Sample records for nh3 temperature-programmed desorption

  1. DFT study of ammonia desorption from the GaN(0001) surface covered with a NH3/NH2 mixture

    NASA Astrophysics Data System (ADS)

    Kempisty, Pawel; Strak, Pawel; Sakowski, Konrad; Krukowski, Stanislaw

    2014-10-01

    Properties of the GaN(0001) surface, fully covered by a mixture of NH3 molecules and NH2 radicals, were investigated by DFT simulations. It is shown that for extremely low ammonia content, the Fermi level at the surface is at valence band maximum (VBM), then at the 25% ammonia in coverage it is depinned, moving upward in the bandgap to reach conduction band minimum (CBM) at higher ammonia percentages. It is shown that the 25% ammonia in the coverage is corresponding to a flat band configuration in accordance with ECR arguments. The stability of the mixed NH2/NH3 coverage with respect to detachment of ammonia molecules or molecular hydrogen was also investigated. It was shown that high ammonia fraction leads to instability of the coverage due to detachment of ammonia or of molecular hydrogen. The instability point is reached for 36% and 41% fraction of ammonia in the coverage for desorption of molecular hydrogen and ammonia, respectively. The energy barrier for detachment of molecular hydrogen is consistently higher since the H2 molecule has to be created first in the course of desorption process. The ammonia is simply detached in the molecular form so that the high energy intermediate configuration is absent.

  2. Reduction Kinetics of Graphene Oxide Determined by Electrical Transport Measurements and Temperature Programmed Desorption

    E-print Network

    and Temperature Programmed Desorption Inhwa Jung, Daniel A. Field, Nicholas J. Clark, Yanwu Zhu, Dongxing Yang, Richard D. Piner, Sasha Stankovich,§ Dmitriy A. Dikin,§ Heike Geisler,| Carl A. Ventrice, Jr

  3. Apparatus for temperature programmed desorption studies of thin films

    Microsoft Academic Search

    Babu R. Chalamala; David Uebelhoer; Robert H. Reuss

    2000-01-01

    A versatile analytical system based on thermal desorption spectroscopy of thin films is presented. We have found the apparatus to be a useful tool for measuring the desorption characteristics of trapped gases in physical vapor deposited thin films and in determining the thermal stability of multi-component thin film compounds and multilayer structures. The system was also found to be a

  4. Temperature programmed desorption from LiAlO 2 treated with H 2

    NASA Astrophysics Data System (ADS)

    Fischer, Albert K.

    1992-09-01

    Temperature programmed desorption (TPD) measurements have been made of H 2O and H 2 desorption from LiAlO 2 treated at 923 K with He-H 2 mixtures containing 990, 495, and 247 vppm H 2. Desorptions were into sweep gases of pure He and into He-H 2 mixtures. The H 2O and H 2 desorption peaks were shown to be the sums of first order subpeaks which had reproducible desorption activation energy and pre-exponential terms. For H 2O desorption, the activation energies were 96, 117, and 134 kJ/mol (23, 28, and 32 kcal/mol). (Earlier work had identified an additional peak with an activation energy of 75 kJ/mol (18 kcal/mol.) Enhancement of desorption of H 2O by H 2 in the sweep gas was confirmed. The enhancement results not from modifying the activation energies and pre-exponential terms for the various sites but from changes in the populations of sites participating in the desorption process so that sites with lower activation energies are increasingly involved. For those runs with He as the sweep gas, desorption of H 2 could be observed. The subpeaks involved had activation energies within approximately 4 kJ/mol (1 kcal/mol) higher than the analogous peaks for H 2O desorption.

  5. Determining desorption pre-exponential factors from temperature-programmed desorption spectra when the surface is nonuniform

    SciTech Connect

    Brown, L.F.; Chemburkar, R.M.

    1991-03-15

    To find desorption pre-exponential factors from temperature-programmed desorption (TPD) spectra, we develop procedures using both the TPD spectra and their derivatives. First, an approximate method is derived using peak temperatures. This method is formally identical with one used for determining pre-exponential factors and desorption activation energies when desorptions are energetically uniform. The method can be used when the pre-exponential factor is constant. We next develop an iterative process that also uses peak temperatures, and again is usable when the pre-exponential factor is constant. This iterative approach should give more exact values of pre-exponential factors than the approximate approach. Using the first derivatives of TPD spectra over the entire range of temperatures leads to a second iterative process. This last procedure allows determination of energy-dependent pre-exponential factors. 8 refs., 13 figs.

  6. An investigation of the desorption of hydrogen from lithium oxide using temperature programmed desorption and diffuse reflectance infrared spectroscopy

    SciTech Connect

    Kopasz, J.P.; Johnson, C.E. [Argonne National Lab., IL (United States). Chemical Technology Div.; Ortiz-Villafuerte, J. [E.S.F.M., I.P.N., Zacatenco (Mexico). Nuclear Engineering Dept.

    1994-09-01

    The addition of hydrogen to the purge stream has been shown to enhance tritium release from ceramic breeder materials. In an attempt to determine the mechanism for this enhancement the authors have investigated the adsorption and desorption of hydrogen and water from lithium oxide (a leading candidate for the breeder material) by temperature programmed desorption and diffuse reflectance infrared spectroscopy. The results from these studies indicate that several different types of hydroxide groups are formed on the lithium oxide surface. They also suggest that under certain conditions hydride species form on the surface. The role of these species in tritium release from lithium oxide is discussed.

  7. Temperature programmed desorption studies of water interactions with Apollo lunar samples 12001 and 72501

    NASA Astrophysics Data System (ADS)

    Poston, Michael J.; Grieves, Gregory A.; Aleksandrov, Alexandr B.; Hibbitts, Charles A.; Dyar, M. Darby; Orlando, Thomas M.

    2015-07-01

    The desorption activation energies for water molecules chemisorbed on Apollo lunar samples 72501 (highlands soil) and 12001 (mare soil) were determined by temperature programmed desorption experiments in ultra-high vacuum. A significant difference in both the energies and abundance of chemisorption sites was observed, with 72501 retaining up to 40 times more water (by mass) and with much stronger adsorption interactions, possibly approaching 1.5 eV. The dramatic difference between the samples may be due to differences in mineralogy and surface exposure age. The distribution function of water desorption activation energies for sample 72501 was used as an initial condition to simulate water persistence through a temperature profile matching the lunar day.

  8. Microsystem with integrated capillary leak to mass spectrometer for high sensitivity temperature programmed desorption

    SciTech Connect

    Quaade, Ulrich J.; Jensen, Soeren; Hansen, Ole

    2004-10-01

    Temperature programmed desorption (TPD) is a method for obtaining information about quantities and binding properties of adsorbed species on a surface. A microfabricated flow system for TPD with an integrated capillary leak to a mass spectrometer is presented. The use of an integrated capillary leak minimizes dead volumes in the system, resulting in increased sensitivity and reduced response time. These properties make the system ideal for TPD experiments in a carrier gas. With CO desorbing from platinum as model system, it is shown that CO desorbing in 10{sup 5} Pa of argon from as little as 0.5 cm{sup 2} of platinum foil gives a clear desorption peak. By using the microfabricated flow system, TPD experiments can be performed in a carrier gas with a sensitivity approaching that of TPD experiments in vacuum.

  9. Solid-phase microextraction with temperature-programmed desorption for the analysis of iodination disinfection byproducts.

    PubMed

    Frazey, P A; Barkley, R M; Sievers, R E

    1998-02-01

    An analytical approach for the determination of chlorination and iodination disinfection byproducts based on solid-phase microextraction (SPME) was developed. Solid-phase microextraction presents a simple, rapid, sensitive, and solvent-free approach to sample preparation in which analytes in either air or water matrixes are extracted into the polymeric coating of an optical fiber. Analytes are subsequently thermally desorbed in the injection port of a gas chromatograph for separation, detection, and quantitation. Thermal degradation of iodoform was observed during desorption from a polyacrylate fiber in initial GC/MS and GC/ECD experiments. Experiments were designed to determine SPME conditions that would allow quantification without significant degradation of analytes. Isothermal and temperature-programmed thermal desorptions were evaluated for efficacy in transferring analytes with wide-ranging volatilities and thermal stabilities into chromatographic analysis columns. A temperature-programmed desorption (TPD) (120-200 degrees C at 5 degrees C/min with an on-column injection port or 150-200 degrees C at 25 degrees C/min with a split/splitless injection port) was able to efficiently remove analytes with wide-ranging volatilities without causing thermal degradation. The SPME-TPD method was linear over 2-3 orders of magnitude with an electron capture detector and detection limits were in the submicrogram per liter range. Precision and detection limits for selected trihalomethanes were comparable to those of EPA method 551. Extraction efficiencies were not affected by the presence of 10 mg/L soap, 15 mg/L sodium iodide, and 6000 mg/L sodium thiosulfate. The SPME-TPD technique was applied to the determination of iodination disinfection byproducts from individual precursor compounds using GC/MS and to the quantitation of iodoform at trace levels in a water recycle system using GC/ECD. PMID:9470491

  10. Analysis of molecular hydrogen formation on low-temperature surfaces in temperature programmed desorption experiments.

    PubMed

    Vidali, G; Pirronello, V; Li, L; Roser, J; Manicó, G; Congiu, E; Mehl, H; Lederhendler, A; Perets, H B; Brucato, J R; Biham, O

    2007-12-13

    The study of the formation of molecular hydrogen on low-temperature surfaces is of interest both because it enables the exploration of elementary steps in the heterogeneous catalysis of a simple molecule and because of its applications in astrochemistry. Here, we report results of experiments of molecular hydrogen formation on amorphous silicate surfaces using temperature-programmed desorption (TPD). In these experiments, beams of H and D atoms are irradiated on the surface of an amorphous silicate sample. The desorption rate of HD molecules is monitored using a mass spectrometer during a subsequent TPD run. The results are analyzed using rate equations, and the energy barriers of the processes leading to molecular hydrogen formation are obtained from the TPD data. We show that a model based on a single isotope provides the correct results for the activation energies for diffusion and desorption of H atoms. These results are used in order to evaluate the formation rate of H2 on dust grains under the actual conditions present in interstellar clouds. It is found that, under typical conditions in diffuse interstellar clouds, amorphous silicate grains are efficient catalysts of H2 formation when the grain temperatures are between 9 and 14 K. This temperature window is within the typical range of grain temperatures in diffuse clouds. It is thus concluded that amorphous silicates are good candidates to be efficient catalysts of H2 formation in diffuse clouds. PMID:17988107

  11. Molecular Hydrogen Formation on Low Temperature Surfaces in Temperature Programmed Desorption Experiments

    E-print Network

    Vidali, G; Li, L; Roser, J; Manico, G; Mehl, R; Lederhendler, A; Perets, H B; Brucato, J R; Biham, O

    2007-01-01

    The study of the formation of molecular hydrogen on low temperature surfaces is of interest both because it allows to explore elementary steps in the heterogeneous catalysis of a simple molecule and because of the applications in astrochemistry. Here we report results of experiments of molecular hydrogen formation on amorphous silicate surfaces using temperature-programmed desorption (TPD). In these experiments beams of H and D atoms are irradiated on the surface of an amorphous silicate sample. The desorption rate of HD molecules is monitored using a mass spectrometer during a subsequent TPD run. The results are analyzed using rate equations and the activation energies of the processes leading to molecular hydrogen formation are obtained from the TPD data. We show that a model based on a single isotope provides the correct results for the activation energies for diffusion and desorption of H atoms. These results can thus be used to evaluate the formation rate of H_2 on dust grains under the actual conditions...

  12. Molecular Hydrogen Formation on Low Temperature Surfaces in Temperature Programmed Desorption Experiments

    NASA Astrophysics Data System (ADS)

    Vidali, G.; Pirronello, V.; Li, L.; Roser, J.; Manico, G.; Mehl, R.; Lederhendler, A.; Perets, H. B.; Brucato, J. R.; Biham, O.

    The study of the formation of molecular hydrogen on low temperature surfaces is of interest both because it allows to explore elementary steps in the heterogeneous catalysis of a simple molecule and because of the applications in astrochemistry. Here we report results of experiments of molecular hydrogen formation on amorphous silicate surfaces using temperature-programmed desorption (TPD). In these experiments beams of H and D atoms are irradiated on the surface of an amorphous silicate sample. The desorption rate of HD molecules is monitored using a mass spectrometer during a subsequent TPD run. The results are analyzed using rate equations and the activation energies of the processes leading to molecular hydrogen formation are obtained from the TPD data. We show that a model based on a single isotope provides the correct results for the activation energies for diffusion and desorption of H atoms. These results can thus be used to evaluate the formation rate of H_2 on dust grains under the actual conditions present in interstellar clouds.

  13. Molecular Hydrogen Formation on Low Temperature Surfaces in Temperature Programmed Desorption Experiments

    E-print Network

    G. Vidali; V. Pirronello; L. Li; J. Roser; G. Manico; R. Mehl; A. Lederhendler; H. B. Perets; J. R. Brucato; O. Biham

    2008-11-21

    The study of the formation of molecular hydrogen on low temperature surfaces is of interest both because it allows to explore elementary steps in the heterogeneous catalysis of a simple molecule and because of the applications in astrochemistry. Here we report results of experiments of molecular hydrogen formation on amorphous silicate surfaces using temperature-programmed desorption (TPD). In these experiments beams of H and D atoms are irradiated on the surface of an amorphous silicate sample. The desorption rate of HD molecules is monitored using a mass spectrometer during a subsequent TPD run. The results are analyzed using rate equations and the activation energies of the processes leading to molecular hydrogen formation are obtained from the TPD data. We show that a model based on a single isotope provides the correct results for the activation energies for diffusion and desorption of H atoms. These results can thus be used to evaluate the formation rate of H_2 on dust grains under the actual conditions present in interstellar clouds.

  14. Using temperature-programmed desorption and the condensation approximation to determine surface site-energy distributions: examining the approximation's bases.

    SciTech Connect

    Brown, L. F. (Lee F.); Travis, B. J. (Bryan J.)

    2004-01-01

    Investigators (e.g., Seebauer 1994, Bogillo and Shkilev 1999) have used the condensation approximation (CA) successfully for determining broad nonuniform surface site-energy distributions (SEDs) from temperature-programmed desorption (TPD) spectra and for identifying constant pre-exponential factors from peak analysis. The CA assumes that at any temperature T, desorption occurs only at sites with a single desorption activation energy (E{sub cdn}). E{sub cdn} is of course a function of T. Further, the approximation assumes that during TPD all sites with desorption energy E{sub cdn} empty at T.

  15. CF3I on a silicon surface: Adsorption, temperature-programmed desorption, and electron-stimulated desorption

    NASA Astrophysics Data System (ADS)

    Sanabia, Jason E.; Moore, John H.; Tossell, John A.

    2002-06-01

    CF3I adsorption on a silicon surface and the effect of low-energy electron bombardment of a CF3I-covered silicon surface are relevant to plasma etching. Dissociative chemisorption of CF3I on Si(100) surface is observed at 370 K. Uptake measurements corroborated by work-function change measurements and temperature-programmed desorption (TPD) gives a sticking probability of at least 0.34plus-or-minus0.05. Molecular orbital calculations yield an adsorption energy greater than 3 eV for dissociative chemisorption of CF3X (X=F, Cl, Br, and I) on Si(100) (modeled by Si9H12) with X transferred to a silicon atom. We conclude that the variation in the sticking probability across the CF3X family is a consequence of the activation energy barrier for C-X bond cleavage. In TPD, SiF4 desorbs at 370 and 840 K, SiF3 radical at 770 K, and atomic iodine at 790 K. The parent CF3I does not desorb. Electron-stimulated desorption (ESD) yields F+, F- and a trace of I+. The threshold for the appearance of F+ is 20 eV and for F- is 29 eV. Dissociative ionization and dipolar dissociation are possible mechanisms for ESD of F+. Dipolar dissociation and harpooning are possible mechanisms for ESD of F-. There is evidence that iodine on the surface quenches the electronically excited states that lead to desorption of F-.

  16. Qualitative and quantitative analysis of complex temperature-programmed desorption data by multivariate curve resolution

    NASA Astrophysics Data System (ADS)

    Rodríguez-Reyes, Juan Carlos F.; Teplyakov, Andrew V.; Brown, Steven D.

    2010-10-01

    The substantial amount of information carried in temperature-programmed desorption (TPD) experiments is often difficult to mine due to the occurrence of competing reaction pathways that produce compounds with similar mass spectrometric features. Multivariate curve resolution (MCR) is introduced as a tool capable of overcoming this problem by mathematically detecting spectral variations and correlations between several m/z traces, which is later translated into the extraction of the cracking pattern and the desorption profile for each desorbate. Different from the elegant (though complex) methods currently available to analyze TPD data, MCR analysis is applicable even when no information regarding the specific surface reaction/desorption process or the nature of the desorbing species is available. However, when available, any information can be used as constraints that guide the outcome, increasing the accuracy of the resolution. This approach is especially valuable when the compounds desorbing are different from what would be expected based on a chemical intuition, when the cracking pattern of the model test compound is difficult or impossible to obtain (because it could be unstable or very rare), and when knowing major components desorbing from the surface could in more traditional methods actually bias the quantification of minor components. The enhanced level of understanding of thermal processes achieved through MCR analysis is demonstrated by analyzing three phenomena: i) the cryogenic desorption of vinyltrimethylsilane from silicon, an introductory system where the known multilayer and monolayer components are resolved; ii) acrolein hydrogenation on a bimetallic Pt-Ni-Pt catalyst, where a rapid identification of hydrogenated products as well as other desorbing species is achieved, and iii) the thermal reaction of Ti[N(CH 3) 2] 4 on Si(100), where the products of surface decomposition are identified and an estimation of the surface composition after the thermal reaction is afforded. Since this work constitutes, to the best of our knowledge, the first effort to introduce multivariate analysis to TPD data, the procedures, algorithms and strategies employed are described in full detail.

  17. A technique for extending the precision and the range of temperature programmed desorption toward extremely low coverages

    Microsoft Academic Search

    Stefan Haegel; Thomas Zecho; Stefan Wehner

    2010-01-01

    In this paper, an improvement of the temperature programmed desorption (TPD) technique is introduced, which facilitates fully automated sampling of TPD spectra with excellent reproducibility, especially useful for extremely low coverages. By averaging many sampled TPD spectra, the range of the TPD technique can be extended toward lower coverages, as well as the quality of the spectra can be improved.

  18. Reactivity of propylene carbonate toward metallic lithium. Temperature programmed desorption study

    SciTech Connect

    Zhuang, G.; Chottiner, G.; Scherson, D.A. [Case Western Univ., Cleveland, OH (United States)

    1995-05-04

    This paper presents temperature programmed desorption (TPD) data for perdeuterated propylene carbonate (PC-d{sub 6}) condensed at cryogenic temperatures on Li films vapor deposited onto polycrystalline (poly) Au and Ag foils and represents an extension of previous work involving the reactivity of tetrahydrofuran (THF) toward Li supported on Ag(poly). The findings suggest that the product of the reaction between PC and metallic Li is a lithium alkylcarbonate. The same type of species has been proposed to be the major constituent of the passive film on Li in PC in electrochemical environments based on in situ Fourier transform infrared spectroscopic studies. Experiments in which PC-d{sub 6} was intentionally mixed with CO{sub 2}, O{sub 2}, or H{sub 2}O showed that in each case the impurity reacts with Li to form the expected products without affecting, other than the net amount, the PC-d{sub 6}Li thermal decomposition pathway. 15 refs., 8 figs., 2 tabs.

  19. Study of the Evolution of Carbon Dioxide from Active Carbon by a Threshold Temperature-Programmed Desorption Method

    Microsoft Academic Search

    S. Haydar; J. P. Joly

    1998-01-01

    A particular Temperature-Programmed Desorption (TPD) method, called ‘Intermittent TPD’, has been applied to the decomposition\\u000a of oxygen groups naturally present at the surface of a microporous active carbon. It is shown that this method provides more\\u000a information on the kinetics of the thermal decomposition of these species than the classical TPD technique. The main result\\u000a is that the decomposition of

  20. Interactions of N-alcohols with self-assembled monolayer surfaces on nickel(111) studied by temperature-programmed desorption

    NASA Astrophysics Data System (ADS)

    Vogt, Andrew Dale

    1999-12-01

    The interactions of molecules with self-assembled monolayer (SAM) surfaces formed on nickel (111) as studied by temperature-programmed desorption (TPD) are discussed. First, the adsorption of 11-mercaptoundecanoic acid (HS(CH 2)10COOH), 11-mercaptoundecanol (HS(CH2) 11OH) and octadecyl mercaptan (HS(CH2)17CH 3) was characterized by X-ray photoelectron spectroscopy (XPS) and angle-dependent XPS (ADXPS). These long-chain functionalized n-alkanethiols adsorbed onto a clean nickel (111) single crystal via their sulfur atom and the alkyl chain and the carboxyl-, hydroxyl- and methyl-terminal groups were disposed away from the nickel surface. The basic concepts of XPS, AMPS and TPD are discussed. Second, TPD showed that the interactions of low-molecular-weight straight-chain alcohols (n- CxH2x+1 OH for x = 1 through 6) with the carboxyl-, hydroxyl- and methyl-terminated SAM surfaces exhibited an alcohol-coverage-dependent effect on the alcohol's desorption energy based on their respective sets of TPD spectra at different alcohol coverages and based on the desorption spectra's subsequent analysis for desorption energy. The threshold TPD method (TTPD) was used to determine the desorption energy as a function of coverage for all alcohol-substrate pairs. For these adsorbate-substrate systems the desorption energies (TTPD) were the lowest (10--25 kJ mol-1) for the lowest relative alcohol coverages and increased to a desorption energy of 40--60 kJ mol-1 that was invariant with relative coverage after reaching a monolayer. The constant desorption energy (TTPD) at high relative coverages suggests there might be a completely formed hydrogen bonding network between adsorbates on the surfaces at alcohol coverages near a monolayer. The Redhead method, the "complete analysis" and the TTPD method are discussed and compared.

  1. The dissociation kinetics of NO on Rh(111) as studied by temperature programmed static secondary ion mass spectrometry and desorption

    NASA Astrophysics Data System (ADS)

    Borg, H. J.; Reijerse, J. F. C.-J. M.; van Santen, R. A.; Niemantsverdriet, J. W.

    1994-12-01

    Temperature programmed static secondary ion mass spectrometry (TPSSIMS) and temperature programmed desorption (TPD) have been used to study the kinetics of adsorption, dissociation, and desorption of NO on Rh(111). At 100 K, NO adsorption is molecular and proceeds via mobile precursor state kinetics with a high initial sticking probability. SSIMS indicates the presence of two distinct NO adsorption states, indicative of threefold adsorption at low coverage, and occupation of bridge sites at higher coverages. Three characteristic coverage regimes appear with respect to NO dissociation. At low coverages ?NO<0.25 ML, NO dissociates completely at temperatures between 275 and 340 K. If we neglect lateral interactions and assume pure first order dissociation kinetics, we find effective values for the activation barrier and preexponential factor of 40±6 kJ/mol and 106±1 s-1 for the dissociation of 0.15-0.20 ML NO. However, if we assume that a NO molecule needs an ensemble of three to four vacant sites in order to dissociate, the preexponential factor and activation energy are ˜1011 s-1 and 65 kJ/mol, in better agreement with transition state theory expectations. The Nads and Oads dissociation products desorb as N2 and O2, respectively, with desorption parameters Edes=118±10 kJ/mol and ?des=1010.1±1.0 s-1 for N2 in the zero coverage limit. At higher coverages, the desorption kinetics of N2 is strongly influenced by the presence of coadsorbed oxygen. In the medium coverage range 0.25desorption barrier of 113±10 kJ/mol and a preexponential of 1013.5±1.0 s-1. Dissociation of NO becomes progressively inhibited due to site blocking, the onset shifting from 275 K at 0.25 ML to 400 K, coinciding with the NO desorption temperature, at a coverage of 0.50 ML. The accumulation of nitrogen and oxygen atoms on the highly covered surface causes a destabilization of the nitrogen atoms, which results in an additional low-temperature desorption state for N2. For high initial NO coverages above 0.50 ML, the dissociation is completely self-inhibited, indicating that all sites required for dissociation are blocked. The desorption of the more weakly bound—presumably bridged—NO does not generate the sites required for dissociation; these become only available after the desorption of—presumably triply coordinated—NO.

  2. New method for the temperature-programmed desorption (TPD) of ammonia experiment for characterization of zeolite acidity: a review.

    PubMed

    Niwa, Miki; Katada, Naonobu

    2013-10-01

    In this review, a method for the temperature-programmed desorption (TPD) of ammonia experiment for the characterization of zeolite acidity and its improvement by simultaneous IR measurement and DFT calculation are described. First, various methods of ammonia TPD are explained, since the measurements have been conducted under the concepts of kinetics, equilibrium, or diffusion control. It is however emphasized that the ubiquitous TPD experiment is governed by the equilibrium between ammonia molecules in the gas phase and on the surface. Therefore, a method to measure quantitatively the strength of the acid site (?H upon ammonia desorption) under equilibrium-controlled conditions is elucidated. Then, a quantitative relationship between ?H and H0 function is proposed, based on which the acid strength ?H can be converted into the H0 function. The identification of the desorption peaks and the quantitative measurement of the number of acid sites are then explained. In order to overcome a serious disadvantage of the method (i.e., no information is provided about the structure of acid sites), the simultaneous measurement of IR spectroscopy with ammonia TPD, named IRMS-TPD (infrared spectroscopy/mass spectrometry-temperature-programmed desorption), is proposed. Based on this improved measurement, Brønsted and Lewis acid sites were differentiated and the distribution of Brønsted OH was revealed. The acidity characterized by IRMS-TPD was further supported by the theoretical DFT calculation. Thus, the advanced study of zeolite acidity at the molecular level was made possible. Advantages and disadvantages of the ammonia TPD experiment are discussed, and understanding of the catalytic cracking activity based on the derived acidic profile is explained. PMID:23868494

  3. Interaction between water molecules and zinc sulfide nanoparticles studied by temperature-programmed desorption and molecular dynamics simulations.

    PubMed

    Zhang, Hengzhong; Rustad, James R; Banfield, Jillian F

    2007-06-14

    We have investigated the bonding of water molecules to the surfaces of ZnS nanoparticles (approximately 2-3 nm sphalerite) using temperature-programmed desorption (TPD). The activation energy for water desorption was derived as a function of the surface coverage through kinetic modeling of the experimental TPD curves. The binding energy of water equals the activation energy of desorption if it is assumed that the activation energy for adsorption is nearly zero. Molecular dynamics (MD) simulations of water adsorption on 3 and 5 nm sphalerite nanoparticles provided insights into the adsorption process and water binding at the atomic level. Water binds with the ZnS nanoparticle surface mainly via formation of Zn-O bonds. As compared with bulk ZnS crystals, ZnS nanoparticles can adsorb more water molecules per unit surface area due to the greatly increased curvature, which increases the distance between adjacent adsorbed molecules. Results from both TPD and MD show that the water binding energy increases with decreasing the water surface coverage. We attribute the increase in binding energy with decreasing surface water coverage to the increasing degree of surface under-coordination as removal of water molecules proceeds. MD also suggests that the water binding energy increases with decreasing particle size due to the further distance and hence lower interaction between adsorbed water molecules on highly curved smaller particle surfaces. Results also show that the binding energy, and thus the strength of interaction of water, is highest in isolated nanoparticles, lower in nanoparticle aggregates, and lowest in bulk crystals. Given that water binding is driven by surface energy reduction, we attribute the decreased binding energy for aggregated as compared to isolated particles to the decrease in surface energy that occurs as the result of inter-particle interactions. PMID:17518448

  4. Characterization of Lewis acid sites on the (100) surface of beta-AlF3: Ab initio calculations of NH3 adsorption.

    PubMed

    Bailey, C L; Wander, A; Mukhopadhyay, S; Searle, B G; Harrison, N M

    2008-06-14

    The current study employs hybrid-exchange density functional theory to show that the Lewis base, NH(3), binds to the beta-AlF(3) (100) surface with a binding energy (BE) of up to -1.96 eV per molecule. This is characteristic of a strong Lewis acid. The binding of NH(3) to the surface is predominately due to electrostatic interactions. There is only a small charge transfer from the NH(3) molecule to the surface. The BE as a function of coverage is computed and used to develop a lattice Monte Carlo model which is used to predict the temperature programed desorption (TPD) spectrum. Comparison with experimental TPD studies of NH(3) from beta-AlF(3) strongly suggests that these structural models and binding mechanisms are good approximations to those that occur on real AlF(3) surfaces. PMID:18554039

  5. Characterization of Lewis acid sites on the (100) surface of ?-AlF3: Ab initio calculations of NH3 adsorption

    NASA Astrophysics Data System (ADS)

    Bailey, C. L.; Wander, A.; Mukhopadhyay, S.; Searle, B. G.; Harrison, N. M.

    2008-06-01

    The current study employs hybrid-exchange density functional theory to show that the Lewis base, NH3, binds to the ?-AlF3 (100) surface with a binding energy (BE) of up to -1.96 eV per molecule. This is characteristic of a strong Lewis acid. The binding of NH3 to the surface is predominately due to electrostatic interactions. There is only a small charge transfer from the NH3 molecule to the surface. The BE as a function of coverage is computed and used to develop a lattice Monte Carlo model which is used to predict the temperature programed desorption (TPD) spectrum. Comparison with experimental TPD studies of NH3 from ?-AlF3 strongly suggests that these structural models and binding mechanisms are good approximations to those that occur on real AlF3 surfaces.

  6. Interaction between Water Molecules and Zinc Sulfide Nanoparticles Studied by Temperature-Programmed Desorption and Molecular Dynamics Simulations.

    SciTech Connect

    Zhang, Hengzon; Rustad, James R.; Banfield, Jillian F.

    2007-05-23

    The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. We have investigated the bonding of water molecules to the surfaces of ZnS nanoparticles (2-3 nm sphalerite) using temperature-programmed desorption (TPD). The activation energy for water desorption was derived as a function of the surface coverage through kinetic modeling of the experimental TPD curves. The binding energy of water equals the activation energy of desorption if it is assumed that the activation energy for adsorption is nearly zero. Molecular dynamics (MD) simulations of water adsorption on 3 and 5 nm sphalerite nanoparticles provided insights into the adsorption process and water binding at the atomic level. Water binds with the ZnS nanoparticle surface mainly via formation of Zn-O bonds. As compared with bulk ZnS crystals, ZnS nanoparticles can adsorb more water molecules per unit surface area due to the greatly increased curvature, which increases the distance between adjacent adsorbed molecules. Results from both TPD and MD show that the water binding energy increases with decreasing the water surface coverage. We attribute the increase in binding energy with decreasing surface water coverage to the increasing degree of surface under-coordination as removal of water molecules proceeds. MD also suggests that the water binding energy increases with decreasing particle size due to the further distance and hence lower interaction between adsorbed water molecules on highly curved smaller particle surfaces. Results also show that the binding energy, and thus the strength of interaction of water, is highest in isolated nanoparticles, lower in nanoparticle aggregates, and lowest in bulk crystals. Given that water binding is driven by surface energy reduction, we attribute the decreased binding energy for aggregated as compared to isolated particles to the decrease in surface energy that occurs as the result of inter-particle interactions.

  7. Selectivity of dielectric heating: temperature-programmed desorption (TPD) experiments and initiation of thermo-chromatographic pulses.

    PubMed

    Roland, Ulf; Buchenhorst, Daniel; Kraus, Markus; Kopinke, Frank-Dieter

    2008-01-01

    The occurrence and extent of selective dielectric heating with microwaves (MW) and radio waves (RW) was studied with a variety of model systems using temperature-programmed desorption (TPD). Over a wide pressure and temperature range, selectivity effects were neither found for polar adsorbates (compared to non-polar compounds) nor expressed by an overheating of metal clusters supported on a nearly MW- and RW-transparent support. In contrast, significant temperature gradients between particles consisting of materials with various dielectric losses could be established under certain conditions. The utilization of adsorbates significantly modifying the dielectric properties of a material was investigated as a further approach to initiate selective dielectric heating. Applying water as a coupling medium, a combined heat and mass transport, which we call a thermo-chromatographic pulse, can be created in a packed-bed column consisting of various zeolites. In this case, selective heating of bed zones by more than 100 K was observed. The suitability of a material for the creation of thermo-chromatographic pulses depends on its dielectric properties as well as on its sorption properties with respect to water or other coupling media. The study provided further insight into not only the potential but also the limitations of selective dielectric heating of solid materials relevant to chemical engineering, environmental technology and sorption processing. PMID:19227066

  8. Dosimeter-Type NOx Sensing Properties of KMnO4 and Its Electrical Conductivity during Temperature Programmed Desorption

    PubMed Central

    Gro?, Andrea; Kremling, Michael; Marr, Isabella; Kubinski, David J.; Visser, Jacobus H.; Tuller, Harry L.; Moos, Ralf

    2013-01-01

    An impedimetric NOx dosimeter based on the NOx sorption material KMnO4 is proposed. In addition to its application as a low level NOx dosimeter, KMnO4 shows potential as a precious metal free lean NOx trap material (LNT) for NOx storage catalysts (NSC) enabling electrical in-situ diagnostics. With this dosimeter, low levels of NO and NO2 exposure can be detected electrically as instantaneous values at 380 °C by progressive NOx accumulation in the KMnO4 based sensitive layer. The linear NOx sensing characteristics are recovered periodically by heating to 650 °C or switching to rich atmospheres. Further insight into the NOx sorption-dependent conductivity of the KMnO4-based material is obtained by the novel eTPD method that combines electrical characterization with classical temperature programmed desorption (TPD). The NOx loading amount increases proportionally to the NOx exposure time at sorption temperature. The cumulated NOx exposure, as well as the corresponding NOx loading state, can be detected linearly by electrical means in two modes: (1) time-continuously during the sorption interval including NOx concentration information from the signal derivative or (2) during the short-term thermal NOx release. PMID:23549366

  9. A technique for extending the precision and the range of temperature programmed desorption toward extremely low coverages

    NASA Astrophysics Data System (ADS)

    Haegel, Stefan; Zecho, Thomas; Wehner, Stefan

    2010-03-01

    In this paper, an improvement of the temperature programmed desorption (TPD) technique is introduced, which facilitates fully automated sampling of TPD spectra with excellent reproducibility, especially useful for extremely low coverages. By averaging many sampled TPD spectra, the range of the TPD technique can be extended toward lower coverages, as well as the quality of the spectra can be improved. This allows for easy extraction of information about the adsorbate-surface bond. A state of the art TPD apparatus with a two chamber setup and a high quality quadrupole mass spectrometer was extended by automated components. These are an automated gas dosing system, ensuring precise dosing of gas, combined with a motor driven sample manipulation unit and a liquid nitrogen cryostat with automatic refilling. In addition all components were controlled by a computer. A large number of TPD cycles could be sampled without the need of interaction of an operator. Here, it is shown for up to more than 400 TPD cycles. This opens a wide range of new interesting applications for the TPD technique, especially in the limit of zero coverage. Here, basic experiments on well known adsorbate systems are shown to view the ability and limit of this approach.

  10. A technique for extending the precision and the range of temperature programmed desorption toward extremely low coverages.

    PubMed

    Haegel, Stefan; Zecho, Thomas; Wehner, Stefan

    2010-03-01

    In this paper, an improvement of the temperature programmed desorption (TPD) technique is introduced, which facilitates fully automated sampling of TPD spectra with excellent reproducibility, especially useful for extremely low coverages. By averaging many sampled TPD spectra, the range of the TPD technique can be extended toward lower coverages, as well as the quality of the spectra can be improved. This allows for easy extraction of information about the adsorbate-surface bond. A state of the art TPD apparatus with a two chamber setup and a high quality quadrupole mass spectrometer was extended by automated components. These are an automated gas dosing system, ensuring precise dosing of gas, combined with a motor driven sample manipulation unit and a liquid nitrogen cryostat with automatic refilling. In addition all components were controlled by a computer. A large number of TPD cycles could be sampled without the need of interaction of an operator. Here, it is shown for up to more than 400 TPD cycles. This opens a wide range of new interesting applications for the TPD technique, especially in the limit of zero coverage. Here, basic experiments on well known adsorbate systems are shown to view the ability and limit of this approach. PMID:20370189

  11. A technique for extending the precision and the range of temperature programmed desorption toward extremely low coverages

    SciTech Connect

    Haegel, Stefan [Experimentalphysik III, Universitaet Bayreuth, 95440 Bayreuth (Germany); Zecho, Thomas [Nuclear Instrumentation, Areva NP GmbH, Paul-Gossen-Strasse 100, 91052 Erlangen (Germany); Wehner, Stefan [Experimentalphysik III, Universitaet Bayreuth, 95440 Bayreuth (Germany); Institut fuer Integrierte Naturwissenschaften-Physik, Universitaet Koblenz-Landau, Universitaetsstrasse 1, 56070 Koblenz (Germany)

    2010-03-15

    In this paper, an improvement of the temperature programmed desorption (TPD) technique is introduced, which facilitates fully automated sampling of TPD spectra with excellent reproducibility, especially useful for extremely low coverages. By averaging many sampled TPD spectra, the range of the TPD technique can be extended toward lower coverages, as well as the quality of the spectra can be improved. This allows for easy extraction of information about the adsorbate-surface bond. A state of the art TPD apparatus with a two chamber setup and a high quality quadrupole mass spectrometer was extended by automated components. These are an automated gas dosing system, ensuring precise dosing of gas, combined with a motor driven sample manipulation unit and a liquid nitrogen cryostat with automatic refilling. In addition all components were controlled by a computer. A large number of TPD cycles could be sampled without the need of interaction of an operator. Here, it is shown for up to more than 400 TPD cycles. This opens a wide range of new interesting applications for the TPD technique, especially in the limit of zero coverage. Here, basic experiments on well known adsorbate systems are shown to view the ability and limit of this approach.

  12. Surface hydration states of commercial high purity ?-Al 2O 3 powders evaluated by temperature programmed desorption mass spectrometry and diffuse reflectance infrared Fourier transform spectroscopy

    Microsoft Academic Search

    Takashi Shirai; Jin Wang Li; Koji Matsumaru; Chanel Ishizaki; Kozo Ishizaki

    2005-01-01

    The surface of three different grades of commercial high-purity ?-Al2O3 powders produced by hydrolysis of aluminum alkoxide, which differ each other in SSA are evaluated by temperature programmed desorption mass spectrometry (TPDMS) and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. For the DRIFT evaluation the powders were heated in situ under vacuum from 25 to 700°C. The TPDMS spectra of

  13. A novel co-precipitation method for preparation of Mn--Ce/TiO2 composites for NOx reduction with NH3 at low temperature.

    PubMed

    Sheng, Zhongyi; Hu, Yufeng; Xue, Jianming; Wang, Xiaoming; Liao, Weiping

    2012-01-01

    Mn--Ce/TiO2 catalyst prepared by a novel co-precipitation method was used in this study for low-temperature selective catalytic reduction (SCR) of NOx with ammonia. The catalyst showed high activity and good SO2 resistance. The NO conversion on the catalyst increased to 100% when 700 ppm of SO2 flowed in, and reached 60.8% in 2.5 h. The characterized results indicated that the catalyst prepared by the new method had good dispersion of the active phase, uniform micro-size particles and large Brunauer-Emmett-Teller surface. The temperature programmed reduction and temperature programmed desorption experiments showed that the improvement in SCR activity on the Mn--Ce/TiO2 catalyst might be due to the increase of active oxygen species and the enhancement of NH3 chemisorption, both of which were conducive to NH3 activation. PMID:23393985

  14. In situ supported MnO(x)-CeO(x) on carbon nanotubes for the low-temperature selective catalytic reduction of NO with NH3.

    PubMed

    Zhang, Dengsong; Zhang, Lei; Shi, Liyi; Fang, Cheng; Li, Hongrui; Gao, Ruihua; Huang, Lei; Zhang, Jianping

    2013-02-01

    The MnO(x) and CeO(x) were in situ supported on carbon nanotubes (CNTs) by a poly(sodium 4-styrenesulfonate) assisted reflux route for the low-temperature selective catalytic reduction (SCR) of NO with NH(3). X-Ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray photoelectron spectroscopy (XPS), H(2) temperature-programmed reduction (H(2)-TPR) and NH(3) temperature-programmed desorption (NH(3)-TPD) have been used to elucidate the structure and surface properties of the obtained catalysts. It was found that the in situ prepared catalyst exhibited the highest activity and the most extensive operating-temperature window, compared to the catalysts prepared by impregnation or mechanically mixed methods. The XRD and TEM results indicated that the manganese oxide and cerium oxide species had a good dispersion on the CNT surface. The XPS results demonstrated that the higher atomic concentration of Mn existed on the surface of CNTs and the more chemisorbed oxygen species exist. The H(2)-TPR results suggested that there was a strong interaction between the manganese oxide and cerium oxide on the surface of CNTs. The NH(3)-TPD results demonstrated that the catalysts presented a larger acid amount and stronger acid strength. In addition, the obtained catalysts exhibited much higher SO(2)-tolerance and improved the water-resistance as compared to that prepared by impregnation or mechanically mixed methods. PMID:23282798

  15. Gas chromatography/mass spectrometry analysis of components of pyridine temperature-programmed desorption spectra from surface of copper-supported catalysts.

    PubMed

    Pribylová, Lenka; Dvorák, Bohumír

    2009-05-01

    The method of pyridine temperature-programmed desorption (TPD) was applied for the measurement of acid properties of in situ reduced copper catalysts on silicate support. A thermal-conductivity detector (TCD) was used for the detection of TPD spectra of pyridine. The combination of flame-ionization detector and thermal conductivity detector shows that the region of TPD spectrum with the peak maxima T(MAX1)=350 degrees C is a superposition of the TCD response on spectra of desorbed pyridine, water and carbon dioxide, desorbing simultaneously from the catalyst surface. The method for the elimination of H(2)O and CO(2) on the layer of NaOH was tested and the pure TPD spectrum of pyridine was obtained. The exact determination of pyridine concentration allows to estimate the amount of weak and medium acid centers of the catalyst. The gas chromatography with the mass spectroscopy (GC-MS) analyses was used for the interpretation of high temperature region of the pyridine TPD spectra (T(MAX2)=620 degrees C). It was found that pyridine bonded on the strong acid centers is decomposed to N(2) and CO under very high temperature. The available chromatographic method for the separation of components present in pyridine TPD spectrum in the high-temperature region was suggested. The method for the quantification of strong acidity of copper-supported catalyst was found. PMID:19303075

  16. Regeneration of field-spent activated carbon catalysts for low-temperature selective catalytic reduction of NOx with NH3

    SciTech Connect

    Jeon, Jong Ki; Kim, Hyeonjoo; Park, Young-Kwon; Peden, Charles HF; Kim, Do Heui

    2011-10-15

    In the process of producing liquid crystal displays (LCD), the emitted NOx is removed over an activated carbon catalyst by using selective catalytic reduction (SCR) with NH3 at low temperature. However, the catalyst rapidly deactivates primarily due to the deposition of boron discharged from the process onto the catalyst. Therefore, this study is aimed at developing an optimal regeneration process to remove boron from field-spent carbon catalysts. The spent carbon catalysts were regenerated by washing with a surfactant followed by drying and calcination. The physicochemical properties before and after the regeneration were investigated by using elemental analysis, TG/DTG (thermogravimetric/differential thermogravimetric) analysis, N2 adsorption-desorption and NH3 TPD (temperature programmed desorption). Spent carbon catalysts demonstrated a drastic decrease in DeNOx activity mainly due to heavy deposition of boron. Boron was accumulated to depths of about 50 {mu}m inside the granule surface of the activated carbons, as evidenced by cross-sectional SEM-EDX analysis. However, catalyst activity and surface area were significantly recovered by removing boron in the regeneration process, and the highest NOx conversions were obtained after washing with a non-ionic surfactant in H2O at 70 C, followed by treatment with N2 at 550 C.

  17. A Study of the Reactions of Ethanol on CeO 2 and Pd\\/CeO 2 by Steady State Reactions, Temperature Programmed Desorption, and In Situ FT-IR

    Microsoft Academic Search

    A. Yee; S. J. Morrison; H. Idriss

    1999-01-01

    The reaction of ethanol on unreduced and H2-reduced CeO2 and 1 wt% Pd\\/CeO2 has been investigated by steady state reactions, temperature programmed desorption (TPD), and in situ Fourier transform infrared (FT-IR) spectroscopy. Steady state reactions have shown a zero reaction order dependency for diatomic oxygen at and above 20%, whilst the addition of Pd to CeO2 decreases the apparent activation

  18. Thermal desorption of circumstellar and cometary ice analogs

    NASA Astrophysics Data System (ADS)

    Martín-Doménech, R.; Muñoz Caro, G. M.; Bueno, J.; Goesmann, F.

    2014-04-01

    Context. Thermal annealing of interstellar ices takes place in several stages of star formation. Knowledge of this process comes from a combination of astronomical observations and laboratory simulations under astrophysically relevant conditions. Aims: For the first time we present the results of temperature programmed desorption (TPD) experiments with pre-cometary ice analogs composed of up to five molecular components: H2O, CO, CO2, CH3OH, and NH3. Methods: The experiments were performed with an ultra-high vacuum chamber. A gas line with a novel design allows the controlled preparation of mixtures with up to five molecular components. Volatiles desorbing to the gas phase were monitored using a quadrupole mass spectrometer, while changes in the ice structure and composition were studied by means of infrared spectroscopy. Results: The TPD curves of water ice containing CO, CO2, CH3OH, and NH3 present desorption peaks at temperatures near those observed in pure ice experiments, volcano desorption peaks after water ice crystallization, and co-desorption peaks with water. Desorption peaks of CH3OH and NH3 at temperatures similar to the pure ices takes place when their abundance relative to water is above ~3% in the ice matrix. We found that CO, CO2, and NH3 also present co-desorption peaks with CH3OH, which cannot be reproduced in experiments with binary water-rich ice mixtures. These are extensively used in the study of thermal desorption of interstellar ices. Conclusions: These results reproduce the heating of circumstellar ices in hot cores and can be also applied to the late thermal evolution of comets. In particular, TPD curves represent a benchmark for the analysis of the measurements that mass spectrometers on board the ESA-Rosetta cometary mission will perform on the coma of comet 67P/Churyumov-Gerasimenko, which will be active before the arrival of Rosetta according to our predictions.

  19. 5, 25832605, 2008 Stomatal NH3

    E-print Network

    Paris-Sud XI, Université de

    grass species such as Phleum pratense and Lolium multiflorum had NH3 compensation points below species (Lolium perenne, Festuca pratensis and Dactylis glomerata) had sufficiently high NH3 compensation

  20. Mn-CeOx/Ti-PILCs for selective catalytic reduction of NO with NH3 at low temperature.

    PubMed

    Shen, Boxiong; Ma, Hongqing; Yao, Yan

    2012-01-01

    Titanium-pillared clays (Ti-PILCs) were obtained by different ways from TiCl4, Ti(OC3H7)4 and TiOSO4, respectively. Mn-CeO(x)/)Ti-PILCs were then prepared and their activities of selective catalytic reduction (SCR) of NO with NH3 at low-temperature were evaluated. Mn-CeO(x)/Ti-PILCs were characterized by X-ray diffraction, N2 adsorption, Fourier transform infrared spectroscopy, thermal analysis, temperature-programmed desorption of ammonia and H2-temperature-programmed reduction. It was found that Ti-pillar tend to be helpful for the enlargement of surface area, pore volume, acidity and the enhancement of thermal stability for Mn-CeO(x)/Ti-PILCs. Mn-CeO(x)/Ti-PILCs catalysts were active for the SCR of NO. Among three resultant Mn-CeO(x)/Ti-PILCs, the catalyst from TiOSO4 showed the highest activity with 98% NO conversion at 220 degrees C, it also exhibited good resistance to H2O and SO2 in flue gas. The catalyst from TiCl4 exhibited the lowest activity due to the unsuccessful pillaring process. PMID:22655365

  1. Adsorption and decomposition of NH3 on Ir(111): A density functional theory study

    NASA Astrophysics Data System (ADS)

    Huang, Wuying; Cheng, Chun; Feng, Eryin

    2013-10-01

    The adsorption and decomposition of NH3 on Ir(111) have been studied using the density functional theory calculations. The recombinative nitrogen desorption has also been investigated. The configurations and stability of NHx(x = 0-3) species have been performed using frequency analysis. The corresponding reaction energies, the activation energies and the structure of the transition states have been determined and analyzed in detail. Including the zero point energy correction, the calculated activation barrier energy for NHx(x = 1-3) dehydrogenation is between 0.94 eV and 1.05 eV, and that for the recombination desorption of N2 is 1.55 eV, which indicates that the N2 recombinative desorption is the rate-limiting step for the NH3 decomposition on Ir(111). The NH3 desorption energy (0.82 eV) is lower than the NH3 dehydrogenation barrier, which indicates that the ammonia rather desorbs than dissociates from a thermodynamic point of view, consistent with the experimental results. But the competition between desorption and dissociation can be controlled in practice via the applied pressure and temperature.

  2. NH3-TPD-MS study of Ce effect on the surface of Mn- or Fe-exchanged zeolites for selective catalytic reduction of NOx by ammonia

    NASA Astrophysics Data System (ADS)

    Stanciulescu, M.; Bulsink, P.; Caravaggio, G.; Nossova, L.; Burich, R.

    2014-05-01

    The selective catalytic reduction (SCR) of NOx with NH3 is considered to be a promising technique for the efficient reduction of highly detrimental NOx emitted from diesel engine vehicles to N2. This study was focused on a series of catalysts with ZSM-5 as support, prepared by Mn- or Fe-exchange followed by wet impregnation of Ce, or Fe or Mn. These catalysts were characterized by temperature-programmed desorption coupled with a mass spectrometer using ammonia (NH3-TPD-MS). Specifically, NH3-TPD-MS was used as a means of identifying the various strengths of acid sites and their relative abundance in an attempt to explain the effect of the catalyst surface acid sites on DeNOx activity. Acid sites with adsorption energies ranging from 47.0 to 75.6 kJ/mol were detected for all of the catalysts. For the same concentration of exchanged metal it was found that the DeNOx activity depends strongly on the type of metal. Furthermore, the acid site strength and distribution depend on the active metal and correlate with the observed DeNOx catalyst activity. Additionally, SEM metal mapping images confirmed the presence of well dispersed active metal on the surface of all catalysts. The catalysts with bimetallic active phase were stable and demonstrated high NOx conversion over a broad temperature range. Impregnation of metal-exchanged zeolites with Ce enhanced the low temperature NOx conversion. Observed differences of activity between the various catalysts of this study may be due to the formation of new ammonia activation sites. The ammonia desorption profile during the elevation of temperature was correlated to the DeNOx activity.

  3. A study of the adsorption of NH 3 and SO 2 on leaf surfaces

    NASA Astrophysics Data System (ADS)

    Van Hove, L. W. A.; Adema, E. H.; Vredenberg, W. J.; Pieters, G. A.

    The adsorption of NH 3 and SO 2 on the external leaf surface of bean ( Phaseolus vulgaris L.) and poplar ( Populus euramericana L.) was studied. The adsorbed quantities increased strongly with increasing air humidity, indicating that water on the leaf surface plays a major role in the interaction of these gases with the leaf surface. On the other hand temperature in the range between 15 and 26°C had no significant influence. The adsorbed quantities of NH 3 at a specific air humidity appeared to be proportional to NH 3 concentration. This proportionality was less clear for SO 2. The affinity of SO 2 for the leaf surface was found to be approximately twice that of NH 3. A mixture of these gases in the air mutually stimulated their adsorption on the leaf. No significant desorption or uptake of these gases through the cuticle could be detected, indicating that the bulk of the adsorbed gases remains associated with the cuticle.

  4. Publisher's Note: "Ab initio potential energy surfaces for NH,,3 -...-NH,,3 -

    E-print Network

    Publisher's Note: "Ab initio potential energy surfaces for NH,,3 - ...-NH,,3 - ... with analytical of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, Poland Received 21 December 2009; published online 12 January 2010 doi:10.1063/1.3291983 This article was originally published online on 10 December

  5. TES/Aura L2 Ammonia (NH3) Lite Nadir (TL2NH3LN)

    Atmospheric Science Data Center

    2015-06-16

    TES/Aura L2 Ammonia (NH3) Lite Nadir (TL2NH3LN) News:  TES News ... Level:  L2 Instrument:  TES/Aura L2 Ammonia Spatial Coverage:  5.3 km nadir Spatial ... OPeNDAP Access:  OPeNDAP Parameters:  Ammonia Order Data:  Reverb:   Order Data ...

  6. Condensation and vaporization studies of CH3OH and NH3 ices: Major implications for astrochemistry

    NASA Astrophysics Data System (ADS)

    Sandford, Scott A.; Allamandola, Louis J.

    1993-11-01

    In an extension of previously reported work on ices containing H2O, CO, CO2, SO2, H2S, and H2, we present measurements of the physical and infrared spectral properties of ices containing CH3OH and NH3. The condensation and sublimation behavior of these ice systems is discussed and surface binding energies are presented for all of these molecules. The surface binding energies can be used to calculate the residence times of the molecules on grain surfaces as a function of temperature. It is demonstrated that many of the molecules used to generate radio maps of and probe conditions in dense clouds, for example CO and NH3, will be significantly depleted from the gas phase by condensation onto dust grains. Attempts to derive total column densities solely from radio maps that do not take condensation effects into account may vastly underestimate the true column densities of any given species. Simple CO condensation onto and vaporization off of grains appears to be capable of explaining the observed depletion of gas phase CO in cold, dense molecular cores. This is not the case for NH3, however, where thermal considerations alone predict that all of the NH3 should be condensed onto grains. The fact that some gas phase NH3 is observed indicates that additional desorption processes must be involved. The surface binding energies of CH3OH, in conjunction with this molecule's observed behavior during warm up in H2O-rich ices, is shown to provide an explanation of the large excess of CH3OH seen in many warm, dense molecular cores. The near-infrared spectrum and associated integrated band strengths of CH3OH-containing ice are given, as are middle infrared absorption band strengths for both CH3OH and NH3.

  7. Condensation and Vaporization Studies of CH3OH and NH3 Ices: Major Implications for Astrochemistry

    NASA Technical Reports Server (NTRS)

    Sandford, Scott A.; Allamandola, Louis J.

    1993-01-01

    In an extension of previously reported work on ices containing H20, CO, CO2, SO2, H2S, and H2, We present measurements of the physical and infrared spectral properties of ices containing CH30H and NH3.The condensation and sublimation behavior of these ice systems is discussed and surface binding energies are presented for all of these molecules. The surface binding energies can be used to calculate the residence times of the molecules on grain surfaces as a function of temperature. It is demonstrated that many of the molecules used to generate radio maps of and probe conditions in dense clouds, for example CO and NH3, will be significantly depleted from the gas phase by condensation onto dust grains. Attempts to derive total column densities solely from radio maps that do not take condensation effects into account may vastly underestimate the true column densities of any given species. Simple CO condensation onto and vaporization off of grains appears to be capable of explaining the observed 87 of gas phase CO in cold, dense molecular cores. This is not the case for NH3, however, where thermal considerations alone predict that all of the NH3 should be condensed onto grains. The fact that some gas phase NH3 is observed indicates that additional desorption processes must be involved. The surface binding energies of CH3OH, in conjunction with this molecule's observed behavior during warm up in H2O-rich ices, is shown to provide an explanation of the large excess of CH3OH seen in many warm, dense molecular cores. The near-infrared spectrum and associated integrated band strengths of CH3OH-containing ice are given, as are middle infrared absorption band strengths for both CH3OH and NH3.

  8. Condensation and vaporization studies of CH3OH and NH3 ices: Major implications for astrochemistry

    NASA Technical Reports Server (NTRS)

    Sandford, Scott A.; Allamandola, Louis J.

    1993-01-01

    In an extension of previously reported work on ices containing H2O, CO, CO2, SO2, H2S, and H2, we present measurements of the physical and infrared spectral properties of ices containing CH3OH and NH3. The condensation and sublimation behavior of these ice systems is discussed and surface binding energies are presented for all of these molecules. The surface binding energies can be used to calculate the residence times of the molecules on grain surfaces as a function of temperature. It is demonstrated that many of the molecules used to generate radio maps of and probe conditions in dense clouds, for example CO and NH3, will be significantly depleted from the gas phase by condensation onto dust grains. Attempts to derive total column densities solely from radio maps that do not take condensation effects into account may vastly underestimate the true column densities of any given species. Simple CO condensation onto and vaporization off of grains appears to be capable of explaining the observed depletion of gas phase CO in cold, dense molecular cores. This is not the case for NH3, however, where thermal considerations alone predict that all of the NH3 should be condensed onto grains. The fact that some gas phase NH3 is observed indicates that additional desorption processes must be involved. The surface binding energies of CH3OH, in conjunction with this molecule's observed behavior during warm up in H2O-rich ices, is shown to provide an explanation of the large excess of CH3OH seen in many warm, dense molecular cores. The near-infrared spectrum and associated integrated band strengths of CH3OH-containing ice are given, as are middle infrared absorption band strengths for both CH3OH and NH3.

  9. Nonthermal surface chemistry: collision-induced reactions of NH3 on Pt{111}

    NASA Astrophysics Data System (ADS)

    Szulczewski, Greg J.; Levis, Robert J.

    1994-07-01

    We report the collision-induced desorption and dissociation of two molecular forms of ammonia bound to a Pt{111} single crystal by a beam of translationaly energetic, neutral noble gas atoms. In this experiment the probability for desorption at low coverage is measured as a function of the collision energy between an Ar atom and chemisorbed ammonia molecule and is found to be independent of the Ar beam angle of incidence. At higher initial ammonia coverages the probability of collision-induced desorption is greater since the NH3/Pt{111} binding energy is much weaker. In addition we observe formation of surface NHx products generated in a process known as collision-induced dissociation.

  10. Ab initio potential energy surfaces for NH(3?-)-NH(3?-) with analytical long range

    NASA Astrophysics Data System (ADS)

    Janssen, Liesbeth M. C.; Groenenboom, Gerrit C.; van der Avoird, Ad; ?uchowski, Piotr S.; Podeszwa, Rafa?

    2009-12-01

    We present four-dimensional ab initio potential energy surfaces for the three different spin states of the NH(?3-)-NH(?3-) complex. The potentials are partially based on the work of Dhont et al. [J. Chem. Phys. 123, 184302 (2005)]. The surface for the quintet state is obtained at the RCCSD(T)/augmented correlation-consistent polarized valence triple-zeta (aug-cc-pVTZ) level of theory and the energy differences with the singlet and triplet states are calculated at the complete active space with nth-order perturbation theory/aug-cc-pVTZ (n =2,3) level of theory. The ab initio potentials are fitted to coupled spherical harmonics in the angular coordinates, and the long range is further expanded as a power series in 1/R. The RCCSD(T) potential is corrected for a size-consistency error of about 0.5×10-6 Eh prior to fitting. The long-range coefficients obtained from the fit are found to be in good agreement with first and second-order perturbation theory calculations.

  11. Studies of Rotational Energy Transfer (RET) in long-range NH3-NH3 collisions in the gas phase (*)

    E-print Network

    Boyer, Edmond

    L-477 Studies of Rotational Energy Transfer (RET) in long-range NH3-NH3 collisions in the gas phase (*) M. Kaimierczak Nonlinear Optics Department, Institute of Physics, A. Mickiewicz University, 60.50E Recently, transfer processes have been the subject of intensive theoretical and experimental

  12. Diffusion measurements of CO, HNCO, H2CO, and NH3 in amorphous water ice

    NASA Astrophysics Data System (ADS)

    Mispelaer, F.; Theulé, P.; Aouididi, H.; Noble, J.; Duvernay, F.; Danger, G.; Roubin, P.; Morata, O.; Hasegawa, T.; Chiavassa, T.

    2013-07-01

    Context. Water is the major component of the interstellar ice mantle. In interstellar ice, chemical reactivity is limited by the diffusion of the reacting molecules, which are usually present at abundances of a few percent with respect to water. Aims: We want to study the thermal diffusion of H2CO, NH3, HNCO, and CO in amorphous water ice experimentally to account for the mobility of these molecules in the interstellar grain ice mantle. Methods: In laboratory experiments performed at fixed temperatures, the diffusion of molecules in ice analogues was monitored by Fourier transform infrared spectroscopy. Diffusion coefficients were extracted from isothermal experiments using Fick's second law of diffusion. Results: We measured the surface diffusion coefficients and their dependence with the temperature in porous amorphous ice for HNCO, H2CO, NH3, and CO. They range from 10-15 to 10-11 cm2 s-1 for HNCO, H2CO, and NH3 between 110 K and 140 K, and between 5-8 × 10-13 cm2 s-1 for CO between 35 K and 40 K. The bulk diffusion coefficients in compact amorphous ice are too low to be measured by our technique and a 10-15 cm2 s-1 upper limit can be estimated. The amorphous ice framework reorganization at low temperature is also put in evidence. Conclusions: Surface diffusion of molecular species in amorphous ice can be experimentally measured, while their bulk diffusion may be slower than the ice mantle desorption kinetics.

  13. Assessment of acid–base strength distribution of ion-exchanged montmorillonites through NH 3 and CO 2TPD measurements

    Microsoft Academic Search

    A. Azzouz; D. Nistor; D. Miron; A. V. Ursu; T. Sajin; F. Monette; P. Niquette; R. Hausler

    2006-01-01

    Distribution of the acid–base strengths of various ion-exchanged montmorillonites was assessed through thermal programmed desorption (TPD) of NH3 and CO2. Accurate acid–base measurements can be achieved via deconvolution of perfectly symmetrical peaks, under optimal carrier gas throughput and heating rate, estimated though a factorial experiment design. No neutral clay samples without interactions with carbon dioxide or ammonia were found. All

  14. Desorption behavior of ammonia from TiO 2-based specimens — ammonia sensing mechanism of double-layer sensors with TiO 2-based catalyst layers

    Microsoft Academic Search

    Yasuhiro Shimizu; Takayuki Okamoto; Yuji Takao; Makoto Egashira

    2000-01-01

    Desorption behavior of gases from the NH3-preadsorbed catalyst and sensing materials used for double-layer semiconductor NH3 sensors has been investigated under different adsorption and desorption conditions. The 0.5 Ir\\/TiO2 catalyst material was found to exhibit mild activity for NH3 oxidation and high activity for reducing NO to N2 in an atmosphere containing NH3 and O2. This nature was considered to

  15. Biodegradation of monohalogenated alkanes by soil NH 3 -oxidizing bacteria

    Microsoft Academic Search

    K. N. Duddleston; D. J. Arp; P. J. Bottomley

    2002-01-01

    .   Although cooxidative biodegradation of monohalogenated hydrocarbons has been well studied in the model NH3-oxidizing bacterium, Nitrosomonas europaea, virtually no information exists about cooxidation of these compounds by native populations of NH3-oxidizing bacteria. To address this subject, nitrifying activity was stimulated to 125–400 nmol NO3\\u000a – produced g–1 soil h–1 by first incubating a Ca(OH)2-amended, silt loam soil (pH 7.0±0.2) at field

  16. NH_3_ and HCO^+^ towards luminous IRAS sources.

    NASA Astrophysics Data System (ADS)

    Schreyer, K.; Henning, T.; Koempe, C.; Harjunpaeae, P.

    1996-02-01

    We have selected 67 objects for observation that are presumably massive young stellar objects. They were from the IRAS Point Source Catalogue based on their infrared flux (Fnu_>=500Jy at 100?m). All objects have been surveyed in the NH_3_(1,1) and (2,2) lines, and a subsample of 53 objects in the rotational line of HCO^+^(J=1-0). 25 objects (37%) were detected in the NH_3_(1,1) line, 18 objects (27%) in the NH_3_(2,2) line, and 38 objects (72%) in the HCO^+^ line. Two objects, IRAS 06058+2138 and IRAS 06061+2151, have been mapped in the two ammonia transitions. From the molecular line data, we have derived the kinetic temperature T_kin_ and the NH_3_ column densities. These data were combined with data from the literature and data derived from the IRAS fluxes (dust colour temperature T_d_, optical depth ?, luminosity). No clear correlations were found; the data are, however, consistent with least square fits found by Wouterloot et al. (1988a). The probability to detect H_2_O maser sources is strongly correlated with the detection of NH_3_ emission: Water maser emission has been seen towards 83% of those objects with clear detections of NH_3_(1,1) and (2,2) lines.

  17. Bias in modeled bi-directional NH3 fluxes associated with temporal averaging of atmospheric NH3 concentrations

    EPA Science Inventory

    Direct flux measurements of NH3 are expensive, time consuming, and require detailed supporting measurements of soil, vegetation, and atmospheric chemistry for interpretation and model parameterization. It is therefore often necessary to infer fluxes by combining measurements of...

  18. The structure and desorption properties of the ammines of the group II halides

    NASA Astrophysics Data System (ADS)

    Jones, Martin Owen; Royse, David M.; Edwards, Peter P.; David, William I. F.

    2013-12-01

    The synthesis of the magnesium halide ammines (Mg(NH3)6Cl2, Mg(NH3)6Br2 and Mg(NH3)6I2) is reported and their structures are identified by high resolution X-ray diffraction. The structures of Mg(NH3)6Br2 and Mg(NH3)6I2 are reported for the first time. The desorption properties of Mg(NH3)6Cl2, Mg(NH3)6Br2 and Mg(NH3)6I2 are examined by thermogravimetric analysis and NMR, and the trends in desorption properties as a function of composition are interpreted using a simple ionic model. It is found that the desorption properties are dependent on the lattice enthalpy of the intermediate and final phases Mg(NH3)2X2, Mg(NH3)X2 and MgX2, that the anion has limited effect on the state of Mg-N bonding and that the desorption temperature of ionic ammines may be tuned by varying the size of the anion.

  19. A Sensitive Survey of Ammonia (NH3) in Comets

    NASA Astrophysics Data System (ADS)

    Magee-Sauer, Karen P.; Villanueva, G. L.; Bonev, B. P.; Paganini, L.; DiSanti, M. A.; Mumma, M. J.

    2012-10-01

    Being the fully reduced form of nitrogen, ammonia (NH3) is a key molecule for understanding the nitrogen chemistry in comets and to properly characterize the primordial conditions under which these icy bodies formed. Yet, its abundance has not been well characterized, even though NH3 is a major reservoir of volatile nitrogen in comets. To date the abundance has been directly measured in only 10 comets, all at radio and infrared wavelengths. This small sample is largely due to the difficulty in measuring emission from NH3 since its emission is normally weak, can be affected by terrestrial extinction, and (without sufficient spectral resolution) is not resolved from other volatile cometary emissions. In this paper, we present a search for NH3 in seven comets using archival data acquired by our Team using the NIRSPEC instrument at the Keck-2 telescope and the CSHELL instrument at the NASA Infrared Telescope Facility, both atop Mauna Kea, HI. Using an updated fluorescence model that is based on millions of ammonia spectral lines (Villanueva et al., in prep.), we present relative abundances of NH3 with respect to H2O. We find the relative abundance of NH3/H2O varies from 0.3% to 1.6% in these seven comets, and we compare this indicator with other properties measured for these comets (isotopic fractionation and mixing ratios of selected primary volatiles). We gratefully acknowledge support from NASA’s Postdoctoral Program (LP), the NASA Astrobiology Institute (PI MJM), NASA’s Planetary Astronomy (PI GLV; PI MJM; PI DiSanti) and Planetary Atmospheres (PI DiSanti, PI Villanueva) programs, and from NSF Planetary Astronomy program (PI BPB).

  20. Enhanced NH3 emission from swine liquid waste

    NASA Astrophysics Data System (ADS)

    Lee, S.; Robarge, W. P.; Walker, J. T.

    2010-12-01

    Swine animal feeding operations are sources of emissions for various gases [ammonia (NH3), hydrogen sulfide (H2S), carbon dioxide (CO2), volatile organic carbons (VOCs)], and fine particulate matter. Gaseous emissions from simple aqueous systems are typically controlled by temperature, pH, wind speed, total dissolved concentration of the chemical species of interest (e.g. NH3+NH4+ = TAN), and the Henry’s law constant. Ammonia emissions from three different sources [ammonium sulfate (AS), swine anaerobic lagoon liquid (SLL), and pit liquid (SPL) from swine housing units] were evaluated using a small flow-through teflon-lined chamber (SFTC; 0.3m × 0.2m × 0.15m) under controlled laboratory conditions. The SFTC was designed for 100% collection efficiency of NH3 gas emitted from the liquids. The internal volume of the chamber, 9 L, was exchanged 1.1 times per minute. All three liquid formulations exhibit the expected response in emissions with changes in temperature and pH. However, NH3 emissions from the SPL and SLL are ~5 times those from pure solutions of AS. Furthermore, the enhancement in NH3 emissions was a function of TAN concentration, decreasing in intensity at higher TAN and approaching rates comparable to the pure solutions of AS. The difference in emissions with solutions of equivalent TAN suggests a synergistic mechanism that is enhancing NH3 emissions in SPL and SLL. Concurrent measurements as part of the National Air Emissions Monitoring Study at the swine operations originally sampled for SPL and SLL document the emissions of CO2, H2S and VOCs (primarily acetic, propionic and butyric acids) at levels that are comparable to observed NH3 emissions. To date, only additions of NaHCO3 to the SPL and SLL have been found to enhance NH3 emissions and exhibit the same response to increasing TAN as exhibited by the original SPL and SLL solutions. Possible reactions that could enhance emissions will be discussed.

  1. Kinetics of the NH3 and CO2 solid-state reaction at low temperature.

    PubMed

    Noble, J A; Theule, P; Duvernay, F; Danger, G; Chiavassa, T; Ghesquiere, P; Mineva, T; Talbi, D

    2014-11-21

    Ammonia and carbon dioxide play an important role in both atmospheric and interstellar ice chemistries. This work presents a theoretical and experimental study of the kinetics of the low-temperature NH3 and CO2 solid-state reaction in ice films, the product of which is ammonium carbamate (NH4(+)NH2COO(-)). It is a first-order reaction with respect to CO2, with a temperature-dependent rate constant fitted to the Arrhenius law in the temperature range 70 K to 90 K, with an activation energy of 5.1 ± 1.6 kJ mol(-1) and a pre-exponential factor of 0.09-0.08(+1.1) s(-1). This work helps to determine the rate of removal of CO2 and NH3, via their conversion into ammonium carbamate, from atmospheric and interstellar ices. We also measure first-order desorption energies of 69.0 ± 0.2 kJ mol(-1) and 76.1 ± 0.1 kJ mol(-1), assuming a pre-exponential factor of 10(13) s(-1), for ammonium carbamate and carbamic acid, respectively. PMID:25198107

  2. Temperature Programmed Liquid Chromatography

    Microsoft Academic Search

    Brian A. Jones

    2005-01-01

    Temperature programming in liquid chromatography is reviewed with an emphasis on instrumental methods, and emerging techniques. Column formats and stationary phases, both open tubular and packed, along with normal, reversed?phase and water—only mobile phases—are discussed. Attention is given particularly to separations with larger bore columns.

  3. Quantifying Dry NH 3 Deposition to an Ombrotrophic Bog from an Automated NH 3 Field Release System

    Microsoft Academic Search

    Ian D. Leith; Lucy J. Sheppard; David Fowler; J. Neil Cape; Matt Jones; Alan Crossley; Ken J. Hargreaves; Y. Sim Tang; Mark Theobald; Mark R. Sutton

    2004-01-01

    Providing an accurate estimate of the dry component of N deposition to low N background, semi-natural habitats, such as bogs and upland moors dominated by Calluna vulgaris is difficult, but essential to relate nitrogen deposition to effects in these communities. To quantify the effects of NH3 inputs to moorland vegetation growing on a bog at a field scale, a field

  4. NH3-SCR denitration catalyst performance over vanadium-titanium with the addition of Ce and Sb.

    PubMed

    Xu, Chi; Liu, Jian; Zhao, Zhen; Yu, Fei; Cheng, Kai; Wei, Yuechang; Duan, Aijun; Jiang, Guiyuan

    2015-05-01

    Selective catalytic reduction technology using NH3 as a reducing agent (NH3-SCR) is an effective control method to remove nitrogen oxides. TiO2-supported vanadium oxide catalysts with different levels of Ce and Sb modification were prepared by an impregnation method and were characterized by X-ray diffractometer (XRD), Brunauer-Emmett-Teller (BET), Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), Raman and Hydrogen temperature-programmed reduction (H2-TPR). The catalytic activities of V5CexSby/TiO2 catalysts for denitration were investigated in a fixed bed flow microreactor. The results showed that cerium, vanadium and antimony oxide as the active components were well dispersed on TiO2, and the catalysts exhibited a large number of d-d electronic transitions, which were helpful to strengthen SCR reactivity. The V5CexSby/TiO2 catalysts exhibited a good low temperature NH3-SCR catalytic activity. In the temperature range of 210 to 400°C, the V5CexSby/TiO2 catalysts gave NO conversion rates above 90%. For the best V5Ce35Sb2/TiO2 catalyst, at a reaction temperature of 210°C, the NO conversion rate had already reached 90%. The catalysts had different catalytic activity with different Ce loadings. With the increase of Ce loading, the NO conversion rate also increased. PMID:25968261

  5. Tunable high-efficient pulsed NH3 terahertz lasers

    NASA Astrophysics Data System (ADS)

    Jiu, Zhi-Xian; Li, Qiang; Zuo, Du-Luo; Miao, Liang; Cheng, Zu-Hai

    2012-03-01

    Experimental studies on a tunable efficient high-efficient pulsed NH3 terahertz (THz) lasers pumped by TEA CO2 lasers are presented. When NH3 is pumped by the different lines with the CO2 lasers, the generation of different terahertz radiations is discussed. The lines of the CO2 lasers are 9R(08), 9P(20), 10R(14), 10R(08), and 10R(06). To improve THz laser energy and photon conversion efficiency, different higher power of the CO2 laser can effectively improve THz laser energy and photon conversion efficiency. When the 9P(20) CO2 lasers with 9.68 J and 4.12 J pump NH3, the corresponding energy conversion efficiencies are 0.28% and 0.19%, increasing by a factor of about 1.5. The generation of terahertz radiations with energy as high as 27.29 mJ and 7.73 mJ are obtained, respectively, increasing by a factor of about 3.5. Meanwhile, for 10R(14) line, the energy conversion efficiencies increase to 8.5 times and the energy of THz lasers increase to 32 times.

  6. Scattering resonances in slow NH3-He collisions

    NASA Astrophysics Data System (ADS)

    Gubbels, Koos B.; van de Meerakker, Sebastiaan Y. T.; Groenenboom, Gerrit C.; Meijer, Gerard; van der Avoird, Ad

    2012-02-01

    We theoretically study slow collisions of NH3 molecules with He atoms, where we focus in particular on the observation of scattering resonances. We calculate state-to-state integral and differential cross sections for collision energies ranging from 10-4 cm-1 to 130 cm-1, using fully converged quantum close-coupling calculations. To describe the interaction between the NH3 molecules and the He atoms, we present a four-dimensional potential energy surface, based on an accurate fit of 4180 ab initio points. Prior to collision, we consider the ammonia molecules to be in their antisymmetric umbrella state with angular momentum j = 1 and projection k = 1, which is a suitable state for Stark deceleration. We find pronounced shape and Feshbach resonances, especially for inelastic collisions into the symmetric umbrella state with j = k = 1. We analyze the observed resonant structures in detail by looking at scattering wavefunctions, phase shifts, and lifetimes. Finally, we discuss the prospects for observing the predicted scattering resonances in future crossed molecular beam experiments with a Stark-decelerated NH3 beam.

  7. Scattering resonances in slow NH3-He collisions.

    PubMed

    Gubbels, Koos B; van de Meerakker, Sebastiaan Y T; Groenenboom, Gerrit C; Meijer, Gerard; van der Avoird, Ad

    2012-02-21

    We theoretically study slow collisions of NH(3) molecules with He atoms, where we focus in particular on the observation of scattering resonances. We calculate state-to-state integral and differential cross sections for collision energies ranging from 10(-4) cm(-1) to 130 cm(-1), using fully converged quantum close-coupling calculations. To describe the interaction between the NH(3) molecules and the He atoms, we present a four-dimensional potential energy surface, based on an accurate fit of 4180 ab initio points. Prior to collision, we consider the ammonia molecules to be in their antisymmetric umbrella state with angular momentum j = 1 and projection k = 1, which is a suitable state for Stark deceleration. We find pronounced shape and Feshbach resonances, especially for inelastic collisions into the symmetric umbrella state with j = k = 1. We analyze the observed resonant structures in detail by looking at scattering wavefunctions, phase shifts, and lifetimes. Finally, we discuss the prospects for observing the predicted scattering resonances in future crossed molecular beam experiments with a Stark-decelerated NH(3) beam. PMID:22360237

  8. The reactions of TiCl3, and of UF4 with TiCl3 in liquid ammonia: unusual coordination spheres in [Ti(NH3)8]Cl3·6NH3 and [UF(NH3)8]Cl3·3.5NH3.

    PubMed

    Woidy, Patrick; Karttunen, Antti J; Rudel, Stefan S; Kraus, Florian

    2015-07-01

    TiCl3 and NH3 form octaammine titanium(iii) chloride ammonia (1/6), [Ti(NH3)8]Cl3·6NH3, which is the first structurally characterized octaammine complex of a transition metal. An excess of TiCl3 reacts with UF4 in liquid NH3 and forms octaammine fluorido uranium(iv) chloride ammonia (1/3.5), [UF(NH3)8]Cl3·3.5NH3. It shows a distorted threefold-capped trigonal-prismatic coordination sphere around U(iv). PMID:26109184

  9. Concentration-dependent NH3 deposition processes for moorland plant species with and without stomata

    Microsoft Academic Search

    M. R. Jones; I. D. Leith; J. A. Raven; D. Fowler; M. A. Sutton; E. Nemitz; J. N. Cape; L. J. Sheppard; R. I. Smith

    2007-01-01

    Currently, in operational modelling of NH3 deposition a fixed value of canopy resistance (R-c) is generally applied, irrespective of the plant species and NH3 concentration. This study determined the effect of NH3 concentration on deposition processes to individual moorland species. An innovative flux chamber system was used to provide accurate continuous measurements of NH3 deposition to Deschampsia cespitosa (L.) Beauv.,

  10. Effect of proton motion on molecular properties in the BrH NH3 complex

    NASA Astrophysics Data System (ADS)

    Aicken, A. M.; Buckingham, A. D.; Tantirungrotechai, Y.

    1999-07-01

    The nuclear magnetic shielding, electric dipole moment and electric field gradient at the nuclei were studied by ab initio computations as a function of the one-dimensional proton transfer coordinate in BrH NH3. The properties are vibrationally averaged along this reaction coordinate for BrH NH3 and BrD NH3. The effect of a matrix has been approximated, as in previous calculations, by surrounding BrH NH3 with three argon atoms.

  11. Enhanced Performance of Perovskite CH3NH3PbI3 Solar Cell by Using CH3NH3I as Additive in Sequential Deposition.

    PubMed

    Xie, Yian; Shao, Feng; Wang, Yaoming; Xu, Tao; Wang, Deliang; Huang, Fuqiang

    2015-06-17

    Sequential deposition is a widely adopted method to prepare CH3NH3PbI3 on mesostructured TiO2 electrode for organic lead halide perovskite solar cells. However, this method often suffers from the uncontrollable crystal size, surface morphology, and residual PbI2 in the resulting CH3NH3PbI3, which are all detrimental to the device performance. We herein present an optimized sequential solution deposition method by introducing different amount of CH3NH3I in PbI2 precursor solution in the first step to prepare CH3NH3PbI3 absorber on mesoporous TiO2 substrates. The addition of CH3NH3I in PbI2 precursor solution can affect the crystallization and composition of PbI2 raw films, resulting in the variation of UV-vis absorption and surface morphology. Proper addition of CH3NH3I not only enhances the absorption but also improves the efficiency of CH3NH3PbI3 solar cells from 11.13% to 13.37%. Photoluminescence spectra suggest that the improvement of device performance is attributed to the decrease of recombination rate of carriers in CH3NH3PbI3 absorber. This current method provides a highly repeatable route for enhancing the efficiency of CH3NH3PbI3 solar cell in the sequential solution deposition method. PMID:26009927

  12. Commercial Fe- or Co-containing carbon nanotubes as catalysts for NH3 decomposition.

    PubMed

    Zhang, Jian; Comotti, Massimiliano; Schüth, Ferdi; Schlögl, Robert; Su, Dang Sheng

    2007-05-21

    Fresh commercial carbon nanotubes (CNTs) containing residual Co or Fe nanoparticles are highly active for NH3 decomposition while the microstructure of CNTs remains unchanged. The catalysts are promising for elimination of NH3 from coal gasification stream and for production of H2 from NH3. PMID:17695228

  13. Removal of high concentrations of NH3 by a combined photoreactor and biotrickling filter system

    Microsoft Academic Search

    Li-Chun Wu; Cheng-Lang Kuo; Ying-Chien Chung

    2011-01-01

    Average emission levels as high as 800 ppmv NH3 have often been found during the anaerobic fermentation process. At these levels, NH3 is regarded as an environmental toxic compound. High concentrations of NH3 gas are difficult to treat in a single treatment process, suggesting that, in terms of economic cost and treatment performance, a coupled system may be a feasible

  14. Ab initio potential energy surfaces for NH((3)sigma(-))-NH((3)sigma(-)) with analytical long range.

    PubMed

    Janssen, Liesbeth M C; Groenenboom, Gerrit C; van der Avoird, Ad; Zuchowski, Piotr S; Podeszwa, Rafa?

    2009-12-14

    We present four-dimensional ab initio potential energy surfaces for the three different spin states of the NH((3)Sigma(-))-NH((3)Sigma(-)) complex. The potentials are partially based on the work of Dhont et al. [J. Chem. Phys. 123, 184302 (2005)]. The surface for the quintet state is obtained at the RCCSD(T)/augmented correlation-consistent polarized valence triple-zeta (aug-cc-pVTZ) level of theory and the energy differences with the singlet and triplet states are calculated at the complete active space with nth-order perturbation theory/aug-cc-pVTZ (n=2,3) level of theory. The ab initio potentials are fitted to coupled spherical harmonics in the angular coordinates, and the long range is further expanded as a power series in 1/R. The RCCSD(T) potential is corrected for a size-consistency error of about 0.5x10(-6) E(h) prior to fitting. The long-range coefficients obtained from the fit are found to be in good agreement with first and second-order perturbation theory calculations. PMID:20001043

  15. Theoretical investigation of HNgNH3(+) ions (Ng = He, Ne, Ar, Kr, and Xe).

    PubMed

    Gao, Kunqi; Sheng, Li

    2015-04-14

    The equilibrium geometries, harmonic frequencies, and dissociation energies of HNgNH3(+) ions (Ng = He, Ne, Ar, Kr, and Xe) were investigated using the following method: Becke-3-parameter-Lee-Yang-Parr (B3LYP), Boese-Matrin for Kinetics (BMK), second-order Møller-Plesset perturbation theory (MP2), and coupled-cluster with single and double excitations as well as perturbative inclusion of triples (CCSD(T)). The results indicate that HHeNH3(+), HArNH3(+), HKrNH3(+), and HXeNH3(+) ions are metastable species that are protected from decomposition by high energy barriers, whereas the HNeNH3(+) ion is unstable because of its relatively small energy barrier for decomposition. The bonding nature of noble-gas atoms in HNgNH3(+) was also analyzed using the atoms in molecules approach, natural energy decomposition analysis, and natural bond orbital analysis. PMID:25877572

  16. Theoretical investigation of HNgNH3+ ions (Ng = He, Ne, Ar, Kr, and Xe)

    NASA Astrophysics Data System (ADS)

    Gao, Kunqi; Sheng, Li

    2015-04-01

    The equilibrium geometries, harmonic frequencies, and dissociation energies of HNgNH3+ ions (Ng = He, Ne, Ar, Kr, and Xe) were investigated using the following method: Becke-3-parameter-Lee-Yang-Parr (B3LYP), Boese-Matrin for Kinetics (BMK), second-order Møller-Plesset perturbation theory (MP2), and coupled-cluster with single and double excitations as well as perturbative inclusion of triples (CCSD(T)). The results indicate that HHeNH3+, HArNH3+, HKrNH3+, and HXeNH3+ ions are metastable species that are protected from decomposition by high energy barriers, whereas the HNeNH3+ ion is unstable because of its relatively small energy barrier for decomposition. The bonding nature of noble-gas atoms in HNgNH3+ was also analyzed using the atoms in molecules approach, natural energy decomposition analysis, and natural bond orbital analysis.

  17. Preparation and Crystal Structures of Ni(NH 3) 2Cl 2 and of Two Modifications of Ni(NH 3) 2Br 2 and Ni(NH 3) 2I 2

    NASA Astrophysics Data System (ADS)

    Leineweber, A.; Jacobs, H.

    2000-07-01

    Diammine nickel(II) halides, Ni(NH3)2X2 (X=Cl, Br, I), were prepared by decomposition of the corresponding hexaammines at 120°C in dynamical vacuum. Their crystal structures are of the Cd(NH3)2Cl2 type ("?-type", space group Cmmm, Z=2): for Ni(NH3)2Cl2, a=8.019 Å, b=8.013 Å, c=3.661 Å; for ?-Ni(NH3)2Br2, a=8.273 Å, b=8.297 Å, c=3.851 Å. Both were obtained by Rietveld refinement of diffractometer data with standard deviations <0.001 Å. For ?-Ni(NH3)2I2, a=b=8.753(3) Å, c=4.127(1) Å, obtained by Guinier film data. In the case of the bromide and the iodide, annealing at 300°C leads to an irreversible structural rearrangement. A new modification is formed which is of the Mg(NH3)2Br2 type ("?-type", space group Pbam, Z=2): for ?-Ni(NH3)2Br2, a=5.865 Å, b=11.723 Å, c=3.856 Å, obtained by Rietveld refinement of diffractometer data with standard deviations <0.001; for ?-Ni(NH3)2I2, 2a=b=12.359(3) Å, c=4.126(1) Å, obtained by Guinier film data. Both types of structures contain infinite chains of edge-sharing octahedra 1?[NiX4/2(NH3)2]. These run parallel to the c-axes of the unit cells of the corresponding structure types and are arranged in different ways relative to one another. The decomposition of hexaammine nickel(II) halides to the corresponding diammines is analyzed in terms of structural analogies.

  18. Electron Impact Ionization of CH4 and NH3

    NASA Astrophysics Data System (ADS)

    Chaluvadi, Hari; Madison, Don; Nixon, Kate; Murray, Andrew; Ning, Chuangang

    2011-10-01

    Experimental and theoretical Triply Differential Cross Sections (TDCS) will be presented for electron-impact ionization of Methane (CH4) and Ammonia (NH3) (same number of electrons and protons) for both the highest occupied molecular orbital (HOMO) and next highest occupied molecular orbital (NHOMO). M3DW (molecular 3-body distorted wave) results will be compared with experiment for coplanar geometry and for perpendicular plane geometry (a plane which is perpendicular to the incident beam direction). In both cases, the final state electron energies and observation angles are symmetric and the final state electron energies range from 1.5 eV to 30 eV. This work is supported by National Science Foundation (NSF) and the NSF TeraGrid computer system.

  19. MetNH3: Metrology for ammonia in ambient air

    NASA Astrophysics Data System (ADS)

    Braban, Christine; Twigg, Marsailidh; Tang, Sim; Leuenberger, Daiana; Ferracci, Valerio; Martin, Nick; Pascale, Celine; Hieta, Tuomas; Pogany, Andrea; Persijn, Stefan; van Wijk, Janneke; Gerwig, Holger; Wirtze, Klaus; Tiebe, Carlo; Balslev-Harder, David; Niederhausen, Bernhardt

    2015-04-01

    Measuring ammonia in ambient air is a sensitive and priority issue due to its harmful effects on human health and ecosystems. The European Directive 2001/81/EC on 'National Emission Ceilings for Certain Atmospheric Pollutants (NEC)' regulates ammonia emissions in the member states. However, there is a lack of regulation to ensure reliable ammonia measurements namely in applicable analytical technology, maximum allowed uncertainty, quality assurance and quality control (QC/QA) procedures as well as in the infrastructure to attain metrological traceability. Validated ammonia measurement data of high quality from air monitoring networks are vitally important for identifying changes due to implementations of environment policies, for understanding where the uncertainties in current emission inventories are derived from and for providing independent verification of atmospheric model predictions. The new EURAMET project MetNH3 aims to develop improved reference gas mixtures by static and dynamic gravimetric generation methods, develop and characterise laser based optical spectrometric standards and establish the transfer from high-accuracy standards to field applicable methods. MetNH3started in June 2014 and in this presentation the first results from the metrological characterisation of a commercially available cavity ring-down spectrometer (CRDS) will be discussed. Also first tests and results from a new design, Controlled Atmosphere Test Facility (CATFAC), which is to be characterised and used to validate the performance of diffusive samplers, denuders and on-line instruments, will be reported. CAFTEC can be used to control test parameters such as ammonia concentration, relative humidity and wind speed. Outline plans for international laboratory and field intercomparisons in 2016 will be presented.

  20. The selective catalytic reduction of NO with NH3 over a novel Ce-Sn-Ti mixed oxides catalyst: Promotional effect of SnO2

    NASA Astrophysics Data System (ADS)

    Yu, Ming'e.; Li, Caiting; Zeng, Guangming; Zhou, Yang; Zhang, Xunan; Xie, Yin'e.

    2015-07-01

    A series of novel catalysts (CexSny) for the selective catalytic reduction of NO by NH3 were prepared by the inverse co-precipitation method. The aim of this novel design was to improve the NO removal efficiency of CeTi by the introduction of SnO2. It was found that the Ce-Sn-Ti catalyst was much more active than Ce-Ti and the best Ce:Sn molar ratio was 2:1. Ce2Sn1 possessed a satisfied NO removal efficiency at low temperature (160-280 °C), while over 90% NO removal efficiency maintained in the temperature range of 280-400 °C at the gas hourly space velocity (GHSV) of 50,000 h-1. Besides, Ce2Sn1 kept a stable NO removal efficiency within a wide range of GHSV and a long period of reacting time. Meanwhile, Ce2Sn1 exhibited remarkable resistance to both respectively and simultaneously H2O and SO2 poisoning due to the introduction of SnO2. The promotional effect of SnO2 was studied by N2 adsorption-desorption, X-ray diffraction (XRD), Raman spectra, X-ray photoelectron spectroscopy (XPS) and H2 temperature programmed reduction (H2-TPR) for detail information. The characterization results revealed that the excellent catalytic performance of Ce2Sn1 was associated with the higher specific surface area, larger pore volume and poorer crystallization. Besides, the introduction of SnO2 could result in not only greater conversion of Ce4+ to Ce3+ but also the increase amount of chemisorbed oxygen, which are beneficial to improve the SCR activity. More importantly, a novel peak appearing at lower temperatures through the new redox equilibrium of 2Ce4+ + Sn2+ ? 2Ce3+ + Sn4+ and higher total H2 consumption can be obtained by the addition of SnO2. Finally, the possible reaction mechanism of the selective catalytic reduction over Ce2Sn1 was also proposed.

  1. Relativistic GW calculations on CH3NH3PbI3 and CH3NH3SnI3 Perovskites for Solar Cell Applications

    NASA Astrophysics Data System (ADS)

    Umari, Paolo; Mosconi, Edoardo; de Angelis, Filippo

    2014-03-01

    Hybrid AMX3 perovskites (A = Cs, CH3NH3; M = Sn, Pb; X = halide) have revolutionized the scenario of emerging photovoltaic technologies, with very recent results demonstrating 15% efficient solar cells. The CH3NH3PbI3/MAPb(I1-xClx)3 perovskites have dominated the field, while the similar CH3NH3SnI3 has not been exploited for photovoltaic applications. Replacement of Pb by Sn would facilitate the large uptake of perovskite-based photovoltaics. Despite the extremely fast progress, the materials electronic properties which are key to the photovoltaic performance are relatively little understood. Density Functional Theory electronic structure methods have so far delivered an unbalanced description of Pb- and Sn-based perovskites. Here we develop an effective GW method incorporating spin-orbit coupling which allows us to accurately model the electronic, optical and transport properties of CH3NH3SnI3 and CH3NH3PbI3, opening the way to new materials design. The different CH3NH3SnI3 and CH3NH3PbI3 electronic properties are discussed in light of their exploitation for solar cells, and found to be dominantly due to relativistic effects. These effects stabilize the CH3NH3PbI3 material towards oxidation, by inducing a deeper valence band edge. Relativistic effects, however, also increase the material band-gap compared to CH3NH3SnI3, due to the valence band energy downshift (~0.7 eV) being only partly compensated by the conduction band downshift (~0.2 eV).

  2. Material properties controlling adsorption kinetics and temperature programmed desorption spectra

    E-print Network

    Ward, Charles A.

    statistical rate theory (SRT) is applied to obtain the expression for the gas adsorption rate on a solid; Chemical potential 1. Introduction When adsorption at a gas­solid interface occurs, there is molecular 0 0 5 8 - 2 #12;SRT receives important experimental support from these cases. For gas adsorption

  3. Analyte separation utilizing temperature programmed desorption of a preconcentrator mesh

    DOEpatents

    Linker, Kevin L. (Albuquerque, NM); Bouchier, Frank A. (Albuquerque, NM); Theisen, Lisa (Albuquerque, NM); Arakaki, Lester H. (Edgewood, NM)

    2007-11-27

    A method and system for controllably releasing contaminants from a contaminated porous metallic mesh by thermally desorbing and releasing a selected subset of contaminants from a contaminated mesh by rapidly raising the mesh to a pre-determined temperature step or plateau that has been chosen beforehand to preferentially desorb a particular chemical specie of interest, but not others. By providing a sufficiently long delay or dwell period in-between heating pulses, and by selecting the optimum plateau temperatures, then different contaminant species can be controllably released in well-defined batches at different times to a chemical detector in gaseous communication with the mesh. For some detectors, such as an Ion Mobility Spectrometer (IMS), separating different species in time before they enter the IMS allows the detector to have an enhanced selectivity.

  4. Ternary nucleation of H2SO4, NH3, and H2O in the atmosphere

    Microsoft Academic Search

    P. Korhonen; M. Kulmala; A. Laaksonen; Y. Viisanen; R. McGraw; J. H. Seinfeld

    1999-01-01

    Classical theory of binary homogeneous nucleation is extended to the ternary system H2SO4-NH3-H2O. For NH3 mixing ratios exceeding about 1 ppt, the presence of NH3 enhances the binary H2SO4-H2O nucleation rate by several orders of magnitude. The Gibbs free energies of formation of the critical H2SO4-NH3-H2O cluster, as calculated by two independent approaches, are in substantial agreement. The finding that

  5. Vibrations and reorientations of NH3 molecules in [Mn(NH3)6](ClO4)2 studied by infrared spectroscopy and theoretical (DFT) calculations.

    PubMed

    Hetma?czyk, Joanna; Hetma?czyk, Lukasz; Migda?-Mikuli, Anna; Mikuli, Edward

    2014-10-24

    The vibrational and reorientational motions of NH3 ligands and ClO4(-) anions were investigated by Fourier transform middle-infrared spectroscopy (FT-IR) in the high- and low-temperature phases of [Mn(NH3)6](ClO4)2. The temperature dependencies of full width at half maximum (FWHM) of the infrared bands at: 591 and 3385cm(-1), associated with: ?r(NH3) and ?as(N-H) modes, respectively, indicate that there exist fast (correlation times ?R?10(-12)-10(-13)s) reorientational motions of NH3 ligands, with a mean values of activation energies: 7.8 and 4.5kJmol(-1), in the phase I and II, respectively. These reorientational motions of NH3 ligands are only slightly disturbed in the phase transition region and do not significantly contribute to the phase transition mechanism. Fourier transform far-infrared and middle-infrared spectra with decreasing of temperature indicated characteristic changes at the vicinity of PT at TC(c)=137.6K (on cooling), which suggested lowering of the crystal structure symmetry. Infrared spectra of [Mn(NH3)6](ClO4)2 were recorded and interpreted by comparison with respective theoretical spectra calculated using DFT method (B3LYP functional, LANL2DZ ECP basis set (on Mn atom) and 6-311+G(d,p) basis set (on H, N, Cl, O atoms) for the isolated equilibrium two models (Model 1 - separate isolated [Mn(NH3)6](2+) cation and ClO4(-) anion and Model 2 - [Mn(NH3)6(ClO4)2] complex system). Calculated optical spectra show a good agreement with the experimental infrared spectra (FT-FIR and FT-MIR) for the both models. PMID:25459713

  6. Spectroscopy of 14NH3 and 15NH3 in the 2.3 ?m spectral range with a new VECSEL laser source

    NASA Astrophysics Data System (ADS)

    ?ermák, P.; Hovorka, J.; Veis, P.; Cacciani, P.; Cosléou, J.; El Romh, J.; Khelkhal, M.

    2014-04-01

    A spectroscopic study of ammonia molecule in the 2.3 ?m water atmospheric window is presented. Compared to previous experimental works a narrow, broadly tunable, continuous laser source was applied in order to obtain high resolution spectra in this range. It was the first application of the newly developed Vertical External Cavity Surface Emitting Laser (VECSEL). The analysis of the absorption spectra of two different isotopologue admixtures allowed to identify 336 14NH3 and 244 15NH3 lines in the studied region from 4275 to 4340 cm-1. These data were compared to previous line list based on experimental data - the HITRAN database and the work of Urban et al., as well as to the theoretical predictions by Yurchenko et al. and Huang et al. Together for 235 14NH3 and 183 15NH3 lines a complete assignment was proposed. From those 63 14NH3 and 114 15NH3 transitions were newly assigned. The complete peaklist of transitions containing ro-vibrational state identifications is presented in Supplementary materials.

  7. Rotational study of the NH3-CO complex: Millimeter-wave measurements and ab initio calculations

    NASA Astrophysics Data System (ADS)

    Surin, L. A.; Potapov, A.; Dolgov, A. A.; Tarabukin, I. V.; Panfilov, V. A.; Schlemmer, S.; Kalugina, Y. N.; Faure, A.; van der Avoird, A.

    2015-03-01

    The rotational spectrum of the van der Waals complex NH3-CO has been measured with the intracavity OROTRON jet spectrometer in the frequency range of 112-139 GHz. Newly observed and assigned transitions belong to the K = 0-0, K = 1-1, K = 1-0, and K = 2-1 subbands correlating with the rotationless (jk)NH3 = 00 ground state of free ortho-NH3 and the K = 0-1 and K = 2-1 subbands correlating with the (jk)NH3 = 11 ground state of free para-NH3. The (approximate) quantum number K is the projection of the total angular momentum J on the intermolecular axis. Some of these transitions are continuations to higher J values of transition series observed previously [C. Xia et al., Mol. Phys. 99, 643 (2001)], the other transitions constitute newly detected subbands. The new data were analyzed together with the known millimeter-wave and microwave transitions in order to determine the molecular parameters of the ortho-NH3-CO and para-NH3-CO complexes. Accompanying ab initio calculations of the intermolecular potential energy surface (PES) of NH3-CO has been carried out at the explicitly correlated coupled cluster level of theory with single, double, and perturbative triple excitations and an augmented correlation-consistent triple zeta basis set. The global minimum of the five-dimensional PES corresponds to an approximately T-shaped structure with the N atom closest to the CO subunit and binding energy De = 359.21 cm-1. The bound rovibrational levels of the NH3-CO complex were calculated for total angular momentum J = 0-6 on this intermolecular potential surface and compared with the experimental results. The calculated dissociation energies D0 are 210.43 and 218.66 cm-1 for ortho-NH3-CO and para-NH3-CO, respectively.

  8. Rotational study of the NH3-CO complex: millimeter-wave measurements and ab initio calculations.

    PubMed

    Surin, L A; Potapov, A; Dolgov, A A; Tarabukin, I V; Panfilov, V A; Schlemmer, S; Kalugina, Y N; Faure, A; van der Avoird, A

    2015-03-21

    The rotational spectrum of the van der Waals complex NH3-CO has been measured with the intracavity OROTRON jet spectrometer in the frequency range of 112-139 GHz. Newly observed and assigned transitions belong to the K = 0-0, K = 1-1, K = 1-0, and K = 2-1 subbands correlating with the rotationless (jk)NH3 = 00 ground state of free ortho-NH3 and the K = 0-1 and K = 2-1 subbands correlating with the (jk)NH3 = 11 ground state of free para-NH3. The (approximate) quantum number K is the projection of the total angular momentum J on the intermolecular axis. Some of these transitions are continuations to higher J values of transition series observed previously [C. Xia et al., Mol. Phys. 99, 643 (2001)], the other transitions constitute newly detected subbands. The new data were analyzed together with the known millimeter-wave and microwave transitions in order to determine the molecular parameters of the ortho-NH3-CO and para-NH3-CO complexes. Accompanying ab initio calculations of the intermolecular potential energy surface (PES) of NH3-CO has been carried out at the explicitly correlated coupled cluster level of theory with single, double, and perturbative triple excitations and an augmented correlation-consistent triple zeta basis set. The global minimum of the five-dimensional PES corresponds to an approximately T-shaped structure with the N atom closest to the CO subunit and binding energy De = 359.21 cm(-1). The bound rovibrational levels of the NH3-CO complex were calculated for total angular momentum J = 0-6 on this intermolecular potential surface and compared with the experimental results. The calculated dissociation energies D0 are 210.43 and 218.66 cm(-1) for ortho-NH3-CO and para-NH3-CO, respectively. PMID:25796250

  9. Calorimetric and IR spectroscopic study of the interaction of NH 3 with variously prepared defective silicalites

    Microsoft Academic Search

    V Bolis; C Busco; S Bordiga; P Ugliengo; C Lamberti; A Zecchina

    2002-01-01

    Nature, population and acidic properties of the hydroxylated species (hydroxyl nests) present in the nanocavities of variously prepared defective silicalites have been characterised by the adsorption of NH3, monitored through the combined use of microcalorimetry and IR spectroscopy. The experimental data (enthalpy of adsorption, stretching frequency of the O–H bonds perturbed by the interaction with NH3) have been compared with

  10. Urban NH3 levels and sources in six major Spanish cities.

    PubMed

    Reche, Cristina; Viana, Mar; Karanasiou, Angeliki; Cusack, Michael; Alastuey, Andrés; Artiñano, Begoña; Revuelta, M Aranzazu; López-Mahía, Purificación; Blanco-Heras, Gustavo; Rodríguez, Sergio; Sánchez de la Campa, Ana M; Fernández-Camacho, Rocío; González-Castanedo, Yolanda; Mantilla, Enrique; Tang, Y Sim; Querol, Xavier

    2015-01-01

    A detailed spatial and temporal assessment of urban NH3 levels and potential emission sources was made with passive samplers in six major Spanish cities (Barcelona, Madrid, A Coruña, Huelva, Santa Cruz de Tenerife and Valencia). Measurements were conducted during two different periods (winter-autumn and spring-summer) in each city. Barcelona showed the clearest spatial pattern, with the highest concentrations in the old city centre, an area characterised by a high population density and a dense urban architecture. The variability in NH3 concentrations did not follow a common seasonal pattern across the different cities. The relationship of urban NH3 with SO2 and NOX allowed concluding on the causes responsible for the variations in NH3 levels between measurement periods observed in Barcelona, Huelva and Madrid. However, the factors governing the variations in A Coruña, Valencia and Santa Cruz de Tenerife are still not fully understood. This study identified a broad variability in NH3 concentrations at the city-scale, and it confirms that NH3 sources in Spanish urban environments are vehicular traffic, biological sources (e.g. garbage containers), wastewater treatment plants, solid waste treatment plants and industry. The importance of NH3 monitoring in urban environments relies on its role as a precursor of secondary inorganic species and therefore PMX. Further research should be addressed in order to establish criteria to develop and implement mitigation strategies for cities, and to include urban NH3 sources in the emission inventories. PMID:25194477

  11. Influence of desorption on the indoor concentration of toxic gases

    Microsoft Academic Search

    Edvard Karlsson; Ueli Huber

    1996-01-01

    A theoretical model is developed which considers the influence of both deposition and desorption processes on the indoor concentration of toxic gases. The model is based on a simplification of the Langmuir theory. Model parameters for NH3, Cl2, the nerve agent sarin, and a simulant for the nerve agent VX are calculated from available experiments with common indoor materials. The

  12. Photosynthesis of Quercus suber is affected by atmospheric NH3 generated by multifunctional agrosystems.

    PubMed

    Pintó-Marijuan, Marta; Da Silva, Anabela Bernardes; Flexas, Jaume; Dias, Teresa; Zarrouk, Olfa; Martins-Loução, Maria Amélia; Chaves, Maria Manuela; Cruz, Cristina

    2013-12-01

    Montados are evergreen oak woodlands dominated by Quercus species, which are considered to be key to biodiversity conservation and ecosystem services. This ecosystem is often used for cattle breeding in most regions of the Iberian Peninsula, which causes plants to receive extra nitrogen as ammonia (NH(3)) through the atmosphere. The effect of this atmospheric NH(3) (NH(3atm)) on ecosystems is still under discussion. This study aimed to evaluate the effects of an NH(3atm) concentration gradient downwind of a cattle barn in a Montado area. Leaves from the selected Quercus suber L. trees along the gradient showed a clear influence of the NH(3) on ?(13)C, as a consequence of a strong limitation on the photosynthetic machinery by a reduction of both stomatal and mesophyll conductance. A detailed study of the impact of NH(3atm) on the photosynthetic performance of Q. suber trees is presented, and new mechanisms by which NH(3) affects photosynthesis at the leaf level are suggested. PMID:24150034

  13. Concentration-dependent NH 3 deposition processes for moorland plant species with and without stomata

    NASA Astrophysics Data System (ADS)

    Jones, M. R.; Leith, I. D.; Raven, J. A.; Fowler, D.; Sutton, M. A.; Nemitz, E.; Cape, J. N.; Sheppard, L. J.; Smith, R. I.

    Currently, in operational modelling of NH 3 deposition a fixed value of canopy resistance ( Rc) is generally applied, irrespective of the plant species and NH 3 concentration. This study determined the effect of NH 3 concentration on deposition processes to individual moorland species. An innovative flux chamber system was used to provide accurate continuous measurements of NH 3 deposition to Deschampsia cespitosa (L.) Beauv., Calluna vulgaris (L.) Hull, Eriophorum vaginatum L., Cladonia spp., Sphagnum spp., and Pleurozium schreberi (Brid.) Mitt. Measurements were conducted across a wide range of NH 3 concentrations (1-140 ?g m -3). NH 3 concentration directly affects the deposition processes to the vegetation canopy, with Rc, and cuticular resistance ( Rw) increasing with increasing NH 3 concentration, for all the species and vegetation communities tested. For example, the Rc for C. vulgaris increased from 14 s m -1 at 2 ?g m -3 to 112 s m -1 at 80 ?g m -3. Diurnal variations in NH 3 uptake were observed for higher plants, due to stomatal uptake; however, no diurnal variations were shown for non-stomatal plants. Rc for C. vulgaris at 80 ?g m -3 was 66 and 112 s m -1 during day and night, respectively. Differences were found in NH 3 deposition between plant species and vegetation communities: Sphagnum had the lowest Rc (3 s m -1 at 2 ?g m -3 to 23 at 80 ?g m -3), and D. cespitosa had the highest nighttime value (18 s m -1 at 2 ?g m -3 to 197 s m -1 at 80 ?g m -3).

  14. Rotational excitation of ortho-NH3 by para-H

    NASA Astrophysics Data System (ADS)

    Danby, G.; Flower, D. R.; Kochanski, E.; Kurdi, L.; Valiron, P.

    1986-09-01

    Inelastic collision cross sections and low-temperature rate coefficients (T between 15 and 300 K) are presented for the process of collisional excitation of ortho-NH3 by para-H2 in its rovibrational ground state (nu = j = 0). The results have been obtained with the quantum mechanical coupled-channels technique, using an ab initio NH3-H2 potential-energy surface. Comparison is made with previous calculations of rate coefficients for the excitation of ortho-NH3 by He.

  15. Shock-excited NH3 (3, 3) masers in the NGC 6334 star-forming region

    NASA Technical Reports Server (NTRS)

    Kraemer, Kathleen E.; Jackson, James M.

    1995-01-01

    We report the discovery of four NH3 (3, 3) masers in the NGC 6334 star formation region. The masers are found in two of the seven far-infrared continuum sources where high-mass star formation is taking place in this molecular cloud. These masers occur at the ends of high-velocity molecular outflows; no maser emission was found near regions without high-velocity outflows. The NH3 masers are not associated with any other type of maser. These results confirm that the NH3 (3, 3) masers are caused by shocks and probably mark the location where the molecular outflow jet impinges upon the ambient medium.

  16. Strain-induced stabilization of Al functionalization in graphene oxide nanosheet for enhanced NH3 storage

    NASA Astrophysics Data System (ADS)

    Li, Yunguo; De Sarkar, Abir; Pathak, Biswarup; Ahuja, Rajeev

    2013-06-01

    Strain effects on the stabilization of Al ad-atom on graphene oxide (GO) nanosheet as well as its implications for NH3 storage have been investigated using first-principles calculations. Tensile strain is found to be very effective in stabilizing the Al ad-atom on GO. It strengthens the C-O bonds through an enhanced charge transfer from C to O atoms. Interestingly, Al's stability is governed by the bond strength of C-O rather than that of Al-O. Optimally strained Al-functionalized GO binds up to 6 NH3 molecules, while it binds no NH3 molecule in unstrained condition.

  17. Selective NH 3 oxidation to N 2 in a wet stream

    Microsoft Academic Search

    Yuejin Li; John N. Armor

    1997-01-01

    Al2O3 and ZSM-5 supported Pd, Rh and Pt catalysts were studied for NH3 oxidation at 200–350°C in comparison with V2O5\\/TiO2 and Co-ZSM-5 catalysts at 250–400°C. The precious metal catalysts are very active for NH3 oxidation in this temperature range. With the addition of 5% H2O vapor, the NH3 conversion is not affected at high temperatures but decreases at 200–250°C. Generally,

  18. Solid state transformation of the crystalline monohydrate (CH3NH3)PbI3(H2O) to the (CH3NH3)PbI3 perovskite.

    PubMed

    Imler, Gregory H; Li, Xia; Xu, Bolei; Dobereiner, Graham E; Dai, Hai-Lung; Rao, Yi; Wayland, Bradford B

    2015-06-30

    Colorless crystals of (CH3NH3·H2O)PbI3 spontaneously lose water at 298 K which triggers a transformation to the black (CH3NH3)PbI3 perovskite in the solid state as a porous microcrystalline solid with nanoscale substructure, but the dihydrate (CH3NH3)4PbI6·2H2O) requires much more forcing conditions to produce (CH3NH3)PbI3. PMID:26083000

  19. Evaluation of a regional air-quality model with bidirectional NH3 exchange coupled to an agroecosystem modelecosystem model

    EPA Science Inventory

    Atmospheric ammonia (NH3) is the primary atmospheric base and an important precursor for inorganic particulate matter and when deposited NH3 contributes to surface water eutrophication, soil acidification and decline in species biodiversity. Flux measurement...

  20. Manipulating bedding materials and PLTto reduce NH(3) emissions from broiler manure.

    PubMed

    Tasistro, Armando S; Cabrera, Miguel L; Ritz, Casey W; Kissel, David E

    2008-04-01

    We studied the effect of five bedding materials (wood shavings, sawdust, peanut hulls, wheat straw and shredded paper) and PLTtrade mark (a commercial formulation of Na bisulfate) in factorial combinations, on NH(3) emissions from broiler manure. Treatments were incubated for 11 days at 25 degrees C and 98% relative humidity. Ammonia was trapped in 0.1N H(2)SO(4) and measured colorimetrically as NH(4)(+), and CO(2) was monitored with an infrared analyzer. Ammonia and CO(2) emissions were suppressed by PLT throughout the study. Wheat straw, wood shavings, and sawdust, with C(total)/N(total)>50 or C(biodegradable)/N>20, had low NH(3) emissions. Total NH(3) emissions from peanut hulls and shredded paper were the highest, probably due to peanut hulls' low C/N ratio and shredded paper's alkaline pH. No significant interactions on NH(3) emissions were detected between PLT and bedding materials. PMID:17572086

  1. PREPARATION, CRYSTAL STRUCTURE AND CARACTERIZATION OF INORGANIC-ORGANIC HYBRID PEROVSKITE [NH3-(CH2)10-NH3] ZnCl4

    E-print Network

    Paris-Sud XI, Université de

    PREPARATION, CRYSTAL STRUCTURE AND CARACTERIZATION OF INORGANIC-ORGANIC HYBRID PEROVSKITE [NH3-(CH2.O.M.A, Université de Bordeaux I, cours de la libération Talence Cedex France ABSTRACT A new perovskite like system by DSC shows that the 2C10ZnCl4 perovskite presents reversible phase transition. Keywords: Perovskite

  2. Calorimetric study on NH 3 insertion reaction into microporous manganese oxides with (2×2) tunnel and (2×?) layered structures

    Microsoft Academic Search

    Z.-M. Wang; H. Kanoh

    2001-01-01

    NH3 insertion mechanism into the (2×2) tunnel structure of a hollandite-type manganese oxide (H-Hol) and the (2×?) layered structure of a birnessite-type manganese oxide (H-Bir) were studied by direct adsorption calorimetry. It was found that H-Bir has a smaller NH3 adsorption enthalpy (??Hd,NH3) compared to H-Hol because of the structural flexibility of its MnO sheets. NH3 insertion into the tunnel

  3. Radiation Damage and Recovery in Polarized 14NH3 Ammonia Targets at Jefferson Lab

    NASA Astrophysics Data System (ADS)

    Maxwell, J. D.

    2011-01-01

    Dynamically nuclear polarized solid ammonia offers an attractive combination of high polarization, comparatively high dilution factor and high radiation damage resistance as a target material in electron scattering experiments. Polarized 14NH3, provided by the University of Virginia Polarized Target Group, was used as target material in two simultaneous experiments at Thomas Jefferson National Accelerator Facility in the spring of 2009. Target polarization performance for both experiments is discussed, as is previously unseen behavior in irradiated 14NH3.

  4. Effects of NH3 plasma passivation on N-channel polycrystalline silicon thin-film transistors

    Microsoft Academic Search

    Huang-Chung Cheng; Fang-Shing Wang; Chun-Yao Huang

    1997-01-01

    The NH3-plasma passivation has been performed on polycrystalline silicon (poly-Si) thin-film transistors (TFT's), It is found that the TFT's after the NH3-plasma passivation achieve better device performance, including the off-current below 0.1 pA\\/?m and the on\\/off current ratio higher than 108, and also better hot-carrier reliability than the H2-plasma devices. Based on optical emission spectroscopy (OES) and secondary ion mass

  5. Measurements of relaxation cross sections for NH3 and OCS with a molecular beam maser spectrometer

    Microsoft Academic Search

    J. H. S. Wang; D. E. Oates; A. Ben-Reuven; S. G. Kukolich

    1973-01-01

    Scattering cross sections for beams of NH3 and OCS are measured using a molecular beam maser spectrometer. The scattering gases used are NH3, OCS, CF3H, CH3F, N2, and He. In order to determine elastic and inelastic contributions to relaxation cross sections, measurements are made for (I) scattering of pure inversion or rotational state molecules, (II) scattering of molecules in a

  6. Chemical dynamics of Ar\\/N_2\\/H2 and Ar\\/NH3 plasma expansions

    Microsoft Academic Search

    Richard Engeln; Jean-Pierre van Helden; Peter van den Oever; Daan Schram; Erwin Kessels; Richard van de Sanden

    2004-01-01

    In unravelling the dynamics leading to the production of NH3 in plasmas produced from mixtures of N2 and H_2, the density of NH3 as well as the density of radicals like NH and NH2 has been measured under varies plasma conditions by means of cavity ring down spectroscopy. In one of the experiments the pressure dependence of the ammonia production

  7. NH3 sensitive chemiresistor sensors using plasma functionalized multiwall carbon nanotubes\\/conducting polymer composites

    Microsoft Academic Search

    Tai-Jin Kim; Si-Dong Kim; Nam-Ki Min; James Jungho Pak; Cheol-Jin Lee; Soo-Won Kim

    2008-01-01

    We present a micromachined NH3 chemiresistor sensor based on O2 plasma functionalized multiwall carbon nanotube (MWCNT)\\/ conducting polymer (CP) composites, and discuss its gas sensing mechanism. The FTIR spectra of plasma-treated MWCNTs indicate that oxygenated groups are created on the surface of CNTs after the plasma treatment. The plasma-functionalized MWCNT\\/PANI sensor exhibits a linear response of 3.34% per ppm NH3

  8. Microwave rotational spectra of the Ar3-NH3 van der Waals tetramer

    NASA Astrophysics Data System (ADS)

    van Wijngaarden, Jennifer; Jäger, Wolfgang

    2002-02-01

    Rotational spectra of the Ar3-NH3 van der Waals tetramer were recorded between 4 and 17 GHz using a pulsed jet Fourier transform microwave spectrometer. Five isotopomers, namely Ar3-NH3, Ar3-15NH3, Ar3-ND3, Ar3-ND2H, and Ar3-NDH2, were studied and the spectra observed are characteristic of oblate symmetric tops. The transitions were assigned to three different K progressions, K=0, K=3, and K=6 of the ground internal rotor state of the complex. A small inversion tunneling splitting was observed for each of the deuterium containing isotopomers. For Ar3-NH3 and Ar3-15NH3, one of these inversion components has a spin statistical weight of zero in the ground state and is, therefore, not observed. The 14N quadrupole hyperfine structure was resolved and included in the fit of the spectroscopic constants for each of the 14N containing isotopomers. The resulting spectroscopic constants were used to estimate the structure of the complex. Furthermore, the 14N nuclear quadruple coupling constants and the inversion tunneling splittings observed for the various isotopomers contain information about the dynamics of the ammonia subunit within the Ar3-NH3 complex.

  9. H2CO and H110 ? observations towards NH3 sources

    NASA Astrophysics Data System (ADS)

    Yuan, Ye; Esimbek, Jarken; Zhou, Jian Jun; Tang, Xin Di; Wu, Gang; Ma, Ying Xiu

    2014-08-01

    We observed the H2CO(110-111) absorption lines and H110 ? radio recombination lines (RRL) toward 180 NH3 sources using the Nanshan 25-m radio telescope. In our observation, 138 sources were found to have H2CO lines and 36 have H110 ? RRLs. Among the 138 detected H2CO sources, 38 sources were first detected. The detection rates of H2CO have a better correlation with extinction than with background continuum radiation. Line center velocities of H2CO and NH3 agree well. The line width ratios of H2CO and NH3 are generally larger than unity and are similar to that of 13CO. The correlation between column densities of H2CO and extinction is better than that between NH3 and extinction. These line width relation and column density relation indicate H2CO is distributed on a larger scale than that of NH3, being similar to the regions of 13CO. The abundance ratios between NH3 and H2CO were found to be different in local clouds and other clouds.

  10. Estimation of global NH3 volatilization loss from synthetic fertilizers and animal manure applied to arable lands and grasslands

    Microsoft Academic Search

    A. F. Bouwman; L. J. M. Boumans; N. H. Batjes

    2002-01-01

    One of the main causes of the low efficiency in nitrogen (N) use by crops is the volatilization of ammonia (NH3) from fertilizers. Information taken from 1667 NH3 volatilization measurements documented in 148 research papers was summarized to assess the influence on NH3 volatilization of crop type, fertilizer type, and rate and mode of application and temperature, as well as

  11. Estimation of global NH3 emissions from synthetic fertilizers and animal manure applied to arable lands and grasslands

    Microsoft Academic Search

    A. F. Bouwman; L. J. M. Boumans; N. H. Batjes

    2002-01-01

    One of the main causes of the low efficiency in nitrogen (N) use by crops is the volatilization of ammonia (NH3) from fertilizers. Information taken from 1667 NH3 volatilization measurements documented in 148 research papers was summarized to assess the influence on NH3 volatilization of crop type, fertilizer type, and rate and mode of application and temperature, as well as

  12. C60-mediated hydrogen desorption in Li-N-H systems.

    PubMed

    Qian, Zhao; Li, Sa; Pathak, Biswarup; Araújo, C Moysés; Ahuja, Rajeev; Jena, Puru

    2012-12-01

    Hydrogen desorption from a LiH + NH(3) mixture is very difficult due to the formation of the stable LiNH(4) compound. Using cluster models and first-principles theory, we demonstrate that the C(60) molecule can in fact significantly improve the thermodynamics of ammonia-mediated hydrogen desorption from LiH due to the stabilization of the intermediate state, LiNH(4). The hydrogen desorption following the path of LiNH(4)-C(60) ? LiNH(3)-C(60) + 1/2H(2) is exothermic. Molecular dynamic simulations show that this reaction can take place even at room temperature (300 K). In contrast, the stable LiNH(4) compound cannot desorb hydrogen at room temperature in the absence of C(60). The introduction of C(60) also helps to restrain the NH(3) gas which is poisonous in proton exchange membrane fuel cell applications. PMID:23138595

  13. C60-mediated hydrogen desorption in Li-N-H systems

    NASA Astrophysics Data System (ADS)

    Qian, Zhao; Li, Sa; Pathak, Biswarup; Moysés Araújo, C.; Ahuja, Rajeev; Jena, Puru

    2012-12-01

    Hydrogen desorption from a LiH + NH3 mixture is very difficult due to the formation of the stable LiNH4 compound. Using cluster models and first-principles theory, we demonstrate that the C60 molecule can in fact significantly improve the thermodynamics of ammonia-mediated hydrogen desorption from LiH due to the stabilization of the intermediate state, LiNH4. The hydrogen desorption following the path of LiNH4-C60 ? LiNH3-{{C}}_{6 0}+\\frac{1}{2}{{H}}_{2} is exothermic. Molecular dynamic simulations show that this reaction can take place even at room temperature (300 K). In contrast, the stable LiNH4 compound cannot desorb hydrogen at room temperature in the absence of C60. The introduction of C60 also helps to restrain the NH3 gas which is poisonous in proton exchange membrane fuel cell applications.

  14. Movement of NH3 through the human urea transporter B: a new gas channel

    PubMed Central

    Musa-Aziz, Raif; Enkavi, Giray; Mahinthichaichan, P.; Tajkhorshid, Emad; Boron, Walter F.

    2013-01-01

    Aquaporins and Rh proteins can function as gas (CO2 and NH3) channels. The present study explores the urea, H2O, CO2, and NH3 permeability of the human urea transporter B (UT-B) (SLC14A1), expressed in Xenopus oocytes. We monitored urea uptake using [14C]urea and measured osmotic water permeability (Pf) using video microscopy. To obtain a semiquantitative measure of gas permeability, we used microelectrodes to record the maximum transient change in surface pH (?pHS) caused by exposing oocytes to 5% CO2/33 mM HCO3? (pHS increase) or 0.5 mM NH3/NH4+ (pHS decrease). UT-B expression increased oocyte permeability to urea by >20-fold, and Pf by 8-fold vs. H2O-injected control oocytes. UT-B expression had no effect on the CO2-induced ?pHS but doubled the NH3-induced ?pHS. Phloretin reduced UT-B-dependent urea uptake (Jurea*) by 45%, Pf* by 50%, and (??pHS*)NH3 by 70%. p-Chloromercuribenzene sulfonate reduced Jurea* by 25%, Pf* by 30%, and (?pHS*)NH3 by 100%. Molecular dynamics (MD) simulations of membrane-embedded models of UT-B identified the monomeric UT-B pores as the main conduction pathway for both H2O and NH3 and characterized the energetics associated with permeation of these species through the channel. Mutating each of two conserved threonines lining the monomeric urea pores reduced H2O and NH3 permeability. Our data confirm that UT-B has significant H2O permeability and for the first time demonstrate significant NH3 permeability. Thus the UTs become the third family of gas channels. Inhibitor and mutagenesis studies and results of MD simulations suggest that NH3 and H2O pass through the three monomeric urea channels in UT-B. PMID:23552862

  15. Effect of Ti or Sn doping on the catalytic performance of MnOx/CeO2 catalyst for low temperature selective catalytic reduction of NO with NH3

    NASA Astrophysics Data System (ADS)

    Xiong, Yan; Tang, Changjin; Dong, Lin

    2015-04-01

    The abatement of nitrogen oxides (NOx) emission from exhaust gases of diesel and stationary sources is a significant challenge for economic and social development. Ceria-based solid solutions were synthesized and used as supports to prepare MnOx/Ce0.8Ti0.2O2 and MnOx/Ce0.8Sn0.2O2 catalysts (Mn/CeTi and Mn/CeSn) for low temperature selective catalytic reduction of NO by NH3 (NH3-SCR). The effects of Ti or Sn doping on the catalytic performance of MnOx/CeO2 catalyst were investigated. Experimental results show that doping of Ti or Sn increases the NO removal efficiency of MnOx/CeO2. The NO conversion of Mn/CeTi catalyst is more than 90 % at temperature window of 175 ~ 300 °C under a gas hour space velocity of 60,000 mL•g-1•h-1. Modified catalysts are also found to exhibit greatly improved resistance to sulfur-poisoning. NH3-TPD results suggest that NH3 desorption on the catalysts is observed over a wide temperature range, due to the variability of adsorbed NH3 species with different thermal stabilities. Doping of Ti and Sn into Mn/CeO2 greatly increased the NH3 adsorption ability of the composites which could promote the SCR reaction. Characterization results also indicate that doping of Ti or Sn brings about catalysts with higher BET surface area, enhanced oxygen storage capacity and increased surface acidity. X-ray photoelectron spectroscopy (XPS) analysis of spent catalysts following SCR reaction in the presence of SO2 verify that the loss of surface Mn species was inhibited by doping of Ti, which contributes to extend the catalyst durability.

  16. Effect of metal ions doping (M = Ti4+, Sn4+) on the catalytic performance of MnOx/CeO2 catalyst for low temperature selective catalytic reduction of NO with NH3

    NASA Astrophysics Data System (ADS)

    Xiong, Yan; Tang, Changjin; Dong, Lin

    2015-04-01

    Key Laboratory of Mesoscopic Chemistry of MOE, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, PR China The abatement of nitrogen oxides (NOx) emission from exhaust gases of diesel and stationary sources is a significant challenge for economic and social development. Ceria-based solid solutions were synthesized and used as supports to prepare MnOx/Ce0.8Ti0.2O2 and MnOx/Ce0.8Sn0.2O2 catalysts (Mn/CeTi and Mn/CeSn) for low temperature selective catalytic reduction of NO by NH3 (NH3-SCR). The effects of Ti or Sn doping on the catalytic performance of MnOx/CeO2 catalyst were investigated. Experimental results show that doping of Ti or Sn increases the NO removal efficiency of MnOx/CeO2. The NO conversion of Mn/CeTi catalyst is more than 90 % at temperature window of 175 ~ 300 °C under a gas hour space velocity of 60,000 mL.g-1.h-1. Modified catalysts are also found to exhibit greatly improved resistance to sulfur-poisoning. NH3-TPD results suggest that NH3 desorption on the catalysts is observed over a wide temperature range, due to the variability of adsorbed NH3 species with different thermal stabilities. Doping of Ti and Sn into Mn/CeO2 greatly increased the NH3 adsorption ability of the composites which could promote the SCR reaction. Characterization results also indicate that doping of Ti or Sn brings about catalysts with higher BET surface area, enhanced oxygen storage capacity and increased surface acidity.

  17. NH3 Abatement in Fluidized Bed Co-Gasification of RDF and Coal

    NASA Astrophysics Data System (ADS)

    Gulyurtlu, I.; Pinto, Filomena; Dias, Mário; Lopes, Helena; André, Rui Neto; Cabrita, I.

    Gasification of wastes may come out as an alternative technology to produce a gas with many potential applications, from direct burning in a boiler or motor to the production of synthetic chemicals and hydrogen. High tar production and high operational costs are preventing gasification wider dissemination. Besides these problems, the presence of NH3 in the syngas may have a negative impact as it can be converted into nitrogen oxides if the gas is further burnt. To reduce NH3 formation it is required a full understanding of how operational parameters contribute to the formation/reduction of this pollutant. A full studyon the effect of fuel composition, temperature and equivalence ratio on the formation of NH3 is given. Experimental results are compared to theoretical ones obtained with FactSage software. It is also analyzed the effect of feedstock mineral matterin NH3 release during gasification. Toaccomplish a significant decrease in the release of NH3, different catalysts and sorbents were tested with the aim of achieving high energy conversions and low environmental impact.

  18. Nitrogen conversion in relation to NH3 and HCN during microwave pyrolysis of sewage sludge.

    PubMed

    Tian, Yu; Zhang, Jun; Zuo, Wei; Chen, Lin; Cui, Yanni; Tan, Tao

    2013-04-01

    The nitrogen conversions in relation to NH3 and HCN were investigated during microwave pyrolysis of sewage sludge. The nitrogen distributions and evolution of nitrogen functionalities in the char, tar, and gas fractions were conducted. The results suggested that the thermal cracking of protein in sludge produced three important intermediate compounds, including the amine-N, heterocyclic-N, and nitrile-N compounds. The deamination of amine-N compounds resulted from labile proteins cracking led to the formation of NH3 (about 7.5% of SS-N) between 300 and 500 °C. The cracking of nitrile-N and heterocyclic-N compounds in the tars from the dehydrogenation and polymerization of amine-N generated HCN (6.6%) from 500 to 800 °C, respectively. Moreover, the ring-opening of heterocyclic-N in the char and tar contributed to the release of NH3 accounting for about 18.3% of SS-N with the temperature increasing from 500 to 800 °C. Specifically, the thermal cracking of amine-N, heterocyclic-N and nitrile-N compounds contributed to above 80% of the total (HCN+NH3) productions. Consequently, it might be able to reduce the HCN and NH3 emissions through controlling the three intermediates production at the temperature of 500-800 °C. PMID:23477529

  19. Investigation of NH3 emissions from new technology vehicles as a function of vehicle operating conditions.

    PubMed

    Huai, Tao; Durbin, Thomas D; Miller, J Wayne; Pisano, John T; Sauer, Claudia G; Rhee, Sam H; Norbeck, Joseph M

    2003-11-01

    The objective of this study was to measure ammonia (NH3) emissions from modern technology vehicles since information is scarce aboutthis importantsource of particulate matter (PM) precursors. Test variables included the emission level to which the vehicle was certified, the vehicle operating conditions, and catalyst age. Eight vehicles with low-emission vehicle (LEV) to super-ultralow-emission vehicle (SULEV) certification levels were tested over the Federal Test Procedure (FTP75), a US06 cycle, a hot running 505, a New York City Cycle (NYCC), and a specially designed Modal Emissions Cycle (MEC01v7) using both as-received and bench-aged catalysts. NH3 emissions in the raw exhaust were measured by tunable diode laser (TDL) absorption spectroscopy. The results show that NH3 emissions depend on driving mode and are primarily generated during acceleration events. More specifically, high NH3 emissions were found for high vehicle specific power (VSP) events and rich operating conditions. For some vehicles, NH3 emissions formed immediately after catalyst light-off during a cold start. PMID:14620808

  20. Bimetallic cerium-copper nanoparticles embedded in ordered mesoporous carbons as effective catalysts for the selective catalytic reduction of NO with NH3.

    PubMed

    Chen, Jinghuan; Cao, Feifei; Qu, Ruiyang; Gao, Xiang; Cen, Kefa

    2015-10-15

    Bimetallic cerium-copper nanoparticles embedded in ordered mesoporous carbons (OMCs) with various Ce/Cu ratios were synthesized by "one-pot" self-assembly method, and their activities for the selective catalytic reduction (SCR) of NO with ammonia were studied. The structural and textural properties, surface chemistry, acidity, and reducibility were investigated by various techniques. Results showed that NO conversion was greatly influenced by the weight ratio of Ce to Cu. An appropriate Ce/Cu ratio in OMCs could enhance catalytic performance; the optimal catalytic performance was obtained with Ce5Cu5-OMC. Ordered mesoporous structures were formed for all synthesized samples. When Ce or Cu was incorporated into the OMCs, the amount of surface acidic oxygen functional groups increased, thereby promoting the acidic properties of the OMCs, especially those of the Cu-rich OMCs. The surface Cu(2+) species may accelerate ammonia activation and may play an important role in SCR reaction. The temperature-programmed reduction results illustrated that the Cu-rich OMCs had better reducibility, and the appropriate Ce/Cu ratio could further enhance the redox ability of the CexCuy-OMC catalysts. The existing redox cycle (Ce(4+)+Cu(+)?Cu(2+)+Ce(3+)) promoted the activation of NH3 and consequently improved NH3-SCR activity. PMID:26093235

  1. Quantifying local traffic contributions to NO2 and NH3 concentrations in natural habitats.

    PubMed

    Gadsdon, Sally R; Power, Sally A

    2009-10-01

    NO(2) and NH(3) concentrations were measured across a Special Area for Conservation in southern England, at varying distances from the local road network. Exceedances of the critical levels for these pollutants were recorded at nearly all roadside locations, extending up to 20 m away from roads at some sites. Further, paired measurements of NH(3) and NO(2) concentrations revealed differences between ground and tree canopy levels. At "background" sites, away from the direct influence of roads, concentrations were higher within tree canopies than at ground level; the reverse pattern was, however, seen at roadside locations. Calculations of pollutant deposition rates showed that nitrogen inputs are dominated by NH(3) at roadside sites. This study demonstrates that local traffic emissions contribute substantially to the exceedance of critical levels and critical loads, and suggests that on-site monitoring is needed for sites of nature conservation value which are in close proximity to local transport routes. PMID:19427723

  2. Facile route to freestanding CH3NH3PbI3 crystals using inverse solubility.

    PubMed

    Kadro, Jeannette M; Nonomura, Kazuteru; Gachet, David; Grätzel, Michael; Hagfeldt, Anders

    2015-01-01

    CH3NH3PbI3 was found to exhibit inverse solubility at high temperatures in ?-butyrolactone. Making use of this unusual, so far unreported phenomenon, we present a facile method for the growth of freestanding crystals of CH3NH3PbI3 from solution without addition of any capping agents or seed particles. Large, strongly faceted crystals could be grown within minutes. This finding may aid in understanding the crystallization process of CH3NH3PbI3 from solution that may lead to improved morphological control of film deposition for a range of device architectures. Our process offers a facile and rapid route to freestanding crystals for use in a broad range of characterization techniques. PMID:26123285

  3. Tuned sensitivity towards H2S and NH3 with Cu doped barium strontium titanate materials

    NASA Astrophysics Data System (ADS)

    Simion, C. E.; Sackmann, A.; Teodorescu, V. S.; Ru?ti, C. F.; Piticescu, R. M.; St?noiu, A.

    2014-11-01

    The different amount of Cu-doped Barium Strontium Titanate (BST) thick film materials have been tested for their gas-sensing performances towards NH3 and H2S under dry and 50% relative humidity (RH) background conditions. The optimum NH3 sensitivity was attained with 0.1mol% Cu-doped BST whereas the selective detection of H2S was highlighted using 5mol% Cu-doped BST material. No cross-sensitivity effects to CO, NO2, CH4 and SO2 were observed for all tested materials operated at their optimum temperature (200°C) under humid conditions (50% RH). The presence of humidity clearly enhances the gas sensitivity to NH3 and H2S detection.

  4. Communications: The electronic spectrum of Li(NH3)4

    NASA Astrophysics Data System (ADS)

    Varriale, Luigi; Tonge, Nicola M.; Bhalla, Nitika; Ellis, Andrew M.

    2010-04-01

    Li(NH3)4 has been proposed as a key entity in lithium-ammonia solutions, but its spectral signature has so far proved impossible to distinguish from other species in these solutions. Here we report the first electronic spectrum of Li(NH3)4 in the gas phase, which was recorded using mass-selective depletion spectroscopy. Strong absorption is observed in the near-infrared and the band system is assigned to the à T22-X˜ A21 transition in a nominally tetrahedral complex. However, the vibrational structure is indicative of a substantial Jahn-Teller effect in the excited electronic state. The broad and structured spectrum confirms a recent theoretical prediction that the electronic spectrum of Li(NH3)4 will strongly overlap with the spectrum of the solvated electron in lithium-ammonia solutions.

  5. Partial phase diagram for the system NH3-H2O - The water-rich region

    NASA Technical Reports Server (NTRS)

    Johnson, M. L.; Schwake, A.; Nicol, M.

    1984-01-01

    Phase boundaries of the H2O-NH3 system for (NH3)/x/(H2O)/1-x/ have been determined with diamond-anvil cells for mixtures in two composition ranges: (1) for x in the range from 0 to 0.3, at pressures up to 4 GPa at 21 C, and (2) for x in the range from 0.46 to 0.50, at pressures up to 5 GPa from 150 to 400 K. Phases were identified visually with a microscope and polarized optics. The NH3.2(H2O) phase is strongly anisotropic with a much smaller refractive index than that of ice VII and cracks in two nonperpendicular networks. NH3.H2O has a refractive index closer to that of Ice VII and does not appear to form cracks. Both phases are colorless. Phase boundaries were determined on both increasing and decreasing pressures, and compositions of the ammonia ices were determined by estimating relative amounts of water and ammonia ices at known overall compositions. For low-ammonia compositions (x equal to or less than 0.15), the following assemblages succedd one another as pressure increases: liquid; liquid and Ice VI (at 1.0 + GPa); liquid and Ice VII (at 2.1 GPa); Ice VII and NH3.H2O (at 3.5 GPa). For x in the range from 0.15 to 0.30, the water ice and liquid fields are replaced by the NH3.2(H2O) and liquid field at pressures down to 1.0 GPa and lower.

  6. Mixing of Dust and NH3 Observed Globally over Anthropogenic Dust Sources

    NASA Technical Reports Server (NTRS)

    Ginoux, P.; Clarisse, L.; Clerbaux, C.; Coheur, P.-F.; Dubovik, O.; Hsu, N. C.; Van Damme, M.

    2012-01-01

    The global distribution of dust column burden derived from MODIS Deep Blue aerosol products is compared to NH3 column burden retrieved from IASI infrared spectra. We found similarities in their spatial distributions, in particular their hot spots are often collocated over croplands and to a lesser extent pastures. Globally, we found 22% of dust burden collocated with NH3, with only 1% difference between land-use databases. This confirms the importance of anthropogenic dust from agriculture. Regionally, the Indian subcontinent has the highest amount of dust mixed with NH3 (26 %), mostly over cropland and during the pre-monsoon season. North Africa represents 50% of total dust burden but accounts for only 4% of mixed dust, which is found over croplands and pastures in Sahel and the coastal region of the Mediterranean. In order to evaluate the radiative effect of this mixing on dust optical properties, we derive the mass extinction efficiency for various mixtures of dust and NH3, using AERONET sunphotometers data. We found that for dusty days the coarse mode mass extinction efficiency decreases from 0.62 to 0.48 square meters per gram as NH3 burden increases from 0 to 40 milligrams per square meter. The fine mode extinction efficiency, ranging from 4 to 16 square mters per gram, does not appear to depend on NH3 concentration or relative humidity but rather on mineralogical composition and mixing with other aerosols. Our results imply that a significant amount of dust is already mixed with ammonium salt before its long range transport. This in turn will affect dust lifetime, and its interactions with radiation and cloud properties

  7. Microwave spectra of, and ab initio calculations for, the Ne 2-NH 3 van der Waals trimer

    NASA Astrophysics Data System (ADS)

    van Wijngaarden, Jennifer; Jäger, Wolfgang

    2002-10-01

    The ground state rotational spectrum of the Ne 2-NH 3 van der Waals trimer was measured in the region between 5 and 19 GHz using a Balle-Flygare type Fourier transform microwave spectrometer. The isotopomers studied include those of 20Ne2 paired with NH 3, 15NH3, ND 3, ND 2H, and NDH 2 as well as those containing 20Ne 22Ne and 22Ne2 bound to NH 3 and 15NH3. Nuclear quadrupole hyperfine splitting for the 14N containing isotopomers was resolved and included in the fit of the spectroscopic constants. Additional splitting due to the inversion of ammonia was observed for each of the deuterium containing species. This tunnelling splitting cannot be observed for the NH 3 and 15NH3 containing isotopomers for nuclear spin statistical reasons. Three ab initio potential energy surfaces were constructed for Ne 2-NH 3 at the CCSD(T) level of theory. Each surface corresponds to a different umbrella angle of NH 3 to simulate the inversion motion. The minimum energy orientation of NH 3 for each of the three potential energy surfaces corresponds to a geometry in which the C3-axis of NH 3 is aligned perpendicular to the Ne-Ne axis with two of the hydrogen atoms pointed toward the Ne atoms. The potential well depth associated with this orientation is 131 cm-1 (597.2 ?H) for the experimental equilibrium geometry of NH 3 with a Ne-Ne bond length of 3.29 Å (fixed) and a Ne-NH 3 bond length of 3.51 Å.

  8. The vibrational spectrum and structure of cis-Rh(NH 3)(CO) 2Cl

    Microsoft Academic Search

    Derek Steele; Paul F. M. Verhoeven

    2001-01-01

    The structure and vibrational spectrum of cis-Rh(NH3)(CO)2Cl has been computed using DFT\\/B-LYP with 6-311G?? for all except the rhodium atom. For this a 6s5p3d basis with an electron core potential was employed. The predicted skeletal structure is in good agreement with reported experimental values of similar rhodium(I) compounds. The computed vibrational frequencies agree well with experimental IR data for cis-Rh(NH3)(CO)2Cl

  9. Parameter identification and synchronization between uncertain stimulated Raman scattering and NH3 laser

    NASA Astrophysics Data System (ADS)

    Li, Chengren; Sun, Jingchang; Ren, Xudong; Yue, Xishuang; He, Yingshi

    2012-08-01

    The parameter identifiers and synchronization controllers are designed based on stability theory in order to realize the synchronization of two chaotic systems with diverse structures and the parameter identification of the uncertain system. The stimulated Raman scattering and NH3 laser are taken as examples. The simulation results show that the global synchronization between the uncertain stimulated Raman scattering and the NH3 laser can be achieved, and all the parameters in the stimulated Raman scattering system can be identified simultaneously. The method is proved effective and feasible.

  10. Ultraviolet-gas phase and -photocatalytic synthesis from CO and NH3. [photolysis products

    NASA Technical Reports Server (NTRS)

    Hubbard, J. S.; Voecks, G. E.; Hobby, G. L.; Ferris, J. P.; Williams, E. A.; Nicodem, D. E.

    1975-01-01

    Ammonium cyanate is identified as the major product of the photolysis of gaseous NH3-CO mixtures at 206.2 or 184.9 nm. Lesser amounts of urea, biurea, biuret semicarbazide, formamide and cyanide are observed. A series of 18 reactions underlying the formation of photolysis products is presented and discussed. Photocatalytic syntheses of C-14-urea, -formamide, and -formaldehyde are carried out through irradiation of (C-14)O and NH3 in the presence of Vycor, silica gel, or volcanic ash shale surfaces. The possible contributions of the relevant reactions to the abiotic synthesis of organic nitrogen compounds on Mars, the primitive earth, and in interstellar space are examined.

  11. Physical and chemical conditions in Perseus globules from NH3 and HC3N observations

    NASA Astrophysics Data System (ADS)

    Bachiller, R.; Cernicharo, J.

    1986-11-01

    Ammonia observations of the globules L 1448 and L 1455 in Perseus show that their dense cores are fragmented in clumps of 1 - 20 M_sun;, which have central densities ? a few 104cm-3 and temperatures ?12K. HC3N observations, when compared to the NH3 observations, show that the ratio R = [NH3]/[HC3N] in the Perseus globules (L 1448, L 1455, and B 1) is ?80 - 90, i.e. about 10 times larger than in the Taurus cloudlets (TMC 1, HCL 2-A, B, C,...). The Perseus globules appear active in forming low mass stars.

  12. Simulation of operation of multiwave remote gas-analyzer based on NH 3-laser

    NASA Astrophysics Data System (ADS)

    Banakh, V. A.; Ponomarev, Yu. N.; Smalikho, I. N.; Firsov, K. M.; Maluta, D. D.; Poliakov, G. A.

    2000-03-01

    Numerical analysis of a multiwave path gas-analyzer, based on a NH 3-laser pumped by CO 2-laser radiation, is performed for model detection of concentrations of a series of molecular species such as NH 3, HCN, phosgene, NHO 3, CO 2, and H 2O. The potentialities of the gas analyzer and uncertainty of the gas concentration detection were estimated for a 4 km horizontal atmospheric path. The estimation took into account the absorption of laser radiation by the atmospheric aerosol and molecular gases under study and distortion of the laser beam due to atmospheric turbulence.

  13. Photo-desorbed species produced by the UV/EUV irradiation of an H2O:CO2:NH3 ice mixture

    NASA Astrophysics Data System (ADS)

    Chen, Y.-J.; Nuevo, M.; Chu, C.-C.; Fan, Y.-G.; Yih, T.-S.; Ip, W.-H.; Fung, H.-S.; Wu, C.-Y. R.

    2011-05-01

    An H2O:CO2:NH3 = 1:1:1 ice mixture, used as a model mixture for cometary and interstellar ices, was irradiated with ultraviolet (UV)/extreme ultraviolet (EUV) photons in the broad 4-20 eV (62-310 nm) energy range at 16 K. The desorbed species were detected in situ by mass spectrometry during photo-irradiation, and a quartz microbalance was used as a substrate to measure the mass of material remaining on the surface. The total mass desorption for this H2O:CO2:NH3 = 1:1:1 ice mixture at 16 K was measured to be 1.8 × 10-18 ?g photon-1, which is comparable to the 1.5 × 10-18 ?g photon-1 measured for pure H2O ice irradiated under the same conditions. The main desorbed species produced during the photolysis of the ices were H2, NH2•, OH•, CO, and O2, along with the starting components H2O, NH3, and CO2. We also tentatively assigned minor mass peaks to larger species such as OCN•/OCN-, HNCO, CH4, H2CO, CH3OH, and HCOOH. This result supports the scenario in which complex organic molecules can be formed in cometary and/or astrophysical ices and desorbed to the gas phase, and helps to better understand the photochemical processes occurring at the surface of Solar System icy bodies such as comets, as well as in cold astrophysical environments such as star-forming regions and protostars.

  14. Pseudohalide-Induced Moisture Tolerance in Perovskite CH3 NH3 Pb(SCN)2 I Thin Films.

    PubMed

    Jiang, Qinglong; Rebollar, Dominic; Gong, Jue; Piacentino, Elettra L; Zheng, Chong; Xu, Tao

    2015-06-22

    Two pseudohalide thiocyanate ions (SCN(-) ) have been used to replace two iodides in CH3 NH3 PbI3 , and the resulting perovskite material was used as the active material in solar cells. In accelerated stability tests, the CH3 NH3 Pb(SCN)2 I perovskite films were shown to be superior to the conventional CH3 NH3 PbI3 films as no significant degradation was observed after the film had been exposed to air with a relative humidity of 95?% for over four hours, whereas CH3 NH3 PbI3 films degraded in less than 1.5?hours. Solar cells based on CH3 NH3 Pb(SCN)2 I thin films exhibited an efficiency of 8.3?%, which is comparable to that of CH3 NH3 PbI3 based cells fabricated in the same way. PMID:25968343

  15. Selective catalytic reduction of NO with NH3 over CeO2-ZrO2-WO3 catalysts prepared by different methods

    NASA Astrophysics Data System (ADS)

    Ning, Ping; Song, Zhongxian; Li, Hao; Zhang, Qiulin; Liu, Xin; Zhang, Jinhui; Tang, Xiaosu; Huang, Zhenzhen

    2015-03-01

    The selective catalytic reduction (SCR) of NO by NH3 has been investigated over the CeO2-ZrO2-WO3 (CZW) catalysts prepared by hydrothermal synthesis, incipient impregnation, co-precipitation and sol-gel methods. The results indicate that the CZW catalyst prepared by hydrothermal method shows the best SCR activity, and more than 90% NO conversion is obtained at 195-450 °C with a gas hourly space velocity of 50,000 h-1. The samples are characterized by XRD, N2 adsorption-desorption, SEM, EDS, XPS, H2-TPR, NH3-TPD and Pyridine-IR techniques. The results imply that the superior SCR activity of CZW catalyst is contributed to the excellent redox property, strong acidity and highest content of chemisorbed oxygen species. Furthermore, the larger surface area and greater total pore volume improve the redox ability and enhance NO conversion at low temperature, while the co-existence of Lewis and Brønsted acid sites enhance the SCR activity at high temperature.

  16. Chemical decoration of CH3NH3PbI3 perovskites with graphene oxides for photodetector applications.

    PubMed

    He, Minhong; Chen, Yani; Liu, Hui; Wang, Jialin; Fang, Xiaosheng; Liang, Ziqi

    2015-05-28

    A facile in situ solution method was developed for chemical decoration of CH3NH3PbI3 perovskites with reduced graphene oxides (rGOs) to significantly improve the photodetector performance. Such CH3NH3PbI3/rGO molecular hybrids show a 6 times higher ON/OFF ratio and notably faster response speed than neat CH3NH3PbI3. PMID:25977949

  17. Effect of NH 3 and thickness of catalyst on growth of carbon nanotubes using thermal chemical vapor deposition

    Microsoft Academic Search

    Yoon-Taek Jang; Jin-Ho Ahn; Yun-Hi Lee; Byeong-Kwon Ju

    2003-01-01

    The growth behavior of carbon nanotubes synthesized from C2H2 using thermal chemical vapor deposition method has been investigated. The formation of catalytic cobalt nanoparticles was much enhanced when using NH3 as the environment gas, whereas NH3 introduced during nanotubes growth does not play a key role in growing the vertically aligned nanotubes. The role of NH3 is to obtain the

  18. The effect of fuel sulfur on NH 3 and other emissions from 2000–2001 model year vehicles

    Microsoft Academic Search

    Thomas D. Durbin; John T. Pisano; T. Younglove; Claudia G. Sauer; Sam H. Rhee; Tao Huai; J. Wayne Miller; Gervase I. MacKay; Albert M. Hochhauser; Michael C. Ingham; Robert A. Gorse; Loren K. Beard; Dominic DiCicco; Neville Thompson; Richard J. Stradling; James A. Rutherford; James P. Uihlein

    2004-01-01

    Atmospheric ammonia (NH3) is an important precursor to secondary particulate matter formation and information is currently scarce on NH3 emissions from advanced low-emission vehicles using low-sulfur fuels. With the continuing reduction in the level of sulfur in gasoline, it is important to understand how this change could impact NH3 emissions, particularly for advanced vehicle technologies. For this study, a total

  19. Low energy structural dynamics and constrained libration of Li(NH3)4, the lowest melting point metal.

    PubMed

    Seel, A G; Zurek, E; Ramirez-Cuesta, A J; Ryan, K R; Lodge, M T J; Edwards, P P

    2014-09-25

    The lattice and molecular dynamics for the solid phases of the lowest melting-point metal, Li(NH3)4, are determined by incoherent inelastic neutron scattering. Measurements of internal molecular displacements and distortions of the Li(NH3)4 units have been modelled and assigned using density functional theory calculations for the solid and molecular system. Inelastic neutron scattering measurement allow for the first determination of NH3 librational transitions. PMID:24988060

  20. Spin transport in CH3NH3PbI3

    NASA Astrophysics Data System (ADS)

    Xu, Qingyu; Liu, Er; Qin, Sai; Shi, Shan; Shen, Kai; Xu, Mingxiang; Zhai, Ya; Dong, Shuai

    2014-10-01

    Organometal trihalide perovskites with the general formula (CH3NH3)PbX3 (X is Cl, I and/or Br) have a composition dependent tunable band gap and long electron-hole diffusion length, which is not only being hotly studied for usage in hybrid solar cells, but also has potential application in organic spintronics. In this work, we prepared CH3NH3PbI3-coated Fe3O4 granular films. CH3NH3PbI3 behaves effectively as a spacer to decouple the Fe3O4 particles and spin-preserved transporting matrix. The magnetoresistance of Fe3O4 particles has been significantly enhanced after CH3NH3PbI3 coating, which is about -6% at 300 K and -10.8% at 150 K under a magnetic field of 10 kOe, about 3 times larger than the values of pure Fe3O4 (-1.9% at 300 K and -3.4% at 150 K).

  1. Engineering analysis of an NH3-air alkaline fuel cell system for vehicular applications

    Microsoft Academic Search

    P. N. Ross Jr.; P. N. Jr

    1982-01-01

    The use of a hydrogen air alkaline fuel cell in a vehicle with liquid anhydrous ammonia as the hydrogen storage medium was examined. In the system analyzed here, hydrogen is supplied to the fuel cell by the catalytic cracking of liquid anhydrous ammonia, making the total system an indirect NH3 air fuel cell system. It was found that the endothermicity

  2. Synthesis and Evaluation of Cu/SAPO-34 Catalysts for NH3-SCR 2: Solid-state Ion Exchange and One-pot Synthesis

    SciTech Connect

    Gao, Feng; Walter, Eric D.; Washton, Nancy M.; Szanyi, Janos; Peden, Charles HF

    2015-01-01

    Cu-SAPO-34 catalysts are synthesized using two methods: solid-state ion exchange (SSIE) and one-pot synthesis. SSIE is conducted by calcining SAPO-34/CuO mixtures at elevated temperatures. For the one-pot synthesis method, Cu-containing chemicals (CuO and CuSO4) are added during gel preparation. A high-temperature calcination step is also needed for this method. Catalysts are characterized with surface area/pore volume measurements, temperature programmed reduction (TPR), electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) spectroscopies, and scanning electron microscopy (SEM). Catalytic properties are examined using standard ammonia selective catalytic reduction (NH3-SCR) and ammonia oxidation reactions. In Cu-SAPO-34 samples formed using SSIE, Cu presents both as isolated Cu2+ ions and unreacted CuO. The former is highly active and selective in NH3-SCR, while the latter catalyzes a side reaction; notably, the non-selective oxidation of NH3 above 350 ºC. Using the one-pot method followed by a high-temperature aging treatment, it is possible to form Cu SAPO-34 samples with predominately isolated Cu2+ ions at low Cu loadings. However at much higher Cu loadings, isolated Cu2+ ions that bind weakly with the CHA framework and CuO clusters also form. These Cu moieties are very active in catalyzing non-selective NH3 oxidation above 350 ºC. Low-temperature reaction kinetics indicate that Cu-SAPO-34 samples formed using SSIE have core-shell structures where Cu is enriched in the shell layers; while Cu is more evenly distributed within the one-pot samples. Reaction kinetics also suggest that at low temperatures, the local environment next to Cu2+ ion centers plays little role on the overall catalytic properties. The authors gratefully acknowledge the US Department of Energy (DOE), Energy Efficiency and Renewable Energy, Vehicle Technologies Office for the support of this work. The research described in this paper was performed at the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US DOE by Battelle under contract number DE-AC05-76RL01830. The authors also thank Shari Li (PNNL) for surface area/pore volume measurements, and Bruce W. Arey (PNNL) for SEM measurements. Discussions with Drs. A. Yezerets, K. Kamasamudram, J.H. Li, N. Currier and J.Y. Luo from Cummins, Inc. and H.Y. Chen and H. Hess from Johnson-Matthey are greatly appreciated.

  3. Development and types of passive samplers for monitoring atmospheric NO2 and NH3 concentrations.

    PubMed

    Tang, Y S; Cape, J N; Sutton, M A

    2001-10-01

    Numerous passive samplers based on the "Palmes-tube" have been developed for ambient air monitoring. In each case, the diffusion path length and/or cross-sectional area are modified to achieve the desired sampling rate. "Tube-type" samplers are low sensitivity samplers suitable for long-term monitoring, whereas the "badge-type" samplers have faster sampling rates suited to short-term monitoring. In the U.K., diffusion tubes are widely used for monitoring nitrogen dioxide (NO2) and ammonia (NH3). The open-ended diffusion tubes are prone to positive bias caused by incursion of wind eddies, leading to a shortening of the diffusion path. By using a porous membrane at the inlet, wind incursion is prevented, but an additional diffusion resistance is imposed and it is necessary to calibrate the tubes against a reference method to obtain an effective sampling rate. For NO2 sampling, positive bias also arises from the reaction of NO with O3 within the sampler. The interference from the chemical reaction is severe close to NO sources, with errors up to 30% for curbside locations when using the "tube-type" sampler. In rural areas, where NO concentrations are small relative to NO2, these errors are small. In some implementations, there is also a negative bias over long sampling periods caused by the degradation of trapped NO2. The low sampling rates of diffusion tubes make them too uncertain for use at background NH3 concentrations (<1 microg NH3 m(-3)) where they significantly overestimate concentrations. Badge-type samplers such as the "Willems badge" samplers permit accurate sampling at low ambient NH3 concentrations, but suffer from saturation at high concentrations and sensitivity to wind speed. A passive sampler optimised for monthly measurements of NH3 is reported here, together with its application in the U.K. National Ammonia Monitoring Network. PMID:12805844

  4. Nucleobases and Prebiotic Molecules in Organic Residues Produced from the Ultraviolet Photo-Irradiation of Pyrimidine in NH3 and H2O+NH3 Ices

    NASA Technical Reports Server (NTRS)

    Nuevo, Michel; Milam, Stefanie N.; Sandford, Scott

    2012-01-01

    Although not yet identified in the interstellar medium (ISM), N-heterocycles including nucleobases the information subunits of DNA and RNA are present in carbonaceous chondrites, which indicates that molecules of biological interest can be formed in non-terrestrial environments via abiotic pathways. Recent laboratory experiments and ab-initio calculations have already shown that the irradiation of pyrimidine in pure H2O ices leads to the formation of a suite of oxidized pyrimidine derivatives, including the nucleobase uracil. In the present work, NH3:pyrimidine and H2O:NH3:pyrimidine ice mixtures with different relative proportions were irradiated with UV photons under astrophysically relevant conditions. Liquid- and gas-chromatography analysis of the resulting organic residues has led to the detection of the nucleobases uracil and cytosine, as well as other species of prebiotic interest such as urea and small amino acids. The presence of these molecules in organic residues formed under abiotic conditions supports scenarios in which extraterrestrial organics that formed in space and were subsequently delivered to telluric planets via comets and meteorites could have contributed to the inventory of molecules that triggered the first biological reactions on their surfaces.

  5. Estimation of global NH3 volatilization loss from synthetic fertilizers and animal manure applied to arable lands and grasslands

    NASA Astrophysics Data System (ADS)

    Bouwman, A. F.; Boumans, L. J. M.; Batjes, N. H.

    2002-06-01

    One of the main causes of the low efficiency in nitrogen (N) use by crops is the volatilization of ammonia (NH3) from fertilizers. Information taken from 1667 NH3 volatilization measurements documented in 148 research papers was summarized to assess the influence on NH3 volatilization of crop type, fertilizer type, and rate and mode of application and temperature, as well as soil organic carbon, texture, pH, CEC, measurement technique, and measurement location. The data set was summarized in three ways: (1) by calculating means for each of the factors mentioned, in which findings from each research paper were weighted equally; (2) by calculating weighted median values corrected for unbalanced features of the collected data; and (3) by developing a summary model using linear regression based on weighted median values for NH3 volatilization and by calculating global NH3 volatilization losses from fertilizer application using 0.5° resolution data on land use and soils. The calculated median NH3 loss from global application of synthetic N fertilizers (78 million tons N per year) and animal manure (33 million tons N per year) amount to 14% (10-19%) and 23% (19-29%), respectively. In developing countries, because of high temperatures and the widespread use of urea, ammonium sulfate, and ammonium bicarbonate, estimated NH3 volatilization loss from synthetic fertilizers amounts to 18%, and in industrialized countries it amounts to 7%. The estimated NH3 loss from animal manure is 21% in industrialized and 26% in developing countries.

  6. Seasonal NH 3 emission estimates for the eastern United States based on ammonium wet concentrations and an inverse modeling method

    Microsoft Academic Search

    Alice B. Gilliland; Robin L. Dennis; Shawn J. Roselle; Thomas E. Pierce

    2003-01-01

    (CMAQ) model and ammonium (NH4 + ) wet concentration data from the National Atmospheric Deposition Program network are used. The results illustrate the strong seasonal differences in NH3 emissions that were anticipated, where NH3 emissions are more than 75% lower during the colder seasons fall and winter as compared to peak emissions during summer. The results also suggest that the

  7. Mechanisms for sealing of porous low-k SiOCH by combined He and NH3 plasma treatment

    E-print Network

    Kushner, Mark

    network during plasma etching or cleaning steps.1,2 Penetration by plasma produced radicalsMechanisms for sealing of porous low-k SiOCH by combined He and NH3 plasma treatment Juline Shoeba of reactants through the pores into the material. Sequential treatment of porous SiOCH by He and NH3 plasmas

  8. Thermal desorption for passive dosimeter 

    E-print Network

    Liu, Wen-Chen

    1981-01-01

    temperature for 21 a passive dosimeter loaded vrith an organic chemical that ould provide the maximum desorption effi- ciency during thermal desorption; 2. To compare desorption efficiencies determined using thermal desorption and solvent desorption... S LIST CF FIGUHES II, THODUCT CI LIT=HATUHE BEVIES . Passive Dosimeter Activated Charcoal Theories of Adsorption Desorption IIethods Solvent Desorption Thermal Desorption Desorption Efficiency Determination Objectives NETHODOLOGY Chemicals...

  9. Thermal desorption effects in chemical vapor deposition of silicon nanoparticles

    Microsoft Academic Search

    W. Thomas Leach; Jian-hong Zhu; John G Ekerdt

    2002-01-01

    Silicon nanoparticles are grown via ultra high vacuum chemical vapor deposition (UHV-CVD) on SiO2 and Si3N4 covered Si(100) substrates using disilane. Temperature programmed desorption spectra demonstrate the presence of H2 and SiO desorption features at 770 and 900K, respectively, which are in the 750–1000K temperature range that is typical for nanoparticle growth via CVD. The lower temperature limit (?750K) for

  10. Desorption Kinetics of Methanol, Ethanol, and Water from Graphene

    SciTech Connect

    Smith, R. Scott; Matthiesen, Jesper; Kay, Bruce D.

    2014-09-18

    The desorption kinetics of methanol, ethanol, and water from graphene covered Pt(111) are investigated. The temperature programmed desorption (TPD) spectra for both methanol and ethanol have well-resolved first, second, third, and multilayer layer desorption peaks. The alignment of the leading edges is consistent with zero-order desorption kinetics from all layers. In contrast, for water the first and second layers are not resolved. At low water coverages (< 1 ML) the initial desorption leading edges are aligned but then fall out of alignment at higher temperatures. For thicker water layers (10 to 100 ML), the desorption leading edges are in alignment throughout the desorption of the film. The coverage dependence of the desorption behavoir suggests that at low water coverages the non-alignment of the desorption leading edges is due to water dewetting from the graphene substrate. Kinetic simulations reveal that the experimental results are consistent with zero-order desorption. The simulations also show that fractional order desorption kinetics would be readily apparent in the experimental TPD spectra.

  11. Reactivity of HNCO with NH 3 at low temperature monitored by FTIR spectroscopy: formation of NH 4+OCN -

    NASA Astrophysics Data System (ADS)

    Raunier, S.; Chiavassa, T.; Marinelli, F.; Allouche, A.; Aycard, J. P.

    2003-01-01

    The reactivity of isocyanic acid (HNCO) with solid ammonia (NH 3) was first studied at 10 K, using FTIR spectroscopy. The ammonium isocyanate (NH 4+OCN -) is formed from a reaction between HNCO and NH 3. Vibrational band assignments for NH 4+OCN - have been given. On the other hand, when HNCO is adsorbed on amorphous NH 3 film, the reaction does not occur. Warming up of this sample at 90 K induces the NH 4+OCN - formation. Quantum calculations showed that the solvation of NH 3 directly bonded to HNCO by at least three NH 3 molecules plays a major role in the NH 4+OCN - formation process and confirmed the spontaneous character of this reaction.

  12. Comparison of the biological NH3 removal characteristics among four inorganic packing materials.

    PubMed

    Hirai, M; Kamamoto, M; Yani, M; Shoda, M

    2001-01-01

    Four inorganic packing materials were evaluated in terms of their availability as a packing material of a packed tower deodorization apparatus (biofilter) from the viewpoints of biological NH3 removal characteristics and some physical properties. Porous ceramics (A), calcinated cristobalite (B), calcinated and formed obsidian (C), granulated and calculated soil (D) were used. The superiority of these packing materials determined based on the values of non-biological removal per unit weight or unit volume of packing material, complete removal capacity of NH3 per unit weight of packing material per day or unit volume of packing material per day and pressure drop of the packed bed was in the order of A approximately = C > B > or = D. Packing materials A and C with high porosity, maximum water content, and suitable mean pore diameter showed excellent removal capacity. PMID:16233018

  13. Potential energy surface and bound states of the NH3-Ar and ND3-Ar complexes.

    PubMed

    Loreau, J; Liévin, J; Scribano, Y; van der Avoird, A

    2014-12-14

    A new, four-dimensional potential energy surface for the interaction of NH3 and ND3 with Ar is computed using the coupled-cluster method with single, double, and perturbative triple excitations and large basis sets. The umbrella motion of the ammonia molecule is explicitly taken into account. The bound states of both NH3-Ar and ND3-Ar are calculated on this potential for total angular momentum values from J = 0 to 10, with the inclusion of Coriolis interactions. The energies and splittings of the rovibrational levels are in excellent agreement with the extensive high-resolution spectroscopic data accumulated over the years in the infrared and microwave regions for both complexes, which demonstrates the quality of the potential energy surface. PMID:25494745

  14. On the reaction CH2O + NH3 Yields CH2NH + H2O

    NASA Technical Reports Server (NTRS)

    Walch, Stephen P.; Bauschlicher, Charles W., Jr.; Ricca, Alessandra; Bakes, E. L. O.; Arnold, James (Technical Monitor)

    2000-01-01

    We study the energetics of CH2O + NH3-Yields CH2NH + H2O in the gas phase at the B3LYP and CCSD(T)levels. This reaction is shown to have a sizeable barrier. Ionization of NH3 reduces the barrier to about 5 kcal/mol. We also show that in water, a proton catalyzed mechanism yields no barriers in excess of the reaction endothermicity. Since this reaction has been proposed as one of the steps in interstellar synthesis of glycine, the simplest amino acid, this work suggests that the formation of amino acids is occurring in and/or on interstellar water ice grains, and not in the gas phase.

  15. Calculations on the rate of the ion-molecule reaction between NH3(+) and H2

    NASA Technical Reports Server (NTRS)

    Herbst, Eric; Defrees, D. J.; Talbi, D.; Pauzat, F.; Koch, W.

    1991-01-01

    The rate coefficient for the ion-molecule reaction NH3(+) + H2 yields NH4(+) + H has been calculated as a function of temperature with the use of the statistical phase space approach. The potential surface and reaction complex and transition state parameters used in the calculation have been taken from ab initio quantum chemical calculations. The calculated rate coefficient has been found to mimic the unusual temperature dependence measured in the laboratory, in which the rate coefficient decreases with decreasing temperature until 50-100 K and then increases at still lower temperatures. Quantitative agreement between experimental and theoretical rate coefficients is satisfactory given the uncertainties in the ab initio results and in the dynamics calculations. The rate coefficient for the unusual three-body process NH3(+) + H2 + He yields NH4(+) + H + He has also been calculated as a function of temperature and the result found to agree well with a previous laboratory determination.

  16. Thin film polypyrrole\\/SWCNTs nanocomposites-based NH 3 sensor operated at room temperature

    Microsoft Academic Search

    Nguyen Van Hieu; Nguyen Quoc Dung; Phuong Dinh Tam; Tran Trung; Nguyen Duc Chien

    2009-01-01

    A PPY\\/SWCNTs nanocomposite-based sensor with relatively high sensitivity and fast response–recovery was developed for detection of NH3 gas at room temperature. The gas-sensitive composite thin film was prepared using chemical polymerization and spin-coating techniques, and characterized by Fourier transformed infrared spectra and field-emission scanning electron microscopy. The results reveal that the conjugated structure of the PPY layer was formed and

  17. Molecular tunneling dynamics of NH3D + in ammonium sulfate and ammonium thiocyanate

    Microsoft Academic Search

    Wes Burrows; Herbert L. Strauss

    1993-01-01

    The kinetics of NH3D+ rotation in ammonium sulfate and ammonium thiocyanate are measured at low temperature (8–60 K). Infrared hole burning of the N–D stretching bands causes reorientation of the ions among distinct positions relative to the crystal lattice, producing nonequilibrium population distributions. The slow relaxation (time scale of minutes to hours) is monitored with a Fourier-transform infrared spectrometer as

  18. Role of NH3 and NH4+ transporters in renal acid-base transport.

    PubMed

    Weiner, I David; Verlander, Jill W

    2011-01-01

    Renal ammonia excretion is the predominant component of renal net acid excretion. The majority of ammonia excretion is produced in the kidney and then undergoes regulated transport in a number of renal epithelial segments. Recent findings have substantially altered our understanding of renal ammonia transport. In particular, the classic model of passive, diffusive NH3 movement coupled with NH4+ "trapping" is being replaced by a model in which specific proteins mediate regulated transport of NH3 and NH4+ across plasma membranes. In the proximal tubule, the apical Na+/H+ exchanger, NHE-3, is a major mechanism of preferential NH4+ secretion. In the thick ascending limb of Henle's loop, the apical Na+-K+-2Cl- cotransporter, NKCC2, is a major contributor to ammonia reabsorption and the basolateral Na+/H+ exchanger, NHE-4, appears to be important for basolateral NH4+ exit. The collecting duct is a major site for renal ammonia secretion, involving parallel H+ secretion and NH3 secretion. The Rhesus glycoproteins, Rh B Glycoprotein (Rhbg) and Rh C Glycoprotein (Rhcg), are recently recognized ammonia transporters in the distal tubule and collecting duct. Rhcg is present in both the apical and basolateral plasma membrane, is expressed in parallel with renal ammonia excretion, and mediates a critical role in renal ammonia excretion and collecting duct ammonia transport. Rhbg is expressed specifically in the basolateral plasma membrane, and its role in renal acid-base homeostasis is controversial. In the inner medullary collecting duct (IMCD), basolateral Na+-K+-ATPase enables active basolateral NH4+ uptake. In addition to these proteins, several other proteins also contribute to renal NH3/NH4+ transport. The role and mechanisms of these proteins are discussed in depth in this review. PMID:21048022

  19. Low energy studies (e,2e) studies from Ammonia (NH3)

    NASA Astrophysics Data System (ADS)

    Chaluvadi, Hari; Madison, Don; Nixon, K. L.; Murray, Andrew J.; Ning, Chuangang; Colgan, James

    2012-10-01

    Experimental and theoretical Triply Differential Cross Sections (TDCS) will be presented for electron-impact ionization of Ammonia (NH3) for highest occupied molecular orbital (HOMO), next highest occupied molecular orbital (NHOMO) and next next highest occupied molecular orbital (N^2HOMO). M3DW (molecular 3-body distorted wave) results will be compared with experiment for coplanar geometry. The final state electron energies and observation angles are symmetric.

  20. High quality interpoly-oxynitride grown by NH3 nitridation and N2O RTA treatment

    Microsoft Academic Search

    Tung Ming Pan; Tan Fu Lei; Wen Luh Yang; Chun Ming Cheng; Tien Sheng Chao

    2001-01-01

    In this letter, a method to grow high quality interpolysilicon-oxynitride (interpoly-oxynitride) film is proposed. Samples, nitridized by NH3 with additional N2O annealing and CVD TEOS deposited on poly-oxynitride (poly-I) with RTA N 2O oxidation, show excellent electrical properties in terms of very high electric breakdown field, low leakage current, high charge to breakdown, and low electron trapping rate. This novel

  1. Preparation of carbon supported cobalt by electrostatic adsorption of [Co(NH 3) 6]Cl 3

    Microsoft Academic Search

    L. D'Souza; J. R. Regalbuto; J. T. Miller

    2008-01-01

    Our previous paper [L. D'Souza, L. Jiao, J.R. Regalbuto, J.T. Miller, A.J. Kropf, J. Catal. 248 (2007) 165] presented the synthesis of cobalt catalysts on carbon (Timrex) and silica supports by strong electrostatic adsorption (SEA), using a cobalt hexaamine chloride ([Co(NH3)6]Cl3, CoHA) precursor. The CoHA undergoes reductive deammination in an uncontrolled manner in the presence of NaOH and adsorbs as

  2. Evolution of Zn based high purity phases under NH 3 gas atmosphere and their PL properties

    Microsoft Academic Search

    Waheed S. Khan; Chuanbao Cao; Faheem K. Butt; Zulfiqar Ali; M. Safdar; Liqing Pan; Qurrat ul Ain; Zahid Usman; Ghulam Nabi

    2011-01-01

    We report here the evolution of zinc based high purity phases with novel morphologies such as Zn3N2 hollow structures, ZnO nanowires and nanopowders, as well as metallic Zn layered hexagonal microparticles at progressively increased reaction temperature of 600°C, 700°C, 800°C under NH3 gas atmosphere using Zn powder precursor and keeping all other experimental parameters unchanged. Growth mechanism for Zn3N2 obtained

  3. Observation of orbiting resonances in He((3)S1) + NH3 Penning ionization.

    PubMed

    Jankunas, Justin; Jachymski, Krzysztof; Hapka, Micha?; Osterwalder, Andreas

    2015-04-28

    Resonances are among the clearest quantum mechanical signatures of scattering processes. Previously, shape resonances and Feshbach resonances have been observed in inelastic and reactive collisions involving atoms or diatomic molecules. Structure in the integral cross section has been observed in a handful of elastic collisions involving polyatomic molecules. The present paper presents the observation of shape resonances in the reactive scattering of a polyatomic molecule, NH3. A merged-beam study of the gas phase He((3)S1) + NH3 Penning ionization reaction dynamics is described in the collision energy range 3.3 ?eV < Ecoll < 10 meV. In this energy range, the reaction rate is governed by long-range attraction. Peaks in the integral cross section are observed at collision energies of 1.8 meV and 7.3 meV and are assigned to ? = 15,16 and ? = 20,21 partial wave resonances, respectively. The experimental results are well reproduced by theoretical calculations with the short-range reaction probability Psr = 0.035. No clear signature of the orbiting resonances is visible in the branching ratio between NH3 (+) and NH2 (+) formation. PMID:25933762

  4. Dynamics of CH3NH3PbI3 from first principles simulations

    NASA Astrophysics Data System (ADS)

    Kachmar, Ali; Carignano, Marcelo

    2015-03-01

    We address the dynamical and optical properties of CH3NH3PbI3 using molecular dynamics simulations based on forces calculated with density functional theory. We have studied the three stable phases of CH3NH3PbI3 but most of the effort was dedicated to the intermediate tetragonal phase, which is stable at standard ambient conditions. In this case, two different system sizes have been considered, one with 8 unit cells (384 atoms) and a larger one with 27 unit cells (1296 atoms). The total simulated time reached 40 ps. Our findings reveal the interplay between the thermal energy of the system and the electronic degrees of freedom. For example, the organic molecule undergoes relatively fast rotations and the energy band gap, approximated by the LUMO-HOMO energy difference, fluctuates around the equilibrium value of ~1.5 eV with a width of 0.2 eV. The rotation of the CH3NH3 molecule is not isotropic, and more importantly, it is quite sensitive to the size of the simulation box. Our study also provides a quantitative measure for the finite size effects affecting the calculated properties and provides a contextual scenario on which to analyze the more typical density functional theory studies based on static calculations on optimal structures. The authors acknowledge the HPC resources of Texas A&M University at Qatar.

  5. Exploring High-Velocity NH_3(6,6) Emission at the Center of our Galaxy

    E-print Network

    Jennifer L. Donovan; Robeson M. Herrnstein; Paul T. P. Ho

    2006-05-11

    Using the NH\\3 (6,6) transition, which samples dense ($\\sim 10^{5}$) molecular gas with an energy above ground of 412 K, we find hot gas at high velocities (--142 to --210 km s$^{-1}$) associated with the central 2 pc of the Galactic center. This material may be either infalling gas due to shocks or tidal stripping, or possibly gas swept from the nuclear region. We identify two high-velocity features, which we call the Southern Runner and the Cap, and correlate these features with others detected in various molecular observations of the Galactic center. The characteristic linewidths of the Southern Runner and Cap, 10 -- 15 \\kms, are similar to those of other hot Galactic center clouds. The estimated H$_{2}$ masses of these clouds are 4$\\times 10^{3}$ M$\\sol$ and 2$\\times 10^{3}$ M$\\sol$, consistent with the masses of the western streamer and northern ridge, NH\\3 (6,6) emission features detected within the central 10 pc at lower velocities. Three possible explanations for this emission are discussed assuming that they lie at the Galactic center, including sweeping by the supernova remnant Sgr A East, infall and/or shock from the circumnuclear disk (CND), and stripping from the central rotating low-velocity NH\\3 (6,6) cloud.

  6. Is there an entrance complex for the F+NH3 reaction?

    PubMed

    Feng, Hao; Sun, Weiguo; Xie, Yaoming; Schaefer, Henry F

    2011-11-01

    Challenges associated with the theoretical and experimental kinetics of the F+NH(3)?HF+NH(2) reaction suggest the need for a more-precise potential surface. We have investigated the reactants and the products of the reaction, as well as the transition state and two complexes, with rather rigorous ab initio methods. The F·····NH(3) complex existing in the entrance valley is predicted to lie 13.7 kcal mol(-1) below the reactants. A small classical barrier of 2.0 kcal mol(-1) separates this entrance well from products HF+NH(2). These results explain the observation by Persky of unprecedented inverse temperature dependence for the F+NH(3) rate constants. The strong hydrogen-bonded complex FH·····NH(2) exists in the exit valley, and with a binding energy of 9.9 kcal mol(-1) relative to separated products. The vibrational frequencies of all stationary points are predicted with the CCSD(T)/aug-cc-pVQZ method. PMID:21928432

  7. Kinetics of OCN- formation from the HNCO + NH3 solid-state thermal reaction

    NASA Astrophysics Data System (ADS)

    Mispelaer, F.; Theule, P.; Duvernay, F.; Roubin, P.; Chiavassa, T.

    2012-04-01

    Context. Solid-state features in infrared astronomical spectra can provide useful information on interstellar ices within different astrophysical environments. Solid OCN- has an absorption feature at 4.62 ?m, which is observed in star formation regions only with a large source-to-source abundance variation. Aims: We aim to investigate the thermal formation mechanism of solid OCN- from HNCO on the basis of kinetic arguments. Methods: We experimentally studied the kinetics of the low-temperature OCN- formation from the purely thermal reaction between HNCO and NH3 in interstellar ice analogs using Fourier transform infrared spectroscopy. We used a rate equation approach, a kinetic Monte Carlo approach and a gamma probability distribution approach to derive kinetic parameters from experimental data. Results: The kinetics can de divided into two-processes, a fast process corresponding to the chemical reaction, and a slow process that we interpret as the spatial orientation of the two reactants within the ice. The three approaches give the same results. The HNCO + NH3 ? OCN- + NH4+ reaction rate follows an Arrhenius law with an activation energy of 0.4 ± 0.1 kJ mol-1 (48 ± 12 K) and a pre-exponential factor of 0.0035 ± 0.0015 s-1. Conclusions: The present experiment has the important implication that the HNCO + NH3 reaction can account for the observed abundances of solid OCN- and the HNCO non detection in young stellar objects.

  8. VizieR Online Data Catalog: MSX high-contrast IRDCs with NH3 (Chira+,

    NASA Astrophysics Data System (ADS)

    Chira, R.-A.; Beuther, H.; Linz, H.; Walmsley, C. M.; Menten; K. M.; Bonfman, L.

    2013-02-01

    Based on MSX data, a catalogue of more than 10,000 candidate IRDCs was compiled. From this catalogue we selected a complete sample of northern hemisphere high-contrast IRDCs with Galactic longitudes >=19.27° (and nine exceptions with Galactic longitudes <19°). The sample was observed in ammonia (1,1) and (2,2) inversion transitions with the Effelsberg 100-m telescope. NH3 parameters are derived for 109 sample sources. For each source galactic coordinates, brightness temperatures, line width FWHMs and optical depths of (1,1) and (2,2) inversion lines and LSR velocity of (1,1) inversion line are given. Furthermore, we derived the rotation and kinetic temperatures, ammonia column densities, kinematic distances and virial masses using the NH3 data. In addition, notes about whether the sources being associated with Spitzer sources or not are given. Using ATLASGAL data, the 870 micron flux densities gas masses, virial parameters, H2 column densities and NH3 abundances are given. In addition, we listed the sample sources where no ammonia which did not fulfil our selection criteria. (4 data files).

  9. Electron paramagnetic resonance study of Cu(II) in the Cu(II) doped (NH4)2[Zn(NH3)2(CrO4)2] and (NH4)2[Cd(NH3)2(CrO4)2]: Orientational disorder of NH3 and dynamically induced structural change

    NASA Astrophysics Data System (ADS)

    Wang, D. M.; Kovacik, I.; Reijerse, E. J.; de Boer, E.

    1992-09-01

    Electron paramagnetic resonance (EPR) spectra recorded at X band on Cu(II) in the Cu(II) doped single crystals of (NH4)2[Zn(NH3)2(CrO4)2] and (NH4)2[Cd(NH3)2(CrO4)2] showed an unusual temperature dependence in the temperature range between 4.2 and 370 K. This unusual temperature dependence is attributed to the dynamics of NH3 molecules. It is concluded that NH3 undergoes an order-disorder transition. This transition occurs at 282±2 K (T*) for (NH4)2[Zn(NH3)2(CrO4)2] and at 300±5 K for (NH4)2[Cd(NH3)2(CrO4)2]. For temperatures above T* the EPR spectra are found independent of temperature. This observation indicates that the NH3 molecules behave as free rotors rotating about their threefold symmetry axis. As the temperature is lowered, the free rotation gradually becomes hindered which leads at T* to site doubling in the EPR spectra. The hindered rotation simultaneously induces a structural change at T* reducing the local symmetry at the Cu(II) site from C2/m to approximately Cs. In the temperature range between T* and about 80 K, the EPR spectra with the magnetic field perpendicular to the threefold axis of NH3 are temperature dependent, but those with the magnetic field parallel to the threefold axis remain unchanged. This behavior is qualitatively interpreted as being due to the torsional oscillation of NH3. At temperatures lower than 80 K, the NH3 molecules exhibit the torsional oscillation of the lowest state and accordingly, all the EPR spectra become temperature independent.

  10. Melting phase relations in the system H2O - NH3 at high pressure

    NASA Astrophysics Data System (ADS)

    Sugimura, E.; Hirose, K.; Komabayashi, T.; Ohishi, Y.; Hirao, N.; Dubrovinsky, L. S.

    2012-12-01

    The density models of Uranus and Neptune constrained by their gravitational moments from Voyager mission suggest that mantles of these planets may be predominantly comprised of water (H2O), methane (CH4), and ammonia (NH3). The impurities in pure water would greatly influence the phase relations in the water-rich system expected in the icy mantle, which must be known to construct a plausible planetary model. One of important effects of the impurity is on the liquidus temperature (Tliq), since it decides the actual presence of solid phase within the icy mantle. In order to determine Tliq in H2O-rich region of the H2O - CH4 - NH3 ternary system, the melting phase relations in the H2O - CH4 and H2O - NH3 systems must be accurately known. However, previous melting experiments on each binary system were limited to several gigapascals, thus need to be explored to higher P-T conditions for application in interiors of Uranus and Neptune. We have investigated high-pressure (P) and -temperature (T) melting phase relations in the H2O - NH3 system based on a combination of visual observation and angle-dispersive x-ray diffraction (XRD) measurements at BL10XU, SPring-8. High-P-T conditions were generated in an externally-resistive heated diamond anvil cell (DAC). Starting material was 20wt% NH3 aqueous solution whose composition was checked via Tliq of the solution measured in a DAC at near atmospheric pressure. The aqueous solution was loaded into a gold-lined hole in a preindented rhenium gasket in order to insulate the sample from rhenium. Pressure was determined from the unit-cell volume of gold liner. Melting and freezing of the sample were detected by monitoring disappearance/appearance of diffraction peaks of solid and diffuse scattering of liquids, as well as observing melting/crystallization of crystal grains under microscope. Up to 20 GPa at room temperature, in addition to ice VII, diffraction peaks of bcc-like phase, which is most likely to be the reported phase VI of ammonia monohydrate (AMH VI), were observed, although the diffraction peaks were either too broad or too few to specify its structure. When temperature was raised until diffuse scattering appeared, the diffraction peaks of AMH VI disappeared, indicating ice VII is the liquidus phase. Newly obtained Tliq were higher than all the exiting melting curves of pure H2O determined in externally-heated DAC by 50 K at 15 GPa at minimum. This contradicts the previous reports that the H2O - NH3 system is eutectic, i.e. Tliq of our sample should be lower than the melting temperature of the H2O end member. We will discuss possible sources for this discrepancy. We also propose a new phase diagram of the system H2O - NH3 and possible implications for the structure of the icy planets.

  11. Characterizing the influence of highways on springtime NO2 and NH3 concentrations in regional forest monitoring plots.

    PubMed

    Watmough, Shaun A; McDonough, Andrew M; Raney, Shanel M

    2014-07-01

    Highways are major sources of nitrogen dioxide (NO2) and ammonia (NH3). In this study, springtime NO2 and NH3 concentrations were measured at 17 Ontario Forest Biomonitoring Network (OFBN) plots using passive samplers. Average springtime NO2 concentrations were between 1.3 ?g m(-3) and 27 ?g m(-3), and NH3 concentrations were between 0.2 ?g m(-3) and 1.7 ?g m(-3), although concentrations measured in May (before leaf out) were typically twice as high as values recorded in June. Average NO2 concentrations, and to a lesser extent NH3, could be predicted by road density at all radii (around the plot) tested (500 m, 1000 m, 1500 m). Springtime NO2 concentrations were predicted for a further 50 OFBN sites. Normalized plant/lichen N concentrations were positively correlated with estimated springtime NO2 and NH3 concentrations. Epiphytic foliose lichen richness decreased with increasing NO2 and NH3, but vascular plant richness was positively related to estimated springtime NO2 and NH3. PMID:24747347

  12. Vehicle specific power approach to estimating on-road NH3 emissions from light-duty vehicles.

    PubMed

    Huai, Tao; Durbin, S Thomas D; Younglove, Ted; Scora, George; Barth, Matthew; Norbeck, Joseph M

    2005-12-15

    NH3 emissions from motor vehicles have been the subject of a number of recent studies due to their potential impact on ambient particulate matter (PM). Highly time-resolved NH3 emissions can be measured and correlated with specific driving events utilizing a tunable diode laser (TDL). It is possible to incorporate NH3 emissions with this new information into models that can be used to predict emissions inventories from vehicles. The newer generation of modal models are based on modal events, with the data collected at second-by-second time resolution, unlike the bag-based emission inventory models such as EMFAC and MOBILE. The development of an NH3 modal model is described in this paper. This represents one of the first attempts to incorporate vehicle NH3 emissions into a comprehensive emissions model. This model was used in conjunction with on-road driving profiles to estimate the emissions of SULEV, ULEV, and LEV vehicles to be 9.4 +/- 4.1, 21.8 +/- 5.2, and 34.9 +/- 6.0 mg/mi, respectively. We also implement this new NH3 model to predict and evaluate the NH3 emission inventory in the South Coast air basin (SoCAB). PMID:16475340

  13. VUV Photolysis of NH_3: a Matrix Isolation Study of the Molecular Interactions Between Amidogen Radical and Ammonia Molecules

    NASA Astrophysics Data System (ADS)

    Krim, L.; Zins, E. L.

    2013-06-01

    The presence of NH_3 in the interstellar medium is very promising in terms of possible exobiologically-relevant reactions. This is the reason why numerous laboratory investigations on reactions involving NH_3 were carried out in the context of astrochemistry. Among other reactions, the photolysis of NH_3 was widely investigated. IR spectroscopy in solid phase as well as in rare-gas matrices suggested the formation of NH_2 radicals. In most of these experiments, samples containing NH_3 were prepared at cryogenic temperatures and further irradiated. On the other hand, since the penetration of the photons inside the solid ices as well as inside matrices is limited, the concentration of the photoproducts is weak, thus hindering possible secondary reaction studies. Furthermore, in addition with ice-grain irradiations, in the interstellar clouds, the gaseous species may be subjected to irradiation during their condensation on ice grains. In order to reproduce this effect, instead of irradiating samples obtained by condensation of NH_3 or NH_3/Ne gases at low temperatures, we carried experiments in which irradiation was carried out during the sample deposition. Thus, the amidogen radical and complexes between this radical and ammonia molecules were prepared and isolated in a neon matrix. The formation of (NH_2)(NH_3), (NH_2)(NH_3)_2 and (NH_2)(NH_3)_3 was clearly established thanks to the comparison between the theoretical and the experimental vibrational frequencies. Thus, such ammonia-containing aggregates may be formed in the interstellar clouds. These complexes, as solvated radicals, may further react with carbon- and oxygen-containing species present on the surface of ice grains. Such reactions may be a first step toward the formation of prebiotic molecules.

  14. Moisture desorption rates from TATB formulations: experiments and kinetic models.

    PubMed

    Glascoe, Elizabeth A; Dinh, Long N; Small, Ward; Overturf, George E

    2012-06-01

    The rate of water desorption from PBX-9502, a formulation containing 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), is measured using temperature-programmed desorption and modeled using conventional kinetic modeling methods. The results of these studies show two stages of moisture release. At lower temperatures, the release is likely assisted by thermal expansion of the TATB and melting of the Kel-F binder. At higher temperatures, a considerable amount of water is released and is attributed to sublimation of the TATB, which exposes new surfaces for water desorption. PMID:22591128

  15. High sensitivity detection of NO2 and NH3 in air using chemical vapor deposition grown graphene

    NASA Astrophysics Data System (ADS)

    Yavari, Fazel; Castillo, Eduardo; Gullapalli, Hemtej; Ajayan, Pulickel M.; Koratkar, Nikhil

    2012-05-01

    We show that graphene films synthesized by chemical-vapor-deposition enables detection of trace amounts of nitrogen dioxide (NO2) and ammonia (NH3) in air at room temperature and atmospheric pressure. The gas species are detected by monitoring changes in electrical resistance of the graphene film due to gas adsorption. The sensor response time was inversely proportional to the gas concentration. Heating the film expelled chemisorbed molecules from the graphene surface enabling reversible operation. The detection limits of ˜100 parts-per-billion (ppb) for NO2 and ˜500 ppb for NH3 obtained using our device are markedly superior to commercially available NO2 and NH3 detectors.

  16. Adsorption and desorption of small molecules for the characterization of solid acids

    Microsoft Academic Search

    Hiromi Matsuhashi; Kazushi Arata

    2006-01-01

    The relative acid strength and acid amount of solid acids has been determined from the adsorption and desorption of small molecules, such as argon. The order of activation energy for desorption of Ar from a solid acid, determined using temperature-programmed desorption (TPD), is sulfated zirconia > Cs2.5H0.5PW12O40 > proton-type zeolites > silica–alumina. The adsorption isotherms were analyzed using Langmuir and Henry equations. The Henry-type adsorption isotherms

  17. Natural bond orbital analysis of molecular interactions: Theoretical studies of binary complexes of HF, H2O, NH3, N2, O2, F2, CO, and CO2 with HF, H2O, and NH3

    Microsoft Academic Search

    Alan E. Reed; Frank Weinhold; Larry A. Curtiss; David J. Pochatko

    1986-01-01

    The binary complexes of HF, H2O, NH3, N2, O2, F2, CO, and CO2 with HF, H2O, and NH3 have been studied by abinitio molecular orbital theory and natural bond orbital (NBO) analysis. Most of the complexes involving N2, O2, F2, CO, and CO2 are found to have both hydrogen-bonded and non-hydrogen-bonded structures. The NBO analysis provides a consistent picture of

  18. Natural bond orbital analysis of molecular interactions Theoretical studies of binary complexes of HF, H2O, NH3, O2, F2, CO, and CO2 with HF, H2O, and NH3

    Microsoft Academic Search

    A. E. Reed; F. Weinhold; L. A. Curtiss; D. J. Pochatko

    1986-01-01

    Ab initio molecular orbital theory and natural bond orbital analysis were applied to the binary complexes of HF, H2O, NH3, N2, O2, F2, CO and CO2 with HF, H2O and NH3. Both hydrogen-bonded and nonhydrogen-bonded structures were found for complexes involving N2, O2, F2, CO, and CO2; these structures were defined by NBO analysis of charge transfer, which is generally

  19. General aspects of the vapor growth of semiconductor crystals - A study based on DFT simulations of the NH3/NH2 covered GaN(0001) surface in hydrogen ambient

    NASA Astrophysics Data System (ADS)

    Kempisty, Pawe?; Strak, Pawe?; Sakowski, Konrad; Krukowski, Stanis?aw

    2014-03-01

    Vapor growth of semiconductors is analyzed using recently obtained dependence of the adsorption energy on the electron charge transfer between the surface adsorbed species and the bulk [Krukowski et al. J. Appl. Phys. 114 (2013) 063507, Kempisty et al. ArXiv1307.5778 (2013)]. Ab initio calculations were performed to study the physical properties of GaN(0001) surface in ammonia-rich conditions, i.e. covered by mixture of NH3 molecules and NH2 radicals. The Fermi level is pinned at valence band maximum (VBM) and conduction band minimum (CBM) for full coverage by NH3 molecules and NH2 radicals, respectively. For the crossover content of ammonia of about 25% monolayer (ML), the Fermi level is unpinned. It was shown that hydrogen adsorption energy depends on the doping in the bulk for the unpinned Fermi level, i.e. for this coverage. Surface structure thermodynamic and mechanical stability criteria are defined and compared. Mechanical stability of the coverage of such surfaces was checked by determination of the desorption energy of hydrogen molecules. Thermodynamic stability analysis indicates that initially equilibrium hydrogen vapor partial pressure steeply increases with NH3 content to attain the crossover NH3/NH2 coverage, i.e. the unpinned Fermi level condition. For such condition the entire range of experimentally accessible pressures belongs showing that vapor growth of semiconductor crystals occurs predominantly for unpinned Fermi level at the surface, i.e. for flat bands. Accordingly, adsorption energy of most species depends on the doping in the bulk that is based on the possible molecular scenario explaining dependence of the growth and the doping of semiconductor crystals on the doping in the bulk.

  20. Spectroscopic line parameters of NH3 and PH3 in the far infrared

    NASA Astrophysics Data System (ADS)

    Husson, N.; Goldman, A.; Orton, G.

    1982-05-01

    NH3 and PH3 rotation and rotation-inversion line parameters in the far to medium IR are calculated for remote sounding purposes of planetary atmospheres; 1607 lines of (N-14)H3, 362 lines of (N-15)H3 and 325 lines of PH3 are compiled. The absolute intensity formulation has been reviewed in the case of rotation and rotation-inversion lines of molecules with C(3v) symmetry. The justification for the general agreement between the authors, and comparisons with other published expressions are given.

  1. Role of phase composition for electronic states in CH3NH3PbI3 prepared from CH3NH3I/PbCl2 solution

    NASA Astrophysics Data System (ADS)

    Naikaew, Atittaya; Prajongtat, Pongthep; Lux-Steiner, Martha Ch.; Arunchaiya, Marisa; Dittrich, Thomas

    2015-06-01

    Modulated surface photovoltage (SPV) spectra have been correlated with the phase composition in layers of CH3NH3PbI3 (MAPbI3) prepared from MAI and PbCl2 and annealed at 100 °C. Depending on the annealing time, different compositions of MAPbI3, MAPbCl3, MACl, PbI2, and an un-identified phase were found. It has been demonstrated that evaporation of MAI and HI is crucial for the development of electronic states in MAPbI3 and that only the appearance and evolution of the phase PbI2 has an influence on electronic states in MAPbI3. With ongoing annealing, (i) a transition from p- to n-type doping was observed with the appearance of PbI2, (ii) shallow acceptor states were distinguished and disappeared in n-type doped MAPbI3, and (iii) a minimum of the SPV response related to deep defect states was found at the transition from p- to n-type doping. The results are discussed with respect to the further development of highly efficient and stable MAPbI3 absorbers for solar cells.

  2. DECHLORINATION OF PCBS, CAHS, HERBICIDES AND PESTICIDES NEAT AND IN SOILS AT 25&DEG;C USING NA/NH3. (R829421E01)

    EPA Science Inventory

    Na/NH3 reductions have been used to dehalogenate polychlorinated biphenyls (PCBs), chlorinated aliphatic hydrocarbons (CAHs) and pesticides at diffusion controlled rates at room temperature in model compound studies in both dry NH3 and when water was adde...

  3. Effect of NH3 on Film Properties of MOCVD Tungsten Nitride from Cl4,,CH3CN...W,,Ni

    E-print Network

    Anderson, Timothy J.

    Instrumentation Center, Department of Materials Science and Engineering, University of Florida, Gainesville deposition MOCVD in the presence and absence of ammonia (NH3) coreactant. Films were analyzed by X at lower deposition temperature increased film resistivity significantly. © 2004 The Electrochemical

  4. Shape of generation pulses and analytical characteristics of differential absorption lidar based on the NH3-CO2 laser

    NASA Astrophysics Data System (ADS)

    Leschenko, N. G.; Stepanov, V. A.; Yastrebkov, A. B.

    2003-06-01

    The method of differential absorption with scattering (DAS) for atmosphere probing by means of NH3-CO2 laser system on the two wavelengths of infrared region far separated from each other is reviewed. The most perspective scheme of remote probing of atmosphere by such method is determined. The efficiency of NH3-CO2 lidar in region 9 - 13 ?m is shown. There was found, that using of passive synchronization of longitudinal modes does not require corrections, taking into account the differences in the generation pulses shape of NH3 and CO2 lasers, if the analysis of a registered signal will be fulfilled on the front of a scattered radiation. The calculations of the probing sensitivity and remoteness on some components of atmosphere polluting, such as CCI4, NH3 and CFCl3 there carried out with lidar equation helping.

  5. Detection of a CO and NH3 gas mixture using carboxylic acid-functionalized single-walled carbon nanotubes

    PubMed Central

    2013-01-01

    Carbon nanotubes (CNT) are extremely sensitive to environmental gases. However, detection of mixture gas is still a challenge. Here, we report that 10 ppm of carbon monoxide (CO) and ammonia (NH3) can be electrically detected using a carboxylic acid-functionalized single-walled carbon nanotubes (C-SWCNT). CO and NH3 gases were mixed carefully with the same concentrations of 10 ppm. Our sensor showed faster response to the CO gas than the NH3 gas. The sensing properties and effect of carboxylic acid group were demonstrated, and C-SWCNT sensors with good repeatability and fast responses over a range of concentrations may be used as a simple and effective detection method of CO and NH3 mixture gas. PMID:23286690

  6. Self-assembly of TiO2\\/polypyrrole nanocomposite ultrathin films and application for an NH3 gas sensor

    Microsoft Academic Search

    Huiling Tai; Yadong Jiang; Guangzhong Xie; Junsheng Yu; Mingjing Zhao

    2007-01-01

    TiO2\\/polypyrrole (PPy) nanocomposite ultrathin films for NH3 gas detection were fabricated by the in situ self-assembly technique. The films were characterized by UV–Vis absorption, FT–IR spectroscopy, and atomic force microscopy (AFM). The electrical properties of TiO2\\/PPy ultrathin film NH3 gas sensors, such as sensitivity, selectivity, reproducibility, and stability were investigated at room temperature in air as well as in N2.

  7. N 2 O, NO, and NH 3 Emissions from Soil after the Application of Organic Fertilizers, Urea and Water

    Microsoft Academic Search

    Hiroko Akiyama; Iain P. McTaggart; Bruce C. Ball; Albert Scott

    2004-01-01

    Agricultural soil is a major source of nitrous oxide (N2O), nitric oxide (NO) and ammonia (NH3). Little information is available on emissions of these gases from soils amended with organic fertilizers at different soil water contents. N2O, NO and NH3 emissions were measured in large-scale incubations of a fresh sandy loam soil and amended with four organic fertilizers, [poultry litter

  8. Free NH 3 quantum rotations in Hofmann clathrates: structure factors and line widths studied by inelastic neutron scattering

    Microsoft Academic Search

    O. Sobolev; P. Vorderwisch; A. Desmedt

    2005-01-01

    Quantum rotations of NH3 groups in Hofmann clathrates Ni–Ni–C6H6 and Ni–Ni–C12H10 have been studied using inelastic neutron scattering. Calculations of the dynamical structure factor for a free uniaxial quantum rotor reproduce the neutron scattering data with respect to their Q- and T-dependence as well as the relative intensities for the 0?1, 0?2 and 1?2 transitions. Though the effective NH3 rotation

  9. FEASIBILITY OF FLUIDIZED-BED BIOREACTOR FOR REMEDIATING WASTE GAS CONTAINING H2S OR NH3

    Microsoft Academic Search

    Ying-Chien Chung; Chia-Ho Liu; Chihpin Huang

    2001-01-01

    Pseudomonas putida for H2S and Arthrobacter oxydans for NH3 were immobilized with Ca-alginate and packed inside glass columns to form fluidized-bed bioreactors. The feasibility of the lab-scale bioreactor for the treatment of H2S or NH3 was examined. Phosphate salt, being added to the nutrient solution as buffer solution, may chelate with Ca in the Ca-alginate beads, resulting in the disintegration

  10. Photolytic aerosol formation in SO 2?HNO 2?H 2O?AIR mixtures, with and without NH 3

    Microsoft Academic Search

    Lars Larsen; Beate Roth; Rita Van Dingenen; Frank Raes

    1997-01-01

    Atmospheric aerosol formation trough nucleation is commonly modelled using binary nucleation theory applied to the H2SO4?H2O mixture (e.g. Raes and Van Dingenen, 1992). Other nucleation pathways have been proposed, of which ternary nucleation of H2SO4, H2O and NH3 seems to be a likely candidate (Coffman and Hegg, 1995). In order to test the effect of NH3 on the nucleation of

  11. NH3-treated WO3 as low-cost and efficient counter electrode for dye-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Song, Dandan; Chen, Zhao; Cui, Peng; Li, Meicheng; Zhao, Xing; Li, Yaoyao; Chu, Lihua

    2015-01-01

    A novel low-cost and efficient counter electrode (CE) was obtained by treating catalytic inert tungsten trioxide (WO3) nanomaterial in NH3 atmosphere at elevated temperatures. The formation of tungsten oxynitride from WO3 after NH3 treatment, as evidenced by X-ray photoelectron spectroscopy and X-ray diffraction, increases the catalytic activity of the CE. Correspondingly, the power conversion efficiency (PCE) of the DSC is significantly increased from 0.9% for pristine WO3 CE to 5.9% for NH3-treated WO3 CE. The photovoltaic performance of DSC using NH3-treated WO3 CE is comparable to that of DSC using standard Pt CE (with a PCE of 6.0%). In addition, it is also shown that NH3 treatment is more efficient than H2 or N2 treatment in enhancing the catalytic performance of WO3 CE. This work highlights the potential of NH3-treated WO3 for the application in DSCs and provides a facile method to get highly efficient and low-cost CEs from catalytic inert metal oxides.

  12. Molecular tunneling dynamics of NH3D + in ammonium sulfate and ammonium thiocyanate

    NASA Astrophysics Data System (ADS)

    Burrows, Wes; Strauss, Herbert L.

    1993-10-01

    The kinetics of NH3D+ rotation in ammonium sulfate and ammonium thiocyanate are measured at low temperature (8-60 K). Infrared hole burning of the N-D stretching bands causes reorientation of the ions among distinct positions relative to the crystal lattice, producing nonequilibrium population distributions. The slow relaxation (time scale of minutes to hours) is monitored with a Fourier-transform infrared spectrometer as the ions tunnel back to their equilibrium distributions. Kinetic models are used to extract rate constants for rotation between orientations. The rate constants range from 0.01 h-1 at 8 K, to about 10 h-1 above 50 K. The higher temperature data is described by barrier transmission calculations with barrier heights of 1000 to 1600 cm-1. The low temperature data agrees with rates calculated from a phonon-assisted tunneling model for transitions between the ground states of the orientations, with energy differences between ground states on the order of 10 cm-1. Calculations of the tunneling rates between quantum states in a potential for the rotation of the NH3D+ ion in ammonium sulfate generated by a point-charge model are also performed and compared to the experimental results.

  13. Determining Surface-Adsorbate Binding Energies from Collision-Induced Desorption Experiments.

    NASA Astrophysics Data System (ADS)

    Szulczewski, Gregory John

    1995-01-01

    The work in this dissertation details the determination of surface-adsorbate bond energies from collision-induced desorption experiments. The collision-induced desorption experiment utilizes an intense, nearly monoenergetic beam of neutral, noble gas atoms to desorb surface bound molecules into the gas phase. A general equation derived from classical mechanics is used to calculate a physisorption or chemisorption bond energy from the threshold energy required to desorb an adsorbate from the surface. The first system studied in this dissertation is the collision-induced desorption of CH_4 physisorbed to Ni{111 } by energetic Ar atoms. A theory is presented to extract the bond energy for this system using a one -dimensional square well to model the Ni-CH_4 interaction. The threshold for desorption scales with the fraction of energy transferred from Ar to CH _4 along the direction of the surface normal. This model calculates the CH_4/Ni {111} bond energy to be 120 meV which is close to experimental value of 126 meV. The second investigation involves the collision -induced desorption of NH_3 chemisorbed on Pt{111}. The absolute cross sections for NH_3 desorption at 0.25 ML were measured by x-ray photoelectron spectroscopy as a function of Ar kinetic energy and incident angle. The threshold desorption energy, 1.95 eV, was independent of the Ar angle of incidence and suggests a strong lateral corrugation in the NH_3/Pt {111} interaction potential. The collision model calculates the NH_3/Pt {111} binding energy to be 1.45 eV. The third system probed by collision-induced desorption was the di-sigma configuration of rm C_2H_4 chemisorbed to Pt{111} at 90 K. An energetic Xe beam was used to desorb rm C_2H_4 and the threshold energy for desorption, 5.2 eV, was independent of the Xe angle of incidence. The model calculates the di-sigma binding energy to be 2.1 eV and predicts that rm C_2H_4 desorbs from the surface in a planar configuration. From this result a thermal desorption mechanism involving a radical intermediate for ethylene was proposed. This mechanism may provide new insight into the hydrogenation of olefins on metals surfaces.

  14. NH3, H2S, and the Radio Brightness Temperature Spectra of the Giant Planets

    NASA Technical Reports Server (NTRS)

    Spilker, Thomas R.

    1995-01-01

    Recent radio interferometer observations of Neptune enable comparisons of the radio brightness temperature (T(sub B)) spectra of all four giant planets. This comparison reveals evidence for fundamental differences in the compositions of Uranus' and Neptune's upper tropospheres, particularly in their ammonia (NH3) and hydrogen sulfide (H2S) mixing ratios, despite those planets' outward similarities. The tropospheric abundances of these constituents yield information about their deep abundances, and ultimately about the formation of the planets from the presolar nebula (Atreya et al.). Figures 1, 2, 3, and 4 show the T(sub B) spectra of Jupiter, Saturn, Uranus, and Neptune, respectively, from 0.1 to tens of cm wavelength. The data shown are collected from many observers. Data for Jupiter, Saturn, and Uranus are those cataloged by de Pater and Massie (1985), plus the Saturn Very Large Array (VLA) data by Grossman et al. Figure 3, Uranus, shows only data acquired since 1973. Before 1973 Uranus' T(sub B) increased steadily as its pole moved into view, causing significant scatter in those data. Neptune data at greater than 1 cm, all taken at the VLA, are collected from de Pater and Richmond, de Pater et al., and Hofstadter. For a variety of reasons, such as susceptibility to source confusion, single-dish data at those wavelengths are much noisier than the more reliable VLA data and have been ignored. Single-dish data by Griffin and Orton shortward of 0.4 cm are shown, along with the Owens Valley Radio Observatory (interferometer) datum at 0.266 cm by Muhleman and Berge. Spectra of Jupiter, Saturn, and Neptune share certain gross characteristics. In each spectrum, T(sub B) at 1.3 cm is approximately 120-140 K, less than approximately 30 K different from that at 0.1 cm. All three spectra show a break in slope at or near 1.3 cm, with T(sub B) increasing fairly rapidly with wavelength longward of 1.3 cm. Visible and IR spectroscopy show that NH3, whose strong inversion spectrum peaks at appropximately 1.3 cm, is an important tropospheric species at Jupiter and Saturn. Its signature on the Jovian radio spectrum is obvious, causing the prominent "hole" at 1.3 cm. At Saturn it is more subdued but is the source of that spectrum's change in slope at 1.3 cm. Radiative transfer models of Jupiter and Saturn with near-solar deep NH3 abundances agree well with the data (e.g., de Pater).

  15. Phase polymorphism of novel [Ru(NH3)6](ClO4)3—Comparison with [Ru(NH3)6](BF4)3. Part II

    NASA Astrophysics Data System (ADS)

    Do??ga, Diana; Mikuli, Edward; Górska, Natalia; Inaba, Akira; Ho?derna-Natkaniec, Krystyna; Nitek, Wojciech

    2013-08-01

    [Ru(NH3)6](ClO4)3 undergoes two phase transitions at: TC1=290.3 K and TC2=74.8 K , thus exhibits three crystalline phases in the temperature range of 5-310 K. For the detected phase transitions, thermal effects were determined. Fourier transform far- and middle-infrared spectra (FT-FIR and FT-MIR), recorded at 8-350 K, suggest that reorientational motions of the NH3 ligands are very fast (?R?10-12 s above TC1) and are significantly slowed down below TC2. X-ray single crystal diffraction (XRSCD) measurements revealed that in the high temperature phase (above TC1) the compound belongs to the cubic Fm3barm (No. 225) space group, whereas in the intermediate phase the unit cell parameter doubles and the space group is Ia3bar(No. 206). 1H NMR studies revealed that the following reorientational motions are liberated during heating: three-fold reorientation of NH3 ligands, three-fold reorientation of the entire [Ru(NH3)6]3+ cation, and isotropic reorientation of this cation. In the high temperature phase I the cations perform isotropic reorientations with the estimated activation energy equal to ca. 30.1 kJ mol-1. Comparison with adequate results obtained earlier for [Ru(NH3)6](BF4)3 and for other similar compounds was made and general regularities were drawn.

  16. Rotational excitation of para-NH3 by para-H2

    NASA Astrophysics Data System (ADS)

    Danby, G.; Flower, D. R.; Valiron, P.; Kochanski, E.; Kurdi, L.

    1987-03-01

    Quantum-mechanical close-coupling calculations have been performed on rotational energy transfer in collisions of para-ammonia with ground-state (j = 0) para-hydrogen. Rate coefficients are given for the temperature range T = 15-300 K. The calculations employed an ab initio potential energy surface derived from separate determinations of the SCF and dispersion energies. The MOLSCAT computer package was used to perform the scattering calculations. Comparison is made with the recent results of Billing and Diercksen (1985 and 1986), who adopted a semiclassical approach as well as a different potential. Conclusions on the accuracy of the potential surface are drawn from comparison with experimental microwave double resonance and pressure broadening work. The extent to which He behaves like ground-state para-He in collisions with NH3 is also investigated.

  17. Impacts of anthropogenic SOx, NOx and NH3 on acidification of coastal waters and shipping lanes

    NASA Astrophysics Data System (ADS)

    Hunter, Keith A.; Liss, Peter S.; Surapipith, Vanisa; Dentener, Frank; Duce, Robert; Kanakidou, Maria; Kubilay, Nilgun; Mahowald, Natalie; Okin, Greg; Sarin, Manmohan; Uematsu, Mitsuo; Zhu, Tong

    2011-07-01

    The acidification of the ocean by anthropogenic CO2 absorbed from the atmosphere is now well-recognized and is considered to have lowered surface ocean pH by 0.1 since the mid-18th century. Future acidification may lead to undersaturation of CaCO3 making growth of calcifying organisms difficult. However, other anthropogenic gases also have the potential to alter ocean pH and CO2 chemistry, specifically SOx and NOx and NH3. We demonstrate using a simple chemical model that in coastal water regions with high atmospheric inputs of these gases, their pH reduction is almost completely canceled out by buffering reactions involving seawater HCO3- and CO32- ions. However, a consequence of this buffering is a significant decrease in the uptake of anthropogenic CO2 by the atmosphere in these areas.

  18. Zwitterion formation in titan ice analogs: reaction between HC3N and NH3.

    PubMed

    Couturier-Tamburelli, Isabelle; Sessouma, Bintou; Chiavassa, Thierry; Piétri, Nathalie

    2012-11-01

    A zwitterion is formed in the laboratory at low temperatures in the solid phase from the thermal reaction of HC(3)N and NH(3). We report for the first time its infrared spectrum. We study its reaction using Fourier transform infrared spectroscopy. Its reaction rate is estimated to be k(T) = 2.9 × 10(5) exp(-2.3 ± 0.1 (kJ mol(-1))/RT). Calculations using density functional theory (B3LYP/6-31g**) are used to characterize all the species (complexes, zwitterions, and transition states) and are in good agreement with the infrared spectra. The structure of the zwitterion is determined planar and it is characterized by a N-C bond around 1.5 Å. PMID:23075265

  19. High NH2D/NH3 ratios in protostellar cores

    E-print Network

    Jennifer Hatchell

    2003-02-27

    Observations of low mass protostars which probe small enough size scales to be within likely CO depletion regions show the highest [NH2D]/[NH3] ratios yet measured, of 4--33%. These molecular D/H ratios are higher than those measured on larger scales, showing that deuterium fractionation increases towards protostellar cores. As in cold clouds, such high ratios can be produced by gas-phase ion-molecule chemistry in the presence of depletion. Grain surface chemistry is less likely to explain the deuterium enhancement, as it would require higher fractionation in ices than current models predict. The link between accretion, depletion and high molecular deuterium fractionation is strongly supported.

  20. Investigation of the stability of Co-doped apatite ionic conductors in NH 3

    NASA Astrophysics Data System (ADS)

    Headspith, D. A.; Orera, A.; Slater, P. R.; Young, N. A.; Francesconi, M. G.

    2010-12-01

    Hydrogen powered solid oxide fuel cells (SOFCs) are of enormous interest as devices for the efficient and clean production of electrical energy. However, a number of problems linked to hydrogen production, storage and transportation are slowing down the larger scale use of SOFCs. Identifying alternative fuel sources to act as intermediate during the transition to the full use of hydrogen is, therefore, of importance. One excellent alternative is ammonia, which is produced on a large scale, is relatively cheap and has the infrastructure for storage and transportation already in place. However, considering that SOFCs operate at temperatures higher than 500 °C, a potential problem is the interaction of gaseous ammonia with the materials in the cathode, anode and solid electrolyte. In this paper, we extend earlier work on high temperature reactions of apatite electrolytes with NH 3 to the transition metal (Co) doped systems, La 9.67Si 5CoO 26 and La 10(Si/Ge) 5CoO 26.5. A combination of PXRD, TGA and XAFS spectroscopy data showed a better structural stability for the silicate systems. Apatite silicates and germanates not containing transition metals tend to substitute nitride anions for their interstitial oxide anions, when reacted with NH 3 at high temperature and, consequentially, lower the interstitial oxide content. In La 9.67Si 5CoO 26 and La 10(Si/Ge) 5CoO 26.5 reduction of Co occurs as a competing process, favouring lower levels of nitride-oxide substitution.

  1. High Resolution Infrared and Microwave Spectra of NH3-HCCH and NH3-OCS Complexes: Studies of Weak C-H\\cdotsN Hydrogen Bond and Electric Multipole Interactions

    NASA Astrophysics Data System (ADS)

    Liu, Xunchen; Xu, Yunjie

    2011-06-01

    C-H\\cdotsN weak hydrogen bond is of much current interest. We report the first high resolution infrared spectroscopic study of a prototypical C-H\\cdotsN bonded system, i.e. NH3-HCCH, at the vicinity of the ?4 band of NH3. The spectrum has been recorded using an infrared spectrometer equipped with an astigmatic multipass cell aligned for 366 passes and a room temperature external cavity quantum cascade laser at the 6 ?m region. The perpendicular band spectrum of symmetric top rotor observed is consistent with the previous microwave and infrared studies at 3 ?m. We also extended the previous microwave measurement to higher J and K. For the related NH3-OCS complex, microwave spectrum of J up to 6 and infrared spectrum at the vicinity of the ?4 band of NH3 have been recorded and analyzed for the first time. Comparison has been made with the previously studied isoelectronic complexes such as NH3-N2O and NH3-CO2. The source of the difference will be discussed with the aid of ab initio calculations. G.T. Fraser, K.R. Leopold, and W. Klemperer, J. Chem. Phys. 80(4), 1423, (1984) G. Hilpert, G.T. Fraser, and A.S. Pine, J. Chem. Phys. 105(15), 6183, (1996) G.T. Fraser, D.D. Nelson, JR., G.J. Gerfen, and W. Klemperer, J. Chem. Phys. 83(11), 5442, (1985) G.T. Fraser, K.R. Leopold, and W. Klemperer, J. Chem. Phys. 81(6), 2577, (1984)

  2. Phase Polymorphism, Molecular Motions and Structural Changes in [Cr(NH3)6](ClO4)3

    NASA Astrophysics Data System (ADS)

    Mikuli, Edward; Górska, Natalia; Wróbel, Stanis?aw; ?ciesi?skic, Jacek; ?ciesi?ska, Ewa

    2007-04-01

    A phase transition in [Cr(NH3)6](ClO4)3 at Thc = 293.5 K (on heating) and Tcc = 293.0 K (on cooling) was determined by differential scanning calorimetry. The temperature dependences of the full width at half maximum of the bands connected with ?r(NH3)F1u and ?d(ClO)E modes suggest that the discovered phase transition is not connected with drastic changes in the speed of reorientational motions of the NH3 ligands nor the ClO4 - anions. Temperature dependence of the FT-FIR spectra and the diffraction patterns show that the discovered phase transition is caused by a change in the crystal structure.

  3. Revealing the role of organic cations in hybrid halide perovskite CH3NH3PbI3

    NASA Astrophysics Data System (ADS)

    Motta, Carlo; El-Mellouhi, Fedwa; Kais, Sabre; Tabet, Nouar; Alharbi, Fahhad; Sanvito, Stefano

    2015-04-01

    The hybrid halide perovskite CH3NH3PbI3 has enabled solar cells to reach an efficiency of about 20%, demonstrating a pace for improvements with no precedents in the solar energy arena. Despite such explosive progress, the microscopic origin behind the success of such material is still debated, with the role played by the organic cations in the light-harvesting process remaining unclear. Here van der Waals-corrected density functional theory calculations reveal that the orientation of the organic molecules plays a fundamental role in determining the material electronic properties. For instance, if CH3NH3 orients along a (011)-like direction, the PbI6 octahedral cage will distort and the bandgap will become indirect. Our results suggest that molecular rotations, with the consequent dynamical change of the band structure, might be at the origin of the slow carrier recombination and the superior conversion efficiency of CH3NH3PbI3.

  4. Doping effect on the adsorption of NH3 molecule onto graphene quantum dot: From the physisorption to the chemisorption

    NASA Astrophysics Data System (ADS)

    Seyed-Talebi, Seyedeh Mozhgan; Beheshtian, J.; Neek-amal, M.

    2013-09-01

    The adsorption of ammonia molecule onto a graphene hexagonal flake, aluminum (Al) and boron (B) doped graphene flakes (graphene quantum dots, GQDs) are investigated using density functional theory. We found that NH3 molecule is absorbed to the hollow site through the physisorption mechanism without altering the electronic properties of GQD. However, the adsorption energy of NH3 molecule onto the Al- and B-doped GQDs increases with respect GQD resulting chemisorption. The adsorption of NH3 onto the Al-doped and B-doped GQDs makes graphene locally buckled, i.e., B- doped and Al-doped GQDs are not planar. The adsorption mechanism onto a GQD is different than that of graphene. This study reveals important features of the edge passivation and doping effects of the adsorption mechanism of external molecules onto the graphene quantum dots.

  5. Re-analysis of the ? of NH3 in C/2002 LINEAR T7 Using CSHELL at the NASA IRTF

    NASA Astrophysics Data System (ADS)

    Magee-Sauer, Karen P.; Villanueva, G. L.; Mumma, M. J.; Bonev, B.; DiSanti, M. A.; Dello Russo, N.; Lippi, M.; Gibb, E. L.

    2008-09-01

    NH3 is the dominant (observable) nitrogen-containing volatile in comets, present at 1% relative to water. At infrared wavelengths, NH3 (?1 band) is difficult to detect since it requires a significant geocentric velocity to shift the strongest NH3 emissions (Q-branch) out of the terrestrial atmospheric water absorption. The P- and R- branches are less dependent on geocentric velocity, but since they are generally weaker lines, they are challenging to detect. The 3-micron region is rich in molecular emissions (HCN, OH, H2O, C2H2, NH2, and other minor species), so that for many lines of the P- and R- branches, the ability to resolve these faint emissions from nearby brighter emission lines requires careful spectral registration of images. Previously, we applied and tested our model of fluorescence efficiency factors for NH3 in C/2002 T7 (LINEAR). The high Doppler shift (- 66 km/s) of C/T7 during early May 2004 made it an excellent target for searching for NH3 through its strongest IR emission lines. While the Q-branch lines were detected with high signal to noise, the sQ33 line of NH3 was on the wing of a deep atmospheric absorption. Other lines were fainter and near brighter emissions or atmospheric absorptions. The ability to accurately use the sQ33 emission and P- and R-branch lines, we discovered that our atmospheric model and algorithms needed improvement. Upgrades to our algorithms include an improved spectral transmittance model and spectral registration routines (Villanueva et al. 2006). This work will present a re-analysis of the 3-micron region from the high quality data set of C/2002 LINEAR T7 using the improved atmospheric transmittance models and data analysis algorithms from Villanueva et al. KM-S would like to acknowledge support from the National Science Foundation RUI Program No. 0407052.

  6. Emission factor of ammonia (NH3) from on-road vehicles in China: tunnel tests in urban Guangzhou

    NASA Astrophysics Data System (ADS)

    Liu, Tengyu; Wang, Xinming; Wang, Boguang; Ding, Xiang; Deng, Wei; Lü, Sujun; Zhang, Yanli

    2014-05-01

    Ammonia (NH3) is the primary alkaline gas in the atmosphere that contributes to formation of secondary particles. Emission of NH3 from vehicles, particularly gasoline powered light duty vehicles equipped with three-way catalysts, is regarded as an important source apart from emissions from animal wastes and soils, yet measured emission factors for motor vehicles are still not available in China, where traffic-related emission has become an increasingly important source of air pollutants in urban areas. Here we present our tunnel tests for NH3 from motor vehicles under ‘real world conditions’ in an urban roadway tunnel in Guangzhou, a central city in the Pearl River Delta (PRD) region in south China. By attributing all NH3 emissions in the tunnel to light-duty gasoline vehicles, we obtained a fuel-based emission rate of 2.92 ± 0.18 g L-1 and a mileage-based emission factor of 229.5 ± 14.1 mg km-1. These emission factors were much higher than those measured in the United States while measured NO x emission factors (7.17 ± 0.60 g L-1 or 0.56 ± 0.05 g km-1) were contrastingly near or lower than those previously estimated by MOBILE/PART5 or COPERT IV models. Based on the NH3 emission factors from this study, on-road vehicles accounted for 8.1% of NH3 emissions in the PRD region in 2006 instead of 2.5% as estimated in a previous study using emission factors taken from the Emission Inventory Improvement Program (EIIP) in the United States.

  7. The Bonding of NO2, NH3, and CH2NY to Models of a (10,0) Carbon Nanotube

    NASA Technical Reports Server (NTRS)

    Walch, Stephen P.

    2004-01-01

    We have studied the bonding of NO2, NH3, and CH2NH to a (10,O) carbon nanotube using the MP2 and ONIOM methods with extended basis sets. We find bond strengths of 3.5, 3.6. and 6.3 kcal/mol for NO2, NH3, and CH2NH, respectively, using the ONIOM method with the high accuracy part treated at the MP2/aug-CC-pVTZ level and the remainder of the CNT approximated at the UFF level and including an estimate of basis set superposition error using the counterpoise method.

  8. Atomic layer deposition of SiO 2 at room temperature using NH 3-catalyzed sequential surface reactions

    Microsoft Academic Search

    J. W. Klaus; S. M. George

    2000-01-01

    Ultrathin SiO2 films were deposited at 300–338K with atomic layer control using NH3-catalyzed sequential surface reactions. The SiO2 deposition was achieved by splitting the reaction SiCl4+2H2O?SiO2+4HCl into two separate SiCl4 and H2O half-reactions. Successive application of the half-reactions in an ABAB… sequence produced atomic layer controlled SiO2 growth. The NH3 catalyst dramatically lowered the necessary deposition temperature from >600 to

  9. Leaching kinetics of low grade zinc oxide ore in NH 3 NH 4 Cl-H 2 O system

    Microsoft Academic Search

    Rui-xiang Wang; Mo-tang Tang; Sheng-hai Yang; Wen-hai Zhagn; Chao-bo Tang; Jing He; Jian-guang Yang

    2008-01-01

    The leaching kinetics of low grade zinc oxide ore in NH3-NH4Cl-H2O system was studied. The effects of ore particle size, reaction temperature and the sum concentration of ammonium ion and\\u000a ammonia on the leaching efficiency of zinc were examined. The leaching kinetics of low-grade zinc oxide ore in NH3-NY4Cl-H2O system follows the kinetic law of shrinking-core model. The results show

  10. Observation of DCl and upper limit to NH3 on Venus

    NASA Astrophysics Data System (ADS)

    Krasnopolsky, Vladimir

    2012-05-01

    To search for DCl in the Venus atmosphere, a spectrum near the D35Cl (1-0) R4 line at 2141.54 cm-1 was observed using the CSHELL spectrograph at NASA IRTF. Least square fitting to the spectrum by a synthetic spectrum results in a DCl mixing ratio of 17.8 ± 6.8 ppb. Comparing to the HCl abundance of 400 ± 30 ppb (Krasnopolsky [2010a] Icarus, 208, 314-322), the DCl/HCl ratio is equal to 280 ± 110 times the terrestrial D/H = 1.56 × 10-4. This ratio is similar to that of HDO/H2O = 240 ± 25 times the terrestrial HDO/H2O from the VEX/SOIR occultations at 70-110 km. Photochemistry in the Venus mesosphere converts H from HCl to that in H2O with a rate of 1.9 × 109 cm-2 s-1 (Krasnopolsky [2012] Icarus, 218, 230-246). The conversion involves photolysis of HCl; therefore, the photochemistry tends to enrich D/H in HCl and deplete in H2O. Formation of the sulfuric acid clouds may affect HDO/H2O as well. The enriched HCl moves down by mixing to the lower atmosphere where thermodynamic equilibriums for H2 and HCl near the surface correspond to D/H = 0.71 and 0.74 times that in H2O, respectively. Time to establish these equilibriums is estimated at ˜3 years and comparable to the mixing time in the lower atmosphere. Therefore, the enriched HCl from the mesosphere gives D back to H2O near the surface. Comparison of chemical and mixing times favors a constant HDO/H2O up to ˜100 km and DCl/HCl equal to D/H in H2O times 0.74. Ammonia is an abundant form of nitrogen in the reducing environments. Thermodynamic equilibriums with N2 and NO near the surface of Venus give its mixing ratio of 10-14 and 6 × 10-7, respectively. A spectrum of Venus near the NH3 line at 4481.11 cm-1 was observed at NASA IRTF and resulted in a two-sigma upper limit of 6 ppb for NH3 above the Venus clouds. This is an improvement of the previous upper limit by a factor of 5. If ammonia exists at the ppb level or less in the lower atmosphere, it quickly dissociates in the mesosphere and weakly affects its photochemistry.

  11. Calculation of structural and spectroscopic parameters of trans-DONO and the NH3···trans-DONO complex. Comparison with analogous parameters of trans-HONO and NH3···trans-HONO.

    PubMed

    Bulychev, Valentin P; Buturlimova, Marina V; Tokhadze, Irina K; Tokhadze, Konstantin G

    2014-08-28

    The frequencies and absolute intensities for transitions between vibrational states of trans-DONO and NH3···trans-DONO are calculated using the approach earlier tested in calculations of trans-HONO and NH3···trans-HONO. The spectroscopic parameters were obtained in the harmonic approximation and from variational solutions of anharmonic Schrödinger equations in one to four dimensions with accurate potential energy and dipole moment surfaces. The calculated frequencies of trans-DONO are in good agreement with the experimental data. Our intensity values for trans-DONO and the frequencies and intensities for NH3···trans-DONO can be useful in interpretation of future experiments. Comparison of the transition frequencies and intensities and the averaged values of O-H (O-D) and N···O distances calculated for trans-DONO and its complex with ammonia with analogous parameters of trans-HONO and NH3···trans-HONO provides information about diverse isotope effects. For example, on H/D substitution the fundamental intensity for the ?2(N?O) mode of the lighter complex increases by a factor of 2.7, and the ?1 transition goes out of resonance with the 2?3 overtone. PMID:25090019

  12. Crystal structure of NH3-dependent NAD+ synthetase from Bacillus subtilis.

    PubMed Central

    Rizzi, M; Nessi, C; Mattevi, A; Coda, A; Bolognesi, M; Galizzi, A

    1996-01-01

    NAD+ synthetase catalyzes the last step in the biosynthesis of nicotinamide adenine dinucleotide. The three-dimensional structure of NH3-dependent NAD+ synthetase from Bacillus subtilis, in its free form and in complex with ATP, has been solved by X-ray crystallography (at 2.6 and 2.0 angstroms resolution, respectively) using a combination of multiple isomorphous replacement and density modification techniques. The enzyme consists of a tight homodimer with alpha/beta subunit topology. The catalytic site is located at the parallel beta-sheet topological switch point, where one AMP molecule, one pyrophosphate and one Mg2+ ion are observed. Residue Ser46, part of the neighboring 'P-loop', is hydrogen bonded to the pyrophosphate group, and may play a role in promoting the adenylation of deamido-NAD+ during the first step of the catalyzed reaction. The deamido-NAD+ binding site, located at the subunit interface, is occupied by one ATP molecule, pointing towards the catalytic center. A conserved structural fingerprint of the catalytic site, comprising Ser46, is very reminiscent of a related protein region observed in glutamine-dependent GMP synthetase, supporting the hypothesis that NAD+ synthetase belongs to the newly discovered family of 'N-type' ATP pyrophosphatases. Images PMID:8895556

  13. Near-infrared spectroscopy of LiNH3: First observation of the electronic spectrum

    NASA Astrophysics Data System (ADS)

    Varriale, Luigi; Bhalla, Nitika; Tonge, Nicola M.; Ellis, Andrew M.; Wright, Timothy G.

    2011-03-01

    Electronic spectra of LiNH3 and its partially and fully deuterated analogues are reported for the first time. The spectra have been recorded in the near-infrared and are consistent with two electronic transitions in close proximity, the tilde A2E-tilde X2A1 and tilde B2A1-tilde X2A1 systems. Vibrational structure is seen in both systems, with the Li-N-H bending vibration (?6) dominant in the tilde A2E-tilde X2A1 system and the Li-N stretch (?3) in the tilde B2A1-tilde X2A1 system. The prominence of the 6_0^1 band in the tilde A2E-tilde X2A1 spectrum is attributed to Herzberg-Teller coupling. The proximity of the tilde B2A1 state, which lies a little more than 200 cm-1 above the tilde A^2E state, is likely to be the primary contributor to this strong vibronic coupling.

  14. Electronic Structure Evolution of Fullerene on CH3NH3PbI3

    NASA Astrophysics Data System (ADS)

    Wang, Chenggong; Wang, Congcong; Liu, Xiaoliang; Bi, Cheng; Shao, Yuchuan; Xiao, Zhengguo; Huang, Jinsong; Gao, Yongli

    2015-03-01

    The thickness dependence of fullerene on CH3NH3PbI3 perovskite film surface has been investigated by using ultraviolet photoemission spectroscopy (UPS), X-ray photoemission spectroscopy (XPS) and inverse photoemission spectroscopy (IPES). The lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) can be observed directly with IPES and UPS. It is observed that the HOMO level in fullerene shifts to lower binding energy. The XPS results show an initial shift of core levels to lower binding energy in the perovskite, which indicates that electrons transfer from the perovskite film to fullerene molecules. We observed that the WF of the perovskite is 5.0 eV and the VBM is 0.6 eV. The band gap of the perovskite is 1.66 eV, which is in accordance with previous reports. We also observed the HOMO level of C60 shifts to lower binding energy, indicating a band bending in the C60 region. The perovskite core levels show a strong initial shift to lower binding energy, indicating electron transfer from the perovskite film to fullerene molecules. The strongest electron transfer happened at 1/4 monolayer of fullerene, and further deposition reduced the transfer as forms fullerene forms C60 solid film. NSF CBET-1437656.

  15. Performance Analysis of Rectifier in NH3-H2O Absorprtion Heat Pump

    NASA Astrophysics Data System (ADS)

    Tsujimori, Atsushi; Ozaki, Eiichi; Nakao, Kazushige

    Heat and mass transfer model for plate-type rectifier was presented in the previous paper and it was found that there existed the distribution of NH3 concentration in boundary layer in vapor and solution phase, which was the resistance to heat and mass transfer. In order to enhance heat and mass transfer, packed tower-type rectifiers have been considered effective and used in the field of chemical engineering. And many data have been accumulated for each rectification-packing with give fluid to design packed tower. But it has rarely be seen to present heat and mass transfer model in order to evaluate the performance of packed tower rectifier without any experimental constant. In this study heat and mass transfer model in packed tower-type rectifier was presented considering the specification of rectification-packing decided by surface area and porosity, and the calculation results were compared with experimental data. As a result it was found that over-all mass transfer coefficient increased as mass flow rate of vapor increased and that the model could expect over-all mass transfer coefficient within 30 [%] difference to experimental data. It was also cleared that mass transfer in packed-type rectifier was two to five times more enhanced than that in plate-type rectifier.

  16. The NH3 Hyperfine Intensity Anomaly in High-Mass Star-Forming Regions

    NASA Astrophysics Data System (ADS)

    Camarata, Matthew A.; Jackson, James M.; Chambers, Edward

    2015-06-01

    Anomalous ammonia (NH3) spectra, exhibiting asymmetric hyperfine satellite intensity profiles in the (J,K) = (1, 1) inversion transition, have been observed in star-forming regions for over 35 years. We present a systematic study of this “hyperfine intensity anomaly” (HIA) toward a sample of 334 high-mass star forming regions: 310 high-mass (?100 {{M}? }) clumps and 24 infrared dark clouds. The HIA is ubiquitous in high-mass star forming regions. Although LTE excitation predicts that the intensity ratios of the outer satellites and inner satellites are exactly unity, for this sample the ensemble average ratios are 0.812 ± 0.004 and 1.125 ± 0.005, respectively. We have quantified the HIA and find no significant relationships between the HIA and temperature, line width, optical depth, and the stage of stellar evolution. The fact that HIAs are common in high-mass star-forming regions suggests that the conditions that lead to HIAs are ubiquitous in these regions. A possible link between HIAs and the predictions of the competitive accretion model of high-mass star formation is suggested; however, the expected trends of HIA strength with clump evolutionary stage, rotational temperature, and line width for evolving cores in competitive accretion models are not found. Thus, the exact gas structures that produce HIAs remain unknown. Turbulent gas structures are a possible explanation, but the details need to be explored.

  17. The efficiency limit of CH3NH3PbI3 perovskite solar cells

    NASA Astrophysics Data System (ADS)

    Sha, Wei E. I.; Ren, Xingang; Chen, Luzhou; Choy, Wallace C. H.

    2015-06-01

    With the consideration of photon recycling effect, the efficiency limit of methylammonium lead iodide (CH3NH3PbI3) perovskite solar cells is predicted by a detailed balance model. To obtain convincing predictions, both AM 1.5 spectrum of Sun and experimentally measured complex refractive index of perovskite material are employed in the detailed balance model. The roles of light trapping and angular restriction in improving the maximal output power of thin-film perovskite solar cells are also clarified. The efficiency limit of perovskite cells (without the angular restriction) is about 31%, which approaches to Shockley-Queisser limit (33%) achievable by gallium arsenide (GaAs) cells. Moreover, the Shockley-Queisser limit could be reached with a 200 nm-thick perovskite solar cell, through integrating a wavelength-dependent angular-restriction design with a textured light-trapping structure. Additionally, the influence of the trap-assisted nonradiative recombination on the device efficiency is investigated. The work is fundamentally important to high-performance perovskite photovoltaics.

  18. Photochemical reactions in interstellar grains photolysis of CO, NH3, and H2O

    NASA Technical Reports Server (NTRS)

    Agarwal, V. K.; Ferris, J. P.; Schutte, W.; Greenberg, J. M.; Briggs, R.

    1985-01-01

    The interstellar grains are currently considered to be the basic building blocks of comets and, possibly, meteorites. To test this theory, a simulation of the organic layer accreted onto interstellar dust particles was prepared by slow deposition of a CO:NH3:H2O gas mixture on an Al block at 10 K, with concomitant irradiation with vacuum UV. The results of the HPLC and IR analyses of the nonvolatile residue formed by photolysis at 10 K are compared with those observed at 77 K and 298 K. Some of the compounds that may be present on the surfaces of interstellar dust particles have been identified, and some specific predictions concerning the types of molecular species present in comets could be drawn. The results also suggest that photochemical reactions may have been important for the formation of meteorite components. The implication of the findings to the questions of the source of organic matter on earth and the origin of life are discussed.

  19. Quasielastic neutron scattering of -NH3 and -BH3 rotational dynamics in orthorhombic ammonia borane

    SciTech Connect

    Hess, Nancy J.; Hartman, Michael R.; Brown, Craig; Mamontov, Eugene; Karkamkar, Abhijeet J.; Heldebrant, David J.; Daemen, Luke L.; Autrey, Thomas

    2008-06-27

    Neutrons scattering techniques are ideally suited to directly probe H in materials due to the large incoherent scattering cross-section of hydrogen atom, and have been invaluable in providing direct insight into the local fluctuations and large amplitude motions in AB. Dihydrogen bonding may have a significant affect on materials to be used to store hydrogen for fuel-cell powered applications. We have noticed a trend of low temperature release of H2 in materials composed of hydridic and protonic hydrogen. This phenomenon has caught our attention and motivated our interest to gain more insight into dihydrogen bonding interactions in AB. We present results from a thorough Quasielastic Neutron Scattering (QENS) investigation of diffusive hydrogen motion in NH311BH3 and ND311BH3 to obtain (1) a direct measure of the rotational energy barriers the protonated species and (2) a confirmation of the 3-site jump model for rotational motion. The amplitude of the energy barrier of rotation of BH3 and NH3 determined by QENS are compared to those determined for BD3 and ND3 determined by 2H NMR studies.

  20. Analysis of desorption species from MOS structure surfaces induced by gate voltages

    NASA Astrophysics Data System (ADS)

    Hirota, Nozomu; Hattori, Ken; Daimon, Hiroshi

    2014-03-01

    Hot carriers, which have energies over the Fermi level, are able to activate surface reaction. A MOS structure is able to generate tunable hot carriers under gate bias-voltages, would be suitable for the hot-carrier injection to surface from the metal side, but not vacuum side. In this research, I desire to make a proposition of catalytic devices using MOS structures. Desorption is one of the important paths in catalytic reaction, and would be observed when the bais-voltage is applied. We found desorption on N2O exposed MOS (Fe/SiO2/ p-Si) structure, detected by a mass spectrometer. The desorption were observed only when the metal surface was in negative polarity, the hole injection. The desorption of CH4 molecules was confirmed by mass analysis with cracking corrections. Since non-polar molecules (e.g., CH4) are hard to adsorb, the origin of CH4 is not adsorbed one as the molecule, but the catalytic reaction. At the same time, NH3 and H2O background intensities decreased. We consider the following scenario. The CH4 is generated from CO and adsorbed H over FexNy/SiO2 surface with hot-carrier activation. The CH4 formation inhibit H2O and NH3 suitable generation via decrease adsorbed H concentration. Most of desorption species can be expl

  1. Selective catalytic reduction of NOx with NH3 over a Cu-SSZ-13 catalyst prepared by a solid state ion exchange method

    SciTech Connect

    Wang, Di; Gao, Feng; Peden, Charles HF; Li, Junhui; Kamasamudram, Krishna; Epling, William S.

    2014-10-28

    A novel solid state method was developed to synthesize Cu-SSZ-13 catalysts with excellent NH3-SCR performance and durable hydrothermal stability. After the solid state ion exchange (SSIE) process, the SSZ framework structure and surface area was maintained. In-situ DRIFTS and NH3-TPD experiments provide evidence that isolated Cu ions were successfully exchanged into the pores, which are the active centers for the NH3-SCR reaction.

  2. Measurements of NH3 and CO2 with distributed-feedback diode lasers near 2.0 m in bioreactor vent gases

    E-print Network

    -feedback diode-laser sensors operating near 2 m. Calculated spectra of NH3 and CO2 were used to determine of a diode-laser sensor used to record gas-phase NH3 and CO2 mole fractions, ex- plain the motivationMeasurements of NH3 and CO2 with distributed-feedback diode lasers near 2.0 m in bioreactor vent

  3. Surface-exchange of NOx and NH3 above a winter wheat field in the Yangtze Delta, China.

    PubMed

    Fang, Shuang-xi; Zhang, Yi; Mu, Yu-jing

    2006-01-01

    A four-dynamic-chamber system was constructed to measure NOx and NH3 surface-exchange between a typical wheat field and the atmosphere in the Yangtze Delta, China. The average fluxes ofNO, NO2 and NH3 were 79, -5.6 and -5.1 ngN/(m2 x s), and 91, -1.8 and 23 ngN/(m2 x s), respectively for the wheat field and the bare soil. The NO flux was positively correlated with soil temperature and the fluxes of NO2 and NH3 were negatively correlated with their ambient concentrations during the investigated period. The compensation point of NO2 between the wheat field and the atmosphere was 11.9 microg/m3. The emissions of NO-N and NH3-N from the urea applied to the wheat field were 2.3% and 0.2%, respectively, which indicated that the main pathway of N loss from the investigated winter wheat field was NO. Application of a mixture of urea and lignin increased the emissions of NO, but also greatly increased the yield of the winter wheat. PMID:17078547

  4. Ab initio simulation of ammonia monohydrate ,,NH3"H2O... and ammonium hydroxide ,,NH4OH...

    E-print Network

    Vocadlo, Lidunka

    Ab initio simulation of ammonia monohydrate ,,NH3"H2O... and ammonium hydroxide ,,NH4OH... A. D pseudopotential plane-wave simulations of the static properties of ammonia monohydrate phase I AMH I and ammonium hydroxide. Our calculated fourth-order logarithmic equation of state, at zero pressure and temperature, has

  5. Proton transfer dynamics of the reaction H3O ,,NH3 ,H2O...NH4

    E-print Network

    Farrar, James M.

    Proton transfer dynamics of the reaction H3O¿ ,,NH3 ,H2O...NH4 ¿ studied using the crossed, Rochester, New York 14627 Received 29 September 2003; accepted 8 October 2003 The proton transfer reaction combination. These results indicate that the proton transfer proceeds through a direct reaction mechanism

  6. Surface modification of polypropylene microporous membranes to improve their antifouling property in MBR: NH 3 plasma treatment

    Microsoft Academic Search

    Hai-Yin Yu; Meng-Xin Hu; Zhi-Kang Xu; Jian-Li Wang; Shu-Yuan Wang

    2005-01-01

    To improve the antifouling property of polypropylene hollow fiber microporous membranes (PPHFMMs) in a membrane bioreactor (MBR) for wastewater treatment, PPHFMMs were subjected to surface modification by NH3 plasma treatment. Structural and morphological changes of the membranes were characterized by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Water contact angle, which reflects the hydrophilicity of the membrane surface,

  7. DFT study of coverage-depended adsorption of NH3 on TiO2-B (100) surface.

    PubMed

    Guo, Xiao-Jing; Liu, Weijia; Fang, Wei; Cai, Lu; Zhu, Yudan; Lu, Linghong; Lu, Xiaohua

    2012-12-28

    A previous study showed that TiO(2)-B (100) surface is very unique. It is characterised by high activity and a loose structure. In this study, we studied the adsorption of ammonia on TiO(2)-B (100) surface at coverages ranging from 1/6 ML to 1 ML using ab initio density functional calculations. We also investigated the adsorption of an isolated ammonia molecule on TiO(2)-B (001) surface to compare the different activities of TiO(2)-B (100) and (001) surfaces towards NH(3). The results showed that the TiO(2)-B (100) surface is more reactive towards NH(3) molecule than TiO(2)-B (001) surface, and the Lewis acid site on TiO(2)-B (100) surface is more acidic. The decrease rate of the average molecular adsorption energy of NH(3) with coverage on TiO(2)-B (100) surface is substantially lower than that on a rutile (011) surface above 1/2 ML coverage due to the open structure of TiO(2)-B (100) surface. The average molecular adsorption energy shows a linear dependence on the coverage of y = 111.0 - 36.3x on TiO(2)-B (100) surface. The possibility of NH(3) molecule onto the Ti(5c) site is nearly equal to forming a dimer with adsorbed NH(3) on TiO(2)-B (100) surface at 5/6 ML coverage. PMID:22955312

  8. Evaluation of a plant material-based air purifier for removing H2S, NH3 and swine manure odour.

    PubMed

    Zhou, Xuezhi; Zhang, Qiang; Huang, Anhong

    2012-12-01

    A plant material-based air purifier (PMAP) was evaluated for odour removal. Laboratory tests were performed using two identical chambers: one treated by PMAP, and one as the control. Swine manure, hydrogen sulphide (H2S) and ammonia (NH3) were tested as odour sources. The test was also conducted in a swine barn. Air samples were taken from test chambers and two rooms in the pig barn and analysed for H2S, NH3 and odour concentrations. When treated with PMAP, the H2S concentration in the sealed chamber was subject to exponential decay, with the decay constant ranging from 0.59 to 0.70 l/h. The H2S concentration was reduced from 20 to 3 ppm in 3 h and to 0.2 ppm in 7h for H2S produced by chemical reaction, and from 0.4 to 0.02 ppm in 3 h for swine manure as the odour source. When an equal amount of ammonia solution was placed in the two test chambers, the NH3 concentration reached a peak value of 25 ppm in the chamber treated by PMAP, and 43 ppm in the control. The NH3 concentration in the treated chamber was reduced to 5 ppm in 3.5 h but stayed at 37 ppm in the control. The PMAP reduced the NH3 concentration from 38 to 10 ppm when swine manure was used as the odour source. The PMAP was capable of reducing swine odour in both laboratory and in-barn conditions. The reduction rate was at least 50%. The results from this research indicate the plant-based materials provide an alternative, environmentally friendly way for odour control. It is also shown that the mode of odour reduction by the PMAP was the removal of odour compounds, in contrast to odour masking, which occurs for most plant materials that have been used for odour control. PMID:23437676

  9. Application of a diffusion-desorption rate equation model in astrochemistry.

    PubMed

    He, Jiao; Vidali, Gianfranco

    2014-01-01

    Desorption and diffusion are two of the most important processes on interstellar grain surfaces; knowledge of them is critical for the understanding of chemical reaction networks in the interstellar medium (ISM). However, a lack of information on desorption and diffusion is preventing further progress in astrochemistry. To obtain desorption energy distributions of molecules from the surfaces of ISM-related materials, one usually carries out adsorption-desorption temperature programmed desorption (TPD) experiments, and uses rate equation models to extract desorption energy distributions. However, the often-used rate equation models fail to adequately take into account diffusion processes and thus are only valid in situations where adsorption is strongly localized. As adsorption-desorption experiments show that adsorbate molecules tend to occupy deep adsorption sites before occupying shallow ones, a diffusion process must be involved. Thus, it is necessary to include a diffusion term in the model that takes into account the morphology of the surface as obtained from analyses of TPD experiments. We take the experimental data of CO desorption from the MgO(100) surface and of D2 desorption from amorphous solid water ice as examples to show how a diffusion-desorption rate equation model explains the redistribution of adsorbate molecules among different adsorption sites. We extract distributions of desorption energies and diffusion energy barriers from TPD profiles. These examples are contrasted with a system where adsorption is strongly localized--HD from an amorphous silicate surface. Suggestions for experimental investigations are provided. PMID:25302396

  10. Comparing approaches to correct for respiratory motion in NH3 PET-CT cardiac perfusion imaging

    PubMed Central

    O’Doherty, Michael J.; Barrington, Sally F.; Morton, Geraint; Marsden, Paul K.

    2013-01-01

    Aim Respiratory motion affects cardiac PET-computed tomography (CT) imaging by reducing attenuation correction (AC) accuracy and by introducing blur. The aim of this study was to compare three approaches for reducing motion-induced AC errors and evaluate the inclusion of respiratory motion correction. Materials and methods AC with a helical CT was compared with averaged cine and gated cine CT, as well as with a pseudo-gated CT, which was produced by applying PET-derived motion fields to the helical CT. Data-driven gating was used to produce respiratory-gated PET and CT images, and 60 NH3 PET scans were attenuation corrected with each of the CTs. Respiratory motion correction was applied to the gated and pseudo-gated attenuation-corrected PET images. Results Anterior and lateral wall intensity measured in attenuation-corrected PET images generally increased when PET-CT alignment improved and decreased when alignment degraded. On average, all methods improved PET-CT liver and cardiac alignment, and increased anterior wall intensity by more than 10% in 36, 33 and 25 cases for the averaged, gated and pseudo-gated CTAC PET images, respectively. However, cases were found where alignment worsened and severe artefacts resulted. This occurred in more cases and to a greater extent for the averaged and gated CT, where the anterior wall intensity reduced by more than 10% in 21 and 24 cases, respectively, compared with six cases for the pseudo-gated CT. Application of respiratory motion correction increased the average anterior and inferior wall intensity, but only 13% of cases increased by more than 10%. Conclusion All methods improved average respiratory-induced AC errors; however, some severe artefacts were produced. The pseudo-gated CT was found to be the most robust method. PMID:24131942

  11. Concentration-Dependent Effects on Intracellular and Surface pH of Exposing Xenopus oocytes to Solutions Containing NH3/NH4+

    PubMed Central

    Jiang, Lihong; Chen, Li-Ming; Behar, Kevin L.

    2010-01-01

    Others have shown that exposing oocytes to high levels of NH3/NH4+ (10–20 mM) causes a paradoxical fall in intracellular pH (pHi), whereas low levels (e.g., 0.5 mM) cause little pHi change. Here we monitored pHi and extra-cellular surface pH (pHS) while exposing oocytes to 5 or 0.5 mM NH3/NH4+. We confirm that 5 mM NH3/NH4+ causes a paradoxical pHi fall (??pHi ? 0.2), but also observe an abrupt pHS fall (??pHS ? 0.2)—indicative of NH3 influx—followed by a slow decay. Reducing [NH3/NH4+] to 0.5 mM minimizes pHi changes but maintains pHS changes at a reduced magnitude. Expressing AmtB (bacterial Rh homologue) exaggerates ??pHS at both NH3/NH4+ levels. During removal of 0.5 or 5 mM NH3/NH4+, failure of pHS to markedly overshoot bulk extracellular pH implies little NH3 efflux and, thus, little free cytosolic NH3/NH4+. A new analysis of the effects of NH3 vs. NH4+ fluxes on pHS and pHi indicates that (a) NH3 rather than NH4+ fluxes dominate pHi and pHS changes and (b) oocytes dispose of most incoming NH3. NMR studies of oocytes exposed to 15N-labeled NH3/NH4+ show no significant formation of glutamine but substantial NH3/NH4+ accumulation in what is likely an acid intracellular compartment. In conclusion, parallel measurements of pHi and pHS demonstrate that NH3 flows across the plasma membrane and provide new insights into how a protein molecule in the plasma membrane—AmtB—enhances the flux of a gas across a biological membrane. PMID:19242745

  12. Thermally stimulated desorption of neutral CF3 from CF3I on Ag(111)

    NASA Astrophysics Data System (ADS)

    Junker, K. H.; Sun, Z.-J.; Scoggins, T. B.; White, J. M.

    1996-03-01

    The low temperature thermal chemistry of CF3I on Ag (111) presents an example of competing reaction pathways; molecular desorption vs desorption of radical CF3. Temperature programmed desorption and angle resolved temperature programmed desorption, complemented with Auger electron spectroscopy and low energy electron diffraction, were used to discern the mechanism of the CF3 radical desorption channel. CF3 desorption is limited to the first monolayer of CF3I; 0.75 ML CF3I is the coverage used for angular dependence measurements. At 90 K most of the CF3I adsorbs molecularly to the metal, but also present under these conditions are dissociative adsorption and thermal decomposition channels limited to C-I bond cleavage. The decomposition product, CF3, desorbs as a radical at high temperatures (˜320 K) with the I remaining on the surface until 850 K. At submonolayer CF3I coverages, thermal activation produces a low temperature (100-150 K) radical desorption channel. Results indicate that low temperature CF3 thermal desorption occurs via dissociative electron attachment to molecular CF3I, yielding radical CF3 and adsorbed iodine.

  13. Temperature programmed desorption and infrared spectroscopic studies of thin water films on MgO(100)

    E-print Network

    Reisler, Hanna

    ) S. Hawkins, G. Kumi, S. Malyk, H. Reisler *, C. Wittig * Department of Chemistry, University.cplett.2005.01.049 * Corresponding authors. Fax: +213 746 4945 (C. Wittig). E-mail addresses: reisler@usc.edu (H. Reisler), wittig@usc.edu (C. Wittig). www.elsevier.com/locate/cplett Chemical Physics Letters 404

  14. Temperature programmed decomposition of thorium oxalate hexahydrate

    NASA Astrophysics Data System (ADS)

    Dash, S.; Krishnan, R.; Kamruddin, M.; Tyagi, A. K.; Raj, Baldev

    2001-06-01

    Temperature programmed decomposition (TPD) of thorium oxalate hexahydrate (TOH) was studied by evolved gas analysis-mass spectrometry (EGA-MS), thermogravimetric analysis (TGA) and powder X-ray diffraction (XRD). The microcrystalline solid exhibited sequential dehydration. The anhydrous compound yielded amorphous phase Th(CO 3) 2 upon CO release arising out of the bond cleavage. The Th(CO 3) 2 phase transformed to nano-crystalline thoria upon decomposition through an oxycarbonate intermediate. The mechanism underlying various conversion stages exhibited control by random nucleation, diffusion and phase boundary interface motion. From the fractional extent of decomposition data, Arrhenius factors like activation energy and pre-exponential factors were evaluated. Based on these studies, a chemical pathway is proposed for the entire decomposition process.

  15. SIGNAL TO NOISE IMPROVEMENTS IN ON-ROAD NO, SO2, AND NH3 MEASUREMENTS USING A MULTI-COMPONENT CLASSICAL LEAST SQUARES

    E-print Network

    Denver, University of

    of their adverse health effects. These aerosols are made through tropospheric acid- base reactions involving ammonia (NH3) with sulfuric and nitric acids formed from atmospheric oxidations of sulfur dioxide (SO2, and NH3 fuel based mass emissions.3 1 Chitjian, M.; Koizumi, J.; Botsford, C.W.; Mansell, G.; Winegar, E

  16. THERMAL DESORPTION TREATMENT

    EPA Science Inventory

    Thermal desorption is an ex situ means to physically separate volatile and some semivolatile contaminants from soil, sediments, sludges, and filter cakes. or wastes containing up to 10% organics or less, thermal desorption can be used alone for site remediation. t also may find a...

  17. Characterization of Cu-SSZ-13 NH3 SCR Catalysts: an in situ FTIR Study

    SciTech Connect

    Szanyi, Janos; Kwak, Ja Hun; Zhu, Haiyang; Peden, Charles HF

    2013-01-23

    The adsorption of CO and NO over Cu-SSZ-13 zeolite catalysts, highly active in the selective catalytic reduction of NOx with NH3, was investigated by FTIR spectroscopy, and the results obtained were compared to those collected from other Cu-ion exchanged zeolites (Y,FAU and ZSM-5). At low CO pressures at room temperature (295 K) CO form monocarbonyls exclusively on the Cu+ ions, while in the presence of gas phase CO dicarbonyls on Cu+ and adsorbed CO on Cu2+ centers form, as well. At low (cryogenic) sample temperatures tricarbonyl formation on Cu+ sites was also observed. The adsorption of NO produces IR bands that can be assigned to nitrosyls bound to both Cu+ and Cu2+ centers, and NO+ species located in charge compensating cationic positions of the chabasite framework. On the reduced Cu-SSZ-13 samples the formation of N2O was also detected. The assignment of the adsorbed NOx species was aided by adsorption experiments with isotopically labeled 15NO. The movement of Cu ions from the sterically hindered six member ring position to the more accessible cavity positions as a result of their interaction with adsorbates (NO and H2O) was clearly evidenced. Comparisons of the spectroscopy data obtained in the static transmission IR system to those collected in the flow-through diffuse reflectance cell points out that care must be taken when conclusions are drawn about the adsorptive and reactive properties of metal cation centers based on a set of data collected under well defined, specific experimental conditions. Financial support was provided by the US Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program. This work was performed in the Environmental Molecular Sciences Laboratory (EMSL) at the Pacific Northwest National Laboratory (PNNL). The EMSL is a national scientific user facility supported by the US DOE, Office of Biological and Environmental Research. PNNL is a multi-program national laboratory operated for the US DOE by Battelle.

  18. Hall mobility in tin iodide perovskite CH3NH3SnI3: Evidence for a doped semiconductor

    NASA Astrophysics Data System (ADS)

    Takahashi, Yukari; Hasegawa, Hiroyuki; Takahashi, Yukihiro; Inabe, Tamotsu

    2013-09-01

    CH3NH3SnI3 is a metal halide perovskite that shows metallic conductivity over a wide temperature range, although ab initio calculations and optical absorption indicate that its band structure is consistent with that of an intrinsic semiconductor. Hall effect measurements of as-grown crystals give a hole concentration of about 9×1017 cm-3 with rather high Hall mobility of about 200 cm2 V-1 s-1 at 250 K. Artificial hole doping enhances the electrical conductivity of the crystals without influencing mobility. These observations indicate that the electronic structure in stoichiometric CH3NH3SnI3 can be described as that of an intrinsic semiconductor with a wide valence band. This situation leads to metal-like conduction with even a trace amount of spontaneous hole doping in the as-grown crystal.

  19. Thermodynamic study of the chemical vapor deposition in the SiCl3CH3-NH3-H2 system

    NASA Astrophysics Data System (ADS)

    Ren, Haitao; Zhang, Litong; Su, Kehe; Zeng, Qingfeng; Guan, Kang; Cheng, Laifei

    2015-03-01

    The gas-phase reaction thermodynamic of the chemical vapor deposition in the SiCl3CH3-NH3-H2 system was investigated with a relatively complete set of 443 species, in which the thermochemistry data include the heat capacities, entropies, enthalpies of formation, and Gibbs energies of formation were calculated. Five condensed phases, silicon carbide (?-SiC and ?-SiC), silicon nitride (Si3N4), graphite (C) and silicon (Si) were taken into consideration. The distribution of the equilibrium concentration of the 443 species was obtained. The effects of temperature and reactant ratios of SiCl3CH3/(SiCl3CH3 + NH3) on the formation and yield of condensed phases were discussed.

  20. Excellent activity and selectivity of Cu-SSZ-13 in the selective catalytic reduction of NOx with NH3

    SciTech Connect

    Kwak, Ja Hun; Tonkyn, Russell G.; Kim, Do Heui; Szanyi, Janos; Peden, Charles HF

    2010-10-21

    Superior activity and selectivity of a Cu ion-exchanged SSZ-13 zeolite in the selective catalytic reduction (SCR) of NOx with NH3 were observed, in comparison to Cu-beta and Cu-ZSM-5 zeolites. Cu-SSZ-13 was not only more active in the NOx SCR reaction over the entire temperature range studied (up to 550 °C), but also more selective toward nitrogen formation, resulting in significantly lower amounts of NOx by-products (i.e., NO2 and N2O) than the other two zeolites. In addition, Cu-SSZ-13 demonstrated the highest activity and N2 formation selectivity in the oxidation of NH3. The results of this study strongly suggest that Cu-SSZ-13 is a promising candidate as a catalyst for NOx SCR with great potential in after-treatment systems for either mobile or stationary sources.

  1. Ceria supported on sulfated zirconia as a superacid catalyst for selective catalytic reduction of NO with NH3.

    PubMed

    Gao, Shan; Chen, Xiongbo; Wang, Haiqiang; Mo, Jiansong; Wu, Zhongbiao; Liu, Yue; Weng, Xiaole

    2013-03-15

    In this paper, ceria supported on sulfated zirconia (CeSZ) as a superacid catalyst was synthesized and the resulted performances for selective catalytic reduction (SCR) of NO with NH(3) were investigated. Experimental results revealed that the sulfation of zirconia supports could greatly improve the SCR activity of the catalysts. Among the tested samples, the CeSZ catalyst with Ce/Zr mole ratio at 0.095 possessed the highest NO conversion (i.e., 98.6% at ca. 420 °C and 180,000 h(-1)). The sulfation had led to a formation of pure tetragonal phase of ZrO(2), a well dispersion of CeO(2), abundant stable superacid sites, increasing surface area and enrichment of Ce(3+) on the surface, all of which were responsible for its excellent performance in SCR of NO with NH(3). PMID:23375804

  2. Collision-induced desorption of ammonia chemisorbed on Pt{111}: From direct measurement of the threshold energy to determination of the surface-adsorbate bond strength

    NASA Astrophysics Data System (ADS)

    Szulczewski, Gregory; Levis, Robert J.

    1995-12-01

    We report the desorption of a chemisorbed polyatomic adsorbate from a transition metal surface by a beam of neutral, energetic Ar atoms. From direct measurement of the threshold energy for collision-induced desorption we calculate the surface-adsorbate bond energy. The absolute cross sections for NH3 desorption at one-quarter of a monolayer coverage were measured for Ar beam energies up to ˜3 eV at incident angles of 0°, 30°, 45°, and 60°. For the NH3/Pt{111} adsorbate-surface system, the threshold desorption energy is found to be 1.95±0.17 eV. Using a classical energy transfer mechanism this threshold energy corresponds to a bond energy of 1.1±0.1 eV using an effective mass of 1 Pt atom. The threshold desorption energy scales with the total energy of the noble gas atoms for each angle of incidence. This result is consistent with a strong lateral corrugation in the NH3/Pt{111} potential energy surface and a similar ejection mechanism at each angle.

  3. Pseudo-stable transitions and instability in chemical heat pumps: the NH 3–CoCl 2 system

    Microsoft Academic Search

    Zine Aidoun; Marten Ternan

    2001-01-01

    Research in our laboratory has been directed toward the development of a chemical heat pump, based on the NH3–CoCl2 system, to provide both refrigeration and heat for the agribusiness industry. In this work the stability of the salt in an inert atmosphere (nitrogen) and in the presence of ammonia was examined experimentally. For a given pressure, the stable composition of

  4. The role of NH3 and hydrocarbon mixtures in GaN pseudo-halide CVD: a quantum chemical study.

    PubMed

    Gadzhiev, Oleg B; Sennikov, Peter G; Petrov, Alexander I; Kachel, Krzysztof; Golka, Sebastian; Gogova, Daniela; Siche, Dietmar

    2014-11-01

    The prospects of a control for a novel gallium nitride pseudo-halide vapor phase epitaxy (PHVPE) with HCN were thoroughly analyzed for hydrocarbons-NH3-Ga gas phase on the basis of quantum chemical investigation with DFT (B3LYP, B3LYP with D3 empirical correction on dispersion interaction) and ab-initio (CASSCF, coupled clusters, and multireference configuration interaction including MRCI+Q) methods. The computational screening of reactions for different hydrocarbons (CH4, C2H6, C3H8, C2H4, and C2H2) as readily available carbon precursors for HCN formation, potential chemical transport agents, and for controlled carbon doping of deposited GaN was carried out with the B3LYP method in conjunction with basis sets up to aug-cc-pVTZ. The gas phase intermediates for the reactions in the Ga-hydrocarbon systems were predicted at different theory levels. The located ?-complexes Ga…C2H2 and Ga…C2H4 were studied to determine a probable catalytic activity in reactions with NH3. A limited influence of the carbon-containing atmosphere was exhibited for the carbon doping of GaN crystal in the conventional GaN chemical vapor deposition (CVD) process with hydrocarbons injected in the gas phase. Our results provide a basis for experimental studies of GaN crystal growth with C2H4 and C2H2 as auxiliary carbon reagents for the Ga-NH3 and Ga-C-NH3 CVD systems and prerequisites for reactor design to enhance and control the PHVPE process through the HCN synthesis. PMID:25316343

  5. Sub-Doppler infrared–infrared double resonance spectroscopy of NH3 using Stark tuning and a diode laser

    Microsoft Academic Search

    W. H. Weber; R. W. Terhune

    1983-01-01

    Double resonance experiments on NH3 are described in which a CO laser pumps a 6 ?m ?4 transition while a tunable diode laser probes a 10 ?m ?2 transition having a common lower level. Four different combinations of pump–probe transitions are studied. The CO laser is Lamb-dip stabilized on the pump transitions, which are tuned into coincidence with it using

  6. Specific Heat and Phase Transition Phenomena in (CH3NH3)5Bi2Cl11

    Microsoft Academic Search

    Makoto Iwata; Takeo Tojo; Tooru Atake; Yoshihiro Ishibashi

    1994-01-01

    Specific heat of (CH3NH3)5Bi2Cl11 was measured by adiabatic calorimetry between 13 K and 325 K. A typical second-order type of anomaly was observed at 307.4 K. The enthalpy and entropy of transition were determined as 3.06 kJ mol-1 and 10.6 J K-1 mol-1, respectively. A broad hump in the curve of specific heat was found around 160 K. Its contribution

  7. Deposition of GaN films on (1 1 1) Si substrates by alternate supply of TMG and NH 3

    Microsoft Academic Search

    Jyh-Rong Gong; Ming-Fa Yeh; Yu-Li Tsai

    2004-01-01

    GaN films were grown on (111) Si substrates at 1000 °C by separate admittances of trimethylgallium (TMG) and ammonia (NH3). To achieve high quality GaN films, the optimization in growth temperature and layer thickness of AlN buffer layer between GaN film and Si substrate is required. Cross-sectional transmission electron microscopic observations of the GaN\\/(111)Si samples show a nearly parallel orientation

  8. Total cross sections for electron scattering from molecules: ${\\\\rm NH}_{3}$ and ${\\\\rm H}_{2}{\\\\rm O}$

    Microsoft Academic Search

    Yufang Liu; Jinfeng Sun; Zhenxin Li; Yuhai Jiang; Lingde Wan

    1997-01-01

    By developing the semi-empirical formula recently obtained for total cross sections of electron scattering from diatomic molecules in the intermediate- and high-energy range, we calculate the total cross sections for electron scattering from molecules (${\\\\rm NH}_{3}$ and ${\\\\rm H}_{2}{\\\\rm O}$) over an incident energy range of 10-1000 eV. The total cross sections have also been calculated by using the complex

  9. Highly sensitive thin film NH 3 gas sensor operating at room temperature based on SnO 2\\/MWCNTs composite

    Microsoft Academic Search

    Nguyen Van Hieu; Luong Thi Bich Thuy; Nguyen Duc Chien

    2008-01-01

    A SnO2\\/MWCNTs composite-based NH3 sensor working at room temperature was fabricated by thin film microelectronic technique. The gas-sensitive composite thin film was prepared by using both commercially available multi-walled carbon nanotubes (MWCNTs) and nanosized SnO2 dispersion. Microstructure and surface morphology of the composite were investigated and they revealed that the MWCNTs were still present and well embedded by SnO2 particles

  10. Estimating NH3 emissions from agricultural fertilizer application in China using the bi-directional CMAQ model coupled to an agro-ecosystem model

    NASA Astrophysics Data System (ADS)

    Fu, X.; Wang, S. X.; Ran, L. M.; Pleim, J. E.; Cooter, E.; Bash, J. O.; Benson, V.; Hao, J. M.

    2015-06-01

    Atmospheric ammonia (NH3) plays an important role in atmospheric aerosol chemistry. China is one of the largest NH3 emitting countries with the majority of NH3 emissions coming from agricultural practices, such as fertilizer application and livestock production. The current NH3 emission estimates in China are mainly based on pre-defined emission factors that lack temporal or spatial details, which are needed to accurately predict NH3 emissions. This study provides the first online estimate of NH3 emissions from agricultural fertilizer application in China, using an agricultural fertilizer modeling system which couples a regional air quality model (the Community Multi-scale Air Quality model, or CMAQ) and an agro-ecosystem model (the Environmental Policy Integrated Climate model, or EPIC). This method improves the spatial and temporal resolution of NH3 emissions from this sector. We combined the cropland area data of 14 crops from 2710 counties with the Moderate Resolution Imaging Spectroradiometer (MODIS) land use data to determine the crop distribution. The fertilizer application rates and methods for different crops were collected at provincial or agricultural region levels. The EPIC outputs of daily fertilizer application and soil characteristics were input into the CMAQ model and the hourly NH3 emissions were calculated online with CMAQ running. The estimated agricultural fertilizer NH3 emissions in this study were approximately 3 Tg in 2011. The regions with the highest modeled emission rates are located in the North China Plain. Seasonally, peak ammonia emissions occur from April to July. Compared with previous researches, this study considers an increased number of influencing factors, such as meteorological fields, soil and fertilizer application, and provides improved NH3 emissions with higher spatial and temporal resolution.

  11. Revealing the role of organic cations in hybrid halide perovskite CH3NH3PbI3

    PubMed Central

    Motta, Carlo; El-Mellouhi, Fedwa; Kais, Sabre; Tabet, Nouar; Alharbi, Fahhad; Sanvito, Stefano

    2015-01-01

    The hybrid halide perovskite CH3NH3PbI3 has enabled solar cells to reach an efficiency of about 20%, demonstrating a pace for improvements with no precedents in the solar energy arena. Despite such explosive progress, the microscopic origin behind the success of such material is still debated, with the role played by the organic cations in the light-harvesting process remaining unclear. Here van der Waals-corrected density functional theory calculations reveal that the orientation of the organic molecules plays a fundamental role in determining the material electronic properties. For instance, if CH3NH3 orients along a (011)-like direction, the PbI6 octahedral cage will distort and the bandgap will become indirect. Our results suggest that molecular rotations, with the consequent dynamical change of the band structure, might be at the origin of the slow carrier recombination and the superior conversion efficiency of CH3NH3PbI3. PMID:25912782

  12. Optical-integrated NH3 sensor design using WO3 thin tllms: influence of gas adsorption and chromic effects

    NASA Astrophysics Data System (ADS)

    Hernández, Hugo E. Lazcano; Pérez, Celia Sánchez; Valenzuela, Augusto García

    2008-04-01

    We propose a new model for the design of optical-integrated (OI) sensor, composed of a surface waveguide covered with a sensitive material (SM) deposited at the surface in the form of thin films. Commonly these last are metallic oxides which becomes highly absorbent in the presence of the gas to be detected. In this way, the optical signal propagating in the waveguide will be attenuated proportionally to the amount of the gas in the surrounding environment. When the sensing is carried out, commonly it is supposed that completely all the volume of the SM increase its absorbance, however this assumption causes that the transmission losses be overestimated; our model, according to the adsorption kinetics of gases, considers the growth of the adsorber layer over the SM as a fourth layer where the optical changes happen. We use this model to design an ammonia NH3 sensor considering tungsten trioxide WO3 as SM. Our model approaches in 102 dB/cm the calculus of the losses, in agreement with that observed in experiments. The refractive index ?'(?) and the absorbance of ??(?) were calculated under inert and NH3 gas conditions, through the analysis of the UV-VIS-NIR transmittance spectra, and the numerical method of Swanepoel, in order to be incorporated in the simulation of the OI proposed structure with a multilayer method software. Experimentally we analyse the influence of thermochromism and photochromism in the response of gasochromism. We tested WO3 samples elaborated by sputtering method with a combination of monoclinic-triclinic crystalline structure, measuring as minimum 200 ppm of NH3 at ? = 1000 nm and at 100 °C. The best sample was tested to NH3 detection, using monochromatic sources: ? = 830 nm, ? = 980 nm and ? = 1550 nm; obtaining intensity attenuations of 10%, 16% and 29%, respectively to 5000 ppm of NH3 at 100 °C. This is a new proposal that can predicts better the interaction between the material and the optical field in optical sensing structures, in comparison with the conventional model.

  13. Temperature programmed decomposition of thorium nitrate pentahydrate

    NASA Astrophysics Data System (ADS)

    Dash, S.; Kamruddin, M.; Ajikumar, P. K.; Tyagi, A. K.; Raj, Baldev; Bera, Santanu; Narasimhan, S. V.

    2000-02-01

    Temperature programmed decomposition (TPD) of thorium nitrate pentahydrate has been studied using evolved gas analysis-mass spectrometry (EGA-MS) in the temperature range 300-1200 K. A thermogravimetric (TGA) investigation was also carried out in the same temperature range. Complexity of the TGA decomposition profile was resolved through use of EGA-MS data. The activation energies and pre-exponential factors were determined for various gas release stages from the fractional extent of decomposition plots. Residues left over after each decomposition stage were analysed using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The XRD investigations revealed formation of a nanocrystalline thoria intermediate product, ultimately agglomerating to a microcrystalline phase. The XPS investigations indicated systematic alteration in the chemical environment around the thorium atom while the Th 4+ oxidation state remained unchanged. This was further corroborated from the analysis of shake-up satellites of Th (4f 5/2) spectra. The O/Th ratios for various intermediate products were also determined.

  14. Temperature programmed decomposition of uranyl nitrate hexahydrate

    NASA Astrophysics Data System (ADS)

    Dash, S.; Kamruddin, M.; Bera, Santanu; Ajikumar, P. K.; Tyagi, A. K.; Narasimhan, S. V.; Raj, Baldev

    1999-01-01

    Temperature programmed decomposition (TPD) of uranyl nitrate hexahydrate has been studied using evolved gas analysis mass spectrometry (EGA-MS) in the temperature range 300-1400 K. Thermogravimetric (TGA) investigations were performed in the temperature range 300-1100 K. An attempt has been made to resolve the complexity of decomposition behaviour through suitable comparison of TGA and EGA-MS data. Kinetic control regimes for various decomposition stages could be deduced from EGA-MS data. The corresponding activation energies and frequency factors were also evaluated. Kinetics based on random nucleation and diffusion was found to be rate controlling. The residue left over after each decomposition stage was analysed by XRD and XPS to determine structure and composition. The ultimate product was found to be a mixture of UO 3H 1.17 and U 3O 8: the former being a topotactic hydrogen spill over compound of UO 3. Complete conversion of this residue to U 3O 8 was noticed during ion beam exposure of the residue which was performed in the course of XPS investigations.

  15. Temperature dependence of internal motions of protein side-chain NH3(+) groups: insight into energy barriers for transient breakage of hydrogen bonds.

    PubMed

    Zandarashvili, Levani; Iwahara, Junji

    2015-01-20

    Although charged side chains play important roles in protein function, their dynamic properties are not well understood. Nuclear magnetic resonance methods for investigating the dynamics of lysine side-chain NH3(+) groups were established recently. Using this methodology, we have studied the temperature dependence of the internal motions of the lysine side-chain NH3(+) groups that form ion pairs with DNA phosphate groups in the HoxD9 homeodomain-DNA complex. For these NH3(+) groups, we determined order parameters and correlation times for bond rotations and reorientations at 15, 22, 28, and 35 °C. The order parameters were found to be virtually constant in this temperature range. In contrast, the bond-rotation correlation times of the NH3(+) groups were found to depend strongly on temperature. On the basis of transition state theory, the energy barriers for NH3(+) rotations were analyzed and compared to those for CH3 rotations. Enthalpies of activation for NH3(+) rotations were found to be significantly higher than those for CH3 rotations, which can be attributed to the requirement of hydrogen bond breakage. However, entropies of activation substantially reduce the overall free energies of activation for NH3(+) rotations to a level comparable to those for CH3 rotations. This entropic reduction in energy barriers may accelerate molecular processes requiring hydrogen bond breakage and play a kinetically important role in protein function. PMID:25489884

  16. Experimental and theoretical study on the spontaneous formation of OCN - ion: reactivity between HNCO and NH 3/H 2O environment at low temperature

    NASA Astrophysics Data System (ADS)

    Raunier, Sébastien; Chiavassa, Thierry; Marinelli, Francis; Aycard, Jean-Pierre

    2004-07-01

    The reactivity of HNCO embedded in NH 3/H 2O mixtures in astrophysical ratio (1/10) is investigated using FT-IR spectroscopy between 10 and 180 K and quantum calculations. A spontaneous reaction is observed at 10 K between HNCO and NH 3, which leads to NH 4+OCN - formation. Theoretically, we show that this can occur if HNCO is both in interaction with lone pair of one NH 3 molecule and surrounded by three H 2O molecules. The OCN - produced is characterized by a band centered at 2167 cm -1, which is well in agreement with the observations provided by infrared space observatory (ISO) spectrometer towards protostellar sources.

  17. Mobile mapping and eddy covariance flux measurements of NH3 emissions from cattle feedlots with a portable laser-based open-path sensor

    NASA Astrophysics Data System (ADS)

    Tao, L.; Sun, K.; Pan, D.; Golston, L.; Stanton, L. G.; Ham, J. M.; Shonkwiler, K. B.; Nash, C.; Zondlo, M. A.

    2014-12-01

    Ammonia (NH3) is the dominant alkaline species in the atmosphere and an important compound in the global nitrogen cycle. There is a large uncertainty in NH3 emission inventory from agriculture, which is the largest source of NH3, including livestock farming and fertilizer applications. In recent years, a quantum cascade laser (QCL)-based open-path sensor has been developed to provide high-resolution, fast-response and high-sensitivity NH3 measurements. It has a detection limit of 150 pptv with a sample rate up to 20 Hz. This sensor has been integrated into a mobile platform mounted on the roof of a car to perform measurement of multiple trace gases. We have also used the sensor for eddy covariance (EC) flux measurements. The mobile sensing method provides high spatial resolution and fast mapping of measured gases. Meanwhile, the EC flux method offers accurate flux measurements and resolves the diurnal variability of NH3emissions. During the DISCOVER-AQ and FRAPPÉ field campaigns in 2014, this mobile platform was used to study NH3 emissions from cattle feedlot near Fort Morgan, Colorado. This specific feedlot was mapped multiple times in different days to study the variability of its plume characteristics. At the same time, we set up another open-path NH3 sensor with LICOR open-path sensors to perform EC flux measurements of NH3, CH4 and CO2 simultaneously in the same cattle feedlot as shown in Fig. 1. NH3/CH4 emission flux ratio show a strong temperature dependence from EC flux measurements. The median value of measured NH3 and CH4 emission flux ratio is 0.60 ppmv/ppmv. In contrast, the median value of ?NH3/?CH4 ratios measured from mobile platform is 0.53 ppmv/ppmv for the same farm. The combination of mobile mapping and EC flux measurements with the same open-path sensors greatly improves understanding of NH3 emissions both spatially and temporally.

  18. Oxygen sorption and desorption properties of selected lanthanum manganites and lanthanum ferrite manganites.

    PubMed

    Nielsen, Jimmi; Skou, Eivind M; Jacobsen, Torben

    2015-06-01

    Temperature-programmed desorption (TPD) with a carrier gas was used to study the oxygen sorption and desorption properties of oxidation catalysts and solid-oxide fuel cell (SOFC) cathode materials (La0.85 Sr0.15 )0.95 MnO3+? (LSM) and La0.60 Sr0.40 Fe0.80 Mn0.20 O3-? (LSFM). The powders were characterized by X-ray diffractometry, atomic force microscopy (AFM), and BET surface adsorption. Sorbed oxygen could be distinguished from oxygen originating from stoichiometry changes. The results indicated that there is one main site for oxygen sorption/desorption. The amount of sorbed oxygen was monitored over time at different temperatures. Furthermore, through data analysis it was shown that the desorption peak associated with oxygen sorption is described well by second-order desorption kinetics. This indicates that oxygen molecules dissociate upon adsorption and that the rate-determining step for the desorption reaction is a recombination of monatomic oxygen. Typical problems with re-adsorption in this kind of TPD setup were revealed to be insignificant by using simulations. Finally, different key parameters of sorption and desorption were determined, such as desorption activation energies, density of sorption sites, and adsorption and desorption reaction order. PMID:25784205

  19. On-board Measurement of HCN and NH3 Emissions from Vehicles During Real-World Driving

    NASA Astrophysics Data System (ADS)

    Moss, J. A.; Baum, M. M.

    2013-12-01

    Emission control systems in light-duty motor vehicles have played an important role in improving regional air quality by dramatically reducing the concentration of criteria pollutants (carbon monoxide, hydrocarbons, and nitrogen oxides) in exhaust emissions. Unintended side-reactions occurring on the surface of three-way catalysts can, however, lead to emission of non-criteria pollutants such as ammonia (NH3) and hydrogen cyanide (HCN). A pair of spectrometers based on tunable diode lasers (TDL) emitting in the near-infrared (1529 nm) and mid-infrared (2975 nm) have been developed for determination of HCN and acetylene (C2H2) emission rates from light-duty motor vehicles in real-time, while driving. Both spectrometers have been evaluated extensively using standard gas mixtures in the laboratory and exhaust from idling and moving vehicles. The TDL spectrometers were incorporated into an on-board instrument suite containing instrumentation for measurement of CO2, HCN, C2H2, NH3 and amines, and exhaust flow rate. On-board measurements were carried out on a fleet of ten vehicles driving a 30 minute circuit representative of real-world urban driving conditions. These measurements afforded emission factors for NH3 (194 × 147 mg km-1) and HCN (3.33 × 3.61 mg km-1), as well as the first report of methylamine emission factors, 0.70 × 0.61 mg km-1. Emissions of both amines were highly correlated (R2 = 0.95). The temporally-resolved TDL spectrometer measurements indicate that the highest HCN and C2H2 emissions occur during specific emission modes that are a function of driving conditions.

  20. Qualifying composition dependent p and n self-doping in CH3NH3PbI3

    NASA Astrophysics Data System (ADS)

    Wang, Qi; Shao, Yuchuan; Xie, Haipeng; Lyu, Lu; Liu, Xiaoliang; Gao, Yongli; Huang, Jinsong

    2014-10-01

    We report the observation of self-doping in perovskite. CH3NH3PbI3 was found to be either n- or p-doped by changing the ratio of methylammonium halide (MAI) and lead iodine (PbI2) which are the two precursors for perovskite formation. MAI-rich and PbI2-rich perovskite films are p and n self-doped, respectively. Thermal annealing can convert the p-type perovskite to n-type by removing MAI. The carrier concentration varied as much as six orders of magnitude. A clear correlation between doping level and device performance was also observed.

  1. Atomic oxygen diffusion on and desorption from amorphous silicate surfaces.

    PubMed

    He, Jiao; Jing, Dapeng; Vidali, Gianfranco

    2014-02-28

    Surface reactions involving atomic oxygen have attracted much attention in astrophysics and astrochemistry, but two of the most fundamental surface processes, desorption and diffusion, are not well understood. We studied diffusion and desorption of atomic oxygen on or from amorphous silicate surfaces under simulated interstellar conditions using a radio-frequency dissociated oxygen beam. Temperature programmed desorption (TPD) experiments were performed to study the formation of ozone from reaction of atomic and molecular oxygen deposited on the surface of a silicate. It is found that atomic oxygen begins to diffuse significantly between 40 K and 50 K. A rate equation model was used to study the surface kinetics involved in ozone formation experiments. The value of atomic oxygen desorption energy has been determined to be 152 ± 20 meV (1764 ± 232 K). The newly found atomic oxygen desorption energy, which is much higher than the well-accepted value, might explain the discrepancy in abundance of molecular oxygen in space between observations and chemical models. PMID:24434834

  2. Application of Cavity-ring Down Spectroscopy to Quantify NH3 Fluxes from Fertilizer Application in the Midwestern U.S.

    NASA Astrophysics Data System (ADS)

    Caldwell, J. A.; Sibble, D.; Heuer, M.; Johnson, E.; Rood, M. J.; Koloutsou-Vakakis, S.; Myles, L.

    2014-12-01

    Ammonia (NH3) emissions from managed agriculture in the Midwestern region of the U.S. contribute to increased levels of particulate matter in the atmosphere and detrimental ecological changes. To better understand the exchange of ammonia between the atmosphere and biosphere and identify the drivers of these processes, measurements of NH3 flux were conducted over a 200 m2 fertilized maize field in Illinois. A flux-gradient system paired with a cavity-ring down spectrometer measured fluxes from pre-cultivation through senescence of the crop. The use of a custom automated exchange mechanism allowed for continuous sampling, both above-canopy and in-canopy. Results indicated diurnal cycling of NH3 with higher concentrations in the early afternoon, although the pattern was not consistent. As expected, fertilization of the field at planting produced a marked increase in NH3 emission from the field.

  3. Determination of a chemisorption bond strength by direct measurement of the threshold energy for collision-induced desorption: Ammonia on Pt{111}

    NASA Astrophysics Data System (ADS)

    Szulczewski, Gregory; Levis, Robert J.

    1994-12-01

    Direct measurement of the threshold desorption energy for collision-induced desorption is used to determine a chemisorption bond energy. In this experiment the absolute cross section for desorption is measured using x-ray photoelectron spectroscopy as a function of the impact energy between a translationally energetic Ar atom and an ammonia molecule chemisorbed to a Pt{111} single crystal. For this adsorbate-surface system the threshold desorption energy is found to be 1.8±0.17 eV and is independent of the angle of incidence of the Ar beam. Using a classical energy transfer mechanism this threshold energy is found to correspond to a bond energy of 1.4±0.13 eV. This represents an upper limit for the bond strength assuming maximum energy transfer between Ar and NH3 and no internal excitation of the adsorbate at the desorption threshold.

  4. Development and uncertainty analysis of a high-resolution NH3 emissions inventory and its implications with precipitation over the Pearl River Delta region, China

    NASA Astrophysics Data System (ADS)

    Zheng, J. Y.; Yin, S. S.; Kang, D. W.; Che, W. W.; Zhong, L. J.

    2012-08-01

    Detailed NH3 emission inventories are important to understand various atmospheric processes, air quality modeling studies, air pollution management, and related environmental and ecological issues. A high-resolution NH3 emission inventory was developed based on state-of-the-science techniques, up-to-date information, and advanced expert knowledge for the Pearl River Delta region, China. To provide model-ready emissions input, this NH3 emissions inventory was spatially allocated to 3 km × 3 km grid cells using source-based spatial surrogates with geographical information system (GIS) technology. For NH3 emissions, 9 source categories and 45 subcategories were identified in this region, and detailed spatial and temporal characteristics were investigated. Results show that livestock is by far the most important NH3 emission source by contributing about 61.7% of the total NH3 emissions in this region, followed by nitrogen fertilizer applications (~23.7%) and non-agricultural sources (~14.6%). Uncertainty analysis reveals that the uncertainties associated with different sources vary from source to source and the magnitude of the uncertainty associated with a specific source mainly depends on the degree of accuracy of the emission factors and activity data as well as the technique used to perform the estimate. Further studies should give priority to the hog, broiler, goose subsectors of the livestock source and N fertilizer application source in order to reduce uncertainties of ammonia emission estimates in this region. The validity of the NH3 emissions inventory is justified by the trend analysis of local precipitation compositions, such as pH values, the Ca2++NH4+/SO42-+ NO3- ratios, and NH4+ concentrations which are directly or indirectly related to NH3 emissions.

  5. Influence of NH 3 flow rate on pyridine-like N content and NO electrocatalytic oxidation of N-doped multiwalled carbon nanotubes

    Microsoft Academic Search

    Wei-Xin LvRui; Rui Zhang; Ting-Liang Xia; Hong-Mei Bi; Ke-Ying Shi

    2011-01-01

    Nitrogen-doped multiwalled carbon nanotubes (N-MWCNTs) have been prepared by pyrolysis of pyridine and iron phthalocyanine\\u000a over an iron catalyst at 850 °C at various ammonia gas (NH3) flow rates. X-ray photoelectron spectroscopy results reveal that the pyridine-like nitrogen (N) content can be controlled\\u000a by changing the flow rate of NH3, and that pyridine-like N plays an important role: it can increase

  6. A pilot field-scale study on biotrickling filter treatment of NH 3 -containing odorous gases from organic waste composting plants

    Microsoft Academic Search

    Nian-tao Xue; Qun-hui Wang; Chuan-fu Wu; Xiao-hong Sun; Wei-min Xie

    2010-01-01

    The use of a biotrickling filter was investigated for a pilot field-scale elimination of NH3 gas and other odorous gases from a composting plant in Tongzhou District, Beijing. The inlet gas flow rate was 3500 m3\\/h and NH3 concentration fluctuated between 2.76–27.84 mg\\/m3, while the average outlet concentration was 1.06 mg\\/m3 with an average of 94.9% removal. Critical volumetric loading

  7. Planar CH3 NH3 PbI3 Perovskite Solar Cells with Constant 17.2% Average Power Conversion Efficiency Irrespective of the Scan Rate.

    PubMed

    Heo, Jin Hyuck; Song, Dae Ho; Han, Hye Ji; Kim, Seong Yeon; Kim, Jun Ho; Kim, Dasom; Shin, Hee Won; Ahn, Tae Kyu; Wolf, Christoph; Lee, Tae-Woo; Im, Sang Hyuk

    2015-06-01

    Planar CH3 NH3 PbI3 perovskite solar cells with constant 17.2% average power conversion efficiency irrespective of the scan rate are described. These properties are attributed to the formation of a pure CH3 NH3 PbI3 thin film by the introduction of a HI solution. Thereby, charge-injection/separation efficiency, charge-collection efficiency, diffusion coefficient, carrier lifetime, and traps are improved. PMID:25914242

  8. [Catalytic performance of a novel ceramic-supported vanadium oxide catalyst for NO reduction with NH3].

    PubMed

    Tian, Liu-qing; Ye, Dai-qi

    2004-01-01

    A novel TiO2/Al2O3/ceramic cordierite honeycomb (CC)-supported V2O5-MoO3-WO3 monolithic catalyst was studied for the selective reduction of NO with NH3. The effects of reaction temperature, space velocity, NH3/NO ratio and oxygen content on selective catalytic reduction (SCR) activity were evaluated. Two other V2O5-MoO3-WO3 monolithic catalysts supported on Al2O3/CC or TiO2/CC support, two types of pellet catalysts supported on TiO2/Al2O3 or Al2O3, as well as three types of pellet catalysts V2O5-MoO3-WO3-Al2O3 and V2O5-MoO3-WO3-TiO2 were tested for comparison. The experiment results showed that this catalyst had a higher catalytic activity for SCR with comparison to others. The results of characterization showed, the preparation method of this catalyst can give rise to a higher Brunauer, Emmett, Teller (BET) surface area and pore volume, which was strongly related with the highly active performance of this catalyst. At the same time, the function of the combined carrier of TiO2/Al2O3 cannot be excluded. PMID:15330412

  9. A novel chemical detector using colorimetric sensor array and pattern recognition methods for the concentration analysis of NH3

    NASA Astrophysics Data System (ADS)

    Luo, Xiao-gang; Liu, Ping; Hou, Chang-jun; Huo, Dan-qun; Dong, Jia-le; Fa, Huan-bao; Yang, Mei

    2010-10-01

    With a colorimetric sensor array comprising chemoresponsive dyes, a simple, rapid, and cost-effective integrated system for differentiating low-concentration gases was described. The system could be used to identify gases by detecting the color change information of the chemoresponsive dyes based on porphyrins before and after reaction with the target gas; the colorimetric sensor array images were collected by a charge coupled device and processed with image analysis to get the color changes of the dyes in the array. Temperature, humidity, and flux of the chamber could be detected and displayed on the personal computer screen. A low-concentration [30-210 ppb (parts per 109)] NH3 was detected by the system. This prototype successfully differentiated four concentration levels of NH3 in less than 1 min. Pattern recognition methods, such as the backpropagation neural network and the radial basis function neural network, validated the effect of the developed sensor system both with 100% classification with feature vectors at single time point as inputs.

  10. Electrical properties and conduction mechanism of [C2H5NH3]2CuCl4 compound

    NASA Astrophysics Data System (ADS)

    Mohamed, C. Ben; Karoui, K.; Jomni, F.; Guidara, K.; Rhaiem, A. Ben

    2015-02-01

    The [(C2H5)NH3]2CuCl4 compound was prepared and characterized by several technique: the X-ray powder diffraction confirms the purity of the synthetized compound, the differential scanning calorimetric show several phase transitions at 236 K, 330 K, 357 K and 371 K, the dialectical properties confirms the ferroelectric-paraelectric phase transition at 238 K, which is reported by V. Kapustianyk et al. (2007) [1]. The two semi-circles observed in the complex impedance identify the presence of the grain interior and grain boundary contributions to the electrical response in this material. The equivalent circuit is modeled by a combination series of two parallel RP-CPE circuits. The temperature dependence of the alternative current conductivity (?g) and direct current conductivity (?dc) confirm the observed transitions in the calorimetric study. The (AC) electrical conduction in [(C2H5)NH3]2CuCl4 was studied by two processes that can be attributed to a hopping transport mechanism: the non-overlapping small polaron tunneling (NSPT) model in phase III and the correlated barrier hopping (CBH) model in phases I, II, IV, V and VI.

  11. A novel chemical detector using colorimetric sensor array and pattern recognition methods for the concentration analysis of NH3.

    PubMed

    Luo, Xiao-gang; Liu, Ping; Hou, Chang-jun; Huo, Dan-qun; Dong, Jia-le; Fa, Huan-bao; Yang, Mei

    2010-10-01

    With a colorimetric sensor array comprising chemoresponsive dyes, a simple, rapid, and cost-effective integrated system for differentiating low-concentration gases was described. The system could be used to identify gases by detecting the color change information of the chemoresponsive dyes based on porphyrins before and after reaction with the target gas; the colorimetric sensor array images were collected by a charge coupled device and processed with image analysis to get the color changes of the dyes in the array. Temperature, humidity, and flux of the chamber could be detected and displayed on the personal computer screen. A low-concentration [30-210 ppb (parts per 10(9))] NH(3) was detected by the system. This prototype successfully differentiated four concentration levels of NH(3) in less than 1 min. Pattern recognition methods, such as the backpropagation neural network and the radial basis function neural network, validated the effect of the developed sensor system both with 100% classification with feature vectors at single time point as inputs. PMID:21034125

  12. Triggering N2 Uptake via Redox Induced Expulsion of Coordinated NH3 and N2 Silylation at Trigonal Bipyramidal Iron

    PubMed Central

    Lee, Yunho; Mankad, Neal P.

    2010-01-01

    The biological reduction of nitrogen to ammonia may occur via one of two predominant pathways in which nitrogenous NxHy intermediates including hydrazine (N2H4), diazene (N2H2), nitride (N3-) and imide (NH2-) may be involved. To test the validity of hypotheses concerning iron’s direct role in the stepwise reduction of N2, iron model systems are needed. Such systems can test the chemical compatibility of iron with various proposed NxHy intermediates, and the reactivity patterns of such species. Here we describe a TBP (SiPR3)Fe-L scaffold (SiPR3 represents [Si(o-C6H4PR2)3]?; R = Ph and iPr) where the apical site is occupied by nitrogenous ligands such as N2, N2H4, NH3 and N2R. The system accommodates terminally bound N2 in the three formal oxidation states (iron(0), +1, and +2). N2 uptake is demonstrated via displacement of its reduction partners NH3 and N2H4, and N2 functionalizaton is illustrated via electrophilic silylation. PMID:20571574

  13. Strong covalency-induced recombination centers in perovskite solar cell material CH3NH3PbI3.

    PubMed

    Agiorgousis, Michael L; Sun, Yi-Yang; Zeng, Hao; Zhang, Shengbai

    2014-10-15

    Inorganic-organic hybrid perovskites are a new family of solar cell materials, which have recently been used to make solar cells with efficiency approaching 20%. Here, we report the unique defect chemistry of the prototype material, CH3NH3PbI3, based on first-principles calculation. We found that both the Pb cations and I anions in this material exhibit strong covalency as characterized by the formation of Pb dimers and I trimers with strong covalent bonds at some of the intrinsic defects. The Pb dimers and I trimers are only stabilized in a particular charge state with significantly lowered energy, which leads to deep charge-state transition levels within the band gap, in contradiction to a recent proposal that this system has only shallow intrinsic defects. Our results show that, in order to prevent the deep-level defects from being effective recombination centers, the equilibrium carrier concentrations should be controlled so that the Fermi energy is about 0.3 eV away from the band edges. Beyond this range, according to a Shockley-Read-Hall analysis, the non-equilibrium carrier lifetime will be strongly affected by the concentration of I vacancies and the anti-site defects with I occupying a CH3NH3 site. PMID:25243595

  14. Low-temperature SCR of NO with NH3 over activated semi-coke composite-supported rare earth oxides

    NASA Astrophysics Data System (ADS)

    Wang, Jinping; Yan, Zheng; Liu, Lili; Zhang, Yingyi; Zhang, Zuotai; Wang, Xidong

    2014-08-01

    The catalysts with different rare earth oxides (La, Ce, Pr and Nd) loaded onto activated semi-coke (ASC) via hydrothermal method are prepared for the selective catalytic reduction (SCR) of NO with NH3 at low temperature (150-300 °C). It is evidenced that CeO2 loaded catalysts present the best performance, and the optimum loading amount of CeO2 is about 10 wt%. Composite catalysts by doping La, Pr and Nd into CeO2 are prepared to obtain further improved catalytic properties. The SCR mechanism is investigated through various characterizations, including XRD, Raman, XPS and FT-IR, the results of which indicate that the oxygen defect plays an important role in SCR process and the doped rare earth elements effectively serve as promoters to increase the concentration of oxygen vacancies. It is also found that the oxygen vacancies in high concentration are favored for the adsorption of O2 and further oxidation of NO, which facilitates a rapid progressing of the following reduction reactions. The SCR process of NO with NH3 at low temperature over the catalysts of ASC composite-supported rare earth oxides mainly follows the Langmuir-Hinshlwood mechanism.

  15. Characterization of an Fe?N-NH2 Intermediate Relevant to Catalytic N2 Reduction to NH3.

    PubMed

    Anderson, John S; Cutsail, George E; Rittle, Jonathan; Connor, Bridget A; Gunderson, William A; Zhang, Limei; Hoffman, Brian M; Peters, Jonas C

    2015-06-24

    The ability of certain transition metals to mediate the reduction of N2 to NH3 has attracted broad interest in the biological and inorganic chemistry communities. Early transition metals such as Mo and W readily bind N2 and mediate its protonation at one or more N atoms to furnish M(NxHy) species that can be characterized and, in turn, extrude NH3. By contrast, the direct protonation of Fe-N2 species to Fe(NxHy) products that can be characterized has been elusive. Herein, we show that addition of acid at low temperature to [(TPB)Fe(N2)][Na(12-crown-4)] results in a new S = 1/2 Fe species. EPR, ENDOR, Mössbauer, and EXAFS analysis, coupled with a DFT study, unequivocally assign this new species as [(TPB)Fe?N-NH2](+), a doubly protonated hydrazido(2-) complex featuring an Fe-to-N triple bond. This unstable species offers strong evidence that the first steps in Fe-mediated nitrogen reduction by [(TPB)Fe(N2)][Na(12-crown-4)] can proceed along a distal or "Chatt-type" pathway. A brief discussion of whether subsequent catalytic steps may involve early or late stage cleavage of the N-N bond, as would be found in limiting distal or alternating mechanisms, respectively, is also provided. PMID:26000443

  16. Evaluation of biochars by temperature programmed oxidation/mass spectroscopy

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Biochar from the thermochemical conversion of biomass was evaluated by Temperature Programmed Oxidation (TPO) coupled with mass spectroscopy. This technique can be used to assess the oxidative reactivity of carbonaceous solids where higher temperature reactivity indicates greater structural order. ...

  17. Effect of humidity on the a.c. impedance of CH3NH3SnCl3 hybrid films

    NASA Astrophysics Data System (ADS)

    Mosca, R.; Ferro, P.; Besagni, T.; Calestani, D.; Chiarella, F.; Licci, F.

    2011-09-01

    Impedance spectroscopy measurements show that complex conductivity of thermally ablated CH3NH3SnCl3 films is strongly enhanced when humidity increases. Coplanar two-electrode test devices are modeled through an equivalent circuit comprising one resistance and two constant phase elements. It is shown that the influence of ambient humidity is mainly resistive. The dynamic responses of the devices to humidification/dehumidification cycles point out that the a.c. current varies by more than three orders of magnitude when humidity is varied between dry air and 80% relative humidity. The rise times are few hundred seconds while fall times are as short as few tens of seconds. This observation suggests that impedance variations are determined by mechanisms involving loosely bound water molecules physisorbed at the surface of the hybrid film. The results obtained are discussed in terms of protonic conduction.

  18. The optoelectronic role of chlorine in CH3NH3PbI3(Cl)-based perovskite solar cells

    PubMed Central

    Chen, Qi; Zhou, Huanping; Fang, Yihao; Stieg, Adam Z.; Song, Tze-Bin; Wang, Hsin-Hua; Xu, Xiaobao; Liu, Yongsheng; Lu, Shirong; You, Jingbi; Sun, Pengyu; McKay, Jeff; Goorsky, Mark S.; Yang, Yang

    2015-01-01

    Perovskite photovoltaics offer a compelling combination of extremely low-cost, ease of processing and high device performance. The optoelectronic properties of the prototypical CH3NH3PbI3 can be further adjusted by introducing other extrinsic ions. Specifically, chlorine incorporation has been shown to affect the morphological development of perovksite films, which results in improved optoelectronic characteristics for high efficiency. However, it requires a deep understanding to the role of extrinsic halide, especially in the absence of unpredictable morphological influence during film growth. Here we report an effective strategy to investigate the role of the extrinsic ion in the context of optoelectronic properties, in which the morphological factors that closely correlate to device performance are mostly decoupled. The chlorine incorporation is found to mainly improve the carrier transport across the heterojunction interfaces, rather than within the perovskite crystals. Further optimization according this protocol leads to solar cells achieving power conversion efficiency of 17.91%. PMID:26068804

  19. Electron-Temperature Dependence of the Recombination of NH4(+)((NH3)(sub n) Ions with Electrons

    NASA Technical Reports Server (NTRS)

    Skrzypkowski, M. P.; Johnson, R.

    1997-01-01

    The two-body recombination of NH4(+)(NH3)(sub 2,3) cluster-ions with electrons has been studied in an afterglow experiment in which the electron temperature T, was elevated by radio-frequency heating from 300 K up to 900 K. The recombination coefficients for the n = 2 and n = 3 cluster ions were found to be equal, alpha(sub 2, sup(2)) = alpha(sub 3, sup(2)) = (4.8 +/- 0.5) x 10(exp - 6)cu cm/s, and to vary with electron temperature as T(sub c, sup -0.65) rather than to be nearly temperature-independent as had been inferred from measurements in microwave-heated plasmas.

  20. Laboratory measurements of the microwave opacity of gaseous ammonia (NH3) under simulated conditions for the Jovian atmosphere

    NASA Astrophysics Data System (ADS)

    Steffes, P. G.; Jenkins, J. M.

    1987-10-01

    Gaseous ammonia (NH3) has long been recognized as a primary source of microwave opacity in the atmosphere of Jupiter. In order to more accurately infer the abundance and distribution of ammonia from radio emission measurements in the 1- to 20-cm wavelength range and radio occultation measurements at 3.6 and 13 cm, the authors have made measurements of the microwave opacity from gaseous ammonia under simulated conditions for the Jovian atmosphere. Measurements of ammonia absorptivity were made at five frequencies from 1.62 to 21.7 GHz (wavelengths from 18.5 to 1.38 cm), at temperatures from 178 to 300K, and at pressures from 1 to 6 atm, in a 90% hydrogen/10% helium atmosphere.

  1. The optoelectronic role of chlorine in CH3NH3PbI3(Cl)-based perovskite solar cells.

    PubMed

    Chen, Qi; Zhou, Huanping; Fang, Yihao; Stieg, Adam Z; Song, Tze-Bin; Wang, Hsin-Hua; Xu, Xiaobao; Liu, Yongsheng; Lu, Shirong; You, Jingbi; Sun, Pengyu; McKay, Jeff; Goorsky, Mark S; Yang, Yang

    2015-01-01

    Perovskite photovoltaics offer a compelling combination of extremely low-cost, ease of processing and high device performance. The optoelectronic properties of the prototypical CH3NH3PbI3 can be further adjusted by introducing other extrinsic ions. Specifically, chlorine incorporation has been shown to affect the morphological development of perovksite films, which results in improved optoelectronic characteristics for high efficiency. However, it requires a deep understanding to the role of extrinsic halide, especially in the absence of unpredictable morphological influence during film growth. Here we report an effective strategy to investigate the role of the extrinsic ion in the context of optoelectronic properties, in which the morphological factors that closely correlate to device performance are mostly decoupled. The chlorine incorporation is found to mainly improve the carrier transport across the heterojunction interfaces, rather than within the perovskite crystals. Further optimization according this protocol leads to solar cells achieving power conversion efficiency of 17.91%. PMID:26068804

  2. The infrared spectra and phase transitions of pure and isotopically impure 2ND3?H2O, 2NH3?D2O, 2NH3?H2O, and 2ND3?D2O between 100 and 15 K

    Microsoft Academic Search

    John E. Bertie; J. Paul Devlin

    1984-01-01

    Infrared transmission spectra of 2NH3 ? H2O, 2NH3 ? D2O, 2ND3 ? H2O, and 2ND3 ? D2O have been measured between 100 and 15 K. Spectra of NH3, ND3, NH2D, ND2H, H2O, D2O, and HOD as dilute or major impurities in the above crystals have also been measured. Information about the site splitting, multiple-site splitting, and unit-cell-group splitting, has been

  3. Optical Properties of Electron Trapped Center in Layered Ionic Crystals (CH3NH3)2CdCl4 and (C2H5NH3)2CdCl4 Irradiated with X-Rays at 15 K

    Microsoft Academic Search

    Takehisa Yoshinari; Tomochika Matsuyama; Hitoshi Yamaoka; Kiyoshi Aoyagi

    1989-01-01

    New optical absorption bands (IR bands) were found at around 10˜20 kcm-1 besides absorption band of Cl2- molecular center in two-dimensional crystals of (CH3NH3)2CdCl4 and (C2H5NH3)2CdCl4 irradiated with X-rays at 15 K. The absorption intensities increase with the X-ray dosage in proportion to that of the Cl2- center and decrease at temperatures higher than 25 K for (CH3NH3)2CdCl4 and 35

  4. Influence of bulking agents on CH4, N2O, and NH3 emissions during rapid composting of pig manure from the Chinese Ganqinfen system*

    PubMed Central

    Sun, Xiang-ping; Lu, Peng; Jiang, Tao; Schuchardt, Frank; Li, Guo-xue

    2014-01-01

    Mismanagement of the composting process can result in emissions of CH4, N2O, and NH3, which have caused severe environmental problems. This study was aimed at determining whether CH4, N2O, and NH3 emissions from composting are affected by bulking agents during rapid composting of pig manure from the Chinese Ganqinfen system. Three bulking agents, corn stalks, spent mushroom compost, and sawdust, were used in composting with pig manure in 60 L reactors with forced aeration for more than a month. Gas emissions were measured continuously, and detailed gas emission patterns were obtained. Concentrations of NH3 and N2O from the composting pig manure mixed with corn stalks or sawdust were higher than those from the spent mushroom compost treatment, especially the sawdust treatment, which had the highest total nitrogen loss among the three runs. Most of the nitrogen was lost in the form of NH3, which accounts for 11.16% to 35.69% of the initial nitrogen. One-way analysis of variance for NH3 emission showed no significant differences between the corn stalk and sawdust treatments, but a significant difference was noted between the spent mushroom compost and sawdust treatments. The introduction of sawdust reduced CH4 emission more than the corn stalks and spent mushroom compost. However, there were no significant differences among the three runs for total carbon loss. All treatments were matured after 30 d. PMID:24711356

  5. Effect of water vapor on NH3-NO/NO2 SCR performance of fresh and aged MnOx-NbOx-CeO2 catalysts.

    PubMed

    Chen, Lei; Si, Zhichun; Wu, Xiaodong; Weng, Duan; Wu, Zhenwei

    2015-05-01

    A MnOx-NbOx-CeO2 catalyst for low temperature selective catalytic reduction (SCR) of NOx with NH3 was prepared by a sol-gel method, and characterized by NH3-NO/NO2 SCR catalytic activity, NO/NH3 oxidation activity, NOx/NH3 TPD, XRD, BET, H2-TPR and in-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). The results indicate that the MnOx-NbOx-CeO2 catalyst shows excellent low temperature NH3-SCR activity in the temperature range of 150-300°C. Water vapor inhibits the low temperature activity of the catalyst in standard SCR due to the inhibition of NOx adsorption. As the NO2 content increases in the feed, water vapor does not affect the activity in NO2 SCR. Meanwhile, water vapor significantly enhances the N2 selectivity of the fresh and the aged catalysts due to its inhibition of the decomposition of NH4NO3 into N2O. PMID:25968280

  6. Study on the correlations between the structure and photoelectric properties of CH3NH3PbI3 perovskite light-harvesting material

    NASA Astrophysics Data System (ADS)

    Xie, Junjie; Liu, Yan; Liu, Jianjun; Lei, Lei; Gao, Qianqian; Li, Jiaqing; Yang, Songwang

    2015-07-01

    The [PbI6] inorganic framework in the CH3NH3PbI3 could be affected by the oxidization effect of I- ions in atmosphere. The [PbI6] octahedral torsion angle increased ?4.94° after the newly prepared CH3NH3PbI3 powders were stored in dry atmosphere for 30 days at 20 °C according to the results of XRD Rietveld refinement and X-ray Absorption Fine Structure. Analyses based on density of states indicated that UV-vis adsorption edge at ?850 cm-1 corresponded to electron transition from I-5p orbitals to empty Pb-6p orbitals. The increased [PbI6] octahedral torsion angle made the band gap energy of CH3NH3PbI3 increased according to First-principle calculation and UV-vis absorption spectra. As a result, the band gap energy of CH3NH3PbI3 were strongly related to the structure of [PbI6] inorganic framework because the electrons diffused along the [PbI6] octahedral chains in CH3NH3PbI3 perovskite.

  7. The effect of wind velocity, air temperature and humidity on NH 3 and SO 2 transfer into bean leaves ( phaseolus vulgaris L.)

    NASA Astrophysics Data System (ADS)

    van Hove, L. W. A.; Vredenberg, W. J.; Adema, E. H.

    The influence of wind velocity, air temperature and vapour pressure deficit of the air (VPD) on NH 3 and SO 2 transfer into bean leaves ( Phaseolus vulgaris L.) was examined using a leaf chamber. The measurements suggested a transition in the properties of the leaf boundary layer at a wind velocity of 0.3-0.4 ms -1 which corresponds to a Recrit value of about 2000. At higher wind velocities the leaf boundary layer resistance ( rb) was 1.5-2 times lower than can be calculated from the theory. Nevertheless, the assessed relationships between rb and wind velocity appeared to be similar to the theoretical derived relationship for rb. The NH 3 flux and in particular the SO 2 flux into the leaf strongly increased at a VPD decline. The increase of the NH 3 flux could be attributed to an increase of the stomatal conductance ( gs). However, the increase of the SO 2 flux could only partly be explained by an increase of gs. An apparent additional uptake was also observed for the NH 3 uptake at a low temperature and VPD. The SO 2 flux was also influenced by air temperature which could be explained by a temperature effect on gs. The results suggest that calculation of the NH 3 and SO 2 flux using data of gs gives a serious understimation of the real flux of these gases into leaves at a low temperature and VPD.

  8. Internal Rotation in CF3ICdotsNH3 and CF3I\\cdotsN(CH3)_3 Probed by Cp-Ftmw Spectroscopy

    NASA Astrophysics Data System (ADS)

    Walker, N. R.; Stephens, S. L.; Legon, A. C.

    2011-06-01

    The pure rotational spectra of CF3ICdotsNH3 and CF3I\\cdotsN(CH3)_3 have been measured by chirped-pulse, Fourier transform microwave (CP-FTMW) spectroscopy between 7 and 18.5 GHz. Both molecules are generated by supersonic expansion of a gas sample containing a small percentage of each precursor in a balance of argon. The spectra of both complexes are consistent with {C}3v prolate symmetric top structures. The observed spectrum of CF3ICdotsNH3 displays evidence for internal rotation of NH3 about the principal axis. More than one hundred transitions of CF3ICdotsNH3 have been assigned to the internal rotor {A} state allowing rotational, centrifugal distortion constants and a nuclear quadrupole coupling constant for the iodine atom to be determined for this state. Measurements performed using a Balle-Flygare FTMW spectrometer further allow determination of a nuclear quadrupole coupling constant for the 14N nucleus. Many transitions in the spectrum of the CF3ICdots15NH3 isotopologue have also been measured and the length of the halogen bond between the iodine and nitrogen atoms has been determined. Measurements of hyperfine components in nine different J''?J' transitions of CF3I\\cdotsN(CH3)_3 have allowed assignment of the spectrum of this complex to determine rotational, centrifugal distortion and nuclear quadrupole coupling constants.

  9. Inkjet printing and instant chemical transformation of a CH3NH3PbI3/nanocarbon electrode and interface for planar perovskite solar cells.

    PubMed

    Wei, Zhanhua; Chen, Haining; Yan, Keyou; Yang, Shihe

    2014-11-24

    A planar perovskite solar cell that incorporates a nanocarbon hole-extraction layer is demonstrated for the first time by an inkjet printing technique with a precisely controlled pattern and interface. By designing the carbon plus CH3NH3I ink to transform PbI2 in?situ to CH3NH3PbI3, an interpenetrating seamless interface between the CH3NH3PbI3 active layer and the carbon hole-extraction electrode was instantly constructed, with a markedly reduced charge recombination compared to that with the carbon ink alone. As a result, a considerably higher power conversion efficiency up to 11.60% was delivered by the corresponding solar cell. This method provides a major step towards the fabrication of low-cost, large-scale, metal-electrode-free but still highly efficient perovskite solar cells. PMID:25255744

  10. P-P heterojunction sensor of self-assembled polyaniline nano-thin film/microstructure silicon array for NH3 detection

    NASA Astrophysics Data System (ADS)

    Tai, Huiling; Xu, Xiaoying; Ye, Zongbiao; Liu, Chunhua; Xie, Guangzhong; Jiang, Yadong

    2015-02-01

    A novel P-P isotype heterojunction sensor was developed by modifying microstructure silicon array (MSSA) with self-assembled polyaniline (PANI) nano-thin film for ammonia (NH3) detection at room temperature, and the comparative study of response performance was focused on sensors with varied etching time of MSSA. The results indicated that PANI nanorods network was successfully deposited on MSSA surface, and PANI/MSSA sensor exhibited superior NH3-sensing properties than PANI/plane silicon sensor, which should be ascribed to three-dimensional structure and p-p heterojunction enhancement effect. Meanwhile, the optimized sensor with 4 min etching time exhibited high response, good reversibility, repeatability and selectivity when exposed to NH3.

  11. Bias-dependent effects in planar perovskite solar cells based on CH3NH3PbI3-xClx films.

    PubMed

    Lyu, Miaoqiang; Yun, Jung-Ho; Ahmed, Rasin; Elkington, Daniel; Wang, Qiong; Zhang, Meng; Wang, Hongxia; Dastoor, Paul; Wang, Lianzhou

    2015-09-01

    A unique bias-dependent phenomenon in CH3NH3PbI3-xClx based planar perovskite solar cells has been demonstrated, in which the photovoltaic parameters derived from the current-voltage (I-V) curves are highly dependent on the initial positive bias of the I-V measurement. In FTO/CH3NH3PbI3-xClx/Au devices, the open-circuit voltage and short-circuit current increased by ca. 337.5% and 281.9% respectively, by simply increasing the initial bias from 0.5V to 2.5V. PMID:25956128

  12. Air-Stable (CAAC)CuCl and (CAAC)CuBH4 Complexes as Catalysts for the Hydrolytic Dehydrogenation of BH3 NH3.

    PubMed

    Hu, Xingbang; Soleilhavoup, Michèle; Melaimi, Mohand; Chu, Jiaxiang; Bertrand, Guy

    2015-05-11

    The first stable copper borohydride complex [(CAAC)CuBH4 ] [CAAC=cyclic(alkyl)(amino)carbene] bearing a single monodentate ligand was prepared by addition of NaBH4 or BH3 NH3 to the corresponding [(CAAC)CuCl] complex. Both complexes are air-stable and promote the catalytic hydrolytic dehydrogenation of ammonia borane. The amount of hydrogen released reaches 2.8 H2 /BH3 NH3 with a turnover frequency of 8400?mol?H?2?molcat (-1) ?h(-1) at 25?°C. In a fifteen-cycle experiment, the catalyst was reused without any loss of efficiency. PMID:25802096

  13. Improved Determination of the 10-00 Rotational Frequency of NH3D+ from the High-resolution Spectrum of the ?4 Infrared Band

    NASA Astrophysics Data System (ADS)

    Doménech, J. L.; Cueto, M.; Herrero, V. J.; Tanarro, I.; Tercero, B.; Fuente, A.; Cernicharo, J.

    2013-07-01

    The high-resolution spectrum of the ?4 band of NH3D+ has been measured by difference frequency IR laser spectroscopy in a multipass hollow cathode discharge cell. From the set of molecular constants obtained from the analysis of the spectrum, a value of 262817 ± 6 MHz (±3?) has been derived for the frequency of the 10-00 rotational transition. This value supports the assignment to NH3D+ of lines at 262816.7 MHz recorded in radio astronomy observations in Orion-IRc2 and the cold prestellar core B1-bS.

  14. Stability domains of water ices in the NH3 - H2O system: experimental results and thermodynamic modelling

    NASA Astrophysics Data System (ADS)

    Grasset, O.; Choukroun, M.

    2009-12-01

    The ammonia compound decreases very significantly the melting curve of water ices. This property is of fundamental importance in planetology because it constrains the nature of the icy mantle within icy moons of the giant planets (1,2). That is why many experimental studies have been conducted for understanding the binary system H2O - NH3 in the temperature - pressure space (1-6). The most surprising effect of the ammonia compound is that it decreases the melting temperature of the ice polymorphs down to 180 K at the eutectic temperature (1,2). This effect has been observed throughout the pressure domain relevant for icy moons from 0 to 1 GPa. In this paper, a review of these efforts, in addition to new results, obtained by the authors with a sapphire anvil cell in the domains where experimental data were lacking (8), will be presented. A thermodynamic description that uses the chemical potential approach can be used for describing the pure water system (7,9). However, most studies that have used this approach were clearly focused on describing the melting curves of the water phase diagram. A new formulation has recently been proposed (9), which allows to compute phase equilibria in the whole P-T domain where ice polymorphs are encountered. In this work, the model has been improved by incorporating the ice II polymorph, and by describing more accurately the behaviour of the binary liquid mixture which is close to a regular symmetric solution (10). This model has been validated in the pure water domain by checking that all stability domains of the ice polymorphs (Ih, II, III, V, and VI) were predicted with an accuracy better than 1%. A very good reproduction of the stability domain of ice Ih in the H2O-NH3 phase diagram is also achieved. It will be shown that the thermodynamic approach allows to predict the stability of each ice polymorphs whatever the pressure and temperature are, in very good agreement with the available experimental data. It appears that the stability domain of some polymorphs, such as ice II and ice V, enlarges with the ammonia concentration, whereas that of ice III diminishes with NH3 concentration, and this phase is expected to disappear above 10 %wt of ammonia in the system. For each polymorph, a whole description of stability domains and melting surfaces will be presented. Implications for the occurrence of liquid oceans within the largest moons will also be briefly discussed. Ref. : 1. Hogenboom et al., Icarus, 1997. 2. Grasset and Pargamin, Planet. Space Sci., 2005. 3. Croft et al., Icarus, 1988. 4. Johnson and Nicol, J. Geoph. Res., 1987. 5Kargel, Icarus, 1992. 6. Leliwa-Kopystynski et al., Icarus, 2002. 7. Chizhov and Nagornov, J. Appl. Mech. Techn. Phys. 1991. 8. Choukroun M., PhD thesis, 2007. 9. Choukroun and Grasset, J. Chem. Phys, 2007. 10.Wood and Fraser, Oxford Univ. Press, 1977.

  15. The reaction NH2 + PH3 yields NH3 + PH2 - Absolute rate constant measurement and implication for NH3 and PH3 photochemistry in the atmosphere of Jupiter

    NASA Technical Reports Server (NTRS)

    Bosco, S. R.; Brobst, W. D.; Nava, D. F.; Stief, L. J.

    1983-01-01

    The rate constant is measured over the temperature interval 218-456 K using the technique of flash photolysis-laser-induced fluorescence. NH2 radicals are produced by the flash photolysis of ammonia highly diluted in argon, and the decay of fluorescent NH2 photons is measured by multiscaling techniques. For each of the five temperatures employed in the study, the results are shown to be indepenent of variations in PH3 concentration, total pressure (argon), and flash intensity. It is found that the rate constant results are best represented for T between 218 and 456 K by the expression k = (1.52 + or - 0.16) x 10 to the -12th exp(-928 + or - 56/T) cu cm per molecule per sec; the error quoted is 1 standard deviation. This is the first determination of the rate constant for the reaction NH2 + PH3. The data are compared with an estimate made in order to explain results of the radiolysis of NH3-PH3 mixtures. The Arrhenius parameters determined here for NH2 + PH3 are then contrasted with those for the corresponding reactions of H and OH with PH3.

  16. An Example of a Reactive Template in the Synthesis of a Novel Layered Aluminum Phosphate, (Al 3P 4O 16) 3-(NH 3(CH 2) 5NH 3) 2+(C 5H 10NH 2) +

    NASA Astrophysics Data System (ADS)

    Chippindale, A. M.; Natarajan, S.; Thomas, J. M.; Jones, R. H.

    1994-07-01

    A new layered aluminum phosphate with P:Al ratio 4:3 has been prepared under nonaqueous conditions in the presence of 1,5-diaminopentane and the structure has been determined by single-crystal X-ray diffraction. The compound crystallizes in the monoclinic space group P2 1/ c ( Z = 4), with lattice parameters a = 9.801(2), b = 14.837(2), c = 17.815(3) Å, ? = 105.65(1)°, and V = 2494.7 Å 3 ( R = 0.042 and Rw = 0.058). The structure consists of AlO 4 and PO 4 tetrahedra linked to form layers. Two organic cations, diprotonated 1,5-diaminopentane and protonated piperidine derived from cyclization of the starting amine, lie between the inorganic layers and are hydrogen bonded to the layers through NH +3 and NH +2 groups, respectively. The two organic cations are located in two crystallographically distinct eight-membered windows within the layers, the piperidinium cations being associated with circular cavities of ˜6.9 Å in diameter, and the 1,5-diaminopentane cations with elliptical cavities (of axes ˜5.9 and 8.0 Å).

  17. Controllable Sequential Deposition of Planar CH3NH3PbI3 Perovskite Films via Adjustable Volume Expansion.

    PubMed

    Zhang, Taiyang; Yang, Mengjin; Zhao, Yixin; Zhu, Kai

    2015-06-10

    We demonstrate a facile morphology-controllable sequential deposition of planar CH3NH3PbI3 (MAPbI3) film by using a novel volume-expansion-adjustable PbI2·xMAI (x: 0.1-0.3) precursor film to replace pure PbI2. The use of additive MAI during the first step of deposition leads to the reduced crystallinity of PbI2 and the pre-expansion of PbI2 into PbI2·xMAI with adjustable morphology, which result in about 10-fold faster formation of planar MAPbI3 film (without PbI2 residue) and thus minimize the negative impact of the solvent isopropanol on perovskites during the MAI intercalation/conversion step. The best efficiency obtained for a planar perovskite solar cell based on PbI2·0.15MAI is 17.22% (under one sun illumination), which is consistent with the stabilized maximum power output at an efficiency of 16.9%. PMID:25996160

  18. The reaction of dichlorodiammineplatinum(II), [PtCl2(NH3)2], isomers with zinc fingers.

    PubMed

    Tsotsoros, Samantha D; Qu, Yun; Farrell, Nicholas P

    2015-02-01

    The interaction of cis-DDP and trans-DDP (DDP=[PtCl2(NH3)2]) with the C-terminal zinc finger (ZF2) of the HIVNCp7 nucleocapsid protein was investigated by fluorescence, circular dichroism, mass spectrometry, and {(1)H, (15)N} HSQC (heteronuclear single quantum coherence) NMR spectroscopy. The rate of reaction differed significantly for the two compounds, with the trans isomer reacting in a significantly faster manner, as expected. {(1)H, (15)N} HSQC NMR of (15)N-labeled compounds with the ZF2 showed the appearance of several new (15)N peaks, consistent with sulfur binding and formation of Pt-S species. Mass spectrometry confirmed the formation of several different Pt-apopeptide/ZF2 adducts. Circular dichroism and fluorescence spectroscopy also indicated conformational changes upon binding while a 33% decrease in fluorescence of the unique tryptophan residue was seen in 72h upon complexation of the cis isomer, while the trans isomer quenched 50% in just 24h. PMID:25528679

  19. Thermal Assisted Oxygen Annealing for High Efficiency Planar CH3NH3PbI3 Perovskite Solar Cells

    PubMed Central

    Ren, Zhiwei; Ng, Annie; Shen, Qian; Gokkaya, Huseyin Cem; Wang, Jingchuan; Yang, Lijun; Yiu, Wai-Kin; Bai, Gongxun; Djuriši?, Aleksandra B.; Leung, Wallace Woon-fong; Hao, Jianhua; Chan, Wai Kin; Surya, Charles

    2014-01-01

    We report investigations on the influences of post-deposition treatments on the performance of solution-processed methylammonium lead triiodide (CH3NH3PbI3)-based planar solar cells. The prepared films were stored in pure N2 at room temperature or annealed in pure O2 at room temperature, 45°C, 65°C and 85°C for 12?hours prior to the deposition of the metal electrodes. It is found that annealing in O2 leads to substantial increase in the power conversion efficiencies (PCEs) of the devices. Furthermore, strong dependence on the annealing temperature for the PCEs of the devices suggests that a thermally activated process may underlie the observed phenomenon. It is believed that the annealing process may facilitate the diffusion of O2 into the spiro-MeOTAD for inducing p-doping of the hole transport material. Furthermore, the process can result in lowering the localized state density at the grain boundaries as well as the bulk of perovskite. Utilizing thermal assisted O2 annealing, high efficiency devices with good reproducibility were attained. A PCE of 15.4% with an open circuit voltage (VOC) 1.04?V, short circuit current density (JSC) 23?mA/cm2, and fill factor 0.64 had been achieved for our champion device. PMID:25341527

  20. Effects of SO2 on selective catalytic reduction of NO with NH3 over a TiO2 photocatalyst

    NASA Astrophysics Data System (ADS)

    Yamamoto, Akira; Teramura, Kentaro; Hosokawa, Saburo; Tanaka, Tsunehiro

    2015-04-01

    The effect of SO2 gas was investigated on the activity of the photo-assisted selective catalytic reduction of nitrogen monoxide (NO) with ammonia (NH3) over a TiO2 photocatalyst in the presence of excess oxygen (photo-SCR). The introduction of SO2 (300 ppm) greatly decreased the activity of the photo-SCR at 373 K. The increment of the reaction temperature enhanced the resistance to SO2 gas, and at 553 K the conversion of NO was stable for at least 300 min of the reaction. X-ray diffraction, FTIR spectroscopy, thermogravimetry and differential thermal analysis, x-ray photoelectron spectroscopy (XPS), elemental analysis and N2 adsorption measurement revealed that the ammonium sulfate species were generated after the reaction. There was a strong negative correlation between the deposition amount of the ammonium sulfate species and the specific surface area. Based on the above relationship, we concluded that the deposition of the ammonium sulfate species decreased the specific surface area by plugging the pore structure of the catalyst, and the decrease of the specific surface area resulted in the deactivation of the catalyst.

  1. Adsorption behavior of Co anchored on graphene sheets toward NO, SO2, NH3, CO and HCN molecules

    NASA Astrophysics Data System (ADS)

    Tang, Yanan; Chen, Weiguang; Li, Chenggang; Pan, Lijun; Dai, Xianqi; Ma, Dongwei

    2015-07-01

    Based on the first-principles of density-functional theory (DFT), the effects of gas adsorption on the change in geometric stability, electronic structure and magnetic properties of graphene with anchored Co (Co-graphene) systems were investigated. A single Co adatom interacts much weaker with pristine graphene (Co/pri-graphene) than with the graphene containing a single vacancy (Co/SV-graphene). The Co dopant provides more electrons to the dangling bonds of carbon atom at defective site and exhibits more positive charges, which makes Co/SV-graphene less prone to be adsorbed by gas molecules in comparison to Co/pri-graphene. It is found that the electronic structure and magnetic properties of Co-graphene systems can be modulated by adsorbing gas molecules. Except the NH3 molecule, the adsorbed NO, SO2, CO or HCN as electron acceptors on the Co/pri-graphene can exhibit semiconducting properties. Among the gas molecules, the strong adsorption of NO molecule can effectively regulate the magnetic properties of Co-graphene systems. Moreover, the stable configuration of Co/SV-graphene is more likely to be the gas sensor for detecting NO and SO2. The results validate that the reactivity of atomic-scale catalyst is supported on graphene sheets, which is expected to be potentially efficient in the gas sensors and electronic device.

  2. GaN materials growth by MOVPE in a new-design reactor using DMHy and NH 3

    NASA Astrophysics Data System (ADS)

    Gautier, S.; Sartel, C.; Ould-Saad, S.; Martin, J.; Sirenko, A.; Ougazzaden, A.

    2007-01-01

    Thin films of GaN were grown on template substrates of 4-?m-thick GaN layers on sapphire substrates by low-pressure metal organic vapour-phase epitaxy (LP-MOVPE) in a new-design reactor with the shape T. Wide range of growth temperature from 520 to 1100 °C was explored. At low temperature growth between 550 and 690 °C, dimethylhydrazine (DMHy) was used as source of atomic nitrogen while ammonia (NH 3) was used at high temperature growth (1000-1100 °C). At low temperature micro-Raman spectroscopy revealed a significant relaxation of the selection rules for the scattering by the optical phonons in the films grown at lower temperatures. Variation of the intensity ratio for E 2H and E 1 phonon modes has been attributed to changes in the structural quality of the films grown at different temperatures. At high temperature, the quality of GaN layers were comparable to that of the substrate before growth.

  3. Density Functional Studies of Stoichiometric Surfaces of Orthorhombic Hybrid Perovskite CH3NH3PbI3

    SciTech Connect

    Wang, Yun [Griffith University, Nathan, Queensland, Australia; Huang, Jingsong [ORNL; Sumpter, Bobby G [ORNL; Zhang, Haimin [Griffith University, Nathan, Queensland, Australia; Liu, Porun [Griffith University, Nathan, Queensland, Australia; Yang, Huagui [Griffith University, Nathan, Queensland, Australia; Zhao, Huijun [Griffith University, Nathan, Queensland, Australia

    2015-01-01

    Organic/inorganic hybrid perovskite materials are highly attractive for dye-sensitized solar cells as demonstrated by their rapid advances in energy conversion efficiency. In this work, the structures, energetics, and electronic properties for a range of stoichiometric surfaces of the orthorhombic perovskite CH3NH3PbI3 are theoretically studied using density functional theory. Various possible spatially and constitutionally isomeric surfaces are considered by diversifying the spatial orientations and connectivities of surface Pb-I bonds. The comparison of the surface energies for the most stable configurations identified for various surfaces shows that the stabilities of stoichiometric surfaces are mainly dictated by the coordination numbers of surface atoms, which are directly correlated with the numbers of broken bonds. Additionally, Coulombic interactions between I anions and organic countercations on the surface also contribute to the stabilization. Electronic properties are compared between the most stable (100) surface and the bulk phase, showing generally similar features except for the lifted band degeneracy and the enhanced bandgap energy for the surface. These studies on the stoichiometric surfaces serve as the first step toward gaining a fundamental understanding of the interfacial properties in the current structural design of perovskite based solar cells, in order to achieve further breakthroughs in solar conversion efficiencies.

  4. Demonstration of isotype GaN/AlN/GaN heterobarrier diodes by NH3-molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Fireman, Micha N.; Browne, David A.; Mazumder, Baishakhi; Speck, James S.; Mishra, Umesh K.

    2015-05-01

    The results of vertical transport through nitride heterobarrier structures grown by ammonia molecular beam epitaxy are presented. Structures are designed with binary layers to avoid the effects of random alloy fluctuations in ternary nitride barriers. The unintentional incorporation of Ga in the AlN growth is investigated by atom probe tomography and is shown to be strongly dependent on both the NH3 flowrate and substrate temperature growth parameters. Once nominally pure AlN layer growth conditions are achieved, structures consisting of unintentionally doped (UID) GaN spacer layers adjacent to a nominally pure AlN are grown between two layers of n+ GaN, from which isotype diodes are fabricated. Varying the design parameters of AlN layer thickness, UID spacer layer thickness, and threading dislocation density show marked effects on the vertical transport characteristics of these structures. The lack of significant temperature dependence, coupled with Fowler-Nordheim and/or Milliken-Lauritsen analysis, point to a prevalently tunneling field emission mechanism through the AlN barrier. Once flatband conditions in the UID layer are achieved, electrons leave the barrier with significant energy. This transport mechanism is of great interest for applications in hot electron structures.

  5. Characteristics of SiO x N y films deposited by inductively coupled plasma enhanced chemical vapor deposition using HMDS\\/NH 3\\/O 2\\/Ar for water vapor diffusion barrier

    Microsoft Academic Search

    J. H. Lee; C. H. Jeong; H. B. Kim; J. T. Lim; S. J. Kyung; G. Y. Yeom

    2006-01-01

    SiOxNy thin films were deposited by inductively coupled plasma enhanced chemical vapor deposition (ICP-PECVD) using hexamethyldisilazane (HMDS, 99.9%)\\/NH3\\/O2\\/Ar at a low temperature, and examined for use as a water vapor diffusion barrier. The film characteristics were investigated as a function of the O2:NH3 ratio. An increase in the O2:NH3 ratio decreased the level of impurities such as –CHx, N–H in

  6. Origin of the visible-light photoactivity of NH3-treated TiO2: Effect of nitrogen doping and oxygen vacancies

    NASA Astrophysics Data System (ADS)

    Chen, Yilin; Cao, Xiaoxin; Lin, Bizhou; Gao, Bifen

    2013-01-01

    N-doped and oxygen-deficient TiO2 photocatalysts were obtained by heating commercial TiO2 in NH3 atmosphere, followed by a postcalcination process. Catalysts were characterized by X-ray diffraction (XRD), N2-sorption BET surface area, X-ray photoelectron spectroscopy (XPS), Elemental analysis (EA), UV/vis diffuse reflectance spectroscopy (DRS), Electron spin resonance (ESR) and Photoluminescence (PL). It shows that the NH3-heat-treatment of TiO2 resulted in not only nitrogen doping but also creation of oxygen vacancies with optical absorption in visible-light region. The postcalcination achieved several beneficial effects including dramatic removal of surface amino species, a rapid decrease in surface Ti3+ species, and a low recombination rate of photogenerated carriers on the co-doped TiO2. The photocatalytic measurement was carried out by the degradation of gas-phase benzene under visible light irradiation. At steady state, the photocatalytic conversion rate of benzene over the postannealed catalyst was 35.8%, accompanied by the yield of 115 ppmv CO2, which was much higher than that on the NH3-treated TiO2 before postcalcination or the H2-treated TiO2 catalysts. Results show that the visible-light activity of the NH3-treated TiO2 is attributed to a synergistic effect of substitutional nitrogen species and oxygen vacancies in TiO2.

  7. Synthesis, structure, and photovoltaic property of a nanocrystalline 2H perovskite-type novel sensitizer (CH3CH2NH3)PbI3

    NASA Astrophysics Data System (ADS)

    Im, Jeong-Hyeok; Chung, Jaehoon; Kim, Seung-Joo; Park, Nam-Gyu

    2012-06-01

    A new nanocrystalline sensitizer with the chemical formula (CH3CH2NH3)PbI3 is synthesized by reacting ethylammonium iodide with lead iodide, and its crystal structure and photovoltaic property are investigated. X-ray diffraction analysis confirms orthorhombic crystal phase with a = 8.7419(2) Å, b = 8.14745(10) Å, and c = 30.3096(6) Å, which can be described as 2 H perovskite structure. Ultraviolet photoelectron spectroscopy and UV-visible spectroscopy determine the valence band position at 5.6 eV versus vacuum and the optical bandgap of ca. 2.2 eV. A spin coating of the CH3CH2NH3I and PbI2 mixed solution on a TiO2 film yields ca. 1.8-nm-diameter (CH3CH2NH3)PbI3 dots on the TiO2 surface. The (CH3CH2NH3)PbI3-sensitized solar cell with iodide-based redox electrolyte demonstrates the conversion efficiency of 2.4% under AM 1.5 G one sun (100 mW/cm2) illumination.

  8. Synthesis, structure, and photovoltaic property of a nanocrystalline 2H perovskite-type novel sensitizer (CH3CH2NH3)PbI3.

    PubMed

    Im, Jeong-Hyeok; Chung, Jaehoon; Kim, Seung-Joo; Park, Nam-Gyu

    2012-01-01

    A new nanocrystalline sensitizer with the chemical formula (CH3CH2NH3)PbI3 is synthesized by reacting ethylammonium iodide with lead iodide, and its crystal structure and photovoltaic property are investigated. X-ray diffraction analysis confirms orthorhombic crystal phase with a?=?8.7419(2) Å, b?=?8.14745(10) Å, and c?=?30.3096(6) Å, which can be described as 2?H perovskite structure. Ultraviolet photoelectron spectroscopy and UV-visible spectroscopy determine the valence band position at 5.6?eV versus vacuum and the optical bandgap of ca. 2.2?eV. A spin coating of the CH3CH2NH3I and PbI2 mixed solution on a TiO2 film yields ca. 1.8-nm-diameter (CH3CH2NH3)PbI3 dots on the TiO2 surface. The (CH3CH2NH3)PbI3-sensitized solar cell with iodide-based redox electrolyte demonstrates the conversion efficiency of 2.4% under AM 1.5?G one sun (100?mW/cm2) illumination. PMID:22738298

  9. Modified two-step deposition method for high-efficiency TiO2/CH3NH3PbI3 heterojunction solar cells.

    PubMed

    Shi, Jiangjian; Luo, Yanhong; Wei, Huiyun; Luo, Jianheng; Dong, Juan; Lv, Songtao; Xiao, Junyan; Xu, Yuzhuan; Zhu, Lifeng; Xu, Xin; Wu, Huijue; Li, Dongmei; Meng, Qingbo

    2014-06-25

    Hybrid organic-inorganic perovskites (e.g., CH3NH3PbI3) are promising light absorbers for the third-generation photovoltaics. Herein we demonstrate a modified two-step deposition method to fabricate a uniform CH3NH3PbI3 capping layer with high-coverage and thickness of 300 nm on top of the mesoporous TiO2. The CH3NH3PbI3 layer shows high light-harvesting efficiency and long carrier lifetime over 50 ns. On the basis of the as-prepared film, TiO2/CH3NH3PbI3 heterojunction solar cells achieve a power conversion efficiency of 10.47% with a high open-circuit voltage of 948 mV, the highest recorded to date for hole-transport-material-free (HTM-free) perovskite-based heterojunction cells. The efficiency exceeding 10% shows promising prospects for the HTM-free solar cells based on organic lead halides. PMID:24830329

  10. N2 Product Internal-State Distributions for the Steady-State Reactions of NO with H2 and NH3 on the Pt(100) Surface

    E-print Network

    Zare, Richard N.

    by resonance enhanced multiphoton ionization. For NO + NH3 the N2 reaction product leaves the surface on well-defined surfaces knowledge of the internal energy distribution of one or all reaction products. Hydrogen recombination reactions on various surfaces1 provide examples of the information that can

  11. A systematic investigation into the conversion of ?-Ga2O3 to GaN nanowires using NH3 and H2: Effects on the photoluminescence properties

    NASA Astrophysics Data System (ADS)

    Othonos, Andreas; Zervos, Matthew; Christofides, Constantinos

    2010-12-01

    GaN nanowires (NWs) with a hexagonal wurtzite crystal structure, diameters of 50 nm and lengths of 10 ?m have been obtained from postgrowth nitridation of monoclinic ?-Ga2O3 NWs using NH3 between 700-1090 °C. The conversion of ?-Ga2O3 to GaN NWs has been investigated in a systematic way by varying the temperature, gas flows and nitridation times using Ar or N2:10% H2. We find that nitridation is most effective at temperatures ?900 °C using NH3 with N2:10% H2 which promotes the efficient conversion of ?-Ga2O3 to GaN, resulting into the enhancement of the band edge emission, suppression of the broad-band photoluminescence (PL) related to oxygen defects and the appearance of red emission due to deep-acceptorlike states. The gradual evolution of the PL spectra from that of ?-Ga2O3 to GaN exhibited a clear, systematic dependence on the nitridation temperature and gas flows and the band to band emission lifetime which was found to be ? ?0.35 ns in all cases. In contrast the nitridation of ?-Ga2O3 NWs using NH3 and Ar is less effective. Therefore, H2 is essential in removing O2 and also effective since it lead to the complete elimination of the ?-Ga2O3 NWs at 1000 °C in the absence of NH3.

  12. Vibrational mode-selected differential scattering of NH3+ methanol (d1, d3, d4): Control of product branching by hydrogen-bonded complex formation

    NASA Astrophysics Data System (ADS)

    Fu, Hungshin; Qian, Jun; Green, Richard J.; Anderson, Scott L.

    1998-02-01

    We report a study of vibrational mode effects and differential scattering in reaction of NH3+ with CD3OD, CD3OH, and CH3OD over the collision energy range from 0.1 to 5 eV. At low collision energies, abstraction of both methyl and hydroxyl D atoms is observed with roughly equal probability, even though methyl D-abstraction should be favored on both energetic and statistical grounds. Branching between the two abstraction reactions is controlled by two different hydrogen-bonded complexes. Formation of these complexes is enhanced by NH3+ umbrella bending, unaffected by the NH3+ symmetric stretch, and inhibited by collision energy. Endoergic proton transfer is mediated at low energies by a third hydrogen-bonded complex, formation of which is enhanced by both umbrella bending and the symmetric stretch. Charge transfer (CT) has a significant cross section only when the NH3+ umbrella bend excitation exceeds the endoergicity. Collision energy and symmetric stretching appear to have no effect on CT. At high collision energies all reactions become direct, with near spectator stripping dynamics. In this energy range product branching appears to be controlled by collision geometry and there are no significant vibrational effects.

  13. Theoretical calculations of the collision cross sections and rate coefficients for the hyperfine transitions of interstellar molecular ortho-NH3 colliding with He

    Microsoft Academic Search

    Ji Chen; Ya-Hui Zhang; Tian-Chun Zhou

    1997-01-01

    In this paper, the collision cross sections and the rate coefficients for the hyperfine transitions of interstellar molecules of ortho-NH3 colliding with He are calculated by solving the coupled equations in the CS (Coupled State) approximation with the R-matrix propagation method. The results provide useful fundamental data for the investigation of astronomical information.

  14. A theoretical calculation of the collision cross section and rate coefficient for the hyperfine transitions of collisions between interstellar ortho-NH 3 and He molecules

    Microsoft Academic Search

    Ji Chen; Ya-Hui Zhang; Tian-Chun Zhou

    1998-01-01

    This paper calculates the collision cross sections and rate coefficients of the hyperfine transitions of collisions between ortho-NH3 and He under the conditions of interstellar molecular clouds by solving the coupled equations in the CS (coupled state) approximation with the R-matrix propagation method.

  15. Brightly Luminescent and Color-Tunable Colloidal CH3NH3PbX3 (X = Br, I, Cl) Quantum Dots: Potential Alternatives for Display Technology.

    PubMed

    Zhang, Feng; Zhong, Haizheng; Chen, Cheng; Wu, Xian-Gang; Hu, Xiangmin; Huang, Hailong; Han, Junbo; Zou, Bingsuo; Dong, Yuping

    2015-04-28

    Organometal halide perovskites are inexpensive materials with desirable characteristics of color-tunable and narrow-band emissions for lighting and display technology, but they suffer from low photoluminescence quantum yields at low excitation fluencies. Here we developed a ligand-assisted reprecipitation strategy to fabricate brightly luminescent and color-tunable colloidal CH3NH3PbX3 (X = Br, I, Cl) quantum dots with absolute quantum yield up to 70% at room temperature and low excitation fluencies. To illustrate the photoluminescence enhancements in these quantum dots, we conducted comprehensive composition and surface characterizations and determined the time- and temperature-dependent photoluminescence spectra. Comparisons between small-sized CH3NH3PbBr3 quantum dots (average diameter 3.3 nm) and corresponding micrometer-sized bulk particles (2-8 ?m) suggest that the intense increased photoluminescence quantum yield originates from the increase of exciton binding energy due to size reduction as well as proper chemical passivations of the Br-rich surface. We further demonstrated wide-color gamut white-light-emitting diodes using green emissive CH3NH3PbBr3 quantum dots and red emissive K2SiF6:Mn(4+) as color converters, providing enhanced color quality for display technology. Moreover, colloidal CH3NH3PbX3 quantum dots are expected to exhibit interesting nanoscale excitonic properties and also have other potential applications in lasers, electroluminescence devices, and optical sensors. PMID:25824283

  16. Superhydrophobic pure silver surface with flower-like structures by a facile galvanic exchange reaction with [Ag(NH3)2]OH.

    PubMed

    Cao, Zongwei; Xiao, Debao; Kang, Longtian; Wang, Zhongliang; Zhang, Shuxiao; Ma, Ying; Fu, Hongbing; Yao, Jiannian

    2008-06-21

    Superhydrophobic pure silver film composed of flower-like microstructures built by interconnected silver nanoplates on a copper plate without any modification was prepared by a facile galvanic exchange reaction between the aqueous [Ag(NH3)2]OH and the copper plate, giving rise to a contact angle as high as 157 degrees . PMID:18535710

  17. Models, predictions, and experimental measurements of far-infrared NH 3 -laser dynamics and comparisons with the Lorenz-Haken model

    Microsoft Academic Search

    C. O. Weiss; R. Vilaseca; N. B. Abraham; R. Corbalán; E. Roldán; G. J. de Valcárcel; J. Pujol; U. Hübner; D. Y. Tang

    1995-01-01

    Dynamics of the intensity and optical field amplitude of a coherently pumped far-infrared NH3-laser are measured and characterized. The experimental findings in certain parameter ranges closely follow the dynamics of the Lorenz model and its generalization for laser systems. Similarities and some specific differences are found in geometrical or statistical characterizations of the attractors. The experimental results are also consistent

  18. SURFATM-NH3: a model combining the surface energy balance and bi-directional exchanges of ammonia applied at the field scale

    NASA Astrophysics Data System (ADS)

    Personne, E.; Loubet, B.; Herrmann, B.; Mattsson, M.; Schjoerring, J. K.; Nemitz, E.; Sutton, M. A.; Cellier, P.

    2009-08-01

    A new biophysical model SURFATM-NH3, simulating the ammonia (NH3) exchange between terrestrial ecosystems and the atmosphere is presented. SURFATM-NH3 consists of two coupled models: (i) an energy budget model and (ii) a pollutant exchange model, which distinguish the soil and plant exchange processes. The model describes the exchanges in terms of adsorption to leaf cuticles and bi-directional transport through leaf stomata and soil. The results of the model are compared with the flux measurements over grassland during the GRAMINAE Integrated Experiment at Braunschweig, Germany. The dataset of GRAMINAE allows the model to be tested in various meteorological and agronomic conditions: prior to cutting, after cutting and then after the application of mineral fertilizer. The whole comparison shows close agreement between model and measurements for energy budget and ammonia fluxes. The major controls on the ground and plant emission potential are the physicochemical parameters for liquid-gas exchanges which are integrated in the compensation points for live leaves, litter and the soil surface. Modelled fluxes are highly sensitive to soil and plant surface temperatures, highlighting the importance of accurate estimates of these terms. The model suggests that the net flux depends not only on the foliar (stomatal) compensation point but also that of leaf litter. SURFATM-NH3 represents a comprehensive approach to studying pollutant exchanges and its link with plant and soil functioning. It also provides a simplified generalised approach (SVAT model) applicable for atmospheric transport models.

  19. SURFATM-NH3: a model combining the surface energy balance and bi-directional exchanges of ammonia applied at the field scale

    NASA Astrophysics Data System (ADS)

    Personne, E.; Loubet, B.; Herrmann, B.; Mattsson, M.; Schjoerring, J. K.; Nemitz, E.; Sutton, M. A.; Cellier, P.

    2009-01-01

    A new biophysical model SURFATM-NH3, simulating the ammonia (NH3) exchange between terrestrial ecosystems and the atmosphere is presented. SURFATM-NH3 consists of two coupled models: (i) an energy budget model and (ii) a pollutant exchange model, which distinguish the soil and plant exchange processes. The model describes the exchanges in terms of adsorption to leaf cuticles and bi-directional transport through leaf stomata and soil. The results of the model are compared with the flux measurements over grassland during the GRAMINAE Integrated Experiment at Braunschweig, Germany. The dataset of GRAMINAE allows the model to be tested in various climatic and agronomic conditions: prior to cutting, after cutting and then after the application of mineral fertilizer. The whole comparison shows close agreement between model and measurements for energy budget and ammonia fluxes. The major controls on the soil and plant emission potential are the physicochemical parameters for liquid-gas exchanges which are integrated in the compensation points for live leaves, litter and the soil surface. Modelled fluxes are highly sensitive to soil and plant surface temperatures, highlighting the importance of accurate estimates of these terms. The model suggests that the net flux depends not only on the foliar (stomatal) compensation point but also that of leaf litter. SURFATM-NH3 represents a comprehensive approach to studying pollutant exchanges and its link with plant and soil functioning. It also provides a simplified generalised approach (SVAT model) applicable for atmospheric transport models.

  20. Calorimetric, spectroscopic and structural investigations of phase polymorphism in [Ru(NH3)6](BF4)3. Part I

    NASA Astrophysics Data System (ADS)

    Do??ga, Diana; Mikuli, Edward; Inaba, Akira; Górska, Natalia; Ho?derna-Natkaniec, Krystyna; Nitek, Wojciech

    2013-01-01

    Four crystalline phases of the coordination compound [Ru(NH3)6](BF4)3 are identified by adiabatic calorimetry. Three phase transitions, one at TC3(IV?III)=30.7 K, the second at TC2(III?II)=91.7 K (both accompanied by comparable entropy changes 3.0 and 3.1 J K-1 mol-1, respectively) and the third at TC1(II?I)=241.6 K (accompanied by an entropy change of 8.1 J K-1 mol-1) were discovered. X-ray single crystal diffraction (at 293 K) demonstrates that phase I is a highly dynamic disordered cubic phase (Fm3¯m, No. 225) with two types of BF4- anions differing in a degree of disorder. In phase II (at 170 K) the structure remains cubic (Ia3¯, No. 206), with two different types of cations and four different types of anions. Splitting of certain IR bands connected with NH3 ligands at the observed phase transitions suggests a lowering of the symmetry of the [Ru(NH3)6]3+ complex cation. Both NH3 ligands and BF4- anions perform fast reorientations (?R?10-12 s), which are significantly slowed down below the phase transition at TC3. 1H NMR studies led to estimate the values of the activation energy of NH3 ligands reorientation in the phases II and I as equal to ˜8 kJ mol-1. In phase I the whole hexammineruthenium(III) cations reorientation as a tumbling process can be noticed. The activation energy value of this motion is ˜24 kJ mol-1. 19F NMR studies give the values of the activation energy of BF4- anions reorientation as ˜6 kJ mol-1. Above the phase transition temperature half of BF4- anions perform a tumbling motion with Ea?8 kJ mol-1.

  1. Ab initio based potential energy surface and kinetics study of the OH + NH3 hydrogen abstraction reaction

    NASA Astrophysics Data System (ADS)

    Monge-Palacios, M.; Rangel, C.; Espinosa-Garcia, J.

    2013-02-01

    A full-dimensional analytical potential energy surface (PES) for the OH + NH3 ? H2O + NH2 gas-phase reaction was developed based exclusively on high-level ab initio calculations. This reaction presents a very complicated shape with wells along the reaction path. Using a wide spectrum of properties of the reactive system (equilibrium geometries, vibrational frequencies, and relative energies of the stationary points, topology of the reaction path, and points on the reaction swath) as reference, the resulting analytical PES reproduces reasonably well the input ab initio information obtained at the coupled-cluster single double triple (CCSD(T)) = FULL/aug-cc-pVTZ//CCSD(T) = FC/cc-pVTZ single point level, which represents a severe test of the new surface. As a first application, on this analytical PES we perform an extensive kinetics study using variational transition-state theory with semiclassical transmission coefficients over a wide temperature range, 200-2000 K. The forward rate constants reproduce the experimental measurements, while the reverse ones are slightly underestimated. However, the detailed analysis of the experimental equilibrium constants (from which the reverse rate constants are obtained) permits us to conclude that the experimental reverse rate constants must be re-evaluated. Another severe test of the new surface is the analysis of the kinetic isotope effects (KIEs), which were not included in the fitting procedure. The KIEs reproduce the values obtained from ab initio calculations in the common temperature range, although unfortunately no experimental information is available for comparison.

  2. Interfacial electronic structure at the CH3NH3PbI3/MoOx interface

    NASA Astrophysics Data System (ADS)

    Liu, Peng; Liu, Xiaoliang; Lyu, Lu; Xie, Haipeng; Zhang, Hong; Niu, Dongmei; Huang, Han; Bi, Cheng; Xiao, Zhengguo; Huang, Jinsong; Gao, Yongli

    2015-05-01

    Interfacial electronic properties of the CH3NH3PbI3 (MAPbI3)/MoOx interface are investigated using ultraviolet photoemission spectroscopy and X-ray photoemission spectroscopy. It is found that the pristine MAPbI3 film coated onto the substrate of poly (3,4-ethylenedioxythiophene) poly(styrenesulfonate)/indium tin oxide by two-step method behaves as an n-type semiconductor, with a band gap of ˜1.7 eV and a valence band edge of 1.40 eV below the Fermi energy (EF). With the MoOx deposition of 64 Å upon MAPbI3, the energy levels of MAPbI3 shift toward higher binding energy by 0.25 eV due to electron transfer from MAPbI3 to MoOx. Its conduction band edge is observed to almost pin to the EF, indicating a significant enhancement of conductivity. Meanwhile, the energy levels of MoOx shift toward lower binding energy by ˜0.30 eV, and an interface dipole of 2.13 eV is observed at the interface of MAPbI3/MoOx. Most importantly, the chemical reaction taking place at this interface results in unfavorable interface energy level alignment for hole extraction. A potential barrier of ˜1.36 eV observed for hole transport will impede the hole extraction from MAPbI3 to MoOx. On the other hand, a potential barrier of ˜0.14 eV for electron extraction is too small to efficiently suppress electrons extracted from MAPbI3 to MoOx. Therefore, such an interface is not an ideal choice for hole extraction in organic photovoltaic devices.

  3. CH 4/NH 3/H 2O spark tholin: Chemical analysis and interaction with Jovian aqueous clouds

    NASA Astrophysics Data System (ADS)

    McDonald, Gene D.; Khare, Bishun N.; Reid Thompson, W.; Sagan, Carl

    1991-12-01

    The organic solid (tholin) produced by spark discharge in a CH 4 + NH 3 + H 2O atmosphere is investigated, along with the separable components of its water-soluble fraction. The chemistry of this material serves as a provisional model for the interaction of Jovian organic heteropolymers with the deep aqueous clouds of Jupiter. Intact (unhydrolyzed) tholin is resolved into four chemically distinct fractions by high-pressure liquid chromatography (HPLC). Gel filtration chromatography reveals abundant components at molecular weights ?600-700 and 200-300 Da. Gas chromatography/mass spectrometry of derivatized hydrolysis products of unfractionated tholin shows about 10% by mass protein and nonprotein amino acids, chiefly glycine, alanine, aspartic acid, ?-alanine, and ?-aminobutyric acid, and 12% by mass other organic acids and hydroxy acids. The stereospecificity of alanine is investigated and shown to be racemic. The four principal HPLC fractions yield distinctly different proportions of amino acids. Chemical tests show that small peptides or organic molecules containing multiple amino acid precursors are a possibility in the intact tholins, but substantial quantities of large peptides are not indicated. Candidate 700-Da molecules have a central unsaturated, hydrocarbon- and nitrile-rich core, linked by acid-labile (ester or amide) bonds to amino acid and carboxylic acid side groups. The core is probably not HCN "polymer." The concentration of amino acids from tholin hydrolysis in the lower aqueous clouds of Jupiter, about 0.1 ? M, is enough to maintain small populations of terrestrial microorganisms even if the amino acids must serve as the sole carbon source.

  4. Rapid screening of pharmaceutical drugs using thermal desorption - SALDI mass spectrometry

    NASA Astrophysics Data System (ADS)

    Grechnikov, A. A.; Kubasov, A. E.; Georgieva, V. B.; Borodkov, A. S.; Nikiforov, S. M.; Simanovsky, Ya O.; Alimpiev, S. S.

    2012-12-01

    A novel approach to the rapid screening of pharmaceutical drugs by surface assisted laser desorption-ionization (SALDI) mass spectrometry with the rotating ball interface coupled with temperature programmed thermal desorption has been developed. Analytes were thermally desorbed and deposited onto the surface of amorphous silicon substrate attached to the rotating ball. The ball was rotated and the deposited analytes were analyzed using SALDI. The effectiveness of coupling SALDI mass spectrometry with thermal desorption was evaluated by the direct and rapid analysis of tablets containing lidocaine, diphenhydramine and propranolol without any sample pretreatment. The overall duration of the screening procedure was 30÷40 sec. Real urine samples were studied for drug analysis. It is shown that with simple preparation steps, urine samples can be quantitatively analyzed using the proposed technique with the detection limits in the range of 0.2÷0.5 ng/ml.

  5. Estimating the agricultural fertilizer NH3 emission in China based on the bi-directional CMAQ model and an agro-ecosystem model

    NASA Astrophysics Data System (ADS)

    Wang, S.

    2014-12-01

    Atmospheric ammonia (NH3) plays an important role in fine particle formation. Accurate estimates of ammonia can reduce uncertainties in air quality modeling. China is one of the largest countries emitting ammonia with the majority of NH3 emissions coming from the agricultural practices, such as fertilizer applications and animal operations. The current ammonia emission estimates in China are mainly based on pre-defined emission factors. Thus, there are considerable uncertainties in estimating NH3 emissions, especially in time and space distribution. For example, fertilizer applications vary in the date of application and amount by geographical regions and crop types. In this study, the NH3 emission from the agricultural fertilizer use in China of 2011 was estimated online by an agricultural fertilizer modeling system coupling a regional air-quality model and an agro-ecosystem model, which contains three main components 1) the Environmental Policy Integrated Climate (EPIC) model, 2) the meso-scale meteorology Weather Research and Forecasting (WRF) model and 3) the CMAQ air quality model with bi-directional ammonia fluxes. The EPIC output information about daily fertilizer application and soil characteristics would be the input of the CMAQ model. In order to run EPIC model, much Chinese local information is collected and processed. For example, Crop land data are computed from the MODIS land use data at 500-m resolution and crop categories at Chinese county level; the fertilizer use rate for different fertilizer types, crops and provinces are obtained from Chinese statistic materials. The system takes into consideration many influencing factors on agriculture ammonia emission, including weather, the fertilizer application method, timing, amount, and rate for specific pastures and crops. The simulated fertilizer data is compared with the NH3 emissions and fertilizer application data from other sources. The results of CMAQ modeling are also discussed and analyzed with field measurements. The estimated agricultural fertilizer NH3 emission in this study is about 3Tg in 2011. The regions with the highest emission rates are located in the North China Plain. Monthly, the peak ammonia emissions occur in April to July.

  6. Desorption of a two-state system: Laser probing of gallium atom spin-orbit states from silicon (100)

    NASA Astrophysics Data System (ADS)

    Carleton, Karen L.; Bourguignon, Bernard; Leone, Stephen R.

    The interactions of gallium atom spin-orbit states with silicon (100) surfaces are studied by temperature programmed desorption (TPD) using laser-induced fluorescence detection. State-resolved sticking coefficients are measured and are found to be unity for both spin-orbit states ( 2P{1}/{2}, 2P{3}/{2}, ?E = 2.5 kcal mol-1, 10.5 kJ mol-1) up to surface temperatures of 1000 K. A Redhead analysis of the state-specific TPD spectra yields essentially identical energies and pre-exponential factors for both spin-orbit states. A statistical branching ratio is observed between the 2P {1}/{2} and 2P {3}/{2} Ga states at the peak of the TPD curves. These results may be accounted for by a rapid interconversion between the two states during the desorption. Since the spin-orbit splitting in this case is small, a rapid interconversion may be anticipated; however, modeling the desorption kinetics yields important features for the desorption of a two-state system. The model shows that the Redhead analysis is not adequate to measure the desorption kinetic parameters of the individual states. The TPD spectra of the two states differ only very slightly because their shape is mainly controlled by the overall rate of desorption for the sum of the two channels. The population ratio between the states allows a direct comparison of the desorption energetics of the two channels. Errors of 5-10 kcal mol -1 can occur in a determination of the desorption energy of a hypothetical, slowly desorbing state if the presence of a rapid desorption channel is ignored. The model can be generalized to describe any multiple channel surface process, including multi-state desorption of the competition between desorption and diffusion into the bulk. These results are of interest in the epitaxial growth of GaAs on Si(100).

  7. Desorption of chlorine organic solvents

    SciTech Connect

    Petrova, N.I.; Nikolaev, K.M.

    1982-03-01

    Adsorption methods are being used more and more widely to treat gaseous discharges containing chlorohydrocarbons. However, recovery of the chlorohydrocarbons has not been studied sufficiently, and the desorption of the solvents with steam is particularly understudied. We investigated desorption of a number of solvents from industrial active carbon AR-3. Desorption was done with live steam in the 105 to 150/sup 0/C. It can be seen from the data that with an increase of the molecular weight of the chlorohydrocarbon, the process of desorption slows down. This is clearly due to the fact that with an increase of the number of chlorine atoms in the molecule there is an increase of dispersion interaction (size of parachors) and latent heat of vaporization, which cause a decrease of the degree of desorption. The rate of desorption increases with an increase in temperature, but most of the investigated chlorine derivatives detach a chlorine ion at elevated temperature in the presence of water and carbon, with formation of HCl, which causes severe equipment corrosion. In addition, phosgene (in the decomposition of C/sub 2/HCl/sub 3/), chlorine organic acids and certain other toxic compounds may be produced. Thus, to reduce the rate of hydrolysis in the desorption of chlorohydrocarbons, especially polychlorinated ones, one should use steam with minimum possible temperature (no more than 110/sup 0/C) with a desorption time of no more than 30 minutes for poorly adsorbable compounds and no more than 45 to 60 minutes for readily absorbable ones. Here the degree of desorption of poorly absorbed compounds is about 100% while that of the readily absorbed ones is from 50 to 75%. The results were used in the design of units for recovery of methylene chloride, dichloroethane and trichloroethylene.

  8. The effects of process conditions on the plasma characteristic in radio-frequency capacitively coupled SiH4/NH3/N2 plasmas: Two-dimensional simulations

    NASA Astrophysics Data System (ADS)

    Liu, Xiang-Mei; Song, Yuan-Hong; Jiang, Wei; Yi, Lin

    2013-04-01

    A two-dimensional (2D) fluid model is presented to study the behavior of silicon plasma mixed with SiH4, N2, and NH3 in a radio-frequency capacitively coupled plasma (CCP) reactor. The plasma-wall interaction (including the deposition) is modeled by using surface reaction coefficients. In the present paper we try to identify, by numerical simulations, the effect of variations of the process parameters on the plasma properties. It is found from our simulations that by increasing the gas pressure and the discharge gap, the electron density profile shape changes continuously from an edge-high to a center-high, thus the thin films become more uniform. Moreover, as the N2/NH3 ratio increases from 6/13 to 10/9, the hydrogen content can be significantly decreased, without decreasing the electron density significantly.

  9. Photoabsorption and photoionization cross sections of NH3, PH3, H2S, C2H2, and C2H4 in the VUV region

    NASA Technical Reports Server (NTRS)

    Xia, T. J.; Chien, T. S.; Wu, C. Y. Robert; Judge, D. L.

    1991-01-01

    Using synchrotron radiation as a continuum light source, the photoabsorption and photoionization cross sections of NH3, PH3, H2S, C2H2, and C2H4 have been measured from their respective ionization thresholds to 1060 A. The vibrational constants associated with the nu(2) totally symmetric, out-of-plane bending vibration of the ground electronic state of PH3(+) have been obtained. The cross sections and quantum yields for producing neutral products through photoexcitation of these molecules in the given spectral regions have also been determined. In the present work, autoionization processes were found to be less important than dissociation and predissociation processes in NH3, PH3, and C2H4. Several experimental techniques have been employed in order to examine the various possible systematic errors critically.

  10. CeO2 doped anatase TiO2 with exposed (001) high energy facets and its performance in selective catalytic reduction of NO by NH3

    NASA Astrophysics Data System (ADS)

    Wang, Haiqiang; Cao, Shuang; Fang, Zheng; Yu, Feixiang; Liu, Yue; Weng, Xiaole; Wu, Zhongbiao

    2015-03-01

    Ceria doped on anatase TiO2 with high energy (001) facets was synthesized in this paper, which was subsequently utilized for selective catalytic reduction (SCR) of NO by NH3. After subjected to a range of analytical techniques, such as XRD, BET, TEM, XPS ESR, H2-TPR and NH3-TPD, it was found that compared with Ce/P25 catalyst, the presence of (001) facets over the TiO2 support had yielded a remarkably high activity at 390-490 °C for NO removal. The unique feature of active-energy (001) facets had enhanced the thermal stability of CeO2 whilst the presence of Ti3+ over the TiO2 surface had effectively facilitated the SCR process, both of which resulted in the remarkable catalytic performance for the catalyst.

  11. Effect of rutile phase on V2O5 supported over TiO2 mixed phase for the selective catalytic reduction of NO with NH3

    NASA Astrophysics Data System (ADS)

    Zhang, Shule; Zhong, Qin; Wang, Yining

    2014-09-01

    A series of V2O5/TiO2 catalysts with different ratios of TiO2 rutile phase was prepared. Focusing on the effect of TiO2 rutile phase on V2O5/TiO2 catalyst for the selective catalytic reduction (SCR) of NO with NH3, the NO conversion for the different catalysts was investigated. The experimental results showed that a small amount of TiO2 rutile phase could improve the NO conversion significantly below 270 °C. Analysis by XRD, NH3-TPD, UV-vis, EPR and DFT calculation showed that the rutile phase of TiO2 supporter decreased the band gap, especially, the conduction band level. It improved the formation of reduced V species and superoxide ions that were important to the low-temperature SCR reaction.

  12. Ion—polar-molecule reactions: A CRESU study of He +, C +, N + + H 2O, NH 3 at 27, 68 and 163 K

    NASA Astrophysics Data System (ADS)

    Marquette, J. B.; Rowe, B. R.; Dupeyrat, G.; Poissant, G.; Rebrion, C.

    1985-12-01

    The first measurements of ion—polar-molecule reaction rate constants at very low temperatures are presented. They have been obtained using the CRESU (cine_.tique de reactions en ecoulement supersonique uniforme) technique for H +.C + and N + ions reacting with H 2O and NH 3 at 27 and 68 K in helium buffer. Additional data have been obtained for N + reactions at 163 K in nitrogen buffer. In the 27-300 K (27-163 K for N + + NH 3) temperature range, all the results yield a power law, k = k0T- n (0 < n < 1), for the rate coefficient of each reaction, which should be applied in interstellar cloud model in place of the room-temperature values. The results are compared with various theoretical calculations. Rather good agreement is found although no general behavior can be simply drawn from these experiments.

  13. The recombination mechanisms leading to amplified spontaneous emission at the true-green wavelength in CH3NH3PbBr3 perovskites

    NASA Astrophysics Data System (ADS)

    Priante, D.; Dursun, I.; Alias, M. S.; Shi, D.; Melnikov, V. A.; Ng, T. K.; Mohammed, O. F.; Bakr, O. M.; Ooi, B. S.

    2015-02-01

    We investigated the mechanisms of radiative recombination in a CH3NH3PbBr3 hybrid perovskite material using low-temperature, power-dependent (77 K), and temperature-dependent photoluminescence (PL) measurements. Two bound-excitonic radiative transitions related to grain size inhomogeneity were identified. Both transitions led to PL spectra broadening as a result of concurrent blue and red shifts of these excitonic peaks. The red-shifted bound-excitonic peak dominated at high PL excitation led to a true-green wavelength of 553 nm for CH3NH3PbBr3 powders that are encapsulated in polydimethylsiloxane. Amplified spontaneous emission was eventually achieved for an excitation threshold energy of approximately 350 ?J/cm2. Our results provide a platform for potential extension towards a true-green light-emitting device for solid-state lighting and display applications.

  14. Organic-inorganic heterostructure electroluminescent device using a layered perovskite semiconductor (C6H5C2H4NH3)2PbI4

    Microsoft Academic Search

    M. Era; S. Morimoto; T. Tsutsui; S. Saito

    1994-01-01

    Using the combination of a layered perovskite compound (C6H5C2H4NH3)2PbI4 (PAPI), which forms a stable exciton with a large binding energy owing to its low-dimensional semiconductor nature and exhibits sharp and strong photoluminescence from the exciton band, and an electron-transporting oxadiazole derivative, we fabricated an organic–inorganic heterostructure electroluminescent (EL) device. The EL spectrum of the device corresponded well to the photoluminescence

  15. Efficient CH3 NH3 PbI3 Perovskite Solar Cells Employing Nanostructured p-Type NiO Electrode Formed by a Pulsed Laser Deposition.

    PubMed

    Park, Jong Hoon; Seo, Jangwon; Park, Sangman; Shin, Seong Sik; Kim, Young Chan; Jeon, Nam Joong; Shin, Hee-Won; Ahn, Tae Kyu; Noh, Jun Hong; Yoon, Sung Cheol; Hwang, Cheol Seong; Seok, Sang Il

    2015-07-01

    Highly transparent and nanostructured nickel oxide (NiO) films through pulsed laser deposition are introduced for efficient CH3 NH3 PbI3 perovskite solar cells. The (111)-oriented nanostructured NiO film plays a key role in extracting holes and preventing electron leakage as hole transporting material. The champion device exhibits a power conversion efficiency of 17.3% with a very high fill factor of 0.813. PMID:26038099

  16. Measurements of gaseous HONO, HNO 3, SO 2, HCl, NH 3, particulate sulfate and PM 2.5 in New York, NY

    Microsoft Academic Search

    Abdul Bari; Vincent Ferraro; Lloyd R. Wilson; Dan Luttinger; Liaquat Husain

    2003-01-01

    Simultaneous measurements of gaseous HONO, HNO3, HCl, SO2, and NH3 for a period of 1 year from July 1999 to June 2000 and fine-fraction particulate (<2.5?m) sulfate (SO42?) from January 1999 to November 2000 were made at Bronx and Manhattan in New York City with an annular denuder system followed by ion chromatography. The hourly PM2.5 mass was measured with

  17. The partial reduction of electron-deficient pyrroles: procedures describing both Birch (Li\\/NH3) and ammonia-free (Li\\/DBB) conditions

    Microsoft Academic Search

    Rhian E Thomas; Timothy J Donohoe

    2007-01-01

    The partial reduction of electron-deficient pyrroles using either Birch (Li\\/NH3) or ammonia-free (Li\\/di-tert-butyl biphenyl) conditions allows formation of pyrroline compounds in good yield and, when combined with a reductive alkylation or similar approach, leads to highly functionalized, synthetically useful compounds. This methodology has been proven in the syntheses of several complex natural products, all of which show interesting biological activity.

  18. High external quantum efficiency and fill-factor InGaN\\/GaN heterojunction solar cells grown by NH3-based molecular beam epitaxy

    Microsoft Academic Search

    J. R. Lang; C. J. Neufeld; C. A. Hurni; S. C. Cruz; E. Matioli; U. K. Mishra; J. S. Speck

    2011-01-01

    High external quantum efficiency (EQE) p-i-n heterojunction solar cells grown by NH3-based molecular beam epitaxy are presented. EQE values including optical losses are greater than 50% with fill-factors over 72% when illuminated with a 1 sun AM0 spectrum. Optical absorption measurements in conjunction with EQE measurements indicate an internal quantum efficiency greater than 90% for the InGaN absorbing layer. By

  19. Vibrational analysis of pyramidal XY3-type molecules based on high-level ab initio potential energy surfaces: application to NH3

    Microsoft Academic Search

    H. Lin; W. Thiel; S. N. Yurchenko; M. Carvajal; P. Jensen

    2003-01-01

    Variational calculations of the vibrational energies of the non-rigid and semirigid XY3 molecules, as ammonia and phosphine respectively, have been carried out [1,2]. In the procedure used is emphasized the umbrella motion due to the corresponding coordinate, for pyramidal non-rigid XY3 molecules, is the responsible of the torsional tunneling between different minima of the Potential Energy Surfaces. For the NH3

  20. The source of 3-?m absorption in Jupiter’s clouds: Reanalysis of ISO observations using new NH3 absorption models

    NASA Astrophysics Data System (ADS)

    Sromovsky, L. A.; Fry, P. M.

    2010-11-01

    A prominent characteristic of jovian near-IR spectra is the widely distributed presence of a strong absorption at wavelengths from about 2.9 ?m to 3.1 ?m, first noticed in a 3-?m spectrum obtained by the Infrared Space Observatory (ISO) in 1996. While Brooke et al. (Brooke, T.Y., Knacke, R.F., Encrenaz, T., Drossart, P., Crisp, D., Feuchtgruber, H. [1998]. Icarus 136, 1-13) were able to fit the ISO spectrum very well using ammonia ice as the sole source of particulate absorption, Irwin et al. (Irwin, P.G.J., Weir, A.L., Taylor, F.W., Calcutt, S.B., Carlson, R.W. [2001]. Icarus 149, 397-415) noted that their best-fit cloud model implied a strong absorption at 2 ?m that was not observed in Galileo NIMS spectra, raising questions about the source of the absorption. Subsequent significant revisions in ammonia gas absorption models (Bowles, N., Calcutt, S., Irwin, P., Temple, J. [2008]. Icarus 196, 612-614) also raised questions about these conclusions because ammonia gas absorption overlaps regions of ammonia ice absorption. Our reanalysis, based on improved ammonia absorption models, finds that the ISO spectrum can be well fit by models that include both NH 3 ice and solid NH 4SH, with the latter substance providing most of the absorption. The component due to NH 3 is very possibly due to NH 3 present as a coating on either large ( r ˜ 15 ?m) NH 4SH particles in a deeper layer at ˜550 mb or on small ( r ˜ 0.3 ?m) photochemical haze particles in a lower pressure layer at ˜370 mb. Neither option creates conflict with the lack of significant NH 3 absorption features at thermal wavelengths.

  1. The interaction of H 2, CO, CO 2, H 2O and NH 3 on ZnO surfaces: an Oniom Study

    Microsoft Academic Search

    João Batista Lopes Martins; Elson Longo; Octavio D. Rodr??guez Salmon; Vicente A. A. Espinoza; Carlton A. Taft

    2004-01-01

    We have used the Oniom method with three layers in order to study the interaction of CO, H2, H2O, NH3 and CO2 molecules with the ZnO (101¯0) surfaces using a (ZnO)348 cluster model. The layers are divided into the high layer at the CCSD level, the medium layer at the RHF level and the low level layer using the UFF

  2. Non-polymer coated Fe3O4 aqueous dispersion with NH3+-surface modification as new magnetite nanoparticles and their biomedical applications

    Microsoft Academic Search

    F. Y. Cheng; D. B. Shieh; C. S. Yeh

    2005-01-01

    Well-dispersed Fe3O4 nanoparticles were synthesized using chemical coprecipitation and the addition of organic acid as adherent in an aqueous solution. The resulting iron oxide particles were manipulated as small as 6 nm diameter in size. The nanoparticles exhibit cationic surface mostly decorated with terminal -NH3+. The in vitro cytotoxicity test revealed excellent biocompatibility to further explore for their potential in

  3. Modeling refraction characteristics of silicon nitride film deposited in a SiH4NH3-N2 plasma using neural network

    Microsoft Academic Search

    Byungwhan Kim; Seung-Soo Han; Tae Seon Kim; Bum Soo Kim; Il Joo Shim

    2003-01-01

    Silicon nitride has been deposited using plasma-enhanced chemical deposition (PECVD) equipment. The PECVD process was characterized by conducting a 26-1 fractional factorial experiment on six experimental factors, including substrate temperature, pressure, radio frequency (RF) power, ammonia NH3, silane SiH4, and nitrogen N2 flow rates. Refractive characteristics of the deposited film were examined by modeling the refractive index as a function

  4. Study of a gold electrode modified by trans-[Ru(NH 3) 4(Ist)SO 4] + to produce an electrochemical sensor for nitric oxide

    Microsoft Academic Search

    Vanessa N. Santos; Murilo F. Cabral; Jefferson S. Ferreira; Alda K. M. Holanda; Sergio A. S. Machado; Jackson R. Sousa; Luiz G. F. Lopes; Adriana N. Correia; Pedro de Lima Neto

    2011-01-01

    The modification of a gold electrode surface by electropolymerization of trans-[Ru(NH3)4(Ist)SO4]+ to produce an electrochemical sensor for nitric oxide was investigated. The influence of dopamine, serotonin and nitrite as interferents for NO detection was also examined using square-wave voltammetry (SWV). The characterization of the modified electrode was carried out by cyclic voltammetry, electrochemical quartz crystal microbalance (EQCM) and SERS techniques.

  5. Internal rotation and halogen bonds in CF3I···NH3 and CF3I···N(CH3)3 probed by broadband rotational spectroscopy.

    PubMed

    Stephens, Susanna L; Walker, Nicholas R; Legon, Anthony C

    2011-12-14

    The rotational spectra of CF(3)I···NH(3) and CF(3)I···N(CH(3))(3) are measured between 6.7 and 18 GHz using a chirped-pulse Fourier transform microwave spectrometer. Transitions in each spectrum are assigned to A and E species associated with ground and excited internal rotor states respectively. Rotational constants, B(0), centrifugal distortion constants, D(J), D(Jm), D(JKm), nuclear quadrupole coupling constants of the (14)N and (127)I atoms, ?(aa)(N) and ?(aa)(I), are determined for each complex. D(JK) is additionally determined for CF(3)I···NH(3). Results are presented for both (14)N and (15)N-substituted isotopologues. All data are consistent with C(3v) symmetric top structures for both complexes. The nuclear quadrupole coupling constants of iodine are determined to be -2230.030(83) MHz and -2241.61(17) MHz in CF(3)I···(14)NH(3) and CF(3)I···(14)N(CH(3))(3) respectively. The data are interpreted through a model that accounts for the internal dynamics of the complexes in order to determine the length of the halogen bond between the iodine and nitrogen atoms, r(N···I). Values of r(N···I) are thus determined to lie in the ranges 3.054 Å > r(N···I) > 3.034 Å and 2.790 Å > r(N···I) > 2.769 Å for CF(3)I···NH(3) and CF(3)I···N(CH(3))(3) respectively. PMID:21997343

  6. Intracavity laser spectroscopy of CH4 and NH3 gases by using a pulse-periodic Cr2+:ZnSe laser

    NASA Astrophysics Data System (ADS)

    Zakharov, N. G.; Savikin, A. P.; Sharkov, V. V.; Eremeykin, O. N.

    2012-01-01

    The results of studying the characteristics of an intracavity laser spectrometer based on a polycrystalline Cr2+:ZnSe laser operating in a pulse-periodic regime with the pulse-repetition rate of 3 kHz and pulse duration of ˜50 ns are presented. Intracavity spectra of absorption of NH3 and CH4 gases in the vicinity of 2.35 ?m are measured. The estimate of the spectrometer sensitivity is provided.

  7. NMR observation of oblique phase in mixed crystals (CH3NH3)2Cu(Cl1-xBrx)4(0.5<=x<=1)

    Microsoft Academic Search

    H. Kubo; Y. Suzuki; K. Hirakawa

    1983-01-01

    It was recently reported by Kimishima that the transition from the ferromagnetic to the antiferromagnet occurs at x ~ 0.9 in a mixed compound of (CH3NH3)2Cu(Cl1-xBrx)4. By the Cl NMR, we show that in the concentration region of the oblique phase, the Br- ions occupy a position on the c-axis, contrary to anticipation.

  8. Highly spin-polarized carrier dynamics and ultralarge photoinduced magnetization in CH3NH3PbI3 perovskite thin films.

    PubMed

    Giovanni, David; Ma, Hong; Chua, Julianto; Grätzel, Michael; Ramesh, Ramamoorthy; Mhaisalkar, Subodh; Mathews, Nripan; Sum, Tze Chien

    2015-03-11

    Low-temperature solution-processed organic-inorganic halide perovskite CH3NH3PbI3 has demonstrated great potential for photovoltaics and light-emitting devices. Recent discoveries of long ambipolar carrier diffusion lengths and the prediction of the Rashba effect in CH3NH3PbI3, that possesses large spin-orbit coupling, also point to a novel semiconductor system with highly promising properties for spin-based applications. Through circular pump-probe measurements, we demonstrate that highly polarized electrons of total angular momentum (J) with an initial degree of polarization Pini ?90% (i.e., -30% degree of electron spin polarization) can be photogenerated in perovskites. Time-resolved Faraday rotation measurements reveal photoinduced Faraday rotation as large as 10°/?m at 200 K (at wavelength ? = 750 nm) from an ultrathin 70 nm film. These spin polarized carrier populations generated within the polycrystalline perovskite films, relax via intraband carrier spin-flip through the Elliot-Yafet mechanism. Through a simple two-level model, we elucidate the electron spin relaxation lifetime to be ?7 ps and that of the hole is ?1 ps. Our work highlights the potential of CH3NH3PbI3 as a new candidate for ultrafast spin switches in spintronics applications. PMID:25646561

  9. Efficient perovskite solar cells based on low-temperature solution-processed (CH3NH3)PbI3 perovskite/CuInS2 planar heterojunctions

    PubMed Central

    2014-01-01

    In this work, the solution-processed CH3NH3PbI3 perovskite/copper indium disulfide (CuInS2) planar heterojunction solar cells with Al2O3 as a scaffold were fabricated at a temperature as low as 250°C for the first time, in which the indium tin oxide (ITO)-coated glass instead of the fluorine-doped tin oxide (FTO)-coated glass was used as the light-incidence electrode and the solution-processed CuInS2 layer was prepared to replace the commonly used TiO2 layer in previously reported perovskite-based solar cells. The influence of the thickness of the as-prepared CuInS2 film on the performance of the ITO/CuInS2(n)/Al2O3/(CH3NH3)PbI3/Ag cells was investigated. The ITO/CuInS2(2)/Al2O3/(CH3NH3)PbI3/Ag cell showed the best performance and achieved power conversion efficiency up to 5.30%. PMID:25278818

  10. Low-Temperature Conformal Atomic Layer Deposition of SiNx Films Using Si2Cl6 and NH3 Plasma.

    PubMed

    Ovanesyan, Rafaiel A; Hausmann, Dennis M; Agarwal, Sumit

    2015-05-27

    A plasma-enhanced atomic layer deposition (ALD) process was developed for the growth of SiNx thin films using Si2Cl6 and NH3 plasma. At substrate temperatures ?400 °C, we show that this ALD process leads to films with >95% conformality over high aspect ratio nanostructures with a growth per cycle of ?1.2 Å. The film growth mechanism was studied using in situ attenuated total reflection Fourier transform infrared spectroscopy. Our data show that on the SiNx growth surface, Si2Cl6 reacts with surface -NH2 groups to form surface -NH species, which are incorporated into the growing film. In the subsequent half cycle, radicals generated in the NH3 plasma abstract surface Cl atoms, and restore an NHx (x = 1,2)-terminated surface. Surface Si-N-Si bonds are also primarily formed during the NH3 plasma half-cycle. The infrared data and Rutherford backscattering combined with hydrogen forward scattering shows that the films contain ?23% H atoms primarily incorporated as -NH groups. PMID:25927250

  11. Dual functions of Lewis acid and base of Se in F2C=Se and their interplay in F 2CSe•••NH 3•••HX.

    PubMed

    Guo, Xin; Li, Qingzhong

    2015-06-01

    High-level quantum chemical calculations of the ternary systems F2CSe???NH3???HX (X=BeH, BH2, OH, CN, OCH3, Cl, and F) and the corresponding binary systems have been carried out in view of geometries, vibrational frequencies, interaction energies, orbital interactions, and electron densities. The molecular electrostatic potentials of F2CSe demonstrate that the Se atom could play a dual role of Lewis acid and base to form a chalcogen bond with NH3 and a hydrogen bond or a covalent interaction with HX, respectively. The chalcogen bond can compete with the hydrogen bond for the complexes involving F2CSe, but the covalent interaction is far stronger than the chalcogen bond. In the ternary complexes, both types of interactions are strengthened by each other, characterized by a shorter binding distance, a larger electron density, and a stronger orbital interaction. The covalent interaction has a greater enhancing effect on the chalcogen bond than the hydrogen bond does, resulting in a prominent shortening of ~0.23 Å distance for the Se???N distance in F2CSe???NH3???BH3. The enhancement of both interactions in the ternary complexes has been understood with the electrostatic potentials and orbital interactions. Graphical Abstract The dual functions of Lewis acid and base of Se in F2CSe are enhanced each other in the ternary complexes. PMID:26016943

  12. Formation of NH(c 1?) and NH(A 3?) in the photolysis of NH 3 HN 3 and HNCO at 121.6 nm

    NASA Astrophysics Data System (ADS)

    Hikida, T.; Maruyama, Y.; Saito, Y.; Mori, Y.

    1988-03-01

    Time profiles of the NH(c 1?) and NH(A 3?) fluorescence intensities were measured in the photolyses of NH 3, HN 3, and HNCO using the Lyman-? line at 121.6 nm. Upon irradiation of NH 3, only NH(c 1?) was observed as a primary product. The emissions from NH(c 1?) and NH(A 3?) were observed when HN 3 was irradiated. The NH triplet state was found to be formed by the sensitized reactions of N 2(B 3? g and B' 3? u-) with HN 3, where N 2(B 3? g, and B' 3? u-) were formed as primary products in the photolysis. The dissociation processes of NH 3 and HN 3 seem to conserve their spin state. On the contrary, the time profiles of fluorescence intensity suggested that NH(c 1?) and NH(A 3?) were formed in the photodissociation of HNCO within the experimental time resolution of a few nanoseconds.

  13. Facile preparation of ordered mesoporous MnCo2O4 for low-temperature selective catalytic reduction of NO with NH3

    NASA Astrophysics Data System (ADS)

    Qiu, Mingying; Zhan, Sihui; Yu, Hongbing; Zhu, Dandan; Wang, Shengqiang

    2015-01-01

    Ordered mesoporous MnCo2O4 nanomaterials were successfully prepared through the nanocasting route using SBA-15 and KIT-6 as hard templates. These mesoporous nanomaterials were characterized using XRD, BET, TEM, NH3-TPD, H2-TPR, NO-TPD, XPS and DRIFT. The low temperature selective catalytic reduction (SCR) activity of NO with NH3 was investigated, which revealed that 3D-MnCo2O4 using KIT-6 as a template can totally clean all NO over a wide temperature range of 100-250 °C with a gas hourly space velocity (GHSV) of 32 000 h-1, while 2D-MnCo2O4 with SBA-15 as a template had 95% conversion rate at the same condition. 3D-MnCo2O4 showed the best performance to clean NO due to its typical three-dimensional porous structure, large specific surface area, abundant active surface oxygen species and Lewis acid sites. All the results indicate that a novel, cheap catalyst for catalytic removal of NO can be designed by controlling the morphology at the nanoscale.Ordered mesoporous MnCo2O4 nanomaterials were successfully prepared through the nanocasting route using SBA-15 and KIT-6 as hard templates. These mesoporous nanomaterials were characterized using XRD, BET, TEM, NH3-TPD, H2-TPR, NO-TPD, XPS and DRIFT. The low temperature selective catalytic reduction (SCR) activity of NO with NH3 was investigated, which revealed that 3D-MnCo2O4 using KIT-6 as a template can totally clean all NO over a wide temperature range of 100-250 °C with a gas hourly space velocity (GHSV) of 32 000 h-1, while 2D-MnCo2O4 with SBA-15 as a template had 95% conversion rate at the same condition. 3D-MnCo2O4 showed the best performance to clean NO due to its typical three-dimensional porous structure, large specific surface area, abundant active surface oxygen species and Lewis acid sites. All the results indicate that a novel, cheap catalyst for catalytic removal of NO can be designed by controlling the morphology at the nanoscale. Electronic supplementary information (ESI) available: Low-angle XRD patterns, Nitrogen physisorption isotherms of SBA-15 and KIT-6; NO conversion in separate NO oxidation reaction over different samples. NH3 oxidation reaction over different samples. See DOI: 10.1039/c4nr06451h

  14. The Release of Trapped Gases from Amorphous Solid Water Films: II. “Bottom-Up” Induced Desorption Pathways

    SciTech Connect

    May, Robert A.; Smith, R. Scott; Kay, Bruce D.

    2013-03-14

    In this (Paper II) and the preceding companion paper (Paper I) we investigate the mechanisms for the release of trapped gases from underneath of amorphous solid water (ASW) films. In Paper I, we focused on the low coverage (pressure) regime where the release mechanism is controlled by crystallization-induced cracks formed in the ASW overlayer. In that regime the results were largely independent of the particular gas underlayer. Here in Paper II, we focus on the high coverage (pressure) regime where new desorption pathways become accessible prior to ASW crystallization. In contrast to the results for the low coverage regime (Paper I), the release mechanism is a function of the multilayer thickness and composition, displaying dramatically different behavior between Ar, Kr, Xe, CH4, N2, O2, and CO. Two primary desorption pathways are observed. The first occurs between 100 and 150 K and manifests itself as sharp, extremely narrow desorption peaks. Temperature programmed desorption is utilized to show that abrupt desorption bursts are due to pressure induced structural failure of the ASW overlyaer. The second pathway occurs at low temperature (typically <100 K) where broad desorption peaks are observed. Desorption through this pathway is attributed to diffusion through pores and connected pathways formed during ASW deposition. The extent of desorption and the lineshape of the low temperature desorption peak are dependent on the substrate on which the gas underlayer is deposited. Angle dependent ballistic deposition of the ASW is used vary the porosity of overlayer and confirm that the low temperature desorption pathway is due to porosity that is inherent in the ASW overlayer during deposition.

  15. GaN CVD Reactions: Hydrogen and Ammonia Decomposition and the Desorption of Gallium

    SciTech Connect

    Bartram, Michael E.; Creighton, J. Randall

    1999-05-26

    Isotopic labeling experiments have revealed correlations between hydrogen reactions, Ga desorption, and ammonia decomposition in GaN CVD. Low energy electron diffraction (LEED) and temperature programmed desorption (TPD) were used to demonstrate that hydrogen atoms are available on the surface for reaction after exposing GaN(0001) to deuterium at elevated temperatures. Hydrogen reactions also lowered the temperature for Ga desorption significantly. Ammonia did not decompose on the surface before hydrogen exposure. However, after hydrogen reactions altered the surface, N15H3 did undergo both reversible and irreversible decomposition. This also resulted in the desorption of N2 of mixed isotopes below the onset of GaN sublimation, This suggests that the driving force of the high nitrogen-nitrogen bond strength (226 kcal/mol) can lead to the removal of nitrogen from the substrate when the surface is nitrogen rich. Overall, these findings indicate that hydrogen can influence G-aN CVD significantly, being a common factor in the reactivity of the surface, the desorption of Ga, and the decomposition of ammonia.

  16. Structural and NMR studies of the series of related [H 3N(CH 2) xNH 3]·AlF 5 (x=6, 8, 10, 12) hybrid compounds

    Microsoft Academic Search

    E Goreshnik; M Leblanc; E Gaudin; F Taulelle; V Maisonneuve

    2002-01-01

    The series of [H3N(CH2)xNH3]·AlF5 (x=6, 8, 10, 12) compounds is synthesized by solvothermal method. Structure determinations are performed by single crystal (x=8, 10) and powder (x=12) techniques. The structures of [H3N(CH2)xNH3]·AlF5 (x=8, 10, 12) are related with the structure of [H3N(CH2)6NH3]·AlF5, which was previously described. They are built up from [AlF2?5]? infinite puckered inorganic chains linked by the diprotonated organic

  17. Effect of Rh particle size on CO desorption from Rh/alumina model catalysts

    NASA Astrophysics Data System (ADS)

    Belton, David N.; Schmieg, Steven J.

    1988-08-01

    The adsorption of CO on small Rh particles on oxidized Al(100) was studied using temperature programmed desorption (TPD) and Auger electron spectroscopy (AES). The desorption data for CO were obtained for two {Rh}/{Al 2O 3} samples as well as for Rh(111). The supported Rh model catalysts were prepared from thermal decomposition of [Rh(CO 2Cl] 2 on an oxidized Al(100) substrate. By varying the substrate temperature and the amount of deposited Rh, samples were prepared with average Rh particles sizes of 20 and 70 Å. TPD data from the 70 Å Rh particles were similar to that from Rh(111), with a major peak at 500 K and a shoulder at 400 K for a saturation CO exposure. TPD from the small particles was very different from Rh(111) and the larger particles, showing a single broad peak centered at 415 K. The data show a particle size effect for the desorption on CO from supported Rh. Redhead analysis of the data for first-order desorption gave an activation energy of 30 kcal/mol for all of the samples at low CO coverages. A more detailed analysis using peak widths and peak temperatures was also performed. These calculations gave a very low activation energy, 19.8 kcal/mol, and preexponential, 1×10 8{cm2}/{s} for the small particles. These very low values were interpreted to mean that multiple desorption states, mobile precursors, or coverage dependent activation energies were affecting the data from the small particles. Calculations of first-order desorption rates showed that desorption states different than those on Rh(111) are the dominant species on the small particles at high CO coverages.

  18. Surface diffusion and desorption kinetics for perfluoro-n-butane on Ru(001)

    NASA Astrophysics Data System (ADS)

    Arena, M. V.; Westre, E. D.; George, S. M.

    1991-03-01

    The surface diffusion and desorption kinetics for perfluoro-n-butane on Ru(001) were examined using laser-induced thermal desorption (LITD) and temperature programmed desorption (TPD) techniques. The surface diffusion displayed Arrhenius behavior and was coverage independent. The surface diffusion parameters for perfluoro-n-butane on Ru(001) were Edif=2.9±0.3 kcal/mol and D0=5.9×10-2±0.2 cm2/s. The desorption parameters for perfluoro-n-butane on Ru(001) were Edes=13.8±0.6 kcal/mol and ?des=2.8×1021±0.1 s-1. In comparison, the surface diffusion parameters for n-butane on Ru(001) were Edif=3.5±0.2 kcal/mol and D0=1.4×10-1±0.2 cm2/s. The desorption parameters for n-butane on Ru(001) were Edes=11.9±0.5 kcal/mol and ?des=3.6×1015±0.1 s-1. The corrugation ratio, defined as ??Edif/Edes, was determined to be ?=0.21 for perfluoro-n-butane on Ru(001). This corrugation ratio was substantially different than the corrugation ratio of ??0.30 measured for n-butane and various other n-alkanes, cycloalkanes and branched alkanes on Ru(001). The comparison between perfluoro-n-butane and the other alkanes indicates that fluorination lowers the surface corrugation ratio on Ru(001). Likewise, fluorination significantly increases the preexponential for desorption from Ru(001). This study illustrates the magnitude of substituent effects on surface diffusion and desorption kinetics for a physisorbed molecule on a single-crystal metal surface.

  19. Promotional effect of fluorine on the selective catalytic reduction of NO with NH3 over CeO2-TiO2 catalyst at low temperature

    NASA Astrophysics Data System (ADS)

    Zhang, Rui; Zhong, Qin; Zhao, Wei; Yu, Lemeng; Qu, Hongxia

    2014-01-01

    In order to investigate the effect of F on CeO2-TiO2 catalyst for the selective catalytic reduction (SCR) of NO with NH3, a series of F-doped CeO2-TiO2 catalysts were prepared by co-precipitation method. Compared with Ce0.3TiF0 catalyst, Ce0.3TiF1.5 catalyst exhibited the best catalytic activity, yielding 92.19% NO conversion at 180 °C. The catalysts were characterized by Brunauer-Emmett-Teller (BET) surface area, X-ray powder diffraction (XRD), photoluminescence (PL) spectra, Raman spectra, X-ray photoelectron spectroscopy (XPS) and Diffused reflectance infrared Fourier transform spectroscopy (DRIFTS) techniques. It was found that the enhanced catalytic activity was ascribed to several beneficial effects produced by the introduction of F: inhibition of the crystallization, decrease of the particle size, increase of the oxygen vacancies (F+ centers) and lattice defects. Raman measurements disclosed the formation of superoxide (O2-) ions in chemisorbed oxygen which was crucial for the formation of reaction intermediates (NO2-, NO3-). The study of DRIFTS proved that the addition of F could bring more ad-NOx and reaction intermediates. The NH3-TPD studies confirmed that the right amount of F could improve the number of acid sites over CeO2-TiO2 catalyst, especially the Lewis acid sites. These factors simultaneously enhanced the catalytic activity for NH3-SCR of NO. The effect of H2O and SO2 on the NO conversion was also investigated in our work.

  20. Relative merits of Cl2 and CO/NH3 plasma chemistries for dry etching of magnetic random access memory device elements

    NASA Astrophysics Data System (ADS)

    Jung, K. B.; Cho, H.; Hahn, Y. B.; Lambers, E. S.; Onishi, S.; Johnson, D.; Hurst, A. T.; Childress, J. R.; Park, Y. D.; Pearton, S. J.

    1999-04-01

    A typical magnetic random access memory stack consists of NiFe/Cu/NiFeCo multilayers, sandwiched by contact and antioxidation layers. For patterning of submicron features without redeposition on the sidewalls, it is desirable to develop plasma etch processes with a significant chlorinated etch component in addition to simple physical sputtering. Under conventional reactive ion etch conditions with Cl2-based plasmas, the magnetic layers do not etch because of the relatively involatile nature of the chlorinated reaction products. However, in high ion density plasmas, such as inductively coupled plasma, etch rates for NiFe and NiFeCo up to ˜700 Å min-1 are achievable. The main disadvantage of the process is residual chlorine on the feature sidewalls, which can lead to corrosion. We have explored several options for avoiding this problem, including use of in situ and ex situ cleaning processes after the Cl2-etching, or by use of a noncorrosive plasma chemistry, namely CO/NH3. In the former case, removal of the chlorine residues with in situ H2 plasma cleaning (to form volatile HCl that is pumped away), followed by ex situ solvent rinsing, appears effective in preventing corrosion. In the latter case, the CO/NH3 plasma chemistry produces metal carbonyl etch products, that are desorbed in the simultaneous presence of an ion flux. The etch rates with CO/NH3 are much lower than with Cl2 over a broad range of source powers (0-1500 W), radio frequency chuck powers (50-450 W), pressures (1-30 mTorr) and plasma compositions. We have tried substitution of CO2 for CO, and addition of Ar to produce faster etch rates, without success. Maximum rates of ˜300 Å min-1 for NiFe and NiFeCo were obtained with CO/NH3 under optimum conditions. The etched sidewalls tend to be sloped because of mask erosion during plasma exposure, in contrast to the case of Cl2-based chemistries where the sidewalls are vertical.

  1. Decomposition of NH3BH3 at sub-ambient pressures: A combined thermogravimetry-differential thermal analysis-mass spectrometry study

    SciTech Connect

    Palumbo, Oriele; Paolone, Annalisa; Rispoli, Pasquale; Cantelli, Rosario; Autrey, Thomas

    2010-03-15

    We report a systematic study of the isothermal decomposition of ammonia borane, NH3BH3, at 363 K as a function of argon pressure ranging between 50 and 1040 mbar using thermogravimetry and differential thermal analysis coupled with mass analysis of the volatile species. During thermal aging at 363 K, evolution of hydrogen, aminoborane and borazine is monitored, with the relative mass loss strongly depending on the pressure in the reaction chamber. Furthermore, the induction period required for hydrogen release at 363 K decreases with decreasing pressure.

  2. New insights from comprehensive on-road measurements of NOx, NO2 and NH3 from vehicle emission remote sensing in London, UK

    NASA Astrophysics Data System (ADS)

    Carslaw, David C.; Rhys-Tyler, Glyn

    2013-12-01

    In this paper we report the first direct measurements of nitrogen dioxide (NO2) in the UK using a vehicle emission remote sensing technique. Measurements of NO, NO2 and ammonia (NH3) from almost 70,000 vehicles were made spanning vehicle model years from 1985 to 2012. These measurements were carefully matched with detailed vehicle information data to understand the emission characteristics of a wide range of vehicles in a detailed way. Overall it is found that only petrol fuelled vehicles have shown an appreciable reduction in total NOx emissions over the past 15-20 years. Emissions of NOx from diesel vehicles, including those with after-treatment systems designed to reduce emissions of NOx, have not reduced over the same period of time. It is also evident that the vehicle manufacturer has a strong influence on emissions of NO2 for Euro 4/5 diesel cars and urban buses. Smaller-engined Euro 4/5 diesel cars are also shown to emit less NO2 than larger-engined vehicles. It is shown that NOx emissions from urban buses fitted with Selective Catalytic Reduction (SCR) are comparable to those using Exhaust Gas Recirculation for Euro V vehicles, while reductions in NOx of about 30% are observed for Euro IV and EEV vehicles. However, the emissions of NO2 vary widely dependent on the bus technology used. Almost all the NOx emission from Euro IV buses with SCR is in the form of NO, whereas EEV vehicles (Enhanced Environmentally friendly Vehicle) emit about 30% of the NOx as NO2. We find similarly low amounts of NO2 from trucks (3.5-12t and >12t). Finally, we show that NH3 emissions are most important for older generation catalyst-equipped petrol vehicles and SCR-equipped buses. The NH3 emissions from petrol cars have decreased by over a factor of three from the vehicles manufactured in the late 1990s compared with those manufactured in 2012. Tables of emission factors are presented for NOx, NO2 and NH3 together with uncertainties to assist the development of new emission inventories.

  3. Nanowires of methylammonium lead iodide (CH3NH3PbI3) prepared by low temperature solution-mediated crystallization.

    PubMed

    Horváth, Endre; Spina, Massimo; Szekrényes, Zsolt; Kamarás, Katalin; Gaal, Richard; Gachet, David; Forró, László

    2014-12-10

    We report the synthesis of Methylammonium Lead Iodide (CH(3)NH(3)PbI(3)) nanowires by a low temperature solution processed crystallization using a simple slip-coating method. The anisotropic particle shape exhibits advantages over nanoparticles in terms of charge transport under illumination. These results provide a basis for solvent-mediated tailoring of structural properties like the crystallite size and orientation in trihalide perovskite thin films, which, once implemented into a device, may ultimately result in an enhanced charge carrier extraction. PMID:25354371

  4. Crystal structure and electric properties of the organic-inorganic hybrid: [(CH2)6(NH3)2]ZnCl4

    NASA Astrophysics Data System (ADS)

    Mostafa, M. F.; El-khiyami, S. S.

    2014-01-01

    The new organic-inorganic hybrid [(CH2)6(NH3)2]ZnCl4, Mr=325.406 crystallized in a triclinic, P1¯, a=7.2816 (5) Å, b=10.0996 (7) Å, c=10.0972 (7) Å, ?=74.368 (4)°, ?=88.046 (4)°, ?=85.974 (3)°, V=713.24 (9) Å3 and Z=2, Dx=1.486 Mg m-3. Differential thermal scanning and x-ray powder diffraction, permittivity and ac conductivity indicated three phase transitions. Conduction takes place via correlated barrier hopping.

  5. The irradiation of pure CH3OH and 1:1 mixture of NH3:CH3OH ices at 30 K using low energy electrons

    NASA Astrophysics Data System (ADS)

    Jheeta, Sohan; Domaracka, A.; Ptasinska, S.; Sivaraman, B.; Mason, N. J.

    2013-01-01

    The results of an experimental investigation of 1 keV electron irradiation of ices (deposited at 30 K) of (i) pure methanol and (ii) of a 1:1 mixture of NH3:CH3OH are reported. Molecular products formed within the ice were detected and monitored using FTIR spectroscopy. The products observed were methyl formate (H3COHCO), methane (CH4), hydroxymethyl (CH2OH), formamide (HCONH2), formic acid (HCOOH), formaldehyde (H2CO), formyl radical (HCO), cyanate ion (OCN-), isocyanic acid (HNCO), carbon monoxide (CO) and carbon dioxide (CO2). The consequences of these results for prebiotic chemistry in the interstellar medium and star forming regions are discussed.

  6. Structural and morphological changes characterizing reversible de-ammination\\/re-ammination processes in NiPt(CN) 4 (NH 3 ) 2

    Microsoft Academic Search

    A. Reller; H.-R. Oswald

    1994-01-01

    The topotactic structural mechanism of de- and re-ammination of single-crystalline NiPt(CN)4(NH3)2 is characterized by means of structural, morphological and thermoanalytical studies. Structural investigations give evidence\\u000a that the two-dimensional structural motif [NiPt(CN)4]? determines the mechanism and the kinetics of both processes. It is shown that the degree of reversibility, in particular\\u000a the exothermic re-ammination, is governed by the conservation of the

  7. Hole-transport materials with greatly-differing redox potentials give efficient TiO2-[CH3NH3][PbX3] perovskite solar cells.

    PubMed

    Abate, Antonio; Planells, Miquel; Hollman, Derek J; Barthi, Vishal; Chand, Suresh; Snaith, Henry J; Robertson, Neil

    2015-01-28

    Two diacetylide-triphenylamine hole-transport materials (HTM) with varying redox potential have been applied in planar junction TiO2-[CH3NH3]PbI3-xClx solar cells leading to high power-conversion efficiencies up to 8.8%. More positive oxidation potential of the HTM gives higher VOC and lower JSC illustrating the role of matching energy levels, however both HTMs gave efficient cells despite a difference of 0.44 V in their redox potentials. PMID:25504144

  8. Search for potential minimum positions in metal-organic hybrids, (C2H5NH3)2CuCl4 and (C6H5CH2CH2NH3)2CuCl4, by using density functional theory

    NASA Astrophysics Data System (ADS)

    Suprayoga, E.; Nugroho, A. A.; Polyakov, A. O.; Palstra, T. T. M.; Watanabe, I.

    2014-12-01

    The ab-initio density functional theory analysis was applied to metal-organic hybrids, (C2H5NH3)2CuCl4 (EA) and (C6H5CH2CH2NH3)2CuCl4 (PEA), in order to estimate possible muons stopping positions. Six potential minimum positions and eight ones were revealed in PA and PEA, respectively. Those potential minimum positions can be regarded as initial stopping positions of injected muons. All of expected potential minimum points in EA were near and around the apical Cl and the CuCl2 plane of the CuCl6 octahedra. Instead, in the case of PEA, two of eight positions were close to the phenyl ring giving a possibility that there would be muon states which couple surrounding electrons via a radical formation.

  9. Fourier-transformed infrared absorption spectroscopy: a tool to characterize the chemical composition of Ar-NH3-SiH4 dielectric barrier discharge

    NASA Astrophysics Data System (ADS)

    Vallade, Julien; Massines, Françoise

    2013-11-01

    This study brings initial insight into the characterization of the gas chemical composition in a dielectric barrier discharge (DBD) by Fourier-transformed infrared absorption spectroscopy. Capitalizing on a double path of the IR beam, measurements were performed in 5 cm long, 2 mm gap plasma. As the IR beam cross-section in the plasma was 2 × 2 mm2, a translation system was used to scan the plasma along the direction of the gas flow with a 2 mm spatial resolution. In the case of Ar-SiH4(67 ppm)-NH3(133 ppm) glow-mode DBD, all IR spectra peaks from 6000 to 800 cm-1 are related to vibrations of Si-H from SiH4 and N-H from NH3. Here, the N-H vibration is observable but non-quantifiable. At 50 kHz excitation, the absolute concentration of SiH4 was measured at different positions and different power values in continuous and modulated modes. In the absence of powder formation in the plasma and for an initial density of 1.6 × 1015 cm-3, all the measurements are fitted by the same exponential decay leading to an energy of 38 eV per dissociated molecule of SiH4. The presence of powders in the plasma reduces SiH4 dissociation rate by a factor larger than 4.

  10. Thermal and plasma-enhanced atomic layer deposition of TiN using TDMAT and NH3 on particles agitated in a rotary reactor.

    PubMed

    Longrie, Delphine; Deduytsche, Davy; Haemers, Jo; Smet, Philippe F; Driesen, Kris; Detavernier, Christophe

    2014-05-28

    Titanium nitride (TiN) shows metallic-type electrical behavior and is therefore an interesting material to improve the conductivity of a wide variety of powders. Atomic layer deposition (ALD) is an excellent technique for achieving the desired ultrathin but conformal coatings. To conformally coat large amounts of particles using ALD, agitation of the particles and efficient reactant usage are necessary. Thermal and plasma-enhanced ALD growth of TiN using tetrakis(dimethylamino)titanium (TDMAT) and NH3 as precursors on agitated particles was performed using a rotary reactor to deposit TiN on ZnO submicrometer powder. The NH3 plasma pulse was monitored using in situ mass spectrometry (MS) and optical emission spectroscopy (OES) measurements to gain insight into the reaction mechanism of the plasma-enhanced process. X-ray photoelectron spectroscopy (XPS) and powder resistivity measurements were performed to determine the influence of the deposition process on the composition and conductivity of the deposited TiN layers. PMID:24801740

  11. Ultracold atom-molecule collisions and bound states in magnetic fields: Tuning zero-energy Feshbach resonances in He-NH (?-3)

    NASA Astrophysics Data System (ADS)

    González-Martínez, Maykel Leonardo; Hutson, Jeremy M.

    2007-02-01

    We have generalized the BOUND and MOLSCAT packages to allow calculations in basis sets where the monomer Hamiltonians are off diagonal and used this capability to carry out bound-state and scattering calculations on He-NH3 and He-NH4 as a function of magnetic field. Following the bound-state energies to the point where they cross thresholds gives very precise predictions of the magnetic fields at which zero-energy Feshbach resonances occur. We have used this to locate and characterize two very narrow Feshbach resonances in He-NH3 . Such resonances can be used to tune elastic and inelastic collision cross sections, and sweeping the magnetic field across them will allow a form of quantum control in which separated atoms and molecules are associated to form complexes. For the first resonance, where only elastic scattering is possible, the scattering length shows a pole as a function of magnetic field and there is a very large peak in the elastic cross section. For the second resonance, however, inelastic scattering is also possible. In this case the pole in the scattering length is dramatically suppressed and the cross sections show relatively small peaks. The peak suppression is expected to be even larger in systems with stronger inelasticity. The results suggest that calculations on ultracold molecular inelastic collisions may be much less sensitive to details of the potential energy surface than has been believed.

  12. On the Landau theory of structural phase transitions in layered perovskites (CH3NH3)2MCl4(M = Mn, Cd, Fe) : comparison with experiments

    NASA Astrophysics Data System (ADS)

    Couzi, Michel

    1991-05-01

    The phase sequence I4/mmm Leftrightarrow Abma Leftrightarrow P4{2}/ncm (THT Leftrightarrow ORT Leftrightarrow TLT), which is a common feature in (CH{3}NH{3}){2}MCl{4} compounds (M = Mn, Cd, Fe), is discussed on the basis of Landau theory, in comparison with available experimental results. Much attention is paid to the “anomalous” behaviour of the c_{66} elasitic constant. After the microscopic model of mean-field type, developed previously by Blinc, Zeks and Kind, and from classical group theoretical considerations, it turns out that a Landau free-energy expansion up to the eighth-order is necessary to obtain a coherent description of all experimental data. La séquence de transitions de phase I4/mmm Leftrightarrow Abma Leftrightarrow P4{2}/ncm (THT Leftrightarrow ORT Leftrightarrow TLT), qui est une caractéristique commune des composés (CH{3}NH{3}){2}MCl{4}(M = Mn, Cd, Fe), est examinée sur la base de la theorie de Landau, en comparaison avec les résultats expérimentaux disponibles. Une attention particulière est portée sur le comportement “anormal” de la constante élastique c_{66}. D'après le modèle microscopique de type champ moyen, développé antérieurement par Blinc, Zeks et Kind, et à aprtir de considérations classiques de théorie des groupes, il apparaît que l'énergie libre de Landau doit être développée à l'ordre huit pour obtenir une description cohérente de l'ensemble des données expérimentales.

  13. Emissions of NH3, CO2 and H2S during swine wastewater management: Characterization of transient emissions after air-liquid interface disturbances

    NASA Astrophysics Data System (ADS)

    Blanes-Vidal, V.; Guàrdia, M.; Dai, X. R.; Nadimi, E. S.

    2012-07-01

    Air contaminants emitted from stored animal wastewater affect human health and the environment. Measurements of gaseous emissions from undisturbed animal wastewater are abundant in the literature. However, in-barn wastewater management is characterized by the frequent occurrence of surface liquid disturbances. Information about emissions during and after wastewater disturbances is scarce. This study evaluates emissions of NH3, CO2 and H2S under transient conditions after wastewater disturbances (caused by slurry addition, water addition and mixing), and describes the mechanisms involved until reaching steady-state conditions. All three disturbances modified the gas emission patterns. Emissions of NH3 immediately decreased after the disturbances (-61% after slurry and water addition and by -91% after mixing), and then gradually increased during 90-200 min. Emissions of CO2 increased during the disturbances (40% during slurry and water addition and 1515% during mixing), and then decreased during up to 30 min after the disturbance. H2S emissions sharply increased during all three disturbances and then decreased for 2 min to 20 min. Emissions under transient conditions were related to the formation of a pH profile. Transient emissions should be considered in gas emission studies as they may represent an important part of the cumulative gas emissions during slurry storage.

  14. Elementary steps of the catalytic NO(x) reduction with NH3: cluster studies on reaction paths and energetics at vanadium oxide substrate.

    PubMed

    Gruber, M; Hermann, K

    2013-12-28

    We consider different reaction scenarios of the selective catalytic reduction (SCR) of NO in the presence of ammonia at perfect as well as reduced vanadium oxide surfaces modeled by V2O5(010) without and with oxygen vacancies. Geometric and energetic details as well as reaction paths are evaluated using extended cluster models together with density-functional theory. Based on earlier work of adsorption, diffusion, and reaction of the different surface species participating in the SCR we confirm that at Brønsted acid sites (i.e., OH groups) of the perfect oxide surface nitrosamide, NH2NO, forms a stable intermediate. Here adsorption of NH3 results in NH4 surface species which reacts with gas phase NO to produce the intermediate. Nitrosamide is also found as intermediate of the SCR near Lewis acid sites of the reduced oxide surface (i.e., near oxygen vacancies). However, here the adsorbed NH3 species is dehydrogenated to surface NH2 before it reacts with gas phase NO to produce the intermediate. The calculations suggest that reaction barriers for the SCR are overall higher near Brønsted acid sites of the perfect surface compared with Lewis acid sites of the reduced surface, examined for the first time in this work. The theoretical results are consistent with experimental findings and confirm the importance of surface reduction for the SCR process. PMID:24387382

  15. Nanoscale charge localization induced by random orientations of organic molecules in hybrid perovskite CH3NH3PbI3.

    PubMed

    Ma, Jie; Wang, Lin-Wang

    2015-01-14

    Perovskite-based solar cells have achieved high solar-energy conversion efficiencies and attracted wide attentions nowadays. Despite the rapid progress in solar-cell devices, many fundamental issues of the hybrid perovskites have not been fully understood. Experimentally, it is well-known that in CH3NH3PbI3 the organic molecules CH3NH3 are randomly orientated at the room temperature, but the impact of the random molecular orientation has not been investigated. Because of the dipole moment of the organic molecule, the random orientation creates a novel system with long-range potential fluctuations unlike alloys or other conventional disordered systems. Using linear scaling ab initio methods, we find that the charge densities of the conduction band minimum and the valence band maximum are localized in nanoscales due to the potential fluctuations. The charge localization causes electron-hole separation and reduces carrier recombination rates, which may contribute to the long carrier lifetime observed in experiments. PMID:25493911

  16. TDLAS-based NH3 mole fraction measurement for exhaust diagnostics during selective catalytic reduction using a fiber-coupled 2.2-µm DFB diode laser

    NASA Astrophysics Data System (ADS)

    Stritzke, Felix; Diemel, Oliver; Wagner, Steven

    2015-04-01

    A new developed tunable diode laser spectrometer for the measurement of ammonia (NH3) mole fractions in exhaust gas matrices with strong CO2 and H2O background at temperatures up to 800 K is presented. In situ diagnostics in harsh exhaust environments during SCR after treatment are enabled by the use of ammonia transitions in the ?2 + ?3 near-infrared band around 2300 nm. Therefore, three lines have been selected, coinciding near 2200.5 nm (4544.5 cm-1) with rather weak temperature dependency and minimal interference with CO2 and H2O. A fiber-coupled 2.2-?m distributed feedback laser diode was used and attached to the hot gas flow utilizing adjustable gas tight high-temperature fiber ports. The spectrometer spans four coplanar optical channels across the measurement plane and simultaneously detects the direct absorption signal via a fiber-coupled detector unit. An exhaust simulation test rig was used to characterize the spectrometer's performance in ammonia-doped hot gas environments. We achieved a temporal resolution of 13 Hz and temperature-dependent precisions of NH3 mole fraction ranging from 50 to 70 ppmV. There the spectrometer achieved normalized ammonia detection limits of 7-10 and 2-3.

  17. Elementary steps of the catalytic NOx reduction with NH3: Cluster studies on reaction paths and energetics at vanadium oxide substrate

    NASA Astrophysics Data System (ADS)

    Gruber, M.; Hermann, K.

    2013-12-01

    We consider different reaction scenarios of the selective catalytic reduction (SCR) of NO in the presence of ammonia at perfect as well as reduced vanadium oxide surfaces modeled by V2O5(010) without and with oxygen vacancies. Geometric and energetic details as well as reaction paths are evaluated using extended cluster models together with density-functional theory. Based on earlier work of adsorption, diffusion, and reaction of the different surface species participating in the SCR we confirm that at Brønsted acid sites (i.e., OH groups) of the perfect oxide surface nitrosamide, NH2NO, forms a stable intermediate. Here adsorption of NH3 results in NH4 surface species which reacts with gas phase NO to produce the intermediate. Nitrosamide is also found as intermediate of the SCR near Lewis acid sites of the reduced oxide surface (i.e., near oxygen vacancies). However, here the adsorbed NH3 species is dehydrogenated to surface NH2 before it reacts with gas phase NO to produce the intermediate. The calculations suggest that reaction barriers for the SCR are overall higher near Brønsted acid sites of the perfect surface compared with Lewis acid sites of the reduced surface, examined for the first time in this work. The theoretical results are consistent with experimental findings and confirm the importance of surface reduction for the SCR process.

  18. Do H-bond features of silica surfaces affect the H2O and NH3 adsorption? Insights from periodic B3LYP calculations.

    PubMed

    Musso, Federico; Ugliengo, Piero; Sodupe, Mariona

    2011-10-20

    The adsorption of a single H(2)O and NH(3) molecule on different fully hydroxylated ?-quartz, cristobalite, and tridymite surfaces has been studied at the B3LYP level of theory, within a periodic approach using basis sets of polarized triple-? quality and accounting for basis set superposition error (BSSE). Fully hydroxylated crystalline silica exhibits SiOH as terminal groups whose distribution and H-bond features depend on both the considered silica polymorph and the crystallographic plane, which gives rise to isolated, H-bond interacting SiOH pairs or infinitely connected H-bond chains. A key point of the present study is to understand how the H-bond features of a dry crystalline silica surface influence its adsorption properties. Results reveal that the silica-adsorbate (H(2)O and NH(3)) interaction energy anticorrelates with the density of SiOH groups at the surface. This counterintuitive observation arises from the fact that pre-existing H-bonds of the dry surface need to be broken to establish new H-bonds between the surface and the adsorbate, which manifests in a sizable energy cost due to surface deformation. A simple method is also proposed to estimate the strength of the pre-existing H-bonds at the dry surfaces, which is shown to anticorrelate with the adsorbate interaction energy, in agreement with the above trends. PMID:21895017

  19. Homoepitaxial growth of a-plane GaN layers by reaction between Ga2O vapor and NH3 gas

    NASA Astrophysics Data System (ADS)

    Sumi, Tomoaki; Taniyama, Yuuki; Takatsu, Hiroaki; Juta, Masami; Kitamoto, Akira; Imade, Mamoru; Yoshimura, Masashi; Isemura, Masashi; Mori, Yusuke

    2015-06-01

    Growth of high-quality a-plane GaN layers was performed by reaction between Ga2O vapor and NH3 gas at a high temperature. Smooth a-plane GaN epitaxial layers were obtained on a-plane GaN seed substrates sliced from thick c-plane GaN crystals. Growth rate increased with increasing Ga2O partial pressure. An a-plane GaN layer with a growth rate of 48 µm/h was obtained. The X-ray rocking curve (XRC) measurement showed that the full widths at half maximum (FWHMs) of GaN(11\\bar{2}0) with the incident beam parallel and perpendicular to the [0001] direction were 29–43 and 29–42 arcsec, respectively. Secondary ion mass spectrometry (SIMS) measurement revealed that oxygen concentration decreased at a high temperature. These results suggest that growth of a-GaN layers using Ga2O vapor and NH3 gas at a high temperature enables the generation of high-quality crystals.

  20. Reaction of [Ni(H2O)6](NO3)2 with gaseous NH3; crystal growth via in-situ solvation

    NASA Astrophysics Data System (ADS)

    Breternitz, Joachim; Farrugia, Louis J.; Godula-Jopek, Agata; Saremi-Yarahmadi, Sina; Malka, Iwona E.; Hoang, Tuan K. A.; Gregory, Duncan H.

    2015-02-01

    Traditional techniques for the growth of crystals are typically lengthy and are based on the slow over-saturation of either solutions or melts. By contrast, the reactions of solids at moderate temperatures and pressures normally lead to the formation of powders of small crystallites. In this paper, we present a new and effective method to grow crystals of surprisingly large sizes (up to ca. 0.05 mm in the largest dimension). We use the reaction of [Ni(H2O)6](NO3)2 with NH3(g) at room temperature to create macro-crystals of [Ni(NH3)6](NO3)2. The synthesis proceeds via simple ligand exchange and crystal growth is facilitated in-situ via the solvent effect of the released water. The nitrate ammine product was characterised by powder X-ray diffraction (PXD) and Scanning Electron Microscopy (SEM). This reaction is important since it demonstrates that aquo complexes can undergo facile ligand exchange with gaseous ammonia under realistic conditions for ammonia storage. The single crystal structure of [Ni(H2O)6](NO3)2 was determined for the first time below ambient temperature (at 100 K). The latter result offers no evidence to support a previously postulated low temperature phase-transformation at 100?T/K?295.

  1. Tunable Optical Properties and Charge Separation in CH3NH3SnxPb1-xI3/TiO2-Based Planar Perovskites Cells.

    PubMed

    Feng, Hong-Jian; Paudel, Tula R; Tsymbal, Evgeny Y; Zeng, Xiao Cheng

    2015-07-01

    A sharp potential drop across the interface of the Pb-rich halide perovskites/TiO2 heterostructure is predicted from first-principles calculations, suggesting enhanced separation of photoinduced charge carriers in the perovskite-based photovoltaic solar cells. The potential drop appears to be associated with the charge accumulation at the polar interface. More importantly, on account of both the ? phase structure of CH3NH3SnxPb1-xI3 for x < 0.5 and the ? phase structure of CH3NH3SnxPb1-xI3 for x ? 0.5, the computed optical absorption spectra from time-dependent density functional theory (TD-DFT) are in very good agreement with the measured spectra from previous experiments. Our TD-DFT computation also confirms the experimental structures of the mixed Pb-Sn organometal halide perovskites. These computation results provide a highly sought answer to the question why the lead-based halide perovskites possess much higher power conversion efficiencies than the tin-based counterparts for solar-cell applications. PMID:26011597

  2. Catalytic reduction of N2 to NH3 by an Fe-N2 complex featuring a C-atom anchor

    PubMed Central

    Creutz, Sidney E.; Peters, Jonas C.

    2014-01-01

    While recent spectroscopic studies have established the presence of an interstitial carbon atom at the center of the iron-molybdenum cofactor (FeMoco) of MoFe-nitrogenase, its role is unknown. We have pursued Fe-N2 model chemistry to explore a hypothesis whereby this C-atom (previously denoted as a light X-atom) may provide a flexible trans interaction with an Fe center to expose an Fe-N2 binding site. In this context, we now report on Fe complexes of a new tris(phosphino)alkyl (CPiPr3) ligand featuring an axial carbon donor. It is established that the iron center in this scaffold binds dinitrogen trans to the Calkyl-atom anchor in three distinct and structurally characterized oxidation states. Fe-Calkyl lengthening is observed upon reduction, reflective of significant ionic character in the Fe-Calkyl interaction. The anionic (CPiPr3)FeN2- species can be functionalized by a silyl electrophile to generate (CPiPr3)Fe-N2SiR3. (CPiPr3)FeN2- also functions as a modest catalyst for the reduction of N2 to NH3 when supplied with electrons and protons at -78 °C under 1 atm N2 (4.6 equiv NH3/Fe). PMID:24350667

  3. Characterization of carbonaceous deposits by temperature-programmed oxidation

    SciTech Connect

    Bond, G.C. [Brunel Univ., Uxbridge (United Kingdom)] [Brunel Univ., Uxbridge (United Kingdom); Dias, C.R.; Portela, M.F. [Instituto Superior Tecnico, Lisbon (Portugal)] [Instituto Superior Tecnico, Lisbon (Portugal)

    1995-10-01

    The reactions of organic compounds on solid catalysts can be accompanied by the formation of heavy by-products which can form a carbonaceous deposit on the surface and cause deactivation. They are of major importance in catalysis research and stimulate considerable interest. Temperature-programmed oxidation (TPO) can play an important role in their characterization: it consists of exposing a sample to a flowing O{sub 2}/inert gas mixture while increasing its temperature, the amount of carbonaceous compounds oxidized being determined by quantification of the O{sub 2} consumed or CO{sub 2} formed. In this work, the authors have used the former method because of the availability of apparatus to measure O{sub 2} concentration by thermal conductivity. The problem with measuring O{sub 2} consumption is that one cannot be certain that only CO{sub 2} is formed, and no CO. The authors report here on the TPO of pure carbon (activated charcoal) in the presence and in the absence of a palladium catalyst, the function of which was to oxidise any CO formed to CO{sub 2} 14 refs., 3 figs., 1 tab.

  4. Effect of surface nanostructure on temperature programmed reaction spectroscopy

    NASA Astrophysics Data System (ADS)

    Rieger, Michael; Rogal, Jutta; Reuter, Karsten

    2008-03-01

    Using the catalytic CO oxidation at RuO2(110) as a showcase, we employ first-principles kinetic Monte Carlo simulations to illustrate the intricate effects on temperature programmed reaction (TPR) spectroscopy data brought about by the mere correlations between the locations of the active sites at a nanostructured surface. Even in the absence of lateral interactions, this nanostructure alone can cause inhomogeneities that cannot be grasped by prevalent mean-field data analysis procedures, which thus lead to wrong conclusions on the reactivity of the different surface species. The RuO2(110) surface studied here exhibits only two prominent active sites, arranged in simple alternating rows. Yet, the mere neglection of this still quite trivial nanostructure leads mean-field TPR data analysis [1] to extract kinetic parameters that are in error by several orders of magnitude and that do not even reflect the relative reactivity of the different surface species correctly [2].[1] S. Wendt, M. Knapp, and H. Over, JACS 126, 1537 (2004).[2] M. Rieger, J. Rogal, and K. Reuter, Phys. Rev. Lett (in press).

  5. Desorption of water from distinct step types on a curved silver crystal.

    PubMed

    Janlamool, Jakrapan; Bashlakov, Dima; Berg, Otto; Praserthdam, Piyasan; Jongsomjit, Bunjerd; Juurlink, Ludo B F

    2014-01-01

    We have investigated the adsorption of H2O onto the A and B type steps on an Ag single crystal by temperature programmed desorption. For this study, we have used a curved crystal exposing a continuous range of surface structures ranging from [5(111) × (100)] via (111) to [5(111) × (110)]. LEED and STM studies verify that the curvature of our sample results predominantly from monoatomic steps. The sample thus provides a continuous array of step densities for both step types. Desorption probed by spatially-resolved TPD of multilayers of H2O shows no dependence on the exact substrate structure and thus confirms the absence of thermal gradients during temperature ramps. In the submonolayer regime, we observe a small and linear dependence of the desorption temperature on the A and B step density. We argue that such small differences are only observable by means of a single curved crystal, which thus establishes new experimental benchmarks for theoretical calculation of chemically accurate binding energies. We propose an origin of the observed behavior based on a "two state" desorption model. PMID:25068782

  6. Probing the formation and evolution of comets via nuclear spin temperatures of C_2H_6, CH_3OH, CH_4, NH_3, and H_2O

    NASA Astrophysics Data System (ADS)

    Villanueva, G.; Mumma, M.; Bonev, B.; DiSanti, M.; Paganini, L.; Magee-Sauer, K.; Gibb, E.

    2014-07-01

    Comets are true remnants of our primordial Solar System, and provide unique clues to its formation and evolution, including the delivery of organics and water to our planet. A key indicator stored in the molecular structure of the nuclear ices is the spin temperature (T_{spin}), derived from spin-isomeric ratios (R_{spin}, e.g., ortho/para). At the time when cometary ices formed, the prevailing temperature defined the relative abundance of the different spin-isomeric species, and herewith R_{spin} and T_{spin} are normally treated as ''remnant thermometers'' probing the formation environments of cometary molecules. Radiative and collisional transitions between the ortho and para states are strongly forbidden and herewith this indicator is preserved over time. Most of our knowledge of this indicator comes from the measurements of the ortho-para ratios in water and NH_2 (a proxy for ammonia), suggesting a common T_{spin} near 30 K. This information is based on a restricted sample of comets, and the measurements are particularly sensitive to the molecular modeling technique and adopted spectral database. Here, we present new methodologies for extracting spin temperatures from ethane (C_2H_6), methane (CH_4), and methanol (CH_3OH), and advanced new models for ortho/para water (H_2O) and ammonia (NH_3). Our H_2O analysis is based on the most complete fluorescence radiative-transfer model to date, which incorporates 1,200 million transitions including those originating from high-energy levels that are activated in comets via a non-resonant cascade. In a similar fashion, we developed non-resonant fluorescence models for NH_3 and HCN, and quantum-band models for the ?_7 band of C_2H_6 and ?_3 band of CH_3OH. All models respect spin-symmetry non-conversion radiative rules, and make use of a realistic solar spectrum for the computation of fluorescence pumps. We applied these new methods to derive spin-isomeric ratios for H_2O, CH_4, C_2H_6, CH_3OH, and NH_3 from three high- quality cometary datasets: 1) C/2007 W1 (Boattini), 2) C/2001 A2 (LINEAR), and 3) 8P/Tuttle. We compare our results to the measured organic compositions for these comets, and present possible formation and evolution scenarios.

  7. Observations of the Partitioning of Trace Acids During CalNex, Bakersfield: HONO, HCl and Oxalic Acid in an NH3-rich Environment

    NASA Astrophysics Data System (ADS)

    Vandenboer, T. C.; Markovic, M. Z.; Sanders, J.; Ren, X.; Murphy, J. G.

    2010-12-01

    The 2010 California Research at the Nexus of Air Quality and Climate Change (CalNex) field campaign supersite in Bakersfield, CA, presented an opportunity to investigate the gas-particle partitioning of trace atmospheric species in a low-sulphur high-NH3 environment. With the demand for cleaner energy, atmospheric S levels are expected to continue to decrease across North America, while restrictions on NH3 emissions are still in preliminary stages. Despite the absence of significant sulphur emissions contributing to particulate matter (PM) formation, California’s San Joaquin Valley still experiences some of the worst air quality in the continental US. Partitioning of other trace gases may become more important in low sulphur regions; here we report our observations of HONO, HCl and oxalic acid partitioning. Observations of the water-soluble composition of atmospheric gases and fine particulate matter (PM2.5) were made with an Ambient Ion Monitor - Ion Chromatography (AIM-IC) system from University Research Glassware (Chapel Hill, NC). The AIM-IC was fitted with a newly designed impactor inlet that minimizes gas and particle losses prior to collection by a wet wall parallel plate denuder and super saturated steam condensation chamber, respectively, situated at a height of 4.5 m for this study. Observations of NH3 indicated ambient levels typically in excess of 10 ppb, up to 60 ppb, and all observed inorganic aerosol was found to be completely neutralized throughout the campaign by NH4+. Mixing ratios of HONO showed excellent agreement with concurrent measurements made by a LOPAP instrument from University of Miami, maximizing during the night at values in the range of 1 - 1.5 ppb. On several nights, particulate NO2- mass loadings in the range of 0.2 ?g m-3 (equivalent to 0.1 ppb HONO) were observed by the AIM-IC. The diurnal pattern of HCl showed maximum mixing ratios of 0.2 - 0.3 ppb occurring near 13:00 PST, and near zero values at night. Intermittent bursts of Cl- were also detected, however the Cl- present in PM2.5 was significantly less than that present as HCl. These online observations are some of the few to date describing simultaneous measurements of both gas and particle phase reservoirs of chlorine as HCl/Cl-. The diurnal pattern of oxalic acid showed maximum mixing ratios less than 0.1 ppb near 16:00 PST and near zero values at night. The presence of oxalate in PM2.5 was observed throughout the campaign with mass loadings in the range of 0 - 0.2 ?g m-3 also maximizing during the day.

  8. Investigation of CH3NH3PbI3 degradation rates and mechanisms in controlled humidity environments using in situ techniques.

    PubMed

    Yang, Jinli; Siempelkamp, Braden D; Liu, Dianyi; Kelly, Timothy L

    2015-02-24

    Perovskite solar cells have rapidly advanced to the forefront of solution-processable photovoltaic devices, but the CH3NH3PbI3 semiconductor decomposes rapidly in moist air, limiting their commercial utility. In this work, we report a quantitative and systematic investigation of perovskite degradation processes. By carefully controlling the relative humidity of an environmental chamber and using in situ absorption spectroscopy and in situ grazing incidence X-ray diffraction to monitor phase changes in perovskite degradation process, we demonstrate the formation of a hydrated intermediate containing isolated PbI6(4-) octahedra as the first step of the degradation mechanism. We also show that the identity of the hole transport layer can have a dramatic impact on the stability of the underlying perovskite film, suggesting a route toward perovskite solar cells with long device lifetimes and a resistance to humidity. PMID:25635696

  9. Nuclear magnetic relaxation in the quasi-two-dimensional (C2H5NH3)2Cd1-xMnxCl4 mixed crystal systems

    NASA Astrophysics Data System (ADS)

    Kim, J. T.; Park, J. K.; Lee, C. H.; Lee, K. W.; Choi, E. H.; Lee, Cheol Eui

    2014-03-01

    We have studied the quasi-two-dimensional layered compound systems (C2H5NH3)2Cd1-xMnxCl4 (0?x?1) by means of 1H nuclear magnetic resonance (NMR) measurements. In contrast to the case of the unmixed crystal compounds (x=0, 1) following a single-exponential type of the NMR spin-lattice relaxation, a stretched-exponential type of recovery, M(t)=M0[1-exp(], was necessary for the stoichiometric composition systems in addition to it, the exponent n depending on the randomly distributed paramagnetic Mn impurity concentration x. The spin-lattice relaxation rate T1S-1 thus obtained showed a maximum at a percolation threshold xc?0.3, in agreement with a percolation theory of the paramagnetic impurity relaxation. The stacking dimensions of the paramagnetic ions were derived from the exponent n as a function of x.

  10. Band Gap Tuning of CH3NH3Pb(Br1-xClx)3 Hybrid Perovskite for Blue Electroluminescence.

    PubMed

    Kumawat, Naresh K; Dey, Amrita; Kumar, Aravindh; Gopinathan, Sreelekha P; Narasimhan, K L; Kabra, Dinesh

    2015-06-24

    We report on the structural, morphological and optical properties of AB(Br1-xClx)3 (where, A = CH3NH3(+), B = Pb(2+) and x = 0 to 1) perovskite semiconductor and their successful demonstration in green and blue emissive perovskite light emitting diodes at room temperature. The bandgap of perovskite thin film is tuned from 2.42 to 3.16 eV. The onset of optical absorption is dominated by excitonic effects. The coulomb field of the exciton influences the absorption at the band edge. Hence, it is necessary to explicitly account for the enhancement of the absorption through the Sommerfield factor. This enables us to correctly extract the exciton binding energy and the electronic bandgap. We also show that the lattice constant varies linearly with the fractional chlorine content satisfying Vegards law. PMID:26050553

  11. Adsorption sensitivity of zigzag GeC nanotube towards N2, CO, SO2, HCN, NH3, and H2CO molecules

    NASA Astrophysics Data System (ADS)

    Samanta, Pabitra Narayan; Das, Kalyan Kumar

    2013-07-01

    Reactivities of the single-walled (6,0) germanium carbide nanotube (GeCNT) towards the small molecules like N2, CO, SO2, HCN, NH3, and H2CO are theoretically studied at the ONIOM(B3LYP/LANL2DZ/6-311++G(d,p):UFF) level. For the adsorption of a single molecule, a pyrene-like ring of the nanotube is chosen as the adsorption site in the high layer of the ONIOM calculations, while a coronene-like ring is considered for the adsorption of the second molecule. The nature of the binding between the nanotube and the adsorbate molecule is analyzed from the computed binding energy, density of states (DOS), charge transfer, and isosurface of total electron density.

  12. The poisoning effect of Na and K on Mn/TiO2 catalyst for selective catalytic reduction of NO with NH3: A comparative study

    NASA Astrophysics Data System (ADS)

    Guo, Rui-tang; Wang, Qing-shan; Pan, Wei-guo; Zhen, Wen-long; Chen, Qi-lin; Ding, Hong-lei; Yang, Ning-zhi; Lu, Chen-zi

    2014-10-01

    Mn/TiO2 catalyst is of high activity for low temperature selective catalytic reduction (SCR) of NO with NH3. And the deposition of alkali metal would lead to the deactivation of Mn/TiO2 catalyst. In this paper, the poisoning effect of Na and K on Mn/TiO2 was investigated based on experimental and theoretical study. It was found that K had a stronger poisoning effect than that of Na. The bad performance of K-Mn/TiO2 may be due to its small surface area, high crystallinity, weak surface acidity, low content of Mn4+ and chemisorbed oxygen, and bad redox ability. The interpretation of the experimental results is supported by DFT calculations.

  13. One-pot synthesis of hierarchical FeZSM-5 zeolites from natural aluminosilicates for selective catalytic reduction of NO by NH3.

    PubMed

    Yue, Yuanyuan; Liu, Haiyan; Yuan, Pei; Yu, Chengzhong; Bao, Xiaojun

    2015-01-01

    Iron-modified ZSM-5 zeolites (FeZSM-5s) have been considered to be a promising catalyst system to reduce nitrogen oxide emissions, one of the most important global environmental issues, but their synthesis faces enormous economic and environmental challenges. Herein we report a cheap and green strategy to fabricate hierarchical FeZSM-5 zeolites from natural aluminosilicate minerals via a nanoscale depolymerization-reorganization method. Our strategy is featured by neither using any aluminum-, silicon-, or iron-containing inorganic chemical nor involving any mesoscale template and any post-synthetic modification. Compared with the conventional FeZSM-5 synthesized from inorganic chemicals with the similar Fe content, the resulting hierarchical FeZSM-5 with highly-dispersed iron species showed superior catalytic activity in the selective catalytic reduction of NO by NH3. PMID:25791958

  14. Characterization of an abnormal photoluminescence behavior upon crystal-phase transition of perovskite CH3NH3PbI3.

    PubMed

    Kong, Weiguang; Ye, Zhenyu; Qi, Zhen; Zhang, Bingpo; Wang, Miao; Rahimi-Iman, Arash; Wu, Huizhen

    2015-07-01

    Solution-processed hybrid perovskite of CH3NH3PbI3 (MAPbI3) exhibits an abnormal luminescence behavior at around the tetragonal-orthorhombic phase transition temperature. The combination of time resolved photoluminescence (PL), variable excitation power PL, and variable-temperature X-ray diffraction (XRD) allows us to clearly interpret the abnormal luminescence features in the phase transition region of MAPbI3. Both PL and XRD results unambiguously prove the coexistence of the tetragonal and orthorhombic phases of MAPbI3 in the temperature range of 150 to 130 K. The two luminescence features observed in the orthorhombic phase at T < 130 K originate from free excitons and donor-acceptor-pair (DAP) transitions, respectively. The comprehensive understanding of optical properties upon phase transition in MAPbI3 will benefit the development of new optoelectronic devices. PMID:26051631

  15. Photolysis of CH4-NH3 mixtures and PH3 as models for the photochemical transformations on the primitive earth and Jupiter

    NASA Technical Reports Server (NTRS)

    Ferris, J. P.; Morimoto, J. Y.; Benson, R.

    1981-01-01

    Methane, ammonia and phosphine are some of the possible constituents of the atmospheres of the Jovian planets and their satellites. Photolysis of NH3 in the presence of CH4 at 185 nm in the temperature range of 25 C to -100 C results in the decomposition of CH4. The reaction is inhibited by added H2 or SF6. These findings are consistent with the reaction of hot hydrogen atoms with CH4 to give the CH3 radical. P2H4 is the initial product formed by the photolysis of PH3 at 206 nm. Kinetic studies established that it is the intermediate in the formation of P4 from PH3. The potential significance of these reactions to the atmospheric photochemistry of the Jovian planets and moons is discussed.

  16. Ion-orbital coupling in Car-Parrinello calculations of hydrogen-bond vibrational dynamics: Case study with the NH3-HCl dimer

    NASA Astrophysics Data System (ADS)

    Ong, S. W.; Lee, B. X. B.; Kang, H. C.

    2011-09-01

    We have performed Car-Parrinello molecular dynamics (CPMD) calculations of the hydrogen-bonded NH3-HCl dimer. Our main aim is to establish how ionic-orbital coupling in CPMD affects the vibrational dynamics in hydrogen-bonded systems by characterizing the dependence of the calculated vibrational frequencies upon the orbital mass in the adiabatic limit of Car-Parrinello calculations. We use the example of the NH3-HCl dimer because of interest in its vibrational spectrum, in particular the magnitude of the frequency shift of the H-Cl stretch due to the anharmonic interactions when the hydrogen bond is formed. We find that an orbital mass of about 100 a.u. or smaller is required in order for the ion-orbital coupling to be linear in orbital mass, and the results for which can be accurately extrapolated to the adiabatic limit of zero orbital mass. We argue that this is general for hydrogen-bonded systems, suggesting that typical orbital mass values used in CPMD are too high to accurately describe vibrational dynamics in hydrogen-bonded systems. Our results also show that the usual application of a scaling factor to the CPMD frequencies to correct for the effects of orbital mass is not valid. For the dynamics of the dimer, we find that the H-Cl stretch and the N-H-Cl bend are significantly coupled, suggesting that it is important to include the latter degree of freedom in quantum dynamical calculations. Results from our calculations with deuterium-substitution show that both these degrees of freedom have significant anharmonic interactions. Our calculated frequency for the H-Cl stretch using the Becke-exchange Lee-Yang-Parr correlation functional compares reasonably well with a previous second-order Møller-Plesset calculation with anharmonic corrections, although it is low compared to the experimental value for the dimer trapped in a neon-matrix.

  17. Ion-orbital coupling in Car-Parrinello calculations of hydrogen-bond vibrational dynamics: case study with the NH3-HCl dimer.

    PubMed

    Ong, S W; Lee, B X B; Kang, H C

    2011-09-14

    We have performed Car-Parrinello molecular dynamics (CPMD) calculations of the hydrogen-bonded NH(3)-HCl dimer. Our main aim is to establish how ionic-orbital coupling in CPMD affects the vibrational dynamics in hydrogen-bonded systems by characterizing the dependence of the calculated vibrational frequencies upon the orbital mass in the adiabatic limit of Car-Parrinello calculations. We use the example of the NH(3)-HCl dimer because of interest in its vibrational spectrum, in particular the magnitude of the frequency shift of the H-Cl stretch due to the anharmonic interactions when the hydrogen bond is formed. We find that an orbital mass of about 100 a.u. or smaller is required in order for the ion-orbital coupling to be linear in orbital mass, and the results for which can be accurately extrapolated to the adiabatic limit of zero orbital mass. We argue that this is general for hydrogen-bonded systems, suggesting that typical orbital mass values used in CPMD are too high to accurately describe vibrational dynamics in hydrogen-bonded systems. Our results also show that the usual application of a scaling factor to the CPMD frequencies to correct for the effects of orbital mass is not valid. For the dynamics of the dimer, we find that the H-Cl stretch and the N-H-Cl bend are significantly coupled, suggesting that it is important to include the latter degree of freedom in quantum dynamical calculations. Results from our calculations with deuterium-substitution show that both these degrees of freedom have significant anharmonic interactions. Our calculated frequency for the H-Cl stretch using the Becke-exchange Lee-Yang-Parr correlation functional compares reasonably well with a previous second-order Møller-Plesset calculation with anharmonic corrections, although it is low compared to the experimental value for the dimer trapped in a neon-matrix. PMID:21932876

  18. DESORPTION OF PYRETHROIDS FROM SUSPENDED SOLIDS

    PubMed Central

    Fojut, Tessa L.; Young, Thomas M.

    2014-01-01

    Pyrethroid insecticides have been widely detected in sediments at concentrations that can cause toxicity to aquatic organisms. Desorption rates play an important role in determining the bioavailability of hydrophobic organic compounds, such as pyrethroids, because these compounds are more likely to be sorbed to solids in the environment and times to reach sorptive equilibrium can be long. In this study, sequential Tenax desorption experiments were performed with three sorbents, three aging times, and four pyrethroids. A biphasic rate model was fit to the desorption data with r2 > 0.99 and the rapid and slow compartment desorption rate constants and compartment fractions are reported. Suspended solids from irrigation runoff water collected from a field that had been sprayed with permethrin one day prior were used in the experiments to compare desorption rates for field-applied pyrethroids to those for laboratory-spiked materials. Suspended solids were used in desorption experiments because suspended solids can be a key source of hydrophobic compounds to surface waters. The rapid desorption rate parameters of field-applied permethrin were not statistically different than those of laboratory spiked permethrin, indicating that the desorption of the spiked pyrethroids is comparable to those added and aged in the field. Sorbent characteristics had the greatest effect on desorption rate parameters; as organic carbon content of the solids increased, the rapid desorption fractions and rapid desorption rate constants both decreased. The desorption rate constant of the slow compartment for sediment containing permethrin aged for 28 d was significantly different from those aged 1 d and 7 d, while desorption in the rapid and slow compartments did not differ between these treatments. PMID:21538493

  19. Crystal structures, lattice potential energies, and thermochemical properties of crystalline compounds (1-C(n)H(2n+1)NH3)2ZnCl4(s) (n = 8, 10, 12, and 13).

    PubMed

    Liu, Yupu; Di, Youying; He, Donghua; Zhou, Qian; Dou, Jianmin

    2011-11-01

    As part of our ongoing project involving the study of (1-C(n)H(2n+1)NH(3))(2)MCl(4)(s) (where M is a divalent metal ion and n = 8-18), we have synthesized the compounds (1-C(n)H(2n+1)NH(3))(2)ZnCl(4)(s) (n = 8, 10, 12, and 13), and the details of the structures are reported herein. All of the compounds were crystallized in the monoclinic form with the space group P2(1)/n for (1-C(8)H(17)NH(3))(2)ZnCl(4)(s), P21/c for (1-C(10)H(21)NH(3))(2)ZnCl(4)(s), P2(1)/c for (1-C(12)H(25)NH(3))(2)ZnCl(4)(s), and P2(1)/m for (1-C(13)H(27)NH(3))(2)ZnCl(4)(s). The lattice potential energies and ionic volumes of the cations and the common anion of the title compounds were obtained from crystallographic data. Molar enthalpies of dissolution of the four compounds at various molalities were measured at 298.15 K in the double-distilled water. According to Pitzer's theory, molar enthalpies of dissolution of the title compounds at infinite dilution were obtained. Finally, using the values of molar enthalpies of dissolution at infinite dilution (?(s)H(m)(?)) and other auxiliary thermodynamic data, the enthalpy change of the dissociation of [ZnCl(4)](2-)(g) for the reaction [ZnCl(4)](2-)(g)? Zn(2+)(g) + 4Cl(-)(g) was obtained, and then the hydration enthalpies of cations were calculated by designing a thermochemical cycle. PMID:21995326

  20. Mapping Observations of the Horsehead Nebula and the NGC 2023 Region in the NH3 (1,1),(2,2) and (3,3) Lines with the Nobeyama 45 m Telescope

    NASA Astrophysics Data System (ADS)

    Ohashi, S.; Kitamura, Y.; Akashi, T.

    2013-10-01

    We performed mapping observations of the Horsehead Nebula and the NGC 2023 region in the NH3 (1,1), (2,2) and (3,3) lines. We identified five dense cores (Cores A to E), and estimated the masses and kinetic temperatures of the cores by analyzing the NH3 lines. For all the cores, the temperature tends to increase in the outer parts, suggesting heating due to the ionized gas from IC 434. Core B is discovered by this work and indicates a sign of infalling motion.

  1. Fabrication of low-resistivity and gold-colored TiN films by halide chemical vapor deposition with a low [NH 3]\\/[TiCl 4] flow ratio

    Microsoft Academic Search

    Wu-Yih Uen; Zhen-Yu Li; Shan-Ming Lan; Tsun-Neng Yang; San-Mao Liao

    2007-01-01

    This work describes the preparation of titanium nitride (TiN) films on Si (111) substrates by atmospheric pressure halide chemical vapor deposition (AP-HCVD). Various TiN films were obtained by exploiting TiCl4+NH3 gas chemistry with flow ratios [NH3]\\/[TiCl4] from 0.2 to 1.4, and deposition temperatures (Td) from 600 to 900 °C. When Td=800 °C gold-colored films with electrical resistivities of under 100 ?? cm were

  2. Ab initio calculation of the NH,,3 -...-NH,,3 -

    E-print Network

    for the storage of the mol- ecules, once they are at rest.12,13 A promising candidate for directly producing ultra and Materials (IMM), Radboud University Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands Joop H. van for Molecules and Materials (IMM), Radboud University Nijmegen, Toernooiveld 1, 6525 ED Nijmegen

  3. Low absorption vitreous carbon reactors for operando XAS: a case study on Cu/Zeolites for selective catalytic reduction of NO(x) by NH3.

    PubMed

    Kispersky, Vincent F; Kropf, A Jeremy; Ribeiro, Fabio H; Miller, Jeffrey T

    2012-02-21

    We describe the use of vitreous carbon as an improved reactor material for an operando X-ray absorption spectroscopy (XAS) plug-flow reactor. These tubes significantly broaden the operating range for operando experiments. Using selective catalytic reduction (SCR) of NO(x) by NH(3) on Cu/Zeolites (SSZ-13, SAPO-34 and ZSM-5) as an example reaction, we illustrate the high-quality XAS data achievable with these reactors. The operando experiments showed that in Standard SCR conditions of 300 ppm NO, 300 ppm NH(3), 5% O(2), 5% H(2)O, 5% CO(2) and balance He at 200 °C, the Cu was a mixture of Cu(I) and Cu(II) oxidation states. XANES and EXAFS fitting found the percent of Cu(I) to be 15%, 45% and 65% for SSZ-13, SAPO-34 and ZSM-5, respectively. For Standard SCR, the catalytic rates per mole of Cu for Cu/SSZ-13 and Cu/SAPO-34 were about one third of the rate per mole of Cu on Cu/ZSM-5. Based on the apparent lack of correlation of rate with the presence of Cu(I), we propose that the reaction occurs via a redox cycle of Cu(I) and Cu(II). Cu(I) was not found in in situ SCR experiments on Cu/Zeolites under the same conditions, demonstrating a possible pitfall of in situ measurements. A Cu/SiO(2) catalyst, reduced in H(2) at 300 °C, was also used to demonstrate the reactor's operando capabilities using a bending magnet beamline. Analysis of the EXAFS data showed the Cu/SiO(2) catalyst to be in a partially reduced Cu metal-Cu(I) state. In addition to improvements in data quality, the reactors are superior in temperature, stability, strength and ease of use compared to previously proposed borosilicate glass, polyimide tubing, beryllium and capillary reactors. The solid carbon tubes are non-porous, machinable, can be operated at high pressure (tested at 25 bar), are inert, have high material purity and high X-ray transmittance. PMID:22158950

  4. 140 H/D isotopomers identified by long-range NMR hyperfine shifts in ruthenium(III) ammine complexes. Hyperconjugation in Ru-NH3 bonding.

    PubMed

    Laidlaw, W Michael; Denning, Robert G; Green, Jennifer C; Boyd, Jonathan; Harmer, Jeffrey; Thompson, Amber L

    2013-06-17

    (1)H NMR spectra of the paramagnetic cyanide-bridged mixed-valence compound [(?(5)-C5H5)Fe(CO)2(?-CN)Ru(NH3)5](CF3SO3)3 (I) have been obtained in several solvents. When traces of partially deuterated water are present, instead of a single cyclopentadienyl (Cp) resonance shifted by the hyperfine interaction, numerous well-resolved resonances are observed. The spectra were simulated satisfactorily by giving the appropriate statistical weight to 140 possible H/D isotopomers formed by deuteration in the five ruthenium(III) ammine ligands. The proliferation of distinct resonances occurs because (a) the hyperfine shifts (HSs) due to each sequential deuteration in a single ammine are different and (b) while deuteration in an ammine cis to the cyanide bridge causes a downfield shift, in the trans ammine it causes an upfield shift that is nearly twice as large. All of these shifts exhibit a 1/T dependence, but temperature-independent components, due to large second-order Zeeman effects at the Ru(III) center, are also present. Combining the results of density functional theory calculations with data from metal-metal charge-transfer optical transitions and with the effect of solvent-induced NMR HSs, it is argued that Fermi contact shifts at the Cp protons are insignificant compared to those due to the dipolar (pseudocontact) mechanism. Analytical expressions are presented for the dependence of the HS on the tetragonal component of the ligand field at the Ru(III) ion. The tetragonal field parameter, defined as the energy by which the 4d(xy) orbital exceeds the mean t(2g) orbital energy, was found to be 147, 52, and 76 cm(-1), in dimethylformamide, acetone, and nitromethane, respectively. The effects of deuteration show that there is a significant component of hyperconjugation in the Ru-ammine interaction and that ND3 is a weaker ? donor than NH3. A single deuteration in an axial ammine increases the tetragonal field parameter (?) by +2.8 cm(-1), resulting in a HS of -37 ppb in the Cp proton resonance, whereas a single deuteration in an equatorial ammine decreases the field by -1.5 cm(-1) with a HS of +20 ppb, despite a nominal separation of seven chemical bonds. We analyze the origin of this remarkable sensitivity, which relies on the favorable characteristics of the Ru(III) low-spin t(2g)(5) configuration, having a spin-orbit coupling constant ? ? 950 cm(-1). PMID:23697337

  5. Thermomagnetic Torque in Nh3 

    E-print Network

    Adair, Thomas W.; McClurg, G. R.

    1970-01-01

    there is no torque. Also, there is no torque in He which has a magnetic moment. This thermomag- netic torque (Scott effect) is related to the Senftle- ben-Beenakker (SB) effect which causes a change of viscosity and thermal conductivity with magnetic field.... Extensive theoretical work has been carried out on the SB effect, and a large amount of theoretical work has been done on the Scott effect. Levi and Beenakker, ' using solutions of the Boltzmann equation based on the third Chapman- Enskog approximation...

  6. Desorption Kinetics of Polyether Lubricants from Surfaces

    Microsoft Academic Search

    Andrew J. Gellman; Kris R. Paserba; Nithya Vaidyanathan

    2002-01-01

    Desorption or evaporation is one of the mechanisms for loss of perfluoropolyalkylether (PFPE) lubricants from the surfaces of data storage media. One approach to minimizing PFPE loss to desorption is the use of lubricants with increasing molecular weight or increasing average chain length. In order to understand the effects of chain length on the lubricant evaporation kinetics we have studied

  7. On metal desorption and brucite regeneration

    Microsoft Academic Search

    G. R. Bochkarev; G. I. Pushkareva

    2006-01-01

    The data on metal desorption from brucite surface under the action of acid and alkaline dissolvents are reported. The desorption\\u000a process is found to associate with the regeneration of a sorbent along with the substantial improvement of its sorption capacity.

  8. Femtosecond time-resolved transient absorption spectroscopy of CH3NH3PbI3 perovskite films: evidence for passivation effect of PbI2.

    PubMed

    Wang, Lili; McCleese, Christopher; Kovalsky, Anton; Zhao, Yixin; Burda, Clemens

    2014-09-01

    CH3NH3PbI3 perovskite layered films deposited on substrates with and without a titania support structure have been prepared and studied using time-resolved femtosecond transient absorption (fs-TA) spectroscopy in the visible light range (450-800 nm). The electron injection dynamics from the photoexcited perovskite layers to the neighboring film structures could be directly monitored via the transient bleaching dynamics of the perovskite at ?750 nm and thus systematically studied as a function of the layer-by-layer architecture. In addition, for the first time we could spectrally distinguish transient bleaching at ?750 nm from laser-induced fluorescence that occurs red-shifted at ?780 nm. We show that an additional bleach feature at ?510 nm appears when PbI2 is present in the perovskite film. The amplitudes of the PbI2 and perovskite TA peaks were compared to estimate relative amounts of PbI2 in the samples. Kinetic analysis reveals that perovskite films with less PbI2 show faster relaxation rates than those containing more PbI2. These fast dynamics are attributed to charge carrier trapping at perovskite grain boundaries, and the slower dynamics in samples containing PbI2 are due to a passivation effect, in line with other recently reported work. PMID:25145978

  9. Cationic Dynamics and Phase Transitions in (CH3NH3)3Bi2Br9 as Studied by Proton Magnetic Resonance

    NASA Astrophysics Data System (ADS)

    Kozio\\l, Piotr; Furukawa, Yoshihiro; Nakamura, Daiyu

    1991-11-01

    Molecular motions and phase transitions in tris(methylammonium) nonabromodibismuthate (III), (CH3NH3)3Bi2Br9, were investigated by measuring the temperature dependences of static and rotating frame 1H spin-lattice relaxation times (T1 ans T1?) and the second moment (M2) of 1H NMR absorptions. Near 80 K in the lowest-temperature phase IV, the orientation of the methylammonium cation is almost fixed but the cation itself is rapidly rotating about the C-N bond axis. On heating, gradual disordering of the cationic orientations takes place in phases IV and III for two thirds of crystallographically nonequivalent cations and in phase II for the remaining cations. Finally, all the cations become to be dynamically disordered and undergo rapid overall reorientations in the room-temperature phase I. The IV-III transition at 108 K may be connected to dynamics of the inorganic (Bi2Br93-)n subsystem rather than the ionic motions. An anomalous behavior of 1H T1?, attributable to cross relaxation between 1H and Br nuclei, was observed.

  10. Surface characterization studies of CuO-CeO2-ZrO2 catalysts for selective catalytic reduction of NO with NH3

    NASA Astrophysics Data System (ADS)

    Zhang, Qiulin; Xu, Lisi; Ning, Ping; Gu, Junjie; Guan, Qingqing

    2014-10-01

    A series of CuO-CeO2-ZrO2 catalysts were prepared by different methods and applied to the selective catalytic reduction of NO with NH3 reaction at low temperature. The results showed that the SCR activities, morphology, particles dimension, and the surface chemical state of CuO-CeO2-ZrO2 catalysts were obviously influenced by the preparation method. The SCR performance results showed that the CuO-CeO2-ZrO2 catalyst prepared by co-precipitation method presented the best activity in the temperature range of 125-180 °C. The characterization results showed that the Ce4+, Ce3+, Cu2+ and Cu+ species were coexistence in the CuO-CeO2-ZrO2 catalysts, and the Cu species mainly existed as Cu2+. It was also found that the high surface area, the synergistic effect between copper and ceria, enhanced acidity and the highly dispersed copper species were responsible for the high SCR activity of the CuO-CeO2-ZrO2 catalyst.

  11. Electron transport in unipolar InGaN/GaN multiple quantum well structures grown by NH3 molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Browne, David A.; Mazumder, Baishakhi; Wu, Yuh-Renn; Speck, James S.

    2015-05-01

    Unipolar-light emitting diode like structures were grown by NH3 molecular beam epitaxy on c plane (0001) GaN on sapphire templates. Studies were performed to experimentally examine the effect of random alloy fluctuations on electron transport through quantum well active regions. These unipolar structures served as a test vehicle to test our 2D model of the effect of compositional fluctuations on polarization-induced barriers. Variables that were systematically studied included varying quantum well number from 0 to 5, well thickness of 1.5 nm, 3 nm, and 4.5 nm, and well compositions of In0.14Ga0.86N and In0.19Ga0.81N. Diode-like current voltage behavior was clearly observed due to the polarization-induced conduction band barrier in the quantum well region. Increasing quantum well width and number were shown to have a significant impact on increasing the turn-on voltage of each device. Temperature dependent IV measurements clearly revealed the dominant effect of thermionic behavior for temperatures from room temperature and above. Atom probe tomography was used to directly analyze parameters of the alloy fluctuations in the quantum wells including amplitude and length scale of compositional variation. A drift diffusion Schrödinger Poisson method accounting for two dimensional indium fluctuations (both in the growth direction and within the wells) was used to correctly model the turn-on voltages of the devices as compared to traditional 1D simulation models.

  12. Synthesis and characterization of vanadium ions containing chlorocadmiumphosphate CdHPO4Cl·[H3N (CH2)6NH3]0.5 crystals

    NASA Astrophysics Data System (ADS)

    Rama Krishna, Ch.; Ravikumar, R. V. S. S. N.

    2014-01-01

    VO2+ ions doped chlorocadmiumphosphate, CdHPO4Cl·[H3N(CH2)6NH3]0.5 crystals were synthesized at room temperature by using an organic amine, Hexa Methylene Di Amine as a templating molecule. The prepared crystals were characterized by powder XRD and several spectroscopic techniques. The powder XRD data was indexed to monoclinic crystal system with the lattice parameters, a=0.429, b=0.772, c=1.622 nm and ?=114.3°. The nature of doped VO2+ ions in the framework material has been identified by optical absorption and electron paramagnetic resonance techniques. FT-IR spectrum exhibited the characteristic vibrations of phosphate anions and hexane diammonium cations. Thermal studies revealed that the prepared crystals withstand its state up to 307 °C. EPR and optical absorption spectrum confirmed that the doped VO2+ ions entered the complex material as distorted octahedral site symmetry. The evaluated bonding parameters revealed a partial covalent bonding between the doped metal ions and ligands.

  13. Photocatalytic property and electronic structure of triple-layered perovskite tantalates, MCa2Ta3O10 (M = Cs, Na, H, and C6H13NH3).

    PubMed

    Machida, Masato; Mitsuyama, Tomohiro; Ikeue, Keita; Matsushima, Shigenori; Arai, Masao

    2005-04-28

    The Dion-Jacobson series of triple-layered perovskite tantalates (MCa2Ta3O10, M = Cs, Na, H, and C6H13NH3) were synthesized to evaluate their photocatalytic activity for overall water splitting to evolve H2/O2 under UV irradiation. The photocatalytic activity was susceptible to the hydration of interlayer space. The hydrous Na phase exhibited much higher activity (H2: 308 micromol.h(-1)) compared to the anhydrous Cs phase (24 micromol.h(-1)) and the hydrous H phase (22 micromol.h(-1)) in the presence of 0.5 wt % Ni impregnated. H2O/D2O isotopic experiment suggested that the hydrated interlayer plays as an active site for water splitting, where the high mobility of water molecule in the interlayer should correlate with the total photocatalytic activity. The FLAPW electronic structure calculation demonstrated that the terminating oxygen site, O4, which faces to the interlayer space, contributes largely to the top of the valence band. Judging from comparison with the double-layered tantalates, MLaTa2O7, in our previous study, the contribution of terminating oxygen site to the band structure is supposed to depend on the number of perovskite layers. PMID:16851907

  14. Domain Walls Conductivity in Hybrid Organometallic Perovskites and Their Essential Role in CH3NH3PbI3 Solar Cell High Performance.

    PubMed

    Rashkeev, Sergey N; El-Mellouhi, Fedwa; Kais, Sabre; Alharbi, Fahhad H

    2015-01-01

    The past several years has witnessed a surge of interest in organometallic trihalide perovskites, which are at the heart of the new generation of solid-state solar cells. Here, we calculated the static conductivity of charged domain walls in n- and p- doped organometallic uniaxial ferroelectric semiconductor perovskite CH3NH3PbI3 using the Landau-Ginzburg-Devonshire (LGD) theory. We find that due to the charge carrier accumulation, the static conductivity may drastically increase at the domain wall by 3 - 4 orders of magnitude in comparison with conductivity through the bulk of the material. Also, a two-dimensional degenerated gas of highly mobile charge carriers could be formed at the wall. The high values of conductivity at domain walls and interfaces explain high efficiency in organometallic solution-processed perovskite films which contains lots of different point and extended defects. These results could suggest new routes to enhance the performance of this promising class of novel photovoltaic materials. PMID:26088321

  15. Experimental and theoretical EPR study of Jahn-Teller-active [HIPTN(3)N]MoL complexes (L = N(2), CO, NH(3)).

    PubMed

    McNaughton, Rebecca L; Roemelt, Michael; Chin, Jia Min; Schrock, Richard R; Neese, Frank; Hoffman, Brian M

    2010-06-30

    The trigonally symmetric Mo(III) coordination compounds [HIPTN(3)N]MoL (L = N(2), CO, NH(3); [HIPTN(3)N]Mo = [(3,5-(2,4,6-i-Pr(3)C(6)H(2))(2)C(6)H(3)NCH(2)CH(2))(3)N]Mo) are low-spin d(3) (S = (1)/(2)) species that exhibit a doubly degenerate (2)E ground state susceptible to a Jahn-Teller (JT) distortion. The EPR spectra of all three complexes and their temperature and solvent dependences are interpreted within a formal "two-orbital" model that reflects the ground-state configuration, describes the vibronic interactions that lead to the JT distortions, and addresses whether these complexes exhibit static or dynamic JT distortions. The electronic and vibronic properties of these complexes are then analyzed through ab initio quantum chemical computations. It is not possible to interpret the spectroscopic properties of the orbitally degenerate [HIPTN(3)N]MoL with DFT methods, so we have resorted to multi-reference wavefunction approaches, the entry level of which is the complete active space self-consistent field (CASSCF) method. Overall, the experimental and computational studies provide new insights into the role of trigonal coordination, as enforced by the [HIPTN(3)N](3-) ligand, in activating the Mo ion for the binding and reduction of N(2). PMID:20429559

  16. Morphology control and mechanisms of CaCO3 crystallization on gas-liquid interfaces of CO2/NH3 bubbles in aqueons-glycine solutions

    NASA Astrophysics Data System (ADS)

    Guan, Xiaomei; Huang, Fangzhi; Li, Jian; Li, Shikuo; Zhang, Xiuzhen; Guo, Degui; Shen, Yuhua; Xie, Anjian

    2015-06-01

    As one of the new methods of materials preparing, interface-regulated mineralization, has been developed and used to fabricate the CaCO3 materials with mimetic construction of natural biogenic structures in the present work. Combined with the effect of glycine at different concentrations, novel gas-liquid interfaces of CO2/NH3 bubbles have been substituted for the traditional settled matrix and utilized as new reaction fields of CaCO3. CaCO3 crystals with delicate hierarchical structures and morphologies, such as scallop-shaped, ellipsoidal and spherical structure, have been obtained at the special glycine-mediated gasliquid interfaces. The effect of glycine concentration and the chemical reaction kinetics have been deeply studied. As a result, we have successfully captured in detail the crystallization behaviors of CaCO3 in different stages, which allow us to put forward a general kinetic model to reveal the formation mechanism of CaCO3 and implicate a straightforward mean to control the morphology and structure.

  17. Experimental and Theoretical EPR Study of Jahn-Teller Active [HIPTN3N]MoL Complexes (L = N2, CO, NH3)

    PubMed Central

    McNaughton, Rebecca L.; Roemelt, Michael; Chin, Jia Min; Schrock, Richard R.; Neese, Frank; Hoffman, Brian M.

    2010-01-01

    The trigonally symmetric Mo(III) coordination compounds [HIPTN3N]MoL (L = N2, CO, NH3; [HIPTN3N]Mo = [(3,5-(2,4,6-i-Pr3C6H2)2C6H3NCH2CH2)3N]Mo) are low-spin d3, S = 1/2) species that exhibit a doubly-degenerate 2E ground state susceptible to a Jahn-Teller (JT) distortion. The EPR spectra of all three complexes and their temperature and solvent dependences are interpreted within a formal ‘2-orbital’ model that reflects the ground-state configuration, describes the vibronic interactions that lead to the JT distortions, and addresses whether these complexes exhibit static or dynamic JT distortions. The electronic and vibronic properties of these complexes are then analyzed through ab initio quantum chemical computations. It is not possible to interpret the spectroscopic properties of the orbitally degenerate [Mo]L with DFT methods, so we have resorted to multireference wavefunction approaches, the entry level of which is the complete active space self-consistent field (CASSCF) method. Overall the experimental and computational studies provide new insights into the role of trigonal coordination, as enforced by the [HIPTN3N]3? ligand, in activating the Mo ion for the binding and reduction of N2. PMID:20429559

  18. Electrical properties, phase transitions and conduction mechanisms of the [(C2H5)NH3]2CdCl4 compound

    NASA Astrophysics Data System (ADS)

    Mohamed, C. Ben; Karoui, K.; Saidi, S.; Guidara, K.; Rhaiem, A. Ben

    2014-10-01

    The [(C2H5)NH3]2CdCl4 hybrid material was prepared and its calorimetric study and electric properties were investigated at low temperature. The X-ray powder diffractogram has shown that the compound is crystallized in the orthorhombic system with Abma space group, and the refined unit cell parameters are a=7.546 Å, b=7.443 Å, and c=21.831 Å. The calorimetric study has revealed two endothermic peaks at 216 K and 357 K, which are confirmed by the variation of fp and ?dc as a function of temperature. The equivalent circuit based on the Z-View-software was proposed and the conduction mechanisms were determined. The obtained results have been discussed in terms of the correlated barrier hopping model (CBH) in phase I (low temperature (OLT)), non-overlapping small polaron tunneling model (NSPT) in phase II (room temperature (ORT)) and the overlapping large polaron tunneling model in phase III (high temperature (OHT)). The density of localized states NF(E) at the Fermi level and the binding energy Wm were calculated. The variation of the dielectric loss log(??) with log(?) was found to follow the empirical law, ??=B ?m(T).

  19. Domain Walls Conductivity in Hybrid Organometallic Perovskites and Their Essential Role in CH3NH3PbI3 Solar Cell High Performance

    PubMed Central

    Rashkeev, Sergey N.; El-Mellouhi, Fedwa; Kais, Sabre; Alharbi, Fahhad H.

    2015-01-01

    The past several years has witnessed a surge of interest in organometallic trihalide perovskites, which are at the heart of the new generation of solid-state solar cells. Here, we calculated the static conductivity of charged domain walls in n- and p- doped organometallic uniaxial ferroelectric semiconductor perovskite CH3NH3PbI3 using the Landau-Ginzburg-Devonshire (LGD) theory. We find that due to the charge carrier accumulation, the static conductivity may drastically increase at the domain wall by 3 – 4 orders of magnitude in comparison with conductivity through the bulk of the material. Also, a two-dimensional degenerated gas of highly mobile charge carriers could be formed at the wall. The high values of conductivity at domain walls and interfaces explain high efficiency in organometallic solution-processed perovskite films which contains lots of different point and extended defects. These results could suggest new routes to enhance the performance of this promising class of novel photovoltaic materials. PMID:26088321

  20. Estimation of retention times of homologous series in temperature programmed gas chromatography

    Microsoft Academic Search

    P. E. Kavanagh; D. Balder; G. Franklin

    1999-01-01

    Summary  It is shown how to estimate the retention times of homologous series members in linear temperature programmed gas chromatography\\u000a with the aid of a spread-sheet. Both the ease of estimation and the accuracy of the estimation depend on whether the homologue\\u000a is eluted during the rising portion of the temperature program or the hold time at the end, and also

  1. Water Adsorption, Desorption, and Clustering on FeO(111)

    SciTech Connect

    Daschbach, John L.; Dohnalek, Zdenek; Liu, Shurong; Smith, R. Scott; Kay, Bruce D.

    2005-05-26

    The adsorption of water on FeO(111) is investigated using temperature programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRAS). Well-ordered 2 ML thick FeO(111) films are grown epitaxially on a Pt(111) substrate. Water adsorbs molecularly on FeO(111) and desorbs with a well resolved monolayer peak. IRAS measurements as a function of coverage are performed for water deposited at 30 and 135 K. For all coverages (0.2 ML and greater) the adsorbed water exhibits significant hydrogen bonding. Differences in IRAS spectra for water adsorbed at 30 and 135 K are subtle but suggest that water adsorbed at 135 K is well ordered. Monolayer nitrogen TPD spectra from water covered FeO(111) surfaces are used to investigate the clustering of the water as a function of deposition or annealing temperature. Temperature dependent water overlayer structures result from differences in water diffusion rates on bare FeO(111) and on water adsorbed on FeO(111). Features in the nitrogen TPD spectra allow the monolayer wetting and 2-dimensional (2D) ordering of water on FeO(111) to be followed. Voids in a partially disordered first water layer exist for water deposited below 120 K and ordered 2D islands are found when depositing water above 120 K.

  2. Hydrogen absorption and desorption by the Li-Al-N-H system.

    PubMed

    Kojima, Yoshitsugu; Matsumoto, Mitsuru; Kawai, Yasuaki; Haga, Tetsuya; Ohba, Nobuko; Miwa, Kazutoshi; Towata, Shin-ichi; Nakamori, Yuko; Orimo, Shin-ichi

    2006-05-18

    Lithium hexahydridoaluminate Li(3)AlH(6) and lithium amide LiNH(2) with 1:2 molar ratio were mechanically milled, yielding a Li-Al-N-H system. LiNH(2) destabilized Li(3)AlH(6) during the dehydrogenation process of Li(3)AlH(6), because the dehydrogenation starting temperature of the Li-Al-N-H system was lower than that of Li(3)AlH(6). Temperature-programmed desorption scans of the Li-Al-N-H system indicated that a large amount of hydrogen (6.9 wt %) can be released between 370 and 773 K. After initial H(2) desorption, the H(2) absorption and the desorption capacities of the Li-Al-N-H system with a nano-Ni catalyst exhibited 3-4 wt % at 10-0.004 MPa and 473-573 K, while the capacities of the system without the catalyst were 1-2 wt %. The remarkably increased capacity was due to the fact that the kinetics was improved by addition of the nano-Ni catalyst. PMID:16686512

  3. Structure of duplex DNA containing the cisplatin 1,2-{Pt(NH3)2}[superscript 2]+-d(GpG) crosslink at 1.77 [Angstrom] resolution

    E-print Network

    Todd, Ryan C.

    We report the 1.77-Å resolution X-ray crystal structure of a dodecamer DNA duplex with the sequence 5?-CCTCTGGTCTCC-3? that has been modified to contain a single engineered 1,2-cis-{Pt(NH3)2}2+-d(GpG) cross-link, the major ...

  4. Selective Catalytic Reduction (SCR) of nitric oxide with ammonia using Cu-ZSM-5 and Va-based honeycomb monolith catalysts: effect of H2 pretreatment, NH3-to-NO ratio, O2, and space velocity 

    E-print Network

    Gupta, Saurabh

    2004-09-30

    .e. higher NH3-to-NO ratio) improved the peak NO reduction but simultaneously resulted in an increase in residual ammonia. Pretreatment of the catalyst sample with H2 (performed only for the Cu-ZSM-5 catalyst) did not produce any perceivable difference in any...

  5. Evaluation of the SO(2) and NH(3) gas adsorption properties of CuO/ZnO/Mn(3)O(4) and CuO/ZnO/NiO ternary impregnated activated carbon using combinatorial materials science methods.

    PubMed

    Romero, Jennifer V; Smith, Jock W H; Sullivan, Braden M; Macdonald, Landan; Croll, Lisa M; Dahn, J R

    2013-02-11

    Impregnated activated carbons (IAC) are widely used materials for the removal of toxic gases in personal respiratory protection applications. The combinatorial method has been employed to prepare IACs containing different types of metal oxides in various proportions and evaluate their adsorption performance for low molecular weight gases, such as SO(2) and NH(3), under dry conditions. Among the metal oxides used for the study, Mn(3)O(4) was found to have the highest capacity for retaining SO(2) gas under dry conditions. NiO and ZnO were found to have similar NH(3) adsorption capacities which are higher than the NH(3) capacities observed for the other metal oxide impregnants used in the study. Although Cu- or Zn-based impregnants and their combinations have been extensively studied and used as gas adsorbents, neither Mn(3)O(4) nor NiO have been incorporated in the formulations used. In this study, ternary libraries of IACs with various combinations of CuO/ZnO/Mn(3)O(4) and CuO/ZnO/NiO were studied and evaluated for their adsorption of SO(2) and NH(3) gases. Combinations of CuO, ZnO, and Mn(3)O(4) were found to have the potential to be multigas adsorbents compared to formulations that contain NiO. PMID:23286549

  6. Experimental (FT-IR and FT-RS) and theoretical (DFT) studies of molecular structure and internal modes of [Mn(NH3)6](NO3)2.

    PubMed

    Druzbicki, Kacper; Mikuli, Edward

    2010-10-01

    Fourier-transform Raman and infrared spectra of [Mn(NH(3))(6)](NO(3))(2) were recorded and interpreted by comparison with respective theoretical spectra calculated using DFT method. The [Mn(NH(3))(6)](2+) cation equilibrium geometry with C(1) symmetry, harmonic vibrational frequencies, infrared and Raman scattering intensities were determined using B3LYP/LAN2LTZ+/6-311+G(d,p) level of theory. The band assignment was based on potential energy distribution (PED) of normal modes. The computations of NO(3)(-) anion frequencies were performed under assumption of D(3h) symmetry, using 6-311+G(d,p) basis set. In order do draw a comparison, additional calculations were performed separately for the [Cd(NH(3))(6)](NO(3))(2) and [Ni(NH(3))(6)](NO(3))(2). The computations were also carried out using selected modern exchange-correlation functionals. A sufficient general agreement between the theoretical and the experimental spectra has been achieved. PMID:20598627

  7. Vibrationally state-selected reactions of ammonia ions. I. NH3+ (v) + O2 Richard J. S. Morrison,a) William E. Conaway, Takayuki Ebata, and Richard N. Zare

    E-print Network

    Zare, Richard N.

    Vibrationally state-selected reactions of ammonia ions. I. NH3+ (v) + O2 Richard J. S. Morrison multiphoton ionization has been applied to the production ofvibrationally state-selected ion beams. Ammonia, vibrationally state- selected ions for reaction dynamics studies. Ammonia is an ideal candidate for state

  8. Measurements of industrial emissions of VOCs, NH3, NO2 and SO2 in Texas using the Solar Occultation Flux method and mobile DOAS

    NASA Astrophysics Data System (ADS)

    Mellqvist, J.; Samuelsson, J.; Rivera, C.; Lefer, B.; Patel, M.

    2007-12-01

    Solar Occultation Flux (SOF) measurements of olefines and alkanes have been conducted to pin-point and quantify the largest sources of olefines and alkanes in the vicinity of Houston and in south eastern Texas during September 2006. The SOF measurements were part of the extensive summer campaign TexAQS 2006, included in the Second Texas Air Quality Study (TexAQS II). The SOF technique is an optical method utilizing the absorption of direct solar infrared radiation in the 1.8-14 micrometer range for retrieval of total columns of various species such as ethylene, propylene, ammonia and alkanes. The instrument is carried on a mobile platform, making it possible to conduct transects of the emission plume downwind an industry, and thus integrate all the molecules of the plume cross section in real time. By multiplying with the plume wind speed, the total flux emerging from the source is obtained. Flux estimates with SOF were obtained for the large petrochemical and refining complexes around the Houston area. This was done in parallell with airborne plume studies by other parties. The primary research goal was to supply a data set for emission inventory comparisons and for input to models looking at the strong ozone production in Texas. The SOF measurements show that the hourly gas emissions from the Houston Ship channel area correspond to about 1 metric ton of ethylene, 1.5 tons of propylene, 12 tons of alkanes, 1/4 ton of NH3 and about 5 tons of SO2 and NO2. For the VOCs this is an order of magnitude or greater than reported VOC emissions in the 2004 inventory.

  9. Effect of glow DBD modulation on gas and thin film chemical composition: case of Ar/SiH4/NH3 mixture

    NASA Astrophysics Data System (ADS)

    Vallade, Julien; Bazinette, Remy; Gaudy, Laura; Massines, Françoise

    2014-06-01

    In recent years, atmospheric pressure plasma-enhanced chemical vapour deposition has been identified as a convenient way to deposit good quality thin films. With this type of process, where the gas mixture is injected on one side of the electrodes, the chemical composition of the gas evolves with the gas residence time in the plasma. The consequence is a possible gradient in the chemical composition over the thickness of in-line coatings. The present work shows that the modulation of the plasma with a square signal significantly reduces this gradient while the drawback of low growth rate is avoided by increasing the discharge power. This study deals with plane/plane glow dielectric barrier discharges (DBDs) in an Ar/NH3/SiH4 gas mixture to make thin films. The 50 kHz discharge power of the glow DBD was varied by increasing voltage and modulating excitation. The impact on (i) the plasma development was observed through emission spectroscopy and (ii) the thin film coating through Fourier transform infrared measurements. It is shown that the modulation significantly decreases the time and the energy needed to achieve stable chemistry, enhances secondary chemistry and limits disturbance induced by impurities because of a slower decrease of SiH4 concentration and thus a higher ratio of SiH4/impurities, all very important points for in-line AP-PECVD development. When the growth rate is limited by diffusion, coating growth continues when the discharge is off, so long as there is a precursor gradient between the surface and the gas bulk. A higher discharge power steepens this gradient, which enhances diffusion from the bulk and thus growth rate.

  10. Canted antiferromagnetism and spin reorientation transition in layered inorganic-organic perovskite (C6H5CH2CH2NH3)2MnCl4.

    PubMed

    Park, Seong-Hun; Oh, In-Hwan; Park, Sungil; Park, Younbong; Kim, Ji Hyun; Huh, Young-Duk

    2012-01-28

    This work presents the synthesis, structure determination and magnetic properties of a new complex, phenethylammonium tetrachloromanganate(II), (C(6)H(5)CH(2)CH(2)NH(3))(2)MnCl(4) (Mn-PEA). Single crystals of Mn-PEA were obtained from methanol solution using the solvent-evaporation method at room temperature. The crystal structure of Mn-PEA was determined by single-crystal X-ray diffraction (orthorhombic, space group Pbca, a = 7.2075(9), b = 7.3012(14), c = 39.413(6) Å and Z = 4). The structure consisted of an extended [MnCl(4)](2-) network and two phenethylammonium cations to form a two-dimensional halide perovskite structure. Temperature-dependent magnetization measurements indicated that Mn-PEA acted as a weak ferromagnet below T(C) = 44.3 K due to spin canting. Below T(C), the magnetic behavior differed significantly from the behavior commonly observed among weak ferromagnets. The susceptibility depended strongly on the crystal orientation, the external magnetic field strength, and the magnetic history. The isothermal magnetization for two orientations revealed a ferromagnetic moment with a spin-canting angle of 0.04° and a spin-flop transitions with H(sf) = 3.5 T. The weak ferromagnetism, which manifested as spontaneous magnetization and magnetic hysteresis near a field strength of zero, was driven by interplay between the easy axis and the antisymmetric Dzyaloshinsky-Moriya (DM) interaction, leading to directional dependent magnetic behavior. PMID:22119750

  11. Experimental investigation of aminoacetonitrile formation through the Strecker synthesis in astrophysical-like conditions: reactivity of methanimine (CH2NH), ammonia (NH3), and hydrogen cyanide (HCN)

    NASA Astrophysics Data System (ADS)

    Danger, G.; Borget, F.; Chomat, M.; Duvernay, F.; Theulé, P.; Guillemin, J.-C.; Le Sergeant D'Hendecourt, L.; Chiavassa, T.

    2011-11-01

    Context. Studing chemical reactivity in astrophysical environments is an important means for improving our understanding of the origin of the organic matter in molecular clouds, in protoplanetary disks, and possibly, as a final destination, in our solar system. Laboratory simulations of the reactivity of ice analogs provide important insight into the reactivity in these environments. Here, we use these experimental simulations to investigate the Strecker synthesis leading to the formation of aminoacetonitrile in astrophysical-like conditions. The aminoacetonitrile is an interesting compound because it was detected in SgrB2, hence could be a precursor of the smallest amino acid molecule, glycine, in astrophysical environments. Aims: We present the first experimental investigation of the formation of aminoacetonitrile NH2CH2CN from the thermal processing of ices including methanimine (CH2NH), ammonia (NH3), and hydrogen cyanide (HCN) in interstellar-like conditions without VUV photons or particules. Methods: We use Fourier Transform InfraRed (FTIR) spectroscopy to monitor the ice evolution during its warming. Infrared spectroscopy and mass spectroscopy are then used to identify the aminoacetonitrile formation. Results: We demonstrate that methanimine can react with -CN during the warming of ice analogs containing at 20 K methanimine, ammonia, and [NH4+ -CN] salt. During the ice warming, this reaction leads to the formation of poly(methylene-imine) polymers. The polymer length depend on the initial ratio of mass contained in methanimine to that in the [NH4+ -CN] salt. In a methanimine excess, long polymers are formed. As the methanimine is progressively diluted in the [NH4+ -CN] salt, the polymer length decreases until the aminoacetonitrile formation at 135 K. Therefore, these results demonstrate that aminoacetonitrile can be formed through the second step of the Strecker synthesis in astrophysical-like conditions.

  12. Trapping in water - an important prerequisite for complex reactivity in astrophysical ices: the case of acetone (CH3)2C = O and ammonia NH3

    NASA Astrophysics Data System (ADS)

    Fresneau, Aurélien; Danger, Grégoire; Rimola, Albert; Theule, Patrice; Duvernay, Fabrice; Chiavassa, Thierry

    2014-10-01

    Water is the most abundant compound in interstellar and cometary ices. Laboratory experiments on ice analogues have shown that water has a great influence on the chemical activity of these ices. In this study, we investigated the reactivity of acetone-ammonia ices, showing that water is an essential component in chemical reactions with high activation energies. In a water-free binary ice, acetone and ammonia do not react due to high activation energy, as the reactants desorb before reacting (at 120 and 140 K, respectively). By contrast, our study shows that under experimental conditions of ˜150 K, this reaction does occur in the presence of water. Here, water traps reactants in the solid phase above their desorption temperatures, allowing them to gather thermal energy as the reaction proceeds. Using infrared spectroscopy and mass spectrometry associated with isotopic labelling, as well as quantum chemical calculations, 2-aminopropan-2-ol (2HN-C(CH3)2-OH) was identified as the acetone-ammonia reaction product. The formation of this product may represent the first step towards formation of 2-aminoisobutyric acid (AIB) in the Strecker synthesis. The activation energy for the formation of 2-aminopropan-2-ol was measured to be 42 ± 3 kJ mol-1, while its desorption energy equalled 61.3 ± 0.1 kJ mol-1. Our work demonstrates that astrophysical water, rather than being a non-thermally reactive species, is crucial for the evolution of complex chemistry occurring in the Universe.

  13. Desorption induced by multiple electronic transitions

    NASA Astrophysics Data System (ADS)

    Misewich, J. A.; Heinz, T. F.; Newns, D. M.

    1992-06-01

    A new mechanism is introduced to describe desorption from surfaces under conditions of strong electronic excitation. When repetitive excitations occur within the relaxation time for the adsorbate-surface vibration, the process of desorption induced by multiple electronic transitions may provide an enhancement of orders of magnitude over a single-excitation mechanism. This generalization of the classic Menzel-Gomer-Redhead picture encompasses within one formalism both single-excitation processes and a thermal limit. The mechanism may be operative in desorption by femtosecond laser pulses.

  14. n-Alkanes on MgO(100). I: Coverage-Dependent Desorption Kinetics of n-Butane

    SciTech Connect

    Tait, Steven L.; Dohnalek, Zdenek; Campbell, C T.; Kay, Bruce D.

    2005-04-22

    High quality temperature programmed desorption (TPD) measurements of n-butane from MgO(100) have been made for a large number of initial butane coverages (0-3.70 ML) and a wide range of heating ramp rates (0.3-10 K/s). We present a TPD analysis technique which allows the coverage-dependent desorption energy to be accurately determined by mathematical inversion of a TPD spectrum, assuming only that the prefactor is coverage-independent. A variational method is used to determine the prefactor that minimizes the difference between a set of simulated TPD spectra and corresponding experimental data. The best fit for butane desorption from MgO is obtained with a prefactor of 1015.7?1.6 s-1. The desorption energy is 34.9?3.4 kJ/mol at 0.5 ML coverage, and varies with coverage. Simulations based on these results can accurately reproduce TPD experiments for submonolayer initial coverages over a wide range of heating ramp rates (0.3-10 K/s). Advantages and limitations of this method are discussed.

  15. Matrix effects in plasma desorption mass spectrometry

    Microsoft Academic Search

    Stephane Bouchonnet; Yannik Hoppilliard; Christine Mauriac

    1993-01-01

    In Plasma Desorption (PD) Mass Spectrometry, valine\\/matrix mixtures have been studied in order to specify the influence of a matrix during the desorption-ionization (DI) of volume. The different matrices used were carboxylic acids (barbituric acid, 2-chloronicotinic acid, 3-chloropropionic acid, cysteine, pentafluorobenzoic acid, picric acid, sinapinic acid) and CsI, an inorganic salt. Three effects are proposed to explain the influence of

  16. Nitrogen isotopic ratios in Barnard 1: a consistent study of the N2H+, NH3, CN, HCN, and HNC isotopologues

    NASA Astrophysics Data System (ADS)

    Daniel, F.; Gérin, M.; Roueff, E.; Cernicharo, J.; Marcelino, N.; Lique, F.; Lis, D. C.; Teyssier, D.; Biver, N.; Bockelée-Morvan, D.

    2013-12-01

    Context. The 15N isotopologue abundance ratio measured today in different bodies of the solar system is thought to be connected to 15N-fractionation effects that would have occurred in the protosolar nebula. Aims: The present study aims at putting constraints on the degree of 15N-fractionation that occurs during the prestellar phase, through observations of D, 13C, and 15N-substituted isotopologues towards B1b. Molecules both from the nitrogen hydride family, i.e. N2H+, and NH3, and from the nitrile family, i.e. HCN, HNC, and CN, are considered in the analysis. Methods: As a first step, we modelled the continuum emission in order to derive the physical structure of the cloud, i.e. gas temperature and H2 density. These parameters were subsequently used as input in a non-local radiative transfer model to infer the radial abundance profiles of the various molecules. Results: Our modelling shows that all the molecules are affected by depletion onto dust grains in the region that encompasses the B1-bS and B1-bN cores. While high levels of deuterium fractionation are derived, we conclude that no fractionation occurs in the case of the nitrogen chemistry. Independently of the chemical family, the molecular abundances are consistent with 14N/15N ~ 300, a value representative of the elemental atomic abundances of the parental gas. Conclusions: The inefficiency of the 15N-fractionation effects in the B1b region can be linked to the relatively high gas temperature ~17 K, which is representative of the innermost part of the cloud. Since this region shows signs of depletion onto dust grains, we cannot exclude the possibility that the molecules were previously enriched in 15N, earlier in the B1b history and that such an enrichment could have been incorporated into the ice mantles. It is thus necessary to repeat this kind of study in colder sources to test such a possibility.

  17. Thermally-induced first-order phase transition in the (FC6H4C2H4NH3)2[PbI4] photoluminescent organic-inorganic material

    NASA Astrophysics Data System (ADS)

    Koubaa, M.; Dammak, T.; Garrot, D.; Castro, M.; Codjovi, E.; Mlayah, A.; Abid, Y.; Boukheddaden, K.

    2012-03-01

    The thermal properties of the perovskite slab alkylammonium lead iodide (FC6H4C2H4NH3)2[PbI4] are investigated using spectroscopic ellipsometry, differential scanning calorimetry, photoluminescence, and Raman spectroscopy. The spectroscopic ellipsometry, performed in the heating mode, clearly evidenced the presence of a singularity at 375 K. This is corroborated by the temperature dependence of the photoluminescence, which pointed out a first-order order-disorder phase transition at ˜375 K, with a hysteresis loop of 40 K width. Raman spectroscopy data suggest that this transition arises from a dynamic rotational disordering of the ammonium headgroups of the alkylammonium chain. In contrast, differential scanning calorimetry measurements on a pellet sample led to an entropy change value ?S ?0.39 J/K/mol at the transition, suggesting the existence of a residual short-range order of the NH3+ on cooling from the high temperature phase.

  18. Dynamics and fragmentation of van der Waals clusters: ,,H2O...n, ,,CH3OH...n, and ,,NH3...n upon ionization by a 26.5 eV soft x-ray laser

    E-print Network

    Rocca, Jorge J.

    Dynamics and fragmentation of van der Waals clusters: ,,H2O...n, ,,CH3OH...n, and ,,NH3...n upon that are typically dominated by the protonated cluster ions H2O nH+ : these species are produced by a fast proton ions H2O 21H+ and H2O 28H+ are identified as "magic number" clusters in this mass spectrum since

  19. Solar Cells: Planar CH3 NH3 PbI3 Perovskite Solar Cells with Constant 17.2% Average Power Conversion Efficiency Irrespective of the Scan Rate (Adv. Mater. 22/2015).

    PubMed

    Heo, Jin Hyuck; Song, Dae Ho; Han, Hye Ji; Kim, Seong Yeon; Kim, Jun Ho; Kim, Dasom; Shin, Hee Won; Ahn, Tae Kyu; Wolf, Christoph; Lee, Tae-Woo; Im, Sang Hyuk

    2015-06-01

    An HI additive enables single-crystalline perovskite thin-films to be formed and reduces trap density, thereby reducing hysteresis and enhancing device performance. S. H. Im and co-workers develop highly efficient planar CH3 NH3 PbI3 perovskite hybrid solar cells with constant average power conversion efficiency irrespective of scan rate, as described on page 3424. PMID:26053453

  20. Evidence and detailed study of a second-order phase transition in the (C6H11NH3)2[PbI4] organic-inorganic hybrid material

    NASA Astrophysics Data System (ADS)

    Yangui, A.; Pillet, S.; Garrot, D.; Triki, S.; Abid, Y.; Boukheddaden, K.

    2015-03-01

    The thermal properties of the organic-inorganic hybrid material (C6H11NH3)2[PbI4] are investigated using diffuse reflectivity, spectroscopic ellipsometry, differential scanning calorimetry, Raman spectroscopy, and X-ray diffraction. The diffuse reflectivity, performed in heating mode, clearly evidences the presence of a singularity at 336 K. This is confirmed by the temperature dependence of the spectroscopic ellipsometry spectra, which points out a second-order phase transition at 336 K with a critical exponent ˜0.5. Differential scanning calorimetry measurements on a polycrystalline powder of (C6H11NH3)2[PbI4] show a reversible phase transition detected at TC = 336 K without hysteresis. Raman spectroscopy data suggest that this transition arises from a change in the interactions between inorganic sheets ({[PbI4]2-}?) and organic protonated molecules ([C6H11NH3]+). The structural analysis from power X-ray diffraction reveals an incomplete order-disorder transition of the cyclohexylammonium cation, causing a subtle contraction of the inter-plane distance. The transition results from repulsive close contacts between the organic molecules in the interlayer spacing.

  1. Ab Initio Quantum Chemical Studies of Reactions in Astrophysical Ices - Reactions Involving CH3OH, CO2, CO, and HNCO in H2CO/NH3/H2O Ices

    NASA Astrophysics Data System (ADS)

    Woon, David E.

    2006-09-01

    While reactions between closed shell molecules generally involve prohibitive barriers in the gas phase, prior experimental and theoretical studies have demonstrated that some of these reactions are significantly enhanced when confined within an icy grain mantle and can occur efficiently at temperatures below 100 K with no additional energy processing. The archetypal case is the reaction of formaldehyde (H2CO) and ammonia (NH3) to yield hydroxymethylamine (NH2CH2OH). In the present work we have characterized reactions involving methanol (CH3OH), carbon dioxide (CO2), carbon monoxide (CO), and isocyanic acid (HNCO) in search of other favorable cases. Most of the emphasis is on CH3OH, which was investigated in the two-body reaction with one H2CO and the three-body reaction with two H2CO molecules. The addition of a second H2CO to the product of the reaction between CH3OH and H2CO was also considered as an alternative route to longer polyoxymethylene polymers of the -CH2O- form. The reaction between HNCO and NH3 was studied to determine if it can compete against the barrierless charge transfer process that yields OCN- and NH4+. Finally, the H2CO + NH3 reaction was revisited with additional benchmark calculations that confirm that little or no barrier is present when it occurs in ice.

  2. Conformational analysis of the adduct cis-[Pt(NH3)2 d(GpG)]+ in aqueous solution. A high field (500-300 MHz) nuclear magnetic resonance investigation.

    PubMed Central

    den Hartog, J H; Altona, C; Chottard, J C; Girault, J P; Lallemand, J Y; de Leeuw, F A; Marcelis, A T; Reedijk, J

    1982-01-01

    A 500, 400 and 300 MHz proton NMR study of the reaction product of cis-Pt(NH3)2Cl2 or cis-[Pt(NH3)2 (H2O)2] (NO3)2 with the deoxydinucleotide d(GpG): cis-[Pt(NH3)2 d(GpG)] was carried out. Complete assignment of the proton resonances by decoupling experiments and computer simulation of the high field part of the spectrum yield proton-proton and proton-phosphorus coupling constants of high precision. Analysis of these coupling constants reveal a 100% N (C3'-endo) conformation for the deoxyribose ring at the 5'-terminal part of the chelated d(GpG) moiety. In contrast, the 3'-terminal -pG part of the molecule displays the normal behaviour for deoxyriboses: the sugar ring prefers to adopt an S (C2'-endo) conformation (about 70%). Extrapolating from this model compound, it is suggested that Pt chelation by a -dGpdG- sequence of DNA would require a S to N conformational change of one deoxyribose moiety as the main conformational alteration and lead to a kink in one strand of the double-helical structure of DNA. PMID:6890203

  3. Adsorption, Desorption, and Displacement Kinetics of H2O and CO2 on Forsterite, Mg2SiO4(011)

    SciTech Connect

    Smith, R. Scott; Li, Zhenjun; Dohnalek, Zdenek; Kay, Bruce D.

    2014-12-18

    We have examined the adsorbate-substrate interaction kinetics of CO2 and H2O on a natural forsterite crystal surface, Mg2SiO4(011), with 10-15% of substitutional Fe2+. We use temperature programmed desorption (TPD) and molecular beam techniques to determine the adsorption, desorption, and displacement kinetics for H2O and CO2. Neither CO2 nor H2O has distinct sub-monolayer desorption peaks but instead both have a broad continuous desorption feature that evolve smoothly into multilayer desorption. Inversion of the monolayer coverage spectra for both molecules reveals that the corresponding binding energies for H2O are greater than that for CO2 on all sites. The relative strength of these interactions is the dominant factor in the competitive adsorption/displacement kinetics. In experiments where the two adsorbates are co-dosed, H2O always binds to the highest energy binding sites available and displaces CO2. The onset of CO2 displacement by H2O occurs between 65 and 75 K.

  4. Hydrodesulfurization and hydrogenation of model compounds on silica–alumina supported bimetallic systems

    Microsoft Academic Search

    V. L Barrio; P. L Arias; J. F Cambra; M. B Güemez; B Pawelec; J. L. G Fierro

    2003-01-01

    Silica–alumina supported Pd catalysts with a second metal such as Cu, Ru or Pt have been prepared (nominal content: 1wt%) and tested in the naphthalene hydrogenation (HYD) and dibenzothiophene hydrodesulfurization (HDS) model reactions. These catalysts were characterized by means of temperature-programmed reduction, NH3 temperature-programmed desorption and photoelectron spectroscopy techniques. The combined use of all these techniques revealed that only in

  5. Determination of the Arrhenius Activation Energy Using a Temperature-Programmed Flow Reactor.

    ERIC Educational Resources Information Center

    Chan, Kit-ha C.; Tse, R. S.

    1984-01-01

    Describes a novel method for the determination of the Arrhenius activation energy, without prejudging the validity of the Arrhenius equation or the concept of activation energy. The method involves use of a temperature-programed flow reactor connected to a concentration detector. (JN)

  6. Detecting Chemical Hazards with Temperature-Programmed Microsensors: Overcoming Complex Analytical Problems with Multidimensional Databases

    Microsoft Academic Search

    Douglas C. Meier; Baranidharan Raman; Steve Semancik

    2009-01-01

    Complex analytical problems, such as detecting trace quantities of hazardous chemicals in challenging environments, require solutions that most effectively extract relevant information about a sample's composition. This review presents a chemiresistive microarray-based approach to identifying targets that combines temperature-programmed elements capable of rapidly generating analytically rich data sets with statistical pattern recognition algorithms for extracting multivariate chemical fingerprints. We describe

  7. Influence of H_2O coadsorption on Electron-Stimulated Desorption of SF_6

    NASA Astrophysics Data System (ADS)

    Kusmierek, D. O.; Faradzhev, N. S.; Madey, T. E.

    2004-03-01

    This work focuses on scattering processes affecting the survival probability and "depth of origin" of low-energy ions (F+, F-), that pass through condensed ultrathin layers of polar H_2O molecules. The ions are generated by electron stimulated desorption (ESD) of SF6 adsorbed on Ru(0001) at 25K. ESD ion angular distribution (ESDIAD) and temperature programmed desorption (TPD) reveal predominantly molecular adsorption of SF6 on Ru(0001) via three F atoms, with the other three pointing away from the surface. Adsorption of overlayers of H_2O leads to changes in both the F+ and F- ion intensities (attenuation and enhancement) as well as dramatic changes in the ion angular distributions. Analysis of these changes gives insight into the role of charge-transfer and elastic scattering processes during the passage of ions through ultrathin polar films, as well as the influence of coadsorbates on adsorption geometry. Interaction of low-energy electrons with condensed SF6 + H_2O films results in the formation of a new chemical species, SOF_2. This has interesting implications for environmental chemistry.

  8. Enhanced desorption of 2,4,6 Trinitrotoluene

    E-print Network

    Aturaliye, Upul Anuruddha

    1997-01-01

    requires that the 'TNT be desorbed and transferred into the aqueous phase. The purpose of this research was to study the influence of surfactants on the desorption of TNT. Furthermore, a comparison of the desorption enhancement capabilities of synthetic...

  9. Reversibility, Dopant Desorption, and Tunneling in the Temperature-Dependent Conductivity of Type-Separated, Conductive Carbon Nanotube Networks

    SciTech Connect

    Barnes, T. M.; Blackburn, J. L.; van de Lagemaat, J.; Coutts, T. J.; Heben, M. J.

    2008-09-01

    We present a comprehensive study of the effects of doping and temperature on the conductivity of single-walled carbon nanotube (SWNT) networks. We investigated nearly type-pure networks as well as networks comprising precisely tuned mixtures of metallic and semiconducting tubes. Networks were studied in their as-produced state and after treatments with nitric acid, thionyl chloride, and hydrazine to explore the effects of both intentional and adventitious doping. For intentionally and adventitiously doped networks, the sheet resistance (R{sub s}) exhibits an irreversible increase with temperature above {approx}350 K. Dopant desorption is shown to be the main cause of this increase and the observed hysteresis in the temperature-dependent resistivity. Both thermal and chemical dedoping produced networks free of hysteresis. Temperature-programmed desorption data showed that dopants are most strongly bound to the metallic tubes and that networks consisting of metallic tubes exhibit the best thermal stability. At temperatures below the dopant desorption threshold, conductivity in the networks is primarily controlled by thermally assisted tunneling through barriers at the intertube or interbundle junctions.

  10. THERMAL DESORPTION OF PETROLEUM CONTAMINATED SOILS

    EPA Science Inventory

    The U.S. Environmental Protection Agency recently funded a study which addresses the treatment of soils contaminated by petroleum hydrocarbons using low temperature thermal desorption (LTTD). he proposed paper will summarize some of the results of that study. TTD has become a maj...

  11. High performance ²?²Cf plasma desorption mass spectrometry 

    E-print Network

    McIntire, Thomas Shane

    1991-01-01

    Track and the Dissemination of Energy. . . 4. The Desorption-Ionization Mechanism Thesis Objectives 1. Instrumental Design Improvements. . . . . . . . . . . 2. Mass Calibration and Accuracy Acceleration Systems . . . . . . . . . , 1. Grid.... Operating the EPG in the Pulsed Deflection Mode . 3. Operating the EPG in the Pulsed Transmission Mode F. Gridless Acceleration Electrode System . G. Calibration and Mass Accuracy . 1. Calibration Methods . 2. Selection of Calibration Ions 3. TOF...

  12. Computational simulation characteristics desorption in TPS aggregates

    NASA Astrophysics Data System (ADS)

    Goldaev, Sergey; Khushvaktov, Alisher

    2014-08-01

    The article describes the modified model of desorption in a continuously operating apparatus in fluidized bed, which allows for a refined timing warm adsorbent particles of spherical shape at a flow of hot air to equalize the temperature along the radius of granules and assess relevant energy costs.

  13. Moisture Absorption and Desorption of Composite Materials

    Microsoft Academic Search

    Chi-Hung Shen; George S. Springer

    1976-01-01

    Expressions are presented for the moisture distribution and the mois ture content as a function of time of one dimensional homogeneous and composite materials exposed either on one side or on both sides to humid air or to water. The results apply during both moisture absorption and desorption when the moisture content and the temperature of the environ ment are

  14. The potential for and challenges of detecting chemical hazards with temperature-programmed microsensors

    Microsoft Academic Search

    D. C. Meier; J. K. Evju; Z. Boger; B. Raman; K. D. Benkstein; C. J. Martinez; C. B. Montgomery; S. Semancik

    2007-01-01

    Several recent demonstrations of the abilities of micro-electromechanical systems (MEMS)-based microsensor technology to detect hazardous compounds and their simulants in a variety of background conditions are presented. In each case, two pairs of conductometric metal oxide sensors (TiO2 and SnO2) produced via chemical vapor deposition are operated using temperature-programmed sensing (TPS). NIST microdevices can utilize this operating mode to sample

  15. Studies on the synthesis and characterization of four trans-planaramineplatinum(II) complexes of the form trans-PtL(NH3)CL2 where L = 2-hydroxypyridine, 3-hydroxypyridine, imidazole, and imidazo(1,2-alpha)pyridine.

    PubMed

    Huq, Fazlul; Daghriri, Hassan; Yu, Jun Qing; Beale, Philip; Fisher, Keith

    2004-08-01

    Four trans-planaramineplatinum(II) complexes code named YH9, YH10, YH11 and YH12, each of the form trans-PtL(NH(3))Cl(2) where L = 2-hydroxypyridine and 3-hydroxypyridine, imidazole, and imidazo(1,2-alpha)pyridine for YH9, YH10, YH11 and YH12, respectively. All of the compounds have significant anticancer activity against human cancer cell lines. YH12 is found to be significantly more active than cisplatin against cisplatin-resistant ovary cell line A2780(cisR). PMID:15276302

  16. Optical Properties of Electron Center in Layered Ionic Crystals (CnH2n+1NH3)2MnCl4: n{=}1, 2, 3 Irradiated with X-Rays at 15 K

    Microsoft Academic Search

    Takehisa Yoshinari; Toru Ebihara; Izumi Kotani; Yasushi Sato; Akira Suzuki; Yasuhiro Seino; Koutaro Masuda; Takahiro Yano; Koujiro Yumura; Katsuaki Wako; Tomochika Matsuyama; Kiyoshi Aoyagi

    1990-01-01

    A new optical absorption band was found at the peak energy of 17 kcm-1 (590 nm) besides the Cl2- band (22.5 kcm-1{=}445 nm) in (CnH2n+1NH3)2MnCl4 (n{=}1, 2, 3) irradiated with X-rays at 15 K. The absorption intensity of the new band increases with the X-ray dosage in proportion to that of the Cl2- band. The intensity thermally decreases in two

  17. Analyses of the ``allowed'' inversion barriers of H2O and NH3: Incompleteness of the Woodward-Hoffmann HOMO-LUMO symmetry ideas due to neglect of molecular orbital terms

    NASA Astrophysics Data System (ADS)

    Edmiston, C.; Jarvie, J.; Bartleson, J.

    1986-06-01

    Walsh's rules correctly attribute the ``bent'' structures of H2O and NH3 to the occupation of the 1?z?3a1 HOMO not occupied in linear BeH2 and planar BH3. In Walsh's molecular orbital (MO) diagram E(3a1) decreases sharply with bending angle S. This has always been attributed incorrectly to changes in the 3a1 MO, mainly due to symmetry-allowed mixing with the LUMO, 4a*1. The forbidden bending of BeH2 and BH3 has been similarly ``explained.'' Using large-basis-set self-consistent field molecular orbital (SCF MO) ?s, we show that the integral Hellmann-Feynman theorem ?EIHF??ESCF much better than does the analogous second-order perturbation theory ?E''(SE'=0 and ?=S2/2, ?H?SH'+?H''). ?EIHF=++?NR??ni2? EIHFi+?NR, ??˜=(?/?)-?0, ?=, ?EIHFi=+, ??˜i=(?i/?i)-?0i, ?i=, ?NA=?H-?NR. Both theories show a large negative <1?z??NA?1?z> term and small <1?z??NA??1?˜z> HOMO-UMO mixing term, which is positive in ?EIHF. The <1?z?SH'?3?*g> HOMO-LUMO mixing term is small even when 3?*g is optimized for the excited state. The ?EIHFis and ?E`is give the usual Walsh diagrams for bending of H2O and NH3, with or without MO partitioning of the nuclear repulsion change (?NR). However ``decoupling'' of the ?'is in ?' makes the ?E`is unreliable. The <1?z??NA?1?z> term acts to create a large allowed barrier to inversion for H2O and CH4, but a strong ?NR nearly destroys an otherwise large barrier for NH3. <1?z??NA?1?z> acts to bend the linear H2O, planar NH3, and planar CH4, with HOMO-LUMO mixing being ``antibending.'' We show that understanding of MO correlation diagrams demands consideration of the ``static'' terms as well as the OMO-UMO mixing terms, which has not been appreciated by earlier workers so far as we are aware.

  18. Temperature-programmed sputtered micromachined gas chromatography columns: an approach to fast separations in oilfield applications.

    PubMed

    Haudebourg, R; Vial, J; Thiebaut, D; Danaie, K; Breviere, J; Sassiat, P; Azzouz, I; Bourlon, B

    2013-01-01

    In a previous study, a new stationary phase deposition technique for micromachined gas chromatography columns was presented. The rerouting of the sputtering technique to this purpose enabled collective and reproducible fabrication of microcolumns in a silicon wafer. Silica-sputtered micromachined columns showed promising separations of light alkanes in isothermal conditions. In order to go beyond the limitations of isothermal separations, the columns were equipped with sputtered platinum filaments to enable high-speed and low-power temperature programming. The separation performances of temperature-programmed silica- or graphite-sputtered microcolumns were investigated: a separation of light alkanes (C1-C5) was completed in 9 s, and heavier alkanes (until C9), cyclic, isomeric, and unsaturated hydrocarbons were also successfully separated. Versatility of these microcolumns was demonstrated with a high-temperature C1-C2 separation and a C1-C5 separation with nitrogen as carrier gas instead of helium. By matching the requirements of a gas chromatography-based monitoring sensor, in terms of low-cost and industry-ready fabrication process, fast temperature programming and analysis, low power consumption, and good versatility (ambient temperature, carrier gas), these columns should be used in various applications related to oilfield gas analyses. PMID:23231068

  19. Desorption of intrinsic cesium from smectite: inhibitive effects of clay particle organization on cesium desorption.

    PubMed

    Fukushi, Keisuke; Sakai, Haruka; Itono, Taeko; Tamura, Akihiro; Arai, Shoji

    2014-09-16

    Fine clay particles have functioned as transport media for radiocesium in terrestrial environments after nuclear accidents. Because radiocesium is expected to be retained in clay minerals by a cation-exchange reaction, ascertaining trace cesium desorption behavior in response to changing solution conditions is crucially important. This study systematically investigated the desorption behavior of intrinsic Cs (13 nmol/g) in well-characterized Na-montmorillonite in electrolyte solutions (NaCl, KCl, CaCl2, and MgCl2) under widely differing cation concentrations (0.2 mM to 0.2 M). Batch desorption experiments demonstrated that Cs(+) desorption was inhibited significantly in the presence of the environmental relevant concentrations of Ca(2+) and Mg(2+) (>0.5 mM) and high concentrations of K(+). The order of ability for Cs desorption was Na(+) = K(+) > Ca(2+) = Mg(2+) at the highest cation concentration (0.2 M), which is opposite to the theoretical prediction based on the cation-exchange selectivity. Laser diffraction grain-size analyses revealed that the inhibition of Cs(+) desorption coincided with the increase of the clay tactoid size. Results suggest that radiocesium in the dispersed fine clay particles adheres on the solid phase when the organization of swelling clay particles occurs because of changes in solution conditions caused by both natural processes and artificial treatments. PMID:25144123

  20. Vibrational Spectroscopy and Thermal Desorption Spectroscopy Studies of Adsorbate Hydrogen Bonding and Surface Chemistry on PLATINUM(111) and NICKEL(111)

    NASA Astrophysics Data System (ADS)

    Gao, Quanyin

    1991-07-01

    Adsorbate-adsorbate interactions, hydrogen bonding and surface reactions, have been studied using Fourier transform reflection absorption infrared spectroscopy (FTRAIR), high resolution electron energy loss spectroscopy (HREELS) and thermal desorption spectroscopy. On Ni(111), the HREELS results reveal that for theta < 0.5, formamide molecules (HCONH_2) are dissociatively adsorbed as eta^2( _{rm C,O})-CONH_2 at 90K. At theta~0.85, non-dissociative adsorption occurs. The hydrogen bonding among adsorbates has been observed for theta > 0.5 characterized by the red shift and peak broadening of the upsilon _{rm a}(NH_2 ) and upsilon_{s}(NH_2) modes as well as enhanced intensity of the omega(NH _2) mode. The results from FTRAIRS, HREELS and TDS reveal two thermal decomposition channels. One leads to the production of NH_3 and CO. The other yields isocyanic acid (HNCO). Possible precursors related to hydrogen bonding effects have been discussed. On Pt(111), dissociative adsorption of HCONH _2 forming NH_3 and CO are found at low dosages at 170K. At saturation monolayer coverages, hydrogen-bonding interactions between the chemisorbed molecules result in 263 cm^{-1} red-shifting of the upsilon(NH _2) vibrational frequency and linewidth broadening of the upsilon_{s}(NH_2) and upsilon_{rm a}(NH _2) modes. For HCOND_2, the linewidths of the corresponding modes are reduced. The isotope effect for linewidth is discussed. Acetic acid (CH_3COOH, CH_3COOD and ^{13 }CD_3COOH(D)) adsorption and reaction have been studied on Pt(111). The HREELS results indicate that for theta< 0.3, dissociative adsorption occurs forming eta ^2(O,O)-CH_3COO. Molecular adsorption occurs at theta~ 0.5 with a finger print peak at ~923 cm^{-1} for CH _3COOH H-bonded dimers. The hydrogen bond energy are estimated to be ~7.3 kcal/mole and the bond length (R_{ rm O{cdots}{cdot}O }) to be of ~2.68 A. Thermal desorption spectroscopy and HREELS results reveal that on Pt(111), acetic acid decomposes into CO and H _2 as the major products upon heating.

  1. Infrared spectroscopy and photodesorption of condensed phase ammonia

    NASA Astrophysics Data System (ADS)

    Szulczewski, G. J.; White, J. M.

    1998-05-01

    We have characterized the adsorption and thermal desorption of thick films of NH 3 and ND 3 condensed on Ag(111) with Fourier transform reflection absorption infrared spectroscopy and temperature programmed desorption. Over the coverage range of 1-50 monolayers, the asymmetric stretch (2513 cm -1 for ND 3 and 3380 cm -1 for NH 3) and symmetric deformation (832 cm -1 for ND 3 and 1078 cm -1 for NH 3) modes of ammonia are the most intense features in the vibrational spectra. Temperature programmed desorption yields an activation energy for thermal desorption of NH 3 and ND 3 multilayers of 23.8 kJ mol -1 and 24.7 kJ mol -1, respectively. At a coverage of 50 ML we used 193 nm light to stimulate molecular desorption from the multilayers and measured time-of-flight spectra. All time-of-flight spectra were bimodal; the average translational energies of the two components were 3150±100 K and 550±50 K. The fast channel is ascribed to ammonia molecules ejected from the vacuum-film interface while the slower channel is ascribed to ammonia molecules desorbing from deeper layers of the film. At 50 ML the angular distribution of photodesorbed ammonia peaks between 20° and 40° off the surface normal.

  2. Thermal desorption study of physical forces at the PTFE surface

    NASA Technical Reports Server (NTRS)

    Wheeler, D. R.; Pepper, S. V.

    1987-01-01

    Thermal desorption spectroscopy (TDS) of the polytetrafluoroethylene (PTFE) surface was successfully employed to study the possible role of physical forces in the enhancement of metal-PTFE adhesion by radiation. The thermal desorption spectra were analyzed without assumptions to yield the activation energy for desorption over a range of xenon coverage from less than 0.1 monolayer to more than 100 monolayers. For multilayer coverage, the desorption is zero-order with an activation energy equal to the sublimation energy of xenon. For submonolayer coverages, the order for desorption from the unirradiated PTFE surface is 0.73 and the activation energy for desorption is between 3.32 and 3.36 kcal/mol; less than the xenon sublimation energy. The effect of irradiation is to increase the activation energy for desorption to as high as 4 kcal/mol at low coverage.

  3. Thermal desorption study of physical forces at the PTFE surface

    NASA Technical Reports Server (NTRS)

    Wheeler, D. R.; Pepper, S. V.

    1985-01-01

    Thermal desorption spectroscopy (TDS) of the polytetrafluoroethylene (PTFE) surface was successfully employed to study the possibile role of physical forces in the enhancement of metal-PTFE adhesion by radiation. The thermal desorption spectra were analyzed without assumptions to yield the activation energy for desorption over a range of xenon coverage from less than 0.1 monolayer to more than 100 monolayers. For multilayer coverage, the desorption is zero-order with an activation energy equal to the sublimation energy of xenon. For submonolayer coverages, the order for desorption from the unirradiated PTFE surface is 0.73 and the activation energy for desorption is between 3.32 and 3.36 kcal/mol; less than the xenon sublimation energy. The effect of irradiation is to increase the activation energy for desorption to as high as 4 kcal/mol at low coverage.

  4. Parametrization of the Stillinger-Weber potential for Si/N/H system and its application to simulations of silicon nitride film deposition with SiH4/NH3

    NASA Astrophysics Data System (ADS)

    Deng, Xiaodi; Song, Yixu; Li, JinChun; Pu, Yikang

    2014-02-01

    We determined the Stillinger-Weber interatomic potential parameters for Si/N/H system based on first principles density functional calculations. This new potential can be used to perform classical molecular dynamics simulation for silicon nitride deposition on Si substrate. During the first principles calculations, cluster models have been carefully and systematically chosen to make sampling of the interatomic potential supersurface more thoroughly. Global optimization method was used to fit the ab initio data into Stillinger-Weber form. We used a recursive method to perform the classical molecular dynamics simulations for silicon nitride (SiN) film growth on Si substrate with SiH4/NH3 gas mixtures. During the simulation, we could clearly observe the silicon nitride film growth progress. In this paper, we present the details of potential derivation and simulation results with different SiH4:NH3 ratios. It is demonstrated that this new potential is suitable to describe the surface reactions of the Si/N/H system and allows us to explore more complex SiN growing process such as plasma-enhanced chemical vapor deposition.

  5. Zinc-diluted magnetic metal formate perovskites: synthesis, structures, and magnetism of [CH3NH3][Mn(x)Zn(1-x)(HCOO)3] (x = 0-1).

    PubMed

    Shang, Ran; Sun, Xuan; Wang, Zhe-Ming; Gao, Song

    2012-06-01

    The preparation, structures, and magnetic properties of a series of metal formate perovskites [CH(3)NH(3)][Mn(x)Zn(1-x)(HCOO)(3)] were investigated. The isostructural solid solution can be prepared in the complete range of x=0-1. The metal-organic perovskite structures consist of an anionic NaCl type [Mn(x)Zn(1-x)(HCOO)(3)(-)] framework with CH(3)NH(3)(+) templates located in the nearly cubic cavities and forming hydrogen bonds to the framework. When the proportion of Mn increased (i.e., x changed from 0 to 1), the lattice dimensions and metal-oxygen and metal-metal distances show a slight, nonlinear increase because of the increased averaged metal ionic radius and the local structure distortion. Through the series, the magnetism changes from the long-range ordering of spin-canted antiferromagnetism for x?0.40 to paramagnetism when x?0.30, and the percolation limit was estimated to be x(P)=0.31(2) for this simple cubic lattice. In the low-temperature region, enhancement of magnetization and the gradual decrease and final disappearance of coercive field, remnant magnetization, and spin-flop field upon dilution were observed through this isotropic Heisenberg magnetic series. IR spectroscopic and thermal properties were also investigated. PMID:22529056

  6. G W quasiparticle band gap of the hybrid organic-inorganic perovskite CH3NH3PbI3 : Effect of spin-orbit interaction, semicore electrons, and self-consistency

    NASA Astrophysics Data System (ADS)

    Filip, Marina R.; Giustino, Feliciano

    2014-12-01

    We study the quasiparticle band gap of the hybrid organic-inorganic lead halide perovskite CH3NH3PbI3 , using many-body perturbation theory based on the G W approximation. We perform a systematic analysis of the band gap sensitivity to relativistic spin-orbit effects, to the description of semicore Pb-5 d and I-4 d electrons, and to the starting Kohn-Sham eigenvalues. We find that the inclusion of semicore states increases the calculated band gap by 0.2 eV, and self-consistency on the quasiparticle eigenvalues using a scissor correction increases the band gap by 0.5 eV with respect to the G0W0 result. These findings allow us to resolve an inconsistency between previously reported G W calculations for CH3NH3PbI3 . Our most accurate band gap is 1.72 eV, and is in good agreement with the measured optical gap after considering a small excitonic shift as determined in experiments.

  7. Adsorption and desorption of mixed molecular ices from a cosmic dust grain analogue surface

    NASA Astrophysics Data System (ADS)

    Wolff, Angela Jean

    Surface science is playing an ever more prominent role in the field of astronomy. More than 220 different molecules have so far been observed in the interstellar medium (ISM), and for several of these molecules, the observed abundance is such that the molecules cannot be formed by gas phase reactions alone. Astronomers have proposed that they are instead formed by heterogeneous reactions that take place on the surface of dust grains. The two alcohols methanol and ethanol are just two of the molecules typically observed in both the gas and solid phase in the ISM. In the solid phase, they are found frozen out with the more abundant water, as molecular ices on the surface of dust grains. Both alcohols can be viewed as evolutionary indicators in the vicinity of hot cores. Hot cores are compact objects found in close to newly formed massive stars they are dense and relatively warm and show atypical gas-phase molecular compositions. The gas-phase composition, and therefore the evolutionary stage of the hot core, can be understood by considering the sublimation behaviour of molecular ices on the dust grains within the molecular cloud. This thesis presents the results of investigations on the adsorption and desorption of methanol and ethanol in both the pure state and in combination with water. In each case the deposition occurs on a highly oriented pyrolytic graphite (HOPG) surface. HOPG is considered to be a suitable interstellar dust grain analogue, as dust grains in the ISM are composed of mainly carbonaceous and silicaceous material. Temperature programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS) studies of methanol and ethanol ices, mixed with water, are presented. The adsorption and desorption of each species deposited on a layer of amorphous solid water ice is compared to those of codeposited ice layers. In all systems, there is evidence for molecular adsorption in a physisorbed state and for interactions between the investigated molecule and the water ice. As expected, the sequentially deposited systems show different behaviour when compared with the codeposited systems. The information obtained from these experiments is of direct relevance to astronomers, as the measured desorption energies can be incorporated directly into astronomical models. This, in turn, helps to lead to a greater understanding of star formation, and hence of the Universe in which we live.

  8. MATRIX-ASSISTED LASER DESORPTION MASS SPECTROMETRY

    Microsoft Academic Search

    Michael J. Stump; Richard C. Fleming; Wei-Hong Gong; Arwah J. Jaber; Jeffrey J. Jones; Charles W. Surber; Charles L. Wilkins

    2002-01-01

    Matrix-assisted laser desorption\\/ionization (MALDI) mass spectrometry is a technique that has attracted widespread interest since its introduction in 1988. It is primarily implemented using time-of-flight or trapped ion mass analyzers and greatly facilitates determination of molecular weights for biomolecules, polymers, and natural products. Numerous publications on these and related applications have appeared during the past ten years. The present brief

  9. Desorption of hexachlorobiphenyl from selected particulate matter 

    E-print Network

    Rorschach, Reagan Cartwright

    1989-01-01

    . INTRODUCTION Objectives CHAPTER IL LITERATURE REVIEW Gas Transfer Solvent Sublation . . Solid-Liquid Mass Transfer . Desorption Mechanisms . CHAPTER III. METHODS AND MATERIALS . . Experimental Apparatus and Procedure Liquid Scintillation Theory Quench...*Cht ~CItll (Autenrieth, 1986), uansport to the cell-water interface would be a function of molecular diffusion. The proposed interface between the phases has given rise to many theories concerning liquid-gas and liquid-solid mass transfer. Liquid-gas mass...

  10. Plutonium sorption and desorption behavior on bentonite.

    PubMed

    Begg, James D; Zavarin, Mavrik; Tumey, Scott J; Kersting, Annie B

    2015-03-01

    Understanding plutonium (Pu) sorption to, and desorption from, mineral phases is key to understanding its subsurface transport. In this work we study Pu(IV) sorption to industrial grade FEBEX bentonite over the concentration range 10(-7)-10(-16) M to determine if sorption at typical environmental concentrations (?10(-12) M) is the same as sorption at Pu concentrations used in most laboratory experiments (10(-7)-10(-11) M). Pu(IV) sorption was broadly linear over the 10(-7)-10(-16) M concentration range during the 120 d experimental period; however, it took up to 100 d to reach sorption equilibrium. At concentrations ?10(-8) M, sorption was likely affected by additional Pu(IV) precipitation/polymerization reactions. The extent of sorption was similar to that previously reported for Pu(IV) sorption to SWy-1 Na-montmorillonite over a narrower range of Pu concentrations (10(-11)-10(-7) M). Sorption experiments with FEBEX bentonite and Pu(V) were also performed across a concentration range of 10(-11)-10(-7) M and over a 10 month period which allowed us to estimate the slow apparent rates of Pu(V) reduction on a smectite-rich clay. Finally, a flow cell experiment with Pu(IV) loaded on FEBEX bentonite demonstrated continued desorption of Pu over a 12 day flow period. Comparison with a desorption experiment performed with SWy-1 montmorillonite showed a strong similarity and suggested the importance of montorillonite phases in controlling Pu sorption/desorption reactions on FEBEX bentonite. PMID:25574607

  11. Ambient pressure laser desorption and laser-induced acoustic desorption ion mobility spectrometry detection of explosives.

    PubMed

    Ehlert, Sven; Walte, Andreas; Zimmermann, Ralf

    2013-11-19

    The development of fast, mobile, and sensitive detection systems for security-relevant substances is of enormous importance. Because of the low vapor pressures of explosives and improvised explosive devices, adequate sampling procedures are crucial. Ion mobility spectrometers (IMSs) are fast and sensitive instruments that are used as detection systems for explosives. Ambient pressure laser desorption (APLD) and ambient pressure laser-induced acoustic desorption (AP-LIAD) are new tools suitable to evaporate explosives in order to detect them in the vapor phase. Indeed, the most important advantage of APLD or AP-LIAD is the capability to sample directly from the surface of interest without any transfer of the analyte to other surfaces such as wipe pads. A much more gentle desorption, compared to classical thermal-based desorption, is possible with laser-based desorption using very short laser pulses. With this approach the analyte molecules are evaporated in a very fast process, comparable to a shock wave. The thermal intake is reduced considerably. The functionality of APLD and AP-LIAD techniques combined with a hand-held IMS system is shown for a wide range of common explosives such as EGDN (ethylene glycol dinitrate), urea nitrate, PETN (pentaerythritol tetranitrate), HMTD (hexamethylene triperoxide diamine), RDX (hexogen), tetryl (2,4,6-trinitrophenylmethylnitramine), and TNT (trinitrotoluene). Detection limits down to the low nanogram range are obtained. The successful combination of IMS detection and APLD/AP-LIAD sampling is shown. PMID:24116702

  12. History of desorption induced by electronic transitions

    NASA Astrophysics Data System (ADS)

    Madey, Theodore E.

    1994-01-01

    Desorption induced by electronic transitions (DIET) encompasses electron- and photon-stimulated desorption (ESD and PSD) of atoms, molecules and ions from surfaces. In this paper, we focus on the key experimental and theoretical developments that have led to a fundamental understanding of DIET processes. We emphasize the effects of ionizing radiation, i.e., electrons and photons with energies ? 10 eV. The first DIET studies were occasioned mainly by the observation of anomalous peaks in mass spectrometers and spurious signals in ionization gauges. These observations were followed in the early 1960's by systematic studies of Redhead, and Menzel and Gomer, who independently proposed a Franck-Condon excitation model for electron-stimulated desorption of ions and neutrals from surfaces. In the years after this seminal work, ESD and PSD developed as fields of active interest to surface scientists. In addition to providing insights into the fundamental mechanisms linking atomic motion and electronic energy dissipation at surfaces, DIET investigations are continuing to impact upon radiation damage processes in areas as diverse as X-ray optics, semiconductor electronics, surface analysis and synthesis of molecules in interplanetary space.

  13. Novel devices for solvent delivery and temperature programming designed for capillary liquid chromatography.

    PubMed

    Coutinho, Lincoln Figueira Marins; Nazario, Carlos Eduardo Domingues; Monteiro, Alessandra Maffei; Lanças, Fernando Mauro

    2014-08-01

    Analyses in chromatographic systems able to save mobile and stationary phases without reducing efficiency and resolution are of current interest. These advantages regarding savings have challenged us to develop a system dedicated to miniaturized liquid chromatography. This paper reports on the development of a high-pressure syringe-type pump, an oven able to perform isothermal and temperature programming and a software program to control these chromatographic devices. The experimental results show that the miniaturized system can generate reproducible and accurate temperature and flow rate. The system was applied to the separation of statins and tetracylines and showed excellent performance. PMID:24838528

  14. Temperature-Programmed Gas-Sensing With Microhotplates: an Opportunity to Enhance Microelectronic Gas Sensor Metrology

    NASA Astrophysics Data System (ADS)

    Geist, Jon; Afridi, Muhammad

    2009-09-01

    It is only recently that the ITRS (International Technical Roadmap for Semiconductors) has identified functional diversification through heterogeneous integration as a key enabler of future industry growth. This paper describes a powerful temperature-programmed gas-sensing technique that has the potential to convert low-cost, integrated, microhotplate-based non-selective, metal-oxide gas sensors into stable, sensitive, and highly selective gas-sensor systems. The paper also points out the importance of heterogeneous integration and temperature sensor stability to support this measurement technique.

  15. Novel bimetallic dispersed catalysts for temperature-programmed coal liquefaction. Final report

    SciTech Connect

    Chunshan Song; Schobert, H.H.; Parfitt, D.P. [and others

    1997-11-01

    Development of new catalysts is a promising approach to more efficient coal liquefaction. It has been recognized that dispersed catalysts are superior to supported catalysts for primary liquefaction of coals, because the control of initial coal dissolution or depolymerization requires intimate contact between the catalyst and coal. This research is a fundamental and exploratory study on catalytic coal liquefaction, with the emphasis on exploring novel bimetallic dispersed catalysts for coal liquefaction and the effectiveness of temperature-programmed liquefaction using dispersed catalysts. The primary objective of this research was to explore novel bimetallic dispersed catalysts from organometallic molecular precursors, that could be used in low concentrations but exhibit relatively high activity for efficient hydroliquefaction of coals under temperature-programmed conditions. We have synthesized and tested various catalyst precursors in liquefaction of subbituminous and bituminous coals and in model compound studies to examine how do the composition and structure of the catalytic precursors affect their effectiveness for coal liquefaction under different reaction conditions, and how do these factors affect their catalytic functions for hydrogenation of polyaromatic hydrocarbons, for cleavage of C-C bonds in polycyclic systems such as 4-(1-naphthylmethyl)bibenzyl, for hydrogenolysis of C-O bond such as that in dinaphthylether, for hydrodeoxygenation of phenolic compounds and other oxygen-containing compounds such as xanthene, and for hydrodesulfurization of polycyclic sulfur compounds such as dibenzothiophene. The novel bimetallic and monometallic precursors synthesized and tested in this project include various Mo- and Fe-based compounds.

  16. Nitriding of titanium and its alloys by N2, NH3 or mixtures of N2 + H2 in a dc arc plasma at low pressures ( or = to torr)

    NASA Technical Reports Server (NTRS)

    Avni, R.

    1984-01-01

    The dc glow discharges in different gas mixtures of Ar + N2, Ar + NH3 or Ar + N2 + H2 result in the surface nitriding of Ti metal and its alloy (Ti6Al4V). Various gas mixtures were used in order to establish the main active species governing the nitriding process, i.e., N, N2, NH, or NH2 as excited or ionized particles. The dc discharge was sampled and analyzed by quadruple mass spectrometry (QPMS) and optical emission spectroscopy (OES), and the nitrided samples were analyzed by scanning electron microscopy (SEM) with an EDAX attachment, microhardness, and Fourier transform infrared reflectance spectrometry (FTIR). It was found that the excited and ionized nitrogen and hydrogen atoms are the main species responsible for the nitriding process in a dc glow discharge.

  17. The Transition from Hydrogen Bonding to Ionization in (HCI)n(NH3)n and (HCI)n(H2O)n Clusters: Consequences for Anharmonic Vibrational Spectroscopy

    NASA Technical Reports Server (NTRS)

    Chaban, Galina M.; Gerber, R. Benny; Janda, Kenneth C.; Kwak, Dochan (Technical Monitor)

    2001-01-01

    Anharmonic vibrational frequencies and intensities are calculated for 1:1 and 2:2 (HCl)(sub n)(NH3)(sub n) and (HCl)(sub n)(H2O)(sub n) complexes, employing the correlation-corrected vibrational self-consistent field method with ab initio potential surfaces at the MP2/TZP computational level. In this method, the anharmonic coupling between all vibrational modes is included, which is found to be important for the systems studied. For the 4:4 (HCl)(sub n)(H2O)(sub n) complex, the vibrational spectra are calculated at the harmonic level, and anharmonic effects are estimated. Just as the (HCl)(sub n)(NH3)(sub n) structure switches from hydrogen-bonded to ionic for n=2, the (HCl)(sub n)(H2O)(sub n) switches to ionic structure for n=4. For (HCl)2(H2O)2, the lowest energy structure corresponds to the hydrogen-bonded form. However, configurations of the ionic form are separated from this minimum by a barrier of less than an O-H stretching quantum. This suggests the possibility of experiments on ionization dynamics using infrared excitation of the hydrogen-bonded form. The strong cooperative effects on the hydrogen bonding, and concomitant transition to ionic bonding, makes an accurate estimate of the large anharmonicity crucial for understanding the infrared spectra of these systems. The anharmonicity is typically of the order of several hundred wave numbers for the proton stretching motions involved in hydrogen or ionic bonding, and can also be quite large for the intramolecular modes. In addition, the large cooperative effects in the 2:2 and higher order (HCl(sub n)(H2O)(sub n) complexes may have interesting implications for solvation of hydrogen halides at ice surfaces.

  18. The tropospheric gas composition of Jupiter's north equatorial belt (NH3, PH3, CH3D, GeH4, H2O) and the Jovian D/H isotropic ratio

    NASA Technical Reports Server (NTRS)

    Kunde, V.; Hanel, R.; Maguire, W.; Gautier, D.; Baluteau, J. P.; Marten, A.; Chedin, A.; Husson, N.; Scott, N.

    1982-01-01

    The gas composition of the troposphere of Jupiter in the clearest regions of the North Equatorial Belt (NEB) was derived from the Voyager 1 IRIS data. The infrared spectrum for this homogeneous cloud free region was modeled to infer altitude profiles for NH3, PH3, GeH4 and H2O. The Profiles for NH3 and PH3 were found to be depleted in the upper troposphere but otherwise in agreement with their solar values at the 1 bar level. The mole fraction for CH3D was determined to be 3.5(+1.0 or -1.3) x 10 to the minus 7th power. The GeH4 mole fraction of 7+ or -2 x 10 to the minus 10th power at the 2 to 3 bar level is a factor of 10 lower than the solar value. The H2O mole fraction is approximately 1 x 0.00001 at the 2.5 bar level and is increasing to approximately 3 x 0.00001 at 4 bars where it is a factor of 30 lower than solar. Using IRIS infrared values for the mole fractions of CH3D and CH4 a value of D/H = 3.6(+1.0 or -1.4)x 0.00001 is derived. Assuming this Jovian D/H ratio is representative of the protosolar nebula, and correcting for chemical galactic evolution, yields a value of 5.5 - 9.0 x 0.00001 for the primordial D/H ratio and an upper limit of 1.8 to 2.4 x 10 to the minus 31st power cu cm for the present day baryon density.

  19. Thermal processing of astrophysical ice analogs using the Interstellar Astrochemistry Chamber

    NASA Astrophysics Data System (ADS)

    Martín Doménech, R.; Muñoz Caro, G. M.

    2015-01-01

    Thermal processing of astrophysical ices takes place in circumstellar environments. Knowledge of this process comes from a combination of astronomical observations and laboratory simulations under astrophysically relevant conditions. For the first time we present the results of temperature programmed desorption (TPD) experiments with realistic pre-cometary ice analogs composed of up to five molecular components: H2O, CO, CO2, CH3OH, and NH3. The experiments were performed with an ultra-high vacuum chamber. Volatiles desorbing to the gas phase were monitored using a quadrupole mass spectrometer, while changes in the ice structure and composition were studied by means of infrared spectroscopy. The TPD curves of water ice containing CO, CO2, CH3OH, and NH3 present desorption peaks at temperatures near those observed in pure ice experiments, volcano desorption peaks after water ice crystallization, and co-desorption peaks with water. Desorption peaks of CH3OH and NH3 at temperatures similar to the pure ices takes place when their abundance relative to water is above — 3 % in the ice matrix. We found that CO, CO2, and NH3 also present co-desorption peaks with CH3OH, which is the only species that segregated enough to allow detection in the IR spectra. These results reproduce the heating of circumstellar ices in hot cores and can be also applied to the late thermal evolution of comets.

  20. Determination of the oxygen content in superconducting and related cuprates using temperature-programmed reduction

    NASA Astrophysics Data System (ADS)

    Halasz, Istvan; Jen, Hung-Wen; Brenner, Alan; Shelef, Mordecai; Kao, Sendjaja; Simon Ng, K. Y.

    1991-06-01

    The oxygen content and reducibilities of four base metal oxides, six nonconducting cuprates, and three superconducting cuprates were investigated by temperature-programmed reduction (TPR) from 30 to 900°C. It was shown that the copper, bismuth, and thallium ions of these oxides were reduced to the zero valence state. Thus, TPR is a useful technique for determining the actual oxygen stoichiometry of cuprates. For multiphase Bi 2CaSr 2Cu 2O 8+ x and Tl 2CaBa 2Cu 2O 8+ x superconductors pretreated in air, x was found to be 2 ± 0.2 and 1 ± 0.2, respectively. Both values are significantly higher than previously reported. The reduction of superconducting and related cuprates required higher temperatures than CuO, but the reducibility of CuO decreased when it was calcined in air at 940°C. The Bi- and Y-based superconducting cuprates exhibited the lowest reducibility among the samples investigated.

  1. Tritium permeation and desorption in reduced activation martensitic steels studied in EXOTIC-9/1 irradiation experiment

    NASA Astrophysics Data System (ADS)

    Fedorov, A. V.; van Til, S.; Magielsen, A. J.; Stijkel, M. P.

    2013-11-01

    The EXOTIC-9/1 has been irradiated in the High Flux Reactor in Petten within the European framework for the development of the helium cooled pebble bed breeder concept. The EXOTIC-9/1 irradiation assembly consists of a pebble bed with Li2TiO3 pebbles enclosed in a EUROFER97 containment. The irradiation of EXOTIC-9/1 proceeded for 301 full power days reaching 1.3 dpa in steel. Irradiation temperatures varied between 613 and 853 K. Tritium permeation in a EUROFER97 containment wall was studied, in-pile, during temperature and purge gas chemistry transients. Under reference purge gas conditions (He + 0.1%H2) permeation proceeded in the diffusion-limited regime. Tritium permeability in EUROFER97 was obtained from analysis of the in-pile data. During the post irradiation examination program a number of EUROFER97 containment wall segments were ramp annealed in a temperature programmed desorption setup. This study determines the amount of tritium retained in the samples and presents analysis of the desorption spectra.

  2. Hydrogen Desorption Behavior of Nickel-Chloride-Catalyzed Stoichiometric Li4BN3H10

    NASA Astrophysics Data System (ADS)

    Pinkerton, Frederick; Meyer, Martin

    2009-03-01

    Li-B-N-H quaternary hydrides with the ?-phase crystal structure form over a range of compositions between Li3BN2H8 and Li4BN3H10 and have up to 11.9 wt% hydrogen capacity. Previous work focused on the non-equilibrium Li3BN2H8 composition created by ball milling because it has maximum hydrogen release and minimum NH3 co-generation. Here we report the hydrogen and NH3 release characteristics of ?-phase material having the equilibrium Li4BN3H10 composition. In the absence of a dehydrogenation catalyst, H2 and NH3 were released simultaneously in roughly equal quantities by weight (or about 10% NH3 by volume) at temperatures above 240 C. Adding Ni in the form of NiCl2 as a dehydrogenation catalyst reduced the H2 release temperature by 122 C. NH3 release, in contrast, still occurred only at the higher temperature. As a result, decomposition occurred in two steps separated in temperature, dominated by H2 gas at low temperature and NH3 at high temperature. The two gases clearly evolved in two distinct reactions that are coincident in uncatalyzed Li4BN3H10, but can be separated by a dehydrogenation catalyst. We expect that NH3 co-generation could be completely eliminated at sufficiently low dehydrogenation temperatures.

  3. Fundamental data on the desorption of pure interstellar ices

    NASA Astrophysics Data System (ADS)

    Brown, Wendy A.; Bolina, Amandeep S.

    2007-01-01

    The desorption of molecular ices from grain surfaces is important in a number of astrophysical environments including dense molecular clouds, cometary nuclei and the surfaces and atmospheres of some planets. With this in mind, we have performed a detailed investigation of the desorption of pure water, pure methanol and pure ammonia ices from a model dust-grain surface. We have used these results to determine the desorption energy, order of desorption and the pre-exponential factor for the desorption of these molecular ices from our model surface. We find good agreement between our desorption energies and those determined previously; however, our values for the desorption orders, and hence also the pre-exponential factors, are different to those reported previously. The kinetic parameters derived from our data have been used to model desorption on time-scales relevant to astrophysical processes and to calculate molecular residence times, given in terms of population half-life as a function of temperature. These results show the importance of laboratory data for the understanding of astronomical situations whereby icy mantles are warmed by nearby stars and by other dynamical events.

  4. THERMAL DESORPTION...NOW YOU'RE COOKIN'

    EPA Science Inventory

    Thermal desorption includes a number of ex situ processes that use either direct or indirect heat exchange to heat a waste material to volatilize organic materials. hermal desorption systems typically operate at soil treatment temperatures in the range of 400 to 600 degrees F to ...

  5. SOFT LASER DESORPTION IONIZATION -MALDI, DIOS AND NANOSTRUCTURES

    E-print Network

    Vertes, Akos

    Chapter 20 SOFT LASER DESORPTION IONIZATION - MALDI, DIOS AND NANOSTRUCTURES Akos Veites Department desorption ionization (MALDI). In this method, the sample is mixed with an organic matrix that efficiently the mass spectrometric determination of their accurate mass. The combination of MALDI with mass

  6. Impact of molecular clustering inside nanopores on desorption processes.

    PubMed

    Tsotsalas, Manuel; Hejcik, Pavel; Sumida, Kenji; Kalay, Ziya; Furukawa, Shuhei; Kitagawa, Susumu

    2013-03-27

    Understanding the sorption kinetics of nanoporous systems is crucial for the development and design of novel porous materials for practical applications. Here, using a porous coordination polymer/quartz crystal microbalance (PCP/QCM) hybrid device, we investigate the desorption of various vapor molecules featuring different degrees of intermolecular (hydrogen bonding) or molecule-framework interactions. Our findings reveal that strong intermolecular interactions lead to the desorption process proceeding via an unprecedented metastable state, wherein the guest molecules are clustered within the pores, causing the desorption rate to be temporarily slowed. The results demonstrate the considerable impact of the chemical nature of an adsorbate on the kinetics of desorption, which is also expected to influence the efficiency of certain processes, such as desorption by gas purge. PMID:23470206

  7. Charge Assisted Laser Desorption/Ionization Mass Spectrometry of Droplets

    PubMed Central

    Jorabchi, Kaveh; Westphall, Michael S.; Smith, Lloyd M.

    2008-01-01

    We propose and evaluate a new mechanism to account for analyte ion signal enhancement in ultraviolet-laser desorption mass spectrometry of droplets in the presence of corona ions. Our new insights are based on timing control of corona ion production, laser desorption, and peptide ion extraction achieved by a novel pulsed corona apparatus. We demonstrate that droplet charging rather than gas-phase ion-neutral reactions is the major contributor to analyte ion generation from an electrically isolated droplet. Implications of the new mechanism, termed charge assisted laser desorption/ionization (CALDI), are discussed and contrasted to those of the laser desorption atmospheric pressure chemical ionization method (LD-APCI). It is also demonstrated that analyte ion generation in CALDI occurs with external electric fields about one order of magnitude lower than those needed for atmospheric pressure matrix assisted laser desorption/ionization or electrospray ionization of droplets. PMID:18387311

  8. An unprecedented two-dimensional polymeric [Zn(OOC–C 6H 4–COO) 2] n 2?[ +H 3N–(CH 2) 3–NH 3 +] n system bearing one-dimensional chain of zinc(II) bis(phthalate) dianions held by propane-1,3-diammonium cations: Crystal structure, thermal and fluorescent properties

    Microsoft Academic Search

    M. Padmanabhan; K. C. Joseph; Vedavati G. Puranik; Xiaoying Huang; Jing Li

    2007-01-01

    A novel zinc(II) phthalate compound, [Zn{C6H4(COO)2}2]n2?[NH3–(CH2)3–NH3]n2+, 1 which contains four different phthalate moieties coordinated to the Zn(II) ion through one each of their carboxylate moieties in a ?1-form and each phthalate moiety acting as a bridging unit with an overall tetrahedral geometry around the metal ion has been prepared and structurally characterized. The structure is unique in the sense that

  9. Field desorption mass spectrometry of oligosaccharides

    PubMed Central

    Linscheid, Michael; D'Angona, Jay; Burlingame, Alma L.; Dell, Anne; Ballou, Clinton E.

    1981-01-01

    Field desorption mass spectrometry has been used to analyze carbohydrate polymers with 5 to 14 hexose units without prior derivatization. In all examples, the molecular weight of the oligosaccharide could be determined by means of the abundant quasimolecular ions of the type MNa+, MH+, MNa22+, and MNa33+. Fragmentation at glycosidic linkages was observed in varying extents. The reduced oligosaccharide Man8GlcNAcH2, obtained from IgM [Cohen, R. E. & Ballou, C. E. (1980) Biochemistry 19, 4345-4358], gave quasimolecular ion signals MNa+ at m/z 1544, MH+ at m/z 1522, MNa22+ at m/z 784, and MNa33+ at m/z 530, all corresponding to its assumed molecular weight of 1519.5. Mycobacterial methylmannose polysaccharides with the general structure ManxMeMany-OCH3 [Yamada, H., Cohen, R. E. & Ballou, C. E. (1979) J. Biol. Chem. 254, 1972-1979] were also successfully analyzed. Man1MeMan13-OCH3, the largest homolog, gave the expected signal of the quasimolecular ion MNa+ at m/z 2506. The larger polysaccharides were analyzed by using a KRATOS MS-50 mass spectrometer with a high-field magnet enabling full sensitivity to be maintained up to 3000 atomic mass units. Polysaccharides up to m/z 1978 were analyzed by using a KRATOS MS-9 mass spectrometer operated at 4 Kv. The signal-to-noise ratio, which becomes a serious problem in field desorption mass spectrometry at low accelerating voltages, and the low instrument sensitivity were improved considerably by our use of a method of adding scans with low total ion currents obtained over a longer desorption time. In this way, we obtained complete sequence information on methylmannose polysaccharides up to Man1MeMan9-OCH3(MNa+ at m/z 1802). Analysis of a presumed Man1MeMan7-OCH3, gave a spectrum consistent only with the structure Man2MeMan6-OCH3, revealing the existence of a methylmannose homolog with 2 unmethylated mannoses at the nonreducing end of the chain. PMID:6940169

  10. The Generation of Surface-bound Exospheres via Electron-Stimulated Desorption (and Related Phenomena): Results from Apollo samples and Hermian Regolith Simulants

    NASA Astrophysics Data System (ADS)

    Bennett, C.; Poston, M.; McLain, J. L.; Orlando, T. M.

    2014-12-01

    The generation of surface-bound exospheres present around the Moon, Mercury and other airless rocky bodies are produced primarily by the interaction of micrometeoroid impacts and charged particles from the solar wind, and magnetospheres with those surfaces. While the study of the interactions of both micrometeoroids and ion sputtering are well investigated, the contributions arising from energetic electron interactions are typically less-well established. Observations from the Fast Imaging Plasma Spectrometer (FIPS), taken < 400 km from the surface, have shown a plasma cusp with energetic heavy ions (i.e. Na+- and O+-groups) for which the source has not been determined. However, the precipitation of keV electrons onto the surfaces of Mercury has recently been inferred from measurements using the X-Ray Spectrometer (XRS) instrument onboard the MESSENGER spacecraft observations of the night-side of Mercury. A newly developed global kinetic transport model suggests that electron-stimulated desorption (ESD), and possibly light ion stimulated desorption (ISD), can directly yield ions that can be transported and dynamically accelerated to the plasma cusp regions observed by FIPS. In addition, keV electrons and ions from the solar wind and Earth's magnetosphere frequently bombard with the lunar surface. Here, we present some of the most recent results from our ongoing work studying the effects of photon-stimulated desorption (PSD), ion-stimulated desorption (ISD) and implantation, as well as electron-stimulated desorption (ESD). Apollo samples collected from both the lunar highland and Mare regions, as well as simulants of the Mercury Regolith have been investigated. The temperature- (100-600 K) and energy-dependence (threshold - 2 keV) of ESD time-of-flight (ToF) results will be presented for these materials along with some preliminary results from our group based on photon-desorption studies of water on lunar material, temperature-programmed desorption (TPD) studies of water covered regolith and dusts, as well as the effects of ion implantation/sputtering using keV H+ ions on ESD-ToF results. The implications of these results in the context of current observations will be discussed.

  11. Ti or Sn doping as a way to increase activity and sulfur tolerance of Mn/CeO2 catalyst for low temperature NH3 selective catalytic reduction of NO

    NASA Astrophysics Data System (ADS)

    Xiong, Yan; Tang, Changjin; Dong, Lin

    2015-04-01

    Mn/CeO2 catalysts modified by doping of Ti or Sn were investigated for low temperature selective catalytic reduction (SCR) of NO by NH3 with the aim of studying the effects of Ti, Sn doping on the catalytic performance. Ceria-based solid solutions (Ce0.8Ti0.2O2 and Ce0.8Sn0.2O2) were synthesized via inverse co-precipitation, and used as supports to prepare MnOx/Ce0.8M0.2O2 (M =Ti4+, Sn4+) catalysts through wetness impregnation method. The results showed that doping of Ti or Sn to the CeO2 support increase the NO removal efficiency. A NO conversion of more than 90 % was obtained over the Mn/CeTi catalyst at the temperature window of 175 ~ 300 °C under a gas hourly space velocity (GHSV) of 60,000 mL•g-1•h-1. Catalysts modified by Ti and Sn were also found to obtain higher SO2 resistance than Mn/CeO2 catalyst. More than 90% NO conversion and 95% N2 selectivity could be provided by Mn/CeTi catalyst in the presence of 100 ppm SO2 at 250 °C for 10 h. A series of characterization techniques, namely XRD, BET, H2-TPR, XPS, NH3-TPD and in situ DRIFTS were used to elucidate the structure and surface properties of the obtained supports and catalysts. The results indicate that doping of Ti or Sn brings about catalysts with favorable properties such as higher BET surface area, better oxygen storage capacity and stronger surface acidity. The relative amount of Mn4+, Ce3+, adsorbed oxygen species and oxygen vacancies on the surface of catalysts are in the order of Mn/CeTi?Mn/CeSn?Mn/CeO2, which is thought to make positive a contribution to the low-temperature SCR activity. The promoted SCR activity is considered as well to be related to the dual redox cycles in Mn/CeTi (Mn4+ + Ce3+ ? Mn3+ + Ce4+, Ce4+ + Ti3+ ? Ce3+ + Ti4+) and Mn/CeSn (Mn4+ + Ce3+ ? Mn3+ + Ce4+, Ce4+ + Sn2+ ? Ce3+ + Sn4+ ) catalysts.

  12. Copper desorption from Gelidium algal biomass.

    PubMed

    Vilar, Vítor J P; Botelho, Cidália M S; Boaventura, Rui A R

    2007-04-01

    Desorption of divalent copper from marine algae Gelidium sesquipedale, an algal waste (from agar extraction industry) and a composite material (the algal waste immobilized in polyacrylonitrile) was studied in a batch system. Copper ions were first adsorbed until saturation and then desorbed by HNO(3) and Na(2)EDTA solutions. Elution efficiency using HNO(3) increases as pH decreases. At pH=1, for a solid to liquid ratio S/L=4gl(-1), elution efficiency was 97%, 95% and 88%, the stoichiometric coefficient for the ionic exchange, 0.70+/-0.02, 0.73+/-0.05 and 0.76+/-0.06 and the selectivity coefficient, 0.93+/-0.07, 1.0+/-0.3 and 1.1+/-0.3, respectively, for algae Gelidium, algal waste and composite material. Complexation of copper ions by EDTA occurs in a molar proportion of 1:1 and the elution efficiency increases with EDTA concentration. For concentrations of 1.4, 0.88 and 0.57 mmoll(-1), the elution efficiency for S/L=4gl(-1), was 91%, 86% and 78%, respectively, for algae Gelidium, algal waste and composite material. The S/L ratio, in the range 1-20gl(-1), has little influence on copper recovery by using 0.1M HNO(3). Desorption kinetics was very fast for all biosorbents. Kinetic data using HNO(3) as eluant were well described by the mass transfer model, considering the average metal concentration in the solid phase and the equilibrium relationship given by the mass action law. The homogeneous diffusion coefficient varied between 1.0 x 10(-7)cm(2)s(-1) for algae Gelidium and 3.0 x 10(-7)cm(2)s(-1) for the composite material. PMID:17276480

  13. Field scale measurements of NH3 emissions

    NASA Astrophysics Data System (ADS)

    Neftel, Albrecht; Ammann, Christof; Kuhn, Uwe; Sintermann, Jörg; Lehuger, Simon; Gärtner, Andrea; Hirschberger, Rainer

    2010-05-01

    The uncertainty in the ammonia emissions after application of organic manure contributes to a large extent to the overall uncertainties of the nitrogen budget of managed grassland systems (Ammann et al., 2009). Due to the sticky nature of the ammonia molecule and the variability of the emission fluxes the experimental determination is still a major challenge and a wide spread range of emission factors can be found in the literature. We report on two field experiments performed in August 2009 at the NitroEurope site in Oensingen, Switzerland. The ammonia emission flux after liquid manure application was investigated simultaneously by various micrometeorological methods: (1) a mass balance approach measuring the horizontal advection flux with open-path FTIR sensors (Gärtner et al., 2008), (2) aerodynamic gradient methods, and (3) eddy covariance measurements based on a novel fast ammonia analyser. Due to the sequential application of the manure and the fast decrease of the ammonia volatilisation, detailed footprint calculations (Neftel et al., 2008) and corrections with a high temporal resolution were crucial for obtaining representative emission fluxes. The plausibility of flux measurements has been evaluated with back trajectories simulations (WindTrax, Flesch et al., 2009). The results of all applied flux measurement methods confirmed the low emission levels found earlier by Spirig et al. (2009). A comparison of the field observations with results of process oriented models showed considerable differences in the temporal course of the ammonia emission indicating the need for improvements of the models. References: Ammann, C., Spirig, C., Leifeld, J. and Neftel, A.: Assessment of the nitrogen and carbon budget of two managed temperate grassland fields, Agric. Ecosyst. Environ., 133, 150-162, 2009. Flesch, T.K., Harper, L.A., Desjardins, R.L., Gao, Z., and Crenna, B.: Multi-Source Emission Determination Using an Inverse-Dispersion Technique. Boundary-Layer Meteorol. 132, 11-30, 2009. Gärtner, A., Hirschberger, R. und Kotzian, F.: Estimation of diffuse ammonia emissions during and after slurry spreading; Gefahrstoffe - Reinhaltung der Luft 68, 149-155, 2008. Neftel, A., Spirig, C. and Ammann, C.: Application and test of a simple tool for operational footprint evaluations, Environ. Pollut., 152, 644-652, 2008. Spirig, C., Flechard, C.R., Neftel, A., Ammann, C.: The annual ammonia budget of fertilised cut grassland. 1- Micrometeorological flux measurements and emissions after slurry application, Biogeosciences Discuss., 6, 9583-9625, 2009

  14. [Desorption characteristics of phosphorus in tea tree rhizosphere soil].

    PubMed

    Yang, Wei; Zhou, Wei-Jun; Bao, Chun-Hong; Miao, Xiao-Lin; Hu, Wen-Min

    2013-07-01

    In order to explore the phosphorus (P) release process and its supply mechanism in tea tree rhizosphere soil, an exogenous P adsorption and culture experiment was conducted to study the P desorption process and characters in the tea tree rhizosphere soils having been cultivated for different years and derived from different parent materials. The least squares method was used to fit the isotherms of P desorption kinetics. There was an obvious difference in the P desorption process between the rhizosphere soils and non-rhizosphere soils. The P desorption ability of the rhizosphere soils was significantly higher than that of the non-rhizosphere soils. As compared with non-rhizosphere soils, rhizosphere soils had higher available P content, P desorption rate, and beta value (desorbed P of per unit adsorbed P), with the average increment being 5.49 mg x kg(-1), 1.7%, and 24.4%, respectively. The P desorption ability of the rhizosphere soils derived from different parent materials was in the order of granite > quaternary red clay > slate. The average available P content and P desorption ability of the rhizosphere soils increased with increasing cultivation years. PMID:24175512

  15. Promotion effects of SiO2 or/and Al2O3 doped CeO2/TiO2 catalysts for selective catalytic reduction of NO by NH3.

    PubMed

    Zhao, Wenru; Tang, Yu; Wan, Yaping; Li, Liang; Yao, Si; Li, Xiaowei; Gu, Jinlou; Li, Yongsheng; Shi, Jianlin

    2014-08-15

    A series of the CeO2-based catalysts loaded on TiO2, TiO2-SiO2, TiO2-Al2O3, and TiO2-SiO2-Al2O3 supports were prepared by incipient impregnation method for the selective catalytic reduction (SCR) of NO by NH3 in the presence of oxygen. The SCR activities of the catalysts with different supports increases in the order of Ce/TiO2 < Ce/TiO2-20SiO2 ? Ce/TiO2-3.5Al2O3 < Ce/TiO2-20SiO2-3.5Al2O3. The Ce/TiO2-20SiO2-3.5Al2O3 catalyst showed 100% NO conversion in the temperature range of 250-425°C and 100% N2 selectivity in the whole temperature range. The catalytic activity of Ce/TiO2-20SiO2-3.5Al2O3 exhibited good stability and strong resistance to SO2 and H2O poisoning. The co-introduction of SiO2 and Al2O3 into TiO2 could increase the amount of chemisorbed oxygen and Lewis acid sites on the surface of catalyst, which should be responsible for the excellent SCR activity. PMID:24996153

  16. A 3D metal halide framework in the organic-inorganic compound (H 3N(CH 2) 2SS(CH 2) 2NH 3) 3Pb 5I 16

    NASA Astrophysics Data System (ADS)

    Louvain, Nicolas; Mercier, Nicolas

    2008-10-01

    A novel organic-inorganic hybrid compound, namely (H 3N(CH 2) 2SS(CH 2) 2NH 3) 3Pb 5I 16, was synthesized from the reaction of lead iodide, cystamine chloride, and concentrated hydriodic acid in ethanol under solvothermal condition. According to the results of X-ray single crystal structural analysis, its 3D inorganic framework was constructed from lead iodide octahedra in corner-, edge- or face-sharing mode, which can be considered as connected staircase-like sheets. Disordered cystamine molecules are located both in the cages defined between two consecutive steps of the staircase-like network and in the channels formed by 10 adjacent bridged PbI 6 octahedra. The formation and high stability of such a unique 3D metal halide network can be partly attributed to the unusual weak interactions between disulfides and iodides ( d(S⋯I) ? 3.55 Å) in the structure. Monoclinic, space group: C2/ c, a = 35.396(2) Å, b = 8.984(1) Å, c = 22.623(2) Å, ? = 120.66(2)°, V = 6188.1(9) Å 3, Z = 4.

  17. Selected ion flow drift tube studies of the reactions of Si + (2P) with HCl, H2O, H2S, and NH3: Reactions which produce atomic hydrogen

    NASA Astrophysics Data System (ADS)

    Glosík, J.; Zakou?il, P.; Lindinger, W.

    1995-10-01

    The reaction rate coefficients, k, for the reactions of ground-state Si+(2P) with HCl, H2O, H2S, and NH3, have been measured as a function of reactant ion/reactant neutral center-of-mass kinetic energy, KECM, in a selected ion flow drift tube (SIFDT) apparatus, operated with helium at a temperature 298±2 K. The values k of the studied reactions have very pronounced, negative energy dependencies; the rate coefficients decrease by about 1 order of magnitude as KECM increase from near thermal values to ˜2 eV. The results are interpreted in terms of a simple model assuming the reactions to proceed via the formation of long-lived complexes. These intermediate complexes decompose back to reactants or forward to products, the unimolecular decomposition rate coefficients for these reactions being k1 and k2, respectively. It is found that a power law of the form k-1/k2=const(KECM)m closely describes each reaction.

  18. A multiple system of high-mass YSOs surrounded by disks in NGC 7538 IRS1 . Gas dynamics on scales of 10-700 AU from CH3OH maser and NH3 thermal lines

    NASA Astrophysics Data System (ADS)

    Moscadelli, L.; Goddi, C.

    2014-06-01

    Context. It has been claimed that NGC 7538 IRS1 is a high-mass young stellar object (YSO) with 30 M?, surrounded by a rotating Keplerian disk, probed by a linear distribution of methanol masers. The YSO is also powering a strong compact Hii region or ionized wind, and is driving at least one molecular outflow. The axis orientations of the different structures (ionized gas, outflow, and disk) are, however, misaligned, which has led to the different competing models proposed to explain individual structures. Aims: We investigate the 3D kinematics and dynamics of circumstellar gas with very high linear resolution, from tens to 1500 AU, with the ultimate goal of building a comprehensive dynamical model for what is considered the best high-mass accretion disk candidate around an O-type young star in the northern hemisphere. Methods: We used high-angular resolution observations of 6.7 GHz CH3OH masers with the EVN, NH3 inversion lines with the JVLA B-Array, and radio continuum with the VLA A-Array. In particular, we employed four different observing epochs of EVN data at 6.7 GHz, spanning almost eight years, which enabled us to measure line-of-sight (l.o.s.) accelerations and proper motions of CH3OH masers, besides l.o.s. velocities and positions (as done in previous works). In addition, we imaged highly excited NH3 inversion lines, from (6,6) to (13,13), which enabled us to probe the hottest molecular gas very close to the exciting source(s). Results: We confirm previous results that five 6.7 GHz maser clusters (labeled from "A" to "E") are distributed over a region extended N-S across ?1500 AU, and are associated with three components of the radio continuum emission. We propose that these maser clusters identify three individual high-mass YSOs in NGC 7538 IRS1, named IRS1a (associated with clusters "B" and "C"), IRS1b (associated with cluster "A"), and IRS1c (associated with cluster "E"). We find that the 6.7 GHz masers distribute along a line, with a regular variation in VLSR with position, along the major axis of the distribution of maser cluster "A" and the combined clusters "B" + "C". A similar VLSR gradient (although shallower) is also detected in the NH3 inversion lines. Interestingly, the variation in VLSR with projected position is not linear but quadratic for both maser clusters. We measure proper motions for 33 maser features, which have an average amplitude (4.8 ± 0.6 km s-1) similar to the variation in VLSR across the maser cluster, and are approximately parallel to the clusters' elongation axes. By studying the time variation in the maser spectrum, we also derive l.o.s. accelerations for 30 features, with typical amplitude of ~ 10-3-10-2 km s-1 yr-1. We modeled the masers in both clusters "A" and "B" + "C" in terms of an edge-on disk in centrifugal equilibrium. Based on our modeling, masers of clusters "B" + "C" may trace a quasi-Keplerian ~1 M?, thin disk, orbiting around a high-mass YSO, IRS1a, of up to ?25 M?. This YSO dominates the bolometric luminosity of the region. The disk traced by the masers of cluster "A" is both massive (?16 M? inside a radius of ?500 AU) and thick (opening angle ?45°), and the mass of the central YSO, IRS1b, is constrained to be at most a few M?. Towards cluster "E", NH3 and 6.7 GHz masers trace more quiescent dynamics than for the other clusters. The presence of a radio continuum peak suggests that the YSO associated with the cluster "E", IRS1c, may be an ionizing, massive YSO as well. Conclusions: We present compelling evidence that NGC 7538 IRS1 is forming not just one single high-mass YSO, but consists of a multiple system of high-mass YSOs, which are surrounded by accretion disks and are probably driving individual outflows. This new model naturally explains all the different orientations and disk/outflow structures proposed for the region in previous models. Table 2 and Appendix A are ava

  19. Structure of duplex DNA containing the cisplatin 1,2-{Pt(NH)3)2}2+-d(GpG) cross-link at 1.77 Å resolution

    PubMed Central

    Todd, Ryan C.; Lippard, Stephen J.

    2010-01-01

    We report the 1.77-Å resolution X-ray crystal structure of a dodecamer DNA duplex with the sequence 5?-CCTCTGGTCTCC-3? that has been modified to contain a single engineered 1,2-cis-{Pt(NH)3)2}2+-d(GpG) cross-link, the major DNA adduct of cisplatin. These data represent a significant improvement in resolution over the previously published 2.6-Å structure. The ammine ligands in this structure are clearly resolved, leading to improved visualization of the cross-link geometry with respect to both the platinum center and to the nucleobases, which adopt a higher energy conformation. Also better resolved are the deoxyribose sugar puckers, which allow us to re-examine the global structure of platinum-modified DNA. Another new feature of this model is the location of four octahedral [Mg(H2O)6]2+] ions associated with bases in the DNA major groove and the identification of 124 ordered water molecules that participate in hydrogen bonding interactions with either the nucleic acid or the diammineplatinum(II) moiety. PMID:20541266

  20. The Effect of Selective Desorption Mechanisms During Interstellar Ice Formation

    NASA Astrophysics Data System (ADS)

    Kalv?ns, J.

    2015-04-01

    Major components of ices on interstellar grains in molecular clouds—water and carbon oxides—occur at various optical depths. This implies that selective desorption mechanisms are at work. An astrochemical model of a contracting low-mass molecular cloud core is presented. Ice was treated as consisting of the surface and three subsurface layers (i.e., sublayers). Photodesorption, reactive desorption, and indirect reactive desorption were investigated. The latter manifests itself through desorption from H+H reaction on grains. Desorption of shallow subsurface species was also included. Modeling results suggest the existence of a “photon-dominated ice” during the early phases of core contraction. Subsurface ice is chemically processed by interstellar photons, which produces complex organic molecules (COMs). Desorption from the subsurface layer results in high COM gas-phase abundances at AV = 2.4–10 mag. This may contribute toward an explanation for COM observations in dark cores. It was found that photodesorption mostly governs the onset of ice accumulation onto grains. Reaction-specific reactive desorption is efficient for small molecules that form via highly exothermic atom-addition reactions. Higher reactive desorption efficiency results in lower gas-phase abundances of COMs. Indirect reactive desorption allows for closely reproducing the observed H2O:CO:CO2 ratio toward a number of background stars. Presumably, this can be done by any mechanism whose efficiency fits with the sequence CO?slant C{{O}2}\\gg {{H}2}O. After the freeze-out has ended, the three sublayers represent chemically distinct parts of the mantle. The likely AV threshold for the appearance of CO ice is 8–10.5 mag. The lower value is supported by observations.