub d} bonds seem persisting in the altered structures. The inter-molecular hydrogen bonds can help to understand the phase separation in polymer/PC{sub 61}BM blends and may be responsible for the existence of liquid PC{sub 61}BM.« less

Conformers and hydrogen bonds in cytidine 5‧-diphosphocholine sodium single crystals grown from a mixture of ethanol and water

NASA Astrophysics Data System (ADS)

Du, Zhenxing; Hu, Yanan; Wang, Pei; Zhou, Jingwei; Xiong, Jian; Ying, Hanjie; Bai, Jianxin

2011-01-01

The molecular structure of cytidine 5'-diphosphocholine sodium (CDPC) grown from a mixture of ethanol and water was determined by X-ray diffraction (XRD). CDPC was found to have an orthorhombic structure with confirmed lattice parameters of a = 6.978 Å, b = 12.406 Å and c = 29.326 Å. This nucleotide coenzyme was highly folded and net-like. Each crystallographic unit consisted of one sodium atom, one pyrophosphate group, one cytosine group, one coordinated water molecule, one pentose molecule, and three lattice water molecules. The interspaces of neighboring CDPC molecules were filled with water molecules and methyl groups. Although the coordinated water was connected to sodium atoms, the lattice water molecules formed chair-shaped water hexamers. The hydrogen bonds which played an important role in maintaining the structure included O sbnd H···O, N sbnd H···O and C sbnd H···O and ranged in length from 2.682 (17) to 3.349 (17) Å. Fourier transform infrared spectroscopy (FTIR) showed a broad absorption in the 400-2000 cm -1 region characteristic of short hydrogen bonds. So for industrial crystallization, methods which could eliminate the influence of hydrogen bonds should be taken, and it would be beneficial for the process of crystallization.

Incorporating nitrogen atoms into cobalt nanosheets as a strategy to boost catalytic activity toward CO2 hydrogenation

NASA Astrophysics Data System (ADS)

Wang, Liangbing; Zhang, Wenbo; Zheng, Xusheng; Chen, Yizhen; Wu, Wenlong; Qiu, Jianxiang; Zhao, Xiangchen; Zhao, Xiao; Dai, Yizhou; Zeng, Jie

2017-11-01

Hydrogenation of CO2 into fuels and useful chemicals could help to reduce reliance on fossil fuels. Although great progress has been made over the past decades to improve the activity of catalysts for CO2 hydrogenation, more efficient catalysts, especially those based on non-noble metals, are desired. Here we incorporate N atoms into Co nanosheets to boost the catalytic activity toward CO2 hydrogenation. For the hydrogenation of CO2, Co4N nanosheets exhibited a turnover frequency of 25.6 h-1 in a slurry reactor under 32 bar pressure at 150 °C, which was 64 times that of Co nanosheets. The activation energy for Co4N nanosheets was 43.3 kJ mol-1, less than half of that for Co nanosheets. Mechanistic studies revealed that Co4N nanosheets were reconstructed into Co4NHx, wherein the amido-hydrogen atoms directly interacted with the CO2 to form HCOO* intermediates. In addition, the adsorbed H2O* activated amido-hydrogen atoms via the interaction of hydrogen bonds.

Boron-Based Hydrogen Storage: Ternary Borides and Beyond

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vajo, John J.

DOE continues to seek reversible solid-state hydrogen materials with hydrogen densities of ≥11 wt% and ≥80 g/L that can deliver hydrogen and be recharged at moderate temperatures (≤100 °C) and pressures (≤100 bar) enabling incorporation into hydrogen storage systems suitable for transportation applications. Boron-based hydrogen storage materials have the potential to meet the density requirements given boron’s low atomic weight, high chemical valance, and versatile chemistry. However, the rates of hydrogen exchange in boron-based compounds are thus far much too slow for practical applications. Although contributing to the high hydrogen densities, the high valance of boron also leads to slowmore » rates of hydrogen exchange due to extensive boron-boron atom rearrangements during hydrogen cycling. This rearrangement often leads to multiple solid phases occurring over hydrogen release and recharge cycles. These phases must nucleate and react with each other across solid-solid phase boundaries leading to energy barriers that slow the rates of hydrogen exchange. This project sought to overcome the slow rates of hydrogen exchange in boron-based hydrogen storage materials by minimizing the number of solid phases and the boron atom rearrangement over a hydrogen release and recharge cycle. Two novel approaches were explored: 1) developing matched pairs of ternary borides and mixed-metal borohydrides that could exchange hydrogen with only one hydrogenated phase (the mixed-metal borohydride) and only one dehydrogenated phase (the ternary boride); and 2) developing boranes that could release hydrogen by being lithiated using lithium hydride with no boron-boron atom rearrangement.« less

Clarifying atomic weights: A 2016 four-figure table of standard and conventional atomic weights

USGS Publications Warehouse

Coplen, Tyler B.; Meyers, Fabienne; Holden, Norman E.

2017-01-01

To indicate that atomic weights of many elements are not constants of nature, in 2009 and 2011 the Commission on Isotopic Abundances and Atomic Weights (CIAAW) of the International Union of Pure and Applied Chemistry (IUPAC) replaced single-value standard atomic weight values with atomic weight intervals for 12 elements (hydrogen, lithium, boron, carbon, nitrogen, oxygen, magnesium, silicon, sulfur, chlorine, bromine, and thallium); for example, the standard atomic weight of nitrogen became the interval [14.00643, 14.00728]. CIAAW recognized that some users of atomic weight data only need representative values for these 12 elements, such as for trade and commerce. For this purpose, CIAAW provided conventional atomic weight values, such as 14.007 for nitrogen, and these values can serve in education when a single representative value is needed, such as for molecular weight calculations. Because atomic weight values abridged to four figures are preferred by many educational users and are no longer provided by CIAAW as of 2015, we provide a table containing both standard atomic weight values and conventional atomic weight values abridged to four figures for the chemical elements. A retrospective review of changes in four-digit atomic weights since 1961 indicates that changes in these values are due to more accurate measurements over time or to the recognition of the impact of natural isotopic fractionation in normal terrestrial materials upon atomic weight values of many elements. Use of the unit “u” (unified atomic mass unit on the carbon mass scale) with atomic weight is incorrect because the quantity atomic weight is dimensionless, and the unit “amu” (atomic mass unit on the oxygen scale) is an obsolete term: Both should be avoided.

Carbon-tuned bonding method significantly enhanced the hydrogen storage of BN-Li complexes.

PubMed

Deng, Qing-ming; Zhao, Lina; Luo, You-hua; Zhang, Meng; Zhao, Li-xia; Zhao, Yuliang

2011-11-01

Through first-principles calculations, we found doping carbon atoms onto BN monolayers (BNC) could significantly strengthen the Li bond on this material. Unlike the weak bond strength between Li atoms and the pristine BN layer, it is observed that Li atoms are strongly hybridized and donate their electrons to the doped substrate, which is responsible for the enhanced binding energy. Li adsorbed on the BNC layer can serve as a high-capacity hydrogen storage medium, without forming clusters, which can be recycled at room temperature. Eight polarized H(2) molecules are attached to two Li atoms with an optimal binding energy of 0.16-0.28 eV/H(2), which results from the electrostatic interaction of the polarized charge of hydrogen molecules with the electric field induced by positive Li atoms. This practical carbon-tuned BN-Li complex can work as a very high-capacity hydrogen storage medium with a gravimetric density of hydrogen of 12.2 wt%, which is much higher than the gravimetric goal of 5.5 wt % hydrogen set by the U.S. Department of Energy for 2015.

First-principles study of hydrogen adsorption in metal-doped COF-10

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu Miaomiao; Sun Qiang; Department of Physics, Virginia Commonwealth University, Richmond, Virginia 23284

2010-10-21

Covalent organic frameworks (COFs), due to their low-density, high-porosity, and high-stability, have promising applications in gas storage. In this study we have explored the potential of COFs doped with Li and Ca metal atoms for storing hydrogen under ambient thermodynamic conditions. Using density functional theory we have performed detailed calculations of the sites Li and Ca atoms occupy in COF-10 and their interaction with hydrogen molecules. The binding energy of Li atom on COF-10 substrate is found to be about 1.0 eV and each Li atom can adsorb up to three H{sub 2} molecules. However, at high concentration, Li atomsmore » cluster and, consequently, their hydrogen storage capacity is reduced due to steric hindrance between H{sub 2} molecules. On the other hand, due to charge transfer from Li to the substrate, O sites provide additional enhancement for hydrogen adsorption. With increasing concentration of doped metal atoms, the COF-10 substrate provides an additional platform for storing hydrogen. Similar conclusions are reached for Ca doped COF-10.« less

Quasi-four-body treatment of charge transfer in the collision of protons with atomic helium: I. Thomas related mechanisms

NASA Astrophysics Data System (ADS)

Safarzade, Zohre; Fathi, Reza; Shojaei Akbarabadi, Farideh; Bolorizadeh, Mohammad A.

2018-04-01

The scattering of a completely bare ion by atoms larger than hydrogen is at least a four-body interaction, and the charge transfer channel involves a two-step process. Amongst the two-step interactions of the high-velocity single charge transfer in an anion-atom collision, there is one whose amplitude demonstrates a peak in the angular distribution of the cross sections. This peak, the so-called Thomas peak, was predicted by Thomas in a two-step interaction, classically, which could also be described through three-body quantum mechanical models. This work discusses a four-body quantum treatment of the charge transfer in ion-atom collisions, where two-step interactions illustrating a Thomas peak are emphasized. In addition, the Pauli exclusion principle is taken into account for the initial and final states as well as the operators. It will be demonstrated that there is a momentum condition for each two-step interaction to occur in a single charge transfer channel, where new classical interactions lead to the Thomas mechanism.

A spectral study of a radio-frequency plasma-generated flux of atomic oxygen

NASA Technical Reports Server (NTRS)

Batten, Carmen E.; Brown, Kenneth G.; Lewis, Beverley W.

1994-01-01

The active environment of a radio-frequency (RF) plasma generator, with and without low-pressure oxygen, has been characterized through the identification of emission lines in the spectral region from 250 to 900 nm. The environment is shown to be dependent on the partial pressure of oxygen and the power applied to the RF generator. Atomic oxygen has been found in significant amounts as well as atomic hydrogen and the molecular oxygen species O2((sup 1)Sigma). The only charged species observed was the singly charged molecular ion O2(+). With a polymer specimen in the plasma chamber, carbon monoxide was also observed. The significance of these observations with respect to previous studies using this type of generator to stimulate material degradation in space is discussed. The possibility of using these generators as atomic oxygen sources in the development of oxygen atom fluorescence sensors is explored.

Electronic and molecular structure of carbon grains

NASA Technical Reports Server (NTRS)

Almloef, Jan; Luethi, Hans-Peter

1990-01-01

Clusters of carbon atoms have been studied with large-scale ab initio calculations. Planar, single-sheet graphite fragments with 6 to 54 atoms were investigated, as well as the spherical C(sub 60) Buckminsterfullerene molecule. Polycyclic aromatic hydrocarbons (PAHs) have also been considered. Thermodynamic differences between diamond- and graphite-like grains have been studied in particular. Saturation of the peripheral bonds with hydrogen is found to provide a smooth and uniform convergence of the properties with increasing cluster size. For the graphite-like clusters the convergence to bulk values is much slower than for the three-dimensional complexes.

Deuterium enrichment by selective photo-induced dissociation of an organic carbonyl compound

DOEpatents

Marling, John B.

1981-01-01

A method for producing a deuterium enriched material by photoinduced dissociation which uses as the working material a gas phase photolytically dissociable organic carbonyl compound containing at least one hydrogen atom bonded to an atom which is adjacent to a carbonyl group and consisting of molecules wherein said hydrogen atom is present as deuterium and molecules wherein said hydrogen atom is present as another isotope of hydrogen. The organic carbonyl compound is subjected to intense infrared radiation at a preselected wavelength to selectively excite and thereby induce dissociation of the deuterium containing species to yield a deuterium enriched stable molecular product. Undissociated carbonyl compound, depleted in deuterium, is preferably redeuterated for reuse.

Method for oxidizing alkanes using novel porphyrins synthesized from dipyrromethanes and aldehydes

DOEpatents

Wijesekera, Tilak; Lyons, James E.; Ellis, Jr., Paul E.

1999-01-01

The invention comprises a method for the oxidation of alkanes to alcohols and for decomposition of hydroperoxides to alcohols utilizing new compositions of matter, which are metal complexes of porphyrins. Preferred complexes have hydrogen, haloalkyl or haloaryl groups in meso positions, two of the opposed meso atoms or groups being hydrogen or haloaryl, and two of the opposed meso atoms or groups being hydrogen or haloalkyl, but not all four of the meso atoms or groups being hydrogen. Other preferred complexes are ones in which all four of the meso positions are substituted with haloalkyl groups and the beta positions are substituted with halogen atoms. A new method of synthesizing porphyrinogens is also disclosed.

Method for hydroperoxide decomposition using novel porphyrins synthesized from dipyrromethanes and aldehydes

DOEpatents

Wijesekera, T.; Lyons, J.E.; Ellis, P.E. Jr.

1998-03-03

The invention comprises a method for the oxidation of alkanes to alcohols and for decomposition of hydroperoxides to alcohols utilizing new compositions of matter, which are metal complexes of porphyrins. Preferred complexes have hydrogen, haloalkyl or haloaryl groups in meso positions, two of the opposed meso atoms or groups being hydrogen or haloaryl, and two of the opposed meso atoms or groups being hydrogen or haloalkyl, but not all four of the meso atoms or groups being hydrogen. Other preferred complexes are ones in which all four of the meso positions are substituted with haloalkyl groups and the beta positions are substituted with halogen atoms. A new method of synthesizing porphyrinogens is also disclosed.

Method for hydroperoxide decomposition using novel porphyrins synthesized from dipyrromethanes and aldehydes

DOEpatents

Wijesekera, Tilak; Lyons, James E.; Ellis, Jr., Paul E.

1998-01-01

The invention comprises a method for the oxidation of alkanes to alcohols and for decomposition of hydroperoxides to alcohols utilizing new compositions of matter, which are metal complexes of porphyrins. Preferred complexes have hydrogen, haloalkyl or haloaryl groups in meso positions, two of the opposed meso atoms or groups being hydrogen or haloaryl, and two of the opposed meso atoms or groups being hydrogen or haloalkyl, but not all four of the meso atoms or groups being hydrogen. Other preferred complexes are ones in which all four of the meso positions are substituted with haloalkyl groups and the beta positions are substituted with halogen atoms. A new method of synthesizing porphyrinogens is also disclosed.

Two Keggin-type heteropolytungstates with transition metal as a central atom: Crystal structure and magnetic study with 2D-IR correlation spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chai, Feng; Chen, YiPing, E-mail: ypchen007@sina.com; State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002

2013-06-01

Two Keggin-type heteropolytungstates, [Co(phen)₃]₃[CoW₁₂O₄₀]·9H₂O 1 (phen=1,10-phenanthroline) and [Fe(phen)₃]₂[FeW₁₂O₄₀]·H₃O·H₂O 2, have been synthesized via the hydrothermal technique and characterized by single crystal X-ray diffraction analyses, IR, XPS, TG analysis, UV–DRS, XRD, thermal-dependent and magnetic-dependent 2D-COS IR (two-dimensional infrared correlation spectroscopy). Crystal structure analysis reveals that the polyanions in compound 1 are linked into 3D supramolecule through hydrogen bonding interactions between lattice water molecules and terminal oxygen atoms of polyanion units, and [Co(phen)₃]²⁺ cations distributed in the polyanion framework with many hydrogen bonding interactions. The XPS spectra indicate that all the Co atoms in 1 are +2 oxidation state, the Fe atomsmore » in 2 existing with +2 and +3 mixed oxidation states. - Graphical abstract: The magnetic-dependent synchronous 2D correlation IR spectra of 1 (a), 2 (b) over 0–50 mT in the range of 600–1000 cm⁻¹, the obvious response indicate two Keggin polyanions skeleton susceptible to applied magnetic field. Highlights: • Two Keggin-type heteropolytungstates with transition metal as a central atom has been obtained. • Compound 1 forms into 3D supramolecular architecture through hydrogen bonding between water molecules and polyanions. • Magnetic-dependent 2D-IR correlation spectroscopy was introduced to discuss the magnetism of polyoxometalate.« less

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

Some of the design features of NASA hydrogen masers are discussed including the large hydrogen source bulb, the palladium purified, the state selector, the replaceable pumps, the small entrance stem, magnetic shields, the elongated storage bulb, the aluminum cavity, the electronics package, and the autotuner. Attention is also given to the reliability and operating life of these hydrogen atomic standards.

Data processing in neutron protein crystallography using positron-sensitive detectors

NASA Astrophysics Data System (ADS)

Schoenborn, B. P.

Neutrons provide a unique probe for localizing hydrogen atoms and for distinguishing hydrogen from deuterons. Hydrogen atoms largely determine the three dimensional structure of proteins and are responsible for many catalytic reactions. The study of hydrogen bonding and hydrogen exchange will therefore give insight into reaction mechanisms and conformational fluctuations. In addition, neutrons provide the ability to distinguish N from C and O and to allow correct orientation of groups such as histidine and glutamine. To take advantage of these unique features of neutron crystallography, one needs accurate Fourier maps depicting atomic structure to a high precision. Special attention is given to subtraction of the high background associated with hydrogen containing molecules, which produces a disproportionately large statistical error.

Atomic and molecular hydrogen in the circumstellar envelopes of late-type stars

NASA Technical Reports Server (NTRS)

Glassgold, A. E.; Huggins, P. J.

1983-01-01

The distribution of atomic and molecular hydrogen in the expanding circumstellar envelopes of cool evolved stars is discussed. The main concern is to evaluate the effects of photodestruction of H2 by galactic UV radiation, including shielding of the radiation by H2 itself and by dust in the envelope. One of the most important parameters is the H/H2 ratio which is frozen out in the upper atmosphere of the star. For stars with photospheric temperatures greater than about 2500 K, atmospheric models suggest that the outflowing hydrogen is mainly atomic, whereas cooler stars should be substantially molecular. In the latter case, photodissociation of H2 and heavy molecules contribute to the atomic hydrogen content of the outer envelope. The presented estimates indicate that atomic hydrogen is almost at the limit of detection in the C-rich star IRC + 10216, and may be detectable in warmer stars. Failure to detect it would have important implications for the general understanding of circumstellar envelopes.

On the Lamb shift in neutral muonic helium

NASA Astrophysics Data System (ADS)

Amusia, Miron; Karshenboim, Savely; Ivanov, Vladimir

2015-05-01

The neutral muonic helium is an exotic atomic system consisting of an electron, muon and a nucleus. We consider it as a hydrogen-like atom with a compound nucleus that is also hydrogen-like system. There are a number of corrections to the Bohr energy levels, which all can be treated as contributions of generic hydrogen-like theory. While the form of those contributions is the same for all hydrogen-like atoms, their relative numerical importance differs from an atom to an atom. Here, the leading contribution to the electronic Lamb shift in the neutral muonic helium is found in a close analytic form together with the most important corrections. We believe that the Lamb shift in the neutral muonic hydrogen is measurable, at least through a measurement of the electronic 1 s - 2 s transition. We present a theoretical prediction for the 1 s - 2 s transitions with the uncertainty of 2 ppm (4 GHz), as well as for the 2 s - 2 p Lamb shift with the uncertainty of 0.6 GHz.

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.

STRUCTURE OF POTASSIUM HYDROGEN MALEATE BY NEUTRON DIFFRACTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peterson, S.W.; Levy, H.A.

1958-10-01

The preliminary results of a neutron diffraction study are presented which confirm the existence in potassium hydrogen maleate of a short, strong, hydrogen bond and show the ion to be at least statistically symmetrical. The hydrogen is strongly linked to both neighboring oxygen atoms, and there is an existing mode of correlated motion of considerable amplitude in which the oxygen atoms are displaced but hydrogen is not. (J.R.D.)

Spectroscopic study of uracil, 1-methyluracil and 1-methyl-4-thiouracil: Hydrogen bond interactions in crystals and ab-initio molecular dynamics

NASA Astrophysics Data System (ADS)

Brela, Mateusz Z.; Boczar, Marek; Malec, Leszek M.; Wójcik, Marek J.; Nakajima, Takahito

2018-05-01

Hydrogen bond networks in uracil, 1-methyluracil and 1-methyl-4-thiouracil were studied by ab initio molecular dynamics as well as analysis of the orbital interactions. The power spectra calculated by ab initio molecular dynamics for atoms involved in hydrogen bonds were analyzed. We calculated spectra by using anharmonic approximation based on the autocorrelation function of the atom positions obtained from the Born-Oppenheimer simulations. Our results show the differences between hydrogen bond networks in uracil and its methylated derivatives. The studied methylated derivatives, 1-methyluracil as well as 1-methyl-4-thiouracil, form dimeric structures in the crystal phase, while uracil does not form that kind of structures. The presence of sulfur atom instead oxygen atom reflects weakness of the hydrogen bonds that build dimers.

Predictive Models for the Free Energy of Hydrogen Bonded Complexes with Single and Cooperative Hydrogen Bonds.

PubMed

Glavatskikh, Marta; Madzhidov, Timur; Solov'ev, Vitaly; Marcou, Gilles; Horvath, Dragos; Varnek, Alexandre

2016-12-01

In this work, we report QSPR modeling of the free energy ΔG of 1 : 1 hydrogen bond complexes of different H-bond acceptors and donors. The modeling was performed on a large and structurally diverse set of 3373 complexes featuring a single hydrogen bond, for which ΔG was measured at 298 K in CCl 4 . The models were prepared using Support Vector Machine and Multiple Linear Regression, with ISIDA fragment descriptors. The marked atoms strategy was applied at fragmentation stage, in order to capture the location of H-bond donor and acceptor centers. Different strategies of model validation have been suggested, including the targeted omission of individual H-bond acceptors and donors from the training set, in order to check whether the predictive ability of the model is not limited to the interpolation of H-bond strength between two already encountered partners. Successfully cross-validating individual models were combined into a consensus model, and challenged to predict external test sets of 629 and 12 complexes, in which donor and acceptor formed single and cooperative H-bonds, respectively. In all cases, SVM models outperform MLR. The SVM consensus model performs well both in 3-fold cross-validation (RMSE=1.50 kJ/mol), and on the external test sets containing complexes with single (RMSE=3.20 kJ/mol) and cooperative H-bonds (RMSE=1.63 kJ/mol). © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

Characterization of an atomic hydrogen source for charge exchange experiments

DOE PAGES

Leutenegger, M. A.; Beiersdorfer, P.; Betancourt-Martinez, G. L.; ...

2016-07-02

Here, 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.

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.

Thermodynamics of single polyethylene and polybutylene glycols with hydrogen-bonding ends: A transition from looped to open conformations

NASA Astrophysics Data System (ADS)

Lee, Eunsang; Paul, Wolfgang

2018-02-01

A variety of linear polymer precursors with hydrogen bonding motifs at both ends enable us to design supramolecular polymer systems with tailored macroscopic properties including self-healing. In this study, we investigate thermodynamic properties of single polyethylene and polybutylene glycols with hydrogen bonding motifs. In this context, we first build a coarse-grained model of building blocks of the supramolecular polymer system based on all-atom molecular structures. The density of states of the single precursor is obtained using the stochastic approximation Monte Carlo method. Constructing canonical partition functions from the density of states, we find the transition from looped to open conformations at transition temperatures which are non-monotonously changing with an increasing degree of polymerization due to the competition between chain stiffness and loop-forming entropy penalty. In the complete range of chain length under investigation, a coexistence of the looped and open morphologies at the transition temperature is shown regardless of whether the transition is first-order-like or continuous. Polyethylene and polybutylene glycols show similar behavior in all the thermodynamic properties but the transition temperature of the more flexible polybutylene glycol is shown to change more gradually.

Insights into the Hydrogen-Atom Transfer of the Blue Aroxyl.

PubMed

Bächle, Josua; Marković, Marijana; Kelterer, Anne-Marie; Grampp, Günter

2017-10-19

An experimental and theoretical study on hydrogen-atom transfer dynamics in the hydrogen-bonded substituted phenol/phenoxyl complex of the blue aroxyl (2,4,6-tri-tert-butylphenoxyl) is presented. The experimental exchange dynamics is determined in different organic solvents from the temperature-dependent alternating line-width effect in the continuous-wave ESR spectrum. From bent Arrhenius plots, effective tunnelling contributions with parallel heavy-atom motion are concluded. To clarify the transfer mechanism, reaction paths for different conformers of the substituted phenol/phenoxyl complex are modelled theoretically. Various DFT and post-Hartree-Fock methods including multireference methods are applied. From the comparison of experimental and theoretical data it is concluded that the system favours concerted hydrogen-atom transfer along a parabolic reaction path caused by heavy-atom motion. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Symmetry of Carrier-Envelope Phase Difference Effects in Strong-Field, Few-Cycle Ionization of Atoms and Molecules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martiny, Christian Per Juul; Madsen, Lars Bojer

2006-09-01

In few-cycle pulses, the exact value of the carrier-envelope phase difference (CEPD) has a pronounced influence on the ionization dynamics of atoms and molecules. We show that, for atoms in circularly polarized light, a change in the CEPD is mapped uniquely to an overall rotation of the system, and results for arbitrary CEPD are obtained by rotation of the results from a single calculation with fixed CEPD. For molecules, this is true only for linear molecules aligned parallel with the propagation direction of the field. The effects of CEPD are classified as geometric or nongeometric. The observations are exemplified bymore » strong-field calculations on hydrogen.« less

Optical properties of an indium doped CdSe nanocrystal: A density functional approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Salini, K.; Mathew, Vincent, E-mail: vincent@cukerala.ac.in; Mathew, Thomas

2016-05-06

We have studied the electronic and optical properties of a CdSe nanocrystal doped with n-type impurity atom. First principle calculations of the CdSe nanocrystal based on the density functional theory (DFT), as implemented in the Vienna Ab Initio Simulation Package (VASP) was used in the calculations. We have introduced a single Indium impurity atom into CdSe nanocrystal with 1.3 nm diameter. Nanocrystal surface dangling bonds are passivated with hydrogen atom. The band-structure, density of states and absorption spectra of the doped and undopted nanocrystals were discussed. Inclusion of the n-type impurity atom introduces an additional electron in conduction band, and significantlymore » alters the electronic and optical properties of undoped CdSe nanocrystal. Indium doped CdSe nannocrystal have potential applications in optoelectronic devices.« less

Prediction of another semimetallic silicene allotrope with Dirac fermions

NASA Astrophysics Data System (ADS)

Wu, Haiping; Qian, Yan; Du, Zhengwei; Zhu, Renzhu; Kan, Erjun; Deng, Kaiming

2017-11-01

Materials with Dirac point are so amazing since the charge carriers are massless and have an effective speed of light. However, among the predicted two-dimensional silicon allotropes with Dirac point, no one has been directly proved by experiment. This fact motivates us to search for other two-dimensional silicon allotropes. As a result, another stable single atomic layer thin silicon allotrope is found with the help of CALYPSO code in this work. This silicene allotrope is composed of eight-membered rings linked by Si-Si bonds with buckling formation. The electronic calculation reveals that it behaves as a nodal line semimetal with the linear energy dispersion relation near the Fermi surface. Notably, the ab initio molecular dynamics simulations display that the original atomic configuration can be remained even at an extremely high temperature of 1000 K. Additionally, hydrogenation could induce a semimetal-semiconductor transition in this silicene allotrope. We hope this work can expand the family of single atomic layer thin silicon allotropes with special applications.

First principles study of size and external electric field effects on the atomic and electronic properties of gallium nitride nanostructures

NASA Astrophysics Data System (ADS)

Yilmaz, Hulusi

A comprehensive density functional theory study of atomic and the electronic properties of wurtzite gallium nitride (GaN) nanostructures with different sizes and shapes is presented and the effect of external electric field on these properties is examined. We show that the atomic and electronic properties of [101¯0] facet single-crystal GaN nanotubes (quasi-1D), nanowires (1D) and nanolayers (2D) are mainly determined by the surface to volume ratio. The shape dependent quantum confinement and strain effects on the atomic and electronic properties of these GaN nanostructures are found to be negligible. Based on this similarity between the atomic and electronic properties of the small size GaN nanostructures, we calculated the atomic and electronic properties of the practical size (28.1 A wall thickness) single-crystal GaN nanotubes through computational much economical GaN nanoslabs (nanolayers). Our results show that, regardless of diameter, hydrogen saturated single-crystal GaN tubes with the wall thickness of 28.1 A are energetically stable and they have a noticeably larger band gap with respect to the band gap of bulk GaN. The band gap of unsaturated single-crystal GaN tubes, on the other hand, is always smaller than the band gap of the wurtzite bulk GaN. In a separate study, we show that a transverse electric field induces a homojunction across the diameter of initially semiconducting GaN single-crystal nanotubes and nanowires. The homojunction arises due to the decreased energy of the electronic states in the higher potential region with respect to the energy of those states in the lower potential region under the transverse electric field. Calculations on single-crystal GaN nanotubes and nanowires of different diameter and wall thickness show that the threshold electric field required for the semiconductor-homojunction induction increases with increasing wall thickness and decreases significantly with increasing diameter.

Precision spectroscopy of the 2S-4P transition in atomic hydrogen

NASA Astrophysics Data System (ADS)

Maisenbacher, Lothar; Beyer, Axel; Matveev, Arthur; Grinin, Alexey; Pohl, Randolf; Khabarova, Ksenia; Kolachevsky, Nikolai; Hänsch, Theodor W.; Udem, Thomas

2017-04-01

Precision measurements of atomic hydrogen have long been successfully used to extract fundamental constants and to test bound-state QED. However, both these applications are limited by measurements of hydrogen lines other than the very precisely known 1S-2S transition. Moreover, the proton r.m.s.charge radius rp extracted from electronic hydrogen measurements currently disagrees by 4 σ with the much more precise value extracted from muonic hydrogen spectroscopy. We have measured the 2S-4P transition in atomic hydrogen using a cryogenic beam of hydrogen atoms optically excited to the initial 2S state. The first order Doppler shift of the one-photon 2S-4P transition is suppressed by actively stabilized counter-propagating laser beams and time-of-flight resolved detection. Quantum interference between excitation paths can lead to significant line distortions in our system. We use an experimentally verified, simple line shape model to take these distortions into account. With this, we can extract a new value for rp and the Rydberg constant R∞ with comparable accuracy as the combined previous H world data.

A theoretical perspective of the nature of hydrogen-bond types - the atoms in molecules approach

NASA Astrophysics Data System (ADS)

Vijaya Pandiyan, B.; Kolandaivel, P.; Deepa, P.

2014-06-01

Hydrogen bonds and their strength were analysed based on their X-H proton-donor bond properties and the parameters of the H-Y distance (Y proton acceptor). Strong, moderate and weak interactions in hydrogen-bond types were verified through the proton affinities of bases (PA), deprotanation enthalpies of acids (DPE) and the chemical shift (σ). The aromaticity and anti-aromaticity were analysed by means of the NICS (0) (nucleus-independent chemical shift), NICS (1) and ΔNICS (0), ΔNICS (1) of hydrogen-bonded molecules. The strength of a hydrogen bond depends on the capacity of hydrogen atom engrossing into the electronegative acceptor atom. The correlation between the above parameters and their relations were discussed through curve fitting. Bader's theory of atoms in molecules has been applied to estimate the occurrence of hydrogen bonds through eight criteria reported by Popelier et al. The lengths and potential energy shifts have been found to have a strong negative linear correlation, whereas the lengths and Laplacian shifts have a strong positive linear correlation. This study illustrates the common factors responsible for strong, moderate and weak interactions in hydrogen-bond types.

Tautomeric and ionisation forms of dopamine and tyramine in the solid state

NASA Astrophysics Data System (ADS)

Cruickshank, Laura; Kennedy, Alan R.; Shankland, Norman

2013-11-01

Crystallisation of the phenylethylamine neurotransmitter dopamine from basic aqueous solution yielded the 3-phenoxide Zwitterionic tautomer, despite this being a minority form in the solution state. In the crystal structure, dopamine has a dimeric [OCCOH]2 hydrogen bonded catechol motif that expands through Nsbnd H⋯O interactions to give a 2-dimensional sheet of classical hydrogen bonds. These sheets are further interconnected by Nsbnd H⋯π interactions. The structurally related base tyramine crystallises under similar conditions as a hemihydrate with all four possible species of tyramine present (cationic, anionic, Zwitterionic and neutral) in the crystal structure. Single crystal X-ray diffraction studies at 121 and 293 K showed dynamic hydrogen atom disorder for the phenol/phenoxide group, suggesting that the tyramine speciation observed arises from a solid-state process.

Stereochemistry of a bifunctional dihydroceramide delta 4-desaturase/hydroxylase from Candida albicans; a key enzyme of sphingolipid metabolism.

PubMed

Beckmann, Christoph; Rattke, Janine; Sperling, Petra; Heinz, Ernst; Boland, Wilhelm

2003-07-21

The stereochemical course of the dihydroceramide delta 4-(E)-desaturase from Candida albicans, cloned and expressed in the yeast Saccharomyces cerevisiae strain sur2 delta, was determined using stereospecifically labelled (2R,3S)-[2,3,4,4-2H4]-palmitic acid as a metabolic probe. Mass spectrometric analysis of the dinitrophenyl-derivatives of the labelled long-chain bases revealed elimination of a single deuterium atom from C(4) (corresponding to the C(4)-HR) along with a hydrogen atom from C(5) (corresponding to the C(5)-HS). This finding is consistent with an overall syn-elimination of the two vicinal hydrogen atoms. Besides the desaturation product sphingosine (93%) minor amounts of a 4-hydroxylated product (phytosphinganine, 7%) were identified that classify the Candida enzyme as a bifunctional desaturase/hydroxylase. Both processes, desaturation and hydroxylation proceed with loss of C(4)-HR from the chiral precursor. This finding is in agreement with a two-step process involving activation of the substrate by removal of the C(4)-HR to give a C-centred radical or radicaloid followed by either disproportionation into an olefin, water and a reduced diiron complex, or to recombination of the primary reactive intermediate with an active site-bound oxygen to yield a secondary alcohol. This result demonstrates the close mechanistic relationship between desaturation and hydroxylation as two different reaction pathways of a single enzyme and strengthens the mechanistic relationship of desaturases from fatty acid metabolism and sphingolipids.

Porphyrins

DOEpatents

Wijesekera, T.; Lyons, J.E.; Ellis, P.E. Jr.

1996-11-05

The invention comprises new compositions of matter, which are iron, manganese, cobalt or ruthenium complexes of porphyrins having hydrogen, haloalkyl or haloaryl groups in meso positions, two of the opposed meso atoms or groups being hydrogen or haloaryl, and two of the opposed meso atoms or groups being hydrogen or haloalkyl, but not all four of the meso atoms or groups being hydrogen. The invention also comprises new compositions of matter in which all four of the meso positions are substituted with haloalkyl groups and the beta positions are substituted with halogen atoms. A new method of synthesizing porphyrinogens is also provided. The novel compositions and others made according to the process of the invention are useful as hydrocarbon conversion catalysts; for example, for the oxidation of alkanes and the decomposition of hydroperoxides.

Porphyrins

DOEpatents

Wijesekera, Tilak; Lyons, James E.; Ellis, Jr., Paul E.

1996-01-01

The invention comprises new compositions of matter, which are iron, manganese, cobalt or ruthenium complexes of porphyrins having hydrogen, haloalkyl or haloaryl groups in meso positions, two of the opposed meso atoms or groups being hydrogen or haloaryl, and two of the opposed meso atoms or groups being hydrogen or haloalkyl, but not all four of the meso atoms or groups being hydrogen. The invention also comprises new compositions of matter in which all four of the meso positions are substituted with haloalkyl groups and the beta positions are substituted with halogen atoms. A new method of synthesizing porphyrinogens is also provided. The novel compositions and others made according to the process of the invention are useful as hydrocarbon conversion catalysts; for example, for the oxidation of alkanes and the decomposition of hydroperoxides.

Ab initio molecular dynamics simulation study of successive hydrogenation reactions of carbon monoxide producing methanol

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pham, Thi Nu; Ono, Shota; Ohno, Kaoru, E-mail: ohno@ynu.ac.jp

Doing ab initio molecular dynamics simulations, we demonstrate a possibility of hydrogenation of carbon monoxide producing methanol step by step. At first, the hydrogen atom reacts with the carbon monoxide molecule at the excited state forming the formyl radical. Formaldehyde was formed after adding one more hydrogen atom to the system. Finally, absorption of two hydrogen atoms to formaldehyde produces methanol molecule. This study is performed by using the all-electron mixed basis approach based on the time dependent density functional theory within the adiabatic local density approximation for an electronic ground-state configuration and the one-shot GW approximation for an electronicmore » excited state configuration.« less

Hydrogen transfer reactions of interstellar Complex Organic Molecules

NASA Astrophysics Data System (ADS)

Álvarez-Barcia, S.; Russ, P.; Kästner, J.; Lamberts, T.

2018-06-01

Radical recombination has been proposed to lead to the formation of complex organic molecules (COMs) in CO-rich ices in the early stages of star formation. These COMs can then undergo hydrogen addition and abstraction reactions leading to a higher or lower degree of saturation. Here, we have studied 14 hydrogen transfer reactions for the molecules glyoxal, glycoaldehyde, ethylene glycol, and methylformate and an additional three reactions where CHnO fragments are involved. Over-the-barrier reactions are possible only if tunneling is invoked in the description at low temperature. Therefore the rate constants for the studied reactions are calculated using instanton theory that takes quantum effects into account inherently. The reactions were characterized in the gas phase, but this is expected to yield meaningful results for CO-rich ices due to the minimal alteration of reaction landscapes by the CO molecules. We found that rate constants should not be extrapolated based on the height of the barrier alone, since the shape of the barrier plays an increasingly larger role at decreasing temperature. It is neither possible to predict rate constants based only on considering the type of reaction, the specific reactants and functional groups play a crucial role. Within a single molecule, though, hydrogen abstraction from an aldehyde group seems to be always faster than hydrogen addition to the same carbon atom. Reactions that involve heavy-atom tunneling, e.g., breaking or forming a C-C or C-O bond, have rate constants that are much lower than those where H transfer is involved.

Spectroscopic study of uracil, 1-methyluracil and 1-methyl-4-thiouracil: Hydrogen bond interactions in crystals and ab-initio molecular dynamics.

PubMed

Brela, Mateusz Z; Boczar, Marek; Malec, Leszek M; Wójcik, Marek J; Nakajima, Takahito

2018-05-15

Hydrogen bond networks in uracil, 1-methyluracil and 1-methyl-4-thiouracil were studied by ab initio molecular dynamics as well as analysis of the orbital interactions. The power spectra calculated by ab initio molecular dynamics for atoms involved in hydrogen bonds were analyzed. We calculated spectra by using anharmonic approximation based on the autocorrelation function of the atom positions obtained from the Born-Oppenheimer simulations. Our results show the differences between hydrogen bond networks in uracil and its methylated derivatives. The studied methylated derivatives, 1-methyluracil as well as 1-methyl-4-thiouracil, form dimeric structures in the crystal phase, while uracil does not form that kind of structures. The presence of sulfur atom instead oxygen atom reflects weakness of the hydrogen bonds that build dimers. Copyright © 2018 Elsevier B.V. All rights reserved.

Measurements of the structure of an ionizing shock wave in a hydrogen-helium mixture

NASA Technical Reports Server (NTRS)

Leibowitz, L. P.

1972-01-01

Shock structure during ionization of a hydrogen-helium mixture was studied using hydrogen line and continuum emission measurements. A reaction scheme is proposed which includes hydrogen dissociation and a two-step excitation-ionization mechanism for hydrogen ionization by atom-atom and atom-electron collisions. Agreement was achieved between numerical calculations and measurements of emission intensity as a function of time for shock velocities from 13 to 20 km/sec in a 0.208 H2 - 0.792 He mixture. The electron temperature was found to be significantly different from the heavy particle temperature during much of the ionization process. Similar time histories for H beta and continuum emission indicate upper level populations of hydrogen in equilibrium with the electron concentration during the relaxation process.

Measurements of the structure of an ionizing shock wave in a hydrogen-helium mixture.

NASA Technical Reports Server (NTRS)

Leibowitz, L. P.

1973-01-01

Shock structure during ionization of a hydrogen-helium mixture has been followed using hydrogen line and continuum emission measurements. A reaction scheme is proposed which includes hydrogen dissociation and a two-step excitation-ionization mechanism for hydrogen ionization by atom-atom and atom-electron collisions. Agreement has been achieved between numerical calculations and measurements of emission intensity as a function of time for shock velocities from 13 to 20 km/sec in a 0.208 H2-0.792 He mixture. The electron temperature was found to be significantly different from the heavy particle temperature during much of the ionization process. Similar time histories for H beta and continuum emission indicate upper level populations of hydrogen in equilibrium with the electron concentration during the relaxation process.

2-Amino-5-chloro-pyrimidin-1-ium hydrogen maleate.

PubMed

Fun, Hoong-Kun; Hemamalini, Madhukar; Rajakannan, Venkatachalam

2012-01-01

In the title salt, C(4)H(5)ClN(3) (+)·C(4)H(3)O(4) (-), the 2-amino-5-chloro-pyrimidinium cation is protonated at one of its pyrimidine N atoms. In the roughly planar (r.m.s. deviation = 0.026 Å) hydrogen malate anion, an intra-molecular O-H⋯O hydrogen bond generates an S(7) ring. In the crystal, the protonated N atom and the 2-amino group of the cation are hydrogen bonded to the carboxyl-ate O atoms of the anion via a pair of N-H⋯O hydrogen bonds, forming an R(2) (2)(8) ring motif. The ion pairs are connected via further N-H⋯O hydrogen bonds and a short C-H⋯O inter-action, forming layers lying parallel to the bc plane.

Fully methylated, atomically flat (111) silicon surface

NASA Astrophysics Data System (ADS)

Fidélis, A.; Ozanam, F.; Chazalviel, J.-N.

2000-01-01

The atomically flat hydrogenated (111) silicon surface has been methylated by anodization in a Grignard reagent and the surface obtained characterized by infrared spectroscopy. 100% substitution of the hydrogen atoms by methyl groups is observed. The resulting surface exhibits preserved ordering and superior chemical stability.

Hydrogen atoms in protein structures: high-resolution X-ray diffraction structure of the DFPase

PubMed Central

2013-01-01

Background Hydrogen atoms represent about half of the total number of atoms in proteins and are often involved in substrate recognition and catalysis. Unfortunately, X-ray protein crystallography at usual resolution fails to access directly their positioning, mainly because light atoms display weak contributions to diffraction. However, sub-Ångstrom diffraction data, careful modeling and a proper refinement strategy can allow the positioning of a significant part of hydrogen atoms. Results A comprehensive study on the X-ray structure of the diisopropyl-fluorophosphatase (DFPase) was performed, and the hydrogen atoms were modeled, including those of solvent molecules. This model was compared to the available neutron structure of DFPase, and differences in the protein and the active site solvation were noticed. Conclusions A further examination of the DFPase X-ray structure provides substantial evidence about the presence of an activated water molecule that may constitute an interesting piece of information as regard to the enzymatic hydrolysis mechanism. PMID:23915572

First-principles study of hydrogen-bonded molecular conductor κ -H3(Cat-EDT-TTF/ST)2

NASA Astrophysics Data System (ADS)

Tsumuraya, Takao; Seo, Hitoshi; Kato, Reizo; Miyazaki, Tsuyoshi

2015-07-01

We theoretically study hydrogen-bonded molecular conductors synthesized recently, κ -H3(Cat-EDT-TTF) 2 and its diselena analog, κ -H3(Cat-EDT-ST) 2, by first-principles density functional theory calculations. In these crystals, two H(Cat-EDT-TTF/ST) units share a hydrogen atom with a short O-H-O hydrogen bond. The calculated band structure near the Fermi level shows a quasi-two-dimensional character with a rather large interlayer dispersion due to the absence of insulating layers, in contrast with conventional molecular conductors. We discuss effective low-energy models based on H(Cat-EDT-TTF/ST) units and its dimers, respectively, where the microscopic character of the orbitals composing them are analyzed. Furthermore, we find a stable structure which is different from the experimentally determined structure, where the shared hydrogen atom becomes localized to one of the oxygen atoms, in which charge disproportionation between the two types of H(Cat-EDT-TTF) units is associated. The calculated potential energy surface for the H atom is very shallow near the minimum points; therefore the probability of the H atom can be delocalized between the two O atoms.

Theoretical study of optical activity of 1:1 hydrogen bond complexes of water with S-warfarin

NASA Astrophysics Data System (ADS)

Dadsetani, Mehrdad; Abdolmaleki, Ahmad; Zabardasti, Abedin

2016-11-01

The molecular interaction between S-warfarin (SW) and a single water molecule was investigated using the B3LYP method at 6-311 ++G(d,p) basis set. The vibrational spectra of the optimized complexes have been investigated for stabilization checking. Quantum theories of atoms in molecules, natural bond orbitals, molecular electrostatic potentials and energy decomposition analysis methods have been applied to analyze the intermolecular interactions. The intermolecular charge transfer in the most stable complex is in the opposite direction from those in the other complexes. The optical spectra and the hyperpolarizabilities of SW-water hydrogen bond complexes have been computed.

Two-dimensional gold nanostructures with high activity for selective oxidation of carbon–hydrogen bonds

PubMed Central

Wang, Liang; Zhu, Yihan; Wang, Jian-Qiang; Liu, Fudong; Huang, Jianfeng; Meng, Xiangju; Basset, Jean-Marie; Han, Yu; Xiao, Feng-Shou

2015-01-01

Efficient synthesis of stable two-dimensional (2D) noble metal catalysts is a challenging topic. Here we report the facile synthesis of 2D gold nanosheets via a wet chemistry method, by using layered double hydroxide as the template. Detailed characterization with electron microscopy and X-ray photoelectron spectroscopy demonstrates that the nanosheets are negatively charged and [001] oriented with thicknesses varying from single to a few atomic layers. X-ray absorption spectroscopy reveals unusually low gold–gold coordination numbers. These gold nanosheets exhibit high catalytic activity and stability in the solvent-free selective oxidation of carbon–hydrogen bonds with molecular oxygen. PMID:25902034

Two-dimensional gold nanostructures with high activity for selective oxidation of carbon-hydrogen bonds.

PubMed

Wang, Liang; Zhu, Yihan; Wang, Jian-Qiang; Liu, Fudong; Huang, Jianfeng; Meng, Xiangju; Basset, Jean-Marie; Han, Yu; Xiao, Feng-Shou

2015-04-22

Efficient synthesis of stable two-dimensional (2D) noble metal catalysts is a challenging topic. Here we report the facile synthesis of 2D gold nanosheets via a wet chemistry method, by using layered double hydroxide as the template. Detailed characterization with electron microscopy and X-ray photoelectron spectroscopy demonstrates that the nanosheets are negatively charged and [001] oriented with thicknesses varying from single to a few atomic layers. X-ray absorption spectroscopy reveals unusually low gold-gold coordination numbers. These gold nanosheets exhibit high catalytic activity and stability in the solvent-free selective oxidation of carbon-hydrogen bonds with molecular oxygen.

Two-dimensional gold nanostructures with high activity for selective oxidation of carbon-hydrogen bonds

NASA Astrophysics Data System (ADS)

Wang, Liang; Zhu, Yihan; Wang, Jian-Qiang; Liu, Fudong; Huang, Jianfeng; Meng, Xiangju; Basset, Jean-Marie; Han, Yu; Xiao, Feng-Shou

2015-04-01

Efficient synthesis of stable two-dimensional (2D) noble metal catalysts is a challenging topic. Here we report the facile synthesis of 2D gold nanosheets via a wet chemistry method, by using layered double hydroxide as the template. Detailed characterization with electron microscopy and X-ray photoelectron spectroscopy demonstrates that the nanosheets are negatively charged and [001] oriented with thicknesses varying from single to a few atomic layers. X-ray absorption spectroscopy reveals unusually low gold-gold coordination numbers. These gold nanosheets exhibit high catalytic activity and stability in the solvent-free selective oxidation of carbon-hydrogen bonds with molecular oxygen.

Properties of Surface-Modification Layer Generated by Atomic Hydrogen Annealing on Poly(ethylene naphthalate) Substrate

NASA Astrophysics Data System (ADS)

Heya, Akira; Matsuo, Naoto

2008-01-01

The surface of a poly(ethylene naphthalate) (PEN) substrate was modified by atomic hydrogen annealing (AHA). In this method, a PEN substrate was exposed to atomic hydrogen generated by cracking hydrogen molecules on heated tungsten wire. The properties of the surface-modification layer by AHA were evaluated by spectroscopic ellipsometry. It is found that the thickness of the modified layer was 5 nm and that the modification layer has a low refractive index compared with the PEN substrate. The modification layer relates to the reduction reaction of the PEN substrate by AHA.

Development of atomic radical monitoring probe and its application to spatial distribution measurements of H and O atomic radical densities in radical-based plasma processing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takahashi, Shunji; Katagiri Engineering Co., Ltd., 3-5-34 Shitte Tsurumi-ku, Yokohama 230-0003; Takashima, Seigo

2009-09-01

Atomic radicals such as hydrogen (H) and oxygen (O) play important roles in process plasmas. In a previous study, we developed a system for measuring the absolute density of H, O, nitrogen, and carbon atoms in plasmas using vacuum ultraviolet absorption spectroscopy (VUVAS) with a compact light source using an atmospheric pressure microplasma [microdischarge hollow cathode lamp (MHCL)]. In this study, we developed a monitoring probe for atomic radicals employing the VUVAS with the MHCL. The probe size was 2.7 mm in diameter. Using this probe, only a single port needs to be accessed for radical density measurements. We successfullymore » measured the spatial distribution of the absolute densities of H and O atomic radicals in a radical-based plasma processing system by moving the probe along the radial direction of the chamber. This probe allows convenient analysis of atomic radical densities to be carried out for any type of process plasma at any time. We refer to this probe as a ubiquitous monitoring probe for atomic radicals.« less

Hydrogen-induced strain localisation in oxygen-free copper in the initial stage of plastic deformation

NASA Astrophysics Data System (ADS)

Yagodzinskyy, Yuriy; Malitckii, Evgenii; Tuomisto, Filip; Hänninen, Hannu

2018-03-01

Single crystals of oxygen-free copper oriented to easy glide of dislocations were tensile tested in order to study the hydrogen effects on the strain localisation in the form of slip bands appearing on the polished specimen surface under tensile straining. It was found that hydrogen increases the plastic flow stress in Stage I of deformation. The dislocation slip localisation in the form of slip bands was observed and analysed using an online optical monitoring system and atomic force microscopy. The fine structure of the slip bands observed with AFM shows that they consist of a number of dislocation slip offsets which spacing in the presence of hydrogen is markedly reduced as compared to that in the hydrogen-free specimens. The tensile tests and AFM observations were accompanied with positron annihilation lifetime measurements showing that straining of pure copper in the presence of hydrogen results in free volume generation in the form of vacancy complexes. Hydrogen-enhanced free-volume generation is discussed in terms of hydrogen interactions with edge dislocation dipoles forming in double cross-slip of screw dislocations in the initial stage of plastic deformation of pure copper.

Molecular dynamic simulations on TKX-50/RDX cocrystal.

PubMed

Xiong, Shuling; Chen, Shusen; Jin, Shaohua

2017-06-01

Dihydroxylammonium 5,5'-bistetrazole-1,1'-diolate (TKX-50) is a newly synthesized energetic material with excellent comprehensive properties. Cyclotrimethylenetrinitramine (RDX) is currently one of the most widely used energetic materials in the world. TKX-50 and RDX supercell models and TKX-50/RDX cocrystal model were constructed based on their crystal cell parameters and the formation mechanism of cocrystal, respectively, then they were simulated by molecular dynamics (MD) simulations. The maximum trigger bond (NNO 2 ) length(L max ), binding energy (E bind ), radial distribution function (RDF), cohesive energy density(CED) and mechanical properties were simulated at different temperatures based on the simulated equilibrium structures of the models. The simulated results indicate that hydrogen bond and van der Waals force interactions exist in the cocrystal system and the hydrogen bonds are mainly derived from the hydrogen atom of TKX-50 with the oxygen or nitrogen atom of RDX. Moreover, TKX-50/RDX cocrystal structure significantly reduces the sensitivity and improves the thermodynamic stability of RDX, and it also shows better mechanical properties than pure TKX-50 and RDX, indicating that it will vastly expand the application scope of the single compound explosives. Copyright © 2017 Elsevier Inc. All rights reserved.

Using low-field NMR to infer the physical properties of glassy oligosaccharide/water mixtures.

PubMed

Aeberhardt, Kasia; Bui, Quang D; Normand, Valéry

2007-03-01

Low-field NMR (LF-NMR) is usually used as an analytical technique, for instance, to determine water and oil contents. For this application, no attempt is made to understand the physical origin of the data. Here we build a physical model to explain the five fit parameters of the conventional free induction decay (FID) for glassy oligosaccharide/water mixtures. The amplitudes of the signals from low-mobility and high-mobility protons correspond to the density of oligosaccharide protons and water protons, respectively. The relaxation time of the high-mobility protons is described using a statistical model for the probability that oligosaccharide hydroxyl groups form multiple hydrogen bonds. The variation of energy of the hydrogen bond is calculated from the average bond distance and the average angle contribution. Applying the model to experimental data shows that hydrogen atoms screen the water oxygen atoms when two water molecules solvate a single hydroxyl group. Furthermore, the relaxation time of the oligosaccharide protons is independent of its molecular weight and the water content. Finally, inversion of the FID using the inverse Laplace transform gives the continuous spectrum of relaxation times, which is a fingerprint of the oligosaccharide.

Origin and Quenching of Novel ultraviolet and blue emission in NdGaO3: Concept of Super-Hydrogenic Dopants.

PubMed

Ghosh, Siddhartha; Saha, Surajit; Liu, Zhiqi; Motapothula, M; Patra, Abhijeet; Yakovlev, Nikolai; Cai, Yao; Prakash, Saurav; Huang, Xiao Hu; Tay, Chuan Beng; Cong, Chun Xiao; Bhatt, Thirumaleshwara; Dolmanan, Surani B; Chen, Jianqiang; Lü, Weiming; Huang, Zhen; Tripathy, Sudhiranjan; Chua, Soo Jin; Yu, Ting; Asta, Mark; Ariando, A; Venkatesan, T

2016-11-03

In this study we report the existence of novel ultraviolet (UV) and blue emission in rare-earth based perovskite NdGaO 3 (NGO) and the systematic quench of the NGO photoluminescence (PL) by Ce doping. Study of room temperature PL was performed in both single-crystal and polycrystalline NGO (substrates and pellets) respectively. Several NGO pellets were prepared with varying Ce concentration and their room temperature PL was studied using 325 nm laser. It was found that the PL intensity shows a systematic quench with increasing Ce concentration. XPS measurements indicated that nearly 50% of Ce atoms are in the 4+ state. The PL quench was attributed to the novel concept of super hydrogenic dopant (SHD)", where each Ce 4+ ion contributes an electron which forms a super hydrogenic atom with an enhanced Bohr radius, due to the large dielectric constant of the host. Based on the critical Ce concentration for complete quenching this SHD radius was estimated to be within a range of 0.85 nm and 1.15 nm whereas the predicted theoretical value of SHD radius for NdGaO3 is ~1.01 nm.

Crystal structure of tetra­aqua­bis­(pyrimidin-1-ium-4,6-diolato-κO 4)manganese(II)

PubMed Central

Shennara, Khaled A.

2017-01-01

The MnII ion in the structure of the mononuclear title compound, [Mn(C4H3N2O2)2(H2O)4], is situated on an inversion center and is coordinated by two O atoms from two deprotonated 4,6-di­hydroxy­pyrimidine ligands and by four O atoms from water mol­ecules giving rise to a slightly distorted octa­hedral coordination sphere. The complex includes an intra­molecular hydrogen bond between an aqua ligand and the non-protonated N ring atom. The extended structure is stabilized by inter­molecular hydrogen bonds between aqua ligands, by hydrogen bonds between N and O atoms of the ligands of adjacent mol­ecules, and by hydrogen bonds between aqua ligands and the non-coordinating O atom of an adjacent mol­ecule. PMID:28435734

Nitrated metalloporphyrins as catalysts for alkane oxidation

DOEpatents

Ellis, Jr., Paul E.; Lyons, James E.

1992-01-01

Alkanes are oxidized by contact with oxygen-containing gas in the presence as catalyst of a metalloporphyrin in which hydrogen atoms in the porphyrin ring have been replaced with one or more nitro groups. Hydrogen atoms in the porphyrin ring may also be substituted with halogen atoms.

Cyano- and polycyanometalloporphyrins as catalysts for alkane oxidation

DOEpatents

Ellis, Jr., Paul E.; Lyons, James E.

1992-01-01

Alkanes are oxidized by contact with oxygen-containing gas in the presence as catalyst of a metalloporphyrin in which hydrogen atoms in the porphyrin ring have been substituted with one or more cyano groups. Hydrogen atoms in the porphyrin ring may also be substituted with halogen atoms.

Inelastic Transitions in Slow Collisions of Anti-Hydrogen with Hydrogen Atoms

NASA Astrophysics Data System (ADS)

Harrison, Robert; Krstic, Predrag

2007-06-01

We calculate excited adiabatic states and nonadiabatic coupling matrix elements of a quasimolecular system containing hydrogen and anti-hydrogen atoms, for a range of internuclear distances from 0.2 to 20 Bohrs. High accuracy is achieved by exact diagonalization of the molecular Hamiltionian in a large Gaussian basis. Nonadiabatic dynamics was calculated by solving MOCC equations. Positronium states are included in the consideration.

SSME - Materials and Methods for Addressing High-Pressure Hydrogen Embrittlement

NASA Technical Reports Server (NTRS)

Matejczk, Daniel; Russell, Dale; Frandsen, Jon; Swanson, Greg

2010-01-01

From the humid, corrosion-friendly atmosphere of KSC, to the extreme heat of ascent, to the cold vacuum of space, the Space Shuttle faced one hostile environment after another. One of those harsh environments the hydrogen environment existed within the shuttle itself. Liquid hydrogen was the fuel that powered the shuttle s complex, powerful, and reusable main engine. Hydrogen provided the high specific impulse the bang per pound of fuel needed to perform the shuttle s heavy lifting duties. Hydrogen, however, was also a potential threat to the very metal of the propulsion system that used it. The diffusion of hydrogen atoms into a metal can make it more brittle and prone to cracking a process called hydrogen embrittlement. This effect can reduce the toughness of carefully selected and prepared materials. A concern that exposure to hydrogen might encourage crack growth was present from the beginning of the Space Shuttle Program, but the rationale for using hydrogen was compelling. This paper outlines the material characterization, anomaly resolution, and path to understanding of hydrogen embrittlement on superalloys through the course of the SSME program. Specific examples of nickel alloy turbine housings and single crystal turbine blades are addressed. The evolution of fracture mechanics analytical methods is also addressed.

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

PubMed

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

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.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bahar, M. K., E-mail: mussiv58@gmail.com

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 andmore » 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.« less

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bonfanti, Matteo, E-mail: matteo.bonfanti@unimi.it; Jackson, Bret; Hughes, Keith H.

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 theorymore » 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.« less

PHYSICAL MODEL FOR RECOGNITION TUNNELING

PubMed Central

Krstić, Predrag; Ashcroft, Brian; Lindsay, Stuart

2015-01-01

Recognition tunneling (RT) identifies target molecules trapped between tunneling electrodes functionalized with recognition molecules that serve as specific chemical linkages between the metal electrodes and the trapped target molecule. Possible applications include single molecule DNA and protein sequencing. This paper addresses several fundamental aspects of RT by multiscale theory, applying both all-atom and coarse-grained DNA models: (1) We show that the magnitude of the observed currents are consistent with the results of non-equilibrium Green's function calculations carried out on a solvated all-atom model. (2) Brownian fluctuations in hydrogen bond-lengths lead to current spikes that are similar to what is observed experimentally. (3) The frequency characteristics of these fluctuations can be used to identify the trapped molecules with a machine-learning algorithm, giving a theoretical underpinning to this new method of identifying single molecule signals. PMID:25650375

Controlling the surface termination of NdGaO3 (110): the role of the gas atmosphere.

PubMed

Cavallaro, Andrea; Harrington, George F; Skinner, Stephen J; Kilner, John A

2014-07-07

In this work the effect of gas atmosphere on the surface termination reconstruction of single crystal NdGaO3 (110) (NGO) during thermal annealing was analyzed. Using Low Energy Ion Scattering (LEIS) it has been possible to study the chemical composition of the first atomic layer of treated NGO single crystal samples. NGO has been analyzed both as-received and after a specific thermal treatment at 1000 °C under different gas fluxes (argon, nitrogen, static air, synthetic air, nitrogen plus 5% hydrogen and wet synthetic air respectively). Thermal annealing of perovskite single crystals, as already reported in the literature, is used to obtain a fully A-cation surface termination. Nevertheless the effect of the gas-atmosphere on this process has not been previously reported. By the use of sequential low energy Ar(+) sputtering combined with the primary ion LEIS analysis, the reconstruction of the outermost atomic layers has allowed the clarification of the mechanism of NGO neodymium surface enrichment. It is proposed that the gallium at the surface is submitted to a reduction/evaporation mechanism caused by low oxygen partial pressure and/or high water pressure in the vector gas. Below the first surface atomic layers of an as-received NGO single-crystal a gallium-rich phase has also been observed.

A Comprehensive Study of Hydrogen Adsorbing to Amorphous Water ice: Defining Adsorption in Classical Molecular Dynamics

NASA Astrophysics Data System (ADS)

Dupuy, John L.; Lewis, Steven P.; Stancil, P. C.

2016-11-01

Gas-grain and gas-phase reactions dominate the formation of molecules in the interstellar medium (ISM). Gas-grain reactions require a substrate (e.g., a dust or ice grain) on which the reaction is able to occur. The formation of molecular hydrogen (H2) in the ISM is the prototypical example of a gas-grain reaction. In these reactions, an atom of hydrogen will strike a surface, stick to it, and diffuse across it. When it encounters another adsorbed hydrogen atom, the two can react to form molecular hydrogen and then be ejected from the surface by the energy released in the reaction. We perform in-depth classical molecular dynamics simulations of hydrogen atoms interacting with an amorphous water-ice surface. This study focuses on the first step in the formation process; the sticking of the hydrogen atom to the substrate. We find that careful attention must be paid in dealing with the ambiguities in defining a sticking event. The technical definition of a sticking event will affect the computed sticking probabilities and coefficients. Here, using our new definition of a sticking event, we report sticking probabilities and sticking coefficients for nine different incident kinetic energies of hydrogen atoms [5-400 K] across seven different temperatures of dust grains [10-70 K]. We find that probabilities and coefficients vary both as a function of grain temperature and incident kinetic energy over the range of 0.99-0.22.

Molecular structure and conformation of N-2-[3'-(methoxysalicylideneimino)benzyl]-3″-methoxysalicylideneimine

NASA Astrophysics Data System (ADS)

Dey, D. K.; Dey, S. P.; Elmali, A.; Elerman, Y.

2001-05-01

The Schiff base, N-2-[3'-(methoxysalicylideneimino)benzyl]-3″-methoxysalicylidene-imine, 1,2-C 6H 4[NCHC 6H 3(OMe-3')OH-2']CH 2NCHC 6H 3(OMe-3″)OH-2″, has been prepared by the reaction of 2-amino-1-benzylamine and 3-methoxysalicylaldehyde ( o-vanillin) in ethanol. The molecular structure has been confirmed by single crystal X-ray crystallography. The crystal is in the monoclinic space group P2 1/ n with a=16.179(5), b=6.715(5), c=18.780(6) Å, β=100.56(3)°, Dcalc=1.293 mg cm -3, V=2006(2) Å 3 and R=0.0357 for 3929 independent reflections. The 1H and 13C NMR spectra in CDCl 3 solution indicate the retention of solid state structure in solution. The title compound is not planar. Intramolecular hydrogen bonds occur between O(1) and N(1) [2.614(2) Å] and between O(2) and N(2) [2.585(2) Å] atoms, the hydrogen atom essentially being bonded to the oxygen atom. Minimum energy conformations from AM1 were calculated as a function of five torsion angles θ1 (C6-C7-N1-C8), θ2 (C14-N2-C15-C16), θ3 (C9-C8-N1-C7), θ4 (C13-C14-N2-C15) and θ5 (C10-C9-C8-N1), varied every 5°. The optimized geometry of the crystal structure corresponding to the non-planar conformation is the most stable conformation in all calculations. The results strongly indicate that the minimum energy conformation is primarily determined by non-bonded hydrogen-hydrogen repulsions.

Porous graphitic carbon nitride synthesized via direct polymerization of urea for efficient sunlight-driven photocatalytic hydrogen production

NASA Astrophysics Data System (ADS)

Zhang, Yuewei; Liu, Jinghai; Wu, Guan; Chen, Wei

2012-08-01

Energy captured directly from sunlight provides an attractive approach towards fulfilling the need for green energy resources on the terawatt scale with minimal environmental impact. Collecting and storing solar energy into fuel through photocatalyzed water splitting to generate hydrogen in a cost-effective way is desirable. To achieve this goal, low cost and environmentally benign urea was used to synthesize the metal-free photocatalyst graphitic carbon nitride (g-C3N4). A porous structure is achieved via one-step polymerization of the single precursor. The porous structure with increased BET surface area and pore volume shows a much higher hydrogen production rate under simulated sunlight irradiation than thiourea-derived and dicyanamide-derived g-C3N4. The presence of an oxygen atom is presumed to play a key role in adjusting the textural properties. Further improvement of the photocatalytic function can be expected with after-treatment due to its rich chemistry in functionalization.Energy captured directly from sunlight provides an attractive approach towards fulfilling the need for green energy resources on the terawatt scale with minimal environmental impact. Collecting and storing solar energy into fuel through photocatalyzed water splitting to generate hydrogen in a cost-effective way is desirable. To achieve this goal, low cost and environmentally benign urea was used to synthesize the metal-free photocatalyst graphitic carbon nitride (g-C3N4). A porous structure is achieved via one-step polymerization of the single precursor. The porous structure with increased BET surface area and pore volume shows a much higher hydrogen production rate under simulated sunlight irradiation than thiourea-derived and dicyanamide-derived g-C3N4. The presence of an oxygen atom is presumed to play a key role in adjusting the textural properties. Further improvement of the photocatalytic function can be expected with after-treatment due to its rich chemistry in functionalization. Electronic supplementary information (ESI) available: Methods for preparing and characterizing UCN, TCN and DCN samples. Methods for examining the photocatalytic hydrogen production. FTIR, XPS, and digital photos of three products are shown in Fig. S1-6. See DOI: 10.1039/c2nr30948c

Collisional excitation of ArH+ by hydrogen atoms

NASA Astrophysics Data System (ADS)

Dagdigian, Paul J.

2018-06-01

The rotational excitation of the 36ArH+ ion in collisions with hydrogen atoms is investigated in this work. The potential energy surface (PES) describing the 36ArH+-H interaction, with the ion bond length r fixed at the average of r over the radial v = 0 vibrational state distribution, was obtained with a coupled cluster method that included single, double, and (perturbatively) triple excitations [RCCSD(T)]. A deep minimum (De = 3135 cm-1) in the PES was found in linear H-ArH+ geometry at an ion-atom separation Re = 4.80a0. Energy-dependent cross-sections and rate coefficients as a function of temperature for this collision pair were computed in close-coupling (CC) calculations. Since the PES possesses a deep well, this is a good system to test the performance of the quantum statistical (QS) method developed by Manolopoulos and co-workers as a more efficient method to compute the cross-sections. Good agreement was found between rate coefficients obtained by the CC and QS methods at several temperatures. In a simple application, the excitation of ArH+ is simulated for conditions under which this ion is observed in absorption.

Stark effect on an excited hydrogen atom

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barratt, C.

1983-07-01

The method of degenerate perturbation theory is used to study the dipolar nature of an excited hydrogen atom in an external electric field. The dependence of the atoms perturbed energy levels on the principal and magnetic quantum numbers, n and m, is investigated, along with the perturbed wave functions.

Preliminary results for a measurement of the n=2 Lamb shift in atomic hydrogen

NASA Astrophysics Data System (ADS)

Bezginov, N.; Valdez, T.; Vutha, A. C.; Kato, K.; Skinner, T. D. G.; Hessels, E. A.

2017-04-01

We perform a measurement of the Lamb shift in atomic hydrogen (n = 2 S1/2 F = 0 to P1/2 F = 1). A beam of protons moving at 0.01 c undergoes charge exchange with hydrogen gas to produce atomic hydrogen in the metastable 2S state. The atoms travel through two microwave regions where we utilize the novel technique of frequency offset separated oscillatory fields (FOSOF). The surviving 2S population is observed using a Lyman-alpha detector. The outcome of this experiment will lead to a measurement of the proton radius, contributing to the resolution of the proton radius puzzle. We present preliminary experimental results, along with systematic studies. This research is funded by NSERC, CRC, CFI and NIST.

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.

Determination of atomic hydrogen in non-thermal hydrogen plasmas by means of molecular beam threshold ionization mass spectrometry.

PubMed

Wang, Wei-Guo; Xu, Yong; Yang, Xue-Feng; Wang, Wen-Chun; Zhu, Ai-Min

2005-01-01

Atomic hydrogen plays important roles in chemical vapor deposition of functional materials, plasma etching and new approaches to chemical synthesis of hydrogen-containing compounds. The present work reports experimental determinations of atomic hydrogen near the grounded electrode in medium-pressure dielectric barrier discharge hydrogen plasmas by means of molecular beam threshold ionization mass spectrometry (MB-TIMS). At certain discharge conditions (a.c. frequency of 24 kHz, 28 kV of peak-to-peak voltage), the measured hydrogen dissociation fraction is decreased from approximately 0.83% to approximately 0.14% as the hydrogen pressure increases from 2.0 to 14.0 Torr. A simulation method for extraction of the approximate electron beam energy distribution function in the mass spectrometer ionizer and a semi-quantitative approach to calibrate the mass discrimination effect caused by the supersonic beam formation and the mass spectrometer measurement are reported. Copyright 2005 John Wiley & Sons, Ltd.

Causes of High-temperature Superconductivity in the Hydrogen Sulfide Electron-phonon System

NASA Astrophysics Data System (ADS)

Degtyarenko, N. N.; Mazur, E. A.

The electron and phonon spectra, as well as the density of electron and phonon states of the stable orthorhombic structure of hydrogen sulfide (SH2) at pressures 100-180 GPa have been calculated. It is found that the set of parallel planes of hydrogen atoms is formed at pressure ∼175 GPa as a result of structural changes in the unit cell of the crystal under pressure. There should be complete concentration of hydrogen atoms in these planes. As a result the electron properties of the system acquire a quasi-two-dimensional character. The features of in phase and antiphase oscillations of hydrogen atoms in these planes leading to two narrow high-energy peaks in the phonon density of states are investigated.

Reasons for high-temperature superconductivity in the electron-phonon system of hydrogen sulfide

NASA Astrophysics Data System (ADS)

Degtyarenko, N. N.; Mazur, E. A.

2015-08-01

We have calculated the electron and phonon spectra, as well as the densities of the electron and phonon states, of the stable orthorhombic structure of hydrogen sulfide SH2 in the pressure interval 100-180 GPa. It is found that at a pressure of 175 GPa, a set of parallel planes of hydrogen atoms is formed due to a structural modification of the unit cell under pressure with complete accumulation of all hydrogen atoms in these planes. As a result, the electronic properties of the system become quasi-two-dimensional. We have also analyzed the collective synphase and antiphase vibrations of hydrogen atoms in these planes, leading to the occurrence of two high-energy peaks in the phonon density of states.

Derived properties from the dipole and generalized oscillator strength distributions of an endohedral confined hydrogen atom

NASA Astrophysics Data System (ADS)

Martínez-Flores, C.; Cabrera-Trujillo, R.

2018-03-01

We report the electronic properties of a hydrogen atom confined by a fullerene molecule by obtaining the eigenvalues and eigenfunctions of the time-independent Schrödinger equation by means of a finite-differences approach. The hydrogen atom confinement by a C60 fullerene cavity is accounted for by two model potentials: a square-well and a Woods-Saxon. The Woods-Saxon potential is implemented to study the role of a smooth cavity on the hydrogen atom generalized oscillator strength distribution. Both models characterize the cavity by an inner radius R 0, thickness Δ, and well depth V 0. We use two different values for R 0 and Δ, found in the literature, that characterize H@C60 to analyze the role of the fullerene cage size and width. The electronic properties of the confined hydrogen atom are reported as a function of the well depth V 0, emulating different electronic configurations of the endohedral cavity. We report results for the hyper-fine splitting, nuclear magnetic screening, dipole oscillator strength, the static and dynamic polarizability, mean excitation energy, photo-ionization, and stopping cross section for the confined hydrogen atom. We find that there is a critical potential well depth value around V 0 = 0.7 a.u. for the first set of parameters and around V 0 = 0.9 a.u. for the second set of parameters, which produce a drastic change in the electronic properties of the endohedral hydrogen system. These values correspond to the first avoided crossing on the energy levels. Furthermore, a clear discrepancy is found between the square-well and Woods-Saxon model potential results on the hydrogen atom generalized oscillator strength due to the square-well discontinuity. These differences are reflected in the stopping cross section for protons colliding with H@C60.

Theoretical study of negatively charged Fe(-)-(H2O)(n ≤ 6) clusters.

PubMed

Castro, Miguel

2012-06-14

Interactions of a singly negatively charged iron atom with water molecules, Fe(-)-(H(2)O)(n≤6), in the gas phase were studied by means of density functional theory. All-electron calculations were performed using the B3LYP functional and the 6-311++G(2d,2p) basis set for the Fe, O, and H atoms. In the lowest total energy states of Fe(-)-(H(2)O)(n), the metal-hydrogen bonding is stronger than the metal-oxygen one, producing low-symmetry structures because the water molecules are directly attached to the metal by basically one of their hydrogen atoms, whereas the other ones are involved in a network of hydrogen bonds, which together with the Fe(δ-)-H(δ+) bonding accounts for the nascent hydration of the Fe(-) anion. For Fe(-)-(H(2)O)(3≤n), three-, four-, five-, and six-membered rings of water molecules are bonded to the metal, which is located at the surface of the cluster in such a way as to reduce the repulsion with the oxygen atoms. Nevertheless, internal isomers appear also, lying less than 3 or 5 kcal/mol for n = 2-3 or n = 4-6. These results are in contrast with those of classical TM(+)-(H(2)O)(n) complexes, where the direct TM(+)-O bonding usually produces high symmetry structures with the metal defining the center of the complex. They show also that the Fe(-) anions, as the TM(+) ions, have great capability for the adsorption of water molecules, forming Fe(-)-(H(2)O)(n) structures stabilized by Fe(δ-)-H(δ+) and H-bond interactions.

Development of optical diagnostics for performance evaluation of arcjet thrusters

NASA Technical Reports Server (NTRS)

Cappelli, Mark A.

1995-01-01

Laser and optical emission-based measurements have been developed and implemented for use on low-power hydrogen arcjet thrusters and xenon-propelled electric thrusters. In the case of low power hydrogen arcjets, these laser induce fluorescence measurements constitute the first complete set of data that characterize the velocity and temperature field of such a device. The research performed under the auspices of this NASA grant includes laser-based measurements of atomic hydrogen velocity and translational temperature, ultraviolet absorption measurements of ground state atomic hydrogen, Raman scattering measurements of the electronic ground state of molecular hydrogen, and optical emission based measurements of electronically excited atomic hydrogen, electron number density, and electron temperature. In addition, we have developed a collisional-radiative model of atomic hydrogen for use in conjunction with magnetohydrodynamic models to predict the plasma radiative spectrum, and near-electrode plasma models to better understand current transfer from the electrodes to the plasma. In the final year of the grant, a new program aimed at developing diagnostics for xenon plasma thrusters was initiated, and results on the use of diode lasers for interrogating Hall accelerator plasmas has been presented at recent conferences.

Hydrogen bonding in goldichite, KFe(SO4)2ṡ4H2O: structure refinement

NASA Astrophysics Data System (ADS)

Yang, Zhuming; Giester, Gerald

2018-02-01

The crystal structure of goldichite KFe(SO4)2ṡ4H2O was determined on a single crystal from the Baiyinchang copper deposit, Gansu, China. [ P121/ c1, a = 10.395(2), b = 10.475(2), c = 9.0875(18) Å, β = 101.65(3)°, V = 969.1(3) Å3, Z = 4]. All non-H atoms were refined with anisotropic displacement parameters and positions of H-atoms were determined by difference Fourier methods and refined from X-ray diffraction data. The crystal structure of goldichite consists of corrugated sheets parallel to the (100) plane by sharing corners between FeO6 octahedra and SO4 tetrahedra. The interstitial potassium atom exhibits a [KO7(H2O)2] nine-fold coordination, which shares edges to form a column parallel to the c-axis and to build a slab with the corrugated sheet. These slabs are linked in the [100] direction through a network of hydrogen bonds. Three types of hydrogen bonds involve links of slabs: Ow(3)-H(3B)···O(1), Ow(6)-H(6B)···O(11) and Ow(9)-H(9B)···O(11). The FTIR spectrum of goldichite shows a strong absorption between 3384 cm-1 and 3592 cm-1, which is in accordance with the O-H···O distances derived from structure data.

Thermal decomposition of silane to form hydrogenated amorphous Si

DOEpatents

Strongin, M.; Ghosh, A.K.; Wiesmann, H.J.; Rock, E.B.; Lutz, H.A. III

Hydrogenated amorphous silicon is produced by thermally decomposing silane (SiH/sub 4/) or other gases comprising H and Si, at elevated temperatures of about 1700 to 2300/sup 0/C, in a vacuum of about 10/sup -8/ to 10/sup -4/ torr. A gaseous mixture is formed of atomic hydrogen and atomic silicon. The gaseous mixture is deposited onto a substrate to form hydrogenated amorphous silicon.

Surface Engineering of a Supported PdAg Catalyst for Hydrogenation of CO2 to Formic Acid: Elucidating the Active Pd Atoms in Alloy Nanoparticles.

PubMed

Mori, Kohsuke; Sano, Taiki; Kobayashi, Hisayoshi; Yamashita, Hiromi

2018-06-22

The hydrogenation of carbon dioxide (CO 2 ) to formic acid (FA; HCOOH), a renewable hydrogen storage material, is a promising means of realizing an economical CO 2 -mediated hydrogen energy cycle. The development of reliable heter-ogeneous catalysts is an urgent yet challenging task associated with such systems, although precise catalytic site design protocols are still lacking. In the present study, we demonstrate that PdAg alloy nanoparticles (NPs) supported on TiO 2 promote the efficient selective hydrogenation of CO 2 to give FA even under mild reaction conditions (2.0 MPa, 100 °C). Specimens made using surface engineering with atomic precision reveal a strong correlation between increased cata-lytic activity and decreased electron density of active Pd atoms resulting from a synergistic effect of alloying with Ag atoms. The isolated and electronically promoted surface-exposed Pd atoms in Pd@Ag alloy NPs exhibit a maximum turnover number of 14,839 based on the quantity of surface Pd atoms, which represents a more than ten-fold increase compared to the activity of monometallic Pd/TiO 2 . Kinetic and density functional theory (DFT) calculations show that the attack on the C atom in HCO 3 - by a dissociated H atom over an active Pd site is the rate-determining step during this reaction, and this step is boosted by PdAg alloy NPs having a low Pd/Ag ratio.

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.

The hydrogen atom in D = 3 - 2ɛ dimensions

NASA Astrophysics Data System (ADS)

Adkins, Gregory S.

2018-06-01

The nonrelativistic hydrogen atom in D = 3 - 2 ɛ dimensions is the reference system for perturbative schemes used in dimensionally regularized nonrelativistic effective field theories to describe hydrogen-like atoms. Solutions to the D-dimensional Schrödinger-Coulomb equation are given in the form of a double power series. Energies and normalization integrals are obtained numerically and also perturbatively in terms of ɛ. The utility of the series expansion is demonstrated by the calculation of the divergent expectation value <(V‧)2 >.

Comparison of palladium and zirconium treated graphite tubes for in-atomizer trapping of hydrogen selenide in hydride generation electrothermal atomization atomic absorption spectrometry

NASA Astrophysics Data System (ADS)

Laborda, Francisco; Medrano, Jesús; Cortés, José I.; Mir, José M.; Castillo, Juan R.

1999-02-01

Zirconium treated graphite tubes were investigated and compared with non-treated and palladium coated ones for in situ trapping of selenium hydride generated in a flow injection system. Selenium was effectively trapped on zirconium treated tubes at trapping temperatures of 300-600°C, similar to those observed for palladium, whereas trapping temperatures higher than 600°C had to be used with non-treated tubes. Zirconium treated tubes used in this work showed good stability up to 300 trapping/atomization cycles, with precision better than 5%, characteristic masses of 42 (peak height) and 133 pg (peak area) of selenium were obtained. Sensitivity of zirconium and palladium treatments were similar, but zirconium offered the advantage of a single application per tube. Detection limits were 0.11 (peak height) and 0.23 ng (peak area) for a 1 ml sample volume.

Theory of the stopping power of fast multicharged ions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yudin, G.L.

1991-12-01

The processes of Coulomb excitation and ionization of atoms by a fast charged particle moving along a classical trajectory are studied. The target electrons are described by the Dirac equation, while the field of the incident particle is described by the Lienard-Wiechert potential. The theory is formulated in the form most convenient for investigation of various characteristics of semiclassical atomic collisions. The theory of sudden perturbations, which is valid at high enough velocities for a high projectile charge, is employed to obtain probabilities and cross sections of the Coulomb excitation and ionization of atomic hydrogen by fast multiply charged ions.more » Based on the semiclassical sudden Born approximation, the ionization cross section and the average electronic energy loss of a fast ion in a single collision with an atom are investigated over a wide specific energy range from 500 keV/amu to 50 MeV/amu.« less

When hydroquinone meets methoxy radical: Hydrogen abstraction reaction from the viewpoint of interacting quantum atoms.

PubMed

Petković, Milena; Nakarada, Đura; Etinski, Mihajlo

2018-05-25

Interacting Quantum Atoms methodology is used for a detailed analysis of hydrogen abstraction reaction from hydroquinone by methoxy radical. Two pathways are analyzed, which differ in the orientation of the reactants at the corresponding transition states. Although the discrepancy between the two barriers amounts to only 2 kJ/mol, which implies that the two pathways are of comparable probability, the extent of intra-atomic and inter-atomic energy changes differs considerably. We thus demonstrated that Interacting Quantum Atoms procedure can be applied to unravel distinct energy transfer routes in seemingly similar mechanisms. Identification of energy components with the greatest contribution to the variation of the overall energy (intra-atomic and inter-atomic terms that involve hydroquinone's oxygen and the carbon atom covalently bound to it, the transferring hydrogen and methoxy radical's oxygen), is performed using the Relative energy gradient method. Additionally, the Interacting Quantum Fragments approach shed light on the nature of dominant interactions among selected fragments: both Coulomb and exchange-correlation contributions are of comparable importance when considering interactions of the transferring hydrogen atom with all other atoms, whereas the exchange-correlation term dominates interaction between methoxy radical's methyl group and hydroquinone's aromatic ring. This study represents one of the first applications of Interacting Quantum Fragments approach on first order saddle points. © 2018 Wiley Periodicals, Inc. © 2018 Wiley Periodicals, Inc.

Hydrogen-bonding Interactions between Apigenin and Ethanol/Water: A Theoretical Study

NASA Astrophysics Data System (ADS)

Zheng, Yan-Zhen; Zhou, Yu; Liang, Qin; Chen, Da-Fu; Guo, Rui; Lai, Rong-Cai

2016-10-01

In this work, hydrogen-bonding interactions between apigenin and water/ethanol were investigated from a theoretical perspective using quantum chemical calculations. Two conformations of apigenin molecule were considered in this work. The following results were found. (1) For apigenin monomer, the molecular structure is non-planar, and all of the hydrogen and oxygen atoms can be hydrogen-bonding sites. (2) Eight and seven optimized geometries are obtained for apigenin (I)-H2O/CH3CH2OH and apigenin (II)-H2O/CH3CH2OH complexes, respectively. In apigenin, excluding the aromatic hydrogen atoms in the phenyl substituent, all other hydrogen atoms and the oxygen atoms form hydrogen-bonds with H2O and CH3CH2OH. (3) In apigenin-H2O/CH3CH2OH complexes, the electron density and the E(2) in the related localized anti-bonding orbital are increased upon hydrogen-bond formation. These are the cause of the elongation and red-shift of the X-H bond. The sum of the charge change transfers from the hydrogen-bond acceptor to donor. The stronger interaction makes the charge change more intense than in the less stable structures. (4) Most of the hydrogen-bonds in the complexes are electrostatic in nature. However, the C4-O5···H, C9-O4···H and C13-O2···H hydrogen-bonds have some degree of covalent character. Furthermore, the hydroxyl groups of the apigenin molecule are the preferred hydrogen-bonding sites.

Surface Treatment of Plastic Substrates using Atomic Hydrogen Generated on Heated Tungsten Wire at Low Temperatures

NASA Astrophysics Data System (ADS)

Heya, Akira; Matsuo, Naoto

2007-06-01

The surface properties of a plastic substrate were changed by a novel surface treatment called atomic hydrogen annealing (AHA). In this method, a plastic substrate was exposed to atomic hydrogen generated by cracking hydrogen molecules on heated tungsten wire. For the substrate, surface roughness was increased and halogen elements (F and Cl) were selectively etched by AHA. AHA was useful for pretreatment before film deposition on a plastic substrate because the changes in surface state relate to adhesion improvement. It is concluded that this method is a promising technique for preparing high-performance plastic substrates at low temperatures.

Hydrogen bonding between hydrides of the upper-right part of the periodic table

NASA Astrophysics Data System (ADS)

Simončič, Matjaž; Urbic, Tomaz

2018-05-01

One of the most important electrostatic interactions between molecules is most definitely the hydrogen bond. Understanding the basis of this interaction may offer us the insight needed to understand its effect on the macroscopic scale. Hydrogen bonding is for example the reason for anomalous properties in compounds like water and naturally life as we know it. The strength of the bond depends on numerous factors, among them the electronegativity of participating atoms. In this work we calculated the strength of hydrogen bonds between hydrides of the upper-right part of the periodic table (C, N, O, F, P, S, Cl, As, Se, Br) using quantum-chemical methods. The aim was to determine what influences the strength of strong and weak hydrogen bonds in simple hydrides. Various relationships were checked. A relation between the strength of the bond and the electronegativity of the participating atoms was found. We also observed a correlation between the strength of hydrogen bonds and the inter-atomic distances, along with the dependence on the charge transfer on the atom of the donor. We also report characteristic geometries of different dimers.

Studies of EUV contamination mitigation

NASA Astrophysics Data System (ADS)

Graham, Samual, Jr.; Malinowski, Michael E.; Steinhaus, Chip; Grunow, Philip A.; Klebanoff, Leonard E.

2002-07-01

Carbon contamination removal was investigated using remote RF-O2, RF-H2, and atomic hydrogen experiments. Samples consisted of silicon wafers coated with 100 Angstrom sputtered carbon, as well as bare Si-capped Mo/Si optics. Samples were exposed to atomic hydrogen or RF plasma discharges at 100 W, 200 W, and 300 W. Carbon removal rate, optic oxidation rate, at-wavelength (13.4 nm) peak reflectance, and optic surface roughness were characterized. Data show that RF- O2 removes carbon at a rate approximately 6 times faster RF- H2 for a given discharge power. However, both cleaning techniques induce Mo/Si optic degradation through the loss of reflectivity associated with surface oxide growth for RF-O2 and an unknown mechanism with hydrogen cleaning. Atomic hydrogen cleaning shows carbon removal rates sufficient for use as an in-situ cleaning strategy for EUVoptics with less risk of optic degradation from overexposures than RF-discharge cleaning. While hydrogen cleaning (RF and atomic) of EUV optics has proven effective in carbon removal, attempts to dissociate hydrogen in co-exposures with EUV radiation have resulted in no detectable removal of carbon contamination.

Theoretical study on the influence of different para-substituents on 13C NMR of the single carbonyl curcumin analogues

NASA Astrophysics Data System (ADS)

Jia, Fei-yun; Ran, Ming; Zhang, Bo

2015-12-01

The structure of eight kinds of different para-substituents curcumin analogues has been optimized at the level of B3LYP/6-31G( d, p), under which the stability has been verified by means of vibration analysis. Moreover, NMR spectra of curcumin analogues compounds have been studied at the level of B3LYP/6-311G( d, p) by GIAO method. The results show that the structure of eight compounds, a larger conjugated system, has good planarity. The effect of ortho-substituents on bond lengths and bond angles is greater than para and meta. Different substituents and different positions of substituents all have different influence on NMR of the single carbonyl curcumin analogues. In general, after the hydrogen atom on the benzene ring is substituted by other groups, the δ value of α-C changes significantly, the δ value of ortho-carbon atom may also have great change, but the δ value change of meta-carbon atoms is not too obvious. The effect of substituent electronegativity on α-C atoms presents obvious regularity, while the influence of conjugate effect on carbon atoms of benzene ring is more complex. Finally, the bigger substituted alkyl is, the more the δ value of α-C increases.

Hydrogen ADPs with Cu Kα data? Invariom and Hirshfeld atom modelling of fluconazole.

PubMed

Orben, Claudia M; Dittrich, Birger

2014-06-01

For the structure of fluconazole [systematic name: 2-(2,4-difluorophenyl)-1,3-bis(1H-1,2,4-triazol-1-yl)propan-2-ol] monohydrate, C13H12F2N6O·H2O, a case study on different model refinements is reported, based on single-crystal X-ray diffraction data measured at 100 K with Cu Kα radiation to a resolution of sin θ/λ of 0.6 Å(-1). The structure, anisotropic displacement parameters (ADPs) and figures of merit from the independent atom model are compared to `invariom' and `Hirshfeld atom' refinements. Changing from a spherical to an aspherical atom model lowers the figures of merit and improves both the accuracy and the precision of the geometrical parameters. Differences between results from the two aspherical-atom refinements are small. However, a refinement of ADPs for H atoms is only possible with the Hirshfeld atom density model. It gives meaningful results even at a resolution of 0.6 Å(-1), but requires good low-order data.

Measurement of the Lamb shift in the hydrogen atom (n = 2)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sokolov, Y.L.; Yakovlev, V.P.

1982-07-01

A principle is proposed for the observation of the stationary interference pattern of two phase-shifted components of the 2p (or 2s) state of the hydrogen atom (Yu. L. Sokolov, Sov. Phys. JETP 36, 243 (1973)); (Proc. 6-th Internat. Conf. on Atomic Phys., Riga, 1978, p. 207). An atomic interferometer, a device analogous in principle to a two-channel optical (such as Michelson's) interferometer, is used to measure the frequency of the (2s/sub 1/2/, F = 0)--(2p/sub 1/2/, F = 0) transition in the hydrogen atom, which is found to equal 909.9014 +- 0.0019 MHz. The corresponding Lamb shift is delta(H, nmore » = 2) = 1057.8594 +- 0.0019 MHz.« less

Aqueous proton transfer across single-layer graphene

DOE PAGES

Achtyl, Jennifer L.; Unocic, Raymond R.; Xu, Lijun; ...

2015-03-17

Proton transfer across single-layer graphene proceeds with large computed energy barriers and is thought to be unfavourable at room temperature unless nanoscale holes or dopants are introduced, or a potential bias is applied. Here we subject single-layer graphene supported on fused ​silica to cycles of high and low pH, and show that protons transfer reversibly from the aqueous phase through the graphene to the other side where they undergo acid–base chemistry with the silica hydroxyl groups. After ruling out diffusion through macroscopic pinholes, the protons are found to transfer through rare, naturally occurring atomic defects. Computer simulations reveal low energymore » barriers of 0.61–0.75 eV for aqueous proton transfer across hydroxyl-terminated atomic defects that participate in a Grotthuss-type relay, while ​pyrylium-like ether terminations shut down proton exchange. In conclusion, unfavourable energy barriers to helium and ​hydrogen transfer indicate the process is selective for aqueous protons.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sung, Z. -H.; Wang, M.; Polyanskii, A. A.

This study shows that low angle grain boundaries (LAGBs) can be created by small 5% strains in high purity (RRR ≥ 200) SRF-grade single crystalline niobium (Nb) and that these boundaries act as hydrogen traps as indicated by the distribution of niobium hydrides (Nb 1-xH x). Nb 1-xH x is detrimental to superconducting radio frequency (SRF) Nb cavities due to its normal conducting properties at cavity operating temperatures. By designing a single crystal tensile sample extracted from a large grain (>5 cm) Nb ingot slice for preferred slip on one slip plane, LAGBs and dense dislocation boundaries developed. With chemicalmore » surface treatments following standard SRF cavity fabrication practice, Nb1-xHx phases were densely precipitated at the LAGBs upon cryogenic cooling (8-10 K/min). Micro-crystallographic analysis confirmed heterogeneous hydride precipitation, which included significant hydrogen atom accumulation in LAGBs. Magneto-optical imaging (MOI) analysis showed that these sites can then act as sites for both premature flux penetration and eventually flux trapping. However, this hydrogen related degradation at LAGBs did not completely disappear even after a 800 °C/2hrs anneal typically used for hydrogen removal in SRF Nb cavities. These findings suggest that hydride precipitation at a LAGB is facilitated by a non-equilibrium concentration of vacancy-hydrogen (H) complexes aided by mechanical deformation and the hydride phase interferes with the recovery process under 800°C annealing.« less

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.

Photoredox-catalyzed deuteration and tritiation of pharmaceutical compounds

PubMed Central

Loh, Yong Yao; Nagao, Kazunori; Hoover, Andrew J.; Hesk, David; Rivera, Nelo R.; Colletti, Steven L.; Davies, Ian W.; MacMillan, David W. C.

2018-01-01

Deuterium- and tritium-labeled pharmaceutical compounds are pivotal diagnostic tools in drug discovery research, providing vital information about the biological fate of drugs and drug metabolites. Herein we demonstrate that a photoredox-mediated hydrogen atom transfer protocol can efficiently and selectively install deuterium (D) and tritium (T) at α-amino sp3 carbon-hydrogen bonds in a single step, using isotopically labeled water (D2O or T2O) as the source of hydrogen isotope. In this context, we also report a convenient synthesis of T2O from T2, providing access to high-specific-activity T2O. This protocol has been successfully applied to the high incorporation of deuterium and tritium in 18 drug molecules, which meet the requirements for use in ligand-binding assays and absorption, distribution, metabolism, and excretion studies. PMID:29123019

Molecular dynamics simulations of fluid methane properties using ab initio intermolecular interaction potentials.

PubMed

Chao, Shih-Wei; Li, Arvin Huang-Te; Chao, Sheng D

2009-09-01

Intermolecular interaction energy data for the methane dimer have been calculated at a spectroscopic accuracy and employed to construct an ab initio potential energy surface (PES) for molecular dynamics (MD) simulations of fluid methane properties. The full potential curves of the methane dimer at 12 symmetric conformations were calculated by the supermolecule counterpoise-corrected second-order Møller-Plesset (MP2) perturbation theory. Single-point coupled cluster with single and double and perturbative triple excitations [CCSD(T)] calculations were also carried out to calibrate the MP2 potentials. We employed Pople's medium size basis sets [up to 6-311++G(3df, 3pd)] and Dunning's correlation consistent basis sets (cc-pVXZ and aug-cc-pVXZ, X = D, T, Q). For each conformer, the intermolecular carbon-carbon separation was sampled in a step 0.1 A for a range of 3-9 A, resulting in a total of 732 configuration points calculated. The MP2 binding curves display significant anisotropy with respect to the relative orientations of the dimer. The potential curves at the complete basis set (CBS) limit were estimated using well-established analytical extrapolation schemes. A 4-site potential model with sites located at the hydrogen atoms was used to fit the ab initio potential data. This model stems from a hydrogen-hydrogen repulsion mechanism to explain the stability of the dimer structure. MD simulations using the ab initio PES show quantitative agreements on both the atom-wise radial distribution functions and the self-diffusion coefficients over a wide range of experimental conditions. Copyright 2008 Wiley Periodicals, Inc.

Quantum Monte Carlo study of the phase diagram of solid molecular hydrogen at extreme pressures

PubMed Central

Drummond, N. D.; Monserrat, Bartomeu; Lloyd-Williams, Jonathan H.; Ríos, P. López; Pickard, Chris J.; Needs, R. J.

2015-01-01

Establishing the phase diagram of hydrogen is a major challenge for experimental and theoretical physics. Experiment alone cannot establish the atomic structure of solid hydrogen at high pressure, because hydrogen scatters X-rays only weakly. Instead, our understanding of the atomic structure is largely based on density functional theory (DFT). By comparing Raman spectra for low-energy structures found in DFT searches with experimental spectra, candidate atomic structures have been identified for each experimentally observed phase. Unfortunately, DFT predicts a metallic structure to be energetically favoured at a broad range of pressures up to 400 GPa, where it is known experimentally that hydrogen is non-metallic. Here we show that more advanced theoretical methods (diffusion quantum Monte Carlo calculations) find the metallic structure to be uncompetitive, and predict a phase diagram in reasonable agreement with experiment. This greatly strengthens the claim that the candidate atomic structures accurately model the experimentally observed phases. PMID:26215251

Concentration of atomic hydrogen in a dielectric barrier discharge measured by two-photon absorption fluorescence

NASA Astrophysics Data System (ADS)

Dvořák, P.; Talába, M.; Obrusník, A.; Kratzer, J.; Dědina, J.

2017-08-01

Two-photon absorption laser-induced fluorescence (TALIF) was utilized for measuring the concentration of atomic hydrogen in a volume dielectric barrier discharge (DBD) ignited in mixtures of Ar, H2 and O2 at atmospheric pressure. The method was calibrated by TALIF of krypton diluted in argon at atmospheric pressure, proving that three-body collisions had a negligible effect on quenching of excited krypton atoms. The diagnostic study was complemented with a 3D numerical model of the gas flow and a zero-dimensional model of the chemistry in order to better understand the reaction kinetics and identify the key pathways leading to the production and destruction of atomic hydrogen. It was determined that the density of atomic hydrogen in Ar-H2 mixtures was in the order of 1021 m-3 and decreased when oxygen was added into the gas mixture. Spatially resolved measurements and simulations revealed a sharply bordered region with low atomic hydrogen concentration when oxygen was added to the gas mixture. At substoichiometric oxygen/hydrogen ratios, this H-poor region is confined to an area close to the gas inlet and it is shown that the size of this region is not only influenced by the chemistry but also by the gas flow patterns. Experimentally, it was observed that a decrease in H2 concentration in the feeding Ar-H2 mixture led to an increase in H production in the DBD.

The quantization of the atom in three acts

NASA Astrophysics Data System (ADS)

Ridgen, J. S.

2001-01-01

The challenge that faced physicists soon after the discovery of the quantum in 1900 was to determine the structure of the atom. Success came through the application of quantum ideas to this challenge. The focus of these efforts was the hydrogen atom. Three very different approaches led to the successful explanation of the Balmer series of hydrogen and, in the process, the foundation for atomic and molecular physics was established.

Palladium-Catalyzed Atom-Transfer Radical Cyclization at Remote Unactivated C(sp3 )-H Sites: Hydrogen-Atom Transfer of Hybrid Vinyl Palladium Radical Intermediates.

PubMed

Ratushnyy, Maxim; Parasram, Marvin; Wang, Yang; Gevorgyan, Vladimir

2018-03-01

A novel mild, visible-light-induced palladium-catalyzed hydrogen atom translocation/atom-transfer radical cyclization (HAT/ATRC) cascade has been developed. This protocol involves a 1,5-HAT process of previously unknown hybrid vinyl palladium radical intermediates, thus leading to iodomethyl carbo- and heterocyclic structures. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

LOX/Hydrogen Coaxial Injector Atomization Test Program

NASA Technical Reports Server (NTRS)

Zaller, M.

1990-01-01

Quantitative information about the atomization of injector sprays is needed to improve the accuracy of computational models that predict the performance and stability margin of liquid propellant rocket engines. To obtain this data, a facility for the study of spray atomization is being established at NASA-Lewis to determine the drop size and velocity distributions occurring in vaporizing liquid sprays at supercritical pressures. Hardware configuration and test conditions are selected to make the cold flow simulant testing correspond as closely as possible to conditions in liquid oxygen (LOX)/gaseous H2 rocket engines. Drop size correlations from the literature, developed for liquid/gas coaxial injector geometries, are used to make drop size predictions for LOX/H2 coaxial injectors. The mean drop size predictions for a single element coaxial injector range from 0.1 to 2000 microns, emphasizing the need for additional studies of the atomization process in LOX/H2 engines. Selection of cold flow simulants, measured techniques, and hardware for LOX/H2 atomization simulations are discussed.

Higher order Stark effect and transition probabilities on hyperfine structure components of hydrogen like atoms

NASA Astrophysics Data System (ADS)

Pal'Chikov, V. G.

2000-08-01

A quantum-electrodynamical (QED) perturbation theory is developed for hydrogen and hydrogen-like atomic systems with interaction between bound electrons and radiative field being treated as the perturbation. The dependence of the perturbed energy of levels on hyperfine structure (hfs) effects and on the higher-order Stark effect is investigated. Numerical results have been obtained for the transition probability between the hfs components of hydrogen-like bismuth.

Rotational excitation of hydrogen molecules by collisions with hydrogen atoms. [interstellar gas energetics

NASA Technical Reports Server (NTRS)

Green, S.; Truhlar, D. G.

1979-01-01

Rate constants for rotational excitation of hydrogen molecules by collisions with hydrogen atoms have been obtained from quantum-mechanical calculations for kinetic temperatures between 100 and 5000 K. These calculations involve the rigid-rotator approximation, but other possible sources of error should be small. The calculations indicate that the early values of Nishimura are larger than accurate rigid-rotator values by about a factor of 20 or more.

Low-temperature Condensation of Carbon

NASA Astrophysics Data System (ADS)

Krasnokutski, S. A.; Goulart, M.; Gordon, E. B.; Ritsch, A.; Jäger, C.; Rastogi, M.; Salvenmoser, W.; Henning, Th.; Scheier, P.

2017-10-01

Two different types of experiments were performed. In the first experiment, we studied the low-temperature condensation of vaporized graphite inside bulk liquid helium, while in the second experiment, we studied the condensation of single carbon atoms together with H2, H2O, and CO molecules inside helium nanodroplets. The condensation of vaporized graphite leads to the formation of partially graphitized carbon, which indicates high temperatures, supposedly higher than 1000°C, during condensation. Possible underlying processes responsible for the instant rise in temperature during condensation are discussed. This suggests that such processes cause the presence of partially graphitized carbon dust formed by low-temperature condensation in the diffuse interstellar medium. Alternatively, in the denser regions of the ISM, the condensation of carbon atoms together with the most abundant interstellar molecules (H2, H2O, and CO), leads to the formation of complex organic molecules (COMs) and finally organic polymers. Water molecules were found not to be involved directly in the reaction network leading to the formation of COMs. It was proposed that COMs are formed via the addition of carbon atoms to H2 and CO molecules ({{C}}+{{{H}}}2\\to {HCH},{HCH}+{CO}\\to {{OCCH}}2). Due to the involvement of molecular hydrogen, the formation of COMs by carbon addition reactions should be more efficient at high extinctions compared with the previously proposed reaction scheme with atomic hydrogen.

Direct observation of individual hydrogen atoms at trapping sites in a ferritic steel

NASA Astrophysics Data System (ADS)

Chen, Y.-S.; Haley, D.; Gerstl, S. S. A.; London, A. J.; Sweeney, F.; Wepf, R. A.; Rainforth, W. M.; Bagot, P. A. J.; Moody, M. P.

2017-03-01

The design of atomic-scale microstructural traps to limit the diffusion of hydrogen is one key strategy in the development of hydrogen-embrittlement-resistant materials. In the case of bearing steels, an effective trapping mechanism may be the incorporation of finely dispersed V-Mo-Nb carbides in a ferrite matrix. First, we charged a ferritic steel with deuterium by means of electrolytic loading to achieve a high hydrogen concentration. We then immobilized it in the microstructure with a cryogenic transfer protocol before atom probe tomography (APT) analysis. Using APT, we show trapping of hydrogen within the core of these carbides with quantitative composition profiles. Furthermore, with this method the experiment can be feasibly replicated in any APT-equipped laboratory by using a simple cold chain.

Fe Isolated Single Atoms on S, N Codoped Carbon by Copolymer Pyrolysis Strategy for Highly Efficient Oxygen Reduction Reaction.

PubMed

Li, Qiheng; Chen, Wenxing; Xiao, Hai; Gong, Yue; Li, Zhi; Zheng, Lirong; Zheng, Xusheng; Yan, Wensheng; Cheong, Weng-Chon; Shen, Rongan; Fu, Ninghua; Gu, Lin; Zhuang, Zhongbin; Chen, Chen; Wang, Dingsheng; Peng, Qing; Li, Jun; Li, Yadong

2018-06-01

Heteroatom-doped Fe-NC catalyst has emerged as one of the most promising candidates to replace noble metal-based catalysts for highly efficient oxygen reduction reaction (ORR). However, delicate controls over their structure parameters to optimize the catalytic efficiency and molecular-level understandings of the catalytic mechanism are still challenging. Herein, a novel pyrrole-thiophene copolymer pyrolysis strategy to synthesize Fe-isolated single atoms on sulfur and nitrogen-codoped carbon (Fe-ISA/SNC) with controllable S, N doping is rationally designed. The catalytic efficiency of Fe-ISA/SNC shows a volcano-type curve with the increase of sulfur doping. The optimized Fe-ISA/SNC exhibits a half-wave potential of 0.896 V (vs reversible hydrogen electrode (RHE)), which is more positive than those of Fe-isolated single atoms on nitrogen codoped carbon (Fe-ISA/NC, 0.839 V), commercial Pt/C (0.841 V), and most reported nonprecious metal catalysts. Fe-ISA/SNC is methanol tolerable and shows negligible activity decay in alkaline condition during 15 000 voltage cycles. X-ray absorption fine structure analysis and density functional theory calculations reveal that the incorporated sulfur engineers the charges on N atoms surrounding the Fe reactive center. The enriched charge facilitates the rate-limiting reductive release of OH* and therefore improved the overall ORR efficiency. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Single-crystal growth, structure refinement and the properties of Bis(glycine) Strontium Chloride

NASA Astrophysics Data System (ADS)

Balaji, S. R.; Balu, T.; Rajasekaran, T. R.

2018-02-01

Single crystals of Bis (glycine) Strontium Chloride (BGSC) were grown by means of slow evaporation process by using analar grade Glycine and Strontium Chloride Hexahydrate as a parent compound from its aqueous solution at room temperature. The final chemical composition, [{{Sr}}{({{{C}}}2{{{H}}}5{{{NO}}}2)}2{{{Cl}}}2].{{{H}}}4{{{O}}}3+{{{H}}}8{{{O}}}3, formed were metallic light colorless block, about the size of 28 mm × 9 mm × 8 mm. A single-crystal x-ray diffraction study revealed an ordered superstructure with orthorhombic symmetry that could be assigned to the space group Pbcn. The structure in BGSC, revealed in the electron density distribution was analyzed by the direct methods (SHELXS-2014) and refined by least squares full matrix method (SHELXL-2014). The crystal structure, including anisotropic atomic displacement parameters for each atom and isotropic atomic displacement parameters for hydrogen atom, was refined to R1 = 0.0395, wR2 = 0.0776 using 1097 independent reflections. The FTIR spectrum of BGSC confirms the protonation of amino groups and the different molecular groups present in BGSC vibrate in different modes. Reverse Indentation Size Effect (RISE) was revealed in BGSC in the micro-hardness analysis using Vicker’s micro-hardness analysis. DTA and DSC results ruled out the possibility of structural change independent of mass change. The AFM studies shows fine nano size fiber like structure of the grown crystals.

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.

Comparative structural and electronic studies of hydrogen interaction with isolated versus ordered silicon nanoribbons grown on Ag(110)

NASA Astrophysics Data System (ADS)

Dávila, M. E.; Marele, A.; De Padova, P.; Montero, I.; Hennies, F.; Pietzsch, A.; Shariati, M. N.; Gómez-Rodríguez, J. M.; Le Lay, G.

2012-09-01

We have investigated the geometry and electronic structure of two different types of self-aligned silicon nanoribbons (SiNRs), forming either isolated SiNRs or a self-assembled 5 × 2/5 × 4 grating on an Ag(110) substrate, by scanning tunnelling microscopy and high resolution x-ray photoelectron spectroscopy. At room temperature we further adsorb on these SiNRs either atomic or molecular hydrogen. The hydrogen absorption process and hydrogenation mechanism are similar for isolated or 5 × 2/5 × 4 ordered SiNRs and are not site selective; the main difference arises from the fact that the isolated SiNRs are more easily attacked and destroyed faster. In fact, atomic hydrogen strongly interacts with any Si atoms, modifying their structural and electronic properties, while molecular hydrogen has first to dissociate. Hydrogen finally etches the Si nanoribbons and their complete removal from the Ag(110) surface could eventually be expected.

Effect of Doping on Hydrogen Evolution Reaction of Vanadium Disulfide Monolayer.

PubMed

Qu, Yuanju; Pan, Hui; Kwok, Chi Tat; Wang, Zisheng

2015-12-01

As cheap and abundant materials, transitional metal dichalcogenide monolayers have attracted increasing interests for their application as catalysts in hydrogen production. In this work, the hydrogen evolution reduction of doped vanadium disulfide monolayers is investigated based on first-principles calculations. We find that the doping elements and concentration affect strongly the catalytic ability of the monolayer. We show that Ti-doping can efficiently reduce the Gibbs free energy of hydrogen adsorption in a wide range of hydrogen coverage. The catalytic ability of the monolayer at high hydrogen coverage can be improved by low Ti-density doping, while that at low hydrogen coverage is enhanced by moderate Ti-density doping. We further show that it is much easier to substitute the Ti atom to the V atom in the vanadium disulfide (VS2) monolayer than other transitional metal atoms considered here due to its lowest and negative formation energy. It is expected that the Ti-doped VS2 monolayer may be applicable in water electrolysis with improved efficiency.

Deciphering the "chemical" nature of the exotic isotopes of hydrogen by the MC-QTAIM analysis: the positively charged muon and the muonic helium as new members of the periodic table.

PubMed

Goli, Mohammad; Shahbazian, Shant

2014-04-14

This report is a primarily survey on the chemical nature of some exotic species containing the positively charged muon and the muonic helium, i.e., the negatively charged muon plus helium nucleus, as exotic isotopes of hydrogen, using the newly developed multi-component quantum theory of atoms in molecules (MC-QTAIM) analysis, employing ab initio non-Born-Oppenhiemer wavefunctions. Accordingly, the "atoms in molecules" analysis performed on various asymmetric exotic isotopomers of the hydrogen molecule, recently detected experimentally [Science, 2011, 331, 448], demonstrates that both the exotic isotopes are capable of forming atoms in molecules and retaining the identity of hydrogen atoms. Various derived properties of atomic basins containing the muonic helium cast no doubt that apart from its short life time, it is a heavier isotope of hydrogen while the properties of basins containing the positively charged muon are more remote from those of the orthodox hydrogen basins, capable of appreciable donation of electrons as well as large charge polarization. However, with some tolerance, they may also be categorized as hydrogen basins though with a smaller electronegativity. All in all, the present study also clearly demonstrates that the MC-QTAIM analysis is an efficient approach to decipher the chemical nature of species containing exotic constituents, which are difficult to elucidate by experimental and/or alternative theoretical schemes.

Hydrogen molecules and hydrogen-related defects in crystalline silicon

NASA Astrophysics Data System (ADS)

Fukata, N.; Sasaki, S.; Murakami, K.; Ishioka, K.; Nakamura, K. G.; Kitajima, M.; Fujimura, S.; Kikuchi, J.; Haneda, H.

1997-09-01

We have found that hydrogen exists in molecular form in crystalline silicon treated with hydrogen atoms in the downstream of a hydrogen plasma. The vibrational Raman line of hydrogen molecules is observed at 4158 cm-1 for silicon samples hydrogenated between 180 and 500 °C. The assignment of the Raman line is confirmed by its isotope shift to 2990 cm-1 for silicon treated with deuterium atoms. The Raman intensity has a maximum for hydrogenation at 400 °C. The vibrational Raman line of the hydrogen molecules is broad and asymmetric. It consists of at least two components, possibly arising from hydrogen molecules in different occupation sites in crystalline silicon. The rotational Raman line of hydrogen molecules is observed at 590 cm-1. The Raman band of Si-H stretching is observed for hydrogenation temperatures between 100 and 500 °C and the intensity has a maximum for hydrogenation at 250 °C.

Hydrogens detected by subatomic resolution protein crystallography in a [NiFe] hydrogenase.

PubMed

Ogata, Hideaki; Nishikawa, Koji; Lubitz, Wolfgang

2015-04-23

The enzyme hydrogenase reversibly converts dihydrogen to protons and electrons at a metal catalyst. The location of the abundant hydrogens is of key importance for understanding structure and function of the protein. However, in protein X-ray crystallography the detection of hydrogen atoms is one of the major problems, since they display only weak contributions to diffraction and the quality of the single crystals is often insufficient to obtain sub-ångström resolution. Here we report the crystal structure of a standard [NiFe] hydrogenase (∼91.3 kDa molecular mass) at 0.89 Å resolution. The strictly anoxically isolated hydrogenase has been obtained in a specific spectroscopic state, the active reduced Ni-R (subform Ni-R1) state. The high resolution, proper refinement strategy and careful modelling allow the positioning of a large part of the hydrogen atoms in the structure. This has led to the direct detection of the products of the heterolytic splitting of dihydrogen into a hydride (H(-)) bridging the Ni and Fe and a proton (H(+)) attached to the sulphur of a cysteine ligand. The Ni-H(-) and Fe-H(-) bond lengths are 1.58 Å and 1.78Å, respectively. Furthermore, we can assign the Fe-CO and Fe-CN(-) ligands at the active site, and can obtain the hydrogen-bond networks and the preferred proton transfer pathway in the hydrogenase. Our results demonstrate the precise comprehensive information available from ultra-high-resolution structures of proteins as an alternative to neutron diffraction and other methods such as NMR structural analysis.

United polarizable multipole water model for molecular mechanics simulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qi, Rui; Wang, Qiantao; Ren, Pengyu, E-mail: pren@mail.utexas.edu

2015-07-07

We report the development of a united AMOEBA (uAMOEBA) polarizable water model, which is computationally 3–5 times more efficient than the three-site AMOEBA03 model in molecular dynamics simulations while providing comparable accuracy for gas-phase and liquid properties. In this coarse-grained polarizable water model, both electrostatic (permanent and induced) and van der Waals representations have been reduced to a single site located at the oxygen atom. The permanent charge distribution is described via the molecular dipole and quadrupole moments and the many-body polarization via an isotropic molecular polarizability, all located at the oxygen center. Similarly, a single van der Waals interactionmore » site is used for each water molecule. Hydrogen atoms are retained only for the purpose of defining local frames for the molecular multipole moments and intramolecular vibrational modes. The parameters have been derived based on a combination of ab initio quantum mechanical and experimental data set containing gas-phase cluster structures and energies, and liquid thermodynamic properties. For validation, additional properties including dimer interaction energy, liquid structures, self-diffusion coefficient, and shear viscosity have been evaluated. The results demonstrate good transferability from the gas to the liquid phase over a wide range of temperatures, and from nonpolar to polar environments, due to the presence of molecular polarizability. The water coordination, hydrogen-bonding structure, and dynamic properties given by uAMOEBA are similar to those derived from the all-atom AMOEBA03 model and experiments. Thus, the current model is an accurate and efficient alternative for modeling water.« less

Atom Probe Analysis of Ex Situ Gas-Charged Stable Hydrides.

PubMed

Haley, Daniel; Bagot, Paul A J; Moody, Michael P

2017-04-01

In this work, we report on the atom probe tomography analysis of two metallic hydrides formed by pressurized charging using an ex situ hydrogen charging cell, in the pressure range of 200-500 kPa (2-5 bar). Specifically we report on the deuterium charging of Pd/Rh and V systems. Using this ex situ system, we demonstrate the successful loading and subsequent atom probe analysis of deuterium within a Pd/Rh alloy, and demonstrate that deuterium is likely present within the oxide-metal interface of a native oxide formed on vanadium. Through these experiments, we demonstrate the feasibility of ex situ hydrogen analysis for hydrides via atom probe tomography, and thus a practical route to three-dimensional imaging of hydrogen in hydrides at the atomic scale.

Single crystal neutron diffraction of hydrous wadsleyite and the reason of sensitivity difference for hydration between upper and lower mantle transition zones

NASA Astrophysics Data System (ADS)

Purevjav, N.; Okuchi, T.; Tomioka, N.; Wang, X.; Hoffmann, C.

2016-12-01

Evidences from seismological and mineralogical studies increasingly indicates that water has been transported from the oceans into the Earth's deep mantle, where the mantle transition zone is believed to be the largest reservoir of this transported water. Wadsleyite and ringwoodite are the major constituents and the most important host minerals absorbing this type of water in the transition zone. These minerals are capable of storing the entire mass of the oceans as a hidden reservoirs. In order to understand the effects of such water on the physical properties and chemical evolution of the Earth's interior, it is essential to determine where in the crystal structure the hydration occurs, and which chemical bonds are altered and weakened after hydration. Here we show the result of a neutron single-crystal Laue diffraction study of hydrous wadsleyite. A crystal of homogenously-hydrated wadsleyite involving 1.4 wt. % of H2O was synthesized by our recently-established slow cooling method, which was an effective way to grow high quality large single crystals [1]. By analyzing this crystal using pulsed neutron beam, we demonstrated that the hydrogen atoms exchange only with Mg2+ at the one of the specific octahedron sites (M3) in wadsleyite. We also determined hydrogen's bonding distances and bonding angle. The results unambiguously demonstrated the unique mechanism of hydrogen incorporation into the wadsleyite crystal structure. We previously found that the hydrogen atoms exchanged with both Mg2+ and Si4+ sites simultaneously in the crystal structure of hydrous ringwoodite [2]. Therefore, the current results show that hydration mechanisms are qualitatively different between the upper and the lower transition zones in the wet mantle. The difference is a vital clue towards understanding why these mantle transition zone minerals show different sensitivity for water in their softening behaviors. In addition, we demonstrated that maximum water concentration in wadsleyite is strictly constrained by its full capacity into M3 site. Also, by this study we demonstrated that single-crystal neutron diffraction is a useful tool for quantitative analysis of H2O concentrations in nominally anhydrous minerals. [1] Okuchi et al., Amer. Miner., 2015; [2] Purevjav et al., Geophys. Res. Lett., 2014.

Electronic and optical properties of hydrogenated silicon carbide nanosheets: A DFT study

NASA Astrophysics Data System (ADS)

Delavari, Najmeh; Jafari, Mahmoud

2018-07-01

Density-functional theory has been applied to investigate the effect of hydrogen adsorption on silicon carbide (SiC) nanosheets, considering six, different configurations for adsorption process. The chair-like configuration is found to be the most stable because of the adsorption of hydrogen atoms by silicon and carbon atoms on the opposite sides. The pure and hydrogenated SiC monolayers are also found to be sp2- and sp3-hybridized, respectively. The binding energy of the hydrogen atoms in the chair-like structure is calculated about -3.845 eV, implying the system to be much more stable than the same study based on graphene, though with nearly the same electronic properties, strongly proposing the SiC monolayer to be a promising material for next generation hydrogen storage. Optical properties presented in terms of the real and the imaginary parts of the dielectric function also demonstrate a decrease in the dielectric constant and the static refractive index due to hydrogen adsorption with the Plasmon frequency of the chair-like, hydrogenated monolayer, occurring at higher energies compared to that of the pure one.

Electrochemically assisted localized etching of ZnO single crystals in water using a catalytically active Pt-coated atomic force microscopy probe

NASA Astrophysics Data System (ADS)

Shibata, Takayuki; Yamamoto, Kota; Sasano, Junji; Nagai, Moeto

2017-09-01

This paper presents a nanofabrication technique based on the electrochemically assisted chemical dissolution of zinc oxide (ZnO) single crystals in water at room temperature using a catalytically active Pt-coated atomic force microscopy (AFM) probe. Fabricated grooves featured depths and widths of several tens and several hundreds of nanometers, respectively. The material removal rate of ZnO was dramatically improved by controlling the formation of hydrogen ions (H+) on the surface of the catalytic Pt-coated probe via oxidation of H2O molecules; this reaction can be enhanced by applying a cathodic potential to an additional Pt-wire working electrode in a three-electrode configuration. Consequently, ZnO can be dissolved chemically in water as a soluble Zn2+ species via a reaction with H+ species present in high concentrations in the immediate vicinity of the AFM tip apex.

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.

The Rydberg constant and proton size from atomic hydrogen

NASA Astrophysics Data System (ADS)

Beyer, Axel; Maisenbacher, Lothar; Matveev, Arthur; Pohl, Randolf; Khabarova, Ksenia; Grinin, Alexey; Lamour, Tobias; Yost, Dylan C.; Hänsch, Theodor W.; Kolachevsky, Nikolai; Udem, Thomas

2017-10-01

At the core of the “proton radius puzzle” is a four-standard deviation discrepancy between the proton root-mean-square charge radii (rp) determined from the regular hydrogen (H) and the muonic hydrogen (µp) atoms. Using a cryogenic beam of H atoms, we measured the 2S-4P transition frequency in H, yielding the values of the Rydberg constant R∞ = 10973731.568076(96) per meterand rp = 0.8335(95) femtometer. Our rp value is 3.3 combined standard deviations smaller than the previous H world data, but in good agreement with the µp value. We motivate an asymmetric fit function, which eliminates line shifts from quantum interference of neighboring atomic resonances.

Conceptual Launch Vehicles Using Metallic Hydrogen Propellant

NASA Astrophysics Data System (ADS)

Cole, John W.; Silvera, Isaac F.; Foote, John P.

2008-01-01

Solid molecular hydrogen is predicted to transform into an atomic solid with metallic properties under pressures >4.5 Mbar. Atomic metallic hydrogen is predicted to be metastable, limited by some critical temperature and pressure, and to store very large amounts of energy. Experiments may soon determine the critical temperature, critical pressure, and specific energy availability. It is useful to consider the feasibility of using metastable atomic hydrogen as a rocket propellant. If one assumes that metallic hydrogen is stable at usable temperatures and pressures, and that it can be affordably produced, handled, and stored, then it may be a useful rocket propellant. Assuming further that the available specific energy can be determined from the recombination of the atoms into molecules (216 MJ/kg), then conceptual engines and launch vehicle concepts can be developed. Under these assumptions, metallic hydrogen would be a revolutionary new rocket fuel with a theoretical specific impulse of 1700 s at a chamber pressure of 100 atm. A practical problem that arises is that rocket chamber temperatures may be too high for the use of this pure fuel. This paper examines an engine concept that uses liquid hydrogen or water as a diluent coolant for the metallic hydrogen to reduce the chamber temperature to usable values. Several launch vehicles are then conceptually developed. Results indicate that if metallic hydrogen is experimentally found to have the properties assumed in this analysis, then there are significant benefits. These benefits become more attractive as the chamber temperatures increase.

Electron-impact ionization of atomic hydrogen at incident electron energies of 15.6, 17.6, 25, and 40 eV

DOE Office of Scientific and Technical Information (OSTI.GOV)

Childers, J. G.; James, K. E.; Hughes, M.

2003-09-01

Absolute doubly differential cross sections for the electron-impact ionization of atomic hydrogen have been measured from near threshold to intermediate energies. The measurements are calibrated to the well-established, accurate differential cross section for electron-impact excitation of the atomic hydrogen transition H(1{sup 2}S{yields}2{sup 2}S+2{sup 2}P). In these experiments background secondary electrons are suppressed by moving the atomic hydrogen target source to and from the collision region. Measurements cover the incident electron energy range of 14.6-40 eV, for scattering angles of 10 degree sign -120 degree sign and are found to be in very good agreement with the results of the mostmore » advanced theoretical models--the convergent close-coupling model and the exterior complex scaling model.« less

Interaction of intense laser pulses with hydrogen atomic clusters

NASA Astrophysics Data System (ADS)

Du, Hong-Chuan; Wang, Hui-Qiao; Liu, Zuo-Ye; Sun, Shao-Hua; Li, Lu; Ma, Ling-Ling; Hu, Bi-Tao

2010-03-01

The interaction between intense femtosecond laser pulses and hydrogen atomic clusters is studied by a simplified Coulomb explosion model. The dependences of average proton kinetic energy on cluster size, pulse duration, laser intensity and wavelength are studied respectively. The calculated results indicate that the irradiation of a femtosecond laser of longer wavelength on hydrogen atomic clusters may be a simple, economical way to produce highly kinetic hydrogen ions. The phenomenon suggests that the irradiation of femtosecond laser of longer wavelength on deuterium atomic clusters may be easier than that of shorter wavelength to drive nuclear fusion reactions. The product of the laser intensity and the squared laser wavelength needed to make proton energy saturated as a function of the squared cluster radius is also investigated. The proton energy distribution calculated is also shown and compared with the experimental data. Our results are in agreement with the experimental results fairly well.

An ab initio cluster study of the chemisorption of atomic cesium and hydrogen on reconstructed surfaces of gallium rich gallium arsenide

NASA Astrophysics Data System (ADS)

Schailey, Ronald

1999-11-01

Chemisorption properties of cesium and hydrogen atoms on the Ga-rich GaAs (100) (2 x 1), (2 x 2), and β(4 x 2) surfaces are investigated using ab initio self-consistent restricted open shell Hartree-Fock (ROHF) total energy calculations with Hay- Wadt effective core potentials. The effects of electron correlation have been included using many-body perturbation theory through second order, with the exception of β(4 x 2) symmetry due to computational limitations. The semiconductor surface is modeled by finite sized hydrogen saturated clusters. The effects of surface relaxation and reconstruction have been investigated in detail. Results are given for the energetics of chemisorption, charge population analysis, HOMO-LUMO gaps, and consequent possibilities of metallization for atomic cesium adsorption. For the chemisorption of atomic hydrogen, the experimentally verified mechanism of surface dimer bond breaking is investigated in detail.

Electron- and photon-stimulated desorption of atomic hydrogen from radiation-modified alkali halide surfaces

NASA Astrophysics Data System (ADS)

Hudson, L. T.; Tolk, N. H.; Bao, C.; Nordlander, P.; Russell, D. P.; Xu, J.

2000-10-01

The desorption yields of excited hydrogen atoms from the surfaces of KCl, KBr, NaCl, NaF, and LiF have been measured as a function of incident photon and electron energy and flux, time of irradiation, dosing pressure of H2 and sample temperature. As these surfaces are exposed to H2 gas during electron or photon bombardment, the fluorescence from excited hydrogen atoms ejected from the surface is monitored. The desorption yields are found to be contingent upon surface damage induced by the incident particle radiation, leading to dissociative adsorption at surface sites containing an excess of alkali metal. A desorption mechanism is presented in which incident electrons or photons induce a valence excitation to a neutral, antibonding state of the surface alkali hydride molecule complex, leading to the desorption of hydrogen atoms possessing several eV of kinetic energy.

Hydrogen atom distribution and hydrogen induced site depopulation for the La{sub 2-x}Mg{sub x}Ni{sub 7}-H system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guzik, Matylda N., E-mail: Matylda.Guzik@ife.no; Physics Department, Institute for Energy Technology, P.O. Box 40, NO-2027 Kjeller; Hauback, Bjorn C.

2012-02-15

La{sub 2-x}Mg{sub x}Ni{sub 7} and its hydrides/deuterides were investigated by high resolution synchrotron powder X-ray and neutron diffraction. Upon deuteration the single phase sample of the intermetallic compound with the refined composition La{sub 1.63}Mg{sub 0.37}Ni{sub 7} (space group: P6{sub 3}/mmc) expands isotropically, in contrast to the Mg free phase. The hydrogen uptake, {approx}9 D/f.u., is higher than in La{sub 2}Ni{sub 7}D{sub 6.5}. The refined composition accounts for La{sub 1.63}Mg{sub 0.37}Ni{sub 7}D{sub 8.8} (beta-phase). Rietveld refinements using the neutron and synchrotron diffraction data suggest that deuterium atoms occupy 5 different interstitial sites within both AB{sub 2} and AB{sub 5} slabs, eithermore » in an ordered or a disordered way. All determined D sites have an occupancy >50% and the shortest D-D contact is 1.96(3) A. It is supposed that a competition between the tendency to form directional bonds and repulsive D-D (H-H) interactions is the most important factor that influences the distribution of deuterium atoms in this structure. A hitherto unknown second, alpha-phase with composition La{sub 1.63}Mg{sub 0.37}Ni{sub 7}D{sub 0.56}, crystallizing with the same hexagonal symmetry as La{sub 1.63}Mg{sub 0.37}Ni{sub 7}D{sub 8.8}, has been discovered. The unit cell parameters for this D-poor phase differ slightly from those of the intermetallic. Alpha-phase displays only one D site (4f, space group: P6{sub 3}/mmc) occupied >50%, which is not populated in the D-rich beta-phase. This hydrogen/deuterium induced site depopulation can be explained by repulsive D-D (H-H) interactions that are likely to influence non-occupancy of certain interstices in metal lattice when absorbing hydrogen. - Graphical abstract: The detailed D atoms arrangement in La{sub 1.63}Mg{sub 0.37}Ni{sub 7}D{sub 8.8} differs significantly from the previously reported La{sub 1.5}Mg{sub 0.5}Ni{sub 7}D{sub 8.9(9.1)}. The present model consists of only five deuterium sites as opposed to nine proposed for La{sub 1.5}Mg{sub 0.5}Ni{sub 7}D{sub 8.9(9.1)}. The reported four remaining deuterium atom positions in La{sub 1.5}Mg{sub 0.5}Ni{sub 7}D{sub 8.9(9.1)} were not found in the investigated La{sub 1.63}Mg{sub 0.37}Ni{sub 7}D{sub 8.8}. The five Ni atoms have deuterium among their nearest neighbors, which surround them in a way similar to configurations observed in some complex transition metal hydrides and already reported for metallic hydrides. In the presented deuterium-rich phase, deformed tetrahedron, rigid trigonal pyramids as well as disordered and deformed saddle-like configuration are observed. Highlights: Black-Right-Pointing-Pointer Alpha- and beta-phase for La{sub 2-x}Mg{sub x}Ni{sub 7}-H system have been characterized. Black-Right-Pointing-Pointer Five different interstitial sites are occupied by deuterium/hydrogen atoms in the beta-phase. Black-Right-Pointing-Pointer One D/H site has been determined in the alpha-phase. Black-Right-Pointing-Pointer Deuterium/hydrogen induced site depopulation during phase transformation is observed. Black-Right-Pointing-Pointer Ni atoms tend to have tetrahedral-like D/H atom coordination.« less

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…

Auroral zone effects on hydrogen geocorona structure and variability

NASA Technical Reports Server (NTRS)

Moore, T. E.; Biddle, A. P.; Waite, J. H., Jr.; Killeen, T. L.

1985-01-01

The effect of diurnal and magnetospheric modulations on the structure of the hydrogen geocorona is analyzed on the basis of recent observations. Particular attention is given to the enhancement of neutral escape by plasma effects, including the recently observed phenomenon of low-altitude ion acceleration. It is found that, while significant fluxes of neutral H should be produced by transverse ion acceleration in the auroral zone, the process is probably insufficient to account for the observed polar depletion of hydrogen atoms. Analysis of recent exospheric temperature measurements from the Dynamics Explorer-2 satellite suggest that neutral heating in and near the high latitude cusp may be the major contributor to depleted atomic hydrogen densities at high latitudes. Altitude profiles of the production rates for escaping neutral hydrogen atoms during periods of maximum, minimum, and typical solar activity are provided.

Highly hydrogen-sensitive thermal desorption spectroscopy system for quantitative analysis of low hydrogen concentration (˜1 × 1016 atoms/cm3) in thin-film samples

NASA Astrophysics Data System (ADS)

Hanna, Taku; Hiramatsu, Hidenori; Sakaguchi, Isao; Hosono, Hideo

2017-05-01

We developed a highly hydrogen-sensitive thermal desorption spectroscopy (HHS-TDS) system to detect and quantitatively analyze low hydrogen concentrations in thin films. The system was connected to an in situ sample-transfer chamber system, manipulators, and an rf magnetron sputtering thin-film deposition chamber under an ultra-high-vacuum (UHV) atmosphere of ˜10-8 Pa. The following key requirements were proposed in developing the HHS-TDS: (i) a low hydrogen residual partial pressure, (ii) a low hydrogen exhaust velocity, and (iii) minimization of hydrogen thermal desorption except from the bulk region of the thin films. To satisfy these requirements, appropriate materials and components were selected, and the system was constructed to extract the maximum performance from each component. Consequently, ˜2000 times higher sensitivity to hydrogen than that of a commercially available UHV-TDS system was achieved using H+-implanted Si samples. Quantitative analysis of an amorphous oxide semiconductor InGaZnO4 thin film (1 cm × 1 cm × 1 μm thickness, hydrogen concentration of 4.5 × 1017 atoms/cm3) was demonstrated using the HHS-TDS system. This concentration level cannot be detected using UHV-TDS or secondary ion mass spectroscopy (SIMS) systems. The hydrogen detection limit of the HHS-TDS system was estimated to be ˜1 × 1016 atoms/cm3, which implies ˜2 orders of magnitude higher sensitivity than that of SIMS and resonance nuclear reaction systems (˜1018 atoms/cm3).

RLE (Research Laboratory of Electronics) Progress Report Number 125.

DTIC Science & Technology

1983-01-01

Optical Communications 32 7.3 Picosecond Optics 35 7.4 Ultrashort Pulse Formation 37 7.5 Femtosecond Laser System 37 7.6 Parametric Scattering with...Figure 3-2: The cross section for 4 photon ionization of atomic hydrogen as calculated by 10 Reinhardt for a single frequency laser . To facilitate...profiles produced by laser intensity I* and at five times that intensity 11 510. As the laser intensity is increased, the ionization profile becomes

Catalysis by Single Atoms: Water Gas Shift and Ethylene Hydrogenation

DTIC Science & Technology

2009-04-20

addition to other microscopic phenomena at region of coefficients . Silicon carbide has a higher loss tangent at 2.4 GHz than most ceramics, and thus...Si 50 35 30 20 Ni 50 — — D. Sample holder and preparation: * The remainder is ZrB2. Graphite sheet ( McMaster -Carr, USA) is cut into different...results. 19 B. Microwave hybrid processing i. Microwave heating: 1. Volumetric Microwave absorption is proportional to the loss

Selective reduction of carboxylic acids to aldehydes with hydrosilane via photoredox catalysis.

PubMed

Zhang, Muliang; Li, Nan; Tao, Xingyu; Ruzi, Rehanguli; Yu, Shouyun; Zhu, Chengjian

2017-09-12

The direct reduction of carboxylic acids to aldehydes with hydrosilane was achieved through visible light photoredox catalysis. The combination of both single electron transfer and hydrogen atom transfer steps offers a novel and convenient approach to selective reduction of carboxylic acids to aldehydes. The method also features mild conditions, high yields, broad substrate scope, and good functional group tolerance, such as alkyne, ester, ketone, amide and amine groups.

Probing the accuracy and precision of Hirshfeld atom refinement with HARt interfaced with Olex2.

PubMed

Fugel, Malte; Jayatilaka, Dylan; Hupf, Emanuel; Overgaard, Jacob; Hathwar, Venkatesha R; Macchi, Piero; Turner, Michael J; Howard, Judith A K; Dolomanov, Oleg V; Puschmann, Horst; Iversen, Bo B; Bürgi, Hans-Beat; Grabowsky, Simon

2018-01-01

Hirshfeld atom refinement (HAR) is a novel X-ray structure refinement technique that employs aspherical atomic scattering factors obtained from stockholder partitioning of a theoretically determined tailor-made static electron density. HAR overcomes many of the known limitations of independent atom modelling (IAM), such as too short element-hydrogen distances, r ( X -H), or too large atomic displacement parameters (ADPs). This study probes the accuracy and precision of anisotropic hydrogen and non-hydrogen ADPs and of r ( X -H) values obtained from HAR. These quantities are compared and found to agree with those obtained from (i) accurate neutron diffraction data measured at the same temperatures as the X-ray data and (ii) multipole modelling (MM), an established alternative method for interpreting X-ray diffraction data with the help of aspherical atomic scattering factors. Results are presented for three chemically different systems: the aromatic hydro-carbon rubrene (orthorhombic 5,6,11,12-tetra-phenyl-tetracene), a co-crystal of zwitterionic betaine, imidazolium cations and picrate anions (BIPa), and the salt potassium hydrogen oxalate (KHOx). The non-hydrogen HAR-ADPs are as accurate and precise as the MM-ADPs. Both show excellent agreement with the neutron-based values and are superior to IAM-ADPs. The anisotropic hydrogen HAR-ADPs show a somewhat larger deviation from neutron-based values than the hydrogen SHADE-ADPs used in MM. Element-hydrogen bond lengths from HAR are in excellent agreement with those obtained from neutron diffraction experiments, although they are somewhat less precise. The residual density contour maps after HAR show fewer features than those after MM. Calculating the static electron density with the def2-TZVP basis set instead of the simpler def2-SVP one does not improve the refinement results significantly. All HARs were performed within the recently introduced HARt option implemented in the Olex2 program. They are easily launched inside its graphical user interface following a conventional IAM.

Probing the accuracy and precision of Hirshfeld atom refinement with HARt interfaced with Olex2

PubMed Central

Fugel, Malte; Hathwar, Venkatesha R.; Turner, Michael J.; Howard, Judith A. K.

2018-01-01

Hirshfeld atom refinement (HAR) is a novel X-ray structure refinement technique that employs aspherical atomic scattering factors obtained from stockholder partitioning of a theoretically determined tailor-made static electron density. HAR overcomes many of the known limitations of independent atom modelling (IAM), such as too short element–hydrogen distances, r(X—H), or too large atomic displacement parameters (ADPs). This study probes the accuracy and precision of anisotropic hydrogen and non-hydrogen ADPs and of r(X—H) values obtained from HAR. These quantities are compared and found to agree with those obtained from (i) accurate neutron diffraction data measured at the same temperatures as the X-ray data and (ii) multipole modelling (MM), an established alternative method for interpreting X-ray diffraction data with the help of aspherical atomic scattering factors. Results are presented for three chemically different systems: the aromatic hydro­carbon rubrene (orthorhombic 5,6,11,12-tetra­phenyl­tetracene), a co-crystal of zwitterionic betaine, imidazolium cations and picrate anions (BIPa), and the salt potassium hydrogen oxalate (KHOx). The non-hydrogen HAR-ADPs are as accurate and precise as the MM-ADPs. Both show excellent agreement with the neutron-based values and are superior to IAM-ADPs. The anisotropic hydrogen HAR-ADPs show a somewhat larger deviation from neutron-based values than the hydrogen SHADE-ADPs used in MM. Element–hydrogen bond lengths from HAR are in excellent agreement with those obtained from neutron diffraction experiments, although they are somewhat less precise. The residual density contour maps after HAR show fewer features than those after MM. Calculating the static electron density with the def2-TZVP basis set instead of the simpler def2-SVP one does not improve the refinement results significantly. All HARs were performed within the recently introduced HARt option implemented in the Olex2 program. They are easily launched inside its graphical user interface following a conventional IAM. PMID:29354269

Phosphorus atomic layer doping in Ge using RPCVD

NASA Astrophysics Data System (ADS)

Yamamoto, Yuji; Kurps, Rainer; Mai, Christian; Costina, Ioan; Murota, Junichi; Tillack, Bernd

2013-05-01

Phosphorus atomic layer doping (P-ALD) in Ge is investigated at temperatures between 100 °C and 400 °C using a single wafer reduced pressure chemical vapor deposition (RPCVD) system. Hydrogen-terminated and hydrogen-free Ge (1 0 0) surfaces are exposed to PH3 at different PH3 partial pressures after interrupting Ge growth. The adsorption and reaction of PH3 proceed on a hydrogen-free Ge surface. For all temperatures and PH3 partial pressures used for the P-ALD, the P dose increased with increasing PH3 exposure time and saturated. The saturation value of the incorporated P dose at 300 °C is ˜1.5 × 1014 cm-3, which is close to a quarter of a monolayer of the Ge (1 0 0) surface. The P dose could be simulated assuming a Langmuir-type kinetics model with a saturation value of Nt = 1.55 × 1014 cm-2 (a quarter of a monolayer), reaction rate constant kr = 77 s-1 and thermal equilibrium constant K = 3.0 × 10-2 Pa-1. An electrically active P concentration of 5-6 × 1019 cm-3, which is a 5-6 times higher thermal solubility of P in Ge, is obtained by multiple P spike fabrication using the P-ALD process.

Formation of the low-resistivity compound Cu{sub 3}Ge by low-temperature treatment in an atomic hydrogen flux

DOE Office of Scientific and Technical Information (OSTI.GOV)

Erofeev, E. V., E-mail: erofeev@micran.ru; Kazimirov, A. I.; Fedin, I. V.

The systematic features of the formation of the low-resistivity compound Cu{sub 3}Ge by low-temperature treatment of a Cu/Ge two-layer system in an atomic hydrogen flux are studied. The Cu/Ge two-layer system is deposited onto an i-GaAs substrate. Treatment of the Cu/Ge/i-GaAs system, in which the layer thicknesses are, correspondingly, 122 and 78 nm, in atomic hydrogen with a flux density of 10{sup 15} at cm{sup 2} s{sup –1} for 2.5–10 min at room temperature induces the interdiffusion of Cu and Ge, with the formation of a polycrystalline film containing the stoichiometric Cu{sub 3}Ge phase. The film consists of vertically orientedmore » grains 100–150 nm in size and exhibits a minimum resistivity of 4.5 µΩ cm. Variations in the time of treatment of the Cu/Ge/i-GaAs samples in atomic hydrogen affect the Cu and Ge depth distribution, the phase composition of the films, and their resistivity. Experimental observation of the synthesis of the Cu{sub 3}Ge compound at room temperature suggests that treatment in atomic hydrogen has a stimulating effect on both the diffusion of Cu and Ge and the chemical reaction of Cu{sub 3}Ge-compound formation. These processes can be activated by the energy released upon the recombination of hydrogen atoms adsorbed at the surface of the Cu/Ge/i-GaAs sample.« less

Rolf Landauer and Charles H. Bennett Award Talk: Experimental development of spin qubits in silicon

NASA Astrophysics Data System (ADS)

Morello, Andrea

The modern information era is built on silicon nanoelectronic devices. The future quantum information era might be built on silicon too, if we succeed in controlling the interactions between individual spins hosted in silicon nanostructures. Spins in silicon constitute excellent solid-state qubits, because of the weak spin-orbit coupling and the possibility to remove nuclear spins from the environment through 28Si isotopic enrichment. Substitutional 31P atoms in silicon behave approximately like hydrogen in vacuum, providing two spin 1/2 qubits - the donor-bound electron and the 31P nucleus - that can be coherently controlled, read out in single-shot, and are naturally coupled through the hyperfine interaction. In isotopically-enriched 28Si, these single-atom qubits have demonstrated outstanding coherence times, up to 35 seconds for the nuclear spin, and 1-qubit gate fidelities well above 99.9% for both the electron and the nucleus. The hyperfine coupling provides a built-in interaction to entangle the two qubits within one atom. The combined initialization, control and readout fidelities result in a violation of Bell's inequality with S = 2 . 70 , a record value for solid-state qubits. Despite being identical atomic systems, 31P atoms can be addressed individually by locally modifying the hyperfine interaction through electrostatic gating. Multi-qubit logic gates can be mediated either by the exchange interaction or by electric dipole coupling. Scaling up beyond a single atom presents formidable challenges, but provides a pathway to building quantum processors that are compatible with standard semiconductor fabrication, and retain a nanometric footprint, important for truly large-scale quantum computers. Work supported by US Army Research Office (W911NF-13-1-0024) and Australian Research Council (CE110001027).

Thermal decomposition of silane to form hydrogenated amorphous Si film

DOEpatents

Strongin, Myron; Ghosh, Arup K.; Wiesmann, Harold J.; Rock, Edward B.; Lutz, III, Harry A.

1980-01-01

This invention relates to hydrogenated amorphous silicon produced by thermally decomposing silano (SiH.sub.4) or other gases comprising H and Si, at elevated temperatures of about 1700.degree.-2300.degree. C., and preferably in a vacuum of about 10.sup.-8 to 10.sup.-4 torr, to form a gaseous mixture of atomic hydrogen and atomic silicon, and depositing said gaseous mixture onto a substrate outside said source of thermal decomposition to form hydrogenated amorphous silicon.

A complete active space valence bond method with nonorthogonal orbitals

NASA Astrophysics Data System (ADS)

Hirao, Kimihiko; Nakano, Haruyuki; Nakayama, Kenichi

1997-12-01

A complete active space self-consistent field (SCF) wave function is transformed into a valence bond type representation built from nonorthogonal orbitals, each strongly localized on a single atom. Nonorthogonal complete active space SCF orbitals are constructed by Ruedenberg's projected localization procedure so that they have maximal overlaps with the corresponding minimum basis set of atomic orbitals of the free-atoms. The valence bond structures which are composed of such nonorthogonal quasiatomic orbitals constitute the wave function closest to the concept of the oldest and most simple valence bond method. The method is applied to benzene, butadiene, hydrogen, and methane molecules and compared to the previously proposed complete active space valence bond approach with orthogonal orbitals. The results demonstrate the validity of the method as a powerful tool for describing the electronic structure of various molecules.

Proton dynamics and the phase diagram of dense water ice.

PubMed

Hernandez, J-A; Caracas, R

2018-06-07

All the different phases of water ice between 2 GPa and several megabars are based on a single body-centered cubic sub-lattice of oxygen atoms. They differ only by the behavior of the hydrogen atoms. In this study, we investigate the dynamics of the H atoms at high pressures and temperatures in water ice from first-principles molecular dynamics simulations. We provide a detailed analysis of the O-H⋯O bonding dynamics over the entire stability domain of the body-centered cubic (bcc) water ices and compute transport properties and vibrational density-of-states. We report the first ab initio evidence for a plastic phase of water and we propose a coherent phase diagram for bcc water ices compatible with the two groups of melting curves and with the multiple anomalies reported in ice VII around 15 GPa.

Thermal O-H Bond Activation of Water as Mediated by Heteronuclear [Al2Mg2O5]•+: Evidence for Oxygen-Atom Scrambling.

PubMed

Geng, Caiyun; Li, Jilai; Weiske, Thomas; Schwarz, Helmut

2018-06-25

Mechanistic insight into the thermal O-H bond activation of water by the cubane-like, prototypical heteronuclear oxide cluster [Al 2 Mg 2 O 5 ] •+ has been derived from a combined experimental/computational study. Experiments in the highly diluted gas phase using Fourier transform ion-cyclotron resonance mass spectrometry show that hydrogen-atom abstraction from water by the cluster cation [Al 2 Mg 2 O 5 ] •+ occurs at ambient conditions accompanied by the liberation of an OH • radical. Due to a complete randomization of all oxygen atoms prior to fragmentation about 83% of the oxygen atoms of the hydroxyl radical released originate from the oxide cluster itself. The experimental findings are supported by detailed high-level quantum chemical calculations. The theoretical analysis reveals that the transfer of a formal hydrogen atom from water to the metal-oxide cation can proceed mechanistically via proton- or hydrogen-atom transfer exploiting different active sites of the cluster oxide. In addition to the unprecedented oxygen-atom scrambling, one of the more general and quite unexpected findings concerns the role of spin density at the hydrogen-acceptor oxide atom. While this feature is so crucial for [M-O] + /CH 4 couples, it is much less important in the O-H bond activation of water.

Reaction kinetics of hydrogen atom abstraction from isopentanol by the H atom and HO2˙ radical.

PubMed

Parab, Prajakta Rajaram; Heufer, K Alexander; Fernandes, Ravi Xavier

2018-04-25

Isopentanol is a potential next-generation biofuel for future applications to Homogeneous Charge Compression Ignition (HCCI) engine concepts. To provide insights into the combustion behavior of isopentanol, especially to its auto-ignition behavior which is linked both to efficiency and pollutant formation in real combustion systems, detailed quantum chemical studies for crucial reactions are desired. H-Abstraction reaction rates from fuel molecules are key initiation steps for chain branching required for auto-ignition. In this study, rate constants are determined for the hydrogen atom abstraction reactions from isopentanol by the H atom and HO2˙ radical by implementing the CBS-QB3 composite method. For the treatment of the internal rotors, a Pitzer-Gwinn-like approximation is applied. On comparing the computed reaction energies, the highest exothermicity (ΔE = -46 kJ mol-1) is depicted for Hα abstraction by the H atom whereas the lowest endothermicity (ΔE = 29 kJ mol-1) is shown for the abstraction of Hα by the HO2˙ radical. The formation of hydrogen bonding is found to affect the kinetics of the H atom abstraction reactions by the HO2˙ radical. Further above 750 K, the calculated high pressure limit rate constants indicate that the total contribution from delta carbon sites (Cδ) is predominant for hydrogen atom abstraction by the H atom and HO2˙ radical.

Studies for the Loss of Atomic and Molecular Species from Io

NASA Technical Reports Server (NTRS)

Smyth, William H.

1998-01-01

Continued effort is reported to improve the emission rates of various emission lines for atomic oxygen and sulfur. Atomic hydrogen has been included as a new species in the neutral cloud model. The pertinent lifetime processes for hydrogen in the plasma torus and the relevant excitation processes for H Lyman-alpha emission in Io's atmosphere are discussed.

Atomic Layer Epitaxy of Aluminum Nitride: Unraveling the Connection between Hydrogen Plasma and Carbon Contamination.

PubMed

Erwin, Steven C; Lyons, John L

2018-06-13

Atomistic control over the growth of semiconductor thin films, such as aluminum nitride, is a long-sought goal in materials physics. One promising approach is plasma-assisted atomic layer epitaxy, in which separate reactant precursors are employed to grow the cation and anion layers in alternating deposition steps. The use of a plasma during the growth-most often a hydrogen plasma-is now routine and generally considered critical, but the precise role of the plasma is not well-understood. We propose a theoretical atomistic model and elucidate its consequences using analytical rate equations, density functional theory, and kinetic Monte Carlo statistical simulations. We show that using a plasma has two important consequences, one beneficial and one detrimental. The plasma produces atomic hydrogen in the gas phase, which is important for removing methyl radicals left over from the aluminum precursor molecules. However, atomic hydrogen also leads to atomic carbon on the surface and, moreover, opens a channel for trapping these carbon atoms as impurities in the subsurface region, where they remain as unwanted contaminants. Understanding this dual role leads us to propose a solution for the carbon contamination problem which leaves the main benefit of the plasma largely unaffected.

Theoretical Investigations of the Electrochemical Reduction of CO on Single Metal Atoms Embedded in Graphene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kirk, Charlotte; Chen, Leanne D.; Siahrostami, Samira

Single transition metal atoms embedded at single vacancies of graphene provide a unique paradigm for catalytic reactions. We present a density functional theory study of such systems for the electrochemical reduction of CO. Theoretical investigations of CO electrochemical reduction are particularly challenging in that electrochemical activation energies are a necessary descriptor of activity. We determined the electrochemical barriers for key proton–electron transfer steps using a state-of-the-art, fully explicit solvent model of the electrochemical interface. The accuracy of GGA-level functionals in describing these systems was also benchmarked against hybrid methods. We find the first proton transfer to form CHO from COmore » to be a critical step in C 1 product formation. On these single atom sites, the corresponding barrier scales more favorably with the CO binding energy than for 211 and 111 transition metal surfaces, in the direction of improved activity. Intermediates and transition states for the hydrogen evolution reaction were found to be less stable than those on transition metals, suggesting a higher selectivity for CO reduction. We present a rate volcano for the production of methane from CO. We identify promising candidates with high activity, stability, and selectivity for the reduction of CO. As a result, this work highlights the potential of these systems as improved electrocatalysts over pure transition metals for CO reduction.« less

Theoretical Investigations of the Electrochemical Reduction of CO on Single Metal Atoms Embedded in Graphene

DOE PAGES

Kirk, Charlotte; Chen, Leanne D.; Siahrostami, Samira; ...

2017-12-18

Single transition metal atoms embedded at single vacancies of graphene provide a unique paradigm for catalytic reactions. We present a density functional theory study of such systems for the electrochemical reduction of CO. Theoretical investigations of CO electrochemical reduction are particularly challenging in that electrochemical activation energies are a necessary descriptor of activity. We determined the electrochemical barriers for key proton–electron transfer steps using a state-of-the-art, fully explicit solvent model of the electrochemical interface. The accuracy of GGA-level functionals in describing these systems was also benchmarked against hybrid methods. We find the first proton transfer to form CHO from COmore » to be a critical step in C 1 product formation. On these single atom sites, the corresponding barrier scales more favorably with the CO binding energy than for 211 and 111 transition metal surfaces, in the direction of improved activity. Intermediates and transition states for the hydrogen evolution reaction were found to be less stable than those on transition metals, suggesting a higher selectivity for CO reduction. We present a rate volcano for the production of methane from CO. We identify promising candidates with high activity, stability, and selectivity for the reduction of CO. As a result, this work highlights the potential of these systems as improved electrocatalysts over pure transition metals for CO reduction.« less

Crystal structure of (eth­oxy­ethyl­idene)di­methyl­aza­nium ethyl sulfate

PubMed Central

Tiritiris, Ioannis; Saur, Stefan; Kantlehner, Willi

2015-01-01

In the title salt, C6H14NO+·C2H5SO4 −, the C—N bond lengths in the cation are 1.2981 (14), 1.4658 (14) and 1.4707 (15) Å, indicating double- and single-bond character, respectively. The C—O bond length of 1.3157 (13) Å shows double-bond character, indicating charge delocalization within the NCO plane of the iminium ion. In the crystal, C—H⋯O hydrogen bonds between H atoms of the cations and O atoms of neighbouring ethyl sulfate anions are present, generating a three-dimensional network. PMID:26870525

Data on inelastic processes in low-energy potassium-hydrogen and rubidium-hydrogen collisions

NASA Astrophysics Data System (ADS)

Yakovleva, S. A.; Barklem, P. S.; Belyaev, A. K.

2018-01-01

Two sets of rate coefficients for low-energy inelastic potassium-hydrogen and rubidium-hydrogen collisions were computed for each collisional system based on two model electronic structure calculations, performed by the quantum asymptotic semi-empirical and the quantum asymptotic linear combinations of atomic orbitals (LCAO) approaches, followed by quantum multichannel calculations for the non-adiabatic nuclear dynamics. The rate coefficients for the charge transfer (mutual neutralization, ion-pair formation), excitation and de-excitation processes are calculated for all transitions between the five lowest lying covalent states and the ionic states for each collisional system for the temperature range 1000-10 000 K. The processes involving higher lying states have extremely low rate coefficients and, hence, are neglected. The two model calculations both single out the same partial processes as having large and moderate rate coefficients. The largest rate coefficients correspond to the mutual neutralization processes into the K(5s 2S) and Rb(4d 2D) final states and at temperature 6000 K have values exceeding 3 × 10-8 cm3 s-1 and 4 × 10-8 cm3 s-1, respectively. It is shown that both the semi-empirical and the LCAO approaches perform equally well on average and that both sets of atomic data have roughly the same accuracy. The processes with large and moderate rate coefficients are likely to be important for non-LTE modelling in atmospheres of F, G and K-stars, especially metal-poor stars.

Estimating inelastic heavy-particle-hydrogen collision data. I. Simplified model and application to potassium-hydrogen collisions

NASA Astrophysics Data System (ADS)

Belyaev, Andrey K.; Yakovleva, Svetlana A.

2017-10-01

Aims: We derive a simplified model for estimating atomic data on inelastic processes in low-energy collisions of heavy-particles with hydrogen, in particular for the inelastic processes with high and moderate rate coefficients. It is known that these processes are important for non-LTE modeling of cool stellar atmospheres. Methods: Rate coefficients are evaluated using a derived method, which is a simplified version of a recently proposed approach based on the asymptotic method for electronic structure calculations and the Landau-Zener model for nonadiabatic transition probability determination. Results: The rate coefficients are found to be expressed via statistical probabilities and reduced rate coefficients. It turns out that the reduced rate coefficients for mutual neutralization and ion-pair formation processes depend on single electronic bound energies of an atom, while the reduced rate coefficients for excitation and de-excitation processes depend on two electronic bound energies. The reduced rate coefficients are calculated and tabulated as functions of electronic bound energies. The derived model is applied to potassium-hydrogen collisions. For the first time, rate coefficients are evaluated for inelastic processes in K+H and K++H- collisions for all transitions from ground states up to and including ionic states. Tables with calculated data are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/606/A147

Combinatorial Search for High-Activity Hydrogen Catalysts Based on Transition-Metal-Embedded Graphitic Carbons

DOE PAGES

Choi, Woon Ih; Wood, Brandon C.; Schwegler, Eric; ...

2015-09-22

Transition metal (TM) atoms in porphyrin–like complexes play important roles in many protein and enzymetic systems, where crystal–field effects are used to modify d–orbital levels. Inspired by the tunable electronic structure of these motifs, a high–throughput computational search for synthetic hydrogen catalysts is performed based on a similar motif of TM atoms embedded into the lattice of graphene. Based on an initial list of 300 possible embedding geometries, binders, and host atoms, descriptors for stability and catalytic activity are applied to extract ten promising candidates for hydrogen evolution, two of which are expected to exhibit high activity for hydrogen oxidation.more » In several instances, the active TM atoms are earth–abundant elements that show no activity in the bulk phase, highlighting the importance of the coordination environment in tuning the d–orbitals. In conclusion, it is found that the most active candidates involve a hitherto unreported surface reaction pathway that involves a Kubas–complex intermediate, which significantly lowers the kinetic barrier associated with hydrogen dissociation and association.« less

Repulsive tip tilting as the dominant mechanism for hydrogen bond-like features in atomic force microscopy imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Alex J.; Sakai, Yuki; Kim, Minjung

2016-05-09

Experimental atomic force microscopy (AFM) studies have reported distinct features in regions with little electron density for various organic systems. These unexpected features have been proposed to be a direct visualization of intermolecular hydrogen bonding. Here, we apply a computational method using ab initio real-space pseudopotentials along with a scheme to account for tip tilting to simulate AFM images of the 8-hydroxyquinoline dimer and related systems to develop an understanding of the imaging mechanism for hydrogen bonds. We find that contrast for the observed “hydrogen bond” feature comes not from the electrostatic character of the bonds themselves but rather frommore » repulsive tip tilting induced by neighboring electron-rich atoms.« less

Silicon as a model ion trap: Time domain measurements of donor Rydberg states

PubMed Central

Vinh, N. Q.; Greenland, P. T.; Litvinenko, K.; Redlich, B.; van der Meer, A. F. G.; Lynch, S. A.; Warner, M.; Stoneham, A. M.; Aeppli, G.; Paul, D. J.; Pidgeon, C. R.; Murdin, B. N.

2008-01-01

One of the great successes of quantum physics is the description of the long-lived Rydberg states of atoms and ions. The Bohr model is equally applicable to donor impurity atoms in semiconductor physics, where the conduction band corresponds to the vacuum, and the loosely bound electron orbiting a singly charged core has a hydrogen-like spectrum according to the usual Bohr–Sommerfeld formula, shifted to the far-infrared because of the small effective mass and high dielectric constant. Manipulation of Rydberg states in free atoms and ions by single and multiphoton processes has been tremendously productive since the development of pulsed visible laser spectroscopy. The analogous manipulations have not been conducted for donor impurities in silicon. Here, we use the FELIX pulsed free electron laser to perform time-domain measurements of the Rydberg state dynamics in phosphorus- and arsenic-doped silicon and we have obtained lifetimes consistent with frequency domain linewidths for isotopically purified silicon. This implies that the dominant decoherence mechanism for excited Rydberg states is lifetime broadening, just as for atoms in ion traps. The experiments are important because they represent a step toward coherent control and manipulation of atomic-like quantum levels in the most common semiconductor and complement magnetic resonance experiments in the literature, which show extraordinarily long spin lattice relaxation times—key to many well known schemes for quantum computing qubits—for the same impurities. Our results, taken together with the magnetic resonance data and progress in precise placement of single impurities, suggest that doped silicon, the basis for modern microelectronics, is also a model ion trap.

Functionalized graphene-Pt composites for fuel cells and photoelectrochemical cells

DOEpatents

Diankov, Georgi; An, Jihwan; Park, Joonsuk; Goldhaber, David J. K.; Prinz, Friedrich B.

2017-08-29

A method of growing crystals on two-dimensional layered material is provided that includes reversibly hydrogenating a two-dimensional layered material, using a controlled radio-frequency hydrogen plasma, depositing Pt atoms on the reversibly hydrogenated two-dimensional layered material, using Atomic Layer Deposition (ALD), where the reversibly hydrogenated two-dimensional layered material promotes loss of methyl groups in an ALD Pt precursor, and forming Pt-O on the reversibly hydrogenated two-dimensional layered material, using combustion by O.sub.2, where the Pt-O is used for subsequent Pt half-cycles of the ALD process, where growth of Pt crystals occurs.

Influence of Hydrogen on Atomized Titanium Powders Sintering

NASA Astrophysics Data System (ADS)

Senkevich, K. S.

2018-07-01

The aim of this work is to study the effect of hydrogen reversible alloying (thermohydrogen processing, THP) on low-temperature sintering of atomized titanium powders. It is stated that alloying with 0.2 to 0.8 wt pct of hydrogen beneficially affects titanium powders sintering. The effect is caused by phase transformations occurring upon hydrogen saturation of powders and dehydrogenation, which substantially intensifies sintering at temperatures from 800 °C to 900 °C. The role of certain THP stages (sintering in hydrogenated state and upon dehydrogenation) on formation of sintered contacts in porous materials is shown.

Hydrogen-bond coordination in organic crystal structures: statistics, predictions and applications.

PubMed

Galek, Peter T A; Chisholm, James A; Pidcock, Elna; Wood, Peter A

2014-02-01

Statistical models to predict the number of hydrogen bonds that might be formed by any donor or acceptor atom in a crystal structure have been derived using organic structures in the Cambridge Structural Database. This hydrogen-bond coordination behaviour has been uniquely defined for more than 70 unique atom types, and has led to the development of a methodology to construct hypothetical hydrogen-bond arrangements. Comparing the constructed hydrogen-bond arrangements with known crystal structures shows promise in the assessment of structural stability, and some initial examples of industrially relevant polymorphs, co-crystals and hydrates are described.

Numerology, hydrogenic levels, and the ordering of excited states in one-electron atoms

NASA Astrophysics Data System (ADS)

Armstrong, Lloyd, Jr.

1982-03-01

We show that the observed ordering of Rydberg states of one-electron atoms can be understood by assuming that these states are basically hydrogenic in nature. Much of the confusion concerning this point is shown to arise from the failure to differentiate between hydrogenic ordering as the nuclear charge approaches infinity, and hydrogenic ordering for an effective charge of one. The origin of κ ordering of Rydberg levels suggested by Sternheimer is considered within this picture, and the predictions of κ ordering are compared with those obtained by assuming hydrogenic ordering.

Influence of Hydrogen on Atomized Titanium Powders Sintering

NASA Astrophysics Data System (ADS)

Senkevich, K. S.

2018-05-01

The aim of this work is to study the effect of hydrogen reversible alloying (thermohydrogen processing, THP) on low-temperature sintering of atomized titanium powders. It is stated that alloying with 0.2 to 0.8 wt pct of hydrogen beneficially affects titanium powders sintering. The effect is caused by phase transformations occurring upon hydrogen saturation of powders and dehydrogenation, which substantially intensifies sintering at temperatures from 800 °C to 900 °C. The role of certain THP stages (sintering in hydrogenated state and upon dehydrogenation) on formation of sintered contacts in porous materials is shown.

Collision cascades enhanced hydrogen redistribution in cobalt implanted hydrogenated diamond-like carbon films

NASA Astrophysics Data System (ADS)

Gupta, P.; Becker, H.-W.; Williams, G. V. M.; Hübner, R.; Heinig, K.-H.; Markwitz, A.

2017-03-01

Hydrogenated diamond-like carbon films produced by C3H6 deposition at 5 kV and implanted at room temperature with 30 keV Co atoms to 12 at.% show not only a bimodal distribution of Co atoms but also a massive redistribution of hydrogen in the films. Resonant nuclear reaction analysis was used to measure the hydrogen depth profiles (15N-method). Depletion of hydrogen near the surface was measured to be as low as 7 at.% followed by hydrogen accumulation from 27 to 35 at.%. A model is proposed considering the thermal energy deposited by collision cascade for thermal insulators. In this model, sufficient energy is provided for dissociated hydrogen to diffuse out of the sample from the surface and diffuse into the sample towards the interface which is however limited by the range of the incoming Co ions. At a hydrogen concentration of ∼35 at.%, the concentration gradient of the mobile unbounded hydrogen atoms is neutralised effectively stopping diffusion towards the interface. The results point towards new routes of controlling the composition and distribution of elements at the nanoscale within a base matrix without using any heat treatment methods. Exploring these opportunities can lead to a new horizon of materials and device engineering needed for enabling advanced technologies and applications.

Local mechanical and electromechanical properties of the P(VDF-TrFE)-graphene oxide thin films

NASA Astrophysics Data System (ADS)

Silibin, M. V.; Bystrov, V. S.; Karpinsky, D. V.; Nasani, N.; Goncalves, G.; Gavrilin, I. M.; Solnyshkin, A. V.; Marques, P. A. A. P.; Singh, Budhendra; Bdikin, I. K.

2017-11-01

Recently, many organic materials, including carbon materials such as carbon nanotubes (CNTs) and graphene (single-walled carbon sheet structure) were studied in order to improve their mechanical and electrical properties. In particular, copolymers of poly (vinylidene fluoride) and poly trifluoroethylene [P(VDF-TrFE)] are promising materials, which can be used as probes, sensors, actuators, etc. Composite thin film of the copolymer P(VDF-TrFE) with graphene oxide (GO) were prepared by spin coating. The obtained films were investigated using piezoresponse force microscopy (PFM). The switching behavior, piezoelectric response, dielectric permittivity and mechanical properties of the films were found to depend on the presence of GO. For understanding the mechanism of piezoresponse evolution of the composite we used models of PVDF chain, its behavior in electrical field and computed the data for piezoelectric coefficients using HyperChem software. The summarized models of graphene oxide based on graphene layer from 96 carbon atoms C: with oxygen and OH groups and with COOH groups arranged by hydrogen were used for PVDF/Graphene oxide complex: 1) with H-side (hydrogen atom) connected from PVDF to graphene oxide, 2) with F-side (fluorine atom) connected from PVDF graphene oxide and 3) Graphene Oxide/PVDF with both sides (sandwich type). Experimental results qualitatively correlate with those obtained in the calculations.

Synthesis, crystal structures, and characterization of double complex salts [Au(en)2][Rh(NO2)6]·2H2O and [Au(en)2][Rh(NO2)6

NASA Astrophysics Data System (ADS)

Plyusnin, Pavel E.; Makotchenko, Evgenia V.; Shubin, Yury V.; Baidina, Iraida A.; Korolkov, Ilya V.; Sheludyakova, Liliya A.; Korenev, Sergey V.

2015-11-01

Double complex salts of rhodium(III) and gold(III) of the composition [Au(en)2][Rh(NO2)6]·2H2O (1) and [Au(en)2][Rh(NO2)6] (2) have been prepared. Crystal structures of the compounds have been determined by single crystal X-ray diffraction. The compounds have been characterized by PXRD, IR, far-IR, CHN and DTA. The complexes have a layered structures. The presence of water in 1 makes the structure of the hydrated DCS less dense as compared to the anhydrous one. The environment of the cation and the anion in the two structures is the same, oxygen atoms of the nitro groups are involved in hydrogen bonds N-H⋯O, N⋯O distances being approximately the same. The structures of 1 and 2 are notable in having shortened contacts between the gold atoms and the oxygen atoms of the nitro groups of the neighboring complex anions. The thermal behavior of the complexes in a hydrogen atmosphere was investigated. The final product of thermolysis prepared at the temperature 600°C is a two-phase mixture of pure metallic gold and the solid solution Rh0.93Au0.07.

Solar Wind Charge Exchange Studies Of Highly Charged Ions On Atomic Hydrogen

NASA Astrophysics Data System (ADS)

Draganić, I. N.; Seely, D. G.; McCammon, D.; Havener, C. C.

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.

Water co-catalyzed selective dehydrogenation of methanol to formaldehyde and hydrogen

NASA Astrophysics Data System (ADS)

Shan, Junjun; Lucci, Felicia R.; Liu, Jilei; El-Soda, Mostafa; Marcinkowski, Matthew D.; Allard, Lawrence F.; Sykes, E. Charles H.; Flytzani-Stephanopoulos, Maria

2016-08-01

The non-oxidative dehydrogenation of methanol to formaldehyde is considered a promising method to produce formaldehyde and clean hydrogen gas. Although Cu-based catalysts have an excellent catalytic activity in the oxidative dehydrogenation of methanol, metallic Cu is commonly believed to be unreactive for the dehydrogenation of methanol in the absence of oxygen adatoms or oxidized copper. Herein we show that metallic Cu can catalyze the dehydrogenation of methanol in the absence of oxygen adatoms by using water as a co-catalyst both under realistic reaction conditions using silica-supported PtCu nanoparticles in a flow reactor system at temperatures below 250 °C, and in ultra-high vacuum using model PtCu(111) catalysts. Adding small amounts of isolated Pt atoms into the Cu surface to form PtCu single atom alloys (SAAs) greatly enhances the dehydrogenation activity of Cu. Under the same reaction conditions, the yields of formaldehyde from PtCu SAA nanoparticles are more than one order of magnitude higher than on the Cu nanoparticles, indicating a significant promotional effect of individual, isolated Pt atoms. Moreover, this study also shows the unexpected role of water in the activation of methanol. Water, a catalyst for methanol dehydrogenation at low temperatures, becomes a reactant in the methanol steam reforming reactions only at higher temperatures over the same metal catalyst.

DFT STUDY OF HYDROGEN STORAGE ON Li- AND Na-DOPED C59B HETEROFULLERENE

NASA Astrophysics Data System (ADS)

Zahedi, Ehsan; Mozaffari, Majid

2014-05-01

Effect of light alkali metal (Li and Na) decorated on the C59B heterofullerene for hydrogen storage is considered using DFT-MPW1PW91 method. Results show that Li and Na atoms strongly prefer to adsorb on top of five-member and six-member ring where a carbon atom is replaced by a boron atom. Significant charge transfer from the alkali metal to the C59B compensates for the electron deficiency of C59B and makes the latter aromatic in nature. Corrected binding energies of hydrogen molecule on the alkali-doped C59B using counterpoise method, structural properties and NBO analysis indicate that first hydrogen molecule is adsorbed physically and does not support minimal conditions of DOE requirement. Finally, positive values of binding energies for the adsorption of a second hydrogen molecule show that alkali doped C59B are capable of storing a maximum of one hydrogen molecule.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kharchenko, V.F., E-mail: vkharchenko@bitp.kiev.ua

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 determinemore » 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.« less

Thermally induced alkylation of diamond.

PubMed

Hoeb, Marco; Auernhammer, Marianne; Schoell, Sebastian J; Brandt, Martin S; Garrido, Jose A; Stutzmann, Martin; Sharp, Ian D

2010-12-21

We present an approach for the thermally activated formation of alkene-derived self-assembled monolayers on oxygen-terminated single and polycrystalline diamond surfaces. Chemical modification of the oxygen and hydrogen plasma-treated samples was achieved by heating in 1-octadecene. The resulting layers were characterized using X-ray photoelectron spectroscopy, thermal desorption spectroscopy, atomic force microscopy, Fourier transform infrared spectroscopy, and water contact angle measurements. This investigation reveals that alkenes selectively attach to the oxygen-terminated sites via covalent C-O-C bonds. The hydrophilic oxygen-terminated diamond is rendered strongly hydrophobic following this reaction. The nature of the process limits the organic layer growth to a single monolayer, and FTIR measurements reveal that such monolayers are dense and well ordered. In contrast, hydrogen-terminated diamond sites remain unaffected by this process. This method is thus complementary to the UV-initiated reaction of alkenes with diamond, which exhibits the opposite reactivity contrast. Thermal alkylation increases the range of available diamond functionalization strategies and provides a means of straightforwardly forming single organic layers in order to engineer the surface properties of diamond.

Nonepitaxial Thin-Film InP for Scalable and Efficient Photocathodes.

PubMed

Hettick, Mark; Zheng, Maxwell; Lin, Yongjing; Sutter-Fella, Carolin M; Ager, Joel W; Javey, Ali

2015-06-18

To date, some of the highest performance photocathodes of a photoelectrochemical (PEC) cell have been shown with single-crystalline p-type InP wafers, exhibiting half-cell solar-to-hydrogen conversion efficiencies of over 14%. However, the high cost of single-crystalline InP wafers may present a challenge for future large-scale industrial deployment. Analogous to solar cells, a thin-film approach could address the cost challenges by utilizing the benefits of the InP material while decreasing the use of expensive materials and processes. Here, we demonstrate this approach, using the newly developed thin-film vapor-liquid-solid (TF-VLS) nonepitaxial growth method combined with an atomic-layer deposition protection process to create thin-film InP photocathodes with large grain size and high performance, in the first reported solar device configuration generated by materials grown with this technique. Current-voltage measurements show a photocurrent (29.4 mA/cm(2)) and onset potential (630 mV) approaching single-crystalline wafers and an overall power conversion efficiency of 11.6%, making TF-VLS InP a promising photocathode for scalable and efficient solar hydrogen generation.

On the thermal stability of graphone

DOE Office of Scientific and Technical Information (OSTI.GOV)

Podlivaev, A. I.; Openov, L. A., E-mail: LAOpenov@mephi.ru

2011-07-15

Molecular dynamics simulation is used to study thermally activated migration of hydrogen atoms in graphone, a magnetic semiconductor formed of a graphene monolayer with one side covered with hydrogen. The temperature dependence of the characteristic time of disordering of graphone via hopping of hydrogen atoms to neighboring carbon atoms is established directly. The activation energy of this process is determined at E{sub a} = (0.05 {+-} 0.01) eV. The small value of E{sub a} is indicative of the extremely low thermal stability of graphone. The low stability presents a serious handicap for practical use of the material in nanoelectronics.

Hyperspherical Symmetry of Hydrogenic Orbitals and Recoupling Coefficients among Alternative Bases

NASA Astrophysics Data System (ADS)

Aquilanti, Vincenzo; Cavalli, Simonetta; Coletti, Cecilia

1998-04-01

Fock's representation of momentum space hydrogenic orbitals in terms of harmonics on the hypersphere S3 of a four-dimensional space is extended to classify alternative bases. These orbitals are of interest for Sturmian expansions of use in atomic and molecular structure calculations and for the description of atoms in fields. Because of the correspondence between the S3 manifold and the SU\\(2\\) group, new sum rules are established which are of relevance for the connection, not only among hydrogen atom orbitals in different bases, but also among the usual vector coupling coefficients and rotation matrix elements.

Effect of Ge atoms on crystal structure and optoelectronic properties of hydrogenated Si-Ge films

NASA Astrophysics Data System (ADS)

Li, Tianwei; Zhang, Jianjun; Ma, Ying; Yu, Yunwu; Zhao, Ying

2017-07-01

Optoelectronic and structural properties of hydrogenated microcrystalline silicon-germanium (μc-Si1-xGex:H) alloys prepared by radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) were investigated. When the Ge atoms were predominantly incorporated in amorphous matrix, the dark and photo-conductivity decreased due to the reduced crystalline volume fraction of the Si atoms (XSi-Si) and the increased Ge dangling bond density. The photosensitivity decreased monotonously with Ge incorporation under higher hydrogen dilution condition, which was attributed to the increase in both crystallization of Ge and the defect density.

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; ...

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 H 2 per litre inmore » 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. 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

On the structural and thermodynamic properties of the ?-hydrogen (?, Ce, Nd and Sm) systems

NASA Astrophysics Data System (ADS)

Blazina, Z.; Drasner, A.

1998-06-01

The 0953-8984/10/22/006/img3 (0953-8984/10/22/006/img4, Ce, Nd and Sm) intermetallic compounds were prepared and studied by means of x-ray powder diffraction. All compounds are single phase and exhibit the same hexagonal symmetry (0953-8984/10/22/006/img5 type; space group 0953-8984/10/22/006/img6) as do their prototype 0953-8984/10/22/006/img7 binaries. The interaction with hydrogen was also studied. It was found that all ternary intermetallics react readily and reversibly with hydrogen to form hydrides with high hydrogen contents of up to four hydrogen atoms per alloy formula unit. The pressure composition desorption isotherms were measured. The entropy, the enthalpy and the Gibbs free energy of formation have been extracted from the equilibrium plateau in the pressure-composition desorption isotherms. The hydrogen capacity and the equilibrium pressure of the 0953-8984/10/22/006/img3-hydrogen systems were compared with the corresponding values for their aluminium analogues and with the values for the 0953-8984/10/22/006/img7-hydrogen systems and briefly discussed. The hydride properties of gallium containing and aluminium containing compounds show great similarities whereby both series of ternary compounds form more stable hydrides and exhibit smaller hydrogen capacities than do the corresponding binaries.

Hydrogen absorption-desorption properties of U 2Ti

NASA Astrophysics Data System (ADS)

Takuya, Yamamoto; Satoru, Tanaka; Michio, Yamawaki

1990-02-01

Hydrogen absorption-desorption properties of U 2Ti intermetallic compound was examined over the temperature range of 298 to 973 K and at hydrogen pressures below 10 5 Pa. It absorbs hydrogen up to 7.6 atoms per F.U. (formula unit) by two step reactions and hence each desorption isotherm is separated into two plateau regions. In the first plateau, a newly-found ternary hydride is formed, where the hydrogen concentration, cH, reaches 2.4 H atoms/F.U. In the second plateau, UH 3 is formed and cH reaches 7.6 H atoms/F.U. The specimen is disintegrated into fine powder in the second plateau, while in the first plateau the ternary hydride which was identified to be UTi 2H x, ( x = 4.8 to 6.2) showed high durability against powdering. It is predicted that UTi 2 can be suitable material for tritium storage.

The Effect of Vicinal Versus Geminal Substitution of Hydrogen by Chlorine: Microwave Spectra and Molecular Structures of the Complexes of 1-CHLORO-1-FLUOROETHYLENE and (E)-1-CHLORO-2-FLUOROETHYLENE with Hydrogen Fluoride

NASA Astrophysics Data System (ADS)

Leung, Helen O.; Marshall, Mark D.; Lee, Alex J.; Bozzi, Aaron T.; Cohen, Paul M.; Lam, Mable

2010-06-01

Previous work in our laboratory has demonstrated that increasing the degree of fluorine substitution in complexes of fluoroethylenes with protic acids results in a weaker primary hydrogen-bonding interaction. This has been interpreted as arising from a decrease in the nucleophilicity of the hydrogen bond-accepting fluorine atom as a consequence of the inductive, electron-withdrawing nature of the additional fluorine atoms. We have recently extended these studies to investigate the effects of substitution with the less electronegative, but more polarizable chlorine atom. Through analysis of their 6-21 GHz Fourier transform microwave spectra, molecular structures are obtained for the complexes of 1-chloro-1-fluoroethylene and the (E) isomer of 1-chloro-2-fluoroethylene with hydrogen fluoride. The structures are compared with each other and with their difluoroethylene counterparts.

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.

Quantum chemical investigation on the role of Li adsorbed on anatase (101) surface nano-materials on the storage of molecular hydrogen.

PubMed

Srinivasadesikan, V; Raghunath, P; Lin, M C

2015-06-01

Lithiation of TiO2 has been shown to enhance the storage of hydrogen up to 5.6 wt% (Hu et al. J Am Chem Soc 128:11740-11741, 2006). The mechanism for the process is still unknown. In this work we have carried out a study on the adsorption and diffusion of Li atoms on the surface and migration into subsurface layers of anatase (101) by periodic density functional theory calculations implementing on-site Coulomb interactions (DFT+U). The model consists of 24 [TiO2] units with 11.097 × 7.655 Å(2) surface area. Adsorption energies have been calculated for different Li atoms (1-14) on the surface. A maximum of 13 Li atoms can be accommodated on the surface at two bridged O, Ti-O, and Ti atom adsorption sites, with 83 kcal mol(-1) adsorption energy for a single Li atom adsorbed between two bridged O atoms from where it can migrate into the subsurface layer with 27 kcal mol(-1) energy barrier. The predicted adsorption energies for H2 on the lithiated TiO2 (101) surface with 1-10 Li atoms revealed that the highest adsorption energies occurred on 1-Li, 5-Li, and 9-Li surfaces with 3.5, 4.4, and 7.6 kcal mol(-1), respectively. The values decrease rapidly with additional H2 co-adsorbed on the lithiated surfaces; the maximum H2 adsorption on the 9Li-TiO2(a) surface was estimated to be only 0.32 wt% under 100 atm H2 pressure at 77 K. The result of Bader charge analysis indicated that the reduction of Ti occurred depending on the Li atoms covered on the TiO2 surface.

Development of low angle grain boundaries in lightly deformed superconducting niobium and their influence on hydride distribution and flux perturbation

NASA Astrophysics Data System (ADS)

Sung, Z.-H.; Wang, M.; Polyanskii, A. A.; Santosh, C.; Balachandran, S.; Compton, C.; Larbalestier, D. C.; Bieler, T. R.; Lee, P. J.

2017-05-01

This study shows that low angle grain boundaries (LAGBs) can be created by small 5% strains in high purity (residual resistivity ratio ≥ 200) superconducting radio frequency (SRF)-grade single crystalline niobium (Nb) and that these boundaries act as hydrogen traps as indicated by the distribution of niobium hydrides (Nb1-xHx). Nb1-xHx is detrimental to SRF Nb cavities due to its normal conducting properties at cavity operating temperatures. By designing a single crystal tensile sample extracted from a large grain (>5 cm) Nb ingot slice for preferred slip on one slip plane, LAGBs and dense dislocation boundaries developed. With chemical surface treatments following standard SRF cavity fabrication practice, Nb1-xHx phases were densely precipitated at the LAGBs upon cryogenic cooling (8-10 K/min). Micro-crystallographic analysis confirmed heterogeneous hydride precipitation, which included significant hydrogen atom accumulation in LAGBs. Magneto-optical imaging analysis showed that these sites can then act as sites for both premature flux penetration and eventually flux trapping. However, this hydrogen related degradation at LAGBs did not completely disappear even after an 800 °C/2 h anneal typically used for hydrogen removal in SRF Nb cavities. These findings suggest that hydride precipitation at an LAGB is facilitated by a non-equilibrium concentration of vacancy-hydrogen (H) complexes aided by mechanical deformation and the hydride phase interferes with the recovery process under 800 °C annealing.

Development of low angle grain boundaries in lightly deformed superconducting niobium and their influence on hydride distribution and flux perturbation

DOE PAGES

Sung, Z. -H.; Wang, M.; Polyanskii, A. A.; ...

2017-05-19

This study shows that low angle grain boundaries (LAGBs) can be created by small 5% strains in high purity (RRR ≥ 200) SRF-grade single crystalline niobium (Nb) and that these boundaries act as hydrogen traps as indicated by the distribution of niobium hydrides (Nb 1-xH x). Nb 1-xH x is detrimental to superconducting radio frequency (SRF) Nb cavities due to its normal conducting properties at cavity operating temperatures. By designing a single crystal tensile sample extracted from a large grain (>5 cm) Nb ingot slice for preferred slip on one slip plane, LAGBs and dense dislocation boundaries developed. With chemicalmore » surface treatments following standard SRF cavity fabrication practice, Nb1-xHx phases were densely precipitated at the LAGBs upon cryogenic cooling (8-10 K/min). Micro-crystallographic analysis confirmed heterogeneous hydride precipitation, which included significant hydrogen atom accumulation in LAGBs. Magneto-optical imaging (MOI) analysis showed that these sites can then act as sites for both premature flux penetration and eventually flux trapping. However, this hydrogen related degradation at LAGBs did not completely disappear even after a 800 °C/2hrs anneal typically used for hydrogen removal in SRF Nb cavities. These findings suggest that hydride precipitation at a LAGB is facilitated by a non-equilibrium concentration of vacancy-hydrogen (H) complexes aided by mechanical deformation and the hydride phase interferes with the recovery process under 800°C annealing.« less

Enhanced etching of tin-doped indium oxide due to surface modification by hydrogen ion injection

NASA Astrophysics Data System (ADS)

Li, Hu; Karahashi, Kazuhiro; Friederich, Pascal; Fink, Karin; Fukasawa, Masanaga; Hirata, Akiko; Nagahata, Kazunori; Tatsumi, Tetsuya; Wenzel, Wolfgang; Hamaguchi, Satoshi

2018-06-01

It is known that the etching yield (i.e., sputtering yield) of tin-doped indium oxide (ITO) by hydrocarbon ions (CH x +) is higher than its corresponding physical sputtering yield [H. Li et al., J. Vac. Sci. Technol. A 33, 060606 (2015)]. In this study, the effects of hydrogen in the incident hydrocarbon ion beam on the etching yield of ITO have been examined experimentally and theoretically with the use of a mass-selected ion beam system and by first-principles quantum mechanical (QM) simulation. As in the case of ZnO [H. Li et al., J. Vac. Sci. Technol. A 35, 05C303 (2017)], mass-selected ion beam experiments have shown that the physical sputtering yield of ITO by chemically inert Ne ions increases after a pretreatment of the ITO film by energetic hydrogen ion injection. First-principles QM simulation of the interaction of In2O3 with hydrogen atoms shows that hydrogen atoms embedded in In2O3 readily form hydroxyl (OH) groups and weaken or break In–O bonds around the hydrogen atoms, making the In2O3 film less resistant to physical sputtering. This is consistent with experimental observation of the enhanced etching yields of ITO by CH x + ions, considering the fact that hydrogen atoms of the incident CH x + ions are embedded into ITO during the etching process.

Hydrogen adsorption site on the Ni?110?-p(1 × 2)-H surface from time-of-flight scattering and recoiling spectrometry (TOF-SARS)

NASA Astrophysics Data System (ADS)

Bu, H.; Roux, C. D.; Rabalais, J. W.

The adsorption site of hydrogen on the Ni{110}-p(1 × 2)-H surface resulting from saturation exposure to H 2 at ˜ 310-350 K has been investigated by time-of-flight scattering and recoiling spectrometry (TOF-SARS). The recoiled neutral plus ion hydrogen atom flux resulting from 2-5 keV Ar + or Ne + pulsed ion beams incident on the surface was monitored as a function of crystal azimuthal angle and beam incidence angle. From classical trajectory calculations and shadowing and blocking analyses, it is concluded that hydrogen atoms are localized at the pseudo-three-fold sites on the (1 × 2) missing-row (MR) reconstructed Ni{110} surface; the (1 × 2) MR reconstruction is induced by hydrogen adsorption shown elsewhere [Surf. Sci. 259 (1991) 253]. Only the pseudo-three-fold site is consistent with all of the experimental data. The coordinates of the hydrogen adsorption site with respect to the nickel lattice were determined. The lateral distance of hydrogen from the 1st-layer Ni <1 overline10> rows is 1.56 ± 0.12 Å and the vertical distance above the substrate is 0.21 ± 0.12 Å, providing NiH bond lengths of 2.0 Å to the two-layer Ni atoms and 1.5 Å to the 2nd-layer Ni atom.

The Potential Role Played by the Fullerene-Like Structures of Interstellar Carbon Dust in the Formation of Molecular Hydrogen in Space

NASA Astrophysics Data System (ADS)

Cataldo, Franco; Iglesias-Groth, Susana

After a general introduction to the problem of formation of molecular hydrogen from atomic hydrogen in the interstellar medium and in the dense molecular clouds in particular, and after the explanation of the key role played by the surfaces on this process, it is proposed that the most suitable carbon surface for the formation of molecular hydrogen (from the radiative association process of atomic hydrogen) can be represented by carbon black rather than by graphite. Furthermore, it is proposed that the fullerene-like structures present in the carbon black graphene sheets are the reaction sites where molecular hydrogen may be formed.

Deposition of device quality low H content, amorphous silicon films

DOEpatents

Mahan, A.H.; Carapella, J.C.; Gallagher, A.C.

1995-03-14

A high quality, low hydrogen content, hydrogenated amorphous silicon (a-Si:H) film is deposited by passing a stream of silane gas (SiH{sub 4}) over a high temperature, 2,000 C, tungsten (W) filament in the proximity of a high temperature, 400 C, substrate within a low pressure, 8 mTorr, deposition chamber. The silane gas is decomposed into atomic hydrogen and silicon, which in turn collides preferably not more than 20--30 times before being deposited on the hot substrate. The hydrogenated amorphous silicon films thus produced have only about one atomic percent hydrogen, yet have device quality electrical, chemical, and structural properties, despite this lowered hydrogen content. 7 figs.

Deposition of device quality low H content, amorphous silicon films

DOEpatents

Mahan, Archie H.; Carapella, Jeffrey C.; Gallagher, Alan C.

1995-01-01

A high quality, low hydrogen content, hydrogenated amorphous silicon (a-Si:H) film is deposited by passing a stream of silane gas (SiH.sub.4) over a high temperature, 2000.degree. C., tungsten (W) filament in the proximity of a high temperature, 400.degree. C., substrate within a low pressure, 8 mTorr, deposition chamber. The silane gas is decomposed into atomic hydrogen and silicon, which in turn collides preferably not more than 20-30 times before being deposited on the hot substrate. The hydrogenated amorphous silicon films thus produced have only about one atomic percent hydrogen, yet have device quality electrical, chemical, and structural properties, despite this lowered hydrogen content.

First-principles calculations of niobium hydride formation in superconducting radio-frequency cavities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ford, Denise C.; Cooley, Lance D.; Seidman, David N.

Niobium hydride is suspected to be a major contributor to degradation of the quality factor of niobium superconducting radio-frequency (SRF) cavities. In this study, we connect the fundamental properties of hydrogen in niobium to SRF cavity performance and processing. We modeled several of the niobium hydride phases relevant to SRF cavities and present their thermodynamic, electronic, and geometric properties determined from calculations based on density-functional theory. We find that the absorption of hydrogen from the gas phase into niobium is exothermic and hydrogen becomes somewhat anionic. The absorption of hydrogen by niobium lattice vacancies is strongly preferred over absorption intomore » interstitial sites. A single vacancy can accommodate six hydrogen atoms in the symmetrically equivalent lowest-energy sites and additional hydrogen in the nearby interstitial sites affected by the strain field: this indicates that a vacancy can serve as a nucleation center for hydride phase formation. Small hydride precipitates may then occur near lattice vacancies upon cooling. Vacancy clusters and extended defects should also be enriched in hydrogen, potentially resulting in extended hydride phase regions upon cooling. We also assess the phase changes in the niobium-hydrogen system based on charge transfer between niobium and hydrogen, the strain field associated with interstitial hydrogen, and the geometry of the hydride phases. The results of this study stress the importance of not only the hydrogen content in niobium, but also the recovery state of niobium for the performance of SRF cavities.« less

Surface loss probability of atomic hydrogen for different electrode cover materials investigated in H₂-Ar low-pressure plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sode, M., E-mail: maik.sode@ipp.mpg.de; Schwarz-Selinger, T.; Jacob, W.

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,more » 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.« less

Computer Animation of a Chemical Reaction.

ERIC Educational Resources Information Center

Eaker, Charles W.; Jacobs, Edwin L.

1982-01-01

Taking a prototype chemical reaction (molecular hydrogen plus hydrogen atom), constructs an accurate semiempirical, generalized diatomics-in-molecules potential energy surface, calculates motions of these atoms on this surface using REACTS trajectory program, and presents results as moving picture on a microcomputer graphics system. Provides…

Research Laboratory of Electronics Annual Report Number 125.

DTIC Science & Technology

1983-01-01

Picosecond Optics 35 7.4 Ultrashort Pulse Formation 37 7.5 Ferntosecond Laser System 37 7.6 Parametric Scattering with Femtosecond Pulses 38 7.7 Near-IR...ionization of atomic hydrogen as calculated by 10 Reinhardt for a single frequency laser . To facilitate comparison, the cross section has been divided by 13...As the intensity increases, the peaks shift to the blue and become broader. Figure 3-3: Ionization profiles produced by laser intensity 10 and at five

Hot hydrogen and oxygen atoms in the upper atmospheres of Venus and Mars

NASA Astrophysics Data System (ADS)

Nagy, A. F.; Kim, J.; Cravens, T. E.

1990-04-01

Optical observations of hot atoms in the atmospheres of Venus and Mars are briefly reviewed. A summary of hot hydrogen and oxygen production and loss processes is given. Results of some recent model calculations as well as a number of new results of the hot hydrogen and oxygen populations are presented and their implication in terms of solar wind interaction processes is discussed.

The First Stars in the Universe and Cosmic Reionization

NASA Astrophysics Data System (ADS)

Barkana, Rennan

2006-08-01

The earliest generation of stars, far from being a mere novelty, transformed the universe from darkness to light. The first atoms to form after the Big Bang filled the universe with atomic hydrogen and a few light elements. As gravity pulled gas clouds together, the first stars ignited and their radiation turned the surrounding atoms into ions. By looking at gas between us and distant galaxies, we know that this ionization eventually pervaded all space, so that few hydrogen atoms remain today between galaxies. Knowing exactly when and how it did so is a primary goal of cosmologists, because this would tell us when the early stars formed and in what kinds of galaxies. Although this ionization is beginning to be understood by using theoretical models and computer simulations, a new generation of telescopes is being built that will map atomic hydrogen throughout the universe.

A Hirshfeld surface analysis, supramolecular structure and magnetic properties of a new Cu(II) complex with the 4-amino-6-methoxypyrimidine ligand

NASA Astrophysics Data System (ADS)

Nbili, W.; Kaabi, K.; Ferenc, W.; Cristovão, B.; Lefebvre, F.; Jelsch, Christian; Ben Nasr, Cherif

2017-02-01

A new Cu(II) complex with the bridge bidentate ligand 4-amino-6-methoxypyrimidine, [Cu(C5H7N3O)(H2O)(NO3)2], has been prepared at room temperature and characterized by single crystal X-ray diffraction and IR spectroscopy. The compound crystallizes in the monoclinic space group C2/c with lattice parameters a = 17.783 (4), b = 11.131 (3), c = 12.594 (3) Å, β = 117.616 (3)°, V = 2209.0 (9) Å3 and Z = 8. The Cu(II) cation is hexa-coordinated, in distorted octahedral fashion, by two nitrogen atoms of two 4-amino-6-methoxypyrimidine ligands, one water oxygen atom and three oxygen atoms of two nitrate anions. In the atomic arrangement, the organic ligands and the 6-connected Cu centers are linked with each other to give a 1-D corrugated chain running along the b-axis direction. The chains are interconnected via Osbnd H⋯O, Csbnd H⋯O, Nsbnd H⋯O hydrogen bonds to form a three dimensional network. The analysis of contacts on the Hirshfeld surface shows that the crystal packing is driven mainly by the electrostatic interactions: the coordination of Cu(II) by O and N as well as strong hydrogen bonds. The vibrational absorption bands were identified by infrared spectroscopy. Magnetic properties were also studied to characterize the complex.

Periodic density functional theory study of ethylene hydrogenation over Co3O4 (1 1 1) surface: The critical role of oxygen vacancies

NASA Astrophysics Data System (ADS)

Lu, Jinhui; Song, JiaJia; Niu, Hongling; Pan, Lun; Zhang, Xiangwen; Wang, Li; Zou, Ji-Jun

2016-05-01

Recently, metal oxides are attracting increasing interests as hydrogenation catalyst. Herein we studied the hydrogenation of ethylene on perfect and oxygen defective Co3O4 (1 1 1) using periodic density functional theory. The energetics and pathways of ethylene hydrogenation to ethane were determined. We have demonstrated that (i) H2 dissociation on Co3O4 is a complicated two-step process through a heterolytic cleavage, followed by the migration of H atom and finally yields the homolytic product on both perfect and oxygen defective Co3O4 (1 1 1) surfaces easily. (ii) After introducing the surface oxygen vacancy, the stepwise hydrogenation of ethylene by atomic hydrogen is much easier than that on perfect surface due to the weaker bond strength of OH group. The strength of Osbnd H bond is a crucial factor for the hydrogenation reaction which involves the breakage of Osbnd H bond. The formation of oxygen vacancy increases the electronic charges at the adjacent surface O, which reduces its capability of further gaining electrons from adsorbed atomic hydrogen and then weakens the strength of Osbnd H bond. These results emphasize the importance of the oxygen vacancies for hydrogenation on metal oxides.

Structure and magnetism of a Mn(III)-Mn(II)-Mn(II)-Mn(III) chain complex.

PubMed

Uhrecký, Róbert; Moncoľ, Ján; Koman, Marian; Titiš, Ján; Boča, Roman

2013-07-14

A novel tetranuclear manganese(II/III) complex with anions of pyridine-2,6-dicarboxylic acid (dipicolinic acid) has been synthesised and magneto-structurally characterised. The crystal structure of [Mn(II)2Mn(III)2(dipic)6(H2O)4]·2CH3OH·4H2O has been determined by single-crystal X-ray diffraction. The tetranuclear complex molecule [Mn(II)2Mn(III)2(dipic)6(H2O)4] is centrosymmetric and two manganese(II) and two manganese(III) atoms are bridged by four dipicolinate ligands. The complex molecules and uncoordinated water and methanol molecules are connected through hydrogen bonds and they form a 3D supramolecular hydrogen-bonding network.

The betainic form of (imidazol-2-yl)phenylphosphinic acid hydrate

PubMed Central

Kunz, Peter C.; Frank, Walter

2010-01-01

Single crystals of the title compound, (imidazolium-2-yl)phenyl­phosphinate monohydrate, C9H9N2O2·H2O, were ob­tained from methanol/water after deprotection and oxidation of bis­(1-diethoxy­methyl­imidazol-2-yl)phenyl­phosphane. In the structure, several N–H⋯O and P—O⋯H–O hydrogen bonds are found. π–π inter­actions between the protonated imidazolyl rings [centroid–centroid distance = 3.977 (2) Å] help to establish the crystal packing. The hydrate water mol­ecule builds hydrogen bridges to three mol­ecules of the phosphinic acid by the O and both H atoms. PMID:21579513

Structural and vibrational spectral investigations of melaminium maleate monohydrate by FTIR, FT-Raman and quantum chemical calculations

NASA Astrophysics Data System (ADS)

Arjunan, V.; Kalaivani, M.; Marchewka, M. K.; Mohan, S.

2013-04-01

The structural investigations of the molecular complex of melamine with maleic acid, namely melaminium maleate monohydrate have been carried out by quantum chemical methods in addition to FTIR, FT-Raman and far-infrared spectral studies. The quantum chemical studies were performed with DFT (B3LYP) method using 6-31G**, cc-pVDZ and 6-311++G** basis sets to determine the energy, structural and thermodynamic parameters of melaminium maleate monohydrate. The hydrogen atom from maleic acid was transferred to the melamine molecule giving the singly protonated melaminium cation. The ability of ions to form spontaneous three-dimensional structure through weak Osbnd H⋯O and Nsbnd H⋯O hydrogen bonds shows notable vibrational effects.

Atomically layer-by-layer diffusion of oxygen/hydrogen in highly epitaxial PrBaCo2O5.5+δ thin films

NASA Astrophysics Data System (ADS)

Bao, Shanyong; Xu, Xing; Enriquez, Erik; Mace, Brennan E.; Chen, Garry; Kelliher, Sean P.; Chen, Chonglin; Zhang, Yamei; Whangbo, Myung-Hwan; Dong, Chuang; Zhang, Qinyu

2015-12-01

Single-crystalline epitaxial thin films of PrBaCo2O5.5+δ (PrBCO) were prepared, and their resistance R(t) under a switching flow of oxidizing and reducing gases were measured as a function of the gas flow time t in the temperature range of 200-800 °C. During the oxidation cycle under O2, the PrBCO films exhibit fast oscillations in their dR(t)/dt vs. t plots, which reflect the oxidation processes, Co2+/Co3+ → Co3+ and Co3+ → Co3+/Co4+, that the Co atoms of PrBCO undergo. Each oscillation consists of two peaks, with larger and smaller peaks representing the oxygen/hydrogen diffusion through the (BaO)(CoO2)(PrO)(CoO2) layers of PrBCO via the oxygen-vacancy-exchange mechanism. This finding paves a significant avenue for cathode materials operating in low-temperature solid-oxide-fuel-cell devices and for chemical sensors with wide range of operating temperature.

Influence of C-H···O Hydrogen Bonds on Macroscopic Properties of Supramolecular Assembly.

PubMed

Ji, Wei; Liu, Guofeng; Li, Zijian; Feng, Chuanliang

2016-03-02

For CH···O hydrogen bonds in assembled structures and the applications, one of the critical issues is how molecular spatial structures affect their interaction modes as well as how to translate the different modes into the macroscopic properties of materials. Herein, coumarin-derived isomeric hydrogelators with different spatial structures are synthesized, where only nitrogen atoms locate at the ortho, meso, or para position in the pyridine ring. The gelators can self-assemble into single crystals and nanofibrous networks through CH···O interactions, which are greatly influenced by nitrogen spatial positions in the pyridine ring, leading to the different self-assembly mechanisms, packing modes, and properties of the nanofibrous networks. Typically, different cell proliferation rates are obtained on the different CH···O bonds driving nanofibrous structures, implying that tiny variation of the stereo-position of nitrogen atoms can be sensitively detected by cells. The study paves a novel way to investigate the influence of isomeric molecular assembly on macroscopic properties and functions of materials.

Structure and stability of solid Xe(H 2) n

DOE PAGES

Somayazulu, Maddury; Dera, Przemyslaw; Smith, Jesse; ...

2015-03-10

Mixtures of xenon and molecular hydrogen form a series of hexagonal, van der Waals compounds at high pressures and at 300 K. Synchrotron, x-ray, single crystal diffraction studies reveal that below 7.5 GPa, Xe(H 2) 8 crystallizes in a P3¯m1 structure that displays pressure-induced occupancy changes of two pairs of xenon atoms located on the 2c and 2d sites (while the third pair on yet another 2c site remains fully occupied). The occupancy becomes 1 at the P3¯m1 to R3 transition and all the xenon atoms occupy the 3d sites in the high-pressure structure. These pressure-induced changes in occupancy coincidemore » with volume changes that maintain the average Xe:H 2 stoichiometry fixed at 1:8. Furthermore, the synchrotron x-ray diffraction and Raman measurements show that this unique hydrogen-bearing compound that can be synthesized at 4.2 GPa and 300 K, quenched at low temperatures to atmospheric pressure, and retained up to 90 K on subsequent warming.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tsuo, Y.S.; Smith, E.B.; Deb, S.K.

A Kaufman ion beam source was used to implant hydrogen atoms into glow-discharge-deposited amorphous silicon materials in which the hydrogen content had been driven out by heating. We found that the hydrogen atoms introduced by this low-energy (less than 700 eV) ion implantation method bonded predominantly as SiH. An air mass one, photo-to-dark-conductivity ratio as high as 5.6 x 10/sup 5/ has been obtained with hydrogen-implanted materials. No light-induced reduction of the photo- and dark conductivities has been observed in these materials after 20 h of AMl illumnination.

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.

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.

Hydrogen maser oscillation at 10 K

NASA Technical Reports Server (NTRS)

Crampton, S. B.; Jones, K. M.; Souza, S. P.

1984-01-01

A low temperature atomic hydrogen maser was developed using frozen atomic neon as the storage surface. The maser has been operated in the pulsed mode at temperatures from 6 K to 11 K and as a self-excited oscillator from 9 K to 10.5 K.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gabriel, O.; Harskamp, W. E. N. van; Schram, D. C.

The cascaded arc is a plasma source providing high fluxes of excited and reactive species such as ions, radicals and rovibrationally excited molecules. The plasma is produced under pressures of some kPa in a direct current arc with electrical powers up to 10 kW. The plasma leaves the arc channel through a nozzle and expands with supersonic velocity into a vacuum-chamber kept by pumps at low pressures. We investigated the case of a pure hydrogen plasma jet with and without an applied axial magnetic field that confines ions and electrons in the jet. Highly excited molecules and atoms were detectedmore » by means of laser-induced fluorescence and optical emission spectroscopy. In case of an applied magnetic field the atomic state distribution of hydrogen atoms shows an overpopulation between the electronic states p = 5, 4 and 3. The influence of the highly excited hydrogen molecules on H{sup -} ion formation and a possible mechanism involving this negative ion and producing atomic hydrogen in state p = 3 will be discussed.« less

Reaction of atomic hydrogen with formic acid.

PubMed

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

2014-04-07

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.

Structural and magnetic properties of FeHx (x=0.25; 0.50; 0.75)

NASA Astrophysics Data System (ADS)

Mikhaylushkin, A. S.; Skorodumova, N. V.; Ahuja, R.; Johansson, B.

2006-05-01

The structural and magnetic properties of the FeHx (x=0.25; 0.50; 0.75) compounds have been studied using the projector augmented wave (PAW) method within the generalized gradient approximation (GGA). We compare the hcp, dhcp and fcc structures and find that for the considered concentrations of hydrogen the hcp structure is most stable in a wide pressure range. The magnetic behavior of iron is crucially influenced by hydrogen. In particular, the local moment on a Fe atom depends on the number of hydrogen atoms in the atom surroundings. Iron atoms, which are crystallographically equivalent in their original structures (hcp, fcc) but have different number of hydrogen neighbors, are shown to have different local magnetic moments. This finding suggests that the experimental observations of two magnetic moments in iron hydride can be explained by nonstoichiometry of the hydride and might not be a direct evidence for the presence of the dhcp phase.

Atom-bond electronegativity equalization method fused into molecular mechanics. I. A seven-site fluctuating charge and flexible body water potential function for water clusters.

PubMed

Yang, Zhong-Zhi; Wu, Yang; Zhao, Dong-Xia

2004-02-08

Recently, experimental and theoretical studies on the water system are very active and noticeable. A transferable intermolecular potential seven points approach including fluctuation charges and flexible body (ABEEM-7P) based on a combination of the atom-bond electronegativity equalization and molecular mechanics (ABEEM/MM), and its application to small water clusters are explored and tested in this paper. The consistent combination of ABEEM and molecular mechanics (MM) is to take the ABEEM charges of atoms, bonds, and lone-pair electrons into the intermolecular electrostatic interaction term in molecular mechanics. To examine the charge transfer we have used two models coming from the charge constraint types: one is a charge neutrality constraint on whole water system and the other is on each water molecule. Compared with previous water force fields, the ABEEM-7P model has two characters: (1) the ABEEM-7P model not only presents the electrostatic interaction of atoms, bonds and lone-pair electrons and their changing in respond to different ambient environment but also introduces "the hydrogen bond interaction region" in which a new parameter k(lp,H)(R(lp,H)) is used to describe the electrostatic interaction of the lone-pair electron and the hydrogen atom which can form the hydrogen bond; (2) nonrigid but flexible water body permitting the vibration of the bond length and angle is allowed due to the combination of ABEEM and molecular mechanics, and for van der Waals interaction the ABEEM-7P model takes an all atom-atom interaction, i.e., oxygen-oxygen, hydrogen-hydrogen, oxygen-hydrogen interaction into account. The ABEEM-7P model based on ABEEM/MM gives quite accurate predictions for gas-phase state properties of the small water clusters (H(2)O)(n) (n=2-6), such as optimized geometries, monomer dipole moments, vibrational frequencies, and cluster interaction energies. Due to its explicit description of charges and the hydrogen bond, the ABEEM-7P model will be applied to discuss properties of liquid water, ice, aqueous solutions, and biological systems.

Nuclear spin polarized H and D by means of spin-exchange optical pumping

NASA Astrophysics Data System (ADS)

Stenger, Jörn; Grosshauser, Carsten; Kilian, Wolfgang; Nagengast, Wolfgang; Ranzenberger, Bernd; Rith, Klaus; Schmidt, Frank

1998-01-01

Optically pumped spin-exchange sources for polarized hydrogen and deuterium atoms have been demonstrated to yield high atomic flow and high electron spin polarization. For maximum nuclear polarization the source has to be operated in spin temperature equilibrium, which has already been demonstrated for hydrogen. In spin temperature equilibrium the nuclear spin polarization PI equals the electron spin polarization PS for hydrogen and is even larger than PS for deuterium. We discuss the general properties of spin temperature equilibrium for a sample of deuterium atoms. One result are the equations PI=4PS/(3+PS2) and Pzz=PSṡPI, where Pzz is the nuclear tensor polarization. Furthermore we demonstrate that the deuterium atoms from our source are in spin temperature equilibrium within the experimental accuracy.

Rocket and spacecraft studies of ultraviolet emissions from astrophysical targets

NASA Technical Reports Server (NTRS)

Fastie, W. G.; Moos, H. W.; Feldman, P. D.; Henry, R. C.

1975-01-01

Rocket and spacecraft far-UV spectral measurements of several astrophysical targets are reviewed. These include observations of Ly-alpha emissions from Arcturus, Apollo-17 far-UV spectrometry of eta UMa and five other stars, Apollo-17 observations of the lunar atmosphere and the diffuse UV background, and far-UV spectral studies of Venus, Jupiter, and Comet Kohoutek. The Arcturus observations indicated a chromosphere with neutral atomic-hydrogen and atomic-oxygen emissions as well as a very weak atomic-carbon line. The planetary studies revealed O I and C I emissions in the Venusian spectrum as well as large Ly-alpha emissions and possible molecular-hydrogen emissions in that of Jupiter. The lunar observations demonstrated that solar protons do not produce an atomic-hydrogen atmosphere on the moon.

Synthesis and crystal structure of the coordination compound of pyridoxine with manganese sulfate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Furmanova, N. G., E-mail: furm@ns.crys.ras.ru; Verin, I. A.; Shyityeva, N.

2011-11-15

The reaction of pyridoxine with manganese sulfate in an aqueous solution gave the coordination compound MnSO{sub 4} {center_dot} 2C{sub 8}H{sub 11}O{sub 3}N {center_dot} 2H{sub 2}O (I). The structure of I was determined from single-crystal X-ray diffraction data. In the centrosymmetric complex (sp. gr. P1-bar, Z = 1), the Mn atom is coordinated by two pyridoxine molecules and two water molecules, thus adopting an octahedral coordination. The sulfate anion is also at a center of symmetry and, consequently, is disordered. The pyridoxine molecules are coordinated to the metal atom through the oxygen atoms of the deprotonated hydroxyl group and the CH{submore » 2}OH group that retains the hydrogen atom. The nitrogen atom is protonated in such a way that the heterocycle assumes a pyridinium character. The crystal structure also contains six water molecules of crystallization. A thermogravimetric study showed that the decomposition of I occurs in several successive steps, such as dehydration, the combustion of organic ligands, and the formation of an inorganic residue.« less

Gas phase reaction of nitric acid with hydroxyl radical without and with water. A theoretical investigation.

PubMed

Gonzalez, Javier; Anglada, Josep M

2010-09-02

The gas phase reaction between nitric acid and hydroxyl radical, without and with a single water molecule, has been investigated theoretically using the DFT-B3LYP, MP2, QCISD, and CCSD(T) theoretical approaches with the 6-311+G(2df,2p) and aug-cc-pVTZ basis sets. The reaction without water begins with the formation of a prereactive hydrogen-bonded complex and has several elementary reactions processes. They include proton coupled electron transfer, hydrogen atom transfer, and proton transfer mechanisms, and our kinetic study shows a quite good agreement of the behavior of the rate constant with respect to the temperature and to the pressure with the experimental results from the literature. The addition of a single water molecule results in a much more complex potential energy surface although the different elementary reactions found have the same electronic features that the naked reaction. Two transition states are stabilized by the effect of a hydrogen bond interaction originated by the water molecule, and in the prereactive hydrogen bond region there is a geometrical rearrangement necessary to prepare the HO and HNO(3) moieties to react to each other. This step contributes the reaction to be slower than the reaction without water and explains the experimental finding, pointing out that there is no dependence for the HNO(3) + HO reaction on water vapor.

Spectral and cyclic voltammetric studies on some intramolecularly hydrogen bonded arylhydrazones: Crystal and molecular structure of 2-(2-(3-nitrophenyl)hydrazono)-5,5-dimethylcyclohexane-1,3-dione

NASA Astrophysics Data System (ADS)

Sethukumar, A.; Arul Prakasam, B.

2010-01-01

A series of arylhydrazone derivatives ( 1- 7) were prepared by the coupling of acetylacetone/dimedone with respective aromatic diazonium salts and characterized by IR, 1H and 13C NMR spectra. The IR and NMR spectral data clearly manifests the effective intramolecular hydrogen bonding in all the cases. Cyclic voltammetric studies certainly indicate that in all the cases the reduced center is C dbnd N bond of hydrazonic moiety. The single crystal X-ray structural analysis of 2-(2-(3-nitrophenyl)hydrazono)-5,5-dimethylcyclohexane-1,3-dione ( 6) is also reported. Single crystal X-ray analysis of 6 evidences the intramolecular hydrogen bonding with the N(2)⋯O(4) distance of 2.642(15) Å, which can be designated as S(6) according to Etter's graph nomenclature. The cyclohexane ring conformation in the molecule ( 6) can be described as an envelope. RAHB studies suggest that the resonance assistance for hydrogen bonding is significantly reduced for the compound ( 6) due to the non-planarity of the six atoms which are involved in resonant cycle S(6) of Etter's graph. The planarity of the resonant cycle S(6) is very much disturbed by the conformational requirement of the cyclohexane ring and hence RAHB concept is less operative in this case.

Calculating Relativistic Transition Matrix Elements for Hydrogenic Atoms Using Monte Carlo Methods

NASA Astrophysics Data System (ADS)

Alexander, Steven; Coldwell, R. L.

2015-03-01

The nonrelativistic transition matrix elements for hydrogen atoms can be computed exactly and these expressions are given in a number of classic textbooks. The relativistic counterparts of these equations can also be computed exactly but these expressions have been described in only a few places in the literature. In part, this is because the relativistic equations lack the elegant simplicity of the nonrelativistic equations. In this poster I will describe how variational Monte Carlo methods can be used to calculate the energy and properties of relativistic hydrogen atoms and how the wavefunctions for these systems can be used to calculate transition matrix elements.

Epi-cleaning of Ge/GeSn heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Di Gaspare, L.; Sabbagh, D.; De Seta, M.

2015-01-28

We demonstrate a very-low temperature cleaning technique based on atomic hydrogen irradiation for highly (1%) tensile strained Ge epilayers grown on metastable, partially strain relaxed GeSn buffer layers. Atomic hydrogen is obtained by catalytic cracking of hydrogen gas on a hot tungsten filament in an ultra-high vacuum chamber. X-ray photoemission spectroscopy, reflection high energy electron spectroscopy, atomic force microscopy, secondary ion mass spectroscopy, and micro-Raman showed that an O- and C-free Ge surface was achieved, while maintaining the same roughness and strain condition of the as-deposited sample and without any Sn segregation, at a process temperature in the 100–300 °C range.

Epi-cleaning of Ge/GeSn heterostructures

NASA Astrophysics Data System (ADS)

Di Gaspare, L.; Sabbagh, D.; De Seta, M.; Sodo, A.; Wirths, S.; Buca, D.; Zaumseil, P.; Schroeder, T.; Capellini, G.

2015-01-01

We demonstrate a very-low temperature cleaning technique based on atomic hydrogen irradiation for highly (1%) tensile strained Ge epilayers grown on metastable, partially strain relaxed GeSn buffer layers. Atomic hydrogen is obtained by catalytic cracking of hydrogen gas on a hot tungsten filament in an ultra-high vacuum chamber. X-ray photoemission spectroscopy, reflection high energy electron spectroscopy, atomic force microscopy, secondary ion mass spectroscopy, and micro-Raman showed that an O- and C-free Ge surface was achieved, while maintaining the same roughness and strain condition of the as-deposited sample and without any Sn segregation, at a process temperature in the 100-300 °C range.

N′-[(E)-3-Chloro-2-fluoro­benzyl­idene]-6-methyl­nicotinohydrazide monohydrate

PubMed Central

Fun, Hoong-Kun; Quah, Ching Kheng; Shyma, P. C.; Kalluraya, Balakrishna; Vidyashree, J. H. S.

2012-01-01

The title compound, C14H11ClFN3O·H2O, exists in an E conformation with respect to the N=C bond. The pyridine ring forms a dihedral angle of 5.00 (9)° with the benzene ring. In the crystal, the ketone O atom accepts one O—H⋯O and one C—H⋯O hydrogen bond, the water O atom accepts one N—H⋯O and two C—H⋯O hydrogen bonds and the pyridine N atom accepts one O—H⋯N hydrogen bond, forming layers parallel to the ab plane. PMID:22798798

4-[(E)-(2,4-Difluoro-phen-yl)(hydroxy-imino)meth-yl]piperidinium picrate.

PubMed

Jasinski, Jerry P; Butcher, Ray J; Yathirajan, H S; Mallesha, L; Mohana, K N

2009-09-05

The title compound, C(12)H(15)F(2)N(2)O(+)·C(6)H(2)N(3)O(7) (-), a picrate salt of 4-[(E)-(2,4-difluoro-phen-yl)(hydroxy-imino)meth-yl]piper-idine, crystallizes with two independent mol-ecules in a cation-anion pair in the asymmetric unit. In the cation, a methyl group is tris-ubstituted by hydroxy-imino, piperidin-4-yl and 2,4-difluoro-phenyl groups, the latter of which contains an F atom disordered over two positions in the ring [occupancy ratio 0.631 (4):0.369 (4)]. The mean plane of the hydr-oxy group is in a synclinical conformation nearly orthogonal [N-C-C-C = 72.44 (19)°] to the mean plane of the piperidine ring, which adopts a slightly distorted chair conformation. The dihedral angle between the mean plane of the 2,4-difluoro-phenyl and piperidin-4-yl groups is 60.2 (3)°. In the picrate anion, the mean planes of the two o-NO(2) and single p-NO(2) groups adopt twist angles of 5.7 (2), 25.3 (7) and 8.3 (6)°, respectively, with the attached planar benzene ring. The dihedral angle between the mean planes of the benzene ring in the picrate anion and those in the hydroxy-imino, piperidin-4-yl and 2,4-difluoro-phenyl groups in the cation are 84.9 (7), 78.9 (4) and 65.1 (1)°, respectively. Extensive hydrogen-bond inter-actions occur between the cation-anion pair, which help to establish the crystal packing in the unit cell. This includes dual three-center hydrogen bonds with the piperidin-4-yl group, the phenolate and o-NO(2) O atoms of the picrate anion at different positions in the unit cell, which form separate N-H⋯(O,O) bifurcated inter-molecular hydrogen-bond inter-actions. Also, the hydr-oxy group forms a separate hydrogen bond with a nearby piperidin-4-yl N atom, thus providing two groups of hydrogen bonds, which form an infinite two-dimensional network along (011).

Investigation of the Mechanism of Electron Capture and Electron Transfer Dissociation of Peptides with a Covalently Attached Free Radical Hydrogen Atom Scavenger.

PubMed

Sohn, Chang Ho; Yin, Sheng; Peng, Ivory; Loo, Joseph A; Beauchamp, J L

2015-11-15

The mechanisms of electron capture and electron transfer dissociation (ECD and ETD) are investigated by covalently attaching a free-radical hydrogen atom scavenger to a peptide. The 2,2,6,6-tetramethylpiperidin-l-oxyl (TEMPO) radical was chosen as the scavenger due to its high hydrogen atom affinity (ca. 280 kJ/mol) and low electron affinity (ca. 0.45 ev), and was derivatized to the model peptide, FQX TEMPO EEQQQTEDELQDK. The X TEMPO residue represents a cysteinyl residue derivatized with an acetamido-TEMPO group. The acetamide group without TEMPO was also examined as a control. The gas phase proton affinity (882 kJ/mol) of TEMPO is similar to backbone amide carbonyls (889 kJ/mol), minimizing perturbation to internal solvation and sites of protonation of the derivatized peptides. Collision induced dissociation (CID) of the TEMPO tagged peptide dication generated stable odd-electron b and y type ions without indication of any TEMPO radical induced fragmentation initiated by hydrogen abstraction. The type and abundance of fragment ions observed in the CID spectra of the TEMPO and acetamide tagged peptides are very similar. However, ECD of the TEMPO labeled peptide dication yielded no backbone cleavage. We propose that a labile hydrogen atom in the charge reduced radical ions is scavenged by the TEMPO radical moiety, resulting in inhibition of N-C α backbone cleavage processes. Supplemental activation after electron attachment (ETcaD) and CID of the charge-reduced precursor ion generated by electron transfer of the TEMPO tagged peptide dication produced a series of b + H (b H ) and y + H (y H ) ions along with some c ions having suppressed intensities, consistent with stable O-H bond formation at the TEMPO group. In summary, the results indicate that ECD and ETD backbone cleavage processes are inhibited by scavenging of a labile hydrogen atom by the localized TEMPO radical moiety. This observation supports the conjecture that ECD and ETD processes involve long-lived intermediates formed by electron capture/transfer in which a labile hydrogen atom is present and plays a key role with low energy processes leading to c and z ion formation. Ab initio and density functional calculations are performed to support our conclusion, which depends most importantly on the proton affinity, electron affinity and hydrogen atom affinity of the TEMPO moiety.

Protein dynamics as seen by (quasi) elastic neutron scattering.

PubMed

Magazù, S; Mezei, F; Falus, P; Farago, B; Mamontov, E; Russina, M; Migliardo, F

2017-01-01

Elastic and quasielastic neutron scattering studies proved to be efficient probes of the atomic mean square displacement (MSD), a fundamental parameter for the characterization of the motion of individual atoms in proteins and its evolution with temperature and compositional environment. We present a technical overview of the different types of experimental situations and the information quasi-elastic neutron scattering approaches can make available. In particular, MSD can crucially depend on the time scale over which the averaging (building of the "mean") takes place, being defined by the instrumental resolution. Due to their high neutron scattering cross section, hydrogen atoms can be particularly sensitively observed with little interference by the other atoms in the sample. A few examples, including new data, are presented for illustration. The incoherent character of neutron scattering on hydrogen atoms restricts the information obtained to the self-correlations in the motion of individual atoms, simplifying at the same time the data analysis. On the other hand, the (often overlooked) exploration of the averaging time dependent character of MSD is crucial for unambiguous interpretation and can provide a wealth of information on micro- and nanoscale atomic motion in proteins. By properly exploiting the broad range capabilities of (quasi)elastic neutron scattering techniques to deliver time dependent characterization of atomic displacements, they offer a sensitive, direct and simple to interpret approach to exploration of the functional activity of hydrogen atoms in proteins. Partial deuteration can add most valuable selectivity by groups of hydrogen atoms. "This article is part of a Special Issue entitled "Science for Life" Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazù and Dr. Federica Migliardo". Copyright © 2016 Elsevier B.V. All rights reserved.

Laser Assisted Free-Free Transition in Electron - Atom Collision

NASA Technical Reports Server (NTRS)

Sinha, C.; Bhatia, A. K.

2011-01-01

Free-free transition is studied for electron-Hydrogen atom system in ground state at very low incident energies in presence of an external homogeneous, monochromatic and linearly polarized laser field. The incident electron is considered to be dressed by the laser in a non perturbative manner by choosing the Volkov solutions in both the channels. The space part of the scattering wave function for the electron is solved numerically by taking into account the effect of electron exchange, short range as well as of the long range interactions. Laser assisted differential as well as elastic total cross sections are calculated for single photon absorption/emission in the soft photon limit, the laser intensity being much less than the atomic field intensity. A strong suppression is noted in the laser assisted cross sections as compared to the field free situations. Significant difference is noted in the singlet and the triplet cross sections.

Electron quantum dynamics in atom-ion interaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sabzyan, H., E-mail: sabzyan@sci.ui.ac.ir; Jenabi, M. J.

2016-04-07

Electron transfer (ET) process and its dependence on the system parameters are investigated by solving two-dimensional time-dependent Schrödinger equation numerically using split operator technique. Evolution of the electron wavepacket occurs from the one-electron species hydrogen atom to another bare nucleus of charge Z > 1. This evolution is quantified by partitioning the simulation box and defining regional densities belonging to the two nuclei of the system. It is found that the functional form of the time-variations of these regional densities and the extent of ET process depend strongly on the inter-nuclear distance and relative values of the nuclear charges, whichmore » define the potential energy surface governing the electron wavepacket evolution. Also, the initial electronic state of the single-electron atom has critical effect on this evolution and its consequent (partial) electron transfer depending on its spreading extent and orientation with respect to the inter-nuclear axis.« less

Analysis of Data on the Cross Sections for Electron-Impact Ionization and Excitation of Electronic States of Atomic Hydrogen (Review)

NASA Astrophysics Data System (ADS)

Shakhatov, V. A.; Lebedev, Yu. A.

2018-01-01

A review is given of experimental and theoretical data on the cross sections for ionization, excitation, and deexcitation of atomic hydrogen. The set of the cross sections required to calculate the electron energy distribution function and find the level-to-level rate coefficients needed to solve balance equations for the densities of neutral and charged particles in hydrogen plasma is determined.

Preliminary neutron crystallographic analysis of selectively CH3-protonated, deuterated rubredoxin from Pyrococcus furiosus

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weiss, Kevin L; Meilleur, Flora; Blakeley, Matthew

2008-01-01

Neutron crystallography is used to locate hydrogen atoms in biological materials and can distinguish between negatively scattering hydrogen and positively scattering deuterium substituted positions in isomorphous neutron structures. Recently, Hauptman and Langs (2003) have shown that neutron diffraction data can be used to solve macromolecular structures by direct methods and that solution is aided by the presence of negatively scattering hydrogen atoms in the structure. Selective labeling protocols allow the design and production of H/D-labeled macromolecular structures in which the ratio of hydrogen to deuterium atoms can be precisely controlled. We have applied methyl-selective labeling protocols to introduce (1H-delta methyl)-leucinemore » and (1H-gamma methyl)-valine into deuterated rubredoxin from Pyrococcus furiosus (PfRd). Here we report on the production, crystallization, and preliminary neutron analysis of the selectively CH3-protonated, deuterated PfRd sample, which provided a high quality neutron data set extending to 1.75 resolution at the new LADI-III instrument at the Insititut Laue-Langevin. Preliminary analysis of neutron density maps allows unambiguous assignment of the positions of hydrogen atoms at the methyl groups of the valine and leucine residues in the otherwise deuterated rubredoxin structure.« less

Atomic Scale Analysis of the Enhanced Electro- and Photo-Catalytic Activity in High-Index Faceted Porous NiO Nanowires

NASA Astrophysics Data System (ADS)

Shen, Meng; Han, Ali; Wang, Xijun; Ro, Yun Goo; Kargar, Alireza; Lin, Yue; Guo, Hua; Du, Pingwu; Jiang, Jun; Zhang, Jingyu; Dayeh, Shadi A.; Xiang, Bin

2015-02-01

Catalysts play a significant role in clean renewable hydrogen fuel generation through water splitting reaction as the surface of most semiconductors proper for water splitting has poor performance for hydrogen gas evolution. The catalytic performance strongly depends on the atomic arrangement at the surface, which necessitates the correlation of the surface structure to the catalytic activity in well-controlled catalyst surfaces. Herein, we report a novel catalytic performance of simple-synthesized porous NiO nanowires (NWs) as catalyst/co-catalyst for the hydrogen evolution reaction (HER). The correlation of catalytic activity and atomic/surface structure is investigated by detailed high resolution transmission electron microscopy (HRTEM) exhibiting a strong dependence of NiO NW photo- and electrocatalytic HER performance on the density of exposed high-index-facet (HIF) atoms, which corroborates with theoretical calculations. Significantly, the optimized porous NiO NWs offer long-term electrocatalytic stability of over one day and 45 times higher photocatalytic hydrogen production compared to commercial NiO nanoparticles. Our results open new perspectives in the search for the development of structurally stable and chemically active semiconductor-based catalysts for cost-effective and efficient hydrogen fuel production at large scale.

Validation of the role of bulk charging of hydrogen in the corrosion fatigue cracking of a low alloy steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Griffiths, A.J.; Hutchings, R.B.; Turnbull, A.

1993-09-01

The enhanced corrosion fatigue crack growth rates of low alloy steels cathodically protected in marine environments results from absorbed hydrogen atoms. Hydrogen atoms are generated at the crack tip, crack walls and the external surface of the specimen (bulk charging). In previous work, Turnbull and Saenz de Santa Maria developed a model to predict the rate of generation of hydrogen atoms at the tips of fatigue cracks for steels cathodically polarized in marine environments. The main prediction from this work was that the external surface of the specimen can be the dominant source of hydrogen atoms at potentials more negativemore » than about [minus]900 mV (SCE), at a cyclic frequency of 0.1 Hz and a stress ratio of 0.5. The relative importance of bulk charging depends on the specific test conditions and is influenced by the applied potential, bulk chemistry, cyclic frequency, specimen thickness, temperature and use of coatings. Since laboratory test times are usually short in relation to the time required for hydrogen transport measured crack growth rates may be lower than those occurring in practice, for which there is sufficient time for full hydrogen charging. The purpose of this study is to verify experimentally the importance of bulk charging. Since the sensitivity of cracking to variations in hydrogen concentration will be material dependent a high strength steel was selected in this initial study because of its sensitivity to hydrogen. This will enable validation of the basic premise that bulk charging can be important, prior to more extensive studies using lower strength alloys.« less

STELLAR 'EGGS' EMERGE FROM MOLECULAR CLOUD (Star-Birth Clouds in M16)

NASA Technical Reports Server (NTRS)

2002-01-01

This eerie, dark structure, resembling an imaginary sea serpent's head, is a column of cool molecular hydrogen gas (two atoms of hydrogen in each molecule) and dust that is an incubator for new stars. The stars are embedded inside finger-like protrusions extending from the top of the nebula. Each 'fingertip' is somewhat larger than our own solar system. The pillar is slowly eroding away by the ultraviolet light from nearby hot stars, a process called 'photoevaporation'. As it does, small globules of especially dense gas buried within the cloud is uncovered. These globules have been dubbed 'EGGs' -- an acronym for 'Evaporating Gaseous Globules'. The shadows of the EGGs protect gas behind them, resulting in the finger-like structures at the top of the cloud. Forming inside at least some of the EGGs are embryonic stars -- stars that abruptly stop growing when the EGGs are uncovered and they are separated from the larger reservoir of gas from which they were drawing mass. Eventually the stars emerge, as the EGGs themselves succumb to photoevaporation. The stellar EGGS are found, appropriately enough, in the 'Eagle Nebula' (also called M16 -- the 16th object in Charles Messier's 18th century catalog of 'fuzzy' permanent objects in the sky), a nearby star-forming region 6,500 light-years away in the constellation Serpens. The picture was taken on April 1, 1995 with the Hubble Space Telescope Wide Field and Planetary Camera 2. The color image is constructed from three separate images taken in the light of emission from different types of atoms. Red shows emission from singly-ionized sulfur atoms. Green shows emission from hydrogen. Blue shows light emitted by doubly- ionized oxygen atoms. Credit: Jeff Hester and Paul Scowen (Arizona State University), and NASA Image files in GIF and JPEG format and captions may be accessed on Internet via anonymous ftp from oposite.stsci.edu in /pubinfo:

Shock-wave processing of C60 in hydrogen

NASA Astrophysics Data System (ADS)

Biennier, L.; Jayaram, V.; Suas-David, N.; Georges, R.; Singh, M. Kiran; Arunan, E.; Kassi, S.; Dartois, E.; Reddy, K. P. J.

2017-03-01

Context. Interstellar carbonaceous particles and molecules are subject to intense shocks in astrophysical environments. Shocks induce a rapid raise in temperature and density which strongly affects the chemical and physical properties of both the gas and solid phases of the interstellar matter. Aims: The shock-induced thermal processing of C60 particles in hydrogen has been investigated in the laboratory under controlled conditions up to 3900 K with the help of a material shock-tube. Methods: The solid residues generated by the exposure of a C60/H2 mixture to a millisecond shock wave were collected and analyzed using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman micro-spectroscopy, and infrared micro-spectroscopy. The gaseous products were analyzed by Gas Chromatography and Cavity Ring Down Spectroscopy. Results: Volatile end-products appear above reflected shock gas temperatures of 2540 K and reveal the substantial presence of small molecules with one or two C atoms. These observations confirm the role played by the C2 radical as a major product of C60 fragmentation and less expectedly highlight the existence of a single C atom loss channel. Molecules with more than two carbon atoms are not observed in the post-shock gas. The analysis of the solid component shows that C60 particles are rapidly converted into amorphous carbon with a number of aliphatic bridges. Conclusions: The absence of aromatic CH stretches on the IR spectra indicates that H atoms do not link directly to aromatic cycles. The fast thermal processing of C60 in H2 over the 800-3400 K temperature range leads to amorphous carbon. The analysis hints at a collapse of the cage with the formation of a few aliphatic connections. A low amount of hydrogen is incorporated into the carbon material. This work extends the range of applications of shock tubes to studies of astrophysical interest.

Structural basis for proficient incorporation of dTTP opposite O6-methylguanine by human DNA polymerase iota.

PubMed

Pence, Matthew G; Choi, Jeong-Yun; Egli, Martin; Guengerich, F Peter

2010-12-24

O(6)-methylguanine (O(6)-methylG) is highly mutagenic and is commonly found in DNA exposed to methylating agents, even physiological ones (e.g. S-adenosylmethionine). The efficiency of a truncated, catalytic DNA polymerase ι core enzyme was determined for nucleoside triphosphate incorporation opposite O(6)-methylG, using steady-state kinetic analyses. The results presented here corroborate previous work from this laboratory using full-length pol ι, which showed that dTTP incorporation occurs with high efficiency opposite O(6)-methylG. Misincorporation of dTTP opposite O(6)-methylG occurred with ∼6-fold higher efficiency than incorporation of dCTP. Crystal structures of the truncated form of pol ι with O(6)-methylG as the template base and incoming dCTP or dTTP were solved and showed that O(6)-methylG is rotated into the syn conformation in the pol ι active site and that dTTP misincorporation by pol ι is the result of Hoogsteen base pairing with the adduct. Both dCTP and dTTP base paired with the Hoogsteen edge of O(6)-methylG. A single, short hydrogen bond formed between the N3 atom of dTTP and the N7 atom of O(6)-methylG. Protonation of the N3 atom of dCTP and bifurcation of the N3 hydrogen between the N7 and O(6) atoms of O(6)-methylG allow base pairing of the lesion with dCTP. We conclude that differences in the Hoogsteen hydrogen bonding between nucleotides is the main factor in the preferential selectivity of dTTP opposite O(6)-methylG by human pol ι, in contrast to the mispairing modes observed previously for O(6)-methylG in the structures of the model DNA polymerases Sulfolobus solfataricus Dpo4 and Bacillus stearothermophilus DNA polymerase I.

Kinetics of self-decomposition and hydrogen atom transfer reactions of substituted phthalimide N-oxyl radicals in acetic acid.

PubMed

Cai, Yang; Koshino, Nobuyoshi; Saha, Basudeb; Espenson, James H

2005-01-07

Kinetic data have been obtained for three distinct types of reactions of phthalimide N-oxyl radicals (PINO(.)) and N-hydroxyphthalimide (NHPI) derivatives. The first is the self-decomposition of PINO(.) which was found to follow second-order kinetics. In the self-decomposition of 4-methyl-N-hydroxyphthalimide (4-Me-NHPI), H-atom abstraction competes with self-decomposition in the presence of excess 4-Me-NHPI. The second set of reactions studied is hydrogen atom transfer from NHPI to PINO(.), e.g., PINO(.) + 4-Me-NHPI <=> NHPI + 4-Me-PINO(.). The substantial KIE, k(H)/k(D) = 11 for both forward and reverse reactions, supports the assignment of H-atom transfer rather than stepwise electron-proton transfer. These data were correlated with the Marcus cross relation for hydrogen-atom transfer, and good agreement between the experimental and the calculated rate constants was obtained. The third reaction studied is hydrogen abstraction by PINO(.) from p-xylene and toluene. The reaction becomes regularly slower as the ring substituent on PINO(.) is more electron donating. Analysis by the Hammett equation gave rho = 1.1 and 1.8 for the reactions of PINO(.) with p-xylene and toluene, respectively.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, June Key, E-mail: junekey@jnu.ac.kr, E-mail: hskim7@jbnu.ac.kr; Hyeon, Gil Yong; Tawfik, Wael Z.

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 ofmore » 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.« less

Energy-transfer processes in neon-hydrogen mixtures excited by electron beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morozov, A.; Kruecken, R.; Ulrich, A.

2005-12-15

Energy- and charge-transfer processes in neon-hydrogen mixtures (500-1400 hPa neon and 0.001-3 hPa hydrogen partial pressures) excited by a pulsed low-energy ({approx}10 keV) electron beam were investigated using time-resolved spectroscopy. Time spectra of the hydrogen Lyman-{alpha} line, neon excimer emission (second continuum), and neon atomic lines (3p-3s transitions) were recorded. The time-integrated intensity of the Lyman-{alpha} emission was measured for the same range of gas mixtures. It is shown that direct energy transfer from Ne{sub 2}* excimers and neon atoms in the four lowest excited states as well as recombination of H{sub 3}{sup +} ions are the main channels populatingmore » atomic hydrogen in the n=2 state. A rate constant of (4.2{+-}1.4)x10{sup -11} cm{sup 3} s{sup -1} was obtained for the charge transfer from Ne{sub 2}{sup +} ions to molecular hydrogen. A lower limit for the depopulation rate constant of Ne{sub 2}* excimers by molecular hydrogen (combination of energy transfer and ionization) was found to be 1.0x10{sup -10} cm{sup 3} s{sup -1}.« less

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

NASA Astrophysics Data System (ADS)

Lee, June Key; Hyeon, Gil Yong; Tawfik, Wael Z.; Choi, Hee Seok; Ryu, Sang-Wan; Jeong, Tak; Jung, Eunjin; Kim, Hyunsoo

2015-05-01

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.

Another Unprecedented Wieland Mechanism Confirmed: Hydrogen Formation from Hydrogen Peroxide, Formaldehyde, and Sodium Hydroxide.

PubMed

Czochara, Robert; Litwinienko, Grzegorz; Korth, Hans-Gert; Ingold, Keith U

2018-03-26

In 1923, Wieland and Wingler reported that in the molecular hydrogen producing reaction of hydrogen peroxide with formaldehyde in basic solution, free hydrogen atoms (H . ) are not involved. They postulated that bis(hydroxymethyl)peroxide, HOCH 2 OOCH 2 OH, is the intermediate, which decomposes to yield H 2 and formate, proposing a mechanism that would nowadays be considered as a "concerted process". Since then, several other (conflicting) "mechanisms" have been suggested. Our NMR and Raman spectroscopic and kinetic studies, particularly the determination of the deuterium kinetic isotope effect (DKIE), now confirm that in this base-dependent reaction, both H atoms of H 2 derive from the CH 2 hydrogen atoms of formaldehyde, and not from the OH groups of HOCH 2 OOCH 2 OH or from water. Quantum-chemical CBS-QB3 and W1BD computations show that H 2 release proceeds through a concerted process, which is strongly accelerated by double deprotonation of HOCH 2 OOCH 2 OH, thereby ruling out a free radical pathway. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Time-dependent density-functional theory simulation of local currents in pristine and single-defect zigzag graphene nanoribbons

DOE Office of Scientific and Technical Information (OSTI.GOV)

He, Shenglai, E-mail: shenglai.he@vanderbilt.edu; Russakoff, Arthur; Li, Yonghui

2016-07-21

The spatial current distribution in H-terminated zigzag graphene nanoribbons (ZGNRs) under electrical bias is investigated using time-dependent density-functional theory solved on a real-space grid. A projected complex absorbing potential is used to minimize the effect of reflection at simulation cell boundary. The calculations show that the current flows mainly along the edge atoms in the hydrogen terminated pristine ZGNRs. When a vacancy is introduced to the ZGNRs, loop currents emerge at the ribbon edge due to electrons hopping between carbon atoms of the same sublattice. The loop currents hinder the flow of the edge current, explaining the poor electric conductancemore » observed in recent experiments.« less

Teaching Bohr Theory.

ERIC Educational Resources Information Center

Latimer, Colin J.

1983-01-01

Discusses some lesser known examples of atomic phenomena to illustrate to students that the old quantum theory in its simplest (Bohr) form is not an antiquity but can still make an important contribution to understanding such phenomena. Topics include hydrogenic/non-hydrogenic spectra and atoms in strong electric and magnetic fields. (Author/JN)

Hydrogen-impurity complexes in III V semiconductors

NASA Astrophysics Data System (ADS)

Ulrici, W.

2004-12-01

This review summarizes the presently available knowledge concerning hydrogen-impurity complexes in III-V compounds. The impurities form shallow acceptors on group III sites (Be, Zn, Cd) and on group V sites (C, Si, Ge) as well as shallow donors on group V sites (S, Se, Te) and on group III sites (Si, Sn). These complexes are mainly revealed by their hydrogen stretching modes. Therefore, nearly all information about their structure and dynamic properties is derived from vibrational spectroscopy. The complexes of shallow impurities with hydrogen have been most extensively investigated in GaAs, GaP and InP. This holds also for Mg-H in GaN. The complexes exhibit a different microscopic structure, which is discussed in detail. The isoelectronic impurity nitrogen, complexed with one hydrogen atom, is investigated in detail in GaAs and GaP. Those complexes can exist in different charge states. The experimental results such as vibrational frequencies, the microscopic structure and the activation energy for reorientation for many of these complexes are in very good agreement with results of ab initio calculations. Different types of oxygen-hydrogen complexes in GaAs and GaP are described, with one hydrogen atom or two hydrogen atoms bonded to oxygen. Three of these complexes in GaAs were found to be electrically active.

PubChem atom environments.

PubMed

Hähnke, Volker D; Bolton, Evan E; Bryant, Stephen H

2015-01-01

Atom environments and fragments find wide-spread use in chemical information and cheminformatics. They are the basis of prediction models, an integral part in similarity searching, and employed in structure search techniques. Most of these methods were developed and evaluated on the relatively small sets of chemical structures available at the time. An analysis of fragment distributions representative of most known chemical structures was published in the 1970s using the Chemical Abstracts Service data system. More recently, advances in automated synthesis of chemicals allow millions of chemicals to be synthesized by a single organization. In addition, open chemical databases are readily available containing tens of millions of chemical structures from a multitude of data sources, including chemical vendors, patents, and the scientific literature, making it possible for scientists to readily access most known chemical structures. With this availability of information, one can now address interesting questions, such as: what chemical fragments are known today? How do these fragments compare to earlier studies? How unique are chemical fragments found in chemical structures? For our analysis, after hydrogen suppression, atoms were characterized by atomic number, formal charge, implicit hydrogen count, explicit degree (number of neighbors), valence (bond order sum), and aromaticity. Bonds were differentiated as single, double, triple or aromatic bonds. Atom environments were created in a circular manner focused on a central atom with radii from 0 (atom types) up to 3 (representative of ECFP_6 fragments). In total, combining atom types and atom environments that include up to three spheres of nearest neighbors, our investigation identified 28,462,319 unique fragments in the 46 million structures found in the PubChem Compound database as of January 2013. We could identify several factors inflating the number of environments involving transition metals, with many seemingly due to erroneous interpretation of structures from patent data. Compared to fragmentation statistics published 40 years ago, the exponential growth in chemistry is mirrored in a nearly eightfold increase in the number of unique chemical fragments; however, this result is clearly an upper bound estimate as earlier studies employed structure sampling approaches and this study shows that a relatively high rate of atom fragments are found in only a single chemical structure (singletons). In addition, the percentage of singletons grows as the size of the chemical fragment is increased. The observed growth of the numbers of unique fragments over time suggests that many chemically possible connections of atom types to larger fragments have yet to be explored by chemists. A dramatic drop in the relative rate of increase of atom environments from smaller to larger fragments shows that larger fragments mainly consist of diverse combinations of a limited subset of smaller fragments. This is further supported by the observed concomitant increase of singleton atom environments. Combined, these findings suggest that there is considerable opportunity for chemists to combine known fragments to novel chemical compounds. The comparison of PubChem to an older study of known chemical structures shows noticeable differences. The changes suggest advances in synthetic capabilities of chemists to combine atoms in new patterns. Log-log plots of fragment incidence show small numbers of fragments are found in many structures and that large numbers of fragments are found in very few structures, with nearly half being novel using the methods in this work. The relative decrease in the count of new fragments as a function of size further suggests considerable opportunity for more novel chemicals exists. Lastly, the differences in atom environment diversity between PubChem Substance and Compound showcase the effect of PubChem standardization protocols, but also indicate that a normalization procedure for atom types, functional groups, and tautomeric/resonance forms based on atom environments is possible. The complete sets of atom types and atom environments are supplied as supporting information.

A Quasi-Laue Neutron Crystallographic Study of D-Xylose Isomerase

NASA Technical Reports Server (NTRS)

Meilleur, Flora; Snell, Edward H.; vanderWoerd, Mark; Judge, Russell A.; Myles, Dean A. A.

2006-01-01

Hydrogen atom location and hydrogen bonding interaction determination are often critical to explain enzymatic mechanism. Whilst it is difficult to determine the position of hydrogen atoms using X-ray crystallography even with subatomic (less than 1.0 Angstrom) resolution data available, neutron crystallography provides an experimental tool to directly localise hydrogeddeuteriwn atoms in biological macromolecules at resolution of 1.5-2.0 Angstroms. Linearisation and isomerisation of xylose at the active site of D-xylose isomerase rely upon a complex hydrogen transfer. Neutron quasi-Laue data were collected on Streptomyces rubiginosus D-xylose isomerase crystal using the LADI instrument at ILL with the objective to provide insight into the enzymatic mechanism (Myles et al. 1998). The neutron structure unambiguously reveals the protonation state of His 53 in the active site, identifying the model for the enzymatic pathway.

DFT investigations of the hydrogenation effect on silicene/graphene hybrids.

PubMed

Drissi, L B; Saidi, E H; Bousmina, M; Fassi-Fehri, O

2012-12-05

We report here a study on the effect of hydrogenation on a new one-atom thick material made of silicon and carbon atoms (silicene/graphene (SG) hybrid) within density functional theory. The structural, electronic and magnetic properties are investigated for non-, semi- and fully hydrogenated SG hybrids in a chair configuration and are compared with their parent materials. Calculations reveal that pure SG is a non-zero band gap semi-conductor with stable planar honeycomb structure. So mixing C and Si in an alternating manner gives another way to generate a finite band gap in one-atom thick materials. Fully hydrogenation makes the gap larger; however half chemical modification with H reduces the gap in favor of ferromagnetism order. The findings of this work open a wide spectrum of possibilities for designing SG-based nanodevices with controlled and tuned properties.

Operating characteristics of a hydrogen-argon plasma torch for supersonic combustion applications

NASA Technical Reports Server (NTRS)

Barbi, E.; Mahan, J. R.; O'Brien, W. F.; Wagner, T. C.

1989-01-01

The residence time of the combustible mixture in the combustion chamber of a scramjet engine is much less than the time normally required for complete combustion. Hydrogen and hydrocarbon fuels require an ignition source under conditions typically found in a scramjet combustor. Analytical studies indicate that the presence of hydrogen atoms should greatly reduce the ignition delay in this environment. Because hydrogen plasmas are prolific sources of hydrogen atoms, a low-power, uncooled hydrogen plasma torch has been built and tested to evaluate its potential as a possible flame holder for supersonic combustion. The torch was found to be unstable when operated on pure hydrogen; however, stable operation could be obtained by using argon as a body gas and mixing in the desired amount of hydrogen. The stability limits of the torch are delineated and its electrical and thermal behavior documented. An average torch thermal efficiency of around 88 percent is demonstrated.

Pixel switching of epitaxial Pd/YHx/CaF2 switchable mirrors

PubMed

Kerssemakers; van der Molen SJ; Koeman; Gunther; Griessen

2000-08-03

Exposure of rare-earth films to hydrogen can induce a metal-insulator transition, accompanied by pronounced optical changes. This 'switchable mirror' effect has received considerable attention from theoretical, experimental and technological points of view. Most systems use polycrystalline films, but the synthesis of yttrium-based epitaxial switchable mirrors has also been reported. The latter form an extended self-organized ridge network during initial hydrogen loading, which results in the creation of micrometre-sized triangular domains. Here we observe homogeneous and essentially independent optical switching of individual domains in epitaxial switchable mirrors during hydrogen absorption. The optical switching is accompanied by topographical changes as the domains sequentially expand and contract; the ridges block lateral hydrogen diffusion and serve as a microscopic lubricant for the domain oscillations. We observe the correlated changes in topology and optical properties using in situ atomic force and optical microscopy. Single-domain phase switching is not observed in polycrystalline films, which are optically homogeneous. The ability to generate a tunable, dense pattern of switchable pixels is of technological relevance for solid-state displays based on switchable mirrors.

Writing with ring currents: selectively hydrogenated polycyclic aromatics as finite models of graphene and graphane

PubMed Central

Fowler, Patrick W.; Gibson, Christopher M.; Bean, David E.

2014-01-01

Alternating partial hydrogenation of the interior region of a polycyclic aromatic hydrocarbon gives a finite model system representing systems on the pathway from graphene to the graphane modification of the graphene sheet. Calculations at the DFT and coupled Hartree–Fock levels confirm that sp2 cycles of bare carbon centres isolated by selective hydrogenation retain the essentially planar geometry and electron delocalization of the annulene that they mimic. Delocalization is diagnosed by the presence of ring currents, as detected by ipsocentric calculation and visualization of the current density induced in the π system by a perpendicular external magnetic field. These induced ‘ring’ currents have essentially the same sense, strength and orbital origin as in the free hydrocarbon. Subjected to the important experimental proviso of the need for atomic-scale control of hydrogenation, this finding predicts the possibility of writing single, multiple and concentric diatropic and/or paratropic ring currents on the graphene/graphane sheet. The implication is that pathways for free flow of ballistic current can be modelled in the same way. PMID:24611026

Positronium formation in e+ plus H- collisions

NASA Technical Reports Server (NTRS)

Straton, Jack C.; Drachman, Richard J.

1990-01-01

Cross sections for positronium formation by capture from the negative hydrogen ion are given. Orthogonalization corrections to the Coulomb (First) Born Approximation (CBA) differential and total cross sections are calculated using approximate H- wave functions of both Lowdin and Chandrasekhar. Various methods of orthogonalizing the unbound projectile to the possible bound states are considered. It is found that treating the atomic nuclei as if they were isotopic spin projections of a single type of nucleon gives cross sections that are an improvement over the CBA.

Tuning the Selectivity of Single-Site Supported Metal Catalysts with Ionic Liquids

DOE PAGES

Babucci, Melike; Fang, Chia -Yu; Hoffman, Adam S.; ...

2017-09-11

1,3-Dialkylimidazolium ionic liquid coatings act as electron donors, increasing the selectivity for partial hydrogenation of 1,3-butadiene catalyzed by iridium complexes supported on high-surface-area γ-Al 2O 3. High-energy-resolution fluorescence detection X-ray absorption near-edge structure (HERFD XANES) measurements quantify the electron donation and are correlated with the catalytic activity and selectivity. Furthermore, the results demonstrate broad opportunities to tune electronic environments and catalytic properties of atomically dispersed supported metal catalysts.

Final Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chidambaram, Dev; Misra, Mano; Heske, Clemens

2014-12-21

The objectives included: Develop high efficiency metal oxide nanotubular array photo-anodes for generating hydrogen by water splitting; Develop density functional theory to understand the effect of the morphology of the nanotubes on the photo-electrochemical (PEC) properties of the photo-anodes; Develop kinetics and formation mechanism of the metal oxide nanotubes under different synthesis conditions; Develop combinatorial approach to prepare hybrid photo-anodes having multiple hetero-atoms incorporation in a single photo anode; Improve the durability of the material; and Scale up the laboratory demonstration to production unit.

Electron-stimulated reactions in layered CO/H2O films: Hydrogen atom diffusion and the sequential hydrogenation of CO to methanol

DOE Office of Scientific and Technical Information (OSTI.GOV)

Petrik, Nikolay G.; Monckton, Rhiannon J.; Koehler, Sven

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 COmore » 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.« less

Methyl group conformation and hydrogen bonds in proteins determined by neutron protein crystallography

NASA Astrophysics Data System (ADS)

Yamaguchi, Atsushi; Shibata, Kouji; Tanaka, Ichiro; Niimura, Nobuo

2009-02-01

Using 'Hydrogen and Hydration in Proteins Data Base' (HHDB) that catalogs all H atom positions in biological macromolecules and in hydration water molecules that have been determined thus far by neutron macromolecular crystallography, methyl group conformation and hydrogen bonds (H.B.) in proteins are explored. It is found that most of the methyl groups belong to the stable staggered conformation but 11% of them seemed to be close to the eclipsed conformation. And geometrical consideration has been done for H.B. involved in α-helices. 125 H.B. were identified as donors for acceptor C dbnd O in the main chain α-helix. For these H.B., it is found that co-linear H.B. were rare, that hydrogen atoms seen from acceptors C dbnd O can localize upon certain arrangements, that H.B. are not parallel to the helix axis but rather inclined to C-terminal direction, and that hydrogen atoms except water are located inside, not outside of cylinders which the backbones of α-helices form.

Theoretical analysis of the electronic properties of the sex pheromone and its analogue derivatives in the female processionary moth Thaumetopoea pytiocampa.

PubMed

Chamorro, Ester R; Sequeira, Alfredo F; Zalazar, M Fernanda; Peruchena, Nélida M

2008-09-15

In the present work, the distribution of the electronic charge density of the natural sex pheromone, the (Z)-13-hexadecen-11-ynyl acetate, in the female processionary moth, Thaumetopoea pytiocampa, and its nine analogue derivatives was studied within the framework of the Density Functional Theory and the Atoms in Molecules (AIM) Theory at B3LYP/6-31G *//B3LYP/6-31++G * * level. Additionally, molecular electrostatic potential (MEP) maps of the previously mentioned compounds were computed and compared. Furthermore, the substitution of hydrogen atoms from the methyl group in the acetate group by electron withdrawing substituents (i.e., halogen atoms) as well as the replacement effect of hydrogen by electron donor substituents (+I effect) as methyl group, were explored. The key feature of the topological distribution of the charge density in analogue compounds, such as the variations of the topological properties encountered in the region formed by neighbouring atoms from the substitution site were presented and discussed. Using topological parameters, such as electronic charge density, Laplacian, kinetic energy density, and potential energy density evaluated at bond critical points (BCP), we provide here a detailed analysis of the nature of the chemical bonding of these molecules. In addition, the atomic properties (population, charge, energy, volume, and dipole moment) were determined on selected atoms. These properties were analyzed at the substitution site (with respect to the natural sex pheromone) and related to the biological activity and to the possible binding site with the pheromone binding protein, (PBP). Moreover, the Laplacian function of the electronic density was used to locate electrophilic regions susceptible to be attacked (by deficient electron atoms or donor hydrogen). Our results indicate that the change in the atomic properties, such as electronic population and atomic volume, are sensitive indicators of the loss of the biological activity in the analogues studied here. The crucial interaction between the acetate group of the natural sex pheromone and the PBP is most likely to be a hydrogen bonding and the substitution of hydrogen atoms by electronegative atoms in the pheromone molecule reduces the hydrogen acceptor capacity. This situation is mirrored by the diminish of the electronic population on carbon and oxygen atoms at the carbonylic group in the halo-acetate group. Additionally, the modified acetate group (with electronegative atoms) shows new charge concentration critical points or regions of concentration of charge density in which an electrophilic attack can also occur. Finally, the use of the topological analysis based in the charge density distribution and its Laplacian function, in conjunction with MEP maps provides valuable information about the steric volume and electronic requirement of the sex pheromone for binding to the PBP.

Surface morphology and grain analysis of successively industrially grown amorphous hydrogenated carbon films (a-C:H) on silicon

NASA Astrophysics Data System (ADS)

Catena, Alberto; McJunkin, Thomas; Agnello, Simonpietro; Gelardi, Franco M.; Wehner, Stefan; Fischer, Christian B.

2015-08-01

Silicon (1 0 0) has been gradually covered by amorphous hydrogenated carbon (a-C:H) films via an industrial process. Two types of these diamond-like carbon (DLC) coatings, one more flexible (f-DLC) and one more robust (r-DLC), have been investigated. Both types have been grown by a radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) technique with acetylene plasma. Surface morphologies have been studied in detail by atomic force microscopy (AFM) and Raman spectroscopy has been used to investigate the DLC structure. Both types appeared to have very similar morphology and sp2 carbon arrangement. The average height and area for single grains have been analyzed for all depositions. A random distribution of grain heights was found for both types. The individual grain structures between the f- and r-type revealed differences: the shape for the f-DLC grains is steeper than for the r-DLC grains. By correlating the average grain heights to the average grain areas for all depositions a limited region is identified, suggesting a certain regularity during the DLC deposition mechanisms that confines both values. A growth of the sp2 carbon entities for high r-DLC depositions is revealed and connected to a structural rearrangement of carbon atom hybridizations and hydrogen content in the DLC structure.

Finite size effect on hydrogen bond cooperativity in (Ala)n polypeptides: A DFT study using numeric atom-centered orbitals

NASA Astrophysics Data System (ADS)

Blum, Volker; Ireta, Joel; Scheffler, Matthias

2007-03-01

An accurate representation of the energetic contribution Ehb of hydrogen bonds to structure formation is paramount to understand the secondary structure stability of proteins, both qualitatively and quantitatively. However, Ehb depends strongly on its environment, and even on the surrounding peptide conformation itself. For instance, a short α-helical polypeptide (Ala)4 can not be stabilized by its single hydrogen bond, whereas an infinite α-helical chain (Ala)∞ is clearly energetically stable over a fully extended conformation. We here use all-electron density functional calculations in the PBE generalized gradient approximation by a recently developed, computationally efficient numeric atom-centered orbital based code^1 to investigate this H-bond cooperativity that is intrinsic to Alanine-based polypeptides (Ala)n (n=1-20,∞). We compare finite and infinite prototypical helical conformations (α, π, 310) on equal footing, with both neutral and ionic termination for finite (Ala)n peptides. Moderately sized NAO basis sets allow to capture Ehb with meV accuracy, revealing a clear jump in Ehb (cooperativity) when two H-bonds first appear in line, followed by slower and more continuous increase of Ehb towards n->∞. ^1 V. Blum, R. Gehrke, P. Havu, V. Havu, M. Scheffler, The FHI Ab Initio Molecular Simulations (aims) Project, Fritz-Haber-Institut, Berlin (2006).

Modeling the CH Stretch Vibrational Spectroscopy of M(+)[Cyclohexane] (M = Li, Na, and K) Ions.

PubMed

Sibert, Edwin L; Tabor, Daniel P; Lisy, James M

2015-10-15

The CH stretch vibrations of M(+)[cyclohexane][Ar] (M = Li, Na, and K) cluster ions were theoretically modeled. Results were compared to the corresponding infrared photodissociation spectra of Patwari and Lisy [ J. Chem. Phys A 2007 , 111 , 7585 ]. The experimental spectra feature a substantial spread in CH stretch vibration frequencies due to the alkali metal cation binding to select hydrogens of cyclohexane. This spread was observed to increase with decreasing metal ion size. Exploring the potential energy landscape revealed the presence of three conformers whose energy minima lie within ∼1 kcal of each other. It was determined that in all conformers the metal ion interacts with three hydrogen atoms; these hydrogen atoms can be either equatorial or axial. The corresponding spectra for these conformers were obtained with a theoretical model Hamiltonian [ J. Chem. Phys. 2013 , 138 , 064308 ] that consists of local mode CH stretches bilinearly coupled to each other and Fermi coupled to lower frequency modes. Frequencies and coupling parameters were obtained from electronic structure calculations that were subsequently scaled on the basis of previous studies. Theoretical spectra of a single low energy conformer were found to match well with the experimental spectra. The relative frequency shifts with changing metal ion size were accurately modeled with parameters generated by using ωB97X-D/6-311++(2d,p) calculations.

Bandgap opening in hydrogenated germanene

NASA Astrophysics Data System (ADS)

Yao, Q.; Zhang, L.; Kabanov, N. S.; Rudenko, A. N.; Arjmand, T.; Rahimpour Soleimani, H.; Klavsyuk, A. L.; Zandvliet, H. J. W.

2018-04-01

We have studied the hydrogenation of germanene synthesized on Ge2Pt crystals using scanning tunneling microscopy and spectroscopy. The germanene honeycomb lattice is buckled and consists of two hexagonal sub-lattices that are slightly displaced with respect to each other. The hydrogen atoms adsorb exclusively on the Ge atoms of the upward buckled hexagonal sub-lattice. At a hydrogen exposure of about 100 L, the (1 × 1) buckled honeycomb structure of germanene converts to a (2 × 2) structure. Scanning tunneling spectra recorded on this (2 × 2) structure reveal the opening of a bandgap of about 0.2 eV. A fully (half) hydrogenated germanene surface is obtained after an exposure of about 9000 L hydrogen. The hydrogenated germanene, also referred to as germanane, has a sizeable bandgap of about 0.5 eV and is slightly n-type.

Fundamental Pathways for the Adsorption and Transport of Hydrogen on TiO2 Surfaces: Origin for Effective Sensing at about Room Temperature.

PubMed

Wang, Zhuo; Xia, Xiaohong; Guo, Meilan; Shao, Guosheng

2016-12-28

Effective detection of hydrogen at lowered temperature is highly desirable in promoting safety in using this abundant gas as a clean energy source. Through first-principle calculations in the framework of density functional theory, we find that the high-energy (002) surface for rutile TiO 2 is significantly more effective in adsorbing hydrogen atoms through dissociating hydrogen molecules. The pathways for the dissociation of hydrogen molecules and sequential migration of hydrogen atoms are identified through searching along various transitional states. Pathways of low potential barriers indicate promise for hydrogen sensing, even close to room temperature. This has been proven through sensors made of thin films of well-aligned rutile nanorods, wherein the high-energy (002) surface dictates the top surface of the active layer of the sensors.

Catalyst and Process Design for the Continuous Manufacture of Rare Sugar Alcohols by Epimerization-Hydrogenation of Aldoses.

PubMed

Lari, Giacomo M; Gröninger, Olivier G; Li, Qiang; Mondelli, Cecilia; López, Núria; Pérez-Ramírez, Javier

2016-12-20

Sugar alcohols are applied in the food, pharmaceutical, polymer, and fuel industries and are commonly obtained by reduction of the corresponding saccharides. In view of the rarity of some sugar substrates, epimerization of a readily available monosaccharide has been proposed as a solution, but an efficient catalytic system has not yet been identified. Herein, a molybdenum heteropolyacid-based catalyst is developed to transform glucose, arabinose, and xylose into less-abundant mannose, ribose, and lyxose, respectively. Adsorption of molybdic acid onto activated carbon followed by ion exchange to the cesium form limits leaching of the active phase, which greatly improves the catalyst stability over 24 h on stream. The hydrogenation of mixtures of epimers is studied over ruthenium catalysts, and it is found that the precursor to the desired polyol is advantageously converted with faster kinetics. This is explained by density functional theory on the basis of its more favorable adsorption on the metal surface and the lower energy barrier for the addition of a hydrogen atom to the primary carbon atom. Finally, different designs for a continuous process for the conversion of glucose into mannitol are studied, and it is uncovered that two reactors in series with one containing the epimerization catalyst and the other containing a mixture of the epimerization and hydrogenation catalysts increases the mannitol/sorbitol ratio to 1.5 from 1 for a single mixed-bed reactor. This opens a prospective route to the efficient valorization of renewables to added-value chemicals. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Free radical generation by ultrasound in aqueous and nonaqueous solutions.

PubMed Central

Riesz, P; Berdahl, D; Christman, C L

1985-01-01

The physical principles underlying the oscillatory behavior of minute gas bubbles in liquids exposed to ultrasound are reviewed. Results from mathematical analyses suggest that these oscillations sometimes become unstable leading to transient cavitation in which a bubble violently collapses during a single acoustic half-cycle producing high temperatures and pressures. The role that micronuclei, resonant bubble size, and rectified diffusion play in the initiation of transient cavitation is explained. Evidence to support these theoretical predictions is presented with particular emphasis on sonoluminescence which provides some non-chemical evidence for the formation of free radicals. Acoustic methods for conducting sonochemical investigations are discussed. In aqueous solutions transient cavitation initially generates hydrogen atoms and hydroxyl radicals which may recombine to form hydrogen and hydrogen peroxide or may react with solutes in the gas phase, at the gas-liquid boundary or in the bulk of the solution. The analogies and differences between sonochemistry and ionizing radiation chemistry are explored. The use of spin trapping and electron spin resonance to identify hydrogen atoms and hydroxyl radicals conclusively and to detect transient cavitation produced by continuous wave and by pulsed ultrasound is described in detail. The study of the chemical effects of cavitation in organic liquids is a relatively unexplored area which has recently become the subject of renewed interest. Examples of the decomposition of solvent and solute, of ultrasonically initiated free-radical polymerization and polymer degradation are presented. Spin trapping has been used to identify radicals in organic liquids, in polymer degradation and in the decomposition of organometallic compounds. PMID:3007091

Atomic Scale Structure of (001) Hydrogen-Induced Platelets in Germanium

NASA Astrophysics Data System (ADS)

David, Marie-Laure; Pizzagalli, Laurent; Pailloux, Fréderic; Barbot, Jean François

2009-04-01

An accurate characterization of the structure of hydrogen-induced platelets is a prerequisite for investigating both hydrogen aggregation and formation of larger defects. On the basis of quantitative high resolution transmission electron microscopy experiments combined with extensive first principles calculations, we present a model for the atomic structure of (001) hydrogen-induced platelets in germanium. It involves broken Ge-Ge bonds in the [001] direction that are dihydride passivated, vacancies, and trapped H2 molecules, showing that the species involved in platelet formation depend on the habit plane. This model explains all previous experimental observations.

Extended atmospheres of outer planet satellites and comets

NASA Technical Reports Server (NTRS)

Smyth, W. H.; Combi, M. R.

1985-01-01

Collisions between neutral hydrogen atoms in the interstellar medium and those in the so-called Titan hydrogen torus may provide an additional lifetime sink for atoms in the Saturn environment. Progress toward re-sorting the Voyager UVS scans of neutral hydrogen in the Saturn system to enable both a factor of two increase in the amount of data to be analyzed as well as to help identify near-Titan hydrogen is discussed. Progress toward development of the cometary carbon and oxygen models is also discussed and a preliminary model run for the H2O source of cometary oxygen is presented.

Hydrogen sulphide in cardiovascular system: A cascade from interaction between sulphur atoms and signalling molecules.

PubMed

Wang, Ming-Jie; Cai, Wen-Jie; Zhu, Yi-Chun

2016-05-15

As a gasotransmitter, hydrogen sulphide exerts its extensive physiological and pathophysiological effects in mammals. The interaction between sulphur atoms and signalling molecules forms a cascade that modulates cellular functions and homeostasis. In this review, we focus on the signalling mechanism underlying the effect of hydrogen sulphide in the cardiovascular system and metabolism as well as the biological relevance to human diseases. Copyright © 2016 Elsevier Inc. All rights reserved.

Adsorption, dissociation and diffusion of hydrogen on the ZrCo surface and subsurface: A comprehensive study using first principles approach

NASA Astrophysics Data System (ADS)

Chattaraj, D.; Kumar, Nandha; Ghosh, Prasenjit; Majumder, C.; Dash, Smruti

2017-11-01

With increasing demand for hydrogen economy driven world, the fundamental research of hydrogen-metal interactions has gained momentum. In this work we report a systematic theoretical study of the stability of different surfaces of intermetallic ZrCo that is a possible candidate as a getter bed for tritium. Our first principles ab initio thermodynamic calculations predict that amongst the (100), (110) and (111) surfaces, the stoichiometric (110) surface is the most stable one over a wide range of Co chemical potential. We have also studied adsorption, dissociation and diffusion of hydrogen on the (110) surface. On the basis of total energy, it is seen that adsorption of molecular hydrogen (H2) on the surface is much weaker than atomic hydrogen. The H2 decomposition on ZrCo surface can easily take place and the dissociation barrier is calculated to be 0.70 eV. The strength of binding of H atom on the surface is more or less independent of surface coverage till 1.0 ML of H. The thermodynamic stability of atomic H adsorbed on the surface, in subsurface and bulk decreases from surface to bulk to subsurface. Though the H atoms are mobile on the surface, their diffusion to the subsurface involves a barrier of about 0.79 eV.

(2E,5E)-2,5-Bis(4-hy-droxy-3-meth-oxy-benzyl-idene)cyclo-penta-none ethanol monosolvate.

PubMed

Da'i, Muhammad; Yanuar, Arry; Meiyanto, Edy; Jenie, Umar Anggara; Supardjan, Amir Margono

2013-04-01

In the title structure, C21H20O5·C2H5OH, the curcumine-type mol-ecule has a double E conformation for the two benzyl-idene double bonds [C=C = 1.342 (4) and 1.349 (4) Å] and is nearly planar with respect to the non-H atoms (r.m.s. deviation from planarity = 0.069 Å). The two phenolic OH groups form bifurcated hydrogen bonds with intra-molecular branches to adjacent meth-oxy O atoms and inter-molecular branches to either a neighbouring mol-ecule or an ethanol solvent mol-ecule. The ethanol O atom donates a hydrogen bond to the keto O atom. These hydrogen bonds link the constituents into layers parallel to (101) in the crystal structure.

catena-Poly[bis-(sulfamethoxazolium) [[trichloridocadmate(II)]-μ-chlorido] monohydrate].

PubMed

Subashini, Annamalai; Muthiah, Packianathan Thomas; Bocelli, Gabriele; Cantoni, Andrea

2007-12-21

In the title compound, {(C(10)H(12)N(3)O(3)S)(2)[CdCl(4)]·H(2)O}(n), the Cd(II) atom is five-coordinate with a distorted trigonal-bipyramidal geometry formed by chloride ions. The Cd atom and two of the Cl atoms lie on a mirror plane. The cation is protonated on the amino group N atom; it is not coordinated to cadmium, but is hydrogen bonded to the chlorido ligands. Each water mol-ecule bridges two chlorido ligands, generating ring motifs along the -Cd-Cl-Cd- chains. The isoxazole unit and the amide groups are linked through a pair of N-H⋯N hydrogen bonds. The crystal structure is stabilized by N-H⋯O, O-H⋯Cl, C-H⋯N, N-H⋯Cl and C-H⋯O hydrogen bonds.

catena-Poly[bis­(sulfamethoxazolium) [[trichloridocadmate(II)]-μ-chlorido] monohydrate

PubMed Central

Subashini, Annamalai; Muthiah, Packianathan Thomas; Bocelli, Gabriele; Cantoni, Andrea

2008-01-01

In the title compound, {(C10H12N3O3S)2[CdCl4]·H2O}n, the CdII atom is five-coordinate with a distorted trigonal–bipyramidal geometry formed by chloride ions. The Cd atom and two of the Cl atoms lie on a mirror plane. The cation is protonated on the amino group N atom; it is not coordinated to cadmium, but is hydrogen bonded to the chlorido ligands. Each water mol­ecule bridges two chlorido ligands, generating ring motifs along the –Cd—Cl—Cd– chains. The isoxazole unit and the amide groups are linked through a pair of N—H⋯N hydrogen bonds. The crystal structure is stabilized by N—H⋯O, O—H⋯Cl, C—H⋯N, N—H⋯Cl and C—H⋯O hydrogen bonds. PMID:21200590

Copernicus observations of interstellar absorption at Lyman alpha

NASA Technical Reports Server (NTRS)

Bohlin, R. C.

1975-01-01

Column densities NH of atomic hydrogen have been derived for 40 OB stars from spectral scans at Lyman alpha obtained by the Copernicus (OAO-3) satellite. The stars are all between 60 and 1100 pc away with a range of mean densities n sub H of 0.01 to 2.5 atoms cm-3. The gas to color-excess ratio in clouds varies from 1 to 3 times the mean outside of clouds. The presence of molecular hydrogen correlates with E(B-V), but the best tracer for H2 is atomic hydrogen. The mean density of the gas for all 40 stars is much smaller than the mean of 0.7 atoms cm-3 obtained from 21-cm observations, because the brightest stars with less than average amounts of matter in the line of sight were selected for observation.

Insight into destabilization mechanism of Mg-based hydrides interstitially co-doped with nonmetals: a DFT study

NASA Astrophysics Data System (ADS)

Wu, Zhen; Zhu, Luying; Yang, Fusheng; Zhang, Zaoxiao; Nyamsi, Serge N.

2018-04-01

Mg-based metal hydride is one of the most promising materials for hydrogen energy storage. However, the high thermal stability due to strong bonding effects between the atoms limits its practical application. In order to reduce the thermal stability, a method of doping double nonmetals into Mg-based system was proposed in this study. The density functional theory (DFT) calculation results showed that the thermal stabilities of both the B-N co-doped Mg-based alloy and its hydride are reduced compared with pure Mg-based system. The relative formation enthalpies of the alloy and its hydride are 0.323 and 0.595 eV atom-1, respectively. The values are much higher than those for either singly B- or N-doped Mg-based system. The more significant destabilization by doping double nonmetal elements than single element is mainly attributed to a dual effect in weakening Mg-Ni/NiH4 bonds, caused by criss-cross interactions between B-Ni and N-Mg bonds.