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1

Decomposition of NH3 on Ir(100): A Temperature Programmed Desorption Study A. K. Santra, B. K. Min, C. W. Yi, Kai Luo, T. V. Choudhary, and D. W. Goodman*  

E-print Network

Decomposition of NH3 on Ir(100): A Temperature Programmed Desorption Study A. K. Santra, B. K. Min 27, 2001 Ammonia adsorption has been studied on an Ir(100) surface in the temperature range 100-410 K. In contrast to previous studies on Ir(111), approximately 12% of the chemisorbed ammonia undergoes stepwise

Goodman, Wayne

2

A dynamic calibration technique for temperature programmed desorption spectroscopy  

NASA Astrophysics Data System (ADS)

A novel, rapid and accurate calibration procedure as a means for quantitative gas desorption measurement by temperature programmed desorption (TPD) spectroscopy is presented. Quantitative measurement beyond the linear regime of the instrument is achieved by associating an instantaneous calibrated molar flow rate of gas to the detector response. This technique is based on fundamental methods, and is independently verified by comparison to the hydrogen desorption capacity of a known standard metal hydride with known stoichiometry. The TPD calibration procedure described here may be used for any pure gas, and the accuracy is demonstrated for the specific case of hydrogen.

Hurst, K. E.; Heben, M. J.; Blackburn, J. L.; Gennett, T.; Dillon, A. C.; Parilla, P. A.

2013-02-01

3

Conductance-Based Temperature Programmed Desorption with Single Defect Resolution  

NASA Astrophysics Data System (ADS)

The controlled functionalization of nanotubes and graphene requires methods of chemically attacking these inert surfaces and of removing unwanted oxidation damage. The appeal of reversible chemistries is rarely achieved: the degraded electrical properties of reduced graphene oxide compared to pristine graphene indicates residual damage that remains poorly understood. Using a high temperature, UHV apparatus to perform electrical measurements in situ, we investigate the thermal desorption of adducts that can restore conductivity in oxidized nanographites. The majority of our measurements are accomplished using SWCNTs, due to their enhanced sensitivity to even single point defects. Discrete conductance jumps accompanying the removal of different types of adducts provide a characterization method that directly distinguishes the relative electronic effects of phenolic, epoxide, and carboxylic defects. The electronic measurements complement more traditional, temperature programmed desorption from bulk material, which is insensitive to electronic disorder.

Pan, Deng; Sims, Patrick C.; Corso, Brad L.; Collins, Philip G.

2011-03-01

4

Reduction Kinetics of Graphene Oxide Determined by Temperature Programmed Desorption  

NASA Astrophysics Data System (ADS)

Graphene oxide, which is an electrical insulator, shows promise for use in several technological applications such as dielectric layers in nanoscale electronic devices or as the active region of chemical sensors. In principle, graphene oxide films could also be used as a precursor for the formation of large-scale graphene films by either thermal or chemical reduction of the graphene oxide. In order to determine the thermal stability and reduction kinetics of graphene oxide, temperature program desorption (TPD) measurements have been performed on multilayer films of graphene oxide deposited on SiO2/Si(100) substrates. The graphene oxide was exfoliated from the graphite oxide source material by slow-stirring in aqueous solution, which produces single-layer platelets with an average lateral size of ˜10 ?m. From the TPD measurements, it was determined that the decomposition process begins at ˜80 ^oC. The primary desorption products of the graphene oxide films for temperatures up to 300 ^oC are H2O, CO2, and CO, with only trace amounts of O2 being detected. An activation energy of 1.4 eV/molecule was determined by assuming an Arrhenius dependence for the decomposition process.

Ventrice, Carl; Clark, Nicholas; Field, Daniel; Geisler, Heike; Jung, Inhwa; Yang, Dongxing; Piner, Richard; Ruoff, Rodney

2009-10-01

5

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

NASA Astrophysics Data System (ADS)

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.

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

2014-10-01

6

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

SciTech Connect

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.

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

1991-03-15

7

Statistical analysis of blister bursts during temperature-programmed desorption of deuterium-implanted polycrystalline tungsten  

NASA Astrophysics Data System (ADS)

During temperature-programmed desorption (TPD) of stress-relieved polycrystalline tungsten samples exposed to a deuterium plasma, short, intense bursts of D2 were observed on the low-temperature flank of the main desorption peak. These bursts are attributed to the rupturing of blisters filled with high-pressure D2 gas. A statistical analysis of the size distribution and temporal correlation of the bursts is presented. The influence of different measurement intervals and TPD heating rates on the observed bursts is simulated based on these statistics and compared to the experimental results. The contribution of bursts to the total D inventory in the sample is also estimated.

Manhard, A.; Toussaint, U. v.; Dürbeck, T.; Schmid, K.; Jacob, W.

2011-12-01

8

Monte Carlo simulations of temperature-programmed and isothermal desorption from single-crystal surfaces  

SciTech Connect

The kinetics of temperature-programmed and isothermal desorption have been simulated with a Monte Carlo model. Included in the model are the elementary steps of adsorption, surface diffusion, and desorption. Interactions between adsorbates and the metal as well as interactions between the adsorbates are taken into account with the Bond-Order-Conservation-Morse-Potential method. The shape, number, and location of the TPD peaks predicted by the simulations is shown to be sensitive to the binding energy, coverage, and coordination of the adsorbates. In addition, the occurrence of lateral interactions between adsorbates is seen to strongly effect the distribution of adsorbates is seen to strongly effect the distribution of adsorbates on the surface. Temperature-programmed desorption spectra of a single type of adsorbate have been simulated for the following adsorbate-metal systems: CO on Pd(100); H{sub 2} on Mo(100); and H{sub 2} on Ni(111). The model predictions are in good agreement with experimental observation. TPD spectra have also been simulated for two species coadsorbed on a surface; the model predictions are in qualitative agreement with the experimental results for H{sub 2} coadsorbed with strongly bound atomic species on Mo(100) and Fe(100) surfaces as well as for CO and H{sub 2} coadsorbed on Ni(100) and Rh(100) surfaces. Finally, the desorption kinetics of CO from Pd(100) and Ni(100) in the presence of gas-phase CO have been examined. The effect of pressure is seen to lead to an increase in the rate of desorption relative to the rate observed in the absence of gas-phase CO. This increase arises as a consequence of higher coverages and therefore stronger lateral interactions between the adsorbed CO molecules.

Lombardo, S.J. (California Inst. of Tech., Pasadena, CA (USA). Dept. of Chemical Engineering Lawrence Berkeley Lab., CA (USA))

1990-08-01

9

The oxidized soot surface: Theoretical study of desorption mechanisms involving oxygenated functionalities and comparison with temperature programed desorption experiments  

NASA Astrophysics Data System (ADS)

The desorption mechanism for oxygenated functionalities on soot is investigated by quantum mechanical calculations on functionalized polycyclic aromatic hydrocarbon (PAH) models and compared with recently published temperature programed desorption-mass spectrometry results. Substituents on PAHs of increasing size (up to 46 carbon atoms in the parent PAH) are chosen to reproduce the local features of an oxidized graphenic soot platelet. Initially, the study is carried out on unimolecular fragmentation (extrusion, in some cases) processes producing HO, CO, or CO2, in model ketones, carboxylic acids, lactones, anhydrides, in one aldehyde, one peroxyacid, one hydroperoxide, one secondary alcohol, and one phenol. Then, a bimolecular process is considered for one of the carboxylic acids. Furthermore, some cooperative effect which can take place by involving two vicinal carboxylic groups (derived from anhydride hydrolysis) is investigated for other four bifunctionalized models. The comparison between the computed fragmentation (desorption) barriers for the assessed mechanisms and the temperature at which maxima occur in TPD spectra (for HO, CO, or CO2 desorption) offers a suggestion for the assignment of these maxima to specific functional groups, i.e., a key to the description of the oxidized surface. Notably, the computations suggest that (1) the desorption mode from a portion of a graphenic platelet functionalized by a carboxylic or lactone groups is significantly dependent from the chemical and geometric local environment. Consequently, we propose that (2) not all carboxylic groups go lost at the relatively low temperatures generally stated, and (3) lactone groups can be identified as producing not only CO2 but also CO.

Barco, Gianluca; Maranzana, Andrea; Ghigo, Giovanni; Causà, Mauro; Tonachini, Glauco

2006-11-01

10

TEMPERATURE-PROGRAMMED DESORPTION: PRINCIPLES, INSTRUMENT DESIGN, AND DEMONSTRATION WITH NAALH4  

SciTech Connect

This article is a brief introduction to temperature-programmed desorption (TPD), an analytical technique devised to analyze, in this case, materials for their potential as hydrogen storage materials. The principles and requirements of TPD are explained and the different components of a generic TPD apparatus are described. The construction of a modified TPD instrument from commercially available components is reported together with the control and acquisition technique used to create a TPD spectrum. The chemical and instrumental parameters to be considered in a typical TPD experiment and the analytical utility of the technique are demonstrated by the dehydrogenation of titanium-doped NaAlH{sub 4} by means of thermally programmed desorption.

Stowe, A; Ragaiy Zidan, R

2006-11-07

11

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

E-print Network

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...

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

2007-01-01

12

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

E-print Network

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.

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

13

H(2)O Outgassing Properties of Fumed and Precipitated Silica Particles by Temperature-Programmed Desorption.  

PubMed

Temperature-programmed desorption was performed at temperatures up to 850 K on as-received fumed and precipitated silica particles. Physisorbed water molecules on both types of silica had activation energies in the range of 38-61 kJ/mol. However, the activation energies of desorption for chemisorbed water varied from approximately 80 to >247 kJ/mol for fumed silica, Cab-O-Sil-M-7D, and approximately 96 to 155 kJ/mol for precipitated silica, Hi-Sil-233. Our results suggest that physisorbed water can be effectively pumped away at room temperature (or preferably at 320 K) in a matter of hours. Chemisorbed water with high activation energies of desorption (>126 kJ/mol) will not escape silica surfaces in 100 years even at 320 K, while a significant amount of the chemisorbed water with medium activation energies (80-109 kJ/mol) will leave the silica surfaces in that time span. Most of the chemisorbed water with activation energies <126 kJ/mol can be pumped away in a matter of days in a good vacuum environment at 500 K. We had previously measured about 0.1-0.4 wt% of water in silica-reinforced polysiloxane formulations containing approximately 21% Cab-O-Sil-M-7D and approximately 4% Hi-Sil-233. Comparing present results with these formulations, we conclude that the adsorbed H(2)O and the Si-OH bonds on the silica surfaces are the major contributors to water outgassing from these types of silica-filled polymers. Copyright 2000 Academic Press. PMID:11017751

Dinh; Balooch; LeMay

2000-10-15

14

Surface Chemistry of Activated Carbons: Combining the Results of Temperature-Programmed Desorption, Boehm, and Potentiometric Titrations  

Microsoft Academic Search

Three samples of activated carbon were used for this study: two of wood and one of coal origin. The samples were further oxidized to study the effect of oxidation on the surface chemistry. The surface chemistry was characterized by using Boehm and potentiometric titrations, temperature-programmed desorption (TPD), and DRFTS. The results showed that oxidation introduces a variety of functional groups

Issa I. Salame; Teresa J. Bandosz

2001-01-01

15

First principles and experimental study of NH3 adsorptions on MnOx surface  

NASA Astrophysics Data System (ADS)

The oxidative abstraction of hydrogen from adsorbed ammonia is the first step in selective catalytic reduction (SCR) and NH3 adsorptions on the MnOx surfaces played a significant role in the mechanism of SCR with NH3. NH3 adsorptions on the Mn2O3 (2 2 2), Mn3O4 (2 1 1) and MnO2 (1 1 0) surfaces were investigated by the density functional theory (DFT) method. With more negative adsorption energy values, the Mn2O3 (2 2 2) and Mn3O4 (2 1 1) surfaces tended to be the favorable adsorption sites for NH3 molecule. In addition, the shorter MnN bonds indicated that NH3 adsorptions took place easily on Mn2O3 (2 2 2) and Mn3O4 (2 1 1) surfaces. According to the ammonia temperature programmed desorption (NH3-TPD) performance, Mn2O3 and Mn3O4 showed significantly higher amount of desorbed NH3, which was in good agreement with the DFT study. Meanwhile, the NH3-SCR performances of Mn2O3 and Mn3O4 for NO conversion below 433 K show higher performance than that of MnO2.

Fang, De; He, Feng; Li, Da; Xie, Junlin

2013-11-01

16

Adsorption and desorption of dibenzothiophene on Ag-titania studied by the complementary temperature-programmed XPS and ESR  

NASA Astrophysics Data System (ADS)

Adsorption, desorption and structure of the surface chemical compounds formed upon interaction of dibenzothiophene (DBT) in solution of n-octane with the sulfur-selective Ag/Titania sorbent for the ultradeep desulfurization of liquid fuels was characterized by the temperature-programmed X-ray photoemission spectroscopy (XPS) and Electron Spin Resonance. Adsorption of DBT proceeds via chemisorption via the oxygen-containing surface groups. Desorption of DBT and thermal regeneration of the “spent” Ag/Titania were studied by the complementary temperature-programmed XPS and ESR from 25 °C to 525 °C, in the high vacuum vs. air. The XPS spectrum of the pure DBT is reported for the first time.

Samokhvalov, Alexander; Duin, Evert C.; Nair, Sachin; Tatarchuk, Bruce J.

2011-02-01

17

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

NASA Astrophysics Data System (ADS)

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.

Vogt, Andrew Dale

1999-12-01

18

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

PubMed

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

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

2008-01-01

19

UV-Raman spectroscopy, X-ray photoelectron spectroscopy, and temperature programmed desorption studies of model and bulk heterogeneous catalysts  

SciTech Connect

X-ray photoelectron spectroscopy (XPS) and Temperature Programmed Desorption (TPD) have been used to investigate the surface structure of model heterogeneous catalysts in ultra-high vacuum (UHV). UV-Raman spectroscopy has been used to probe the structure of bulk model catalysts in ambient and reaction conditions. The structural information obtained through UV-Raman spectroscopy has been correlated with both the UHV surface analysis and reaction results. The present day propylene and ethylene polymerization catalysts (Ziegler-Natta catalysts) are prepared by deposition of TiCl{sub 4} and a Al(Et){sub 3} co-catalyst on a microporous Mg-ethoxide support that is prepared from MgCl{sub 2} and ethanol. A model thin film catalyst is prepared by depositing metallic Mg on a Au foil in a UHV chamber in a background of TiCl{sub 4} in the gas phase. XPS results indicate that the Mg is completely oxidized to MgCl{sub 2} by TiCl{sub 4} resulting in a thin film of MgCl{sub 2}/TiCl{sub x}, where x = 2, 3, and 4. To prepare an active catalyst, the thin film of MgCl{sub 2}/TiCl{sub x} on Au foil is enclosed in a high pressure cell contained within the UHV chamber and exposed to {approx}1 Torr of Al(Et){sub 3}.

Tewell, Craig R.

2002-08-19

20

Low-temperature selective catalytic reduction of NO with NH3 over nanoflaky MnOx on carbon nanotubes in situ prepared via a chemical bath deposition route  

NASA Astrophysics Data System (ADS)

Nanoflaky MnOx on carbon nanotubes (nf-MnOx@CNTs) was in situ synthesized by a facile chemical bath deposition route for low-temperature selective catalytic reduction (SCR) of NO with NH3. This catalyst was mainly characterized by the techniques of X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), N2 adsorption-desorption analysis, X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR) and NH3 temperature-programmed desorption (NH3-TPD). The SEM, TEM, XRD results and N2 adsorption-desorption analysis indicated that the CNTs were surrounded by nanoflaky MnOx and the obtained catalyst exhibited a large surface area as well. Compared with the MnOx/CNT and MnOx/TiO2 catalysts prepared by an impregnation method, the nf-MnOx@CNTs presented better NH3-SCR activity at low temperature and a more extensive operating temperature window. The XPS results showed that a higher atomic concentration of Mn4+ and more chemisorbed oxygen species existed on the surface of CNTs for nf-MnOx@CNTs. The H2-TPR and NH3-TPD results demonstrated that the nf-MnOx@CNTs possessed stronger reducing ability, more acid sites and stronger acid strength than the other two catalysts. Based on the above mentioned favourable properties, the nf-MnOx@CNT catalyst has an excellent performance in the low-temperature SCR of NO to N2 with NH3. In addition, the nf-MnOx@CNT catalyst also presented favourable stability and H2O resistance.Nanoflaky MnOx on carbon nanotubes (nf-MnOx@CNTs) was in situ synthesized by a facile chemical bath deposition route for low-temperature selective catalytic reduction (SCR) of NO with NH3. This catalyst was mainly characterized by the techniques of X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), N2 adsorption-desorption analysis, X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR) and NH3 temperature-programmed desorption (NH3-TPD). The SEM, TEM, XRD results and N2 adsorption-desorption analysis indicated that the CNTs were surrounded by nanoflaky MnOx and the obtained catalyst exhibited a large surface area as well. Compared with the MnOx/CNT and MnOx/TiO2 catalysts prepared by an impregnation method, the nf-MnOx@CNTs presented better NH3-SCR activity at low temperature and a more extensive operating temperature window. The XPS results showed that a higher atomic concentration of Mn4+ and more chemisorbed oxygen species existed on the surface of CNTs for nf-MnOx@CNTs. The H2-TPR and NH3-TPD results demonstrated that the nf-MnOx@CNTs possessed stronger reducing ability, more acid sites and stronger acid strength than the other two catalysts. Based on the above mentioned favourable properties, the nf-MnOx@CNT catalyst has an excellent performance in the low-temperature SCR of NO to N2 with NH3. In addition, the nf-MnOx@CNT catalyst also presented favourable stability and H2O resistance. Electronic supplementary information (ESI) available: TEM images, XRD patterns, N2 adsorption-desorption isotherms, TG-DTA curves, in situ time-resolved XRD patterns, stability test and H2O resistance study of the catalysts. See DOI: 10.1039/c3nr02631k

Fang, Cheng; Zhang, Dengsong; Cai, Sixiang; Zhang, Lei; Huang, Lei; Li, Hongrui; Maitarad, Phornphimon; Shi, Liyi; Gao, Ruihua; Zhang, Jianping

2013-09-01

21

The role of zinc(II) in the absorption-desorption of CO2 by aqueous NH3, a potentially cost-effective method for CO2 capture and recycling.  

PubMed

The absorption of CO2 by aqueous NH3 solutions has been investigated at atmospheric pressure and 0 degrees C. The CO2 absorption is fast and occurs with high efficiency (88-99%). The maximum CO2-removal efficiency increases slightly with the NH3 concentration. Addition of zinc(II) salts (as chloride, nitrate or sulfate) to the NH3 absorbent solution increases the overall CO2-absorption capacity without appreciably affecting the removal efficiency. Stripping of pure CO2 from HCO3(-) solutions is achieved by adding the calculated amount of ZnII salts, which under ambient conditions lead to rapid release of about 30-35% of the initially captured CO2. At the same time, about 65-70% of the captured CO2 is transformed into solid basic zinc carbonates. The recovery of these valuable solid products and the release of only 1/3 of free CO2 at room temperature and pressure reduces the cost of the overall process of CO2 capture, making it a potentially attractive method for CO2 capture on a larger scale. PMID:18605211

Mani, Fabrizio; Peruzzini, Maurizio; Barzagli, Francesco

2008-01-01

22

Thermal desorption of circumstellar and cometary ice analogs  

NASA Astrophysics Data System (ADS)

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.

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

2014-04-01

23

Thermomagnetic Torque in Nh3  

E-print Network

of (H/P) significantly less than (H/P), q, except for oxygen, which has two peaks one T, Vf . AD AI R, III AND G. R. M c C I U RG TABLE I . Senftleben-Beenakker parameter (H/I') f /2 for thermal conductivity and viscosity compared to Scott- torque... 5 000 14 800 DISCUSSION Measurements here indicate that NH3 has a Scott torque in the positive direction. A torque in the of which gives (H/P) ~ larger than (H/P)?2. The gas HD likewise has two Scott peaks and exhibits an anomalously small...

Adair, Thomas W.; McClurg, G. R.

1970-01-01

24

In situ supported MnOx-CeOx on carbon nanotubes for the low-temperature selective catalytic reduction of NO with NH3  

NASA Astrophysics Data System (ADS)

The MnOx and CeOx 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 NH3. X-Ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR) and NH3 temperature-programmed desorption (NH3-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 H2-TPR results suggested that there was a strong interaction between the manganese oxide and cerium oxide on the surface of CNTs. The NH3-TPD results demonstrated that the catalysts presented a larger acid amount and stronger acid strength. In addition, the obtained catalysts exhibited much higher SO2-tolerance and improved the water-resistance as compared to that prepared by impregnation or mechanically mixed methods.The MnOx and CeOx 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 NH3. X-Ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR) and NH3 temperature-programmed desorption (NH3-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 H2-TPR results suggested that there was a strong interaction between the manganese oxide and cerium oxide on the surface of CNTs. The NH3-TPD results demonstrated that the catalysts presented a larger acid amount and stronger acid strength. In addition, the obtained catalysts exhibited much higher SO2-tolerance and improved the water-resistance as compared to that prepared by impregnation or mechanically mixed methods. Electronic supplementary information (ESI) available: SEM images and EDS analysis, TEM images, and XPS spectrum of samples. See DOI: 10.1039/c2nr33006g

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

2013-01-01

25

Temperature-programmed decomposition desorption of mercury species over activated carbon sorbents for mercury removal from coal-derived fuel gas  

SciTech Connect

The mercury (Hg{sup 0}) removal process for coal-derived fuel gas in the integrated gasification combined cycle (IGCC) process will be one of the important issues for the development of a clean and highly efficient coal power generation system. Recently, iron-based sorbents, such as iron oxide (Fe{sub 2}O{sub 3}), supported iron oxides on TiO{sub 2}, and iron sulfides, were proposed as active mercury sorbents. The H{sub 2}S is one of the main impurity compounds in coal-derived fuel gas; therefore, H{sub 2}S injection is not necessary in this system. HCl is also another impurity in coal-derived fuel gas. In this study, the contribution of HCl to the mercury removal from coal-derived fuel gas by a commercial activated carbon (AC) was studied using a temperature-programmed decomposition desorption (TPDD) technique. The TPDD technique was applied to understand the decomposition characteristics of the mercury species on the sorbents. The Hg{sup 0}-removal experiments were carried out in a laboratory-scale fixed-bed reactor at 80-300{sup o}C using simulated fuel gas and a commercial AC, and the TPDD experiments were carried out in a U-tube reactor in an inert carrier gas (He or N{sub 2}) after mercury removal. The following results were obtained from this study: (1) HCl contributed to the mercury removal from the coal-derived fuel gas by the AC. (2) The mercury species captured on the AC in the HCl{sup -} and H{sub 2}S-presence system was more stable than that of the H{sub 2}S-presence system. (3) The stability of the mercury surface species formed on the AC in the H{sub 2}S-absence and HCl-presence system was similar to that of mercury chloride (HgClx) species. 25 refs., 12 figs., 1 tab.

M. Azhar Uddin; Masaki Ozaki; Eiji Sasaoka; Shengji Wu [Okayama University, Okayama (Japan). Faculty of Environmental Science and Technology

2009-09-15

26

Low Temperature Catalyst for NH3 Removal  

NASA Technical Reports Server (NTRS)

Air revitalization technologies maintain a safe atmosphere inside spacecraft by the removal of C02, ammonia (NH3), and trace contaminants. NH3 onboard the International Space Station (ISS) is produced by crew metabolism, payloads, or during an accidental release of thermal control refrigerant. Currently, the ISS relies on removing NH3 via humidity condensate and the crew wears hooded respirators during emergencies. A different approach to cabin NH3 removal is to use selective catalytic oxidation (SCO), which builds on thermal catalytic oxidation concepts that could be incorporated into the existing TCCS process equipment architecture on ISS. A low temperature platinum-based catalyst (LTP-Catalyst) developed at KSC was used for converting NH3 to H20 and N2 gas by SCO. The challenge of implementing SCO is to reduce formation of undesirable byproducts like NOx (N20 and NO). Gas mixture analysis was conducted using FTIR spectrometry in the Regenerable VOC Control System (RVCS) Testbed. The RVCS was modified by adding a 66 L semi-sealed chamber, and a custom NH3 generator. The effect of temperature on NH3 removal using the LTP-Catalyst was examined. A suitable temperature was found where NH3 removal did not produce toxic NO, (NO, N02) and N20 formation was reduced.

Monje, Oscar; Melendez, Orlando

2013-01-01

27

Plasma-assisted CuO/CeO2/TiO2-?-Al2O3 catalysts for NO + CH4 reaction and NO temperature programmed desorption studies  

NASA Astrophysics Data System (ADS)

The removal of NO and CH4 has been studied with a hybrid system integrating plasma activation and four Cu-based catalysts. The best catalytic performance was observed for catalysts obtained from CuO/CeO2/TiO2/?-Al2O3.The efficiency of NO removal decreased with the order: 12%CuO/10%CeO2/15%TiO2/?-Al2O3 > 12%CuO/15%TiO2/?-Al2O3 > 12%CuO/?-Al2O3 > 12% CuO/TiO2. Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD) Temperature-programmed reduction (H2-TPR) and NO temperature-programmed desorption (NO-TPD) experiments were carried out to gain insight into the synergetic effects with the catalysts. The results revealed that copper species existed as bulk CuO crystalline for all the catalysts, H2-TPR suggested that the Cu2+ incorporated TiO2 or CeO2 lattice and crystalline CuO might be the most active component for NO removal, and NO-TPD studies indicated that 12%CuO/10%CeO2/15%TiO2/?-Al2O3 catalyst had lower NO desorption temperature and larger peak area, which seemed to be responsible for the better catalytic activity over NO + CH4 reactions than other catalysts.

Li, Huijuan; Jiang, Xiaoyuan; Zheng, Xiaoming

2013-09-01

28

5, 25832605, 2008 Stomatal NH3  

E-print Network

.9 in Dactylis glomerata. The observed dif- ferences in apoplastic NH + 4 and pH resulted in a large span species (Lolium perenne, Festuca pratensis and Dactylis glomerata) had sufficiently high NH3 compensation

Paris-Sud XI, Université de

29

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)

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.

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

2014-05-01

30

Acidity and basicity of hydrotalcite derived mixed Mg-Al oxides studied by test reaction of MBOH conversion and temperature programmed desorption of NH{sub 3} and CO{sub 2}  

SciTech Connect

Mg-Al hydrotalcites intercalated with five different interlayer anions--CO{sub 3}{sup 2-}, SO{sub 4}{sup 2-}, Cl{sup -}, HPO{sub 4}{sup 2-} or terephthalate--were synthesized by either the coprecipitation or ion-exchange method. The structure of the as-synthesized samples and the presence of intended anions in the interlayer gallery of hydrotalcites were determined by X-ray diffraction and FTIR spectroscopy. On calcination at 600 deg. C the materials were transformed into mixed metal oxides. The kind of the counterbalancing anions present in the parent hydrotalcite influences strongly textural parameters of the obtained Mg-Al oxides. Both temperature-programmed desorption of NH{sub 3} and CO{sub 2}, and test reaction of 2-methyl-3-butyn-2-ol (MBOH) conversion were used to determine the acidity and basicity of the samples. The hydrotalcite derived mixed Mg-Al oxides showed the presence of Broensted and Lewis acid and base sites. However, the strong basic character of the solids caused that acetone and acetylene were observed as the major products of MBOH conversion.

Kustrowski, Piotr; Chmielarz, Lucjan; Bozek, Ewa; Sawalha, Murad; Roessner, Frank

2004-02-02

31

Chemical functionalization of boron-nitride nanotubes with NH3 and amino functional groups.  

PubMed

We have investigated properties of chemically modified boron nitride nanotubes (BNNTs) with NH(3) and four other amino functional groups (NH(2)CH(3), NH(2)CH(2)OCH(3), NH(2)CH(2)COOH, and NH(2)COOH) on the basis of density functional theory calculations. Unlike the case of carbon nanotubes, we found that NH(3) can be chemically adsorbed on top of the boron atom, with a charge transfer from NH(3) to the BNNT. The minimum-energy path calculation shows that a small energy barrier is encountered during the adsorption. Similarly, a small energy barrier (about 0.42 eV) is also involved in the desorption, suggesting that both adsorption and desorption can be realized even at room temperature. For chemically modified BNNTs with various amino functional groups, the adsorption energies are typically less than that of NH(3) on the BNNT. The trend of adsorption-energy change can be correlated with the trend of relative electron-withdrawing or -donating capability of the amino functional groups. Overall, the chemical modification of BNNTs with the amino groups results in little changes in the electronic properties of BNNTs. However, the chemical reactivity of the BNNTs can be enhanced by the chemical modification with the amino group containing -COOH. PMID:16953642

Wu, Xiaojun; An, Wei; Zeng, Xiao Cheng

2006-09-13

32

Growth of an Ultrathin Zirconia Film on Pt3Zr Examined by High-Resolution X-ray Photoelectron Spectroscopy, Temperature-Programmed Desorption, Scanning Tunneling Microscopy, and Density Functional Theory  

PubMed Central

Ultrathin (?3 Å) zirconium oxide films were grown on a single-crystalline Pt3Zr(0001) substrate by oxidation in 1 × 10–7 mbar of O2 at 673 K, followed by annealing at temperatures up to 1023 K. The ZrO2 films are intended to serve as model supports for reforming catalysts and fuel cell anodes. The atomic and electronic structure and composition of the ZrO2 films were determined by synchrotron-based high-resolution X-ray photoelectron spectroscopy (HR-XPS) (including depth profiling), low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and density functional theory (DFT) calculations. Oxidation mainly leads to ultrathin trilayer (O–Zr–O) films on the alloy; only a small area fraction (10–15%) is covered by ZrO2 clusters (thickness ?0.5–10 nm). The amount of clusters decreases with increasing annealing temperature. Temperature-programmed desorption (TPD) of CO was utilized to confirm complete coverage of the Pt3Zr substrate by ZrO2, that is, formation of a closed oxide overlayer. Experiments and DFT calculations show that the core level shifts of Zr in the trilayer ZrO2 films are between those of metallic Zr and thick (bulklike) ZrO2. Therefore, the assignment of such XPS core level shifts to substoichiometric ZrOx is not necessarily correct, because these XPS signals may equally well arise from ultrathin ZrO2 films or metal/ZrO2 interfaces. Furthermore, our results indicate that the common approach of calculating core level shifts by DFT including final-state effects should be taken with care for thicker insulating films, clusters, and bulk insulators. PMID:25688293

2014-01-01

33

The Inverse Modeling of NH3 Bidirectional Fluxes in CMAQ for NH3 Emission Estimates in the East United States  

NASA Astrophysics Data System (ADS)

NH3 bidirectional exchange is an important mechanism to control soil acidification and nitrification in biogeochemical cycles, and to affect emission/deposition processes of NH3 in atmospheric Chemistry Transport Models (CTMs). The latter is key to estimating NH3 emissions as well as ambient NH3 concentrations. However, current CTMs do not include NH3 bidirectional exchange because of the high uncertainties in parameterizations of such mechanism and a lack of observations for evaluation. Our study on the evaluation of NH3 using both surface and space based observations suggested the possibility that bidirectional exchange of NH3 might reduce the bias and error between model vs observation in North Carolina summer by improving estimated NH3 vertical profiles. With recent in-situ and satellite observations over North Carolina region and NH3 bidirectional exchange mechanism, we will assess NH3 emissions using inverse modeling techniques. The forward model, Community Multiscale Air Quality (CMAQ, v 5.0) model with NH3 bidirectional exchange was run for 12 km Continent Unites States (CONUS) domain from June 1st - August 31st, 2009. NH3 bidirectional fluxes from fertilizer applications were estimated using soil ammonium and pH from specific fertilizer application and management practices output from USDA agro-ecosystem model, Environmental Policy Integrated Climate (EPIC). We used inverse modeling approaches to optimize CMAQ NH3 concentration with surface observations such as Carolina Ammonia Monitoring Network (CAMNet) and Ammonia Monitoring Network (AMoN), and CMAQ Representative Volume Mixing Ratio (RVMR) with Topospheric Emission Spectrometer (TES) RVMR. A new NH3 emission estimate is compared with previous estimates. We also demonstrate how bidirectional exchange mechanism affects ambient NH3 vertical structure in the surface boundary layer, NH3 deposition velocity, and its atmospheric lifetime.

Jeong, G.; Bash, J. O.; Henze, D. K.

2011-12-01

34

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

NASA Technical Reports Server (NTRS)

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.

Sandford, Scott A.; Allamandola, Louis J.

1993-01-01

35

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

NASA Technical Reports Server (NTRS)

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.

Sandford, Scott A.; Allamandola, Louis J.

1993-01-01

36

Addition of NH3 to Al3O3-.  

PubMed

Recent computational studies on the addition of ammonia (NH3) to the Al3O3- cluster anion [A. Guevara-Garcia, A. Martinez, and J. V. Ortiz, J. Chem. Phys. 122, 214309 (2005)] have motivated experimental and additional computational studies, reported here. Al3O3- is observed to react with a single NH3 molecule to form the Al3O3NH3- ion in mass spectrometric studies. This is in contrast to similarly performed studies with water, in which the Al3O5H4- product was highly favored. However, the anion PE spectrum of the ammoniated species is very similar to that of Al3O4H2-. The adiabatic electron affinity of Al3O3NH3 is determined to be 2.35(5) eV. Based on comparison between the spectra and calculated electron affinities, it appears that NH3 adds dissociatively to Al3O3-, suggesting that the time for the Al3O3-NH3 complex to either overcome or tunnel through the barrier to proton transfer (which is higher for NH3 than for water) is short relative to the time for collisional cooling in the experiment. PMID:16774304

Wyrwas, Richard B; Jarrold, Caroline Chick; Das, Ujjal; Raghavachari, Krishnan

2006-05-28

37

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

Microsoft Academic Search

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

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

2006-01-01

38

Physical Temperature Measurements of L1551 from NH3 Observations  

NASA Astrophysics Data System (ADS)

We present NH3 and HC7N images of dark cloud L1551 produced from archive observations of the Robert C. Byrd Green Bank Telescope (GBT). The observations were fully calibrated with the GBT pipeline, and the NH3 line strengths are used to compute the physical temperature and number density of NH3 in the region. The observations of dark cloud L1551 reveal regions of strong emission of NH3 (1,1) emission and much weaker emission of NH3 (2,2) and HC7N J=21-20 lines. We were able to determine a physical-temperature range of 11 to 19 Kelvin for this cloud, but feel that the methods used to obtain these data are applicable beyond this single object. Therefore, we further present our method for using the NH3 (1,1) line fits to constrain model fits of the density, velocity, and temperature distributions of the other transitions. These data were produced using the spectral-line data-reduction pipeline and are provided as examples of data available from the GBT archive.

Towner, Allison P.; Hosmer, L.; Langston, G.

2013-01-01

39

Reaction pathway investigation on the selective catalytic reduction of NO with NH3 over Cu/SSZ-13 at low temperatures.  

PubMed

The mechanism of the selective catalytic reduction of NO with NH3 was studied using Cu/SSZ-13. The adspecies of NO and NH3 as well as the active intermediates were investigated using in situ diffuse reflectance infrared Fourier transform spectroscopy and temperature-programmed surface reaction. The results revealed that three reactions were possible between adsorbed NH3 and NOx. NO2(-) could be generated by direct formation or NO3(-) reduction via NO. In a standard selective catalytic reduction (SCR) reaction, NO3(-) was hard to form, because NO2(-) was consumed by ammonia before it could be further oxidized to nitrates. Additionally, adsorbed NH3 on the Lewis acid site was more active than NH4(+). Thus, SCR mainly followed the reaction between Lewis acid site-adsorbed NH3 and directly formed NO2(-). Higher Cu loading could favor the formation of active Cu-NH3, Cu-NO2(-), and Cu-NO3(-), improving the SCR activity at low temperature. PMID:25485842

Su, Wenkang; Chang, Huazhen; Peng, Yue; Zhang, Chaozhi; Li, Junhua

2015-01-01

40

Urban NH3 levels and sources in a Mediterranean environment  

NASA Astrophysics Data System (ADS)

Urban NH3 concentrations were mapped in Barcelona (Spain) by means of passive samplers (dosimeters). Average NH3 levels were 9.5 ?g m-3 in summer and 4.4 ?g m-3 in winter, higher than those reported in other urban background sites in Europe, this being especially notable in summer. During this season, values were significantly higher at urban background than at traffic sites, probably indicating the impact of emissions from biological sources, such as humans, sewage systems and garbage containers. Thus, the volatilization of NH3 from the aerosol phase seems to be significant enough during summer to dominate over traffic emissions. Conversely, in winter levels were higher at traffic sites, suggesting a contribution from vehicle emissions. Indeed, NH3 levels decreased by 55% with increasing distance (50 m) to the direct emissions from traffic. A significant correlation between NH3 concentrations averaged for the different districts of the city and the number of waste containers per hm2 was also obtained, highlighting the necessity for controlling and reducing the emissions from garbage collection systems. The urban topography of the Barcelona historical city centre, characterised by narrow streets with a high population density, seemed to exert a strong influence on NH3 levels, with levels reaching up to 30 ?g m-3 as a consequence of limited dispersion and ventilation conditions. The impact of the sewage system emissions was also detected with an increase of levels when measuring immediately above the source, even though further studies are required to evaluate the relevance of these emissions.

Reche, Cristina; Viana, Mar; Pandolfi, Marco; Alastuey, Andrés; Moreno, Teresa; Amato, Fulvio; Ripoll, Anna; Querol, Xavier

2012-09-01

41

Laboratory simulations of pre-cometary ice processes: thermal desorption, UV and X-ray irradiation.  

NASA Astrophysics Data System (ADS)

The formation of ice mantles on pre-cometary dust grains was simulated experimentally under ultrahigh vacuum conditions. An ice mixture containing H2O, CO, CO2, CH3OH, and NH3 was deposited at 8 K. The ice layer was either irradiated by UV or X-rays, or warmed up in a controlled way. The ice was monitored by infrared spectroscopy in transmittance and the species in the gas phase were detected by quadrupole mass spectroscopy (QMS). The temperature programmed desorption (TPD) of a complex ice mixture with up to five molecular components can aid to interpret the data collected by mass spectrometers on board cometary missions like Rosetta during the flyby. The irradiation experiments led to the formation of many photo-products. We will focus on those made by irradiation of ices containing H2S to study the formation of the detected sulfurbearing species in comets, such as S2.

Muñoz Caro, G. M.; Bueno-López, J.; Jiménez-Escobar, A.; Cruz-Diaz, G. A.; Chen, Y.-J.; Ciaravella, A.; Cecchi-Pestellini, C.; Goesmann, F.

2012-09-01

42

Microwave and infrared characterization of several weakly bound NH3 complexesa)  

NASA Astrophysics Data System (ADS)

We present the results of microwave and infrared spectroscopic studies of several van der Waals complexes of NH3. These results were obtained with a molecular beam electric resonance spectrometer. The microwave spectroscopy of the complexes (NH3)2 and Ar-NH3 show that both systems are nonrigid. The observed dipole moments for (NH3)2[0.74(2) D] and (ND3)2[0.57(1) D] are not compatible with the presently accepted theoretical structure. Ar-NH3, which has a complicated and currently unassigned microwave spectrum, exhibits Q branch inversion transitions near 19 GHz which indicate that the NH3 subunit is likely to be a near-free rotor. Infrared studies of the complexes NH3-HCCH, NH3-CO2, (NH3)2, Ar-NH3, NH3-OCS, NH3-N2O, and NH3-HCN have been carried out with a line tunable CO2 laser. Only for NH3-HCN were no infrared resonances discovered. Photodissociative transitions are observed in all of the other systems. Band origins for the photodissociative infrared transitions involving the ?2 umbrella motion of NH3 were determined for NH3-HCCH [984.4(9) cm-1], NH3-CO2 [987.1(2) cm-1]. NH3-OCS [981.5(15) cm-1], and NH3-N2O [980(2) cm-1]. The observation of an infrared transition for Ar-NH3 at 938.69 cm-1, which is 40 cm-1 lower than the band origins in the other NH3 complexes, lends support to the model of Ar-NH3 mentioned above. NH3-HCCH, NH3-CO2, (NH3)2, and Ar-NH3 were studied in microwave-infrared double resonance experiments in order to eliminate much of the inhomogeneous broadening present in their infrared spectra and to aid in the rotational assignment of the infrared spectra. Linewidths were determined for NH3-HCCH (0.15 GHz) and for NH3-CO2 [14(6) GHz]. An important result of this study is that the dissociation energies of all the complexes studied, except for NH3-HCN, are established to be less than 990 cm-1, i.e., 2.8 kcal/mol.

Fraser, G. T.; Nelson, D. D., Jr.; Charo, A.; Klemperer, W.

1985-03-01

43

INVERSE MODEL ESTIMATION AND EVALUATION OF SEASONAL NH 3 EMISSIONS  

EPA Science Inventory

The presentation topic is inverse modeling for estimate and evaluation of emissions. The case study presented is the need for seasonal estimates of NH3 emissions for air quality modeling. The inverse modeling application approach is first described, and then the NH...

44

Ionization of NH3 and CH4 by electron impact  

NASA Astrophysics Data System (ADS)

Calculated triple differential cross sections are presented for the ionization of NH3 and CH4 molecules by electron impact. The cross sections are determined for symmetrical coplanar and perpendicular geometrical arrangements. The obtained results reproduce in most cases the main features observed in the experimental data for both geometries.

Tóth, Istvan; Campeanu, Radu I.; Nagy, Ladislau

2015-01-01

45

Anharmonic vibrational spectroscopy calculations for (NH3)(HF) and (NH3)(DF): fundamental, overtone, and combination transitions.  

PubMed

In order to study the effects of hydrogen bonding on the spectroscopic properties of (NH3)(HF) and (NH3)(DF) complexes, vibrational spectra (including fundamental, overtone and combination transitions) were calculated using the vibrational self consistent field (VSCF) method. This ab initio VSCF method accounts for both one-dimensional anharmonicity and pair-wise mode-mode couplings for all vibrational modes of the molecule, using points on the potential energy surface (at the MP2/TZP level of theory in this study). An analysis of the coupling strength shows surprisingly important coupling effects from pair-wise interactions not expected to be major. This indicates the benefits of including all pair-wise mode-mode couplings for weakly bound systems. Hydrogen bonding induces approximately 20% red shifts for the HF and DF stretch frequencies. The corrections due to anharmonicity for these modes are -6% and -5%, respectively. The anharmonic corrections for the intermolecular stretch of (NH3)(HF) and (NH3)(DF) are each about -5%. The NH3 umbrella motion has virtually no anharmonic correction in the complex, whereas free ammonia experiences a -15% correction. Also, the closing motion as well as the opening motion is restricted. The 1 + 1 combination transition of the proton stretching and intermolecular stretching modes has remarkably large intensity, larger even than the intensities for the first overtone of the proton stretching modes. The anharmonic frequency for the fundamental HF stretch, 3268 cm(-1), is in good agreement with the experimental gas phase result, 3215 cm(-1). A comparison to solid rare-gas matrix data shows that the VSCF frequencies are a consistent improvement over the harmonic approximation. The experimental data also support the use of the MP2 level of theory for the associated electronic structure calculations. PMID:19791384

Brindle, Carrie A; Chaban, Galina M; Gerber, R Benny; Janda, Kenneth C

2005-03-01

46

Preparation of highly active manganese oxides supported on functionalized MWNTs for low temperature NOx reduction with NH3  

NASA Astrophysics Data System (ADS)

Manganese oxide catalysts (MnOx) supported on functionalized multi-walled carbon nanotubes (FMWNTs) for low temperature selective catalytic reduction (LTSCR) of nitrogen oxides (NOx) with NH3 in the presence of excess O2 were prepared by the incipient wetness impregnation method. These catalysts were characterized by N2 adsorption, Fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), X-ray diffraction (XRD), thermal gravimetric analysis (TGA) and H2-temperature programmed reduction (H2-TPR) methods. The effects of reaction temperature, MnOx loading, calcination temperature and calcination time were investigated. The presence of surface nitrate species under moderate calcination conditions may play a favorable role in the LTSCR of NOx with NH3. Under the reaction conditions of 200 °C, 1 bar, NO = NH3 = 900 ppm, O2 = 5 vol%, GHSV = 30,000 h-1 and 12 wt% MnOx, NOx conversion and N2 selectivity were 97% and 99.5%, respectively. The SCR activity was reduced in the presence of 100 ppm SO2 and 2.5 vol% H2O from 97% to 92% within 6 h at 200 °C, however such an effect was shown to be reversible by exposing the catalyst to a helium flow for 2 h at 350 °C due to thermal decomposition of ammonium sulphate salts.

Pourkhalil, Mahnaz; Moghaddam, Abdolsamad Zarringhalam; Rashidi, Alimorad; Towfighi, Jafar; Mortazavi, Yadollah

2013-08-01

47

Advanced ammonia (NH3) monitoring system for industrial applications  

Microsoft Academic Search

The present paper describes an Electro-Optical Monitoring System developed for the real time in-situ monitoring of Ammonia (NH3) emissions, at very low concentrations in air, well below the hazardous levels. Ammonia is the starting chemical for almost all industrially produced nitrogen compounds and is therefore one of the most important inorganic raw materials. Due to its unique chemical and physical

Oded Spector; Esther Jacobson

1999-01-01

48

Cs5Sn9(OH)·4NH3  

PubMed Central

The title compound, penta­caesium nona­stannide hydroxide tetra­ammonia, crystallized from a solution of CsSnBi in liquid ammonia. The Sn9 4? unit forms a monocapped quadratic anti­prism. The hydroxide ion is surrounded by five caesium cations, which form a distorted quadratic pyramidal polyhedron. A three-dimensional network is formed by Cs—Sn [3.8881?(7)?Å to 4.5284?(7)?Å] and Cs—NH3 [3.276?(7)–3.636?(7)?Å] contacts. PMID:24940189

Friedrich, Ute; Korber, Nikolaus

2014-01-01

49

Sensing Mechanisms for Carbon Nanotube Based NH3 Gas Detection  

SciTech Connect

There has been an argument on carbon nanotube (CNT) based gas detectors with a field-effect transistor (FET) geometry: do the response signals result from charge transfer between adsorbed gas molecules and the CNT channel and/or from the gas species induced Schottky barrier modulation at the CNT/metal contacts? To differentiate the sensing mechanisms, we employed three CNTFET structures, i.e., (1) the entire CNT channel and CNT/electrode contacts are accessible to NH3 gas; (2) the CNT/electrode contacts are passivated with a Si3N4 thin film, leaving the CNT channel open to the gas and, in contrast, (3) the CNT channel is covered with the film, while the contacts are open to the gas. We suggest that the Schottky barrier modulation at the contacts is the dominant mechanism from room temperature to 150°C. At higher temperatures, the charge transfer process contributes to the response signals. There is a clear evidence that the adsorption of NH3 on the CNT channel is facilitated by environmental oxygen.

Peng, Ning; Zhang, Qing; Chow, Chee L.; Tan, Ooi K.; Marzari, Nicola N.

2009-03-31

50

First NH3 detection of the Orion Bar  

NASA Astrophysics Data System (ADS)

Odin has successfully observed three regions in the Orion A cloud, i.e. Ori KL, Ori S and the Orion Bar, in the 572.5 GHz rotational ground state line of ammonia, ortho-NH3 (J,K) = (1,0) -> (0,0), and the result for the Orion Bar represents the first detection in an ammonia line. Several velocity components are present in the data. Specifically, the observed line profile from the Orion Bar can be decomposed into two components, which are in agreement with observations in high-J CO lines by Wilson et al. (\\cite{wilson01}). Using the source model for the Orion Bar by these authors, our Odin observation implies a total ammonia abundance of NH3/H2 = 5x 10-9. Based on observations with Odin, a Swedish-led satellite project funded jointly by the Swedish National Space Board (SNSB), the Canadian Space Agency (CSA), the National Technology Agency of Finland (Tekes) and Centre National d'Études Spatiales (CNES). The Swedish Space Corporation has been the industrial prime contractor.

Larsson, B.; Liseau, R.; Bergman, P.; Bernath, P.; Black, J. H.; Booth, R. S.; Buat, V.; Curry, C. L.; Encrenaz, P.; Falgarone, E.; Feldman, P.; Fich, M.; Florén, H. G.; Frisk, U.; Gerin, M.; Gregersen, E. M.; Harju, J.; Hasegawa, T.; Johansson, L. E. B.; Kwok, S.; Lecacheux, A.; Liljeström, T.; Mattila, K.; Mitchell, G. F.; Nordh, L. H.; Olberg, M.; Olofsson, G.; Pagani, L.; Plume, R.; Ristorcelli, I.; Sandqvist, Aa.; Schéele, F. v.; Tothill, N. F. H.; Volk, K.; Wilson, C. D.; Hjalmarson, Å.

2003-05-01

51

Structure-Activity Relationships in NH3-SCR over Cu-SSZ-13 as Probed by Reaction Kinetics and EPR Studies  

SciTech Connect

Cu-SSZ-13 catalysts with various Cu loadings were prepared via solution ion exchange. The hydrated samples were studied with Electron Paramagnetic Resonance (EPR). Cu2+ ion coordination numbers were obtained by analyzing the hyperfine structures while Cu-Cu distances were estimated from line broadening of the EPR features. By coupling EPR and temperature-programmed reduction (TPR) results, two Cu2+ ion locations were suggested. Standard and fast NH3-SCR, as well as non-selective NH3 oxidation reactions were carried out over these catalysts at high space velocities. For the SCR reaction, intra-particle diffusion limitation was found throughout the reaction temperatures investigated. Although clear structure-activity relationships cannot be derived, the reaction results allow for reactant diffusivities and Cu2+ ion locations to be estimated. The slower NH3 oxidation reaction, on the other hand, is kinetically limited at low temperatures, and, therefore, allows for a correlation between Cu2+ ion location and reaction kinetics to be made. Furthermore, the dynamic Cu2+ ion motion as a function of temperature could also be derived from the NH3 oxidation kinetics.

Gao, Feng; Walter, Eric D.; Karp, Eric M.; Luo, Jin-Yong; Tonkyn, Russell G.; Kwak, Ja Hun; Szanyi, Janos; Peden, Charles HF

2013-04-01

52

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

PubMed

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

Gao, Kunqi; Sheng, Li

2015-04-14

53

Elevated CO2 decreases the Photorespiratory NH3 production but does not decrease the NH3 compensation point in rice leaves.  

PubMed

The exchange of gaseous NH3 between the atmosphere and plants plays a pivotal role in controlling the global NH3 cycle. Photorespiration generates NH3 through oxygenation instead of carboxylation by the CO2-fixing enzyme, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO). The future increase in the atmospheric CO2 concentration, [CO2], is expected to reduce plant NH3 production by suppressing RuBisCO oxygenation (Vo). We measured the net leaf NH3 uptake rate (FNH3) across NH3 concentrations in the air (na) ranging from 0.2 to 1.6 nmol mol(-1) at three [CO2] values (190, 360 and 750 µmol mol(-1)) using rice plants. We analyzed leaf NH3 gas exchange using a custom-made whole-leaf chamber system, and determined the NH3 compensation point (?), a measure of potential NH3 emission, as the x-intercept of the linear relationship of FNH3 as a function of na. Our ? values were lower than those reported for other plant species. ? did not decrease under elevated [CO2], although leaf NH4 (+) content decreased with decreasing Vo at higher [CO2]. This was also the case for ? estimated from the pH and NH4 (+) concentration of the leaf apoplast solution (?'). ?' of rice plants, grown at elevated [CO2] for months in a free-air CO2 enrichment facility, was also not decreased by elevated [CO2]. These results suggest that suppression of RuBisCO oxygenation by elevated [CO2] does not decrease potential leaf NH3 emission in rice plants. PMID:24951312

Miyazawa, Shin-Ichi; Hayashi, Kentaro; Nakamura, Hirofumi; Hasegawa, Toshihiro; Miyao, Mitsue

2014-09-01

54

Analyte separation utilizing temperature programmed desorption of a preconcentrator mesh  

DOEpatents

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.

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

2007-11-27

55

[UO2(NH3)5]Br2·NH3: synthesis, crystal structure, and speciation in liquid ammonia solution by first-principles molecular dynamics simulations.  

PubMed

Pentaammine dioxido uranium(vi) dibromide ammonia (1/1), [UO2(NH3)5]Br2·NH3, was synthesized in the form of yellow crystals by the reaction of uranyl bromide, UO2Br2, with dry liquid ammonia. The compound crystallizes orthorhombic in space group Cmcm and is isotypic to [UO2(NH3)5]Cl2·NH3 with a = 13.2499(2), b = 10.5536(1), c = 8.9126(1) Å, V = 1246.29(3) Å(3) and Z = 4 at 123 K. The UO2(2+) cation is coordinated by five ammine ligands and the coordination polyhedron can be best described as pentagonal bipyramid. Car-Parrinello molecular dynamics simulations are reported for [UO2(NH3)5](2+) in the gas phase and in liquid NH3 solution (using the BLYP density functional). According to free-energy simulations, solvation by ammonia has only a small effect on the uranyl-NH3 bond strength. PMID:25797497

Woidy, Patrick; Bühl, Michael; Kraus, Florian

2015-04-01

56

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

NASA Astrophysics Data System (ADS)

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).

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

2014-03-01

57

Relativistic GW calculations on CH3NH3PbI3 and CH3NH3SnI3 perovskites for solar cell applications.  

PubMed

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(I(1-x)Cl(x))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). PMID:24667758

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

2014-01-01

58

Chemisorption of NH 3 at the open ends of boron nitride nanotubes: a DFT study  

Microsoft Academic Search

Considering the thermodynamic aspects and reaction pathways of chemical adsorption of NH3 molecule at the open ends of boron nitride nanotubes (BNNTs), theoretically, it was found that the open-ended BNNTs are able\\u000a to cleave the N–H bond of NH3 via a one- or two-stepwise mechanism. The N-enriched and B-enriched open-ended BNNTs show a nucleophilic and electrophilic\\u000a behavior toward the NH3,

Ali Ahmadi; Javad Beheshtian; Nasser L. Hadipour

2011-01-01

59

A theoretical room-temperature line list for 15NH3  

NASA Astrophysics Data System (ADS)

A new room temperature line list for 15NH3 is presented. This line list comprised of transition frequencies and Einstein coefficients has been generated using the 'spectroscopic' potential energy surface NH3-Y2010 and an ab initio dipole moment surface. The 15NH3 line list is based on the same computational procedure used for the line list for 14NH3 BYTe reported recently and should be as accurate. Comparisons with experimental frequencies and intensities are presented. The synthetic spectra show excellent agreement with experimental spectra.

Yurchenko, Sergei N.

2015-02-01

60

The initial kinetics of NH3/NH4(+) efflux from L3 Teladorsagia circumcincta.  

PubMed

The initial rate of NH(3)/NH(4)(+) accumulation in a medium containing L(3) Teladorsagia circumcincta was 0.18-0.6 pmol h(-1) larva(-1), which increased linearly with larval density. However it appeared that the larva-generated external concentration of NH(3)/NH(4)(+) did not exceed about 130 ?M. The rate of NH(3)/NH(4)(+) accumulation increased with temperature between 4 °C and 37 °C, declined with increasing pH or increasing external NH(3)/NH(4)(+) concentration and was not significantly affected by the concentration of the phosphate buffer or by exsheathing the larvae. We infer from these data that the efflux of NH(3)/NH(4)(+) is a diffusive process and that the secreted or excreted NH(3)/NH(4)(+) is generated enzymatically rather than dissociating from the surface of the nematode. The enzymatic source of the NH(3)/NH(4)(+) is yet to be identified. Since the concentration of NH(3)/NH(4)(+) in the rumen and abomasum is higher than 130 ?M, it is unlikely that T. circumcincta contributes to it, but NH(3)/NH(4)(+) may be accumulated from the rumen fluid by the nematode. PMID:22562002

Muhamad, Noorzaid; Walker, Lisa R; Pedley, Kevin C; Simcock, David C; Brown, Simon

2012-09-01

61

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

NASA Astrophysics Data System (ADS)

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 3385 cm-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 4.5 kJ mol-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 TCc = 137.6 K (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.

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

2015-02-01

62

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

NASA Astrophysics Data System (ADS)

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.

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

63

Time Resolved Measurement of Ecosystem-Atmosphere NH3 Exchange Using the Eddy Covariance Technique  

NASA Astrophysics Data System (ADS)

Quantifying ammonia fluxes between the land surface and atmosphere is required for effective control of air quality, improving agricultural practices, and understanding natural ecosystem function. Ammonia (NH3) is emitted in large but uncertain amounts from animal agriculture, in lesser amounts from imperfect use of nitrogen fertilizers in crop agriculture, from catalytic converters used on automobiles and other energy related industrial processes, and exchanged between the ecosystem and atmosphere by natural ecosystem processes on vast spatial scales. To address the need for accurate, time-resolved NH3 flux measurements, we have developed an eddy covariance (EC) instrument for direct measurements of NH3 flux. EC flux measurements of NH3 were not previously possible because instruments were not sufficiently sensitive at high frequencies required to capture rapid variations in surface layer NH3 concentrations. To overcome this hurdle we combined a tunable-diode-laser (TDL) spectrometer with a fast-response NH3 sampling inlet and automated pulse-response calibration system. Laboratory tests of the inlet system demonstrate that the response to 10 ppb step in NH3 concentration is well described by a double exponential model with (1/e) times of 0.3 (85% response) and 1.5 (15% response) seconds. This response combined with a routinely measured instrument stability of ~ 0.1 ppb (on 30 minute timescales) indicates that the instrumental contribution to noise in NH3 flux measurements is ~ 0.2 umol NH3 m-2 hr-1, sufficient to stringently test models for NH3 exchange under most conditions. Recent results of field work to verify the instrument performance and observe examples of NH3 exchange will be presented.

Fischer, M. L.; Littlejohn, D.

2005-12-01

64

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

PubMed

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

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

65

Effects of atmospheric ammonia (NH 3) on terrestrial vegetation: a review  

Microsoft Academic Search

At the global scale, among all N (nitrogen) species in the atmosphere and their deposition on to terrestrial vegetation and other receptors, NH3 (ammonia) is considered to be the foremost. The major sources for atmospheric NH3 are agricultural activities and animal feedlot operations, followed by biomass burning (including forest fires) and to a lesser extent fossil fuel combustion. Close to

S. V Krupa

2003-01-01

66

Dynamics of gas phase Ne(*) + NH3 and Ne(*) + ND3 Penning ionisation at low temperatures.  

PubMed

Two isotopic chemical reactions, Ne(*) + NH3, and Ne(*) + ND3, have been studied at low collision energies by means of a merged beams technique. Partial cross sections have been recorded for the two reactive channels, namely, Ne(*) + NH3 ? Ne + NH3(+) + e(-), and Ne(*) + NH3 ? Ne + NH2(+) + H + e(-), by detecting the NH3(+) and NH2(+) product ions, respectively. The cross sections for both reactions were found to increase with decreasing collision energy, Ecoll, in the range 8 ?eV < Ecoll < 20 meV. The measured rate constant exhibits a curvature in a log(k)-log(Ecoll) plot from which it is concluded that the Langevin capture model does not properly describe the Ne(*) + NH3 reaction in the entire range of collision energies covered here. Calculations based on multichannel quantum defect theory were performed to reproduce and interpret the experimental results. Good agreement was obtained by including long range van der Waals interactions combined with a 6-12 Lennard-Jones potential. The branching ratio between the two reactive channels, ? = [NH2(+)]/[NH2(+)] + [NH3(+)], is relatively constant, ? ? 0.3, in the entire collision energy range studied here. Possible reasons for this observation are discussed and rationalized in terms of relative time scales of the reactant approach and the molecular rotation. Isotopic differences between the Ne(*) + NH3 and Ne(*) + ND3 reactions are small, as suggested by nearly equal branching ratios and cross sections for the two reactions. PMID:24985633

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

2014-06-28

67

Dynamics of gas phase Ne* + NH3 and Ne* + ND3 Penning ionisation at low temperatures  

NASA Astrophysics Data System (ADS)

Two isotopic chemical reactions, Ne* + NH3, and Ne* + ND3, have been studied at low collision energies by means of a merged beams technique. Partial cross sections have been recorded for the two reactive channels, namely, Ne* + NH3 ? Ne + NH_3^+ + e-, and Ne* + NH3 ? Ne + NH_2^++ H + e-, by detecting the NH_3^+ and NH_2^+ product ions, respectively. The cross sections for both reactions were found to increase with decreasing collision energy, Ecoll, in the range 8 ?eV < Ecoll < 20 meV. The measured rate constant exhibits a curvature in a log(k)-log(Ecoll) plot from which it is concluded that the Langevin capture model does not properly describe the Ne* + NH3 reaction in the entire range of collision energies covered here. Calculations based on multichannel quantum defect theory were performed to reproduce and interpret the experimental results. Good agreement was obtained by including long range van der Waals interactions combined with a 6-12 Lennard-Jones potential. The branching ratio between the two reactive channels, ? = [NH_2^+]/[NH_2^+]+[NH_3^+], is relatively constant, ? ? 0.3, in the entire collision energy range studied here. Possible reasons for this observation are discussed and rationalized in terms of relative time scales of the reactant approach and the molecular rotation. Isotopic differences between the Ne* + NH3 and Ne* + ND3 reactions are small, as suggested by nearly equal branching ratios and cross sections for the two reactions.

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

2014-06-01

68

Urban NH3 levels and sources in six major Spanish cities.  

PubMed

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

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

69

SEASONAL NH 3 EMISSIONS FOR ANNUAL 2001 CMAQ SIMULATION: INVERSE MODEL ESTIMATION AND EVALUATION  

EPA Science Inventory

The formation of ammonium nitrate aerosols is often limited by ammonia (NH3), and sulfate aerosols are predominantly in the form of ammonium sulfate. While NH3plays a central role in the prediction of nitrate and sulfate aerosols, inherent uncertainty exist...

70

Transformation from chemisorption to physisorption with tube diameter and gas concentration: Computational studies on NH3 adsorption in BN nanotubes  

NASA Astrophysics Data System (ADS)

Using first-principles computations, we studied NH3 adsorption on a series of zigzag (n,0) single-walled BN nanotubes (BNNTs) and the effect of gas coverage. Tube diameter and NH3 coverage play important roles on the tube-NH3 interaction. Chemisorption of a single NH3 molecule on top of B site is energetically preferable for all the tubes studied, but the adsorption energy decreases sharply with increasing tube diameter, and then gradually approaches the value for NH3 physisorption on BN graphene layer. On the sidewall of (10,0) BNNT, NH3 molecules prefer to pair arrangement on top of B and N atoms opposite in the same hexagon. At low coverages, NH3 molecules are partly chemically bound to BNNTs. With the increase of NH3 coverage, hydrogen bonds form between the adsorbed NH3 molecules or between the NH3 molecules and N atoms in BNNTs. When the coverage reaches 25%, the chemisorption of NH3 transforms to physisorption completely. NH3 adsorption does not modify the overall band structures of BNNTs, irrespective of NH3 coverage, but the band gap is narrowed due to the NH3-tube coupling and tube deformation.

Li, Yafei; Zhou, Zhen; Zhao, Jijun

2007-11-01

71

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

PubMed

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

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

72

Towards validation of ammonia (NH3) measurements from the IASI satellite  

NASA Astrophysics Data System (ADS)

Limited availability of ammonia (NH3) observations is currently a barrier for effective monitoring of the nitrogen cycle. It prevents a full understanding of the atmospheric processes in which this trace gas is involved and therefore impedes determining its related budgets. Since the end of 2007, the Infrared Atmospheric Sounding Interferometer (IASI) satellite has been observing NH3 from space at a high spatiotemporal resolution. This valuable data set, already used by models, still needs validation. We present here a first attempt to validate IASI-NH3 measurements using existing independent ground-based and airborne data sets. The yearly distributions reveal similar patterns between ground-based and space-borne observations and highlight the scarcity of local NH3 measurements as well as their spatial heterogeneity and lack of representativity. By comparison with monthly resolved data sets in Europe, China and Africa, we show that IASI-NH3 observations are in fair agreement but that they are characterized by a smaller variation in concentrations. The use of hourly and airborne data sets to compare with IASI individual observations allows to investigate the impact of averaging as well as the representativity of independent observations for the satellite footprint. The importance of considering the latter and the added value of densely located airborne measurements at various altitudes to validate IASI-NH3 columns are discussed. Perspectives and guidelines for future validation work on NH3 satellite observations are presented.

Van Damme, M.; Clarisse, L.; Dammers, E.; Liu, X.; Nowak, J. B.; Clerbaux, C.; Flechard, C. R.; Galy-Lacaux, C.; Xu, W.; Neuman, J. A.; Tang, Y. S.; Sutton, M. A.; Erisman, J. W.; Coheur, P. F.

2014-12-01

73

Dynamics of gas phase Ne$^*$ + NH$_3$ and Ne$^*$ + ND$_3$ Penning ionization at low temperatures  

E-print Network

Two isotopic chemical reactions, $\\mathrm{Ne}^*$ + NH$_3$, and $\\mathrm{Ne}^*$ + ND$_3$, have been studied at low collision energies by means of a merged beams technique. Partial cross sections have been recorded for the two reactive channels, namely $\\mathrm{Ne}^*$ + NH$_3$ $\\rightarrow$ Ne + NH$_3^+$ + $e^-$, and $\\mathrm{Ne}^*$ + NH$_3$ $\\rightarrow$ Ne + NH$_2^+$ + H + $e^-$, by detecting the NH$_3^+$ and NH$_2^+$ product ions, respectively. The cross sections for both reactions were found to increase with decreasing collision energy, $E_{coll}$, in the range 8 $\\mu$eV$reaction in the entire range of collision energies covered here. Calculations based on multichannel quantum defect theory were performed to reproduce and interpret the experimental results. Good agreement was obtained by including long range van der Waals interactions combined with a 6-12 Lennard-Jones potential. The branching ratio between the two reactive channels, $\\Gamma = \\frac{[NH_2^+]}{[NH_2^+]+[NH_3^+]}$, is relatively constant, $\\Gamma\\approx 0.3$, in the entire collision energy range studied here. Possible reasons for this observation are discussed and rationalised in terms of relative time scales of the reactant approach and the molecular rotation. Isotopic differences between the $\\mathrm{Ne}^*$ + NH$_3$ and $\\mathrm{Ne}^*$ + ND$_3$ reactions are small, as suggested by nearly equal branching ratios and cross sections for the two reactions.

Justin Jankunas; Benjamin Bertsche; Krzysztof Jachymski; Michal Hapka; Andreas Osterwalder

2014-05-02

74

Matrix Isolation Spectroscopy and Nuclear Spin Conversion of NH3 and ND3 in Solid Parahydrogen  

NASA Astrophysics Data System (ADS)

We present matrix isolation infrared absorption spectra of NH3 and ND3 trapped in solid parahydrogen (pH2) at temperatures around 1.8 K. We used the relatively slow nuclear spin conversion (NSC) of NH3 and ND3 in freshly deposited pH2 samples as a tool to assign the sparse vibration-inversion-rotation (VIR) spectra of NH3 in the regions of the -2, -4, 2-4, -1, and -3 bands and ND3 in the regions of the -2, -4, -1, and -3 fundamentals. Partial assignments are also presented for various combination bands of NH3. Detailed analysis of the -2 bands of NH3 and ND3 indicates that both isotopomers are nearly free rotors; that the vibrational energy is blue-shifted by 1-2%; and that the rotational constants and inversion tunneling splitting are 91-94% and 67-75%, respectively, of the gas-phase values. The line shapes of the VIR absorptions are narrow (0.2-0.4 cm-1) for upper states that cannot rotationally relax and broad (>1 cm-1) for upper states that can rotationally relax. We report and assign a number of NH3-induced infrared absorption features of the pH2 host near 4150 cm-1, along with a cooperative transition that involves simultaneous vibrational excitation of a pH2 molecule and rotation-inversion excitation of NH3. The NSCs of NH3 and ND3 were found to follow first-order kinetics with rate constants at 1.8 K of k = 1.88(16) - 10-3 s-1 and k = 1.08(8) - 10-3 s-1, respectively. These measured rate constants are compared to previous measurements for NH3 in an Ar matrix and with the rate constants measured for other dopant molecules isolated in solid pH2.

Ruzi, Mahmut; Anderson, David T.

2013-10-01

75

Matrix isolation spectroscopy and nuclear spin conversion of NH3 and ND3 in solid parahydrogen.  

PubMed

We present matrix isolation infrared absorption spectra of NH3 and ND3 trapped in solid parahydrogen (pH2) at temperatures around 1.8 K. We used the relatively slow nuclear spin conversion (NSC) of NH3 and ND3 in freshly deposited pH2 samples as a tool to assign the sparse vibration-inversion-rotation (VIR) spectra of NH3 in the regions of the ?2, ?4, 2?4, ?1, and ?3 bands and ND3 in the regions of the ?2, ?4, ?1, and ?3 fundamentals. Partial assignments are also presented for various combination bands of NH3. Detailed analysis of the ?2 bands of NH3 and ND3 indicates that both isotopomers are nearly free rotors; that the vibrational energy is blue-shifted by 1-2%; and that the rotational constants and inversion tunneling splitting are 91-94% and 67-75%, respectively, of the gas-phase values. The line shapes of the VIR absorptions are narrow (0.2-0.4 cm(-1)) for upper states that cannot rotationally relax and broad (>1 cm(-1)) for upper states that can rotationally relax. We report and assign a number of NH3-induced infrared absorption features of the pH2 host near 4150 cm(-1), along with a cooperative transition that involves simultaneous vibrational excitation of a pH2 molecule and rotation-inversion excitation of NH3. The NSCs of NH3 and ND3 were found to follow first-order kinetics with rate constants at 1.8 K of k = 1.88(16) × 10(-3) s(-1) and k = 1.08(8) × 10(-3) s(-1), respectively. These measured rate constants are compared to previous measurements for NH3 in an Ar matrix and with the rate constants measured for other dopant molecules isolated in solid pH2. PMID:23594210

Ruzi, Mahmut; Anderson, David T

2013-10-01

76

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

NASA Astrophysics Data System (ADS)

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).

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.

77

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

NASA Technical Reports Server (NTRS)

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.

Kraemer, Kathleen E.; Jackson, James M.

1995-01-01

78

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...

79

Synthesis, crystal structures and properties of the trimetaphosphimates NaBa(PO 2NH) 3, KSr(PO 2NH) 3?4H 2O, and NH 4Sr(PO 2NH) 3?4H 2O  

NASA Astrophysics Data System (ADS)

The three double salts sodium barium tri- ?-imidocyclotriphosphate, NaBa(PO 2NH) 3 ( 1), potassium strontium tri- ?-imidocyclotriphosphate tetrahydrate, KSr(PO 2NH) 3?4H 2O ( 2), and ammonium strontium tri- ?-imidocyclotriphosphate tetrahydrate, NH 4Sr(PO 2NH) 3?4H 2O ( 3), were synthesized by combining equimolar aqueous solutions of Na 3(PO 2NH) 3?4H 2O, K 3(PO 2NH) 3, or (NH 4) 3(PO 2NH) 3?H 2O, respectively, with the corresponding alkaline earth nitrate. In case of compound 1, suitable single crystals for X-ray crystal structure determination were solely obtained using gel crystallization in gelatine gels. The structures of 2 and 3 were found to be isotypic. All crystal structures were solved by single-crystal X-ray methods ( 1: C2/m, a=1084.5(2), b=1025.0(2), c=796.2(2) pm, ?=115.18(3)°, Z=4, R=0.023; 2: P2/n, a=1087.2(2), b=1049.6(2), c=1191.2(2) pm, ?=111.98(3)°, Z=4, R=0.025; 3: P2/n, a=1088.4(2), b=1048.5(2), c=1196.9(2) pm, ?=111.43(3)°, Z=4, R=0.025). In both structure types, the P 3N 3 rings of the trimetaphosphimate ions exhibit a chair conformation. In the crystal, the trimetaphosphimate ions act as mono and bidentate ligands of the alkali ions, and additionally as tridentate ones in case of the alkaline earth ions. Besides the oxygen atoms, the nitrogen atoms of the (PONH)33- rings contribute to the coordination of the cations as well. In 2 and 3, crystal water molecules complete the coordination of the metal ions. Extended hydrogen bonding reinforces the three-dimensional interconnection of the ions and the crystal water molecules in the structures of all three compounds.

Correll, Sascha; Sedlmaier, Stefan; Schnick, Wolfgang

2005-10-01

80

Probe of NH3 and CO adsorption on the very outermost surface of a porous TiO2 adsorbent using photoluminescence spectroscopy.  

PubMed

We report the first measurements of the kinetics of adsorption on the very outermost surface sites of a porous material compared to measurements made of adsorption on the interior sites. NH(3) and CO were employed in this study as representative of slow diffusion and fast diffusion, respectively, through porous TiO(2). Adsorption of NH(3) at 200 K occurs mainly at the very near surface (~20 nm) region as observed by photoluminescence (PL) spectroscopy, and its distribution by surface diffusion through the powder is highly retarded as judged by transmission IR spectroscopy. In contrast, the adsorption of CO in the near-surface region at 120 K is followed by the fast distribution of CO by surface diffusion into TiO(2) powder, causing the near-surface CO coverage to lag behind the coverage in the bulk. In the desorption process, the near-surface region delivers adsorbed CO molecules into the gas phase, accompanied by the supply of diffusing CO molecules from the interior. As a result, the adsorption/desorption processes for CO in the near-surface region of porous TiO(2) show a pronounced hysteresis effect. As surface diffusion is retarded at lower temperatures, the hysteresis effect gradually disappears. PMID:22394240

Stevanovic, Ana; Yates, John T

2012-04-01

81

Cross sections for direct and dissociative ionization of NH3 and CS2 by electron impact  

NASA Technical Reports Server (NTRS)

A crossed electron beam-molecular beam collision geometry is used to measure cross sections for the production of positive ions by electron impact on NH3 and CS2. Ionization cross-section data for NH3 and the values of various cross sections are presented, as well as ionization efficiency curves for CS2. Considerable differences are found between the various results on NH3. The present values are close to the data of Djuric et al. (1981). The semiempirical calculations of Hare and Meath (1987) differ considerably in the absolute values of cross sections. Discrepancies were observed in comparisons of cross sections of other fragment ions resulting from the ionization and dissociate ionization of NH3.

Rao, M. V. V. S.; Srivastava, S. K.

1991-01-01

82

Indirect measurement of N-14 quadrupolar coupling for NH3 intercalated in potassium graphite  

NASA Technical Reports Server (NTRS)

A method for indirect measurement of the nuclear quadrupolar coupling was developed and applied to NH3 molecules in the graphite intercalation compound K(NH3)4.3C24, which has a layered structure with alternating carbon and intercalant layers. Three triplets were observed in the H-1 NMR spectra of the compound. The value of the N-14 quadrupolar coupling constant of NH3 (3.7 MHz), determined indirectly from the H-1 NMR spectra, was intermediate between the gas value of 4.1 MHz and the solid-state value of 3.2 MHz. The method was also used to deduce the (H-1)-(H-1) and (N-14)-(H-1) dipolar interactions, the H-1 chemical shifts, and the molecular orientations and motions of NH3.

Tsang, T.; Fronko, R. M.; Resing, H. A.

1987-01-01

83

Role of the support on the behavior of Ag-based catalysts for NH3 selective catalytic oxidation (NH3-SCO)  

NASA Astrophysics Data System (ADS)

In this work four supports with different textural properties (Al2O3, SiO2, NaY and TiO2) are used to evaluate the formation of different silver species and their effect on the NH3-SCO performance. Characterization analyses have shown that the predominant Ag0 species and the oxidized Ag species (Ag+ and Agn?+) are located on the four catalysts with different ratio of Ag0/oxidized Ag. Small Ag0 particle with high dispersion which is obtained on 10 wt% Ag/Al2O3 (5 nm, Ag0 ratio = 97.7%) shows an excellent catalytic performance for SCO reaction at low temperatures (a complete NH3 conversion at 180 °C and a high N2 selectivity of 89%). In addition, a certain amount of oxidized Ag species formed on the catalysts, especially for the NaY and SiO2 support, as well as the surface acidity of catalysts have also been found to play an important role in the enhanced N2 selectivity above 140 °C by promoting iSCR reaction involving NO as an intermediate for N2 formation. A model to relate the silver species with the performance of NH3-SCO is proposed, which is very significant for the further optimization of the catalyst (e.g. choosing a suitable support) for NH3-SCO reaction and its practical application in the future.

Qu, Zhenping; Wang, Hui; Wang, Shudong; Cheng, Hao; Qin, Yuan; Wang, Zhong

2014-10-01

84

Transformation from chemisorption to physisorption with tube diameter and gas concentration: Computational studies on NH3 adsorption in BN nanotubes  

Microsoft Academic Search

Using first-principles computations, we studied NH3 adsorption on a series of zigzag (n,0) single-walled BN nanotubes (BNNTs) and the effect of gas coverage. Tube diameter and NH3 coverage play important roles on the tube-NH3 interaction. Chemisorption of a single NH3 molecule on top of B site is energetically preferable for all the tubes studied, but the adsorption energy decreases sharply

Yafei Li; Zhen Zhou; Jijun Zhao

2007-01-01

85

Analysis and theory of multilayer desorption: Ag on Re  

NASA Astrophysics Data System (ADS)

A multilayer lattice gas model is set up to calculate the temperature programmed desorption spectra and other data for silver on rhenium. A careful comparison of experimental and theoretical desorption spectra implies that the surface is partially stepped with the step density likely increasing as one approaches the desorption range. Experimental temperature inhomogeneities of a few percent across the surface are suggested by careful isosteric and threshold Arrhenius analyses and theoretical modeling. A rate subtraction procedure commonly used to analyze multilayer desorption data is shown to be unnecessary. Layer plots are presented and some general features for overlapping desorption peaks are discussed.

Payne, S. H.; LeDue, J. M.; Michael, J. C.; Kreuzer, H. J.; Wagner, R.; Christmann, K.

2002-06-01

86

3-D agricultural air quality modeling: Impacts of NH3/H2S gas-phase reactions and bi-directional exchange of NH3  

NASA Astrophysics Data System (ADS)

Accurately simulating the transport and fate of reduced nitrogen (NHx = ammonia (NH3) + ammonium (NH4+))- and sulfur-containing compounds emitted from agricultural activities represents a major challenge in agricultural air quality modeling. In this study, the Community Multiscale Air Quality (CMAQ) modeling system is further developed and improved by implementing 22 ammonia (NH3)/hydrogen sulfide (H2S) related gas-phase reactions and adjusting a few key parameters (e.g., emission potential) for bi-directional exchange of NH3 fluxes. Several simulations are conducted over the eastern U.S. domain at a 12-km horizontal resolution for January and July 2002 to examine the impacts of those improved treatments on air quality. The 5th generation mesoscale model (MM5) and CMAQ predict an overall satisfactory and consistent performance with previous modeling studies, especially for 2-m temperature, 2-m relative humidity, ozone (O3), and fine particulate matter (PM2.5). High model biases exist for precipitation in July and also dry/wet depositions. The updated model treatments contribute to O3, NHx, and PM2.5 by up to 0.4 ppb, 1.0 ?g m-3, and 1.0 ?g m-3 in January, respectively, and reduce O3 by up to 0.8 ppb and contribute to NHx and PM2.5 by up to 1.2 and 1.1 ?g m-3 in July, respectively. The spatial distributions of O3 in both months and sulfur dioxide (SO2) in January are mainly affected by inline dry deposition velocity calculation. The spatial distributions of SO2 and sulfate (SO42-) in July are affected by both inline dry deposition velocity and NH3/H2S reactions. The variation trends of NH3, NHx, ammonium nitrate (NH4NO3), PM2.5 and total nitrogen (TN) are predominated by bi-directional exchange of NH3 fluxes. Uncertainties of NH3 emission potentials and empirical constants used in the bi-directional exchange scheme may significantly affect the concentrations of NHx and PM2.5, indicating that a more accurate and explicit treatment for those parameters should be considered in the future work.

Wang, Kai; Zhang, Yang

2014-12-01

87

Electronic structures at the interface between Au and CH3NH3PbI3.  

PubMed

The electronic properties of interfaces formed between Au and organometal triiodide perovskite (CH3NH3PbI3) are investigated using ultraviolet photoemission spectroscopy (UPS), inverse photoemission spectroscopy (IPES) and X-ray photoemission spectroscopy (XPS). It is found that the CH3NH3PbI3 film coated onto the substrate of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS)/indium tin oxide (ITO) by a two-step method presents n-type semiconductor behavior, with a band gap of 1.7 eV and a valence band (VB) edge of 1.0 eV below the Fermi energy (EF). An interface dipole of 0.1 eV is observed at the CH3NH3PbI3/Au interface. The energy levels of CH3NH3PbI3 shift upward by ca. 0.4 eV with an Au coverage of 64 Å upon it, resulting in band bending, hence a built-in field in CH3NH3PbI3 that encourages hole transport to the interface. Hole accumulation occurs in the vicinity of the interface, facilitating the hole transfer from CH3NH3PbI3 to Au. Furthermore, the shift of the VB maximum of CH3NH3PbI3 toward the EF indicates a decrease of energy loss as holes transfer from CH3NH3PbI3 to Au. PMID:25407902

Liu, Xiaoliang; Wang, Chenggong; Lyu, Lu; Wang, Congcong; Xiao, Zhengguo; Bi, Cheng; Huang, Jinsong; Gao, Yongli

2015-01-14

88

Concentration-dependent NH 3 deposition processes for mixed moorland semi-natural vegetation  

NASA Astrophysics Data System (ADS)

Dry deposition modelling typically assumes that canopy resistance ( Rc) is independent of ammonia (NH 3) concentration. An innovative flux chamber system was used to provide accurate continuous measurements of NH 3 deposition to a moorland composed of a mixture of Calluna vulgaris (L.) Hull, Eriophorum vaginatum L. and Sphagnum spp. Ammonia was applied at a wide range of concentrations (1-100 ?g m -3). The physical and environmental properties and the testing of the chamber are described, as well as results for the moorland vegetation using the 'canopy resistance' and 'canopy compensation point' interpretations of the data. Results for moorland plant species demonstrate that NH 3 concentration directly affects the rate of NH 3 deposition to the vegetation canopy, with Rc and cuticular resistance ( Rw) increasing with increasing NH 3 concentrations. Differences in Rc were found between night and day: during the night Rc increases from 17 s m -1 at 10 ?g m -3 to 95 s m -1 at 80 ?g m -3, whereas during the day Rc increases from 17 s m -1 at 10 ?g m -3 to 48 s m -1 at 80 ?g m -3. The lower resistance during the day is caused by the stomata being open and available as a deposition route to the plant. Rw increased with increasing NH 3 concentrations and was not significantly different between day and night (at 80 ?g m -3 NH 3 day Rw=88 s m -1 and night Rw=95 s m -1). The results demonstrate that assessments using fixed Rc will over-estimate NH 3 deposition at high concentrations (over ˜15 ?g m -3).

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

89

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

NASA Astrophysics Data System (ADS)

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.

Maxwell, J. D.

2011-01-01

90

Adsorption and thermal desorption on stepped surfaces  

NASA Astrophysics Data System (ADS)

A lattice gas model for the adsorption and thermal desorption on stepped surfaces is formulated with different adsorption sites on the terraces, the lower base and the upper edge of the steps and including various lateral interactions. We employ transfer matrix techniques to get the equilibrium properties, correlation functions and temperature-programmed desorption spectra. A systematic study is presented on the effect of varying terrace widths for atomic, molecular and dissociative adsorption with attractive and/or repulsive lateral interactions. We also present preliminary fits to experimental data on Xe, CO and hydrogen desorption from stepped Pt(111) surfaces.

Payne, S. H.; Kreuzer, H. J.

1998-03-01

91

Unipolar self-doping behavior in perovskite CH3NH3PbBr3  

NASA Astrophysics Data System (ADS)

Recent theoretical and experimental reports have shown that the perovskite CH3NH3PbI3 exhibits unique ambipolar self-doping properties. Here, we show by density-functional theory calculation that its sister perovskite, CH3NH3PbBr3, exhibits a unipolar self-doping behavior—CH3NH3PbBr3 presents only good p-type conductivity under thermal equilibrium growth conditions. We further show that despite a large bandgap of 2.2 eV, all dominant defects in CH3NH3PbBr3 create shallow levels, which partially explains the ultra-high open-circuit voltages achieved by CH3NH3PbBr3-based thin-film solar cells. Our results suggest that the perovskite CH3NH3PbBr3 can be both an excellent solar cell absorber and a promising low-cost hole-transport material for lead halide perovskite solar cells.

Shi, Tingting; Yin, Wan-Jian; Hong, Feng; Zhu, Kai; Yan, Yanfa

2015-03-01

92

Effects of in-situ NH3 post plasma treatment on the surface passivation layer  

NASA Astrophysics Data System (ADS)

Hydrogenated silicon nitride (SiNx:H) using plasma enhanced chemical vapor deposition is widely used in photovoltaic industry as an antireflection coating and passivation layer. The samples with or without in-situ NH3 post-plasma treatment had the following structures: SiNx/N-type Si/SiNx versus in-situ NH3 post-plasma treated SiNx/N-type Si/SiNx. The wafer was dipped in saw-damage-etching solution and wet cleaning process was treated. After the dry process with N2 atmosphere, SiNx thin film was deposited on back surface. Then SiNx thin film was deposited on the front surface with or without in-situ NH3 post-plasma treatment process. In order to minimize the plasma induced surface damage, we used lower power than the process power during the NH3 post-plasma treatment. After the in-situ NH3 post-plasma-treatment, we analyzed the effect of this in-situ NH3 post-plasma-treatment for passivation. The minority carrier lifetime was observed by means of quasi-steady-state photoconductance and microwave photoconductance.

Lee, Kyung Dong; Kang, Min Gu; Kim, Young Do; Tark, Sung Ju; Park, Sungeun; Kim, Donghwan

2011-12-01

93

Na3[B20H17NH3]: synthesis and liposomal delivery to murine tumors.  

PubMed Central

The polyhedral borane ion [n-B20H18]2- reacts with liquid ammonia in the presence of a suitable base to produce an apical-equatorial (ae) isomer of the [B20H17NH3]3- ion, [1-(2'-B10H9)-2-NH3B10H8]3-. The structure of this product has been confirmed by 11B NMR spectroscopy and x-ray crystallography. This species undergoes acid-catalyzed rearrangement to an apical-apical (a2) isomer, [1-(1'-B10H9)-2-NH3B10H8]3-, whose structure has been determined by 11B NMR spectroscopy. The sodium salts of both the ae and the a2 isomers of [B20H17NH3]3- have been encapsulated within small unilamellar liposomes, composed of distearoyl phosphatidylcholine/cholesterol (1:1), and investigated as boron-delivery agents for boron neutron capture therapy (BNCT) of cancer. The biodistribution of boron was determined after the injection of liposomal suspensions into BALB/c mice bearing EMT6 tumors. Both [B20H17NH3]3- isomers exhibited excellent tumor uptake and selectivity at very low injected doses, achieving peak tumor boron concentrations of 30-40 micrograms of B/g of tissue and tumor/blood boron ratios of approximately 5. The enhanced retention of the [B20H17NH3]3- isomers by EMT6 tumors may be attributed to their facile intracellular oxidation to an extremely reactive NH3-substituted [n-B20H18]2- ion, the electrophilic [B20H17NH3]- ion. Both isomers of [B20H17NH3]3- are at least 0.5 V more easily oxidized than other previously investigated species containing 20 boron atoms. In another experiment, [ae-B20H17NH3]3- was encapsulated in liposomes prepared with 5% PEG-2000-distearoyl phosphatidylethanolamine in the liposome membrane. As expected, these liposomes exhibited a longer circulation lifetime in the biodistribution experiment, resulting in the continued accumulation of boron in the tumor over the entire 48-hr experiment and reaching a maximum of 47 micrograms of B/g of tumor. PMID:8159700

Feakes, D A; Shelly, K; Knobler, C B; Hawthorne, M F

1994-01-01

94

Effects of atmospheric ammonia (NH3) on terrestrial vegetation: a review.  

PubMed

At the global scale, among all N (nitrogen) species in the atmosphere and their deposition on to terrestrial vegetation and other receptors, NH3 (ammonia) is considered to be the foremost. The major sources for atmospheric NH3 are agricultural activities and animal feedlot operations, followed by biomass burning (including forest fires) and to a lesser extent fossil fuel combustion. Close to its sources, acute exposures to NH3 can result in visible foliar injury on vegetation. NH3 is deposited rapidly within the first 4-5 km from its source. However, NH3 is also converted in the atmosphere to fine particle NH4+ (ammonium) aerosols that are a regional scale problem. Much of our current knowledge of the effects of NH3 on higher plants is predominantly derived from studies conducted in Europe. Adverse effects on vegetation occur when the rate of foliar uptake of NH3 is greater than the rate and capacity for in vivo detoxification by the plants. Most to least sensitive plant species to NH3 are native vegetation > forests > agricultural crops. There are also a number of studies on N deposition and lichens, mosses and green algae. Direct cause and effect relationships in most of those cases (exceptions being those locations very close to point sources) are confounded by other environmental factors, particularly changes in the ambient SO2 (sulfur dioxide) concentrations. In addition to direct foliar injury, adverse effects of NH3 on higher plants include alterations in: growth and productivity, tissue content of nutrients and toxic elements, drought and frost tolerance, responses to insect pests and disease causing microorganisms (pathogens), development of beneficial root symbiotic or mycorrhizal associations and inter species competition or biodiversity. In all these cases, the joint effects of NH3 with other air pollutants such as all-pervasive O3 or increasing CO2 concentrations are poorly understood. While NH3 uptake in higher plants occurs through the shoots, NH4+ uptake occurs through the shoots, roots and through both pathways. However, NH4+ is immobile in the soil and is converted to NO3- (nitrate). In agricultural systems, additions of NO3- to the soil (initially as NH3 or NH4+) and the consequent increases in the emissions of N2O (nitrous oxide, a greenhouse gas) and leaching of NO3- into the ground and surface waters are of major environmental concern. At the ecosystem level NH3 deposition cannot be viewed alone, but in the context of total N deposition. There are a number of forest ecosystems in North America that have been subjected to N saturation and the consequent negative effects. There are also heathlands and other plant communities in Europe that have been subjected to N-induced alterations. Regulatory mitigative approaches to these problems include the use of N saturation data or the concept of critical loads. Current information suggests that a critical load of 5-10 kg ha(-1) year(-1) of total N deposition (both dry and wet deposition combined of all atmospheric N species) would protect the most vulnerable terrestrial ecosystems (heaths, bogs, cryptogams) and values of 10-20 kg ha(-1) year(-1) would protect forests, depending on soil conditions. However, to derive the best analysis, the critical load concept should be coupled to the results and consequences of N saturation. PMID:12713921

Krupa, S V

2003-01-01

95

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

PubMed

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

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

2013-04-01

96

Thermal Durability of Cu-CHA NH3-SCR Catalysts for Diesel NOx Reduction  

SciTech Connect

Multiple catalytic functions (NOx conversion, NO and NH3 oxidation, NH3 storage) of a commercial Cu-zeolite urea/NH3-SCR catalyst were assessed in a laboratory fixed-bed flow reactor system after differing degrees of hydrothermal aging. Catalysts were characterized by using x-ray diffraction (XRD), 27Al solid state nuclear magnetic resonance (NMR) and transmission electron microscopy (TEM) / energy dispersive X-ray (EDX) spectroscopy to develop an understanding of the degradation mechanisms during catalyst aging. The catalytic reaction measurements of laboratory-aged catalysts were performed, which allows us to obtain a universal curve for predicting the degree of catalyst performance deterioration as a function of time at each aging temperature. Results show that as the aging temperature becomes higher, the zeolite structure collapses in a shorter period of time after an induction period. The decrease in SCR performance was explained by zeolite structure destruction and/or Cu agglomeration, as detected by XRD/27Al NMR and by TEM/EDX, respectively. Destruction of the zeolite structure and agglomeration of the active phase also results in a decrease in the NO/NH3 oxidation activity and the NH3 storage capacity of the catalyst. Selected laboratory aging conditions (16 h at 800oC) compare well with a 135,000 mile vehicle-aged catalyst for both performance and characterization criteria.

Schmieg, Steven J.; Oh, Se H.; Kim, Chang H.; Brown, David B.; Lee, Jong H.; Peden, Charles HF; Kim, Do Heui

2012-04-30

97

Experimental verification of the high pressure crystal structures in NH3BH3  

NASA Astrophysics Data System (ADS)

A detailed high-pressure study on NH3BH3 has been carried out using in situ synchrotron X-ray diffraction (XRD) and Raman scattering with a diamond anvil cell up to 20 and 33 GPa, respectively. The Rietveld refinement based on the XRD pattern and analysis of Raman data indicate two first-order phase transitions from the ambient pressure I4 mm structure (?-NH3BH3) to a high pressure Cmc21 phase (?-NH3BH3) at 2.14 GPa, and further into a monoclinic P21 (Z = 2) phase (?-NH3BH3) at 9.67 GPa. Fitting the measured volumetric compression data to the third order Birch-Murnaghan equation of state reveals a bulk modulus of B0 = 9.9 ± 0.5 and 17.0 ± 3.0 GPa (with fixed B0' = 4) for the ?-NH3BH3 below and above 5 GPa, respectively. Still, with the splitting of the NBH rock mode in Raman experiment, it is concluded that a second-order isostructural phase transition occurs at 5 GPa. By analyzing the dihydrogen bonding framework, the origin of the isostructural phase transition is attributed to the number of dihydrogen bondings per molecule in the Cmc21 phase increasing from 12 to 14 at 5 GPa.

Huang, Yanping; Huang, Xiaoli; Zhao, Zhonglong; Li, Wenbo; Jiang, Shuqing; Duan, Defang; Bao, Kuo; Zhou, Qiang; Liu, Bingbing; Cui, Tian

2014-06-01

98

Experimental verification of the high pressure crystal structures in NH3BH3.  

PubMed

A detailed high-pressure study on NH3BH3 has been carried out using in situ synchrotron X-ray diffraction (XRD) and Raman scattering with a diamond anvil cell up to 20 and 33 GPa, respectively. The Rietveld refinement based on the XRD pattern and analysis of Raman data indicate two first-order phase transitions from the ambient pressure I4 mm structure (?-NH3BH3) to a high pressure Cmc21 phase (?-NH3BH3) at 2.14 GPa, and further into a monoclinic P21 (Z = 2) phase (?-NH3BH3) at 9.67 GPa. Fitting the measured volumetric compression data to the third order Birch-Murnaghan equation of state reveals a bulk modulus of B0 = 9.9 ± 0.5 and 17.0 ± 3.0 GPa (with fixed B0 (') = 4) for the ?-NH3BH3 below and above 5 GPa, respectively. Still, with the splitting of the NBH rock mode in Raman experiment, it is concluded that a second-order isostructural phase transition occurs at 5 GPa. By analyzing the dihydrogen bonding framework, the origin of the isostructural phase transition is attributed to the number of dihydrogen bondings per molecule in the Cmc21 phase increasing from 12 to 14 at 5 GPa. PMID:24985654

Huang, Yanping; Huang, Xiaoli; Zhao, Zhonglong; Li, Wenbo; Jiang, Shuqing; Duan, Defang; Bao, Kuo; Zhou, Qiang; Liu, Bingbing; Cui, Tian

2014-06-28

99

Density dependence of the 5 micron infrared spectrum of NH3  

NASA Technical Reports Server (NTRS)

Measurements of dilute mixtures of NH3 in H2 were made in the window region 1900-2100/cm of the NH3 spectrum to determine is behavior with increasing pressure of H2. The spectra of pure H2, pure NH3, and mixtures of the two, in the total pressure range from 2.38 to 8.17 atm at 309 K, were obtained with a 975-cm white-cell. Synthetic spectra were calculated using precise line strengths, line positions, and a Lorentz profile. The experimental and calculated spectra are in reasonably good agreement, except that the former is super-imposed on a rather flat background not given by the calculation. A possible mechanism for this background is suggested.

Chapados, Camille; Bjoraker, Gordon L.; Birnbaum, George

1990-01-01

100

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

NASA Astrophysics Data System (ADS)

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.

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

2014-11-01

101

Silicene as a highly sensitive molecule sensor for NH3, NO and NO2.  

PubMed

On the basis of first-principles calculations, we demonstrate the potential application of silicene as a highly sensitive molecule sensor for NH3, NO, and NO2 molecules. NH3, NO and NO2 molecules chemically adsorb on silicene via strong chemical bonds. With distinct charge transfer from silicene to molecules, silicene and chemisorbed molecules form charge-transfer complexes. The adsorption energy and charge transfer in NO2-adsorbed silicene are larger than those of NH3- and NO-adsorbed silicones. Depending on the adsorbate types and concentrations, the silicene-based charge-transfer complexes exhibit versatile electronic properties with tunable band gap opening at the Dirac point of silicene. The calculated charge carrier concentrations of NO2-chemisorbed silicene are 3 orders of magnitude larger than intrinsic charge carrier concentration of graphene at room temperature. The results present a great potential of silicene for application as a highly sensitive molecule sensor. PMID:24595614

Hu, Wei; Xia, Nan; Wu, Xiaojun; Li, Zhenyu; Yang, Jinlong

2014-04-21

102

Mixing of Dust and NH3 Observed Globally over Anthropogenic Dust Sources  

NASA Technical Reports Server (NTRS)

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

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

2012-01-01

103

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

NASA Technical Reports Server (NTRS)

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.

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

1975-01-01

104

NH3 sensor based on CSA doped PANi-SnO2 nanohybrid  

NASA Astrophysics Data System (ADS)

The PANi-SnO2 hybrid nanocomposite based thin films doped with 10-50 wt % CSA were deposited on the glass substrates using the spin coating technique. The sensor response in relation to the CSA doping concentration and the gas concentration has been systematically studied. A significant sensitivity (91%) towards 100 ppm NH3 operating at room temperature is observed for the 30 wt % CSA doped PANi-SnO2 nanohybrid. The sensing mechanism of CSA doped PANi-SnO2 materials to NH3 was presumed to be the effect of p-n heterojunctions.

Khuspe, G. D.; Navale, S. T.; Chougule, M. A.; Mulik, R. N.; Godse, P. R.; Sen, Shashwati; Patil, V. B.

2014-04-01

105

Impact of In Situ NH3 Preannealing on Sub100 nm Tungsten Polymetal Gate Electrode during the Sealing Nitride Formation  

Microsoft Academic Search

We investigated the effects of in situ NH3 preannealing immediately before sealing nitride deposition on the wordline sheet resistance (Rs) of a tungsten polymetal gate electrode (W\\/WNx\\/poly-Si). While in situ NH3 preannealing is very effective for the suppression of W-O whisker formation, it was found that excessively long-time NH3 preannealing could cause an unexpectedly abnormal increase in the wordline Rs

Kwan-Yong Lim; Jung-Ho Lee; Heung-Jae Cho; Jae-Geun Oh; Byung-Seop Hong; Se-Aug Jang; Yong Soo Kim; Hong-Seon Yang; Hyun-Chul Sohn

2004-01-01

106

Effects of NH 3 Plasma Treatment of the Substrate on Metal Organic Chemical Vapor Deposition of Copper Films  

Microsoft Academic Search

Surface modification by NH3 plasma treatment enabled selective copper (Cu) chemical vapor deposition (CVD) andchanged the structure of the deposited Cu film. After NH3 plasma treatment of the substrate, Cu nucleation was suppressedon borophosphosilicate glass (BPSG), while Cu films were formed on TiN. NH3 plasma treatment was not as effective as N2 plasma treatment in inducing the selectivity. The lower

Young Suk Kim; Donggeun Jung; Dong Joon Kim; Suk-Ki Min

1998-01-01

107

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

PubMed

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

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

2014-09-25

108

Time resolved UV-spectroscopy of NH3 molecules vibrationally excited by CO2 laser radiation  

Microsoft Academic Search

The excitation of ammonia by a pulsed CO2 laser is investigated with emphasis on processes associated with collisions with argon. The previously reported multiphoton dissociation of NH3 under collisionless conditions; and the excitation mechanisms of nonresonant low vibrational levels were clarified to allow an appropriate selection of laser lines. A repertory was made of all vibrational rotational levels up to

H. Holbach

1980-01-01

109

Ground-based FTIR measurements of NH3 total columns and comparison with IASI data  

NASA Astrophysics Data System (ADS)

Atmospheric ammonia (NH3) dominates global emissions of total reactive nitrogen. It has an impact on human health, as a precursor of fine particulate matter, and on Earth's ecosystems, via deposition. The main source of global NH3 emissions is agriculture, the remaining ones being the oceans, natural vegetation, humans, wild animals and biomass burning. The global atmospheric budget of NH3 is still very uncertain in chemical models, highlighting the critical need for satellite and ground-based observations. We present, for the first time, time-series (2009 - 2011) of NH3 total columns obtained from ground-based FTIR measurements. These observations are performed at Reunion Island (21°S, 55°E), one of the two subtropical stations, in Southern Hemisphere, of the ground-based Network for the Detection of Atmospheric Composition Change (NDACC) equipped with FTIR instruments. The seasonal and inter-annual variabilities of ammonia observed at Reunion Island from the ground are compared to the ones derived from recent IASI data obtained with a new retrieval method based on the calculation of a Hyperspectral Range Index.

Vigouroux, Corinne; De Mazière, Martine; Desmet, Filip; Hermans, Christian; Langerock, Bavo; Scolas, Francis; Van Damme, Martin; Clarisse, Lieven; Coheur, Pierre-François

2013-04-01

110

Spin transport in CH3NH3PbI3  

NASA Astrophysics Data System (ADS)

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).

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

2014-10-01

111

Parametrization of electron impact ionization cross sections for CO, CO2, NH3 and SO2  

NASA Technical Reports Server (NTRS)

The electron impact ionization and dissociative ionization cross section data of CO, CO2, CH4, NH3, and SO2, measured in the laboratory, were parameterized utilizing an empirical formula based on the Born approximation. For this purpose an chi squared minimization technique was employed which provided an excellent fit to the experimental data.

Srivastava, Santosh K.; Nguyen, Hung P.

1987-01-01

112

Estimation of NH3 Bi-Directional Flux from Managed Agricultural Soils  

EPA Science Inventory

The Community Multi-Scale Air Quality model (CMAQ v4.7) contains a bi-directional ammonia (NH3) flux option that computes emission and deposition of ammonia derived from commercial fertilizer via a temperature dependent parameterization of canopy and soil compensation ...

113

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

SciTech Connect

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.

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

2015-01-01

114

Towards a carbon independent and CO2-free electrochemical membrane process for NH3 synthesis.  

PubMed

Ammonia is exclusively synthesized by the Haber-Bosch process starting from precious carbon resources such as coal or CH4. With H2O, H2 is produced and with N2, NH3 can be synthesized at high pressures and temperatures. Regrettably, the carbon is not incorporated into NH3 but emitted as CO2. Valuable carbon sources are consumed which could be used otherwise when carbon sources become scarce. We suggest an alternative process concept using an electrochemical membrane reactor (ecMR). A complete synthesis process with N2 production and downstream product separation is presented and evaluated in a multi-scale model to quantify its energy consumption. A new micro-scale ecMR model integrates mass, species, heat and energy balances with electrochemical conversions allowing further integration into a macro-scale process flow sheet. For the anodic oxidation reaction H2O was chosen as a ubiquitous H2 source. Nitrogen was obtained by air separation which combines with protons from H2O to give NH3 using a hypothetical catalyst recently suggested from DFT calculations. The energy demand of the whole electrochemical process is up to 20% lower than the Haber-Bosch process using coal as a H2 source. In the case of natural gas, the ecMR process is not competitive under today's energy and resource conditions. In future however, the electrochemical NH3 synthesis might be the technology-of-choice when coal is easily accessible over natural gas or limited carbon sources have to be used otherwise but for the synthesis of the carbon free product NH3. PMID:24557153

Kugler, K; Ohs, B; Scholz, M; Wessling, M

2014-04-01

115

Sublimation studies of CO, N2, CH4 and NH3 ice mixtures  

NASA Astrophysics Data System (ADS)

The ability of water to retain molecules with lower temperatures of sublimation (hereafter volatiles) is well known. This fact can influence the interstellar medium gas phase composition; as well as help us to understand the jumps in the cometary brightness (outbursts) produced by the explosions of water ice grains because of gases trapped within their structure. Our group is carrying out experiments to study the ability of volatiles, of high temperature of sublimation (CO2 , NH3 ,...), to retain volatiles of lower sublimation temperature (hereafter hypervolatiles) such as nitrogen, carbon monoxide or methane. All these molecules are relevant in many astro-physical scenarios and in some cases can be the most abundant, as is carbon dioxide on Mars; then they could influence these scenarios in a similar way water does. The contribution will show our latest results obtained using ammonia as the retainer of hypervolatiles. Experiments were carried out in a high vacuum system (base pressure 1·10-7 mbar). Results presented here concern two kinds of experiments: mixtures of hypervolatiles and NH3, dominated by NH3, and layered experiments, where the hypervolatile and NH3 were deposited independently. In these layered experiments two different possibilities were explored. Firstly, depositing the hy-pervolatile and covering it with a thicker layer of ammonia, and secondly, depositing ammonia and covering it with a thinner layer of hypervolatile. Once deposition had taken place, the sample holder was warmed up at a constant rate (1 K/min). Sublimation was monitored with a quartz crystal microbalance (QCMB) and a quadrupole mass spectrometer (QMS). Despite there being slight differences among different hypervolatile molecules and among different de-position forms, the experiments conclude that ammonia retains hypervolatiles even up to the sublimation temperature of NH3 when they were deposited either in the form of mixtures or as a set of consecutive layers.

Ángel Satorre Aznar, Miguel; Leliwa-Kopystynki, Jacek; Santonja Molto, Carmina; Luna Molina, Ramon

116

Nucleobases and prebiotic molecules in organic residues produced from the ultraviolet photo-irradiation of pyrimidine in NH(3) and H(2)O+NH(3) ices.  

PubMed

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 H(2)O ices leads to the formation of a suite of oxidized pyrimidine derivatives, including the nucleobase uracil. In the present work, NH(3):pyrimidine and H(2)O:NH(3):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. PMID:22519971

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

2012-04-01

117

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)

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.

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

2012-01-01

118

Density functional study of adsorption properties of NO and NH3 over CuO/?-Al2O3 catalyst  

NASA Astrophysics Data System (ADS)

Currently, selective catalytic reduction (SCR) of NOx with NH3 has been widely applied to reduce the emission of nitrogen oxides from mobile and stationary sources. But the detailed SCR reaction mechanism is still controversial and lacks the related comparative study of molecule modeling. The SCR reaction belongs to the gas-solid multiphase reaction, in which the adsorption of NH3 and NO by the catalysts plays an important role. In the present study, the adsorption properties of NH3 and NO on both the dry and partially hydroxylated ?-Al2O3 (1 1 0) surfaces supported CuO were revealed using the density-function theory (DFT) calculations. The results showed that NH3 could be adsorbed strongly on the dry (1 1 0) surface in the form of coordinated NH3 and NH4+. Some of the coordinated NH3 could then undergo H-abstraction and form the -NH2 species. NO could be adsorbed weakly on the dry surface, and could also be adsorbed as bidentate nitrates or bridged nitrites. However, the adsorption activation of NH3 and NO on the partially hydroxylated surface was much weaker. The results of the DFT calculations are in good agreement with the experimental results and provided detailed clues to understand the adsorption mechanism of NH3 and NO on the CuO/?-Al2O3 catalysts.

Cao, Fan; Su, Sheng; Xiang, Jun; Sun, Lushi; Hu, Song; Zhao, Qingsen; Wang, Pengying; Lei, Siyuan

2012-11-01

119

Closed-loop control of a SCR system using a NOx sensor cross-sensitive to NH3  

E-print Network

Closed-loop control of a SCR system using a NOx sensor cross-sensitive to NH3 A.Bonfils , Y. Creff for an automotive selective catalytic reduction (SCR) system, for which the feedback is based on a NOx sensor measurement. This NOx sensor is cross-sensitive to NH3, which is critical for control purposes: a study

120

SIMPLE DESIGN FOR AUTOMATION OF TUNGSTEN(VI) OXIDE TECHNIQUE FOR MEASUREMENT OF NH3, AND HNO3  

EPA Science Inventory

The tungstic acid technique for collection and analysis of NH3 and HNO3 concentrations in the ambient air has been automated in a simple and cost-effective design. The design allows complete separation of HNO3 and NH3 during detection. Unattended operation in field trials has bee...

121

Study of Reaction NH3 + H NH2 + H2 by a Simple Program to Determine the Reaction Rate  

E-print Network

Study of Reaction NH3 + H NH2 + H2 by a Simple Program to Determine the Reaction Rate Patr´icia R developed a simple program to determine the reaction rate by using conventional transition state theory abstraction in the reaction NH3 + H NH2 + H2 is used as a model to demonstrate usage of the program. The rate

122

Molecular Modeling of Interactions in Zeolites: An Ab Initio Embedded Cluster Study of NH3 Adsorption in Chabazite  

E-print Network

ARTICLES Molecular Modeling of Interactions in Zeolites: An Ab Initio Embedded Cluster Study of NH3 approach for modeling interactions in zeolites and an application of this model to the study of NH3 and NH4 relaxation in zeolite calculations is addressed. After considering the effects of electron correlation, basis

Truong, Thanh N.

123

Adsorption and Desorption of HCI on Pt(111)  

SciTech Connect

The adsorption and desorption of HCl on Pt(111) is investigated by temperature programmed desorption (TPD), infrared reflection absorption spectroscopy (IRAS), and low energy electron diffraction (LEED). Five peaks are identified in the TPD spectra prior to the onset of multilayer desorption. For (theta > 0.38 ML, theta = 1.5x1015 cm-2) HCl adsorbs molecularly at 20 K as an amorphous solid with two desorption peaks at 70 and 77 K. A third peak at 84 K is tentatively assigned to molecularly adsorbed HCl. Peaks at ~135 and 200 K are assigned to recombinative desorption of dissociated HCl, in agreement with earlier studies. Kinetic analysis is conducted and the results demonstrate a strong coverage dependent desorption energy for theta < 0.25 ML. The LEED data indicates that at low temperature the adsorbed HCl clusters into ordered islands with a (3 x 3) structure and a local coverage of 4/9 with respect to the Pt(111) substrate.

Daschbach, John L.; Kim, Jooho; Ayotte, Patrick; Smith, R. Scott; Kay, Bruce D.

2005-07-26

124

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

NASA Astrophysics Data System (ADS)

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.

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

2014-12-01

125

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

PubMed

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

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

2014-12-14

126

On the reaction CH2O + NH3 Yields CH2NH + H2O  

NASA Technical Reports Server (NTRS)

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.

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

2000-01-01

127

Planetary fluids He and NH3 at high shock pressures and temperatures  

NASA Astrophysics Data System (ADS)

Liquid He at 4.3 K and 1 atm was shocked to 16 GPa (160 kbar) and 12,000 K and double-shocked to 56 GPa and 21,000 K. Liquid perturbation theory was used to determine an effective interatomic potential from which the equation of state of He can be obtained over a wide range of densities and temperatures in the envelopes of the outer plants. A new fast optical pyrometer and a cryogenic specimen holder for liquid NH3 were developed to measure shock temperatures of 4400 and 3600 K at pressures of 59 and 48 GPa. These conditions correspond to those in the ice layers in Uranus and Neptune. The shock temperature data are in reasonable agreement with an equation of state by Ree based on an intermolecular potential derived from NH3 Hugoniot data.

Nellis, W. J.; Radousky, H. B.; Mitchell, A. C.; Holmes, N. C.; Ross, M.; Young, D. A.

1985-04-01

128

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

PubMed

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

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

2001-01-01

129

Performance Analysis of Rectifier in NH3-H2O Absorption Heat Pump  

NASA Astrophysics Data System (ADS)

Characteristic of stripping section of packed-tower type rectifierwas presentedin previous paper. In order to improve NH3 concentration inrefrigerant vapor, enriching section is considered effective. Refrigerant vapor from stripping section of rectifier and reflux solution from partial condenser flow into this section, and the proportion of solution flow rate to vapor flow rate of enriching section called reflux ratio is much smaller than that of stripping section. So the effect of reflux ratio on rectification process might be larger. In this paper the effect of reflux flow rate and NH3 concentration in reflux solution is investigated experimentally. As a result, it was derived that the performance of enriching section was mainly decided by reflux ratio. Then the effect of rectification performance on heat rate of partial condenser and evaporator was evaluated using the experimental result of enriching section performance.

Tsujimori, Atushi; Ozaki, Eiichi; Nakao, Kazushige

130

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

NASA Technical Reports Server (NTRS)

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.

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

1991-01-01

131

Estimation of NH 3 bi-directional flux from managed agricultural soils  

NASA Astrophysics Data System (ADS)

The Community Multi-Scale Air Quality model (CMAQ) is used to assess regional air quality conditions for a wide range of chemical species throughout the United States (U.S.). CMAQ representation of the regional nitrogen budget is limited by its treatment of ammonia (NH 3) soil emission from, and deposition to underlying surfaces as independent rather than tightly coupled processes, and by its reliance on soil emission estimates that do not respond to variable meteorology and ambient chemical conditions. The present study identifies an approach that addresses these limitations, lends itself to regional application, and will better position CMAQ to meet future assessment challenges. These goals were met through the integration of the resistance-based flux model of Nemitz et al. (2001) with elements of the United States Department of Agriculture EPIC (Environmental Policy Integrated Climate) model. Model integration centers on the estimation of ammonium and hydrogen ion concentrations in the soil required to estimate soil NH 3 flux. The EPIC model was calibrated using data collected during an intensive 2007 field study in Lillington, North Carolina. A simplified process model based on the nitrification portion of EPIC was developed and evaluated. It was then combined with the Nemitz et al. (2001) model and measurements of near-surface NH 3 concentrations to simulate soil NH 3 flux at the field site. Finally, the integrated flux (emission) results were scaled upward and compared to recent national ammonia emission inventory estimates. The integrated model results are shown to be more temporally resolved (daily), while maintaining good agreement with established soil emission estimates at longer time-scales (monthly). Although results are presented for a single field study, the process-based nature of this approach and NEI comparison suggest that inclusion of this flux model in a regional application should produce useful assessment results if nationally consistent sources of driving soil and agricultural management information are identified.

Cooter, Ellen J.; Bash, Jesse O.; Walker, John T.; Jones, M. R.; Robarge, Wayne

2010-06-01

132

Reaction rate constant of SO3+NH3 in the gas phase  

Microsoft Academic Search

The reaction rate constant of SO3+NH3 in the gas phase was measured using a photofragment emission flow tube technique. The reaction rate constant at room temperature is (6.9+\\/-1.5)×10-11 cm3 molecule-1 s-1 at He pressures of 1-2 torr. This measured reaction rate is new information for studying the formation process of ammounium sulfates in the atmosphere. The reaction rate constant of

Gaunlin Shen; Masako Suto; L. C. Lee

1990-01-01

133

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

NASA Astrophysics Data System (ADS)

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.

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

2012-10-01

134

Benchmarking of ONIOM method for the study of NH 3 dissociation at open ends of BNNTs  

Microsoft Academic Search

The reliability of ONIOM approach have been examined in calculations of adsorption energies, transition structures, change\\u000a of HOMO-LUMO energy gaps and equilibrium geometries of the interaction between NH3 and N-enriched (A) or B-enriched (B) open ended boron nitride nanotubes. To these ends, four models of the A or B, with different inner and outer layers have been studied. In addition,

Ali Ahmadi; Javad Beheshtian; Mohammad Kamfiroozi

135

Desorption Kinetics of Methanol, Ethanol, and Water from Graphene  

SciTech Connect

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.

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

2014-09-18

136

Basis set superposition error in calculations of nonadditive effects in Li(NH 3) n and Li(NH 3) n+ ( n=1-4) clusters  

NASA Astrophysics Data System (ADS)

The effect of the basis set superposition error is investigated at both SCF and correlated levels, using the pairwise additive function counterpoise (PAFC), the site-site function counterpoise (SSFC), and the White and Davidson method, for [Li(NH 3) n] q+ ( n=1-4; q=0, 1) clusters. The PAFC method gives results surprisingly close to the ones obtained with the SSFC approximation. The SSFC, and White and Davidson methods give the possibility of a meaningful decomposition of the total interaction energy of the many-body cluster into its n-body components. The obtained results show that the White-Davidson method is more correct, and always gives the BSSE corrections with the right sign. Moreover it is presented that the effect of the geometry distortions of the interacting particles is so small, that it can be omitted.

Mierzwicki, Krzysztof; Latajka, Zdzis?aw

2000-07-01

137

The influence of NH 3 -attaching on the NMR parameters in the zigzag BN nanotube  

NASA Astrophysics Data System (ADS)

Two models of (10, 0) boron nitride nanotubes (BNNTs), perfect and Ammonia-attached, were studied in order to evaluate the influence of NH 3-attaching on the B-11 and N-15 nuclear magnetic resonance in the (10, 0) boron-nitride nanotube (BNNT) for the first time. At first, based on density functional theory (DFT) each of the structures was optimized using B3LYP/6-31G (d) model chemistry. At the next step, the chemical-shielding (CS) tensors were calculated using the B3LYP/6-31G (d, p) level of theory in both of the relaxed forms and were converted to experimentally measurable nuclear magnetic resonance (NMR) parameters, i.e. chemical-shielding isotropic (CSI) and chemical-shielding anisotropic (CSA). Our calculation revealed that in the NH 3-attached BNNT (the most stable model) the B atom chemically bonded to the NH 3 molecule has the largest chemical-shielding isotropic (CSI) and the smallest chemical-shielding anisotropic (CSA) values among the other boron nuclei. Additionally, the NMR parameters of those nuclei directly bonded to the boron dramatically change while those of the other B nuclei remain almost unchanged.

Zahedi, Ehsan; Bodaghi, Ali; Seif, Ahmad; Boshra, Asadollah

2011-02-01

138

Imaging studies of the photodissociation of NH3+ and ND3+ cations.  

PubMed

Velocity map ion imaging methods have been used to study the photofragmentation dynamics of state-selected NH3+ and ND3+ cations. The cations were prepared in selected nu2+ bending vibrational levels of the ground (x2A'') electronic state by two-photon resonant, three-photon ionization of NH3(ND3), via several different nu2' levels of the and ' Rydberg states. Subsequent excitation to the A2E state by absorption of a 207.6 nm photon resulted in N-H(D) bond fission and NH2+(ND2+) fragment ion formation. These fragments exhibit isotropic recoil velocity distributions, which peak at low kinetic energy but extend to the maximum allowed by energy conservation. Such findings accord with conclusions from earlier electron induced photoionization and photoelectron-photoion coincidence studies of NH3 at similar total energies (defined relative to the ground-state neutral) and, as previously, can be rationalized in terms of excitation to the Jahn-Teller distorted state, rapid radiationless transfer via one or more conical intersections linking the and state potential energy surfaces (PESs) and subsequent unimolecular decay on the latter PES. Weak NH2+ and NH+ fragment ion signals are also observed when exciting with the ionization laser only; imaging these fragment ions provides some insights into their likely formation mechanisms. PMID:19216561

Webb, Alexander D; Nahler, N Hendrik; Ashfold, Michael N R

2009-04-23

139

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

NASA Astrophysics Data System (ADS)

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).

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

2013-02-01

140

Recent Searches for the Radio Lines of NH_3 in Comets  

E-print Network

Radio observations in the ammonia inversion lines of four comets, C/2001 A2 (LINEAR), 153P/Ikeya-Zhang, C/2001 Q4 (NEAT) and C/2002 T7 (LINEAR), were performed at the Effelsberg 100-m Radio Telescope during their respective close approaches to Earth. None of the four lowest energy metastable lines (J,K=J),J=1--4, could be detected in these comets. We derive the following 3 sigma upper bounds on the NH_3 production rate, and c omparing to the corresponding water production rates, percentage NH_3 abundances relative to H_2O: Q(NH_3) Comet 153P/Ikeya-Zhang. At 0.74% or less, the ammonia-to-water ratios are factors of 2 below the value for C/1995 O1 (Hale-Bopp) and 1P/Halley, suggesting chemical diversity between comets. The 18-cm lines of OH were clearly detected in the two comets observed during the 2004 campaign, thereby validating the cometary ephemerides.

J. Hatchell; M. K. Bird; F. F. S. van der Tak; W. A. Sherwood

2005-05-20

141

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

NASA Astrophysics Data System (ADS)

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.

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

2012-12-01

142

Adsorption and desorption of hydrogen on Rh(311) and comparison with other Rh surfaces  

NASA Astrophysics Data System (ADS)

We present LEED and thermal desorption data for hydrogen adsorption on Rh(311). An anisotropic lattice gas model with first, second and third nearest neighbor and trio interactions is set up and solved using transfer matrix techniques to explain equilibrium structural data and temperature-programmed desorption consistently. A comparison with results for hydrogen on Rh(110) and Rh(111) is made.

Payne, S. H.; Kreuzer, H. J.; Frie, W.; Hammer, L.; Heinz, K.

1999-02-01

143

Removal of high concentration of NH3 and coexistent H2S by biological activated carbon (BAC) biotrickling filter.  

PubMed

High efficiency of NH3 and H2S removal from waste gases was achieved by the biotrickling filter. Granular activated carbon (GAC), inoculated with Arthrobacter oxydans CH8 for NH3 removal and Pseudomonas putida CH11 for H2S removal, was used as packing material. Under conditions in which 100% H2S was removed, extensive tests to eliminate high concentrations of NH3 emission-including removal characteristics, removal efficiency, and removal capacity of the system-were performed. The results of the Bed Depth Service Time (BDST) experiment suggested that physical adsorption of NH3 gas by GAC was responsible for the first 10 days, after which NH3 gas was biodegraded by inoculated microorganisms. The dynamic steady state between physical adsorption and biodegradation was about two weeks. After the system achieved equilibrium, the BAC biotrickling filter exhibited high adaptation to shock loading, elevated temperature, and flow rate. Greater than 96% removal efficiency for NH3 was achieved during the 140-day operating period when inlet H2S loading was maintained at 6.25 g-S/m3/h. During the operating period, the pH varied between 6.5 and 8.0 after the physical adsorption stage, and no acidification or alkalinity was observed. The results also demonstrated that NH3 removal was not affected by the coexistence of H2S while gas retention time was the key factor in system performance. The retention time of at least 65 s is required to obtain a greater than 95% NH3 removal efficiency. The critical loading of NH3 for the system was 4.2 g-N/m3/h, and the maximal loading was 16.2 g-N/m3/h. The results of this study could be used as a guide for further design and operation of industrial-scale systems. PMID:16051088

Chung, Ying-Chien; Lin, Yu-Yen; Tseng, Ching-Ping

2005-11-01

144

Experimental and theoretical studies of reactions of neutral vanadium and tantalum oxide clusters with NO and NH3.  

PubMed

Reactions of neutral vanadium and tantalum oxide clusters with NO, NH(3), and an NO/NH(3) mixture in a fast flow reactor are investigated by time of flight mass spectrometry and density functional theory (DFT) calculations. Single photon ionization through a 46.9 nm (26.5 eV) extreme ultraviolet (EUV) laser is employed to detect both neutral cluster distributions and reaction products. Association products VO(3)NO and V(2)O(5)NO are detected for V(m)O(n) clusters reacting with pure NO, and reaction products, TaO(3,4)(NO)(1,2), Ta(2)O(5)NO, Ta(2)O(6)(NO)(1-3), and Ta(3)O(8)(NO)(1,2) are generated for Ta(m)O(n) clusters reacting with NO. In both instances, oxygen-rich clusters are the active metal oxide species for the reaction M(m)O(n)+NO?M(m)O(n)(NO)(x). Both V(m)O(n) and Ta(m)O(n) cluster systems are very active with NH(3). The main products of the reactions with NH(3) result from the adsorption of one or two NH(3) molecules on the respective clusters. A gas mixture of NO:NH(3) (9:1) is also added into the fast flow reactor: the V(m)O(n) cluster system forms stable, observable clusters with only NH(3) and no V(m)O(n)(NO)(x)(NH(3))(y) species are detected; the Ta(m)O(n) cluster system forms stable, observable mixed clusters, Ta(m)O(n)(NO)(x)(NH(3))(y), as well as Ta(m)O(n)(NO)(x) and Ta(m)O(n)(NH(3))(y) individual clusters, under similar conditions. The mechanisms for the reactions of neutral V(m)O(n) and Ta(m)O(n) clusters with NO/NH(3) are explored via DFT calculations. Ta(m)O(n) clusters form stable complexes based on the coadsorption of NO and NH(3). V(m)O(n) clusters form weakly bound complexes following the reaction pathway toward end products N(2)+H(2)O without barrier. The calculations give an interpretation of the experimental data that is consistent with the condensed phase reactivity of V(m)O(n) catalyst and suggest the formation of intermediates in the catalytic chemistry. PMID:21054039

Heinbuch, S; Dong, F; Rocca, J J; Bernstein, E R

2010-11-01

145

Enhancement of NH3 Gas Sensitivity at Room Temperature by Carbon Nanotube-Based Sensor Coated with Co Nanoparticles  

PubMed Central

Multi-walled carbon nanotube (MWCNT) film has been fabricated onto Pt-patterned alumina substrates using the chemical vapor deposition method for NH3 gas sensing applications. The MWCNT-based sensor is sensitive to NH3 gas at room temperature. Nanoclusters of Co catalysts have been sputtered on the surface of the MWCNT film to enhance gas sensitivity with respect to unfunctionalized CNT films. The gas sensitivity of Co-functionalized MWCNT-based gas sensors is thus significantly improved. The sensor exhibits good repeatability and high selectivity towards NH3, compared with alcohol and LPG. PMID:23364198

Nguyen, Lich Quang; Phan, Pho Quoc; Duong, Huyen Ngoc; Nguyen, Chien Duc; Nguyen, Lam Huu

2013-01-01

146

Enhancement of NH3 gas sensitivity at room temperature by carbon nanotube-based sensor coated with Co nanoparticles.  

PubMed

Multi-walled carbon nanotube (MWCNT) film has been fabricated onto Pt-patterned alumina substrates using the chemical vapor deposition method for NH(3) gas sensing applications. The MWCNT-based sensor is sensitive to NH(3) gas at room temperature. Nanoclusters of Co catalysts have been sputtered on the surface of the MWCNT film to enhance gas sensitivity with respect to unfunctionalized CNT films. The gas sensitivity of Co-functionalized MWCNT-based gas sensors is thus significantly improved. The sensor exhibits good repeatability and high selectivity towards NH(3), compared with alcohol and LPG. PMID:23364198

Nguyen, Lich Quang; Phan, Pho Quoc; Duong, Huyen Ngoc; Nguyen, Chien Duc; Nguyen, Lam Huu

2013-01-01

147

Rovibrational spectra of ammonia. II. Detailed analysis, comparison, and prediction of spectroscopic assignments for 14NH3,15NH3, and 14ND3  

NASA Astrophysics Data System (ADS)

Several aspects of ammonia rovibrational spectra have been investigated using the new HSL-2 potential energy surface that includes an approximate correction for nonadiabatic effects. The unprecedented accuracy of rovibrational energy levels and transition energies computed using HSL-2 was demonstrated in Part I of this study. For 14NH3, new assignments for a few ?3 + ?4 band transitions and energy levels are suggested, and discrepancies between computed and HITRAN energy levels in the 2?4 band are analyzed (2?4 is the most difficult band below 5000 cm-1). New assignments are suggested for existing or missing 2?4 levels. Several new vibrational bands are identified from existing, unassigned HITRAN data, including 2?2 + ?4, (?3 + ?4) -A'/A'', ?1 + 2?2, and 2?2 + 2?4. The strong mixing between the 2?4 and 2?2 + ?4 bands is carefully examined and found to be the source of the difficulties in the experimental modeling of 2?4. Discussion is presented for preliminary J = 10 results, where the overall root-mean-square error is estimated to be less than 0.039 cm-1. The analysis of the 4?2 band demonstrates both the reliability and the accuracy of predictions from HSL-2. The full list of computed J = 0 band origins (with assignments) and the inversion splittings up to 7000-8000 cm-1 above the zero-point energy are presented. J = 0-2 levels are reported for those bands below 5100 cm-1 that are missing from the HITRAN database. For 15NH3, excellent agreement is found for the available ?2 and ?3 + ?4(E) transition energies, but significant deficiencies are shown for HITRAN levels and several corrections are suggested. The 15N isotopic effects are presented for the J = 0-6 levels of 13 HITRAN bands. For 14ND3, we reproduce the pure rotational inversion spectra line frequencies with an accuracy similar to that for 14NH3. However, it is not possible to reproduce simultaneously all four pairs of inversion-split vibrational fundamentals to better than 0.05 cm-1 uncertainty. It is suggested that a reanalysis of some suspicious 14ND3 fundamental bands is required. The analyses presented here and in Part I show that rovibrational energy levels and transition frequencies computed with HSL-2 (with nonadiabatic corrections) remain highly accurate well beyond the experimental data used in the refinement procedure. Calculations using HSL-2 are capable of revealing many deficiencies in experimental analyses of ammonia spectra and provide reliable predictions with similar accuracy. It is expected that the results of this study will be useful in the future interpretation of high-resolution spectra from laboratory experiments or from astronomical observations. The present work represents a very significant advance in the state of our knowledge of the spectroscopy of ammonia and its isotopologues.

Huang, Xinchuan; Schwenke, David W.; Lee, Timothy J.

2011-01-01

148

On the nature of the interaction in donor-acceptor van der Waals complexes: BH 3…CO, BF 3…CO, BH 3…NH 3 and BF 3…NH 3  

Microsoft Academic Search

Ab initio calculations at the MP2\\/6–31G?? level have been carried out to analyze the nature of the interaction in BH3…CO, BF3…CO, BH3…NH3 and BF3…NH3 van der Waals complexes. There is a good correlation between charge transfer, as measured by a method based on the expansion of the MOs of a complex system in terms of the MOs of its fragments,

V. M. Rayón; J. A. Sordo

1998-01-01

149

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

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

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

1986-01-01

150

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

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

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

1986-01-01

151

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)

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.

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

2014-03-01

152

M dependence in the analysis of NH3-He microwave double resonance experiments  

NASA Technical Reports Server (NTRS)

New close-coupled calculations of laboratory-frame, m-dependent cross sections for rotational excitation in NH3-He collisions are used to examined the validity of using degeneracy averaged values in the analysis of four-level double resonance experiments. It is found that the proper use of m-dependent cross sections and absorption probabilities produces only minor changes in the calculated Delta I/I (the fractional change in the signal absorption intensity when pumping radiation is applied) and does not, therefore, resolve the discrepancies between theoretical and experimental values that were noted in previous studies.

Davis, S. L.; Green, S.

1983-01-01

153

Identification of forbidden vibration-rotation transitions in 15NH3  

NASA Astrophysics Data System (ADS)

Forbidden ?k - l = 3 vibration-rotation transitions have been observed in the ?4 band of 15NH3. The analysis of these transitions, together with previously published data on the allowed transitions, has made it possible to determine a set of molecular parameters, including for the first time the rotational constant C as well as the centrifugal distortion constants DK and HKKK, which are necessary for the calculation of energy levels. Some weak forbidden transitions in the ?2 band have also been observed.

Urban, Š.; D'Cunha, Romola; Narahari Rao, K.

1984-07-01

154

An Innovative Measurement for Testing the Nanocatalyst Degradation Efficiency of NH3  

NASA Astrophysics Data System (ADS)

This study develops a low-cost, fast and innovative measurement method for testing the efficiency of photocatalysts in the degradation of gaseous concentrations. In the past, photocatalyst tests of catalyst response to gases mainly relied on measurement with either GC/MS (Gas Chromatography/Mass Spectrometer) or FTIR (Fourier Transform Infrared Spectroscopy), to monitor the reaction process. However, these two instruments are very expensive, and the processes are complicated and time-consuming. The major devices of the measurement method developed by this study are UV/VIS spectrophotometer and quartz cuvettes. The experimental procedures are not only simple but fast. In the experiment, a gas of a specific concentration is first injected into an enclosed quartz cuvette. The cuvette is then placed in the UV/VIS spectrophotometer to carry out tests to obtain an absorption spectrum. Thus, a calibration curve of UV light absorbance intensity vs. various gaseous concentrations can also be obtained using the same method. The degradation efficiency of the different photocatalysts is to be measured. Quartz plates are coated with two different types of TiO2 nanocatalysts. The coated plates are then placed in separate cuvettes. After injecting NH3 into a quartz cuvette, the cuvette is then put under the UV light irradiation to perform the degradation experiment. Afterwards, the cuvette is transferred to the UV/VIS spectrophotometer for testing. The absorbance intensity of the absorption spectra is then compared with the calibration curves. Based on the change of the gaseous concentration, the degradation efficiency of the photocatalyst is determined. The experimental results reveal that the self-made TiO2 nanocatalyst has excellent degradation efficiency towards NH3. When NH3 is exposed to UV irradiation for 60 minutes, the gaseous concentration can be reduced to 10.35% of the original concentration. However, the commercial TiO2 nanocatalyst can only reduce the gaseous concentration to 50.2% of the original concentration. In addition, the degradation reaction rate constant of the self-made TiO2 nanocatalyst towards NH3 is as high as 0.029 min-1.

Jwo, C. S.; Chen, D. M.; Chang, H.; Chen, J. Z.; Tien4, D. C.

2006-10-01

155

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...

156

Effects of NH 3 Plasma Treatment of the Substrate on Metal Organic Chemical Vapor Deposition of Copper Films  

NASA Astrophysics Data System (ADS)

Surface modification by NH3 plasma treatment enabled selective copper (Cu) chemical vapor deposition (CVD) andchanged the structure of the deposited Cu film. After NH3 plasma treatment of the substrate, Cu nucleation was suppressedon borophosphosilicate glass (BPSG), while Cu films were formed on TiN. NH3 plasma treatment was not as effective as N2 plasma treatment in inducing the selectivity. The lower efficiency of the NH3 plasma in inducing the selectivitycan be explained by the generation of NH++ or H species. A Cu film deposited on plasma-treated TiN showed larger grainsand enhanced (111) preferential orientation compared with that deposited on untreated TiN, which could be explained in termsof surface energy minimization.

Kim, Young; Jung, Donggeun; Kim, Dong; Min, Suk-Ki

1998-08-01

157

Control of Charge Transport in the Perovskite CH3 NH3 PbI3 Thin Film.  

PubMed

Carrier density and transport properties in the CH3 NH3 PbI3 thin film have been investigated. It is found that the carrier density, the depletion field, and the charge collection and transport properties in the CH3 NH3 PbI3 absorber film can be controlled effectively by different concentrations of reactants. That is, the carrier properties and the self-doping characteristics in CH3 NH3 PbI3 films are strongly influenced by the reaction thermodynamic and kinetic processes. Furthermore, by employing mixed solvents with ethanol and isopropanol to deposit the CH3 NH3 PbI3 film, the charge collection and transport efficiencies are improved significantly, thereby yielding an overall enhanced cell performance. PMID:25581504

Shi, Jiangjian; Wei, Huiyun; Lv, Songtao; Xu, Xin; Wu, Huijue; Luo, Yanhong; Li, Dongmei; Meng, Qingbo

2015-03-16

158

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

PubMed Central

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

2013-01-01

159

Characterization of Biochar using Temperature Programmed Oxidation  

Technology Transfer Automated Retrieval System (TEKTRAN)

Biochar from the fast pyrolysis of biomass was characterized by Temperature Programmed Oxidation. This technique can be used to assess the oxidative reactivity of carbonaceous solids where higher temperature reactivity indicates greater structural order. The samples examined include soy and barley...

160

Impact of atmospheric NH 3 deposition on plant growth and functioning — a case study with Brassica oleracea L  

Microsoft Academic Search

Brassica oleraceaL. (curly kale) was exposed to 0, 2, 4, 6 and 8?l l?1NH3during one week and the impact on growth and N compounds was determined. Exposure to NH3increased shoot biomass production at 2 and 4?l l?1, but resulted in an inhibition of shoot and root growth at 6 and 8?l l?1. Shoot to root ratio was not affected up

Ana Castro; Ineke Stulen; Luit J. De Kok

161

Thermal Stability of MOCVD and HVPE GaN Layers in H2, HCl, NH3 and N2  

E-print Network

The recent development of GaN based blue light emitting diodes (LEDs) and lasers [1] and high powerThermal Stability of MOCVD and HVPE GaN Layers in H2, HCl, NH3 and N2 M. A. Mastro1 ) (a), O. M.60.Dv; 81.15.Gh; S7.14 This work represents a complete study of GaN annealed in H2, HCl, NH3 and N2

Anderson, Timothy J.

162

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

NASA Astrophysics Data System (ADS)

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.

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

2015-01-01

163

Paper based platform for colorimetric sensing of dissolved NH3 and CO2.  

PubMed

Paper, a cheap and ubiquitous material, has great potential to be used as low-cost, portable and biodegradable platform for chemical and biological sensing application. In this paper, we are exploring a low-cost, flexible and reliable method to effectively pattern paper for capturing optical dyes and for flow-based delivery of target samples for colorimetric chemical sensing. In this paper, we target the detection of ammonia (NH3) and carbon dioxide (CO2), two of the important environmental and health biomarkers. By functionalizing the paper platform with diverse cross-reactive dyes sensitive to NH3 and CO2, their selective sensing within a certain pH range, as well as their detection at different concentrations can be achieved. The images of paper based device were captured by a flatbed scanner and processed in MATLAB(®) using a RGB model and PCA for quantitative analysis. Paper based devices with readout using ubiquitous consumer electronic devices (e.g. smartphones, flatbed scanner) are considered promising approaches for disease screening in developing countries with limited resources. PMID:25241151

Chen, Yu; Zilberman, Yael; Mostafalu, Pooria; Sonkusale, Sameer R

2015-05-15

164

UV induced Chemistry of Polycyclic Aromatic Hydrocarbons in NH_3-containing Interstellar Ice Analogues  

NASA Astrophysics Data System (ADS)

Polycyclic Aromatic Hydrocarbons are expected to be widely present in the interstellar medium. For the typical temperatures in space, they will freeze out on icy dust grains, like other species, such as water and ammonia. Optical spectra of PAHs in water ice have become available recently using a new setup at Leiden (OASIS - Optical Absorption Setup for Ice Spectroscopy). This setup allows to study the time resolved PAH and PAH photoproduct behavior upon hard UV photolysis, evidencing an active PAH chemistry in the ice for temperatures in the 15-150 K regime. The matrix surrounding turns out to be very important. As an extension of the previous PAH:H2O ices, here the first results are presented for UV irradiated PAH:NH3 and PAH:NH3/H2O ices. In this way PAH destruction and molecule formation can be monitored in situ and on line. It is found that whereas H2O ices particularly result in the formation of PAH-cations, ammonia seems to favor the formation of anions in the ice. After photolysis is stopped, the PAH anion signal vanishes. At this stage these results are interpreted by assuming that charged species form in interstellar ice by electron transfer from ammonia photoproducts, rather than acid-base proton transfer.

Cuylle, S. H.; Tenenbaum, E. D.; Bouwman, J.; Linnartz, H.

2011-05-01

165

Etude calorimétrique et structure cristalline du putrescinium monohydrogénomonophosphate dihydrate NH 3(CH 2) 4NH 3HPO 42H 2O  

NASA Astrophysics Data System (ADS)

Chemical preparation, calorimetric studies, and crystal structure are given for a new monophosphate. The putrescinium monohydrogen monophosphate dihydrate salt is monoclinic with the unit cell dimensions a = 6.541(1) Å, b = 16.648(3) Å, c = 9.175(1) Å, ? = 95.74(1)°, V = 994.1(5) Å 3, Dm = 1.498 Mgm -3, Dx = 1.484 Mgm -3, ? = 2.732 mm -1, space group {P2 1}/{c} with Z = 4. The structure was solved by the Patterson method and refined to a final value of 0.046 for 1732 observed independent reflections. The structure shows a layer arrangement perpendicular to the overlinec axis: planes of the [HPO 4] 2- tetrahedra alternate with planes of the [(CH 2) 4(NH 3) 2] 2+ dication. The zeolitic water molecules are located between these planes separated by a distance of 2.294 Å. The monohydrogen phosphate group is roughly tetrahedral with the symmetry 3 m. The P?O distances in this group range from 1.495(2) to 1.592(2) Å. The amino groups of putrescine are protonated. The putrescinium dication has an extensive all- trans configuration with a noncrystallographic inversion center. The cohesion and the stability of the atomic arrangement result from three kinds of hydrogen bonds, N?H····O, P?OH····O(w), and O(W)?H····O. The differential scanning calorimetric study shows that the dehydration of this salt occurs in two steps respectively at 105 and 121°C with a loss of one water molecule per step. The anhydrous salt undergoes four phase transitions respectively at temperatures of 133, 143, 159, and 165°C.

Kamoun, Slaheddine; Jouini, Amor

1990-11-01

166

Trends of NO-, NO 2-, and NH 3-emissions from gasoline-fueled Euro-3- to Euro-4-passenger cars  

NASA Astrophysics Data System (ADS)

Vehicular emissions of reactive nitrogen compounds (RNCs) such as nitric oxide (NO), nitrogen dioxide (NO 2), and ammonia (NH 3) have a substantial impact on urban air quality. NO and NO 2 support the photochemical formation of ozone, and NH 3 is involved in the atmospheric formation of secondary aerosols. Vehicular NO is mainly formed during combustion, whereas NO 2 and NH 3 are both secondary pollutants of the catalytic converter systems. Herein we report on tail-pipe RNC emissions of gasoline-fueled Euro-3- and Euro-4-passenger cars at transient driving from 0 to 150 km h -1. Two sets of 10 in-use vehicles with comparable engine size and mileage were studied with time-resolved chemical ionization-mass spectrometry (CI-MS). Each vehicle was tested in 7 different driving cycles including the legislative European (EDC) and the US FTP-75 driving cycles. Mean emission factors (EFs) for different traffic situations are reported and effects of cold start, velocity, acceleration, and deceleration are discussed. Furthermore, critical operating conditions supporting the de novo formation of NH 3 have been identified. In the EDC, mean NO- and NH 3-EFs of 57±26 and 16±12 mg km -1 were obtained for Euro-3-vehicles; those of the Euro-4-technology were lower by about 25% and 33% at the levels of 43±46 and 10±7 mg km -1, respectively. NO 2 emissions of the investigated three-way catalyst (TWC) vehicles accounted for <1% of the detected RNCs, whereas NH 3 was found to be the dominant RNC for most vehicle conditions. Molar NH 3 proportions varied from about 0.4-0.8, as soon as catalyst light-off occurred. NO was found in large excess only during the cold-start period. Catalyst light-off is indicated by a fast transition from NO- to NH 3-rich exhaust. Velocity and acceleration had pronounced effects on the RNC emission characteristics. Mean velocity-dependent EFs for NO and NH 3 varied by about one order of magnitude from 10 to 74 and 15 to 161 mg km -1 for Euro-3-vehicles and from 12 to 44 and 7 to 144 mg km -1 for the Euro-4 fleet. We conclude that the investigated Euro-3- and Euro-4-vehicles are mainly operated under slightly reducing conditions, where the NH 3 emissions dominate over those of the NO. Under these conditions, both vehicle fleets on an average fulfilled the valid Euro-3 and Euro-4 limits for nitrogen oxides (NO x) of 150 and 80 mg km -1, respectively (as NO 2 equivalents).

Heeb, Norbert V.; Saxer, Christian J.; Forss, Anna-Maria; Brühlmann, Stefan

167

Temperature programmed decomposition of uranyl nitrate hexahydrate  

Microsoft Academic Search

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

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

1999-01-01

168

Electronic transport properties of BN sheet on adsorption of ammonia (NH3) gas.  

PubMed

We report the detection of ammonia gas through electronic and transport properties analysis of boron nitride sheet. The density functional theory (DFT) based ab initio approach has been used to calculate the electronic and transport properties of BN sheet in presence of ammonia gas. Analysis confirms that the band gap of the sheet increases due to presence of ammonia. Out of different positions, the bridge site is the most favorable position for adsorption of ammonia and the mechanism of interaction falls between weak electrostatic interaction and chemisorption. On relaxation, change in the bond angles of the ammonia molecule in various configurations has been reported with the distance between NH3 and the sheet. An increase in the transmission of electrons has been observed on increasing the bias voltage and I-V relationship. This confirms that, the current increases on applying the bias when ammonia is introduced while a very small current flows for pure BN sheet. PMID:25666919

Srivastava, Anurag; Bhat, Chetan; Jain, Sumit Kumar; Mishra, Pankaj Kumar; Brajpuriya, Ranjeet

2015-03-01

169

Perfomance Analysi of Rectifier in NH3-H2O Absorption Heat Pump  

NASA Astrophysics Data System (ADS)

In order to design a rectifier in NH3-H2O absorption heat pump, the heat and mass transfer model for packed tower-type rectifiers was presented in the previous paper and it was found that the model could predict over-all mass transfer coefficient within 30(%) difference to the experimental data. Though the approximate calculation to design rectifiers is increasing important, the method of this prediction need many reiteration along the vapor and solution flow, which might not be the simplified way to design packed tower-type rectifier Thus the approximate pr . edicting method was presented in this paper. In this way, over-all mass transfer Coefficient was easily deriveded using the rectification characteristic that was determined by the dimension and geometry of rectification packing. The calculation results showed good agreement with the experimental data, regardless of kinds of rectification packing.

Tsujimori, Atsushi; Ozaki, Eiichi; Nakao, Kazushige

170

VLBI Observations and NH3 Mapping of the Star-forming Region NGC2264  

NASA Astrophysics Data System (ADS)

We have measured the annual parallax of the water maser source associated with star forming region NGC2264 from observations with VLBI Exploration of Radio Astrometry (VERA). We detected masers at V LSR = 7.2 km s-1. We discussed its driving sources of detected maser spots. One of the maser spots was associated with a centimeter continuum source observed with VLA. Neither optical, infrared nor X-ray sources is catalogued near the spot. The other maser spot is located close to an X-ray source, although there is no optical or infrared counterpart. The proper motion of the former spot was (??, ??) = (23.91 ± 4.29, -29.81 ± 4.27) and the proper motion of latter spot was (??, ??) = (-0.96 ± 0.58, -6.05 ± 3.06). For the latter spot, the peculiar motion is ˜ 150 km s-1 and it has the high velocity and this may be a jet or an outflow from a young star. The observed parallax is 1.365 ± 0.098 mas, corresponding to the distance of 738+57 -50 pc. This value is constant with the photometric distance of NGC2264 previously measured. The fitting result of the parallax is shown in figure 1. We also observed in NH3 (1,1), (2,2), (3,3) lines of NGC2264 with the Kashima 34m telescope. We estimated the star formation efficiency (SFE) of NGC2264 from the dense molecular mass of NH3 and the stellar mass calculated by Teixeira et al. (2012). The SFE is 9 - 12% which is consistent with previous results.

Kamezaki, Tatsuya; Imura, Kenji; Nagayama, Takumi; Omodaka, Toshihiro; Handa, Toshihiro; Yamaguchi, Yoshiyuki; Chibueze, James O.; Sunada, Kazuyoshi; Nakano, Makoto

2013-03-01

171

Validation of flux measurements with artificial sources: simulating CH4 from cows and NH3 emissions from medium plot scales  

NASA Astrophysics Data System (ADS)

Mitigation of ammonia (NH3) emissions with detrimental environmental effects as well as of greenhouse gas emissions (GHG: CO2, N2O, CH4) are key challenges faced by the agricultural production sector. While NH3 originates mainly from polluted surfaces, e.g. after slurry application, the main source for CH4 emissions are cows and other ruminating animals, representing point sources. There are two widespread state-of-the-art techniques to determine agricultural emissions: eddy covariance (EC) flux measurements and Lagrangian stochastic (LS) dispersion modelling, namely the WindTrax (WT) model. Whereas GHG emissions can be measured with both techniques, NH3 emissions are usually not feasible with EC measurements due to the stickiness of NH3 molecules on surfaces. In addition, point sources render difficulties for the interpretation of EC flux data. We tested the EC technique and the WT model using artificial sources with known gas release rates. i) The effect of a point source on EC fluxes was investigated by placing an artificial CH4 source with known release rate upwind of the EC tower at two different heights and during different wind conditions. ii) The WT model was checked with a NH3 release grid of 314 m2 of known source strength. Ambient NH3 concentrations were measured by open path DOAS systems and impinger sampling. The CH4 concentration timeseries influenced by the point source showed a similar pattern as in the presence of cows upwind of the EC system. CH4 release rates from the point source were reproduced by the EC flux measurement with stationary background conditions only. The experiments with the NH3 release showed that WT performs well for emission determination, even in complex terrain (asphalt surrounded by grassland) with associated micrometeorology, given a realistic description of the vertical profile of wind velocity. Calculated gas recoveries ranged between 73 to 105%. Such a result is encouraging considering the immanent uncertainties from a NH3 experiment (variable background concentration, relatively small downwind concentrations, NH3 interception on ground/tubing).

Sintermann, Jörg; Felber, Raphael; Häni, Christoph; Ammann, Christof; Neftel, Albrecht

2014-05-01

172

Long-term operation of a biofilter for simultaneous removal of H2S and NH3.  

PubMed

Simultaneous removal of NH3 and H2S was investigated using two types of biofilters--one packed with wood chips and the other with granular activated carbon (GAC). Experimental tests and measurements included analyses of removal efficiency (RE), metabolic products, and results of long-term operation (around 240 days). The REs for NH3 and H2S were 92 and 99.9%, respectively, before deactivation. After deactivation, the RE for NH3 and H2S were decreased to 30-50% and 75%, respectively. The activity of nitrifying bacteria was inhibited by high concentrations of H2S (over 200 ppm) but recovered gradually after H2S addition was ceased. However, the Thiobacillus thioparus as sulfur oxidizing bacteria did not show inhibition at the NH3 concentration under 150-ppm conditions. The deactivation of the biofilter was caused by metabolic products [elemental sulfur and (NH4)2SO4] accumulating on the packing materials during the extended operation. The removal capacities for NH3 and H2S were 6.0-8.0 and 45-75 mg N, S/L/hr, respectively. PMID:12540044

Kim, Heesung; Kim, Young Jun; Chung, Jong Shik; Quan, Xie

2002-12-01

173

Synthesis and structure of a new open-framework zinc phosphate: [Zn 3(PO 4) 2(HPO 4) 0.5] ?0.5[(NH 3(CH 2) 2(NH 3)] 2+H 2O  

Microsoft Academic Search

A new open-framework zinc phosphate, [Zn3(PO4)2(HPO4)0.5]?[0.5(NH3(CH2)2(NH3)]2+H2O, having Zn–O–Zn linkages was synthesized by hydrothermal technique. The structure consists of a network of ZnO4 and PO4 tetrahedra in which the vertices are shared. Water molecules are present in a 6-membered channel and the protonated ethylenediamine molecule is in the middle of a 8-membered channel, creating alternating hydrophobic and hydrophilic channels.

D Chidambaram; S Natarajan

1998-01-01

174

Effect of residual H2O on epitaxial AlN film growth on 4H-SiC by alternating doses of TMA and NH3  

NASA Astrophysics Data System (ADS)

An epitaxial AlN film was synthesized on 4H-SiC using alternate doses of trimethyl aluminum (TMA) and anhydrous ammonia (a-NH3) at 540 °C. The growth per cycle (GPC) at the temperature was limited to 0.27 Å/cycle under the minute amount of residual H2O. The formation of an inert Al-O-Al bond generated by the recombinative desorption of two Al-OH species to produce H2O has been proposed as a possible reason for the low deposition rate. By eliminating any present moisture in the reactor system, the GPC increased to 1.5 Å/cycle. The suppression of the OH group generation at 540 °C made it possible to deposit nearly stoichiometric AlN film which has the crystallinity with the preferred orientation along the (0 0 0 1) direction on 4H-SiC templates. The measured RMS surface roughness was comparable to that achieved by molecular beam epitaxy (MBE).

Perng, Ya-Chuan; Kim, Taeseung; Chang, Jane P.

2014-09-01

175

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

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

176

Microstructures and properties of CH3NH3PbI3-xClx hybrid solar cells  

NASA Astrophysics Data System (ADS)

Halide-perovskite CH3NH3PbI3 was produced on mesoporous TiO2 layer by spin-coating a precursor solution of PbCl2 and CH3NH3I in dimethylformamide. The role of the annealing process and chlorine (Cl) doping for the perovskite-phase formation was investigated. It was found that crystallization of the perovskite materials was stimulated by the annealing process, and that longer annealing time is necessary for the Cl-doped perovskite compared with that of non-doped perovskite phase.

Suzuki, Kohei; Suzuki, Atsushi; Zushi, Masahito; Oku, Takeo

2015-02-01

177

Depletion of the heaviest stable N isotope is associated with NH4+/NH3 toxicity in NH4+-fed plants  

PubMed Central

Background In plants, nitrate (NO3-) nutrition gives rise to a natural N isotopic signature (?15N), which correlates with the ?15N of the N source. However, little is known about the relationship between the ?15N of the N source and the 14N/15N fractionation in plants under ammonium (NH4+) nutrition. When NH4+ is the major N source, the two forms, NH4+ and NH3, are present in the nutrient solution. There is a 1.025 thermodynamic isotope effect between NH3 (g) and NH4+ (aq) which drives to a different ?15N. Nine plant species with different NH4+-sensitivities were cultured hydroponically with NO3- or NH4+ as the sole N sources, and plant growth and ?15N were determined. Short-term NH4+/NH3 uptake experiments at pH 6.0 and 9.0 (which favours NH3 form) were carried out in order to support and substantiate our hypothesis. N source fractionation throughout the whole plant was interpreted on the basis of the relative transport of NH4+ and NH3. Results Several NO3--fed plants were consistently enriched in 15N, whereas plants under NH4+ nutrition were depleted of 15N. It was shown that more sensitive plants to NH4+ toxicity were the most depleted in 15N. In parallel, N-deficient pea and spinach plants fed with 15NH4+ showed an increased level of NH3 uptake at alkaline pH that was related to the 15N depletion of the plant. Tolerant to NH4+ pea plants or sensitive spinach plants showed similar trend on 15N depletion while slight differences in the time kinetics were observed during the initial stages. The use of RbNO3 as control discarded that the differences observed arise from pH detrimental effects. Conclusions This article proposes that the negative values of ?15N in NH4+-fed plants are originated from NH3 uptake by plants. Moreover, this depletion of the heavier N isotope is proportional to the NH4+/NH3 toxicity in plants species. Therefore, we hypothesise that the low affinity transport system for NH4+ may have two components: one that transports N in the molecular form and is associated with fractionation and another that transports N in the ionic form and is not associated with fractionation. PMID:21575190

2011-01-01

178

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

NASA Technical Reports Server (NTRS)

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.

Walch, Stephen P.

2004-01-01

179

Novel inorganic ionic compounds based on Re 6 chalcocyanide cluster complexes: synthesis and crystal structures of [CuNH 3(trien)] 2[Re 6S 8(CN) 6] · 7H 2O, [CuNH 3(trien)] 2[Re 6Se 8(CN) 6] and [CuNH 3(trien)] 2[Re 6Te 8(CN) 6] · H 2O  

Microsoft Academic Search

Three new octahedral rhenium chalcocyanide cluster compounds [CuNH3(trien)]2[Re6S8(CN)6]·7H2O (1), [CuNH3(trien)]2[Re6Se8(CN)6] (2) and [CuNH3(trien)]2[Re6Te8(CN)6]·H2O (3) exhibiting ionic structures have been obtained by the diffusion of an ammonia solution of KCs3[Re6S8(CN)6] (for 1), K4[Re6Se8(CN)6]·3.5H2O (for 2) or Cs4[Re6Te8(CN)6]·2H2O (for 3) into a glycerol solution of CuCl2·2H2O in the presence of trien (trien=triethylenetetramine). The compounds have been characterized by single-crystal X-ray diffraction. All

Konstantin A Brylev; Nikolai G Naumov; Gabriel Peris; Rosa Llusar; Vladimir E Fedorov

2003-01-01

180

Water desorption from nanostructured graphite surfaces.  

PubMed

Water interaction with nanostructured graphite surfaces is strongly dependent on the surface morphology. In this work, temperature programmed desorption (TPD) in combination with quadrupole mass spectrometry (QMS) has been used to study water ice desorption from a nanostructured graphite surface. This model surface was fabricated by hole-mask colloidal lithography (HCL) along with oxygen plasma etching and consists of a rough carbon surface covered by well defined structures of highly oriented pyrolytic graphite (HOPG). The results are compared with those from pristine HOPG and a rough (oxygen plasma etched) carbon surface without graphite nanostructures. The samples were characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The TPD experiments were conducted for H2O coverages obtained after exposures between 0.2 and 55 langmuir (L) and reveal a complex desorption behaviour. The spectra from the nanostructured surface show additional, coverage dependent desorption peaks. They are assigned to water bound in two-dimensional (2D) and three-dimensional (3D) hydrogen-bonded networks, defect-bound water, and to water intercalated into the graphite structures. The intercalation is more pronounced for the nanostructured graphite surface in comparison to HOPG surfaces because of a higher concentration of intersheet openings. From the TPD spectra, the desorption energies for water bound in 2D and 3D (multilayer) networks were determined to be 0.32 ± 0.06 and 0.41 ± 0.03 eV per molecule, respectively. An upper limit for the desorption energy for defect-bound water was estimated to be 1 eV per molecule. PMID:24018989

Clemens, Anna; Hellberg, Lars; Grönbeck, Henrik; Chakarov, Dinko

2013-12-21

181

Adsorption capacity of H2O, NH3, CO, and NO2 on the pristine graphene  

NASA Astrophysics Data System (ADS)

First-principles together with statistical mechanics calculations have been performed to study the adsorption behavior of H2O, NH3, CO, and NO2 on the pristine graphene. In the first-principles calculations, we find that the most recent van der Waals (vdW) density functional vdW-DF2 gives even larger binding energies (Eb) that those obtained with the local density approximation, indicating vdW-DF2 may be inappropriate for describing the interaction between these molecules and graphene. With the potential energy curves of the molecules on graphene calculated by the density functional theory, the adsorption capacity (n) of the molecules on the pristine graphene is calculated with the statistical mechanics method. NO2 has the largest n of the order of 108 cm-2 among the four molecules on graphene at room temperature and concentration of 1.0 ppm, but still smaller by almost two order than that on graphene devices estimated from the experimental results. This is probably due to the strong binding of NO2 to the graphene edges with terminating oxygen atoms with Eb as large as 1.0 eV. The calculations of the adsorption capacity of small polar molecules on the pristine graphene and comparison with the experimental values may contribute to the understanding of the mechanism and designing of graphene based gas sensors.

Lin, Xianqing; Ni, Jun; Fang, Chao

2013-01-01

182

Observation of period doubling in an all-optical resonator containing NH3 gas  

NASA Astrophysics Data System (ADS)

It is pointed out that systems exhibiting period-doubling cascades to chaotic behavior while governed by deterministic equations have attracted great interest. Ikeda (1979) showed that an optically bistable ring resonator containing a two-level system can show a period-doubling cascade, a sufficiently strong CW input beam yielding an output oscillating at twice the resonator round-trip time t(R). On further increase of the input field the output period doubles to chaos. The present investigation is concerned with observations of 2t(R) oscillation, with some indications of 4t(R), in an all-optical system very similar to Ikeda's original proposal. A passive ring resonator was pumped by a transversely excited atmosphere (TEA) CO2 laser pulse. The employed line lies 1.23 GHz above the aR(11) transition of the NH3 gas contained in a 1-m intracacity cell at pressures of 9-15 Torr, where it acts as a homogeneously broadened two-level system. The obtained results show that molecular gases pumped by CO2 lasers are extremely promising media for the study of chaos in all-optical systems.

Harrison, R. G.; Firth, W. J.; Emshary, C. A.; Al-Saidi, I. A.

1983-08-01

183

Selective Catalytic Reduction Operation with Heavy Fuel Oil: NOx, NH3, and Particle Emissions.  

PubMed

To meet stringent NOx emission limits, selective catalytic reduction (SCR) is increasingly utilized in ships, likely also in combination with low-priced higher sulfur level fuels. In this study, the performance of SCR was studied by utilizing NOx, NH3, and particle measurements. Urea decomposition was studied with ammonia and isocyanic acid measurements and was found to be more effective with heavy fuel oil (HFO) than with light fuel oil. This is suggested to be explained by the metals found in HFO contributing to metal oxide particles catalyzing the hydrolysis reaction prior to SCR. At the exhaust temperature of 340 °C NOx reduction was 85-90%, while at lower temperatures the efficiency decreased. By increasing the catalyst loading, the low temperature behavior of the SCR was enhanced. The drawback of this, however, was the tendency of particle emissions (sulfate) to increase at higher temperatures with higher loaded catalysts. The particle size distribution results showed high amounts of nanoparticles (in 25-30 nm size), the formation of which SCR either increased or decreased. The findings of this work provide a better understanding of the usage of SCR in combination with a higher sulfur level fuel and also of ship particle emissions, which are a growing concern. PMID:25780953

Lehtoranta, Kati; Vesala, Hannu; Koponen, Päivi; Korhonen, Satu

2015-04-01

184

DFT based study of transition metal nano-clusters for electrochemical NH3 production.  

PubMed

Theoretical studies of the possibility of producing ammonia electrochemically at ambient temperature and pressure without direct N2 dissociation are presented. Density functional theory calculations were used in combination with the computational standard hydrogen electrode to calculate the free energy profile for the reduction of N2 admolecules and N adatoms on transition metal nanoclusters in contact with an acidic electrolyte. This work has established linear scaling relations for the dissociative reaction intermediates NH, NH2, and NH3. In addition, linear scaling relations for the associative reaction intermediates N2H, N2H2, and N2H3 have been determined. Furthermore, correlations between the adsorption energies of N, N2, and H have been established. These scaling relations and the free energy corrections are used to establish volcanoes describing the onset potential for electrochemical ammonia production and hence describe the potential determining steps for the electrochemical ammonia production. The competing hydrogen evolution reaction has also been analyzed for comparison. PMID:23598667

Howalt, J G; Bligaard, T; Rossmeisl, J; Vegge, T

2013-05-28

185

Absorption coefficients of solid NH3 from 50 to 7000 per cm  

NASA Technical Reports Server (NTRS)

Thin-film spectra of solid NH3 at a resolution of 1 per cm were used to determine its absorption coefficient over the range 50-7000 per cm. The thin films were formed inside a liquid N2 cooled dewar using a variety of substrates and dewar windows. The spectra were recorded with two Fourier spectrometers, one covering the range from 1 to 4 microns and the other from 2.6 to 200 microns. The thickness of the films was measured with a laser interference technique. The absorption coefficients were determined by application of Lambert's law and by a fitting procedure to the observed spectra using thin-film theory. Good agreement was found with the absorption coefficients recently determined by other investigators over a more restricted wavelength range. A metastable phase was observed near a temperature of 90 K and its absorption coefficient is reported. No other major spectral changes with temperature were noted for the range 88-120 K.

Sill, G.; Fink, U.; Ferraro, J. R.

1980-01-01

186

Hydrophobic recovery of VUV/NH3 modified polyolefin surfaces: Comparison with plasma treatments in nitrogen  

NASA Astrophysics Data System (ADS)

Film samples of two very pure polyolefins (low density polyethylene, LDPE and biaxially oriented polypropylene, BOPP) were surface-modified by two different methods, namely vacuum ultraviolet (VUV) irradiation with a Kr resonant lamp in low-pressure NH3 gas, and atmospheric pressure glow discharge (APGD) plasma treatment in pure N2 gas. Samples were then stored in air and the time-dependence of surface properties (the surface energy and chemical composition) was monitored using several complementary surface-sensitive techniques: contact angle goniometry (CAG), X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). We show that the main mechanism responsible for hydrophobic recovery is the motion of polymer chains and chain segments, which governs an apparent "loss" of functional groups, within the first monolayers of the surface (˜1 nm). Finally, comparing BOPP samples modified by both techniques, we show that aging can be reduced by crosslinking near the surface, as illustrated by depth-sensing nano-indentation measurements.

Truica-Marasescu, F.; Guimond, S.; Jedrzejowski, P.; Wertheimer, M. R.

2005-07-01

187

Performance Analysis of Rectifier in NH3-H2O Absorprtion Heat Pump  

NASA Astrophysics Data System (ADS)

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.

Tsujimori, Atsushi; Ozaki, Eiichi; Nakao, Kazushige

188

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

NASA Technical Reports Server (NTRS)

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.

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

1985-01-01

189

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

SciTech Connect

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.

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

2014-10-28

190

Low-temperature SCR of NO x with NH 3 over activated carbon fiber composite-supported metal oxides  

Microsoft Academic Search

In previous works, the authors were involved in the preparation and optimization of Nomex-based activated carbon fibers (ACFs) monoliths and their use as catalytic supports of manganese oxides for the selective catalytic reduction (SCR) of NOx with NH3 at low temperature. Thus, a low density monolith made of carbonized Nomex™ rejects was fabricated and submitted to different surface conditioning treatments

Gregorio Marbán; Raquel Antuña; Antonio B Fuertes

2003-01-01

191

Effects of NH3 and N2 additions to hot filament activated CH4 H2 gas mixtures  

E-print Network

densities, and NH column densities, in a hot filament HF reactor designed for diamond chemical vapor in the formation of N atoms with calculated steady state number densities 1013 cm 3 in the case of 1% NH3 additions to participate in diamond growth. The deduced reduction in CH3 number density due to competing gas phase

Bristol, University of

192

Observations and analysis of the Jovian spectrum in the 10-micron nu-2 band of NH3  

NASA Technical Reports Server (NTRS)

Observations of the nu-2 band of NH3 in the Jovian atmosphere have been made at resolutions varying from 4 per cm to 0.15 per cm. The observations have been interpreted by computation of synthetic atmospheric spectra. Derived atmospheric parameters include a pressure of 0.5 atm at 145 K and a minimum temperature of 118 K.

Lacy, J. H.; Larrabee, A. I.; Wollman, E. R.; Geballe, T. R.; Townes, C. H.; Bregman, J. D.; Rank, D. M.

1975-01-01

193

Role of hydrogen-bonding and its interplay with octahedral tilting in CH3NH3PbI3.  

PubMed

First principles calculations on the hybrid perovskite CH3NH3PbI3 predict strong hydrogen-bonding which influences the structure and dynamics of the methylammonium cation and reveal its interaction with the tilting of the PbI6 octahedra. The calculated atomic coordinates are in excellent agreement with neutron diffraction results. PMID:25766075

Lee, Jung-Hoon; Bristowe, Nicholas C; Bristowe, Paul D; Cheetham, Anthony K

2015-03-26

194

Galvanic deposition of Rh and Ru on randomly structured Ti felts for the electrochemical NH3 synthesis.  

PubMed

Nowadays NH3 is exclusively synthesized by the Haber process. Unfortunately, the energy demand and the CO2 emissions due to H2 production are high. Hydrogen production utilizes precious carbon sources such as coal and natural gas. In the past we proposed an alternative process concept using a membrane electrode assembly in an electrochemical membrane reactor (ecMR). At the anode H2O is oxidized at an IrMMO catalyst to form protons. By applying an external potential to the ecMR N2 is reduced to NH3 at the cathode. Just recently Rh and Ru were identified as possible cathodic electrocatalysts by DFT calculations. We present an easy and highly efficient method for galvanic coatings of Rh and Ru on randomly structured Ti felts to be used in a membrane electrode assembly. Linear sweep voltammetry measurements give a slightly higher activity of Ru for the liquid phase electrochemical NH3 synthesis. The NH4(+) concentration reached is 8 times higher for Ru than for Rh. From an economical point of view, Ru is also more feasible for an electrochemical NH3 synthesis process. Such electrodes can now be evaluated in an ecMR in comparison to recently demonstrated Ti-based electrodes. PMID:25556769

Kugler, Kurt; Luhn, Mareike; Schramm, Jean André; Rahimi, Khosrow; Wessling, Matthias

2015-02-01

195

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

E-print Network

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

Farrar, James M.

196

Formation of TiO2 Thin Films using NH3 as Catalyst by Metalorganic Chemical Vapor Deposition  

NASA Astrophysics Data System (ADS)

We have studied metalorganic chemical vapor deposition of TiO2 thin films using titanium tetra-isopropoxide [TTIP, Ti(O--C3H7)4] and NH3 as a catalyst at deposition temperatures ranging from 250 to 365°C. At deposition temperatures above 330°C, pyrolytic self-decomposition of TTIP is dominant regardless of the use of NH3, and the activation energy for TiO2 film formation is 152 kJ/mol. At deposition temperatures below 330°C, the films can be formed with the help of the catalytic activity of NH3, and the activation energy is reduced to 55 kJ/mol. TiO2 films deposited through the pyrolytic self-decomposition of TTIP have an anatase structure before and after performing post-deposition annealing in oxygen ambient for 30 min at 750°C. On the other hand, the as-deposited films formed through the catalytic reaction of TTIP with NH3 incorporate nitrogen impurities and have microcrystallites of the rutile structure within the amorphous matrix. However, the post-deposition annealing, the nitrogen impurities are completely removed from the films, and the films are converted into polycrystalline TiO2 films with the rutile structure, which have a high dielectric constant of 82 and a low leakage current.

Jung, Sung-Hoon; Kang, Sang-Won

2001-05-01

197

Comparison of the NH3 Removal Characteristics by Trickle-Bed Air Biofilter Packed with Four Inorganic Packing Materials  

Microsoft Academic Search

Four inorganic packing materials were evaluated in terms of their availability as a packing material in trickle-bed air biofilter (TBAB) of biological NH3 removal characteristics. The nitrification rate is in the order of zeolite > active carbon > ceramic pellets > multi-face ball. The highest nitrification rate for zeolite, polypropylene multi-face ball, ceramic pellets and active carbon were 275, 136,

Jiao Zhang

2010-01-01

198

Surface-enhanced Raman spectroscopy and temperature-programmed desorption of benzene, pyridine and C(60)  

Microsoft Academic Search

A surface-enhanced Raman scattering (SERS) -active surface consisting of a silver film over silica nanospheres (AgFON\\/SiOsb2) was developed for use in an ultrahigh vacuum (UHV) environment. The surface is demonstrated to be temporally and thermally stable and able to withstand repeated dosing with adsorbate. It can also be regenerated in vacuum until it eventually loses enhancement due to surface contamination.

Maritoni Litorja

1997-01-01

199

DNA interactions of new cytotoxic tetrafunctional dinuclear platinum complex trans,trans-[{PtCl2(NH3)}2(piperazine)].  

PubMed

A new tetrafunctional dinuclear platinum complex trans,trans-[{PtCl2(NH3)}2(piperazine)] with sterically rigid linking group was designed, synthesized and characterized. In this novel molecule, the DNA-binding features of two classes of the platinum compounds with proven antitumor activity are combined, namely trans oriented bifunctional mononuclear platinum complexes with a heterocyclic ligand and polynuclear platinum complexes. DNA-binding mode of this new complex was analyzed by various methods of molecular biology and biophysics. The complex coordinates DNA in a unique way and interstrand and intrastrand cross-links are the predominant lesions formed in DNA in cell-free media and in absence of proteins. An intriguing aspect of trans,trans-[{PtCl2(NH3)}2(piperazine)] is that, using a semi-rigid linker, interstrand cross-linking is diminished relative to other dinuclear platinum complexes with flexible linking groups and lesions that span several base pairs, such as tri- and tetrafunctional adducts, become unlikely. In addition, in contrast to the inability of trans,trans-[{PtCl2(NH3)}2(piperazine)] to cross-link two DNA duplexes, the results of the present work convincingly demonstrate that this dinuclear platinum complex forms specific DNA lesions which can efficiently cross-link proteins to DNA. The results substantiate the view that trans,trans-[{PtCl2(NH3)}2(piperazine)] or its analogues could be used as a tool for studies of DNA properties and their interactions or as a potential antitumor agent. The latter view is also corroborated by the observation that trans,trans-[{PtCl2(NH3)}2(piperazine)] is a more effective cytotoxic agent than cisplatin against human tumor ovarian cell lines. PMID:17400194

Brabec, Viktor; Christofis, Petros; Slámová, Martina; Kostrhunová, Hana; Nováková, Olga; Najajreh, Yousef; Gibson, Dan; Kaspárková, Jana

2007-06-15

200

How are CH3OH, HNC/HCN, and NH3 Formed in the Interstellar Medium?  

NASA Astrophysics Data System (ADS)

Simulation experiments for the formation of CH3OH, HNC/HCN, and NH3 in solid-phase reactions were performed. CH3OH and H2CO were formed as major products from the 100 eV electron-irradiated mixed CH4/H2O solid at 10 K. There found to be two pathways for the formation of methanol with about equal importance, i.e., the recombination reaction: CH3 + OH --> CH3OH, and the insertion reaction: CH2+H2O --> CH3OH. One CH3OH molecule was formed per 60 electron irradiation with the electron energy of 100 eV. By using mixed H2O/CD4 ice, it was confirmed that formaldehyde was formed by the insertion reaction, C + H2O -->H2CO. A mixed gas of N2/HCN (50/1) at a few Torr was activated by a dc discharge and was deposited on the gold-plated copper substrate at 10, 15, and 20 K. During the deposition of plasma-activated sample gas, D atoms produced by the dc discharge of D2 were simultaneously sprayed over the solid film. The association reactions of CN with D at 10 K were found to generate DNC and DCN with the intensity ratio DNC/DCN of about 3 in the infrared absorption spectra. This high ratio is in line with the high abundance ratios of HNC/HCN observed in the dark clouds. The formation of DNC and DCN became negligible at 20 K, due to the decrease of the sticking probability of D atoms on the solid surface. Ammonia was not detected as a reaction product from reaction of D with N atoms trapped in the N2 matrix.

Hiraoka, Kenzo; Mochizuki, Noritaka; Wada, Akira

2006-09-01

201

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

PubMed Central

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

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

2013-01-01

202

Desorption From Interstellar Ices  

E-print Network

The desorption of molecular species from ice mantles back into the gas phase in molecular clouds results from a variety of very poorly understood processes. We have investigated three mechanisms; desorption resulting from H_2 formation on grains, direct cosmic ray heating and cosmic ray induced photodesorption. Whilst qualitative differences exist between these processes (essentially deriving from the assumptions concerning the species-selectivity of the desorption and the assumed threshold adsorption energies, E_t) all three processes are found to be potentially very significant in dark cloud conditions. It is therefore important that all three mechanisms should be considered in studies of molecular clouds in which freeze-out and desorption are believed to be important. Employing a chemical model of a typical static molecular core and using likely estimates for the quantum yields of the three processes we find that desorption by H_2 formation probably dominates over the other two mechanisms. However, the physics of the desorption processes and the nature of the dust grains and ice mantles are very poorly constrained. We therefore conclude that the best approach is to set empirical constraints on the desorption, based on observed molecular depletions - rather than try to establish the desorption efficiencies from purely theoretical considerations. Applying this method to one such object (L1689B) yields upper limits to the desorption efficiencies that are consistent with our understanding of these mechanisms.

J. F. Roberts; J. M. C. Rawlings; S. Viti; D. A. Williams

2007-08-24

203

Adsorption and desorption of CO on Ru(0 0 0 1): A comprehensive analysis  

NASA Astrophysics Data System (ADS)

A comprehensive theory of the adsorption of CO on Ru(0 0 0 1) is developed to describe equilibrium properties and the adsorption and desorption kinetics. The basis is a multi-site lattice gas model with site exclusion and lateral interactions between CO molecules out to second neighbour unit cells. The theory reproduces the coverage and temperature dependence of coverage isobars, heat of adsorption, structural data, sticking coefficients, and isothermal and temperature-programmed desorption rates in a consistent manner.

Payne, S. H.; McEwen, J.-S.; Kreuzer, H. J.; Menzel, D.

2005-12-01

204

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  

NASA Astrophysics Data System (ADS)

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 stronger in H-bonded than in non-H-bonded complexes. The internal rotation barrier (1 kcal/mol) of the H2O-CO2 complex was found to be primarily of electrostatic origin with only a small charge transfer contribution. The role of electrostatic interactions, effect of electron correlation, and comparison of theory with experiment are also discussed.

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

1986-05-01

205

[NH3, N2O, CH4 and CO2 emissions from growing process of caged broilers].  

PubMed

To obtain Ammonia and greenhouse gas (GHG) emission factors of caged broilers, ammonia (NH3), methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2) emissions of broilers aged 0 d to 42 days were monitored in caged broilers production systems located in Shandong province. Gas concentrations of incoming and exhaust air streams were measured by using INNOVA 1312 multi-gas monitor with multi-channel samplers. Building ventilation rates were determined by on site FANS (Fan Assessment Numeration System) measurement systems. The NH3 emission factors showed a trend of increase at the beginning and then decreased with the broiler ages. The NH3 emission rates were 8.5 to 342.1 mg x (d x bird)(-1) and the average daily emission rate was 137.9 mg x (d x bird)(-1) [48.6 g x (d x AU)(-1)] over the 42-d period. The GHGs emission rates were 19.5-351.9 mg x (d x bird)(-1) with an average of 154.5 mg x (d x bird)(-1) [54.4 g x (d x AU)(-1)] for CH4, and 2.2- 152.9 g x (d x bird)(-10 with an average of 65.9 g x (d x bird)(-1) [23.2 kg x (d x AU)(-1)] for CO2. No emission of N2O was observed. The CH4 and CO2 emission rates increased with the increase of broilers ages. The total NH3 emission over the 42 d growing period averaged (5.65 +/- 1.02) g x (bird x life cycle)(-1). The NH3 emission contribution in different growth phase to the total emission were 33.6% in growth phase 1 (0-17 day, GP1), 36.4% in GP2 (18-27 days), and 29.9% in GP3 (28-42 days), respectively. The NH3 emission in GP2 was significantly higher than emission in GP1 and GP3. CH4 and CO2 cumulative emission rates were (6.30 +/- 0.16) g x (bird(-1) x life cycle)(-1) and (2.68 +/- 0.18) kg x (bird x life cycle)(-1), respectively. The cumulative emission rates of CH4 and CO2 in GP3 were significantly higher than emission rates in GP2 and in GP1, accounting for 50% of total emissions. The results of this study could provide the data support for mitigation of gas emission from broilers production. PMID:23947019

Zhou, Zhong-Kai; Zhu, Zhi-Ping; Dong, Hong-Min; Chen, Yong-Xing; Shang, Bin

2013-06-01

206

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

E-print Network

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

Denver, University of

207

J. Phys. Chem. 1991, 95, 5163-5168 5763 that the stable cluster ions ((NH3),,.(CH$N),IH+ and  

E-print Network

J. Phys. Chem. 1991, 95, 5163-5168 5763 that the stable cluster ions ((NH3),,.(CH$N),IH+ and I(NH3) structure with icosahedral (Ih)symmetry.' Haufler et ale6have partially hydrogenated C, using Birch curvature for a fully saturated Ih C6OH60 is even greater. These results suggest that, rather than bonding

Brenner, Donald W.

208

Temperature programmed decomposition of uranyl nitrate hexahydrate  

NASA Astrophysics Data System (ADS)

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.

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

1999-01-01

209

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...

210

Effect of tube radius on the exohedral chemical functionalization of boron-nitride zigzag nanotubes with NH3  

NASA Astrophysics Data System (ADS)

The interaction between zigzag BNNTs with chirality index n=3-10 and ammonia has been studied at the level of B3LYP/6-31G*. Ammonia can be chemically adsorbed on (3,0) to (7,0) BNNTs and physically adsorbed on other studied BNNTs. From NBO analysis charge transfer occur from NH3 to BNNTs and change in the natural electron configuration of B atom of BNNTs at adsorption site for the (3,0) and (4,0) BNNTs cases is larger than others. The DOS result show that after functionalization of BNNTs with NH3 molecules electronic properties of tubes are largely preserved and can be viewed as some kind of harmless modification. Electronic analysis revealed that the interaction of zigzag BNNTs with ammonia is more electrostatic (ionic) in nature, rather than the sole covalent and electrostatic nature increased with increasing of tube diameter.

Zahedi, Ehsan

2012-09-01

211

Theoretical study of the F + NH3 and F + ND3 reactions: mechanism and comparison with experiment.  

PubMed

We study the barrierless and highly exothermic F + NH(3) and F + ND(3) abstraction reactions using quasiclassical trajectory calculations based on an analytical potential energy surface developed in our research group. The calculations correctly reproduce the experimental evidence that the vibrational fraction deposited into the DF product for the F + ND(3) reaction is greater than into HF for the F + NH(3) reaction and that the vibrational distribution is inverted in the HF(v') and the DF(v') products. Of special interest is that recent crossed-beam experiments reported by Yang and co-workers at 4.5 kcal mol(-1) are reproduced for both reactions, with a mainly forward symmetry associated with direct trajectories, and a small sideways-backward symmetry contribution associated with "nearly trapped" trajectories due to a "yo-yo" mechanism, different from the previously suggested mechanism of a long-lived complex. PMID:22032654

Espinosa-García, J; Monge-Palacios, M

2011-12-01

212

The role of copper species on Cu/?-Al2O3 catalysts for NH3-SCO reaction  

NASA Astrophysics Data System (ADS)

UV-vis spectra, XRD, H2-TPR, TEM and ESR were used to characterize a series of Cu/?-Al2O3 catalysts, which were prepared by incipient wetness impregnation using copper nitrate, copper acetate or copper sulfate as precursors, to study the role of Cu species on Cu/?-Al2O3 catalysts for NH3-SCO reaction. It was found that the mixture of CuO phase and CuAl2O4 phase formed on various Cu/?-Al2O3 catalysts, and the Cu species and dispersion had significant influence on the Cu/?-Al2O3 activity. Highly dispersed CuO phase on the support would be related with its high activity for the NH3-SCO reaction.

Liang, Chunxia; Li, Xinyong; Qu, Zhenping; Tade, Moses; Liu, Shaomin

2012-02-01

213

Evaluating 4 years of atmospheric ammonia (NH3) over Europe using IASI satellite observations and LOTOS-EUROS model results  

NASA Astrophysics Data System (ADS)

Monitoring ammonia (NH3) concentrations on a global to regional scale is a challenge. Due to the limited availability of reliable ground-based measurements, the determination of NH3 distributions generally relies on model calculations. Novel remotely sensed NH3burdens provide valuable insights to complement traditional assessments for clear-sky conditions. This paper presents a first quantitative comparison between Atmospheric Sounding Interferometer (IASI) satellite observations and LOTOS-EUROS model results over Europe and Western Russia. A methodology to account for the variable retrieval sensitivity of the measurements is described. Four years of data (2008-2011) highlight three main agricultural hot spot areas in Europe: the Po Valley, the continental part of Northwestern Europe, and the Ebro Valley. The spatial comparison reveals a good overall agreement of the NH3 distributions not only in these source regions but also over remote areas and over sea when transport is observed. On average, the measured columns exceed the modeled ones, except for a few cases. Large discrepancies over several industrial areas in Eastern Europe and Russia point to underestimated emissions in the underlying inventories. The temporal analysis over the three hot spot areas reveals that the seasonality is well captured by the model when the lower sensitivity of the satellite measurements in the colder months is taken into account. Comparison of the daily time series indicates possible misrepresentations of the timing and magnitude of the emissions. Finally, specific attention to biomass burning events shows that modeled plumes are less spread out than the observed ones. This is confirmed for the 2010 Russian fires with a comparison using in situ observations.

Van Damme, M.; Wichink Kruit, R. J.; Schaap, M.; Clarisse, L.; Clerbaux, C.; Coheur, P.-F.; Dammers, E.; Dolman, A. J.; Erisman, J. W.

2014-08-01

214

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

Microsoft Academic Search

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

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

1997-01-01

215

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

PubMed

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

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

2014-11-01

216

Ultrasensitive room temperature NH3 sensor based on a graphene-polyaniline hybrid loaded on PET thin film.  

PubMed

This research was motivated by the need to develop a smart ammonia (NH3) sensor based on a flexible polyethylene terephthalate (PET) thin film loaded with a reduced graphene oxide-polyaniline (rGO-PANI hybrid) using in situ chemical oxidative polymerization. The sensor not only exhibited high sensitivity, good selectivity and a fast response at room temperature but was also flexible, cheap and had wearable characteristics. PMID:25845668

Bai, Shouli; Zhao, Yangbo; Sun, Jianhua; Tian, Ye; Luo, Ruixian; Li, Dianqing; Chen, Aifan

2015-04-16

217

Study of the electron ion recombination in high pressure flowing afterglow: recombination of NH 4· + (NH 3) 2  

Microsoft Academic Search

Rate coefficients for the dissociative recombination of O2+ and NH4·+ (NH3)2 with electrons have been measured using the high pressure flowing afterglow (HPFA) technique. The electron energy distribution function, effective temperature, and electron number density of the recombination dominated plasma have been measured by a Langmuir probe at pressures up to 11 Torr. The measured value of the recombination rate

J Glos??k; G Bánó; R Plašil; A Luca; P Zakou?il

1999-01-01

218

Effect of H 2 O and NH 3 contaminants on the epitaxial growth of silver on sodium chloride  

Microsoft Academic Search

Summary  The influence of H2O and NH3 contaminants on the epitaxial growth of Ag films on (100) NaCl substrate was studied. The contamination effect on NaCl cleaved\\u000a in air due to the H2O atmospheric vapours was removed with a prolonged treatment of the NaCl substrate in vacuum at 10?2 Torr. The positive contaminating effects are interpreted, through quite a general model,

G. F. Missiroli; F. Zignani

1970-01-01

219

Model-based control system design in a urea-SCR aftertreatment system based on NH 3 sensor feedback  

Microsoft Academic Search

This paper presents preliminary control system simulation results in a urea-selective catalytic reduction (SCR) aftertreatment\\u000a system based on NH3 sensor feedback. A four-state control-oriented lumped parameter model is used to analyze the controllability and observability\\u000a properties of the urea-SCR plant. A model-based estimator is designed via simulation and a control system is developed with\\u000a design based on a sliding mode

M. Devarakonda; G. Parker; J. H. Johnson; V. Strots

2009-01-01

220

Activity analysis of trans-[RuCl 2(NH 3) 4] + incorporated into Nafion membrane for water oxidation catalyst  

Microsoft Academic Search

Activity of trans-tetraamminedichlororuthenium(III) complex as water oxidation catalyst was studied both in a homogeneous aqueous solution (AS) and in a heterogeneous Nafion membrane (HM) using Ce(IV) oxidant. This trans-[RuCl2(NH3)4]+ was more active than any other mononuclear ammine ruthenium complex studied before. In the AS, the rate of evolved dioxygen is second order with respect to the complex concentration, indicating that

Hidenobu Shiroishi; Satoshi Yamashita; Masao Kaneko

2001-01-01

221

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)

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

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

2015-01-01

222

Effect of phosphogypsum and dicyandiamide as additives on NH3, N20 and CH4 emissions during composting.  

PubMed

A laboratory scale experiment of composting in a forced aeration system using pig manure with cornstalks was carried out to investigate the effects of both phosphogypsum and dicyandiamide (DCD, C2H4N4) as additives on gaseous emissions and compost quality. Besides a control, there were three amended treatments with different amounts of additives. The results indicated that the phosphogypsum addition at the rate of 10% of mixture dry weight decreased NH3 and CH4 emissions significantly during composting. The addition of DCD at the rate of 0.2% of mixture dry weight together with 10% of phosphogypsum further reduced the N2O emission by affecting the nitrification process. Reducing the phosphogypsum addition to 5% in the presence of 0.2% DCD moderately increased the NH3 emissions but not N2O emission. The additives increased the ammonium content and electrical conductivity significantly in the final compost. No adverse effect on organic matter degradation or the germination index of the compost was found in the amended treatments. It was recommended that phosphogypsum and DCD could be used in composting for the purpose of reducing NH3, CH4 and N2O emissions. Optimal conditions and dose of DCD additive during composting should be determined with different materials and composting systems in further study. PMID:24218845

Luo, Yiming; Li, Guoxue; Luo, Wenhai; Schuchardt, Frank; Jiang, Tao; Xu, Degang

2013-07-01

223

Operational characteristics of effective removal of H2S and NH3 waste gases by activated carbon biofilter.  

PubMed

Simultaneous removal of hydrogen sulfide (H2S) and ammonia (NH3) gases from gaseous streams was studied in a biofilter packed with granule activated carbon. Extensive studies, including the effects of carbon (C) source on the growth of inoculated microorganisms and gas removal efficiency, product analysis, bioaerosol emission, pressure drop, and cost evaluation, were conducted. The results indicated that molasses was a potential C source for inoculated cell growth that resulted in removal efficiencies of 99.5% for H2S and 99.2% for NH3. Microbial community observation by scanning electron microscopy indicated that granule activated carbon was an excellent support for microorganism attachment for long-term waste gas treatment. No disintegration or breakdown of biofilm was found when the system was operated for 140 days. The low bioaerosol concentration emitted from the biofilter showed that the system effectively avoided the environmental risk of bioaerosol emission. Also, the system is suitable to apply in the field because of its low pressure drop and treatment cost. Because NH3 gas was mainly converted to organic nitrogen, and H2S gas was converted to elemental sulfur, no acidification or alkalinity phenomena were found because of the metabolite products. Thus, the results of this study demonstrate that the biofilter is a feasible bioreactor in the removal of waste gases. PMID:15115374

Chung, Ying-Chien; Lin, Yu-Yen; Tseng, Ching-Ping

2004-04-01

224

Theory of dissociative and nondissociative adsorption and desorption  

NASA Astrophysics Data System (ADS)

Based on nonequilibrium thermodynamics we formulate a general theory of the kinetics of adsorption, desorption, and dissociation of gases at surfaces. We begin with a concise formulation of dissociation equilibrium at surfaces and then derive the kinetic equations for adsorption, desorption, and dissociation. For the explicit calculations we employ a lattice gas model for homonuclear molecules with both atoms and molecules present on the surface. Lateral interactions between all species are accounted for. In a series of model calculations we discuss equilibrium properties, such as heats of adsorption, and examine the role of dissociation dis-equilibrium on the time evolution of an adsorbate during temperature programmed desorption. The further effect of (attractive or repulsive) lateral interactions on the kinetics is elucidated in further model calculations. As a realistic example we apply the theory to oxygen on Pt(111).

Kreuzer, H. J.; Payne, S. H.; Drozdowski, A.; Menzel, D.

1999-04-01

225

Thermal desorption of 3He from T@C 60  

NASA Astrophysics Data System (ADS)

The interaction of recoil tritium (T), with an initial kinetic energy of 2.7 MeV with C 60 molecules, is studied in a 6Li( n, ?) T activated homogenized compound matrix of Li 2CO 3 and C 60. Liquid scintillation spectrometry coupled with high pressure liquid chromatography (HPLC) revealed endohedral T insertion into the fullerene cage upon extraction of the fullerene species into the organic phase. Solid state temperature programmed desorption profiles of the activated compound target showed the desorption of 3He gas (as a ?- decay product from T) from the endohedral T@C 60 at 882 °C. The deconvoluted evolved gas analysis-mass spectral (EGA-MS) data provided a 25% probability of T@C 60 formation upon nuclear activation of the compound target. The non-isothermal kinetics of the tritium desorption, studied as a function of temperature, revealed the process to be diffusion controlled.

Sahoo, Rashmi R.; Patnaik, Archita

2001-11-01

226

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

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

227

Theoretical NH{_3} Spectra in 5800-7000 CM-1 Region and CO{_2} IR Intensity: Updates  

NASA Astrophysics Data System (ADS)

Recently we have successfully applied the "Best Theory + High-resolution Experimental Data" strategy to NH{_3} and CO{_2}. The essential strategy is to refine a high quality, purely ab initio potential energy surface (PES) with reliable high resolution experimental data, so the IR line lists computed on the refined PES and dipole moment surface (DMS) can go beyond simple data reproduction. The goal is to make reliable predictions for higher J/K/energy rovibrational transitions with similar accuracies, i.e. 0.01-0.03 cm-1. The reliability and accuracy of data included in the refinement largely determines the quality of predictions and the ultimate merit of our work. With recent 14NH{_3} experiments in 5800 - 7000 cm-1, the effective coverage (with 0.01-0.03 cm-1 accuracy) of our NH{_3} PES has extended to this complex spectral region. Excellent agreement between current experiment analysis and our primitive HSL-3 PES refinement will be presented, and source of discrepancies will be discussed. The synergy between the experiments and theory is of great value. For CO{_2}, we have updated the theoretical IR intensity of the 12C16O{_2} line list with a more reliable DMS, then carried out very detailed comparisons with both pure experimental data and HITRAN/CDSD models. Results suggest that our line lists should be useful for the astronomical or earth-based detection of CO{_2} isotopologues. X. Huang, D.W. Schwenke, and T.J. Lee, J. Chem. Phys. 129, 214304 (2008); J. Chem. Phys. 134, 044320/044321 (2011). X. Huang, D.W. Schwenke, S.A. Tashkun, and T.J. Lee J. Chem. Phys. 136, submitted (2012).

Huang, Xinchuan; Schwenke, David W.; Lee, Timothy J.; Sung, Keeyoon; Brown, Linda R.; Tashkun, Sergey A.

2012-06-01

228

Observation of Scattering Resonances in the Penning Ionization of NH$_3$ by He($^3$S$_1$) at Low Collision Energies  

E-print Network

A merged-beam study of the gas phase He($^3$S$_1$) + NH$_3$ Penning ionization reaction dynamics in the collision energy range 3.3 $\\mu$eV $<$ E $<$ 10 meV is presented. In this energy range the reaction rate is governed by long-range attraction. Shape resonances are observed at collision energies of 1.8 meV and 7.3 meV and are assigned to $\\ell$=15,16 and $\\ell$=20,21 partial waves, respectively. The experimental results are well reproduced by theoretical calculations with the short-range reaction probability $P_{sr}=0.035$.

Justin Jankunas; Krzysztof Jachymski; Michal Hapka; Andreas Osterwalder

2014-10-21

229

Optical Activity of Incommensurate Phases of (C3H7NH3)2MnCl4  

NASA Astrophysics Data System (ADS)

By applying the HAUP (high-accuracy universal polarimeter) method, (C3H7NH3)2MnCl4 was found to be optically active in its incommensurate phases, e.g., g33{=}1.1× 10-5 in the ? phase at 83.0°C and g33{=}2.4× 10-5 in the \\varepsilon phase at -139.0°C. The temperature dependence of g33 was obtained. Commensurate domains were found to begin to grow below -139°C in the \\varepsilon phase.

Saito, Kazuya; Kobayashi, Jinzo

1991-09-01

230

Microstructures and photovoltaic properties of perovskite-type CH3NH3PbI3 compounds  

NASA Astrophysics Data System (ADS)

TiO2/CH3NH3PbI3-based photovoltaic devices were fabricated. The microstructures of these devices were investigated by X-ray diffraction, transmission electron microscopy, and their calculations. Structure analysis indicated phase transformation of the perovskite structure from a tetragonal to a cubic system by annealing, which resulted in the improvement of photovoltaic properties of the devices. Effects of a multiple spin-coating method using a mixture solution were also investigated. The result showed an increase in the efficiencies of the devices, due to the microstructural change of the perovskite compound layers.

Oku, Takeo; Zushi, Masahito; Imanishi, Yuma; Suzuki, Atsushi; Suzuki, Kohei

2014-12-01

231

A microscopic theory of the phase transitions in Me(NH 3) 6(AB 4) 2-type compounds  

NASA Astrophysics Data System (ADS)

The phase transitions in Me(NH 3) 6(AB 4) 2 compounds are explained by means of the competitive effects of interactions of AB 4 anions and their coupling to the random field of librations of hexamine complex cations. The model of a discrete 3-vector analogue of Ising metamagnet in the external random field in the limit of infinite range interactions is solved exactly by means of the multidimensional Laplace method. The appearance of two ordered phases, two different specific heat anomalies, the lowering of the crystal field symmetry, spontaneous strains in ordered phases and P- T phase diagram result from the theory.

Otwinowski, M.; Stankowski, J.

1984-03-01

232

Improved low temperature NH3-SCR performance of FeMnTiOx mixed oxide with CTAB-assisted synthesis.  

PubMed

FeMnTiOx mixed oxide is prepared by the CTAB-assisted co-precipitation method, and the transformation of anatase into rutile is inhibited by CTAB to some extent. The catalyst obtained in the present work shows nearly 100% NO conversion at 100-350 °C, more than 80% N2 selectivity at 75-200 °C, and excellent H2O durability for the selective catalytic reduction of NO by NH3 with a space velocity of 30?000 mL g(-1) h(-1). PMID:25628073

Wu, Shiguo; Yao, Xiaojiang; Zhang, Lei; Cao, Yuan; Zou, Weixin; Li, Lulu; Ma, Kaili; Tang, Changjin; Gao, Fei; Dong, Lin

2015-02-10

233

Action of an irritant (NH3) on the pathogeny of a respiratory disease induced experimentally by Pasteurella multocida in the rabbit  

E-print Network

Action of an irritant (NH3) on the pathogeny of a respiratory disease induced experimentally. In traditional or semi-intensive production units as well as in breeding herds, this procedure does not provide

Paris-Sud XI, Université de

234

Growth of CH3NH3PbI3 cuboids with controlled size for high-efficiency perovskite solar cells  

NASA Astrophysics Data System (ADS)

Perovskite solar cells with submicrometre-thick CH3NH3PbI3 or CH3NH3PbI3–xClx active layers show a power conversion efficiency as high as 15%. However, compared to the best-performing device, the average efficiency was as low as 12%, with a large standard deviation (s.d.). Here, we report perovskite solar cells with an average efficiency exceeding 16% and best efficiency of 17%. This was enabled by the growth of CH3NH3PbI3 cuboids with a controlled size via a two-step spin-coating procedure. Spin-coating of a solution of CH3NH3I with different concentrations follows the spin-coating of PbI2, and the cuboid size of CH3NH3PbI3 is found to strongly depend on the concentration of CH3NH3I. Light-harvesting efficiency and charge-carrier extraction are significantly affected by the cuboid size. Under simulated one-sun illumination, average efficiencies of 16.4% (s.d.?±?0.35), 16.3% (s.d.?±?0.44) and 13.5% (s.d.?±?0.34) are obtained from solutions of CH3NH3I with concentrations of 0.038?M, 0.050?M and 0.063 M, respectively. By controlling the size of the cuboids of CH3NH3PbI3 during their growth, we achieved the best efficiency of 17.01% with a photocurrent density of 21.64?mA?cm–2, open-circuit photovoltage of 1.056?V and fill factor of 0.741.

Im, Jeong-Hyeok; Jang, In-Hyuk; Pellet, Norman; Grätzel, Michael; Park, Nam-Gyu

2014-11-01

235

Electrodeposition of PbO and its in situ conversion to CH3NH3PbI3 for mesoscopic perovskite solar cells.  

PubMed

The perovskite CH3NH3PbI3 was prepared on a mesoscopic TiO2 film, starting from electrodepositing PbO, to iodination to PbI2, and then interdiffusion reaction with CH3NH3I. The as-prepared film was used as a light absorber for the perovskite solar cells, exhibiting a high PCE of 12.5% under standard AM 1.5 conditions. PMID:25493293

Cui, Xue-Ping; Jiang, Ke-Jian; Huang, Jin-Hua; Zhou, Xue-Qin; Su, Mei-Ju; Li, Shao-Gang; Zhang, Qian-Qian; Yang, Lian-Min; Song, Yan-Lin

2015-01-28

236

Growth of CH3NH3PbI3 cuboids with controlled size for high-efficiency perovskite solar cells.  

PubMed

Perovskite solar cells with submicrometre-thick CH(3)NH(3)PbI(3) or CH(3)NH(3)PbI(3-x)Cl(x) active layers show a power conversion efficiency as high as 15%. However, compared to the best-performing device, the average efficiency was as low as 12%, with a large standard deviation (s.d.). Here, we report perovskite solar cells with an average efficiency exceeding 16% and best efficiency of 17%. This was enabled by the growth of CH(3)NH(3)PbI(3) cuboids with a controlled size via a two-step spin-coating procedure. Spin-coating of a solution of CH(3)NH(3)I with different concentrations follows the spin-coating of PbI(2), and the cuboid size of CH(3)NH(3)PbI(3) is found to strongly depend on the concentration of CH(3)NH(3)I. Light-harvesting efficiency and charge-carrier extraction are significantly affected by the cuboid size. Under simulated one-sun illumination, average efficiencies of 16.4% (s.d. ± 0.35), 16.3% (s.d. ± 0.44) and 13.5% (s.d. ± 0.34) are obtained from solutions of CH(3)NH(3)I with concentrations of 0.038 M, 0.050 M and 0.063 M, respectively. By controlling the size of the cuboids of CH(3)NH(3)PbI(3) during their growth, we achieved the best efficiency of 17.01% with a photocurrent density of 21.64 mA cm(-2), open-circuit photovoltage of 1.056 V and fill factor of 0.741. PMID:25173829

Im, Jeong-Hyeok; Jang, In-Hyuk; Pellet, Norman; Grätzel, Michael; Park, Nam-Gyu

2014-11-01

237

Improvement of TiN Flow Modulation Chemical Vapor Deposition from TiCl4 and NH3 by Introducing Ar Purge Time  

NASA Astrophysics Data System (ADS)

TiN films were deposited by using TiCl4/NH3 flow modulation chemical vapor deposition (FMCVD). FMCVD consists of repetitive TiN deposition periods by TiCl4/NH3, each of which is followed by Cl reduction period. TiN deposition periods are typically 3 s and Cl reduction periods are 1 s. The effect of the number of deposition/reduction cycles and the effect of the partial pressure of TiCl4 and NH3 on film uniformity and resistivity were investigated. For a total reduction period of 100 s, increasing the number of reduction periods from 100× 1-s periods to 300× 0.33-s periods decreased the step coverage. This decrease in coverage was due to residual TiCl4 during the Cl reduction period by NH3 that cleared out TiCl4 at a constant rate, independent of the length of the period of reduction cycle. An Ar purge cycle was used between the deposition and reduction cycles to allow the residual TiCl4 to clear out before the NH3 was used for the film reduction cycle. This significantly improved the film step coverage from 50% to over 90%. The minimum film resistivity occurred when the NH3 partial pressure was 0.25 Torr. NH3 partial pressure less than 0.25 Torr inhibited film reduction, and NH3 partial pressure higher than 0.25 Torr enhanced the deposition rate, which also inhibited film reduction. By using the optimum conditions determined in this study, we could obtain TiN films that had film resistivity of about 240 ??\\cdotcm and step coverage of about 98% at 410°C.

Jun, Keeyoung; Im, Ik-Tae; Shimogaki, Yukihiro

2004-04-01

238

Fabrication of hexagonal GaN on the surface of ?-Ga 2O 3 single crystal by nitridation with NH 3  

Microsoft Academic Search

The fabrication of GaN on the surface of a bulk ?-Ga2O3 single crystal by nitridation with NH3 was investigated for the purpose of using it as a substrate for GaN epitaxial growth. A ?-Ga2O3 single crystal was prepared using a floating zone furnace with double ellipsoidal mirrors, and its polished (100) plane was nitridated in NH3 atmosphere at 850 °C

Shigeo Ohira; Masayuki Yoshioka; Takamasa Sugawara; Kazuo Nakajima; Toetsu Shishido

2006-01-01

239

Efficient Hybrid Mesoscopic Solar Cells with Morphology-Controlled CH3NH3PbI3-xClx Derived from Two-Step Spin Coating Method.  

PubMed

A morphology-controlled CH3NH3PbI3-xClx film is synthesized via two-step solution deposition by spin-coating a mixture solution of CH3NH3Cl and CH3NH3I onto the TiO2/PbI2 film for the first time. It is revealed that the existence of CH3NH3Cl is supposed to result in a preferential growth along the [110] direction of perovskite, which can improve both the crystallinity and surface coverage of perovskite and reduce the pinholes. Furthermore, the formation process of CH3NH3PbI3-xClx perovskite is explored, in which intermediates containing chlorine are suggested to exist. 13.12% of power conversion efficiency has been achieved for the mesoscopic cell, higher than 12.08% of power conversion efficiency of the devices fabricated without CH3NH3Cl via the same process. The improvement mainly lies in the increasing open-circuit photovoltage which is ascribed to the reduction of reverse saturation current density. PMID:25587643

Xu, Yuzhuan; Zhu, Lifeng; Shi, Jiangjian; Lv, Songtao; Xu, Xin; Xiao, Junyan; Dong, Juan; Wu, Huijue; Luo, Yanhong; Li, Dongmei; Meng, Qingbo

2015-02-01

240

A facile, solvent vapor-fumigation-induced, self-repair recrystallization of CH3NH3PbI3 films for high-performance perovskite solar cells.  

PubMed

A high-quality CH3NH3PbI3 film is crucial in the manufacture of a high-performance perovskite solar cell. Here, a recrystallization process via facile fumigation with DMF vapor has been successfully introduced to self-repair of CH3NH3PbI3 films with poor coverage and low crystallinity prepared by the commonly used one-step spin-coating method. We found that the CH3NH3PbI3 films with dendritic structures can spontaneously transform to the uniform ones with full coverage and high crystallinity by adjusting the cycles of the recrystallization process. The mesostructured perovskite solar cells based on these repaired CH3NH3PbI3 films showed reproducible optimal power conversion efficiency (PCE) of 11.15% and average PCE of 10.25 ± 0.90%, which are much better than that of devices based on the non-repaired CH3NH3PbI3 films. In addition, the hysteresis phenomenon in the current-voltage test can also be effectively alleviated due to the quality of the films being improved in the optimized devices. Our work proved that the fumigation of solvent vapor can modify metal organic perovskite films such as CH3NH3PbI3. It offers a novel and attractive way to fabricate high-performance perovskite solar cells. PMID:25733191

Zhu, Weidong; Yu, Tao; Li, Faming; Bao, Chunxiong; Gao, Hao; Yi, Yong; Yang, Jie; Fu, Gao; Zhou, Xiaoxin; Zou, Zhigang

2015-03-12

241

NH3 assisted photoreduction and N-doping of graphene oxide for high performance electrode materials in supercapacitors.  

PubMed

Nitrogen-doped graphene was synthesized by simple photoreduction of graphene oxide (GO) deposited on nickel foam under NH3 atmosphere. The combination of photoreduction and NH3 not only reduces the GO in a shorter time but also induces nitrogen doping easily. The nitrogen doped content of N-rGO@NF reaches a high of 5.99 at% with 15 min of irradiation. The nitrogen-doped graphene deposited on Ni foam (N-rGO@NF) can be directly used as an electrode for supercapacitors, without any conductive agents and polymer binders. In the electrochemical measurement, N-rGO@NF displays remarkable electrochemical performance. In particular, the N-rGO@NF irradiated for 45 min at a high current density of 92.3 A g(-1) retained about 77% (190.4 F g(-1)) of its initial specific capacitance (247.1 F g(-1) at 0.31 A g(-1)). Furthermore, the stable voltage window could be extended to 2.0 and 1.5 V by using Li2SO4 and a mixed Li2SO4/KOH electrolyte, and the maximum energy density was high up to 32.6 and 21.2 Wh kg(-1), respectively. The results show that compared to Li2SO4, a mixed electrolyte (Li2SO4/KOH) more efficiently balances the relationship between the high energy densities and high power densities. PMID:25553955

Huang, Haifu; Luo, Guangsheng; Xu, Lianqiang; Lei, Chenglong; Tang, Yanmei; Tang, Shaolong; Du, Youwei

2015-02-01

242

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

NASA Astrophysics Data System (ADS)

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.

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

2015-02-01

243

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

PubMed Central

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

Lee, Yunho; Mankad, Neal P.

2010-01-01

244

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

NASA Astrophysics Data System (ADS)

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.

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

2010-10-01

245

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

PubMed

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

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

2010-10-01

246

The H2O southern Galactic Plane Survey(HOPS): NH3 (1,1) and (2,2) catalogues  

E-print Network

The H2O Southern Galactic Plane Survey (HOPS) has mapped a 100 degree strip of the Galactic plane (-70deg > l > 30deg, |b| 10^4 cm^{-3}). In this paper we present the NH3 (1,1) and (2,2) data, which have a resolution of 2 arcmin and cover a velocity range of +/-200 km/s. The median sensitivity of the NH3 data-cubes is sigma_Tmb = 0.20 +/1 0.06 K. For the (1,1) transition this sensitivity equates to a 3.2 kpc distance limit for detecting a 20 K, 400 Msun cloud at the 5-sigma level. Similar clouds of mass 5,000 Msun would be detected as far as the Galactic centre, while 30,000 Msun clouds would be seen across the Galaxy. We have developed an automatic emission finding procedure based on the ATNF DUCHAMP software and have used it to create a new catalogue of 669 dense molecular clouds. The catalogue is 100 percent complete at the 5-sigma detection limit (Tmb = 1.0 K). A preliminary analysis of the ensemble cloud properties suggest that the near kinematic distances are favoured. The cloud positions are consisten...

Purcell, C R; Walsh, A J; Whiting, M T; Breen, S L; Britton, T; Brooks, K J; Burton, M G; Cunningham, M R; Green, J A; Harvey-Smith, L; Hindson, L; Hoare, M G; Indermuehle, B; Jones, P A; Lo, N; Lowe, V; Phillips, C J; Thompson, M A; Urquhart, J S; Voronkov, M A; White, G L

2012-01-01

247

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

NASA Astrophysics Data System (ADS)

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.

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

2014-08-01

248

Kinetics of hydrogen adsorption and desorption on Si(100) surfaces  

NASA Astrophysics Data System (ADS)

The kinetics of molecular hydrogen reactions at the Si (100) surface has been studied by simulation to extract the physics underlying two unexpected experimental observations: apparently first-order desorption kinetics and an increase in sticking probability with hydrogen coverage. At a partially H-terminated Si(100) surface, each Si dimer assumes an unoccupied dimer (UOD), singly occupied dimer (SOD), or doubly occupied dimer (DOD) structure. In our hydrogen reaction model based on an inter-dimer mechanism, a site consisting of an adjacent pair of a DOD and a UOD (DOD/UOD) is a key component for the desorption and adsorption kinetics of hydrogen at the Si(100) surface. To simulate reaction kinetics of both reactions, DU (D: DOD, U: UOD) and SS (S: SOD) pathways are proposed: DU pathway claims that the adsorption as well as desorption of hydrogen takes place at common sites having a cis-configured SOD/SOD pair that is transformed transiently from a DOD/UOD pair by H(D) diffusion. Thus the adsorption obeys the so-called 4H mechanism, but the desorption obeys the 2H mechanism. SS pathway claims that the adsorption occurs at sites having a UOD/UOD pair, and the desorption occurs at sites having a cis-configured SOD/SOD pair that is generated by diffusion of isolated SODs. To simulate temperature-programmed-desorption spectra and sticking probability vs coverage curves, thermo-statistics for a lattice-gas system characterized with parameters for hydrogen pairing and dimer clustering is used to evaluate equilibrium populations of DOD/UOD pairs and isolated SODs. The model simulation based on the above reaction model successfully reproduces all of the complicated, coverage dependent adsorption and desorption reactions of hydrogen at Si(100) surfaces. Specifically, at high coverage above 0.1 ML majority of the adsorption and desorption proceed along the DU pathway. Hence, it is suggested that the adsorption and desorption in the high coverage regime are not microscopically reversible. On the other hand, at low coverages below 0.1 ML, the simulation shows up that the majority of adsorption proceeds along the SS pathway, and the desorption by the DU pathway. Since both reactions obey the 2H mechanism, it is suggested that the desorption and adsorption in the low coverage regime are microscopically reversible.

Narita, Yuzuru; Inanaga, Shoji; Namiki, Akira

2013-06-01

249

NH3 assisted photoreduction and N-doping of graphene oxide for high performance electrode materials in supercapacitors  

NASA Astrophysics Data System (ADS)

Nitrogen-doped graphene was synthesized by simple photoreduction of graphene oxide (GO) deposited on nickel foam under NH3 atmosphere. The combination of photoreduction and NH3 not only reduces the GO in a shorter time but also induces nitrogen doping easily. The nitrogen doped content of N-rGO@NF reaches a high of 5.99 at% with 15 min of irradiation. The nitrogen-doped graphene deposited on Ni foam (N-rGO@NF) can be directly used as an electrode for supercapacitors, without any conductive agents and polymer binders. In the electrochemical measurement, N-rGO@NF displays remarkable electrochemical performance. In particular, the N-rGO@NF irradiated for 45 min at a high current density of 92.3 A g-1 retained about 77% (190.4 F g-1) of its initial specific capacitance (247.1 F g-1 at 0.31 A g-1). Furthermore, the stable voltage window could be extended to 2.0 and 1.5 V by using Li2SO4 and a mixed Li2SO4/KOH electrolyte, and the maximum energy density was high up to 32.6 and 21.2 Wh kg-1, respectively. The results show that compared to Li2SO4, a mixed electrolyte (Li2SO4/KOH) more efficiently balances the relationship between the high energy densities and high power densities.Nitrogen-doped graphene was synthesized by simple photoreduction of graphene oxide (GO) deposited on nickel foam under NH3 atmosphere. The combination of photoreduction and NH3 not only reduces the GO in a shorter time but also induces nitrogen doping easily. The nitrogen doped content of N-rGO@NF reaches a high of 5.99 at% with 15 min of irradiation. The nitrogen-doped graphene deposited on Ni foam (N-rGO@NF) can be directly used as an electrode for supercapacitors, without any conductive agents and polymer binders. In the electrochemical measurement, N-rGO@NF displays remarkable electrochemical performance. In particular, the N-rGO@NF irradiated for 45 min at a high current density of 92.3 A g-1 retained about 77% (190.4 F g-1) of its initial specific capacitance (247.1 F g-1 at 0.31 A g-1). Furthermore, the stable voltage window could be extended to 2.0 and 1.5 V by using Li2SO4 and a mixed Li2SO4/KOH electrolyte, and the maximum energy density was high up to 32.6 and 21.2 Wh kg-1, respectively. The results show that compared to Li2SO4, a mixed electrolyte (Li2SO4/KOH) more efficiently balances the relationship between the high energy densities and high power densities. Electronic supplementary information (ESI) available: Digital images of nickel foam, GO deposited in nickel foam, N-rGO@NF, and N-rGO@NF electrodes (1.0 × 1.0 cm); Digital images: (1) N-rGO@NF sheet was put into 1 M FeCl3 at room temperature dissolve the Ni metal and (2) a whole N-rGO sheet without Ni foam support after nickel etching; image of film with fragile features after being irradiated by a high-pressure Hg lamp (500 W) in Ar and NH3 atmosphere. See DOI: 10.1039/c4nr05776g

Huang, Haifu; Luo, Guangsheng; Xu, Lianqiang; Lei, Chenglong; Tang, Yanmei; Tang, Shaolong; Du, Youwei

2015-01-01

250

Emissions of NO and NH3 from a Typical Vegetable-Land Soil after the Application of Chemical N Fertilizers in the Pearl River Delta  

PubMed Central

Cropland soil is an important source of atmospheric nitric oxide (NO) and ammonia (NH3). Chinese croplands are characterized by intensive management, but limited information is available with regard to NO emissions from croplands in China and NH3 emissions in south China. In this study, a mesocosm experiment was conducted to measure NO and NH3 emissions from a typical vegetable-land soil in the Pearl River Delta following the applications of 150 kg N ha?1 as urea, ammonium nitrate (AN) and ammonium bicarbonate (ABC), respectively. Over the sampling period after fertilization (72 days for NO and 39 days for NH3), mean NO fluxes (± standard error of three replicates) in the control and urea, AN and ABC fertilized mesocosms were 10.9±0.9, 73.1±2.9, 63.9±1.8 and 66.0±4.0 ng N m?2 s?1, respectively; mean NH3 fluxes were 8.9±0.2, 493.6±4.4, 144.8±0.1 and 684.7±8.4 ng N m?2 s?1, respectively. The fertilizer-induced NO emission factors for urea, AN and ABC were 2.6±0.1%, 2.2±0.1% and 2.3±0.2%, respectively. The fertilizer-induced NH3 emission factors for the three fertilizers were 10.9±0.2%, 3.1±0.1% and 15.2±0.4%, respectively. From the perspective of air quality protection, it would be better to increase the proportion of AN application due to its lower emission factors for both NO and NH3. PMID:23527173

Li, Dejun

2013-01-01

251

Experimental and theoretical study of line shift and mixing in the ?4 band of NH3 perturbed by N2  

NASA Astrophysics Data System (ADS)

The shift coefficients and line-mixing parameters of rovibrational inversion transitions in the ?4 band of ammonia (NH3) perturbed by nitrogen (N2) have been measured at room temperature with a high-resolution Fourier transform spectrometer. The collisional shift and line mixing are obtained from the non-linear least-square multi-pressure fitting techniques. Comparison is made with the results of theoretical calculation based on semi-classical model extended to the case of symmetric top molecule with inversion motion. The shifts and the line-mixing parameters are calculated using, respectively the approach developed by Robert and Bonamy and the state-to-state cross-section. The agreement is satisfactory on the average. Good agreement is also obtained for line mixing with previous measurements.

Dhib, Mohamed; Aroui, Hassen; Orphal, Johannes

2007-10-01

252

Line shift and mixing in the ?4 and 2 ?2 band of NH 3 perturbed by H 2 and Ar  

NASA Astrophysics Data System (ADS)

Pressure induced line shift and line mixing parameters have been measured for 66 rovibrational lines in the ?4 band and for 10 lines in the 2 ?2 band of NH 3 perturbed by H 2 and Ar at room temperature ( T = 296 K). These lines with J values ranging from 2 to 10 are located in the spectral range 1450-1600 cm -1. Experiments were made with a high-resolution Fourier transform spectrometer. The line shifts and line mixing parameters have been derived from the non-linear least-square multi-pressure fitting technique. The shift coefficients are compared with those calculated from the Robert-Bonamy formalism (RB). The results are generally in satisfactory agreement with the experimental data.

Dhib, M.; Echargui, M. A.; Aroui, H.; Orphal, J.; Hartmann, J.-M.

2005-09-01

253

A theoretical investigation of gaseous absorption by water droplets from SO2-HNO3-NH3-CO2-HCl mixtures  

NASA Technical Reports Server (NTRS)

A physical-chemical model is developed and used to investigate gaseous absorption by water droplets from trace gas mixtures. The model is an extension of that of Carmichael and Peters (1979) and includes the simultaneous absorption of SO2, NH3, HNO3, CO2, and HCl. Gas phase depletion is also considered. Presented results demonstrate that the absorption behavior of raindrops is strongly dependent on drop size, fall distance, trace gas concentrations, and the chemical and physical properties of the constituents of the mixture. In addition, when gas phase depletion is considered, the absorption rates and equilibrium values are also dependent on the precipitation rate itself. Also, the trace constituents liquid phase concentrations may be a factor of six or more lower when gas depletion is considered then when the depletion is ignored. However, the hydrogen ion concentration may be insensitive to the gas phase depletion.

Adewuyi, Y. G.; Carmichael, G. R.

1982-01-01

254

Photolysis products of CO, NH3 aND H2O and their significance to reactions on interstellar grains  

NASA Technical Reports Server (NTRS)

With the increase in evidence that interstellar grains are the basic building blocks of comets and with the realization that comet collisions with the earth have probably occured at a much higher frequency than earlier assumed it may be presumed that interstellar dust chemistry played an important role in the early chemistry of the earth. As a part of the study of the photochemical processes taking place on interstellar grains the photolysis of mixtures of CO, NH3 and H2O was performed at 10 K, 77K and 298K. The reaction products were determined by GC/MS and HPLC analysis to be lactic acid, glycolic acid, hydroxyacetamide, urea, biuret, oxamic acid, oxamide, glyceric acid and glyceramide. Ethylene glycol and glycerol were also detected but is is not clear at present whether these are true photoproducts or contaminants. The mechanism of formation of these molecules are discussed as well as their possible significance to the origins of life.

Ferris, J. P.

1986-01-01

255

Toward a chemiresistive ammonia (NH3) gas sensor based on viral-templated gold nanoparticles embedded in polypyrrole nanowires  

NASA Astrophysics Data System (ADS)

Preliminary studies toward the assembly of a gold-polypyrrole (PPy) peapod-like chemiresistive ammonia (NH3) gas sensors are presented. The proposed synthesis process will use electropolymerization to embed gold nanoparticles in polypyrrole nanowires. Viral-templating of gold nanoparticles and PPy electrodeposition via cyclic voltammetry are the focus of this investigation. A gold-binding M13 bacteriophage was used as a bio-template to assemble continuous chains of gold nanoparticles on interdigitated Pt working electrodes. The dimensions of the resulting nanowire-like structures were examined and the electrical resistance measured. PPy films were electropolymerized using an interdigitated planar, Pt electrode integrated counter and reference electrode. Morphological characterization of the polymer films was completed.

Yan, Yiran; Zhang, Miluo; Su, Heng Chia; Myung, Nosang V.; Haberer, Elaine D.

2014-08-01

256

Two mixed-NH3/amine platinum (II) anticancer complexes featuring a dichloroacetate moiety in the leaving group  

NASA Astrophysics Data System (ADS)

Two mixed-NH3/amine platinum (II) complexes of 3-dichoroacetoxylcyclobutane-1, 1-dicarboxylate have been prepared in the present study and characterized by elemental analysis and IR, HPLC-MS and 1H, 13C-NMR. The complexes exist in equilibrium between two position isomeric forms and undergo hydrolysis reaction in aqueous solution, releasing the platinum pharmacophores and dichloroacetate which is a small-molecular cell apoptosis inducer. Both complexes were evaluated for in vitro cytotoxic profile in A549, SGC-7901 and SK-OV-3 caner cells as well as in BEAS-2B normal cells. They exhibit markedly cytoxicity toward cancer cells by selectively inducing the apoptosis of cancer cells, whereas leaving normal cells less affected. They have also the ability to overcome the resistance of SK-OV-3 cancer cells to cisplatin. Our findings offer an alternative novel way to develop platinum drugs which can both overcome the drug resistance and selectively target tumor cells.

Liu, Weiping; Su, Jia; Jiang, Jing; Li, Xingyao; Ye, Qingsong; Zhou, Hongyu; Chen, Jialin; Li, Yan

2013-08-01

257

Isolates identification and characteristics of microorganisms in biotrickling filter and biofilter system treating H2S and NH3.  

PubMed

A combination system of biotrickling filter (BTF) and biofilter (BF), adopting surfactant-modified clinoptilolite and surfactant-modified wood chip as the media respectively, was applied to treat H2S and NH3 simultaneously. The identification and sole carbon sources utilization patterns of isolates in the combination system were studied by Biolog system. The isolates were identified as Bacillus sphaericus, Geobacillus themoglucosidasius (55 degrees C) and Micrococcus luteus (ATCC 9341) in BTF, and Aspergillus sydowii (Bainier & Sartory) Thorm & Church in BF. Among 95 substrate classes supplied by Biolog system, the carboxylic acids and methyl esters had the highest utilization extent for the four species, followed by the amino acids and peptides. The descending sequence of carbon sources utilization capability of isolates was A. sydowii (52.6%), M. luteus (39.5%), B. sphaericus (21.6%), and G. thermoglucosidasius (17.7%). PMID:17966875

Guang-Hui, Yu; Xiao-Jun, Xu; Pin-Jing, He

2007-01-01

258

Inactivation of Na,K-ATPase following Co(NH3)4ATP binding at a low affinity site in the protomeric enzyme unit.  

PubMed

The Na(+)-dependent or E1 stages of the Na,K-ATPase reaction require a few micromolar ATP, but submillimolar concentrations are needed to accelerate the K(+)-dependent or E2 half of the cycle. Here we use Co(NH(3))(4)ATP as a tool to study ATP sites in Na,K-ATPase. The analogue inactivates the K(+) phosphatase activity (an E2 partial reaction) and the Na,K-ATPase activity in parallel, whereas ATP-[(3)H]ADP exchange (an E1 reaction) is affected less or not at all. Although the inactivation occurs as a consequence of low affinity Co(NH(3))(4)ATP binding (K(D) approximately 0.4-0.6 mm), we can also measure high affinity equilibrium binding of Co(NH(3))(4)[(3)H]ATP (K(D) = 0.1 micro m) to the native enzyme. Crucially, we find that covalent enzyme modification with fluorescein isothiocyanate (which blocks E1 reactions) causes little or no effect on the affinity of the binding step preceding Co(NH(3))(4)ATP inactivation and only a 20% decrease in maximal inactivation rate. This suggests that fluorescein isothiocyanate and Co(NH(3))(4)ATP bind within different enzyme pockets. The Co(NH(3))(4)ATP enzyme was solubilized with C(12)E(8) to a homogeneous population of alphabeta protomers, as verified by analytical ultracentrifugation; the solubilization did not increase the Na,K-ATPase activity of the Co(NH(3))(4)ATP enzyme with respect to parallel controls. This was contrary to the expectation for a hypothetical (alphabeta)(2) membrane dimer with a single ATP site per protomer, with or without fast dimer/protomer equilibrium in detergent solution. Besides, the solubilized alphabeta protomer could be directly inactivated by Co(NH(3))(4)ATP, to less than 10% of the control Na,K-ATPase activity. This suggests that the inactivation must follow Co(NH(3))(4)ATP binding at a low affinity site in every protomeric unit, thus still allowing ATP and ADP access to phosphorylation and high affinity ATP sites. PMID:12591931

Ward, Douglas G; Cavieres, José D

2003-04-25

259

Adsorption-desorption kinetics of the monomer-dimer mixture  

NASA Astrophysics Data System (ADS)

The kinetics of the monomer-dimer mixtures is formulated in the framework of the kinetic lattice gas model. The so-called local evolution rules are used to derive the hierarchy of coupled differential equations for coverage and other correlators, when processes like adsorption, desorption and diffusion are included. The hierarchy of equation is truncated by using mean-field (m,n) closures. Equilibrium properties are analyzed. In particular, adsorption isotherms as a function of the nearest neighbor lateral interaction are presented. The irreversible kinetics are also considered. Temperature-programmed-desorption (TPD) with readsorption is of special interest and this experiment is simulated under different conditions giving different spectra. In these spectra, the influence of adsorbate mobility is analyzed in two dimensions by Monte Carlo simulations.

Boscoboinik, J. A.; Manzi, S. J.; Pereyra, V. D.

2010-04-01

260

Low Dislocation Densities of Nitride-Based Light-Emitting Diodes with a Preflow of NH3 Source before Growth of AlN Buffer Layer  

NASA Astrophysics Data System (ADS)

In this study, the AlN buffer layer grown on c-plane sapphire (Al2O3) substrates by metal-organic chemical vapor deposition (MOCVD) was controlled by a preflow of the NH3 source. With the treatment of NH3 preflow, the monolayer of AlN was formed on the surface of a sapphire substrate by the decomposition of the NH3 source and Al2O3 substrate. It was found that the density of threading dislocations significantly decreased owing to the abatement of lattice mismatch between a GaN layer and a sapphire substrate. At an injection current of 350 mA, the light output intensity of the light-emitting diode (LED) with NH3 preflow was increased by 14.1% compared with that of a conventional LED. On the other hand, LEDs with NH3 preflow treatment could endure electrostatic discharge (ESD) surges up to -3000 V and caused a low rate of light output degradation at a high ambient temperature.

Wang, Chun-Kai; Chiou, Yu-Zung; Sun, De-Jun; Chiang, Tsung-Hsun

2013-01-01

261

Vacuum-Assisted Thermal Annealing of CH3NH3PbI3 for Highly Stable and Efficient Perovskite Solar Cells.  

PubMed

Solar cells incorporating lead halide-based perovskite absorbers can exhibit impressive power conversion efficiencies (PCEs), recently surpassing 15%. Despite rapid developments, achieving precise control over the morphologies of the perovskite films (minimizing pore formation) and enhanced stability and reproducibility of the devices remain challenging, both of which are necessary for further advancements. Here we demonstrate vacuum-assisted thermal annealing as an effective means for controlling the composition and morphology of the CH3NH3PbI3 films formed from the precursors of PbCl2 and CH3NH3I. We identify the critical role played by the byproduct of CH3NH3Cl on the formation and the photovoltaic performance of the perovskite film. By completely removing the byproduct through our vacuum-assisted thermal annealing approach, we are able to produce pure, pore-free planar CH3NH3PbI3 films with high PCE reaching 14.5% in solar cell device. Importantly, the removal of CH3NH3Cl significantly improves the device stability and reproducibility with a standard deviation of only 0.92% in PCE as well as strongly reducing the photocurrent hysteresis. PMID:25549113

Xie, Feng Xian; Zhang, Di; Su, Huimin; Ren, Xingang; Wong, Kam Sing; Grätzel, Michael; Choy, Wallace C H

2015-01-27

262

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

PubMed

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

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

2014-11-24

263

A facile, solvent vapor-fumigation-induced, self-repair recrystallization of CH3NH3PbI3 films for high-performance perovskite solar cells  

NASA Astrophysics Data System (ADS)

A high-quality CH3NH3PbI3 film is crucial in the manufacture of a high-performance perovskite solar cell. Here, a recrystallization process via facile fumigation with DMF vapor has been successfully introduced to self-repair of CH3NH3PbI3 films with poor coverage and low crystallinity prepared by the commonly used one-step spin-coating method. We found that the CH3NH3PbI3 films with dendritic structures can spontaneously transform to the uniform ones with full coverage and high crystallinity by adjusting the cycles of the recrystallization process. The mesostructured perovskite solar cells based on these repaired CH3NH3PbI3 films showed reproducible optimal power conversion efficiency (PCE) of 11.15% and average PCE of 10.25 +/- 0.90%, which are much better than that of devices based on the non-repaired CH3NH3PbI3 films. In addition, the hysteresis phenomenon in the current-voltage test can also be effectively alleviated due to the quality of the films being improved in the optimized devices. Our work proved that the fumigation of solvent vapor can modify metal organic perovskite films such as CH3NH3PbI3. It offers a novel and attractive way to fabricate high-performance perovskite solar cells.A high-quality CH3NH3PbI3 film is crucial in the manufacture of a high-performance perovskite solar cell. Here, a recrystallization process via facile fumigation with DMF vapor has been successfully introduced to self-repair of CH3NH3PbI3 films with poor coverage and low crystallinity prepared by the commonly used one-step spin-coating method. We found that the CH3NH3PbI3 films with dendritic structures can spontaneously transform to the uniform ones with full coverage and high crystallinity by adjusting the cycles of the recrystallization process. The mesostructured perovskite solar cells based on these repaired CH3NH3PbI3 films showed reproducible optimal power conversion efficiency (PCE) of 11.15% and average PCE of 10.25 +/- 0.90%, which are much better than that of devices based on the non-repaired CH3NH3PbI3 films. In addition, the hysteresis phenomenon in the current-voltage test can also be effectively alleviated due to the quality of the films being improved in the optimized devices. Our work proved that the fumigation of solvent vapor can modify metal organic perovskite films such as CH3NH3PbI3. It offers a novel and attractive way to fabricate high-performance perovskite solar cells. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr00225g

Zhu, Weidong; Yu, Tao; Li, Faming; Bao, Chunxiong; Gao, Hao; Yi, Yong; Yang, Jie; Fu, Gao; Zhou, Xiaoxin; Zou, Zhigang

2015-03-01

264

Real Time Monitoring of NH3 Concentration Using Diffusion Scrubber Sampling Technique and Result of Application to the Processing of Chemically Amplified Resists  

NASA Astrophysics Data System (ADS)

The application of chemically amplified resist is known to cause a problem in the accurate measurement of the concentration of basic gas species ( NH3, N-methylpyrrolidone (NMP)) in a clean room environment because it is sensitive to its environment. Among various methods of measurement, diffusion scrubber sampling method was selected and tested. The environmental sensitivity of a commercial chemically amplified resist, APEX-E, was also tested. For the concentration measurement, the method proved to be suitable for automation and good for measuring NH3 concentration as low as the sub ppb level (limit of detection ˜0.08 ppb). Some measurement results concerning various aspects of application are presented. Test results of the environmental stability of chemically amplified resists showed that NH3 concentration should be controlled to at least under 7.5 ppb for maintaining the process stability.

Park, Jungchul; Bae, Eunyoung; Park, Chungeun; Han, Woosung; Koh, Youngbum; Lee, Moonyoung; Lee, Jonggil

1995-12-01

265

Performance of InGaN/GaN light-emitting diodes grown using NH3 with oxygen-containing impurities  

NASA Astrophysics Data System (ADS)

The performance of InGaN/GaN light-emitting diodes (LEDs) fabricated using NH3 was varied by intentionally adding H2O, O2, or CO. The oxygen concentration in the active layer varied with the type of impurity, which was related to the binding energy of the impurity. When a small amount of oxygen was incorporated in the InGaN active layer without Si doping through an oxygen-containing impurity, the light output power of the LED was improved. On the other hand, the light output power of the LED gradually deteriorated with increasing oxygen concentration. The oxygen-containing impurities affected the light output power of the LEDs. When NH3 with any oxygen-containing impurities was purified using a purification system giving a guaranteed impurity concentration of less than 10 ppb, the light output power of the LED was recovered to that of the LED fabricated with pure NH3.

Okada, Narihito; Tadatomo, Kazuyuki; Yamane, Keisuke; Mangyo, Hirotaka; Kobayashi, Yoshihiko; Ono, Hiroyuki; Ikenaga, Kazutada; Yano, Yoshiki; Matsumoto, Koh

2014-08-01

266

p-n junctions on Ga-face GaN grown by NH3 molecular beam epitaxy with low ideality factors and low reverse currents  

NASA Astrophysics Data System (ADS)

A comprehensive analysis of forward and reverse current of Ga-face GaN p-n junctions grown by NH3 molecular beam epitaxy (NH3-MBE) on metal organic chemical vapor deposition (MOCVD) GaN:Fe on sapphire is presented. NH3-MBE has a great potential for growing low leakage vertical devices due to its nitrogen-rich growth. Diodes with the lowest n-doping of n˜3.5×1017 cm-3 exhibit an extremely low reverse current of 2.6×10-7 A/cm2 at -40 V and an ideality factor of 1.3, which is lower than the state-of-the-art Ga-face p-n junctions grown on sapphire by MOCVD. An explanation for the difficulty for observing low ideality factors in GaN is presented.

Hurni, Christophe A.; Bierwagen, Oliver; Lang, Jordan R.; McSkimming, Brian M.; Gallinat, Chad S.; Young, Erin C.; Browne, David A.; Mishra, Umesh K.; Speck, James S.

2010-11-01

267

Adsorption, Desorption, and Diffusion of Nitrogen in a Model Nanoporous Material: I. Surface Limited Desorption Kinetics in Amorphous Solid Water  

SciTech Connect

The adsorption and desorption kinetics of N2 on porous amorphous solid water (ASW) films were studied using molecular beam techniques, temperature programmed desorption (TPD), and reflection-absorption infrared spectroscopy (RAIRS). The ASW films were grown on Pt(111) at 23 K by ballistic deposition from a collimated H2O beam at various incident angles to control the film porosity. The experimental results show that the N2 condensation coefficient is essentially unity until near saturation, independent of the ASW film thickness. This means that N2 transport within the porous films is rapid. The TPD results show that the desorption of a fixed dose of N2 shifts to higher temperature with ASW film thickness. Kinetic analysis of the TPD spectra shows that a film thickness rescaling of the coverage dependent activation energy curve results in a single master curve. Simulation of the TPD spectra using this master curve results in a quantitative fit to the experiments over a wide range of ASW thicknesses (up to 1000 layers, ~0.5 mm). The success of the rescaling model indicates that N2 transport within the porous film is rapid enough to maintain a uniform distribution throughout the film on a time scale faster than desorption.

Zubkov, Tykhon; Smith, R. Scott; Engstrom, Todd R.; Kay, Bruce D.

2007-11-14

268

Thermal Decomposition and Desorption of Diethylamido of Tetrakis (Diethylamido)Zirconium (TDEAZr) on Si(100)  

Microsoft Academic Search

The thermal decomposition pathway and desorption of diethylamido of tetrakis (diethylamido)zirconium [TDEAZr, Zr(N(C2H5)2) 4] on Si(100) were studied using temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). During TPD experiments, ethylethyleneimine (C2H5N=CHCH3), diethylamine [NH(C2H5)2], acetonitrile (CH3CN), ethylene (C2H4) and hydrogen (H2) desorbed as the main decomposition products of diethylamido, which was chemisorbed on Si(100) through the scission of the zirconium-diethylamido

Joonhee Jeong; Sungwon Lim; Kijung Yong

2003-01-01

269

Electron transport through metallic single wall carbon nanotubes with adsorbed NO2 and NH3 molecules: A first-principles study  

NASA Astrophysics Data System (ADS)

In this Letter, variations in the transport characteristics of metallic single wall carbon nanotubes (SWCNTs) due to the absorption of NO2 and NH3 molecules on the surface are investigated using the Landauer formalism combined with the non-equilibrium Green's function techniques and ab initio electronic structure obtained using density functional theory (DFT). The electronic structure, charge distribution, transmission spectrum and I-V characteristics of the SWCNT are significantly changed on adsorption which is reflected in the conductance and transport characteristics of the SWCNT. Thus, we conclude that these systems can be used in CNT based NO2 and NH3 gas sensors.

Sivasathya, S.; Thiruvadigal, D. John; Mathi Jaya, S.

2014-08-01

270

CH3NH3PbI3 from non-iodide lead salts for perovskite solar cells via the formation of PbI2.  

PubMed

We report the formation of CH3NH3PbI3 from more soluble, non-iodide lead salts like Pb(SCN)2 and Pb(NO3)2. When exposed to CH3NH3I vapours, the colourless lead salts turned yellow before the formation of the black perovskite. Investigation of this yellow intermediate suggests that anion exchange (converting lead salts to PbI2) precedes the perovskite formation. PCEs of 7.6% and 8.4% were achieved for the devices formed from Pb(SCN)2 and Pb(NO3)2, respectively. PMID:25824113

Balaji, Ganapathy; Joshi, Pranav H; Abbas, Hisham A; Zhang, Liang; Kottokkaran, Ranjith; Samiee, Mehran; Noack, Max; Dalal, Vikram L

2015-04-01

271

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)

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 independent 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 constrasted with those for the corresponding reactions of H and OH with PH3.

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

1983-01-01

272

Emissions of Volatile Inorganic Halogens, Carboxylic Acids, NH3, and SO2 From Experimental Burns of Southern African Biofuels  

NASA Astrophysics Data System (ADS)

As part of SAFARI 2000, biofuels (savanna grasses, shrubs, woody plants, litter, agricultural waste, and charcoal) were sampled during late summer and early autumn in the savannah of Kruger National Park, the Kalahari of Etosha National Park, and the Miombo woodlands in Zambia and Malawi. Sixty subsamples were experimentally burned under semi-controlled conditions at the Max Planck Institute for Chemistry in Mainz, Germany. Emissions were sampled with tandem mist chambers to quantify HCl, CH3COOH, HCOOH, NH3, and SO2 and with a high-volume filter pack to quantify volatile inorganic Cl, Br, and I. The elemental compositions of the fuel and ash from each burn were also analyzed. Molar emission ratios of these species relative to CO, CO2, and the elemental composition of the fuel will be calculated and used to estimate regional emissions from biomass burning over southern Africa. The relative contributions of each species to elemental mass balances during burns will also be assessed. >http://jurgenlobert.org/projects/mpi_safari/ and

Keene, W. C.; Lobert, J. M.; Lobert, J. M.; Maben, J. R.; Scharffe, D. H.; Crutzen, P. J.; Crutzen, P. J.

2001-12-01

273

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

PubMed Central

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

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

274

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

NASA Astrophysics Data System (ADS)

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.

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

2014-10-01

275

Using 3-D OFEM for movement correction and quantitative evaluation in dynamic cardiac NH3 PET images  

NASA Astrophysics Data System (ADS)

Various forms of cardiac pathology, such as myocardial ischemia and infarction, can be characterized with 13NH3-PET images. In clinical situation, polar map (bullseye image), which derived by combining images from multiple planes (designated by the circle around the myocardium in the above images), so that information of the entire myocardium can be displayed in a single image for diagnosis. However, image artifact problem always arises from body movement or breathing motion in image acquisition period and results in indefinite myocardium disorder region shown in bullseye image. In this study, a 3-D motion and movement correction method is developed to solve the image artifact problem to improve the accuracy of diagnostic bullseye image. The proposed method is based on 3-D optical flow estimation method (OFEM) and cooperates with the particular dynamic imaging protocol, which snaps serial PET images (5 frames) in later half imaging period. The 3-D OFEM assigns to each image point in the visual 3-D flow velocity field, which associates with the non-rigid motion of the time-varying brightness of a sequence of images. It presents vectors of corresponding images position between frames for motion correction. To validate the performance of proposed method, 10 normal and 20 abnormal whole-body dynamic PET imaging studies were applied, and the results show that the bullseye images, which generated by corrected images, present clear and definite tissue region for clinical diagnosis.

Lin, Hong-Dun; Yang, Bang-Hung; Chen, Chih-Hao; Wu, Liang-Chih; Liu, Ren-Shyan; Chung, Being-Tau; Lin, Kang-Ping

2005-04-01

276

Two mixed-NH3/amine platinum (II) anticancer complexes featuring a dichloroacetate moiety in the leaving group  

PubMed Central

Two mixed-NH3/amine platinum (II) complexes of 3-dichoroacetoxylcyclobutane-1, 1-dicarboxylate have been prepared in the present study and characterized by elemental analysis and IR, HPLC-MS and 1H, 13C-NMR. The complexes exist in equilibrium between two position isomeric forms and undergo hydrolysis reaction in aqueous solution, releasing the platinum pharmacophores and dichloroacetate which is a small-molecular cell apoptosis inducer. Both complexes were evaluated for in vitro cytotoxic profile in A549, SGC-7901 and SK-OV-3 caner cells as well as in BEAS-2B normal cells. They exhibit markedly cytoxicity toward cancer cells by selectively inducing the apoptosis of cancer cells, whereas leaving normal cells less affected. They have also the ability to overcome the resistance of SK-OV-3 cancer cells to cisplatin. Our findings offer an alternative novel way to develop platinum drugs which can both overcome the drug resistance and selectively target tumor cells. PMID:23955304

Liu, Weiping; Su, Jia; Jiang, Jing; Li, Xingyao; Ye, Qingsong; Zhou, Hongyu; Chen, Jialin; Li, Yan

2013-01-01

277

An analytical approach to evaluate the performance of graphene and carbon nanotubes for NH3 gas sensor applications.  

PubMed

Carbon, in its variety of allotropes, especially graphene and carbon nanotubes (CNTs), holds great potential for applications in variety of sensors because of dangling ?-bonds that can react with chemical elements. In spite of their excellent features, carbon nanotubes (CNTs) and graphene have not been fully exploited in the development of the nanoelectronic industry mainly because of poor understanding of the band structure of these allotropes. A mathematical model is proposed with a clear purpose to acquire an analytical understanding of the field-effect-transistor (FET) based gas detection mechanism. The conductance change in the CNT/graphene channel resulting from the chemical reaction between the gas and channel surface molecules is emphasized. NH3 has been used as the prototype gas to be detected by the nanosensor and the corresponding current-voltage (I-V) characteristics of the FET-based sensor are studied. A graphene-based gas sensor model is also developed. The results from graphene and CNT models are compared with the experimental data. A satisfactory agreement, within the uncertainties of the experiments, is obtained. Graphene-based gas sensor exhibits higher conductivity compared to that of CNT-based counterpart for similar ambient conditions. PMID:24991510

Akbari, Elnaz; Arora, Vijay Kumar; Enzevaee, Aria; Ahmadi, Mohamad T; Saeidmanesh, Mehdi; Khaledian, Mohsen; Karimi, Hediyeh; Yusof, Rubiyah

2014-01-01

278

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

PubMed

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

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

2015-02-01

279

High intrinsic carrier mobility and photon absorption in the perovskite CH3NH3PbI3.  

PubMed

The carrier transport and optical properties of the hybrid organic-inorganic perovskite CH3NH3PbI3 are investigated using first-principles approaches. We found that the electron and hole mobilities could reach surprisingly high values of 7-30 × 10(3) and 1.5-5.5 × 10(3) cm(2) V(-1) s(-1), respectively, and both are estimated to be much higher than the current experimental measurements. The high carrier mobility is ascribed to the intrinsically small effective masses of anti-bonding band-edge states. The above results imply that there is still space to improve the performance of related solar cells. This material also has a sharp photon absorption edge and an absorption coefficient as high as 10(5) cm(-1), both of which contribute to effective utilization of solar radiation. Although band-edge states are mainly derived from the inorganic ions of Pb and I, thermal movement of the organic base has indirect influences on the bandgap and carrier effective masses, resulting in the temperature-dependent solar cell efficiencies. PMID:25855411

Wang, Youwei; Zhang, Yubo; Zhang, Peihong; Zhang, Wenqing

2015-04-21

280

An analytical approach to evaluate the performance of graphene and carbon nanotubes for NH3 gas sensor applications  

PubMed Central

Summary Carbon, in its variety of allotropes, especially graphene and carbon nanotubes (CNTs), holds great potential for applications in variety of sensors because of dangling ?-bonds that can react with chemical elements. In spite of their excellent features, carbon nanotubes (CNTs) and graphene have not been fully exploited in the development of the nanoelectronic industry mainly because of poor understanding of the band structure of these allotropes. A mathematical model is proposed with a clear purpose to acquire an analytical understanding of the field-effect-transistor (FET) based gas detection mechanism. The conductance change in the CNT/graphene channel resulting from the chemical reaction between the gas and channel surface molecules is emphasized. NH3 has been used as the prototype gas to be detected by the nanosensor and the corresponding current–voltage (I–V) characteristics of the FET-based sensor are studied. A graphene-based gas sensor model is also developed. The results from graphene and CNT models are compared with the experimental data. A satisfactory agreement, within the uncertainties of the experiments, is obtained. Graphene-based gas sensor exhibits higher conductivity compared to that of CNT-based counterpart for similar ambient conditions. PMID:24991510

Akbari, Elnaz; Enzevaee, Aria; Ahmadi, Mohamad T; Saeidmanesh, Mehdi; Khaledian, Mohsen; Karimi, Hediyeh; Yusof, Rubiyah

2014-01-01

281

Sub-doppler spectroscopy of the ?2 band of NH 3 using microwave modulation sidebands of CO 2 laser lines  

NASA Astrophysics Data System (ADS)

Microwave modulation sidebands of CO 2 laser lines were used for sub-Doppler saturation spectroscopy in the ?2 fundamental of NH 3. Fifteen transitions were observed and their positions were determined with an absolute frequency accuracy of typically ±100 kHz. The intensities of the observed Lamb dips and crossover dips could be shown to be consistent with theory. In addition, the electronic quadrupole hyperfine splittings due to the 14N nucleus on five transitions were resolved. From this the quadrupole coupling constant eqQ in the ?2 state was determined as ( eqQ) ( v2=1, s) = -4442 ± 156 kHz and ( eqQ) ( v2=1, a) = -4329 ± 375 kHz for the lower and upper inversion levels, respectively. The observed increase of 296 kHz in the magnitude of eqQ upon vibrational excitation could be shown to be consistent with its dependence on hybridization and ionicity of the N?H bond.

Magerl, Gottfried; Schupita, Walter; Frye, Joan M.; Kreiner, Welf A.; Oka, Takeshi

1984-09-01

282

The 2.9-4.2 micron spectrum of Saturn: Clouds and CH 4, PH 3, and NH 3  

NASA Astrophysics Data System (ADS)

We have used synthetic spectra to analyze a medium resolution 2.9-4.2 ?m spectrum of Saturn's temperate region observed at UKIRT using CGS4. The synthetic spectra include CH 4, PH 3, and NH 3 lines, for which mixing ratios were adopted from recent Cassini results. The observed absorption features in the spectrum are well accounted for by lines of these molecular species formed 22 +/- 8 km above the 1 bar pressure level at ˜610 mbar. The influence of optically thin haze particles at higher altitudes on the spectrum is not pronounced, with higher spectral resolution probably required to constrain the effects of haze in this wavelength region. Fluorescent line emission by CH 4 in its ? and ?+?-? bands, detected in the 3.2-3.5 ?m region, originates between 400 km (˜0.06 mbar) and 800 km (˜0.01 ?bar) above the 1 bar level, with peak contributions from the two major contributing bands at 550 km (˜3 ?bar) and 700 km (˜0.1 ?bar), respectively.

Kim, Sang J.; Geballe, T. R.

2005-12-01

283

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

NASA Astrophysics Data System (ADS)

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.

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

2015-04-01

284

Synthesis, structure, and photovoltaic property of a nanocrystalline 2H perovskite-type novel sensitizer (CH3CH2NH3)PbI3  

PubMed Central

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

2012-01-01

285

Origin of the visible-light photoactivity of NH3-treated TiO2: Effect of nitrogen doping and oxygen vacancies  

NASA Astrophysics Data System (ADS)

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.

Chen, Yilin; Cao, Xiaoxin; Lin, Bizhou; Gao, Bifen

2013-01-01

286

Low-temperature surface formation of NH3 and HNCO: hydrogenation of nitrogen atoms in CO-rich interstellar ice analogues  

NASA Astrophysics Data System (ADS)

Solid-state astrochemical reaction pathways have the potential to link the formation of small nitrogen-bearing species, like NH3 and HNCO, and prebiotic molecules, specifically amino acids. To date, the chemical origin of such small nitrogen-containing species is still not well understood, despite the fact that ammonia is an abundant constituent of interstellar ices towards young stellar objects and quiescent molecular clouds. This is mainly because of the lack of dedicated laboratory studies. The aim of this work is to experimentally investigate the formation routes of NH3 and HNCO through non-energetic surface reactions in interstellar ice analogues under fully controlled laboratory conditions and at astrochemically relevant temperatures. This study focuses on the formation of NH3 and HNCO in CO-rich (non-polar) interstellar ices that simulate the CO freeze-out stage in dark interstellar cloud regions, well before thermal and energetic processing start to become relevant. We demonstrate and discuss the surface formation of solid HNCO through the interaction of CO molecules with NH radicals - one of the intermediates in the formation of solid NH3 upon sequential hydrogenation of N atoms. The importance of HNCO for astrobiology is discussed.

Fedoseev, G.; Ioppolo, S.; Zhao, D.; Lamberts, T.; Linnartz, H.

2015-01-01

287

Leaf age-related differences in apoplastic NH4+ concentration, pH and the NH3 compensation point for a wild perennial  

Microsoft Academic Search

Extracts of the foliar apoplast of leaves of different ages of Luzula sylvatica (Huds.) Gaud. were prepared by vacuum infiltration and centrifugation. Measure- ments of pH and NHq 4 concentration were performed on extracts. From these bioassay measurements the relative magnitude of NH3 compensation points for leaves of different ages were inferred. Young leaves were found to have much higher

P. W. Hill; J. A. Raven; M. A. Sutton

2002-01-01

288

Thermally-activated recombination in one component of (CH3NH3)PbI3/TiO2 observed by photocurrent spectroscopy.  

PubMed

Photocurrent measurements on devices containing perovskite (CH3NH3)PbI3 show two distinct spectral responses when deposited in a mesoporous oxide matrix, compared with one response for planar perovskite alone. With a TiO2 matrix, the shorter wavelength response has an inverted temperature response with increasing performance on cooling. PMID:25820818

Cottingham, Patrick; Wallace, David C; Hu, Ke; Meyer, Gerald; McQueen, Tyrel M

2015-04-14

289

Characterization of Lewis acid sites on the ,,100... surface of -AlF3: Ab initio calculations of NH3 adsorption  

E-print Network

to catalyze reactions that are usually only catalyzed by very strong Lewis acids such as SbF5.1 HS-AlF3Characterization of Lewis acid sites on the ,,100... surface of -AlF3: Ab initio calculations of NH The current study employs hybrid-exchange density functional theory to show that the Lewis base, NH3, binds

290

On the Surface Formation of NH3 and HNCO in Dark Molecular Clouds - Searching for Wöhler Synthesis in the Interstellar Medium  

NASA Astrophysics Data System (ADS)

Despite its potential to reveal the link between the formation of simple species and more complex molecules (e.g., amino acids), the nitrogen chemistry of the interstellar medium (ISM) is still poorly understood. Ammonia (NH _{3}) is one of the few nitrogen-bearing species that have been observed in interstellar ices toward young stellar objects (YSOs) and quiescent molecular clouds. The aim of the present work is to experimentally investigate surface formation routes of NH _{3} and HNCO through non-energetic surface reactions in interstellar ice analogues under fully controlled laboratory conditions and at astrochemically relevant cryogenic temperatures. This study focuses on the formation of NH _{3} and HNCO in CO-rich (non-polar) interstellar ices that simulate the CO freeze-out stage in interstellar dark cloud regions, well before thermal and energetic processing start to become predominant. Our work confirms the surface formation of ammonia through the sequential addition of three hydrogen/deuterium atoms to a single nitrogen atom at low temperature. The H/D fractionation of the formed ammonia is also shown. Furthermore, we show the surface formation of solid HNCO through the interaction of CO molecules with NH radicals - one of the intermediates in the formation of solid NH _{3}. Finally, we discuss the implications of HNCO in astrobiology, as a possible starting point for the formation of more complex prebiotic species.

Fedoseev, Gleb; Lamberts, Thanja; Linnartz, Harold; Ioppolo, Sergio; Zhao, Dongfeng

291

The Impact of Fertilizer Type and Application Method on the Loss of Greenhouse (CO2, N2O, CH4), and Air Quality (NH3) Gases  

Technology Transfer Automated Retrieval System (TEKTRAN)

An experiment initiated in the Spring of 2007 at the Sand Mountain Agricultural Experiment Station in Crossville, AL will be discussed. The objective of this experiment is to evaluate the loss of NH3 from different land management (conventional tillage vs. conservation tillage), fertilizers (urea-a...

292

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)

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.

Othonos, Andreas; Zervos, Matthew; Christofides, Constantinos

2010-12-01

293

Composition-dependent photoluminescence intensity and prolonged recombination lifetime of perovskite CH3NH3PbBr(3-x)Cl(x) films.  

PubMed

Mixed halide perovskites CH3NH3PbBr3-xClx (x = 0.6-1.2) with different compositions of halogens exhibit drastically changed optical properties. In particular, the thin films prepared with these perovskites demonstrate extraordinary photoluminescence emission intensities and prolonged recombination lifetimes up to 446 ns, which are desirable for light emitting and photovoltaic applications. PMID:25144835

Zhang, Meng; Yu, Hua; Lyu, Miaoqiang; Wang, Qiong; Yun, Jung-Ho; Wang, Lianzhou

2014-10-11

294

Real Time Monitoring of NH3 Concentration Using Diffusion Scrubber Sampling Technique and Result of Application to the Processing of Chemically Amplified Resists  

Microsoft Academic Search

The application of chemically amplified resist is known to cause a problem in the accurate measurement of the concentration of basic gas species ( NH3, N-methylpyrrolidone (NMP)) in a clean room environment because it is sensitive to its environment. Among various methods of measurement, diffusion scrubber sampling method was selected and tested. The environmental sensitivity of a commercial chemically amplified

Eunyoung Bae; Woosung Han; Youngbum Koh; Moonyoung Lee; Jonggil Lee

1995-01-01

295

Transformation of the Excited State and Photovoltaic Efficiency of CH3NH3PbI3 Perovskite upon Controlled Exposure to Humidified Air.  

PubMed

Humidity has been an important factor, in both negative and positive ways, in the development of perovskite solar cells and will prove critical in the push to commercialize this exciting new photovoltaic technology. The interaction between CH3NH3PbI3 and H2O vapor is investigated by characterizing the ground-state and excited-state optical absorption properties and probing morphology and crystal structure. These undertakings reveal that H2O exposure does not simply cause CH3NH3PbI3 to revert to PbI2. It is shown that, in the dark, H2O is able to complex with the perovskite, forming a hydrate product similar to (CH3NH3)4PbI6·2H2O. This causes a decrease in absorption across the visible region of the spectrum and a distinct change in the crystal structure of the material. Femtosecond transient absorption spectroscopic measurements show the effect that humidity has on the ultrafast excited state dynamics of CH3NH3PbI3. More importantly, the deleterious effects of humidity on complete solar cells, specifically on photovoltaic efficiency and stability, are explored in the light of these spectroscopic understandings. PMID:25590693

Christians, Jeffrey A; Miranda Herrera, Pierre A; Kamat, Prashant V

2015-02-01

296

The Challenge of Deciphering Linkage Isomers in Mixtures of Oligomeric Complexes Derived from 9-Methyladenine and trans-(NH3 )2 Pt(II) Units.  

PubMed

Metal coordination to N9-substituted adenines, such as the model nucleobase 9-methyladenine (9MeA), under neutral or weakly acidic pH conditions in water preferably occurs at N1 and/or N7. This leads, not only to mononuclear linkage isomers with N1 or N7 binding, but also to species that involve both N1 and N7 metal binding in the form of dinuclear or oligomeric species. Application of a trans-(NH3 )2 Pt(II) unit and restriction of metal coordination to the N1 and N7 sites and the size of the oligomer to four metal entities generates over 50 possible isomers, which display different feasible connectivities. Slowly interconverting rotamers are not included in this number. Based on (1) H?NMR spectroscopic analysis, a qualitative assessment of the spectroscopic features of N1,N7-bridged species was attempted. By studying the solution behavior of selected isolated and structurally characterized compounds, such as trans-[PtCl(9MeA-N7)(NH3 )2 ]ClO4 ?2H2 O or trans,trans-[{PtCl(NH3 )2 }2 (9MeA-N1,N7)][ClO4 ]2 ?H2 O, and also by application of a 9MeA complex with an (NH3 )3 Pt(II) entity at N7, [Pt(9MeA-N7)(NH3 )3 ][NO3 ]2 , which blocks further cross-link formation at the N7 site, basic NMR spectroscopic signatures of N1,N7-bridged Pt(II) complexes were identified. Among others, the trinuclear complex trans-[Pt(NH3 )2 {?-(N1-9MeA-N7)Pt(NH3 )3 }2 ][ClO4 ]6 ?2H2 O was crystallized and its rotational isomerism in aqueous solution was studied by NMR spectroscopy and DFT calculations. Interestingly, simultaneous Pt(II) coordination to N1 and N7 acidifies the exocyclic amino group of the two 9MeA ligands sufficiently to permit replacement of one proton each by a bridging heterometal ion, Hg(II) or Cu(II) , under mild conditions in water. PMID:25737270

Ibáñez, Susana; Mihály, Béla; Sanz Miguel, Pablo J; Steinborn, Dirk; Pretzer, Irene; Hiller, Wolf; Lippert, Bernhard

2015-04-01

297

Hot ammonia around young O-type stars. II. JVLA imaging of highly excited metastable NH3 masers in W51-North  

NASA Astrophysics Data System (ADS)

Context. This paper is the second in a series of ammonia (NH3) multilevel imaging studies in high-mass star forming regions. Aims: We want to identify the location of the maser emission from highly excited levels of ammonia within the W51 IRS2 high-mass star forming complex that was previously discovered in a single dish monitoring program. Methods: We have used the Karl Jansky Very Large Array (JVLA) at the 1 cm band to map five highly excited metastable inversion transitions of NH3, (J,K) = (6,6), (7, 7), (9, 9), (10, 10), and (13, 13), in W51 IRS2 with ~0.?2 angular resolution. Results: We present detections of both thermal (extended) ammonia emission in the five inversion lines, with rotational states ranging in energy from about 400 K to 1700 K, and point-like ammonia maser emission in the (6, 6), (7, 7), and (9, 9) lines. For the point-like emission, we estimate lower limits to the peak brightness temperatures of 1.7 × 105 K, 6 × 103 K, and 1 × 104 K for the (6, 6), (7, 7), and (9, 9) transitions, respectively, confirming their maser nature. The thermal ammonia emits around a local standard of rest velocity of VLSR = 60 km s-1, near the cloud's systemic velocity, appears elongated in the east-west direction across 4'' and is confined by the HII regions W51d (to the north), W51d1 (to the east), and W51d2 (to the west). The NH3 masers are observed in the eastern tip of the dense clump traced by thermal NH3, offset by 0.?65 to the east from its emission peak, and have a peak velocity at ~47.5 km s-1. No maser components are detected near the systemic velocity. The NH3 masers arise close to but separated from (0.?65 or 3500 AU) the rare vibrationally excited SiO masers, which are excited in a powerful bipolar outflow driven by the deeply embedded high-mass young stellar object (YSO) W51-North. This means that the two maser species cannot be excited by the same object. Interestingly, the NH3 masers originate at the same sky position as a peak in a submm line of SO2 imaged with the Submillimeter Array, tracing a face-on circumstellar disk or ring around W51-North. In addition, the thermal emission from the most highly excited NH3 lines, (10, 10) and (13, 13), shows two main condensations, the dominant one towards W51-North with the SiO and H2O masers, and a weaker peak at the NH3 maser position. Conclusions: We propose a scenario where the ring seen in SO2 emission is a circumbinary disk surrounding (at least) two high-mass YSOs, W51-North (exciting the SiO masers) and a nearby companion (exciting the NH3 masers), separated by 3500 AU. This finding indicates a physical connection (in a binary) between the two rare SiO and NH3 maser species.

Goddi, C.; Henkel, C.; Zhang, Q.; Zapata, L.; Wilson, T. L.

2015-01-01

298

High-performance temperature-programmed microfabricated gas chromatography columns  

Microsoft Academic Search

This paper reports the first development of high-performance, silicon-glass micro-gas chromatography (?GC) columns having integrated heaters and temperature sensors for temperature programming, and integrated pressure sensors for flow control. These 3-m long, 150-?m wide and 250-?m deep columns, integrated on a 3.3 cm square die, were fabricated using a silicon-on-glass dissolved wafer process. Demonstrating the contributions to heat dissipation from

Masoud Agah; Joseph A. Potkay; Gordon Lambertus; Richard Sacks; Kensall D. Wise

2005-01-01

299

CH 4/NH 3/H 2O spark tholin: Chemical analysis and interaction with Jovian aqueous clouds  

NASA Astrophysics Data System (ADS)

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.

McDonald, Gene D.; Khare, Bishun N.; Reid Thompson, W.; Sagan, Carl

1991-12-01

300

Hydrogen-release mechanisms in LiNH2BH3·NH3BH3: A theoretical study  

NASA Astrophysics Data System (ADS)

The molecular mechanism of the dehydrogenation of LiNH2BH3·NH3BH3 to form [LiN2B2H] by the loss of five molar equiv of H2 at two consecutive temperatures of 373 K and 501 K has been investigated using computational quantum chemistry methods (B3LYP, MP2 and CCSD(T) methods). The intermediate LiNHBH2·NH2BH2 can be obtained through the pathway A at 373 K, in which LiH structures are formed by the transfer of hydridic H- from NH2BH3- to Li+ followed by the redox reactions of H?+ and H?- to form two molar equiv of H2. The intermediate LiNH2BHdbnd NHBH3 can also be generated via the pathway B at 373 K, in which a new Nsbnd B bond forms and two equiv of H2 are released by the redox reactions. At 501 K, the predominant final product P1 (LiNBNBH) is given most likely through the formation of LiH and a series of redox reactions with the loss of three molar equiv of H2 in the pathway A. Meanwhile, the products P2 (LiNBBNH) and P3 [Li(sbnd NBBNsbnd)H] may be also obtained by the dehydrogenation via a sequence of redox reactions of H?+ and H?- to release three equiv of H2 at the temperature of 501 K. The present study would be helpful for experimental chemists to design better hydrogen-storage media.

Tao, Jingcong; Lv, Naixia; Wen, Li; Qi, Yong; Lv, Xiaobo

2015-02-01

301

COMPOUND IDENTIFICATION IN ORGANIC AEROSOLS USING TEMPERATURE-PROGRAMMED THERMAL DESORPTION PARTICLE BEAM MASS SPECTROMETRY. (R826235)  

EPA Science Inventory

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

302

Study of the Thermal Decomposition of Some Components of Biomass by Desorption Mass Spectrometry  

NASA Astrophysics Data System (ADS)

The investigation of thermal transformations of lignin samples have been carried out using temperature programmed desorption mass spectrometry method (TPD-MS). Main stages and products of lignin pyrolysis have been identified. The first stages (Tmax = 230 °C and Tmax = 300 °C) are attributed to thermal transformations of lignin peripheral polysaccharide fragments such as hemicellulose and cellulose respectively. The second stage (Tmax = 335 °C) is associated with desorption of lignin structural elements in the molecular forms as a result of depolymerization processes of polymeric blocks of lignin. The third stage (Tmax = 370 °C) correspond to a deeper decomposition of lignin and characterized by desorption of smaller structural fragments in molecular forms (m/z = 110, pyrocatechol). Pressure-temperature curves of pyrolysis of lignin samples have been analyzed.

Palianytsia, Borys; Kulik, Tetiana; Dudik, Olesia; Cherniavska, Tetiana; Tonkha, Oksana

303

An Investigation of Ammonia Extraction from Liquid Manure Using a Gas-Permeable Membrane Pollution of air, soil and water caused by excessive ammonia (NH3) emission and deposition from animal  

E-print Network

Pollution of air, soil and water caused by excessive ammonia (NH3) emission and deposition from animal polytetrafluoroethylene (ePTFE) membrane, may provide a solution for controlling NH3 emission to the environment by circulating an acid solution through a tubular GPM submerged into the liquid dairy manure. During

Mukhtar, Saqib

304

Novel bimetallic dispersed catalysts for temperature-programmed coal liquefaction  

SciTech Connect

Development of new catalysts is a promising approach to more efficient coal liquefaction. It has been recognized that 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 the development of novel bimetallic dispersed catalysts for temperature-programmed liquefaction. The ultimate goal of the present research is to develop novel catalytic hydroliquefaction process using highly active dispersed catalysts. The primary objective of this research is to develop novel bimetallic dispersed catalysts from organometallic molecular that can be used in low precursors concentrations (< 1 %) but exhibit high activity for efficient hydroliquefaction of coals under temperature-programmed conditions. The major technical approaches are, first, to prepare the desired heteronuclear organometallic molecules as catalyst precursors that contain covalently bound, two different metal atoms and sulfur in a single molecule. Such precursors will generate finely dispersed bimetallic catalysts such as Fe-Mo, Co-Mo and Ni-Mo binary sulfides upon thermal decomposition. The second major technical approach is to perform the liquefaction of coals unpregnated with the organometallic precursors under temperature-programmed conditions, where the programmed heat-up serves as a step for both catalyst activation and coal pretreatment or preconversion. Two to three different complexes for each of the Fe-Mo, Co-Mo, and Ni-Mo combinations will be prepared. Initial catalyst screening tests will be conducted using a subbituminous coal and a bituminous coal. Effects of coal rank and solvents will be examined with the selected bimetallic catalysts which showed much higher activity than the dispersed catalysts from conventional precursors.

Song, Chunshan; Schobert, H.H.

1993-02-01

305

Sestak–Berggren function in temperature-programmed reduction  

Microsoft Academic Search

From the peculiarities of Temperature-programmed reduction (TPR) method and using the Sestak–Berggren conversion function,\\u000a we describe first the TPR curve simulation procedure. The influence of the Sestak–Berggren exponents on the TPR peak maximum\\u000a and shape is demonstrated, by analyzing several synthetic TPR profiles. Finally, the kinetic parameters of Au\\/CeO2 promoted with yttrium as well as those of Au\\/CeO2–Al2O3 promoted with

G. Munteanu; E. Segal

2010-01-01

306

Morphology-photovoltaic property correlation in perovskite solar cells: One-step versus two-step deposition of CH3NH3PbI3  

NASA Astrophysics Data System (ADS)

Perovskite CH3NH3PbI3 light absorber is deposited on the mesoporous TiO2 layer via one-step and two-step coating methods and their photovoltaic performances are compared. One-step coating using a solution containing CH3NH3I and PbI2 shows average power conversion efficiency (PCE) of 7.5%, while higher average PCE of 13.9% is obtained from two-step coating method, mainly due to higher voltage and fill factor. The coverage, pore-filling, and morphology of the deposited perovskite are found to be critical in photovoltaic performance of the mesoporous TiO2 based perovskite solar cells.

Im, Jeong-Hyeok; Kim, Hui-Seon; Park, Nam-Gyu

2014-08-01

307

Enhanced phosphorescence from nanocrystalline/microcrystalline materials based on (CH3NH3)(1-naphthylmethyl ammonium)2Pb2Cl7 and similar compounds  

NASA Astrophysics Data System (ADS)

A broad phosphorescence band, with three main maxima at ca 500, 536 and 577 nm, was observed at room temperature, either from a mixture of (1-naphthylmethyl ammonium)2PbCl4 and CH3NH3PbCl3, or from (CH3NH3)(1-naphthylmethyl ammonium)2Pb2Cl7, or some Cl-Br analogues, in the form of suspensions in toluene or in the form of grinding deposits on quartz plates. It was attributed to supermigration of energy from the Wannier excitons of PbCl3 component to the triplet state of organic component (i.e., 1-naphthylmethyl group) of particulate material. This new effect seems to be a consequence of excitonic superradiance of particulate PbCl3.

Papavassiliou, George C.; Pagona, Georgia; Mousdis, George A.; Karousis, Nikolaos

2013-05-01

308

The recombination mechanisms leading to amplified spontaneous emission at the true-green wavelength in CH3NH3PbBr3 perovskites  

NASA Astrophysics Data System (ADS)

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.

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

309

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)

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.

Zhang, Shule; Zhong, Qin; Wang, Yining

2014-09-01

310

Direct Observation of Long Electron-Hole Diffusion Distance beyond 1 Micrometer in CH3NH3PbI3 Perovskite Thin Film  

E-print Network

In high performance perovskite based on CH3NH3PbI3, the formerly reported short charge diffusion distance is a confliction to thick working layer in solar cell devices. We carried out a study on charge diffusion in spin-coated CH3NH3PbI3 perovskite thin film by transient fluorescent spectroscopy. A thickness-dependent fluorescent lifetime was found. This effect correlates to the defects at crystal grain boundaries. By coating the film with electron or hole transfer layer, PCBM or Spiro-OMeTAD respectively, we observed the charge transfer directly through the fluorescent decay. One-dimensional diffusion model was applied to obtain long charge diffusion distances, which is ~1.3 micron for electrons and ~5.2 micron for holes. This study gives direct support to the high performance of perovskite solar cells.

Li, Yu; Li, Yunlong; Wang, Wei; Bian, Zuqiang; Xiao, Lixin; Wang, Shufeng; Gong, Qihuang

2015-01-01

311

Desorption of a two-state system: Laser probing of gallium atom spin-orbit states from silicon (100)  

NASA Astrophysics Data System (ADS)

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).

Carleton, Karen L.; Bourguignon, Bernard; Leone, Stephen R.

312

Characterization and performance of V 2 O 5 \\/CeO 2 for NH 3 SCR of NO at low temperatures  

Microsoft Academic Search

A series of CeO2 supported V2O5 catalysts with various loadings were prepared with different calcination temperatures by the incipient impregnation. The\\u000a catalysts were evaluated for low temperature selective catalytic reduction (SCR) of NO with ammonia (NH3). The effects of O2 and SO2 on catalytic activity were also studied. The catalysts were characterized by specific surface areas (SBET) and X-ray diffraction

Caiting Li; Qun Li; Pei Lu; Huafei Cui; Guangming Zeng

313

First detection of NH3 (10 -> 00) from a low mass cloud core. On the low ammonia abundance of the rho Oph A core  

Microsoft Academic Search

Odin has successfully observed the molecular core rho Oph A in the 572.5 GHz rotational ground state line of ammonia, NH3 (JK = 10 -> 00). The interpretation of this result makes use of complementary molecular line data obtained from the ground (C17O and CH3OH) as part of the Odin preparatory work. Comparison of these observations with theoretical model calculations

R. Liseau; B. Larsson; A. Brandeker; P. Bergman; P. Bernath; J. H. Black; R. Booth; V. Buat; C. Curry; P. Encrenaz; E. Falgarone; P. Feldman; M. Fich; H. Florén; U. Frisk; M. Gerin; E. Gregersen; J. Harju; T. Hasegawa; Å. Hjalmarson; L. Johansson; S. Kwok; A. Lecacheux; T. Liljeström; K. Mattila; G. Mitchell; L. Nordh; M. Olberg; G. Olofsson; L. Pagani; R. Plume; I. Ristorcelli; Aa. Sandqvist; F. v. Schéele; G. Serra; N. Tothill; K. Volk; C. Wilson

2003-01-01

314

Liquid phase deposition of TiO2 nanolayer affords CH3NH3PbI3/nanocarbon solar cells with high open-circuit voltage.  

PubMed

Hybrid organic/inorganic perovskite solar cells are attracting intense attention and further developments largely hinge on understanding the fundamental issues involved in the cell operation. In this paper, a liquid phase deposition (LPD) method is developed to design and grow a TiO2 nanolayer at room temperature for carbon-based perovskite solar cells. The TiO2 nanolayer grown on FTO glass is compact but polycrystalline consisting of tiny anatase TiO2 nanocrystals intimately stacked together. By directly exploiting this TiO2 nanolayer in a solar cell of TiO2 nanolayer/CH3NH3PbI3/nanocarbon, we have achieved a Voc as high as 1.07 V, the highest value reported so far for hole transporter-free CH3NH3PbI3 solar cells. This is rationalized by the slower electron injection and longer electron lifetime due to the TiO2 nanolayer, which enhances the electron accumulation in CH3NH3PbI3 and consequently the Voc. By employing a rutile TiO2 nanorod (NR) array as a base structure for the LPD-TiO2 nanolayer to support the CH3NH3PbI3 layer, the photocurrent density is considerably increased without obviously compromising the Voc (1.01 V). As a result, the power conversion efficiency is boosted from 3.67% to 8.61%. More elaborate engineering of the TiO2 nanolayer by LPD in conjunction with judicious interfacing with other components has the potential to achieve higher performances for this type of solar cell. PMID:25406400

Chen, Haining; Wei, Zhanhua; Yan, Keyou; Yi, Ya; Wang, Jiannong; Yang, Shihe

2015-01-01

315

Layer-by-Layer Growth of CH3 NH3 PbI3-x Clx for Highly Efficient Planar Heterojunction Perovskite Solar Cells.  

PubMed

A layer-by-layer approach is developed to prepare uniform and compact CH3 NH3 PbI3-x Clx perovskite films for perovskite solar cells with a high efficiency up to 15.12% and an improved stability. Moreover, a record high efficiency of 12.25% is achieved for these flexible perovskite solar cells. This study represents an important step forward in developing high-performance and stable perovskite solar cells. PMID:25534887

Chen, Yonghua; Chen, Tao; Dai, Liming

2015-02-01

316

Full Printable Processed Mesoscopic CH3NH3PbI3/TiO2 Heterojunction Solar Cells with Carbon Counter Electrode  

PubMed Central

A mesoscopic methylammonium lead iodide (CH3NH3PbI3) perovskite/TiO2 heterojunction solar cell is developed with low-cost carbon counter electrode (CE) and full printable process. With carbon black/spheroidal graphite CE, this mesoscopic heterojunction solar cell presents high stability and power conversion efficiency of 6.64%, which is higher than that of the flaky graphite based device and comparable to the conventional Au version. PMID:24185501

Ku, Zhiliang; Rong, Yaoguang; Xu, Mi; Liu, Tongfa; Han, Hongwei

2013-01-01

317

Competitive solvation of NH 3 and H 2O by a phenol ion studied by liquid beam — multiphoton ionization — mass spectrometry  

Microsoft Academic Search

Phenol in an aqueous ammonia solution was introduced into a vacuum as a continuous liquid flow (liquid beam) and was irradiated with a laser beam of 272 nm. Ions produced by two-photon ionization in the liquid beam and ejected from it were analyzed by a time-of-flight mass spectrometer. The mass spectrum assignable to C6H5OH+ (H2O)n (NH3)m, H3O+ and NH4+ shows

Fumitaka Mafuné; Yuichiro Hashimoto; Tamotsu Kondow

1997-01-01

318

Application of commercial automotive sensor manufacturing methods for NO x \\/NH 3 mixed potential sensors for on-board emissions control  

Microsoft Academic Search

The article details the application of commercial manufacturing methods towards the development of NOx\\/NH3 sensors for vehicle on-board emissions control. These sensors possess a unique mixed potential sensor design. This unique LANL (Los Alamos National Laboratory) design results in improved sensitivity, selectivity and response time over conventional mixed potential sensors incorporating a stable three-phase interface using a porous electrolyte coated

Praveen K. Sekhar; Eric. L. Brosha; Rangachary Mukundan; Wenxia Li; Mark A. Nelson; Ponnusamy Palanisamy; Fernando H. Garzon

2010-01-01

319

Site preference of NH3-adsorption on Co, Pt and CoPt surfaces: the role of charge transfer, magnetism and strain.  

PubMed

Oxidation of Co at the surface poses a major problem in the cyclable use of CoPt, a cost-effective catalyst for proton exchange membrane fuel cells. This can be alleviated by attaching a ligand selectively to Co-sites to stop its oxidation without compromising the catalytic activity. Here, we present a comparative analysis of adsorption of NH3 on the (0001) surface of Co in the HCP structure and (111) surfaces of Pt and CoPt alloy in the FCC structure, using first-principles density functional theoretical calculations. While NH3 binds more strongly with the Pt surface than with the Co surface, we find that its binding with the Co atom is stronger than that with the Pt atom on the surface of the CoPt alloy. Our analysis of the charge density and electronic structure shows how this originates from (a) the electron transfer from the minority spin d-band of Co to Pt, and (b) shift in the energy of d-bands and the magnetic moments of Co atoms on the surface of the CoPt alloy relative to those on the (0001) surface of Co. Hybridization of the d-states of Co in CoPt with pz states of N in NH3 used to stop Co oxidation also results in improving the charge transfer from Co to Pt that is relevant to the catalytic activity of CoPt. We finally present the analysis of how the interaction of NH3 with the CoPt surface can be tuned with strain. PMID:25760894

Bhattacharjee, S; Gupta, K; Jung, N; Yoo, S J; Waghmare, U V; Lee, S C

2015-04-14

320

Nuclear Overhauser effect studies of the conformation of Co(NH3)4ATP bound to kidney Na,K-ATPase  

SciTech Connect

Transferred nuclear Overhauser effect measurements (in the two-dimensional mode) have been used to determine the three-dimensional conformation of an ATP analogue, Co(NH3)4ATP, at the active site of sheep kidney Na,K-ATPase. Previous studies have shown that Co(NH3)4ATP is a competitive inhibitor with respect to MnATP for the Na,K-ATPase. Nine unique proton-proton distances on ATPase-bound Co(NH3)4ATP were determined from the initial build-up rates of the cross-peaks of the 2D-TRNOE data sets. These distances, taken together with previous 31P and 1H relaxation measurements with paramagnetic probes, are consistent with a single nucleotide conformation at the active site. The bound (Co(NH3)4ATP) adopts an anti conformation, with a glycosidic torsion angle of 35{degrees}, and the conformation of the ribose ring is slightly N-type (C2'-exo, C3'-endo). The delta and gamma torsional angles in this conformation are 100 degrees and 178 degrees, respectively. The nucleotide adopts a bent configuration, in which the triphosphate chain lies nearly parallel to the adenine moiety. Mn2+ bound to a single, high-affinity site on the ATPase lies above and in the plane of the adenine ring. The distances from enzyme-bound Mn2+ to N6 and N7 are too large for first coordination sphere complexes, but are appropriate for second-sphere complexes involving, for example, intervening hydrogen-bonded water molecules. The NMR data also indicate that the structure of the bound ATP analogue is independent of the conformational state of the enzyme.

Stewart, J.M.; Jorgensen, P.L.; Grisham, C.M. (Univ. of Virginia, Charlottesville (USA))

1989-05-30

321

Evaporation heat transfer coefficient in single circular small tubes for flow natural refrigerants of C 3H 8, NH 3, and CO 2  

Microsoft Academic Search

An experimental study of evaporation heat transfer coefficients for single circular small tubes was conducted for the flow of C3H8, NH3, and CO2 under various flow conditions. The test matrix encompasses the entire quality range from 0.0 to 1.0, mass fluxes from 50 to 600kgm?2s?1, heat fluxes from 5 to 70kWm?2, and saturation temperatures from 0 to 10°C. The test

A. S. Pamitran; Kwang-Il Choi; Jong-Taek Oh; Nasruddin

2011-01-01

322

Delaminated Fe 2O 3Pillared Clay: Its Preparation, Characterization, and Activities for Selective Catalytic Reduction of No by NH 3  

Microsoft Academic Search

A delaminated Fe2O3-pillared clay catalyst was prepared for the selective catalytic reduction (SCR) of NO by NH3 at above 300°C. The delaminated pillared clay was characterized by inductively coupled plasma-atomic emission spectroscopy chemical analysis, X-ray diffraction structure and line broadening analyses, micropore size probing, and Mössbauer analysis. These analyses showed that the catalyst contained fragmented Fe2O3-pillared clay forming \\

J. P. Chen; M. C. Hausladen; R. T. Yang

1995-01-01

323

Transient-state biodegradation behavior of a horizontal biotrickling filter in co-treating gaseous H2S and NH3.  

PubMed

A horizontal biotrickling filter (HBTF) was used to inoculate autotrophic sulfide-oxidizing and ammonia-oxidizing microbial consortiums over H2S-exhausted carbon for co-treating H2S and NH3 waste gas in a long-term operation. In this study, several aspects (i.e., pH change, shock loading and starvation) of the dynamic behavior of the HBTF were investigated. The metabolic products of N and S bearing species in recycling liquid and biological activities of the biofilm were analyzed to explain the observed phenomena and further explore the fundamentals behind. In the pH range of 4-8.5, although the removal efficiencies of H2S and NH3 remained 96-98% and 100%, respectively, the metabolic products demonstrated different removal mechanisms and pathways. NH4-N and NO2/NO3-N were dominated at pH < or = 6 and > or = 7, respectively, indicating the differentiated contributions from physical/chemical adsorption and bio-oxidation. Moreover, the HBTF demonstrated a good dynamic stability to withstand shock loadings by recovering immediately to the original. During shock loading, only 15.4% and 17.9% of captured H2S and NH3 was biodegraded, respectively. After 2, 11, and 48 days of starvation, the HBTF system reached a full performance within reasonable re-startup times (2-80 h), possibly due to the consumption of reduced S and N species in biomass or activated carbon thus converted into SO4-S and NO3-N during starvation period. The results helped to understand the fundamental knowledge by revealing the effects of pH and transient loadings linked with individual removal mechanism for H2S and NH3 co-treatment in different conditions. PMID:18998123

Jiang, Xia; Yan, Rong; Tay, Joo Hwa

2009-01-01

324

Modelling of manure production by pigs and NH3, N2O and CH4 emissions. Part II: effect of animal housing, manure storage and treatment practices.  

PubMed

A model has been developed to predict pig manure evolution (mass, dry and organic matter, N, P, K, Cu and Zn contents) and related gaseous emissions (methane (CH4), nitrous oxide (N2O) and ammonia (NH3)) from pig excreta up to manure stored before spreading. This model forms part of a more comprehensive model including the prediction of pig excretion. The model simulates contrasted management systems, including different options for housing (slatted floor or deep litter), outside storage of manure and treatment (anaerobic digestion, biological N removal processes, slurry composting (SC) with straw and solid manure composting). Farmer practices and climatic conditions, which have significant effects on gaseous emissions within each option, have also been identified. The quantification of their effects was based on expert judgement from literature and local experiments, relations from mechanistic models or simple emission factors, depending on existing knowledge. The model helps to identify relative advantages and weaknesses for each system. For example, deep-litter with standard management practices is associated with high-greenhouse gas (GHG) production (+125% compared to slatted floor) and SC on straw is associated with high NH3 emission (+15% compared to slatted floor). Another important result from model building and first simulations is that farmer practices and the climate induce an intra-system (for a given infrastructure) variability of NH3 and GHG emissions nearly as high as inter-system variability. For example, in deep-litter housing systems, NH3 and N2O emissions from animal housing may vary between 6% and 53%, and between 1% and 19% of total N excreted, respectively. Thus, the model could be useful to identify and quantify improvement margins on farms, more precisely or more easily than current methodologies. PMID:22444661

Rigolot, C; Espagnol, S; Robin, P; Hassouna, M; Béline, F; Paillat, J M; Dourmad, J-Y

2010-08-01

325

Ammonia emissions in the United States, European Union, and China derived by high-resolution inversion of ammonium wet deposition data: Interpretation with a new agricultural emissions inventory (MASAGE_NH3)  

NASA Astrophysics Data System (ADS)

We use the adjoint of a global 3-D chemical transport model (GEOS-Chem) to optimize ammonia (NH3) emissions in the U.S., European Union, and China by inversion of 2005-2008 network data for NH4+ wet deposition fluxes. Optimized emissions are derived on a 2° × 2.5° grid for individual months and years. Error characterization in the optimization includes model errors in precipitation. Annual optimized emissions are 2.8 Tg NH3-N a-1 for the contiguous U.S., 3.1 Tg NH3-N a-1 for the European Union, and 8.4 Tg NH3-N a-1 for China. Comparisons to previous inventories for the U.S. and European Union show consistency (˜±15%) in annual totals but some large spatial and seasonal differences. We develop a new global bottom-up inventory of NH3 emissions (Magnitude And Seasonality of Agricultural Emissions model for NH3 (MASAGE_NH3)) to interpret the results of the adjoint optimization. MASAGE_NH3 provides information on the magnitude and seasonality of NH3 emissions from individual crop and livestock sources on a 0.5° × 0.5° grid. We find that U.S. emissions peak in the spring in the Midwest due to corn fertilization and in the summer elsewhere due to manure. The seasonality of European emissions is more homogeneous with a well-defined maximum in spring associated with manure and mineral fertilizer application. There is some evidence for the effect of European regulations of NH3 emissions, notably a large fall decrease in northern Europe. Emissions in China peak in summer because of the summertime application of fertilizer for double cropping.

Paulot, F.; Jacob, D. J.; Pinder, R. W.; Bash, J. O.; Travis, K.; Henze, D. K.

2014-04-01

326

Electron-hole diffusion lengths > 175 ?m in solution-grown CH3NH3PbI3 single crystals  

NASA Astrophysics Data System (ADS)

Long, balanced electron and hole diffusion lengths greater than 100 nanometers in the polycrystalline organolead trihalide compound CH3NH3PbI3 are critical for highly efficient perovskite solar cells. We found that the diffusion lengths in CH3NH3PbI3 single crystals grown by a solution-growth method can exceed 175 micrometers under 1 sun (100 mW cm?2) illumination and exceed 3 millimeters under weak light for both electrons and holes. The internal quantum efficiencies approach 100% in 3-millimeter-thick single-crystal perovskite solar cells under weak light. These long diffusion lengths result from greater carrier mobility, longer lifetime, and much smaller trap densities in the single crystals than in polycrystalline thin films. The long carrier diffusion lengths enabled the use of CH3NH3PbI3 in radiation sensing and energy harvesting through the gammavoltaic effect, with an efficiency of 3.9% measured with an intense cesium-137 source.

Dong, Qingfeng; Fang, Yanjun; Shao, Yuchuan; Mulligan, Padhraic; Qiu, Jie; Cao, Lei; Huang, Jinsong

2015-02-01

327

Efficient perovskite solar cells based on low-temperature solution-processed (CH3NH3)PbI3 perovskite/CuInS2 planar heterojunctions  

PubMed Central

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

2014-01-01

328

Solar cells. Electron-hole diffusion lengths > 175 ?m in solution-grown CH3NH3PbI3 single crystals.  

PubMed

Long, balanced electron and hole diffusion lengths greater than 100 nanometers in the polycrystalline organolead trihalide compound CH3NH3PbI3 are critical for highly efficient perovskite solar cells. We found that the diffusion lengths in CH3NH3PbI3 single crystals grown by a solution-growth method can exceed 175 micrometers under 1 sun (100 mW cm(-2)) illumination and exceed 3 millimeters under weak light for both electrons and holes. The internal quantum efficiencies approach 100% in 3-millimeter-thick single-crystal perovskite solar cells under weak light. These long diffusion lengths result from greater carrier mobility, longer lifetime, and much smaller trap densities in the single crystals than in polycrystalline thin films. The long carrier diffusion lengths enabled the use of CH3NH3PbI3 in radiation sensing and energy harvesting through the gammavoltaic effect, with an efficiency of 3.9% measured with an intense cesium-137 source. PMID:25636799

Dong, Qingfeng; Fang, Yanjun; Shao, Yuchuan; Mulligan, Padhraic; Qiu, Jie; Cao, Lei; Huang, Jinsong

2015-02-27

329

Behaviors of Absolute Densities of N, H, and NH3 at Remote Region of High-Density Radical Source Employing N2-H2 Mixture Plasmas  

NASA Astrophysics Data System (ADS)

For an innovation of molecular-beam-epitaxial (MBE) growth of gallium nitride (GaN), the measurements of absolute densities of N, H, and NH3 at the remote region of the radical source excited by plasmas have become absolutely imperative. By vacuum ultraviolet absorption spectroscopy (VUVAS) at a relatively low pressure of about 1 Pa, we obtained a N atom density of 9×1012 cm-3 for a pure nitrogen gas used, a H atom density of 7×1012 cm-3 for a gas composition of 80% hydrogen mixed with nitrogen gas were measured. The maximum density 2×1013 cm-3 of NH3 was measured by quadruple mass spectrometry (QMS) at H2/(N2+H2)=60%. Moreover, we found that N atom density was considerably affected by processing history, where the characteristic instability was observed during the pure nitrogen plasma discharge sequentially after the hydrogen-containing plasma discharge. These results indicate imply the importance of establishing radical-based processes to control precisely the absolute densities of N, H, and NH3 at the remote region of the radical source.

Chen, Shang; Kondo, Hiroki; Ishikawa, Kenji; Takeda, Keigo; Sekine, Makoto; Kano, Hiroyuki; Den, Shoji; Hori, Masaru

2011-01-01

330

Synthesis, characterization and application of Y3Fe5O12 nanocatalyst for green production of NH3 using magnetic induction method (MIM)  

NASA Astrophysics Data System (ADS)

Y3Fe5O12 (YIG) was prepared through sol-gel technique and sintered at three different temperatures (1000-1200?C). Various characterizations on the morphological and structural properties of produced YIG have been done as to understand the potential of this unique magnetic type nanomaterial to be used in the catalyst application for ammonia synthesis at ambient or green production environment. YIG catalyst exposed under magnetic induction of 0.1 T produced about 242.56?mol/h.g-cat yield of ammonia (NH3) at freezing reaction temperature of 0?C. About 95.88% improvements of NH3 yield is produced in comparison with the absence of magnetic induction reaction condition (10?mol/h.g-cat). Synthesis at 25?C yielded reduction about 0.90% lower than the synthesis at 0?C temperature. Thus, it is proven that the temperature engaged the dominant roles in affecting the catalytic effect of YIG catalyst for NH3 production. Further parametric studies should be conducted as to explore the robustness of YIG catalyst for new route of ammonia production until the commercial scale-up could be achieved.

Razak, Jeefferie Abd; Sufian, Suriati; Ku Shaari, Ku Zilati; Puspitasari, Poppy; Hoe, Tshai Kim; Yahya, Noorhana

2012-09-01

331

Hydride-assisted growth of GaN nanowires on Au/Si(0 0 1) via the reaction of Ga with NH 3 and H 2  

NASA Astrophysics Data System (ADS)

High quality, straight GaN nanowires (NWs) with diameters of 50 nm and lengths up to 3 ?m have been grown on Si(0 0 1) using Au as a catalyst and the direct reaction of Ga with NH 3 and N 2:H 2 at 900 °C. These exhibited intense, near band edge photoluminescence at 3.42 eV in comparison to GaN NWs with non-uniform diameters obtained under a flow of Ar:NH 3, which showed much weaker band edge emission due to strong non-radiative recombination. A significantly higher yield of ?-Ga 2O 3 NWs with diameters of ?50 nm and lengths up to 10 ?m were obtained, however, via the reaction of Ga with residual O 2 under a flow of Ar alone. The growth of GaN NWs depends critically on the temperature, pressure and flows in decreasing order of importance but also the availability of reactive species of Ga and N. A growth mechanism is proposed whereby H 2 dissociates on the Au nanoparticles and reacts with Ga giving Ga xH y thereby promoting one-dimensional (1D) growth via its reaction with dissociated NH 3 near or at the top of the GaN NWs while suppressing at the same time the formation of an underlying amorphous layer. The higher yield and longer ?-Ga 2O 3 NWs grow by the vapor liquid solid mechanism that occurs much more efficiently than nitridation.

Zervos, Matthew; Othonos, Andreas

2010-09-01

332

Highly Spin-Polarized Carrier Dynamics and Ultralarge Photoinduced Magnetization in CH3NH3PbI3 Perovskite Thin Films.  

PubMed

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

Giovanni, David; Ma, Hong; Chua, Julianto; Grätzel, Michael; Ramesh, Ramamoorthy; Mhaisalkar, Subodh; Mathews, Nripan; Sum, Tze Chien

2015-03-11

333

Enhanced Photovoltaic Performance of CH3NH3PbI3 Perovskite Solar Cells through Interfacial Engineering Using Self-Assembling Monolayer.  

PubMed

Morphology control is critical to achieve high efficiency CH3NH3PbI3 perovskite solar cells (PSC). The surface properties of the substrates on which crystalline perovskite thin films form are expected to affect greatly the crystallization and, thus, the resulting morphology. However, this topic is seldom examined in PSC. Here we developed a facile but efficient method of modifying the ZnO-coated substrates with 3-aminopropanioc acid (C3-SAM) to direct the crystalline evolution and achieve the optimal morphology of CH3NH3PbI3 perovskite film. With incorporation of the C3-SAM, highly crystalline CH3NH3PbI3 films were formed with reduced pin-holes and trap states density. In addition, the work function of the cathode was better aligned with the conduction band minimum of perovskite for efficient charge extraction and electronic coupling. As a result, the PSC performance remarkably increased from 9.81(±0.99)% (best 11.96%) to 14.25(±0.61)% (best 15.67%). We stress the importance of morphology control through substrate surface modification to obtain the optimal morphology and device performance of PSC, which should generate an impact on developing highly efficient PSC and future commercialization. PMID:25650811

Zuo, Lijian; Gu, Zhuowei; Ye, Tao; Fu, Weifei; Wu, Gang; Li, Hanying; Chen, Hongzheng

2015-02-25

334

Glycolaldehyde, methyl formate and acetic acid adsorption and thermal desorption from interstellar ices  

NASA Astrophysics Data System (ADS)

We have undertaken a detailed investigation of the adsorption, desorption and thermal processing of the astrobiologically significant isomers glycolaldehyde, acetic acid and methyl formate. Here, we present the results of laboratory infrared and temperature programmed desorption (TPD) studies of the three isomers from model interstellar ices adsorbed on a carbonaceous dust grain analogue surface. Laboratory infrared data show that the isomers can be clearly distinguished on the basis of their infrared spectra, which has implications for observations of interstellar ice spectra. Laboratory TPD data also show that the three isomers can be distinguished on the basis of their thermal desorption behaviour. In particular, TPD data show that the isomers cannot be treated the same way in astrophysical models of desorption. The desorption of glycolaldehyde and acetic acid from water-dominated ices is very similar, with desorption being mainly dictated by water ice. However, methyl formate also desorbs from the surface of the ice, as a pure desorption feature, and therefore desorbs at a lower temperature than the other two isomers. This is more clearly indicated by models of the desorption on astrophysical time-scales corresponding to the heating rate of 25 and 5 M? stars. For a 25 M? star, our model shows that a proportion of the methyl formate can be found in the gas phase at earlier times compared to glycolaldehyde and acetic acid. This has implications for the observation and detection of these molecules, and potentially explains why methyl formate has been observed in a wider range of astrophysical environments than the other two isomers.

Burke, Daren J.; Puletti, Fabrizio; Brown, Wendy A.; Woods, Paul M.; Viti, Serena; Slater, Ben

2015-02-01

335

Thermal desorption for passive dosimeter  

E-print Network

for Occupa- tional Safety and Health (NIQSH). ~ This method involves adsorption of the conteminants in a collection tube con- taining two separate portions of activated charcoal and subsequent desorption with carbon disulfide, followed by gas... popular for area and personal monitoring. However, as with the sorbent tube, a desorbing agent must be used to desorb the sorbate for analysis in its original form. Carbon disulfide, which is most frequently recommended by NIOSH for solvent desorption...

Liu, Wen-Chen

1981-01-01

336

Dry deposition of nitrogen compounds (NO2, HNO3, NH3), sulfur dioxide and ozone in West and Central African ecosystems using the inferential method  

NASA Astrophysics Data System (ADS)

This work is part of the IDAF program (IGAC-DEBITS-AFRICA) and is based on the long term monitoring of gas concentrations (1998-2007) established on seven remote sites representative of major African ecosystems. Dry deposition fluxes were estimated by the inferential method using on one hand surface measurements of gas concentrations (NO2, HNO3, NH3, SO2, and O3) and on the other hand simulated dry deposition velocities (Vd). Vd were calculated using the big-leaf model of Zhang et al. (2003b). In the model of deposition, surface and meteorological conditions specific to IDAF sites have been adapted in order to simulate Vd representative of major African ecosystems. The monthly, seasonal and annual mean variations of gaseous dry deposition fluxes (NO2, HNO3, NH3, O3, and SO2) are analyzed. Along the latitudinal transect of ecosystems, the annual mean dry deposition fluxes of nitrogen compounds range from 0.4 ± 0.0 to 0.8 ± 0.2 kg N ha-1 yr-1 for NO2, from 0.7 ± 0.1 to 1.0 ± 0.3 kg N ha-1 yr-1 for HNO3, and from 2.3 ± 0.8 to 10.5 ± 5.0 kg N ha-1 yr-1 for NH3 over the study period (1998-2007). The total nitrogen dry deposition flux (NO2+HNO3+NH3) is more important in forests (11.2-11.8 kg N ha-1 yr-1) than in wet and dry savannas (3.4-5.3 kg N ha-1 yr-1). NH3 dominated nitrogen dry deposition, representing 67-80% of the total. The annual mean dry deposition fluxes of ozone range between 11.3 ± 4.7 and 17.5 ± 3.0 kg ha-1 yr-1 in dry savannas, 17.5 ± 3.0 and 19.2 ± 2.9 kg ha-1 yr-1 in wet savannas, and 10.6 ± 2.0 and 13.2 ± 3.6 kg ha-1 yr-1 in forests. Lowest O3 dry deposition fluxes in forests are correlated to low measured O3 concentrations, lower of a factor of 2-3, compared to others ecosystems. Along the ecosystem transect, annual mean of SO2 dry deposition fluxes present low values and a small variability (0.5 to 1 kg S ha-1 yr-1). No specific trend in the interannual variability of these gaseous dry deposition fluxes is observed over the study period.

Adon, M.; Galy-Lacaux, C.; Yoboue, V.; Delon, C.; Solmon, F.; Kaptue Tchuente, A. T.

2013-05-01

337

Dry deposition of nitrogen compounds (NO2, HNO3, NH3), sulfur dioxide and ozone in west and central African ecosystems using the inferential method  

NASA Astrophysics Data System (ADS)

This work is part of the IDAF program (IGAC-DEBITS-AFRICA) and is based on the long-term monitoring of gas concentrations (1998-2007) established at seven remote sites representative of major African ecosystems. Dry deposition fluxes were estimated by the inferential method using on the one hand surface measurements of gas concentrations (NO2, HNO3, NH3, SO2 and O3) and on the other hand modeled exchange rates. Dry deposition velocities (Vd) were calculated using the big-leaf model of Zhang et al. (2003b). The bidirectional approach is used for NH3 surface-atmosphere exchange (Zhang et al., 2010). Surface and meteorological conditions specific to IDAF sites have been used in the models of deposition. The seasonal and annual mean variations of gaseous dry deposition fluxes (NO2, HNO3, NH3, O3 and SO2) are analyzed. Along the latitudinal transect of ecosystems, the annual mean dry deposition fluxes of nitrogen compounds range from -0.4 to -0.8 kg N ha-1 yr-1 for NO2, from -0.7 to -1.0 kg N ha-1 yr-1 for HNO3 and from -0.7 to -8.3 kg N ha-1 yr-1 for NH3 over the study period (1998-2007). The total nitrogen dry deposition flux (NO2+HNO3+NH3) is more important in forests (-10 kg N ha-1 yr-1) than in wet and dry savannas (-1.6 to -3.9 kg N ha-1 yr-1). The annual mean dry deposition fluxes of ozone range between -11 and -19 kg ha-1 yr-1 in dry and wet savannas, and -11 and -13 kg ha-1 yr-1 in forests. Lowest O3 dry deposition fluxes in forests are correlated to low measured O3 concentrations, lower by a factor of 2-3, compared to other ecosystems. Along the ecosystem transect, the annual mean of SO2 dry deposition fluxes presents low values and a small variability (-0.5 to -1 kg S ha-1 yr-1). No specific trend in the interannual variability of these gaseous dry deposition fluxes is observed over the study period.

Adon, M.; Galy-Lacaux, C.; Delon, C.; Yoboue, V.; Solmon, F.; Kaptue Tchuente, A. T.

2013-11-01

338

Facile preparation of ordered mesoporous MnCo2O4 for low-temperature selective catalytic reduction of NO with NH3  

NASA Astrophysics Data System (ADS)

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

Qiu, Mingying; Zhan, Sihui; Yu, Hongbing; Zhu, Dandan; Wang, Shengqiang

2015-01-01

339

Desorption and sublimation kinetics for fluorinated aluminum nitride surfaces  

SciTech Connect

The adsorption and desorption of halogen and other gaseous species from surfaces is a key fundamental process for both wet chemical and dry plasma etch and clean processes utilized in nanoelectronic fabrication processes. Therefore, to increase the fundamental understanding of these processes with regard to aluminum nitride (AlN) surfaces, temperature programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS) have been utilized to investigate the desorption kinetics of water (H{sub 2}O), fluorine (F{sub 2}), hydrogen (H{sub 2}), hydrogen fluoride (HF), and other related species from aluminum nitride thin film surfaces treated with an aqueous solution of buffered hydrogen fluoride (BHF) diluted in methanol (CH{sub 3}OH). Pre-TPD XPS measurements of the CH{sub 3}OH:BHF treated AlN surfaces showed the presence of a variety of Al-F, N-F, Al-O, Al-OH, C-H, and C-O surfaces species in addition to Al-N bonding from the AlN thin film. The primary species observed desorbing from these same surfaces during TPD measurements included H{sub 2}, H{sub 2}O, HF, F{sub 2}, and CH{sub 3}OH with some evidence for nitrogen (N{sub 2}) and ammonia (NH{sub 3}) desorption as well. For H{sub 2}O, two desorption peaks with second order kinetics were observed at 195 and 460?°C with activation energies (E{sub d}) of 51?±?3 and 87?±?5?kJ/mol, respectively. Desorption of HF similarly exhibited second order kinetics with a peak temperature of 475?°C and E{sub d} of 110?±?5?kJ/mol. The TPD spectra for F{sub 2} exhibited two peaks at 485 and 585?°C with second order kinetics and E{sub d} of 62?±?3 and 270?±?10?kJ/mol, respectively. These values are in excellent agreement with previous E{sub d} measurements for desorption of H{sub 2}O from SiO{sub 2} and AlF{sub x} from AlN surfaces, respectively. The F{sub 2} desorption is therefore attributed to fragmentation of AlF{sub x} species in the mass spectrometer ionizer. H{sub 2} desorption exhibited an additional high temperature peak at 910?°C with E{sub d}?=?370?±?10?kJ/mol that is consistent with both the dehydrogenation of surface AlOH species and H{sub 2} assisted sublimation of AlN. Similarly, N{sub 2} exhibited a similar higher temperature desorption peak with E{sub d}?=?535?±?40?kJ/mol that is consistent with the activation energy for direct sublimation of AlN.

King, Sean W., E-mail: sean.king@intel.com; Davis, Robert F. [Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States); Nemanich, Robert J. [Department of Physics, North Carolina State University, Raleigh, North Carolina 27695 (United States)

2014-09-01

340

GaN CVD Reactions: Hydrogen and Ammonia Decomposition and the Desorption of Gallium  

SciTech Connect

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.

Bartram, Michael E.; Creighton, J. Randall

1999-05-26

341

Thermal reaction and desorption behaviors of 2,5-diiodothiophene on clean and passivated Au surfaces  

NASA Astrophysics Data System (ADS)

Thermal reactions and desorption behaviors of 2,5-diiodothiophene on Au were studied with temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES). Diiodo-substituted hetero-cyclic molecules are an important precursor molecule for photochemical production of conjugated polymers. This paper describes the surface reactions and multilayer structure of 2,5-diiodothiophene in the absence of photon irradiation. 2,5-Diiodothiophene adsorbs molecularly on Au at 100 K. At 200-300 K, the C-I bond of the molecule dissociates producing atomic iodine. The C-I bond cleavage appears to induce further dissociation of the thiophene ring structure. The iodine species desorb at 600-750 K from the surface. The dissociated carbon and sulfur remain on the Au surface even at 800 K. The desorption of thin multilayers occurs at ˜220 K. During the desorption of these layers, a clustering process seems to occur. The desorption of thick multilayer occurs at ˜235 K.

Liu, Guangming; Ryoo, Kunkul; Kim, Seong H.

2007-07-01

342

New insight into the promoting role of process on the CeO2-WO3/TiO2 catalyst for NO reduction with NH3 at low-temperature.  

PubMed

This study aimed at investigating the reason of high catalytic activity for CeO2-WO3/TiO2 catalyst from the aspects of WO3 interaction with other species and the NO oxidation process. Analysis by X-ray diffractometry, photoluminescence spectra, diffuse reflectance UV-visible, X-ray photoelectron spectroscopy, density functional theory calculations, electron paramagnetic resonance spectroscopy, temperature-programmed-desorption of NO and in situ diffuse reflectance infrared transform spectroscopy showed that WO3 could interact with CeO2 to improve the electron gaining capability of CeO2 species. In addition, WO3 species acted as electron donating groups to transfer the electrons to CeO2 species. The two aspects enhanced the formation of reduced CeO2 species to improve the formation of superoxide ions. Furthermore, the Ce species were the active sites for the NO adsorption and the superoxide ions over the catalyst needed oxidizing the adsorbed NO to improve the NO oxidation. This process was responsible for the high catalytic activity of CeO2-WO3/TiO2 catalyst. PMID:25746195

Zhang, Shule; Zhong, Qin; Shen, Yuge; Zhu, Li; Ding, Jie

2015-06-15

343

Complexes of XeHXe(+) with Simple Ligands: A Theoretical Investigation on (XeHXe(+))L (L = N2, CO, H2O, NH3).  

PubMed

The structure, stability, and harmonic frequencies of the (XeHXe(+))L complexes (L = N2, CO, H2O, NH3) were investigated by ab initio and density functional theory (DFT) calculations. Their bonding situation was also assayed by natural bond orbital (NBO), atoms-in-molecules (AIM), and energy decomposition (EDA) analyses. For any L, we located a linear and a T-shaped isomer, whose energy difference progressively increases in the order N2 < CO < H2O < NH3 and ranges from nearly 0 to 4.5 kcal mol(-1). The absolute complexation energies of both the linear and the T-shaped isomers also increase in the same order, and their EDA analysis revealed the prevailing contribution of electrostatic interactions. The noncovalent character of the bonding between XeHXe(+) and L was confirmed by the AIM analysis. In particular, we based our investigation on the joint use of numerical AIM indices and graphic examination of the local Hamiltonian kinetic energy density, K(r). Interestingly, this function visually identifies the "covalent" regions occupied by XeHXe(+) and L and the "noncovalent" zones existing between them, which include, in particular, the bond critical point located on the Xe-L bond paths. Only for the linear (XeHXe(+))NH3 did the AIM analysis suggest an onset of covalency in the xenon-nitrogen interaction. Further work is in progress to examine the effectiveness of K(r), and its plotted forms, as a function of the bonding situation of noble-gas compounds. PMID:25285705

Borocci, Stefano; Giordani, Maria; Grandinetti, Felice

2015-03-19

344

Laboratory measurements of the W band (3.2 mm) properties of phosphine (PH3) and ammonia (NH3) under simulated conditions for the outer planets  

NASA Astrophysics Data System (ADS)

A model, based on the Van Vleck-Weisskopf line shape, was developed for the centimeter-wavelength opacity of PH3, which provides an order of magnitude improvement over previous models [Hoffman et al., 2001]. New laboratory measurements indicate that the model is also accurate at 94 GHz (3.2 mm) under conditions for the outer planets. Measurements of the opacity and refractivity of PH3 in a hydrogen/helium (H2/He) atmosphere were conducted at 94 GHz (3.2 mm) at pressures of 0.5 and 2 bars and at temperatures of 293 K and 213 K. Additionally, new high-precision laboratory measurements of the opacity and refractivity of NH3 in an H2/He atmosphere were conducted at the same frequency at pressures from 0.5 to 2 bars and at temperatures of 204 K, 211 K, and 290 K. Results show that existing models, which predict NH3 opacity in an H2/He environment, understate the absorption due to the pressure broadened rotational lines. A new model is proposed for use at 94 GHz (3.2 mm) which uses a Ben-Reuven line shape [Ben-Reuven, 1966] for the inversion lines and a Kinetic line shape [Gross, 1955] for the rotational lines. Results of measurements of both PH3 and NH3 can be used to better interpret maps of Saturn's emission at this wavelength and can potentially be used to deduce spatial variations in the abundances of both gases in the atmosphere of Saturn.

Mohammed, Priscilla N.; Steffes, Paul G.

2004-07-01

345

Hole-transport materials with greatly-differing redox potentials give efficient TiO2-[CH3NH3][PbX3] perovskite solar cells.  

PubMed

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

Abate, Antonio; Planells, Miquel; Hollman, Derek J; Barthi, Vishal; Chand, Suresh; Snaith, Henry J; Robertson, Neil

2015-01-28

346

Nanowires of methylammonium lead iodide (CH3NH3PbI3) prepared by low temperature solution-mediated crystallization.  

PubMed

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

Horváth, Endre; Spina, Massimo; Szekrényes, Zsolt; Kamarás, Katalin; Gaal, Richard; Gachet, David; Forró, László

2014-12-10

347

Decomposition of NH3BH3 at sub-ambient pressures: A combined thermogravimetry-differential thermal analysis-mass spectrometry study  

SciTech Connect

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.

Palumbo, Oriele; Paolone, Annalisa; Rispoli, Pasquale; Cantelli, Rosario; Autrey, Thomas

2010-03-15

348

VUV dissociative excitation cross sections of H2O, NH3, and CH4 by electron impact. [Vacuum Ultra-Violet  

NASA Technical Reports Server (NTRS)

Absolute excitation functions for excited fragments resulting from electron bombardment of H2O, NH3, and CH4 by low-energy electrons (0 to 300 eV) have been measured in the vacuum ultraviolet (1100 to 1950 A). The predominant emission for each molecule was the H Lyman-alpha line, while the O I, N I, C I, and C II emissions were at least an order of magnitude weaker. Absolute cross sections at 100 eV are given along with the appearance potential of the various processes and the possible dissociative-excitation channels through which such processes proceed.

Morgan, H. D.; Mentall, J. E.

1974-01-01

349

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)

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.

Carslaw, David C.; Rhys-Tyler, Glyn

2013-12-01

350

High Magnetic Hardness for the Canted Antiferromagnetic, Ferroelectric, and Ferroelastic Layered Perovskite-like (C2H5NH3)2[Fe(II)Cl4].  

PubMed

An unusual high magnetic hardness for the layered perovskite-like (C2H5NH3)2[Fe(II)Cl4], in addition to its already found canted antiferromagnetism, ferroelasticity, and ferroelectricity, which are absent for (CH3NH3)2[Fe(II)Cl4], has been observed. The additional CH2 in the ethylammonium compared to methylammonium allows more degrees of freedom and therefore numerous phase transitions which have been characterized by single-crystal structure determinations from 383 to 10 K giving the sequence from tetragonal to orthorhombic to monoclinic (I4/mmm ? P42/ncm ? Pccn ? Pcab ? C2/c) accompanied by both tilting and rotation of the FeCl6 octahedra. The magnetic properties on single crystal and powder samples at high temperature are similar for both compounds, but at TN (C2H5NH3)2[Fe(II)Cl4] is a proper canted antiferromagnet unlike the hidden canting observed for (CH3NH3)2[Fe(II)Cl4]. The canting angle is 0.6° toward the c-axis, and thus the moments lie in the easy plane of the iron-chloride layer defined by a critical exponent ? = 0.18. The isothermal magnetizations for the field along the three orthogonal crystallographic axes show wider hysteresis for H ? c and is present at all temperature below 98 K. The coercive field increases as the temperature is lowered, and at T < 20 K it is difficult to reverse all the moments with the available 50 kOe of the SQUID for both single crystal and powder samples. The shape of the virgin magnetization after zero-field-cool (ZFC) indicates that the high coercive field is due to domain wall pinning. Thus, there are unusual associated anomalies such as asymmetric hysteresis and history dependence. The difference in magnetic hardness of the two compounds suggests that magnetic, electric, and elastic domains are intricately manifested and therefore raise the key question of how the different domains interact. PMID:25736878

Han, Jing; Nishihara, Sadafumi; Inoue, Katsuya; Kurmoo, Mohamedally

2015-03-16

351

Hot ammonia around young O-type stars. I. JVLA imaging of NH3 (6, 6) to (14, 14) in NGC 7538 IRS1  

NASA Astrophysics Data System (ADS)

Context. The formation of massive (O-type) stars through the same accretion processes as low-mass stars is problematic, mainly because of the feedback massive stars provide to the environment, which halts the accretion. In order to constrain theoretical models of high-mass star formation, observational signatures of mass accretion in O-type forming stars are desirable. The high-mass star forming region NGC 7538 IRS1 (distance = 2.7 kpc) is an ideal target, because VLBI measurements of CH3OH masers recently identified a triple system of high-mass young stellar object (YSOs) in the region: IRS1a, IRS1b, and IRS1c. The first two YSOs seem to be surrounded by rotating disks. Aims: We want to characterize physical conditions and kinematics of circumstellar molecular gas around O-type young stars. Sub-arcsecond resolution observations of highly-excited lines from high-density tracers are useful, since these probe the hottest and densest gas, which presumably is close to O-type forming stars, i.e., in disks and the innermost portions of envelopes. Methods: Using the Karl Jansky Very Large Array (JVLA), we have mapped the hot and dense molecular gas in the hot core associated with NGC 7538 IRS1, with ~0.''2 angular resolution, in seven metastable (J = K) inversion transitions of ammonia (NH3): (J,K) = (6, 6), (7, 7), (9, 9), (10, 10), (12, 12), (13, 13), and (14, 14). These lines arise from energy levels between ~400 K and ~1950 K above the ground state, and are observed in absorption against the HC-HII region associated with NGC 7538 IRS1. The CH3OH JK = 132 - 131 and CH3CN (2-1) lines were also included in our spectral setup, but only the former was detected. We also obtained sensitive continuum maps at frequencies between 25 and 35 GHz. Results: For each transition, we produced resolved images of total intensity and velocity field, as well as position-velocity diagrams. The intensity maps show that the NH3 absorption follows the continuum emission closely. With a 500 AU linear resolution, we resolve the elongated north-south NH3 structure into two compact components: the main core and a southernmost component. Previous observations of the radio continuum with a 0.''08 (or 200 AU) resolution, resolved in turn the compact core in two (northern and southern) components. The velocity maps of the compact core show a clear velocity gradient in all lines, which is indicative of rotation. It is possible that the rotation is not in an accretion disk but in a (circumbinary) envelope, containing ~40 M? (dynamical mass). The core hosts a binary system of massive YSOs, associated with the two (northern and southern) components of the radio continuum, which have a separation of about 500 AU and velocities around -59 km s-1 and -56.4 km s-1, respectively. The southernmost component, separated by 1000 AU and resolved in our NH3 maps (0.''2 beamsize) from the core, is associated with a third massive YSO, with a velocity around -60 km s-1. These features correspond to the triple system of high-mass YSOs IRS1a, IRS1b, and IRS1c. In addition, we derive rotational temperatures, NH3 column densities, H2 gas densities, and gas masses from the NH3 data. Surprisingly, measurements of the hyperfine structure show total optical depths of 10-26 even for these highly-excited lines, among the largest found so far in hot NH3 in high-mass star forming regions. From ratios of optical depths as well as rotational temperature diagrams of the observed ortho and para transitions, we derive a rotational temperature ~ 280 K, NH3 column densities ~ 1.4-2.5 × 1019 cm-2, total H2 volume densities ~ 3.5-6.2 × 1010 cm-3, and a total gas mass in the range of 19-34 M? (the latter two assume [NH3]/[H2] = 10-7), for the main core. For the southern component, we derive a temperature of 110 K, a molecular density of ~ 0.7-2 × 1010 cm-3 and a gas mass in the range of 4-12 M?. Conclusions: We conclude that NGC 7538 IRS1 is the densest hot molecular core known to date, containing a rotating envelope which hosts a multiple system of high-mass YSOs, possibly surrounded b

Goddi, C.; Zhang, Q.; Moscadelli, L.

2015-01-01

352

Preparation of Single Phase Films of CH3NH3Pb(I1-xBrx)3 with Sharp Optical Band Edges  

E-print Network

?inorganic perovskite (CH3NH3PbI3?xClx) solar cells now show photovoltaic (PV) performance1?4 approaching 18%,5,6 and high charge-carrier mobilities.7 Perovskite films have also shown promising photoluminescence quantum efficiencies (PLQEs) of more than 70% and lasing... . 2014, 5, 1035?1039. (17) Miller, O. D.; Yablonovitch, E.; Kurtz, S. R. Strong Internal and External Luminescence as Solar Cells Approach the Shockley? Queisser Limit. IEEE J. Photovoltaics 2012, 2, 303?311. (18) Le Bail, A.; Duroy, H.; Fourquet, J. L...

Sadhanala, Aditya; Deschler, Felix; Thomas, Tudor H; Dutton, Siân E.; Goedel, Karl C.; Hanusch, Fabian C.; Lai, May L.; Steiner, Ullrich; Bein, Thomas; Docampo, Pablo; Cahen, David; Friend, Richard H.

2014-07-09

353

Effect of Rh particle size on CO desorption from Rh/alumina model catalysts  

NASA Astrophysics Data System (ADS)

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.

Belton, David N.; Schmieg, Steven J.

1988-08-01

354

Measurement of Xe desorption rates from Pt(111): Rates for an ideal surface and in the defect-dominated regime  

NASA Astrophysics Data System (ADS)

The rate of thermal desorption of Xe from a Pt(111) surface has been measured over a range of 7 orders of magnitude using a combination of molecular-beam techniques. Rates up to ˜104 s-1, corresponding to residence times as short as 100 ?s, were extracted from the time-of-arrival distributions for atoms leaving the surface after short Xe beam pulses were applied. Rates as low as 10-3 s-1 were measured using a time-delayed flash-desorption technique. For intermediate rates, the transient decay of the desorbing Xe was recorded directly following the closing of a beam shutter. Temperature programmed desorption (TPD) spectra show first-order desorption kinetics and also reveal the presence of ``defect'' sites with substantially higher Xe binding energy which dominate the desorption kinetics at low coverages (below 0.005 Xe monolayers). These defects can be specifically saturated with CO molecules, permitting the measurement of rates characteristic of an ideal Pt(111) surface. An Arrhenius plot of these desorption rates is found to be linear over the entire range covered (80-160 K), giving an adsorption energy, ??, of 245±15 meV and a preexponential, ?, of 14+24-8 ×1011 s-1. In contrast, a similar plot for rates which are controlled by the presence of defect sites gives ??=410±40 meV and ?=9+40-8 ×1015 s-1. A desorption model including the effect of defects is developed which relates the desorption rate to the microscopic behavior of Xe atoms on terraces and at defects. This model leads to an estimate for the preexponential factor for defect-dominated desorption which is quite consistent with the very large measured value, and allows the simulation of TPD spectra and isothermal coverage decay curves, which involve coverages both higher and lower than the defect-site density.

Rettner, C. T.; Bethune, D. S.; Schweizer, E. K.

1990-01-01

355

Antitumor activity of polyoxomolybdate, [NH3Pri]6[Mo7O24].3H2O, against, human gastric cancer model.  

PubMed

Polyoxometalates are negatively charged inorganic compounds which contain metal ions such as tungsten, molybdenum, vanadium etc. and which make clusters with the surrounding oxygen atoms. [NH3Pri]6[Mo7O24].3H2O (PM-8) was found to be a significant antitumor polyoxomolybdates. It had already been reported that the PM-8 suppressed the growth of Co-4 human colon cancer, MX-1 human breast cancer and OAT human lung cancer xenografted in nude mice. However, the mechanism of the antitumor activity has not been clarified. In this study, the antitumor activity of one of the metal oxide clusters (polyoxometalates), hexabis(isopropylammonium) heptamolybdate trihydrate, [NH3Pri]6[Mo7O24].3H2O (PM-8) were shown in an MTS assay. DNA ladder formation and detection of apoptotic bodies in nuclei were revealed that antitumor activity of PM-8 in MKN45 cells was due to apoptosis. It is concluded that the observation of significant tumor growth suppression of PM-8 in MKN45-bearing mice results from the induction of apoptosis. PM-8 shows promise as a novel anti-cancer agent. PMID:16860528

Mitsui, S; Ogata, A; Yanagie, H; Kasano, H; Hisa, T; Yamase, T; Eriguchi, M

2006-08-01

356

Nanoscale charge localization induced by random orientations of organic molecules in hybrid perovskite CH3NH3PbI3.  

PubMed

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

Ma, Jie; Wang, Lin-Wang

2015-01-14

357

Catalytic reduction of N2 to NH3 by an Fe-N2 complex featuring a C-atom anchor  

PubMed Central

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

Creutz, Sidney E.; Peters, Jonas C.

2014-01-01

358

A new analysis of charge transfer and polarization for ligand-metal bonding - Model studies of Al4CO and Al4NH3  

NASA Technical Reports Server (NTRS)

The nature of the bonding of CO and NH3 ligands to Al is analyzed, and the intra-unit charge polarization and inter-unit donation for the interaction of ligands with metals are studied. The consequences of metal-to-ligand and ligand-to-metal charge transfer are separately considered by performing a constrained space orbital variation (CSOV) with the electrons of the metal member of the complex in the field of frozen ligand. The electrons of the metal atoms are then frozen in the relaxed distribution given by the CSOV SCF wave function and the ligand electrons are allowed to relax. Quantitative measures of the importance of inter-unit charge transfers and intra-unit polarization are obtained using results of SCF studies of Al4CO and Al4NH3 clusters chosen to simulate the adsorption of the ligands at an on-top side of the Al(111) surface. The electrostatic attraction of the effective dipole moments of the metal and ligand units makes an important contribution to the bond.

Bagus, P. S.; Hermann, K.; Bauschlicher, C. W., Jr.

1984-01-01

359

Sensitive gas analysis system on a microchip and application for on-site monitoring of NH3 in a clean room.  

PubMed

A portable, highly sensitive, and continuous ammonia gas monitoring system was developed with a microfluidic chip. The system consists of a main unit, a gas pumping unit, and a computer which serves as an operation console. The size of the system is 45 cm width × 30 cm depth × 30 cm height, and the portable system was realized. A highly efficient and stable extraction method was developed by utilizing an annular gas/liquid laminar flow. In addition, a stable gas/liquid separation method with a PTFE membrane was developed by arranging a fluidic network in three dimensions to achieve almost zero dead volume at the gas/liquid extraction part. The extraction rate was almost 100% with a liquid flow rate of 3.5 ?L/min and a gas flow rate of 100 mL/min (contact time of ~15 ms), and the concentration factor was 200 times by calculating the NH(3) concentration (w/w unit) in the gas and liquid phases. Stable phase separation and detection was sustained for more than 3 weeks in an automated operation, which was sufficient for the monitoring application. The lower limit of detection calculated based on a signal-to-noise ratio of 3 was 84 ppt, which showed good detectability for NH(3) analysis. We believe that our system is a very powerful tool for gas analysis due to the advantages of portable size, high sensitivity, and continuous monitoring, and it is particularly useful in the semiconductor field. PMID:21615143

Hiki, Shinichiro; Mawatari, Kazuma; Aota, Arata; Saito, Maki; Kitamori, Takehiko

2011-06-15

360

Quasi-two-dimensional S =1/2 magnetism of Cu[ C6H2 (COO)4][ C2H5NH3 ] 2  

NASA Astrophysics Data System (ADS)

We report structural and magnetic properties of the spin-1/2 quantum antiferromagnet Cu[ C6H2(COO) 4 ][ C2H5NH3 ] 2 by means of single-crystal x-ray diffraction, magnetization, heat capacity, and electron-spin-resonance (ESR) measurements on polycrystalline samples, as well as band-structure calculations. The triclinic crystal structure of this compound features CuO4 plaquette units connected into a two-dimensional framework through anions of the pyromellitic acid [ C6H2(COO) 4 ]4 -. The ethylamine cations [ C2H5NH3]+ are located between the layers and act as spacers. Magnetic susceptibility and heat capacity measurements establish a quasi-two-dimensional, weakly anisotropic, and nonfrustrated spin-1/2 square lattice with the ratio of the couplings Ja/Jc?0.7 along the a and c directions, respectively. No clear signatures of the long-range magnetic order are seen in thermodynamic measurements down to 1.8 K. However, the gradual broadening of the ESR line suggests that magnetic ordering occurs at lower temperatures. Leading magnetic couplings are mediated by the organic anion of the pyromellitic acid and exhibit a nontrivial dependence on the Cu-Cu distance, with the stronger coupling between those Cu atoms that are farther apart.

Nath, R.; Padmanabhan, M.; Baby, S.; Thirumurugan, A.; Ehlers, D.; Hemmida, M.; Krug von Nidda, H.-A.; Tsirlin, A. A.

2015-02-01

361

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)

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.

Gruber, M.; Hermann, K.

2013-12-01

362

Facile preparation of ordered mesoporous MnCo2O4 for low-temperature selective catalytic reduction of NO with NH3.  

PubMed

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. PMID:25578309

Qiu, Mingying; Zhan, Sihui; Yu, Hongbing; Zhu, Dandan; Wang, Shengqiang

2015-01-28

363

The role of isolated Cu(2+) location in structural stability of Cu-modified SAPO-34 in NH3-SCR of NO.  

PubMed

In this study, three different methods (ion exchange, wet mixing and impregnation) were employed to prepare Cu-modified SAPO-34 molecular sieves. All these freshly prepared catalysts showed excellent activities towards the selective catalytic reduction (SCR) of NO with NH3 (NH3-SCR) no matter which preparation method was used. However, hydrothermal ageing significantly reduced the catalytic activities of those catalysts prepared by the wet-mixing and impregnation methods, respectively. The results of X-ray powder diffraction, H2-TPR and electron paramagnetic resonance measurements for these catalysts suggested that the decrease in catalytic activity may be attributed to the migration of Cu(2+) ion to the centre of the hexagonal prism (site III), the formation of CuxOy and the collapse of the molecular framework during hydrothermal ageing. The degrees of structural collapse of each Cu-modified molecular sieve were different, probably due to Cu(2+) species in different sites (in the ellipsoidal cavity (site I) for ion-exchange sample, near the eight-ring window (site IV) for the wet-mixing and impregnation samples). Cu(2+) located at site I was more stable than that located at site IV. PMID:25413111

Yan, Chundi; Cheng, Hao; Yuan, Zhongshan; Wang, Shudong

2015-01-01

364

ENGINEERING BULLETIN: THERMAL DESORPTION TREATMENT.  

EPA Science Inventory

Thermal desorption is an EX SITU means to physically separate volatile and some semivolatile contaminants from soil, sediments, sludge, and filter cakes by heating them at temperatures high enough to volatilize the organic contaminants. For wastes containing up to 10 percent orga...

365

ENGINEERING BULLETIN: THERMAL DESORPTION TREATMENT  

EPA Science Inventory

Thermal desorption is an EX SITU means to physically separate volatile and some semivolatile contaminants from soil, sediments, sludge, and filter cakes by heating them at temperatures high enough to volatilize the organic contaminants. or wastes containing up to 10 percent organ...

366

Adsorption and desorption behavior of n-butane and isobutane on Pt(111) and Sn/Pt(111) surface alloys  

SciTech Connect

The adsorption/desorption behavior of n-butane and isobutane on Pt(111) and the p(2[times]2) Sn/Pr(111) and ([radical]3[times] [radical]3)R30[degrees] Sn/Pt(111) surface alloys has been examine using a combination of adsorption kinetics measurements utilizing a collimated molecular beam and temperature programmed desorption (TPD) mass spectroscopy. Initial sticking probabilities for both molecules on Pt(111) and the surface alloys at temperatures below the monolayer desorption threshold are essentially unity (S[sub 0] [>=] 0.95). The monolayer saturation coverages of n-butane and isobutane were also independent of the amount of Sn in the surface layer. The desorption activation energies measured by TPD for the monolayer states of both n-butane and isobutane progressively decrease by 5-8 kJ/mol compared to Pt(111) as the surface concentration of Sn increases from 0.25 to 0.33 atom fraction in the respective surface alloys. The decrease in the desorption activation energy scales linearly with the Sn concentration. No thermal decomposition of either molecule on any surface occurred during TPD measurements. Molecular interactions probed by adsorption and desorption of saturated C[sub 4] hydrocarbons are not influenced as strongly by the presence of Sn in the Pt(111) surface as previously observed for unsaturated molecules, such as ethylene and isobutylene. 30 refs., 9 figs.

Xu, C.; Koel, B.E. (Univ. of Southern California, Los Angeles, CA (United States)); Paffett, M.T. (Los Alamos National Lab., NM (United States))

1994-01-01

367

Adsorption and desorption of CO on Pt(1 1 1): a comprehensive analysis  

NASA Astrophysics Data System (ADS)

A comprehensive theory of the adsorption of CO on Pt(1 1 1) is developed to describe equilibrium properties as well as the adsorption and desorption kinetics. The basis is a multi-site lattice gas model which allows for adsorption at on-top and bridge sites, and includes site exclusion and lateral interactions out to second neighbour unit cells as well as a mean field to account for long ranged dipolar interactions between CO molecules. The theory reproduces the coverage and temperature dependence of pressure isotherms, partial coverages, heat of adsorption, total sticking coefficients, and isothermal and temperature-programmed desorption rates. The quality of the fits and the internal consistency of the theory are such that a number of minor inconsistencies in available experimental data can be identified and discussed.

McEwen, J.-S.; Payne, S. H.; Kreuzer, H. J.; Kinne, M.; Denecke, R.; Steinrück, H.-P.

2003-11-01

368

Adsorbate order-disorder effects on recombinative thermal desorption: Equivalence between dynamic Monte Carlo simulations and self-consistent cluster approximations  

NASA Astrophysics Data System (ADS)

The thermally activated desorption of dissociated diatomic species from a metallic surface is described as a lattice-gas problem on a square lattice with nearest- and next-nearest neighbor interactions between the adsorbates and investigated within dynamic Monte Carlo simulations. In the limit of fast diffusion with respect to desorption, it can be shown that the desorption rate depends directly on the local order induced by the interactions within the adsorbate layer. Therefore, by employing an appropriate quasi-equilibrium cluster approximation for the local order (beyond the quasi-chemical approximation), a differential equation can be derived that depends on self-consistently calculated structure forms, reproducing quantitatively the temperature-programmed desorption spectra simulated with the Monte Carlo procedure. In this way it can be shown that the time evolution obtained from the dynamic Monte Carlo algorithm is indeed "correct,'' and on the other hand, that it can be successfully substituted by a "cheaper'' cluster approximation.

Weinketz, Sieghard; Cabrera, G. G.

1997-01-01

369

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)

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.

Vandenboer, T. C.; Markovic, M. Z.; Sanders, J.; Ren, X.; Murphy, J. G.

2010-12-01

370

Optical detection of CO and CO2 temperature dependent desorption from carbon nanotube clusters.  

PubMed

The development of new materials relies on high precision methods to quantify adsorption/desorption of gases from surfaces. One commonly used approach is temperature programmed desorption spectroscopy. While this approach is very accurate, it requires complex instrumentation, and it is limited to performing experiments under high vacuum, thus restricting experimental scope. An alternative approach is to integrate the surface of interest directly onto a detector face, creating an active substrate. One surface that has applications in numerous areas is the carbon nanotube (CNT). As such, an active substrate that integrates a CNT surface on a sensor and is able to perform measurements in ambient environments will have significant impact. In the present work, we have developed an active substrate that combines an optical sensor with a CNT cluster substrate. The optical sensor is able to accurately probe the temperature dependent desorption of carbon monoxide and carbon dioxide gases from the CNT cluster surface. This active substrate will enable a wide range of temperature dependent desorption measurements to be performed from a scientifically interesting material system. PMID:25189292

Chistiakova, M V; Armani, A M

2014-10-01

371

Density functional theory study on the full ALD process of silicon nitride thin film deposition via BDEAS or BTBAS and NH3.  

PubMed

A detailed reaction mechanism has been proposed for the full ALD cycle of Si3N4 deposition on the ?-Si3N4(0001) surface using bis(diethylamino)silane (BDEAS) or bis(tertiarybutylamino)silane (BTBAS) as a Si precursor with NH3 acting as the nitrogen source. Potential energy landscapes were derived for all elementary steps in the proposed reaction network using a periodic slab surface model in the density functional approximation. Although the dissociative reactivity of BTBAS was slightly better than that of BDEAS, the thermal deposition process was still found to be an inherently high temperature process due to the high activation energies during the dissociative chemisorption of both precursors and the surface re-amination steps. These results underline the need to develop new precursors and alternative nitrogen sources when low temperature thermal silicon nitride films are targeted. PMID:25072273

Huang, Liang; Han, Bo; Han, Bing; Derecskei-Kovacs, Agnes; Xiao, Manchao; Lei, Xinjian; O'Neill, Mark L; Pearlstein, Ronald M; Chandra, Haripin; Cheng, Hansong

2014-09-14

372

Effective hole extraction using MoOx-Al contact in perovskite CH3NH3PbI3 solar cells  

NASA Astrophysics Data System (ADS)

We report an 11.4%-efficient perovskite CH3NH3PbI3 solar cell using low-cost molybdenum oxide/aluminum (i.e., MoOx/Al) as an alternative top contact to replace noble/precious metals (e.g., Au or Ag) for extracting photogenerated holes. The device performance of perovskite solar cells using a MoOx/Al top contact is comparable to that of cells using the standard Ag top contact. Analysis of impedance spectroscopy measurements suggests that using 10-nm-thick MoOx and Al does not affect charge-recombination properties of perovskite solar cells. Using a thicker (20-nm) MoOx layer leads to a lower cell performance caused mainly by a reduced fill factor. Our results suggest that MoOx/Al is promising as a low-cost and effective hole-extraction contact for perovskite solar cells.

Zhao, Yixin; Nardes, Alexandre M.; Zhu, Kai

2014-05-01

373

Origin and elimination of photocurrent hysteresis by fullerene passivation in CH3NH3PbI3 planar heterojunction solar cells.  

PubMed

The large photocurrent hysteresis observed in many organometal trihalide perovskite solar cells has become a major hindrance impairing the ultimate performance and stability of these devices, while its origin was unknown. Here we demonstrate the trap states on the surface and grain boundaries of the perovskite materials to be the origin of photocurrent hysteresis and that the fullerene layers deposited on perovskites can effectively passivate these charge trap states and eliminate the notorious photocurrent hysteresis. Fullerenes deposited on the top of the perovskites reduce the trap density by two orders of magnitude and double the power conversion efficiency of CH(3)NH(3)PbI(3) solar cells. The elucidation of the origin of photocurrent hysteresis and its elimination by trap passivation in perovskite solar cells provides important directions for future enhancements to device efficiency. PMID:25503258

Shao, Yuchuan; Xiao, Zhengguo; Bi, Cheng; Yuan, Yongbo; Huang, Jinsong

2014-01-01

374

Origin and elimination of photocurrent hysteresis by fullerene passivation in CH3NH3PbI3 planar heterojunction solar cells  

NASA Astrophysics Data System (ADS)

The large photocurrent hysteresis observed in many organometal trihalide perovskite solar cells has become a major hindrance impairing the ultimate performance and stability of these devices, while its origin was unknown. Here we demonstrate the trap states on the surface and grain boundaries of the perovskite materials to be the origin of photocurrent hysteresis and that the fullerene layers deposited on perovskites can effectively passivate these charge trap states and eliminate the notorious photocurrent hysteresis. Fullerenes deposited on the top of the perovskites reduce the trap density by two orders of magnitude and double the power conversion efficiency of CH3NH3PbI3 solar cells. The elucidation of the origin of photocurrent hysteresis and its elimination by trap passivation in perovskite solar cells provides important directions for future enhancements to device efficiency.

Shao, Yuchuan; Xiao, Zhengguo; Bi, Cheng; Yuan, Yongbo; Huang, Jinsong

2014-12-01

375

N- and O-heterocycles Produced from the Irradiation of Benzene and Naphthalene in H2O/NH3-containing Ices  

NASA Astrophysics Data System (ADS)

Aromatic heterocyclic molecules are an important class of molecules of astrophysical and biological significance that include pyridine, pyrimidine, and their derivatives. Such compounds are believed to exist in interstellar and circumstellar environments, though they have never been observed in the gas phase. Regardless of their presence in the gas phase in space, numerous heterocycles have been reported in carbonaceous meteorites, which indicates that they are formed under astrophysical conditions. The experimental work described here shows that N- and O-heterocyclic molecules can form from the ultraviolet (UV) irradiation of the homocyclic aromatic molecules benzene (C6H6) or naphthalene (C10H8) mixed in ices containing H2O and NH3. This represents an alternative way to generate aromatic heterocycles to those considered before and may have important implications for astrochemistry and astrobiology.

Materese, Christopher K.; Nuevo, Michel; Sandford, Scott A.

2015-02-01

376

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)

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.

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

377

A new mechanism of H 2B?NH 2 formation in the reaction of B 2H 6 with NH 3  

NASA Astrophysics Data System (ADS)

The mechanisms of the reactions of diborane with ammonia have been investigated by ab initio molecular orbital methods. The activation barrier of the formation of aminoborane, H 2B?NH 2, from the adduct, H 3B:NH 3, of borane and ammonia is high (over 40 kcal/mol), because it is a reaction essentially forbidden by the Woodward—Hoffmann rule. A new cyclic transition state is found in the aminoborane formation mechanism. The barrier for this cyclic transition state is about 17 kcal/mol from the isolated diborane and ammonia at the MP4/6-31G(d,p)//MP2/6-31G(d,p)+ZPE level

Sakai, Shogo

1994-01-01

378

Quantum chemical topology description of the hydrogen transfer between the ethynyl radical and ammonia (C 2H rad + NH 3) - The electron localization function study  

NASA Astrophysics Data System (ADS)

The topological analysis of the Electron Localization Function (ELF) has been carried out for the hydrogen abstraction pathway between ethynyl radical (HCC rad ) and ammonia (NH 3). The IRC path, minima (HCC⋯HNH 2, HCCH⋯NH 2) and transition structure have been calculated at the UB3LYP/6-311++G(2d, 2p) computational level. The 'closed-shell' and 'spin-polarized' formula of ELF are used for an analysis. A detailed study of the topology of ELF (the basin population and spin density redistribution) shows that the reaction consists of three main steps distinguished on the IRC path. First, the N-H bond in ammonia is broken, then the hydrogen atom with a population of ca. 0.7 e is transferred and finally the C-H bond in acetylene is formed. It is interesting to note that all chemically important changes occur after the transition state.

Berski, Slawomir; Latajka, Zdzis?aw

2006-08-01

379

Doppler spectroscopy of NH3 and SF6 in the 10-?m range with a tunable AgGaS2 difference-frequency spectrometer  

NASA Astrophysics Data System (ADS)

A continuous-wave mid-IR diode-laser-based, dual-cavity difference-frequency spectrometer employing silver thiogallate (AgGaS2) as the down-conversion material, and producing only 30 nW of usable mid-IR output, is used to record Doppler spectra of NH3 and SF6 around 10.2 ?m and 10.5 ?m over the 90-GHz range. The tuning procedure of the spectrometer as well as a baseline noise cancellation technique based on analogue signal ratioing are described. The device can potentially be used for ultra-high-resolution saturation spectroscopy, pending an improvement of the down-conversion efficiency to 1-?W power.

Zondy, J.-J.; Vedenyapine, V.; Kaing, T.; Lee, D.; Yelisseyev, A.; Isaenko, L.; Lobanov, S.

380

Phase transition in organic-inorganic perovskite (C9H19NH3)2 PbI2Br2 of long-chain alkylammonium  

NASA Astrophysics Data System (ADS)

Single perovskite slab alkylammonium lead iodides bromides (C9H19NH3)2PbI2Br2 is a new member of the family of hybrid organic-inorganic perovskite compounds. It exhibits a single structural phase transition with changes in the conformation of alkylammonium chains below room temperature. Differential scanning calorimetry (DSC), powder X-ray diffraction and FT-Raman spectroscopy were used to investigate this phase transition. These changes were characterized by a decreased conformational disorder of the methylene units of the alkyl chains. Phase transition was examined in light of the interesting optical properties of this material, as well as the relevance of this system as models for phase transitions in lipid bilayers.

Abid, H.; Trigui, A.; Mlayah, A.; Hlil, E. K.; Abid, Y.

2012-01-01

381

Comparison of the frequencies of NH3, CO2, H2O, N2O, CO, and CH4 as infrared calibration standards  

NASA Technical Reports Server (NTRS)

The absolute accuracies of infrared calibration standards for the line positions have been investigated using a 0.0056-kayser-resolution (unapodized) Fourier-transform spectrum recorded from 550 to 5000 kayser. The spectrum has been obtained using a multicell arrangement containing the various molecular species. Detailed comoparisons reveal that standards for CO2, CH4, and N2O obtained from laser research and NH3 from Fourier-transform spectrometer research are consistent within the accuracies of the present data (+ or 0.0001 kayser). However, certain N2O, H2O, and CO values in the 1100-to 2300 kayser region are systematically high by 0.0001 to 0.0004 kayser. Correction factors for the H2O and CO standards are obtained to bring these into agreement with the laser values. In addition, corrected values for the 2nu-2 and nu-1 bands of N2O at 9 microns are reported.

Brown, L. R.; Toth, R. A.

1985-01-01

382

One-pot synthesis of hierarchical FeZSM-5 zeolites from natural aluminosilicates for selective catalytic reduction of NO by NH3  

PubMed Central

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

Yue, Yuanyuan; Liu, Haiyan; Yuan, Pei; Yu, Chengzhong; Bao, Xiaojun

2015-01-01

383

One-pot synthesis of hierarchical FeZSM-5 zeolites from natural aluminosilicates for selective catalytic reduction of NO by NH3.  

PubMed

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

Yue, Yuanyuan; Liu, Haiyan; Yuan, Pei; Yu, Chengzhong; Bao, Xiaojun

2015-01-01

384

Chaotic regimes of antiferromagnetic resonance in a quasi-two-dimensional easy-axis antiferromagnet (NH_3)_2 (CH_2)_4 MnCl_4  

E-print Network

Chaotic regimes of the microwave energy absorption are experimentally observed and analyzed for two-dimensional metallorganic antiferromagnet (NH_3)_2(CH_2)_4MnCl_4 at low temperatures under the conditions of nonlinear antiferromagnetic resonance. Relaxation oscillations of energy absorption are investigated in detail. Their frequency spectra, frequency-amplitude characteristics, and dependences of absorbed power on driving power and static magnetic field are studied. It is shown that the dynamics of relaxation oscillations undergoes a transition to chaos by "irregular periods". Peculiarities of the transition are described consistently. Among other things, the conditions for the emergence of energy absorption regimes with a spike-like and a saw-tooth signal structure are determined, and the characteristics of chaotic oscillations such as the dimensions of strange attractors are calculated. The chaotic dynamics is found to be high-dimensional with a large contribution from noise which is of deterministic origin in the antiferromagnet under investigation.

Mikhail M. Bogdan; Mikhail I. Kobets; Eugene N. Khats'ko

2001-04-11

385

Investigation of CH3NH3PbI3 Degradation Rates and Mechanisms in Controlled Humidity Environments Using in Situ Techniques.  

PubMed

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

Yang, Jinli; Siempelkamp, Braden D; Liu, Dianyi; Kelly, Timothy L

2015-02-24

386

Magnetic phase diagram of the nearly 2D Heisenberg ferromagnet (CH 3NH 3) 2CuCl 4 in a transverse magnetic field  

NASA Astrophysics Data System (ADS)

The magnetic phase diagram of the nearly 2D ferromagnet (CH 3NH 3) 2CuCl 4 ( TC=8.85 K) in magnetic fields applied perpendicular to the easy axis is obtained. In this system, the ferromagnetic moments lie in planes ( ab planes) formed by the Cu atoms and point along the a crystallographic direction. For field applied along b-axis (intermediate anisotropy axis), a second-order transition to the paramagnetic phase occurs at the field of 80 Oe at the lowest measured temperature ( T=1.8 K). When the field is applied in a direction perpendicular to the Cu planes ( c-axis) the paramagnetic phase is reached only above 1500 Oe after a double transition. The first transition (˜500 Oe) is suggested to be an order-order transition in which a spin reorientation occurs. The obtained in-plane and out-of-plane anisotropy are HAin=80 and HAout=1500 Oe, respectively.

Becerra, C. C.; Paduan-Filho, A.

2003-12-01

387

Porous and shape-anisotropic single crystals of the semiconductor perovskite CH3NH3PbI3 from a single-source precursor.  

PubMed

Significant progress in solar-cell research is currently made by the development of metal-organic perovskites (MOPs) owing to their superior properties, such as high absorption coefficients and effective transport of photogenerated charges. As for other semiconductors, it is expected that the properties of MOPs may be significantly improved by a defined nanostructure. However, their chemical sensitivity (e.g., towards hydrolysis) prohibits the application of methods already known for the synthesis of other nanomaterials. A new and general method for the synthesis of various (CH3NH3)PbI3 nanostructures from a novel single-source precursor is presented. Nanoporous MOP single crystals are obtained by a crystal-to-crystal transformation that is accompanied by spinodal demixing of the triethylene glycol containing precursor structure. Selective binding of a capping agent can be used to tune the particle shape of the MOP nanocrystals. PMID:25470357

Kollek, Tom; Gruber, Dominik; Gehring, Julia; Zimmermann, Eugen; Schmidt-Mende, Lukas; Polarz, Sebastian

2015-01-19

388

Tonoplast Intrinsic Proteins AtTIP2;1 and AtTIP2;3 Facilitate NH3 Transport into the Vacuole1  

PubMed Central

While membrane transporters mediating ammonium uptake across the plasma membrane have been well described at the molecular level, little is known about compartmentation and cellular export of ammonium. (The term ammonium is used to denote both NH3 and NH4+ and chemical symbols are used when specificity is required.) We therefore developed a yeast (Saccharomyces cerevisiae) complementation approach and isolated two Arabidopsis (Arabidopsis thaliana) genes that conferred tolerance to the toxic ammonium analog methylammonium in yeast. Both genes, AtTIP2;1 and AtTIP2;3, encode aquaporins of the tonoplast intrinsic protein subfamily and transported methylammonium or ammonium in yeast preferentially at high medium pH. AtTIP2;1 expression in Xenopus oocytes increased 14C-methylammonium accumulation with increasing pH. AtTIP2;1- and AtTIP2;3-mediated methylammonium detoxification in yeast depended on a functional vacuole, which was in agreement with the subcellular localization of green fluorescent protein-fusion proteins on the tonoplast in planta. Transcript levels of both AtTIPs were influenced by nitrogen supply but did not follow those of the nitrogen-derepressed ammonium transporter gene AtAMT1;1. Transgenic Arabidopsis plants overexpressing AtTIP2;1 did not show altered ammonium accumulation in roots after ammonium supply, although AtTIP2;1 mRNA levels in wild-type plants were up-regulated under these conditions. This study shows that AtTIP2;1 and AtTIP2;3 can mediate the extracytosolic transport of methyl-NH2 and NH3 across the tonoplast membrane and may thus participate in vacuolar ammonium compartmentation. PMID:15665250

Loqué, Dominique; Ludewig, Uwe; Yuan, Lixing; von Wirén, Nicolaus

2005-01-01

389

HfO2/GeOxNy/Ge gate stacks with sub-nanometer capacitance equivalent thickness and low interface trap density by in situ NH3 plasma pretreatment  

NASA Astrophysics Data System (ADS)

The native oxides on Ge substrates can be transformed into GeOxNy by in situ NH3 plasma pretreatment. The interfacial and electrical properties of HfO2 caps gate stacks on Ge with and without ultrathin GeOxNy barrier layers have been investigated thoroughly. HfO2/GeOxNy/Ge stacking structure shows a sharp and flat interface between HfO2 and Ge substrates without recognized interfacial layer. In situ NH3 plasma pretreatment effectively improves the electrical properties such as higher accumulation capacitance, smaller frequency dispersion, and lower interface trap density (Dit) than without NH3 plasma pretreatment. It is ascribed to that fact that the GeOxNy barrier layer between HfO2 and Ge substrates shows better thermal stability and suppresses the Ge outdiffusion. The 3-nm-thick HfO2 gate stacks on Ge with 60 s NH3 plasma pretreatment exhibit a capacitance equivalent thickness of 0.96 nm and a leakage current density of 1.12 mA/cm2 at +1 V gate bias with acceptable Dit value of 3.42 × 1012 eV-1 cm-2. These results indicate that the surface nitridation by in situ NH3 plasma pretreatment may be a promising approach for the realization of high quality Ge-based transistor devices.

Cao, Yan-Qiang; Chen, Jun; Liu, Xiao-Jie; Li, Xin; Cao, Zheng-Yi; Ma, Yuan-Jie; Wu, Di; Li, Ai-Dong

2015-01-01

390

DESORPTION OF PYRETHROIDS FROM SUSPENDED SOLIDS  

PubMed Central

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

Fojut, Tessa L.; Young, Thomas M.

2014-01-01

391

Double functions of porous TiO2 electrodes on CH3NH3PbI3 perovskite solar cells: Enhancement of perovskite crystal transformation and prohibition of short circuiting  

NASA Astrophysics Data System (ADS)

In order to analyze the crystal transformation from hexagonal PbI2 to CH3NH3PbI3 by the sequential (two-step) deposition process, perovskite CH3NH3PbI3 layers were deposited on flat and/or porous TiO2 layers. Although the narrower pores using small nanoparticles prohibited the effective transformation, the porous-TiO2 matrix was able to help the crystal transformation of PbI2 to CH3NH3PbI3 by sequential two-step deposition. The resulting PbI2 crystals in porous TiO2 electrodes did not deteriorate the photovoltaic effects. Moreover, it is confirmed that the porous TiO2 electrode had served the function of prohibiting short circuits between working and counter electrodes in perovskite solar cells.

Murugadoss, Govindhasamy; Mizuta, Gai; Tanaka, Soichiro; Nishino, Hitoshi; Umeyama, Tomokazu; Imahori, Hiroshi; Ito, Seigo

2014-08-01

392

Stable and low-cost mesoscopic CH3NH3PbI2 Br perovskite solar cells by using a thin poly(3-hexylthiophene) layer as a hole transporter.  

PubMed

Mesoscopic perovskite solar cells using stable CH3 NH3 PbI2 Br as a light absorber and low-cost poly(3-hexylthiophene) (P3HT) as hole-transporting layer were fabricated, and a power conversion efficiency of 6.64?% was achieved. The partial substitution of iodine with bromine in the perovskite led to remarkably prolonged charge carrier lifetime. Meanwhile, the replacement of conventional thick spiro-MeOTAD layer with a thin P3HT layer has significantly reduced the fabrication cost. The solar cells retained their photovoltaic performance well when they were exposed to air without any encapsulation, presenting a favorable stability. The combination of CH3 NH3 PbI2 Br and P3HT may render a practical and cost-effective solid-state photovoltaic system. The superior stability of CH3 NH3 PbI2 Br is also promising for other photoconversion applications. PMID:25358456

Zhang, Meng; Lyu, Miaoqiang; Yu, Hua; Yun, Jung-Ho; Wang, Qiong; Wang, Lianzhou

2015-01-01

393

Observing in-phase single-quantum 15N multiplets for NH/NH3+ groups with two-dimensional heteronuclear correlation spectroscopy  

NASA Astrophysics Data System (ADS)

Two-dimensional (2D) F1- 1H-coupled HSQC experiments provide 3:1:1:3 and 1:0:1 multiplets for AX 3 and AX 2 spin systems, respectively. These multiplets occur because, in addition to the 2H groups in proteins ( Figs. 2 and 3). Data were collected with Varian 800- or 750-MHz NMR systems. Fig. 2 displays spectra recorded on the Lys57 NH3+ group of the HoxD9 homeodomain bound to 24-bp DNA. Owing to formation of an ion-pair with a DNA phosphate group, this NH3+ group exhibits relatively slow hydrogen-exchange with water molecules and the 1H- 15N cross peak from this group can clearly be observed [2]. Just as expected from considerations above, F1- 1H-coupled HSQC ( Fig. 2A) and F1- 1H-coupled HISQC ( Fig. 2B) exhibits in-phase quartets of 3:1:1:3 and 1:3:3:1 types, respectively. Actual intensity ratios deviate from these numbers because the relaxation rates for inner and outer components of the quartet are different due to cross-correlations [2,5,9]. Fig. 3 shows spectra recorded on side-chain NH 2 groups of glutamine (Gln) residues in proteins. Panels A, B and C display spectra recorded on Gln20 in the 15N-labeled HMGB1 A-domain. The rotational correlation time ?r for this protein at 25 °C is 9 ns [10]. The NH 2 group exhibited 1:0:1 triplets in the F1- 1H-coupled HSQC spectrum ( Fig. 3A) and 1:2:1 triplets in the F1- 1H-coupled HISQC spectrum ( Fig. 3B). The J-coupling was measured to be 89 Hz. For a system with a long ?r, the relaxation rates of individual triplet components for a AX 2 spin system can be quite different because of cross-correlations between distinct relaxation mechanisms [11]. Such a case is clearly seen in the spectra measured on the Gln12 NH 2 groups in the 2H/ 15N-lableled HoxD9 homeodomain bound to 24-bp DNA at 16 °C ( Fig. 3D, E and F). The value of ?r is 15 ns for this system. In this case, the downfield components are substantially shaper than the other components in triplets. Although one may think that removal of 1H-decoupling from the original HISQC experiment [2] would simply result in 1:3:3:1 and 1:2:1 multiplets, such a pulse sequence ( Fig. 1C) does not give the desired multiplets. This occurs because the anti-phase single-quantum terms generated in the t1-period also become 1H magnetizations detectable in the t2 acquisition period. In fact, the spectra measured with the simplistic pulse sequence on the same NH3+ and NH 2 groups ( Figs. 2C and 3C, F) are very different from those measured with the AP purge scheme ( Figs. 2B and 3B, E). Intensity ratios are far from 1:3:3:1 for NH3+ and 1:2:1 for NH 2; indeed, the multiplets in Fig. 3C and F are more similar to 1:0:1 triplets. In addition, some contributions from the anti-phase terms occur with 90°-shifted phases that cause dispersive distortion of the multiplets, which is evident especially in Fig. 2C. Thus, the AP purge scheme is essential to obtain 1:3:3:1 and 1:2:1 multiplets. In conclusion, we have demonstrated the 2D F1- 1H-coupled 1H- 15N correlation experiment that permits observation of in-phase 1:3:3:1 quartets for NH3+ groups and 1:2:1 triplets for NH 2 groups along the F1 axis. This experiment provides a means to distinguish AX, AX 2, and AX 3 spin systems in a straightforward manner. It is particularly useful when 1H chemical shifts are degenerated. For example, the deprotonated state of an alkyl amino group (NH 2) shows a single 1H resonance because of rapid chiral inversion [12]. In such a case, it is hard to distinguish AX and AX 2 spin systems with F1- 1H-coupled HSQC unless J-coupling is already known, because a 1:0:1 triplet appears to be a doublet. A 1:2:1 triplet is easier to interpret. It should be noted that a rapid hydrogen exchange with a rate greater than 2 ?J can cause the self-decoupling effect that results in a 15N singlet even in absence of 1H-decoupling. Considering the range of 1JNH coupling constants, however, it is likely that such a rapid hydrogen exchange simply broadens the signal beyond the detection limit in the present case, because the hydrogen exchange also increases 1H transverse relaxation ra

Takayama, Yuki; Sahu, Debashish; Iwahara, Junji

2008-10-01

394

Studies on surface structure of M x O y \\/MoO 3\\/CeO 2 system (M = Ni, Cu, Fe) and its influence on SCR of NO by NH 3  

Microsoft Academic Search

MoO3\\/CeO2 and MxOy\\/MoO3\\/CeO2 (M=Fe, Cu, Ni) catalysts had been characterized by XRD, TPR, LRS, NH3-adsorbed in situ FT-IR and activity test for selective catalytic reduction (SCR) of NO by NH3. The results suggested that the addition of NiO, CuO and Fe2O3 to MoO3\\/CeO2 catalysts had led to the different structures of surface molybdena species, i.e., isolated regular tetrahedral, highly distorted

Jie Zhu; Fei Gao; Lihui Dong; Wujiang Yu; Lei Qi; Zhe Wang; Lin Dong; Yi Chen

2010-01-01

395

Organic solvent desorption from two tegafur polymorphs.  

PubMed

Desorption behavior of 8 different solvents from ? and ? tegafur (5-fluoro-1-(tetrahydro-2-furyl)uracil) has been studied in this work. Solvent desorption from samples stored at 95% and 50% relative solvent vapor pressure was studied in isothermal conditions at 30 °C. The results of this study demonstrated that: solvent desorption rate did not differ significantly for both phases; solvent desorption in all cases occurred faster from samples with the largest particle size; and solvent desorption in most cases occurred in two steps. Structure differences and their surface properties were not of great importance on the solvent desorption rates because the main factor affecting desorption rate was sample particle size and sample morphology. Inspection of the structure packing showed that solvent desorption rate and amount of solvent adsorbed were mainly affected by surface molecule arrangement and ability to form short contacts between solvent molecule electron donor groups and freely accessible tegafur tetrahydrofuran group hydrogens, as well as between solvents molecule proton donor groups and fluorouracil ring carbonyl and fluoro groups. Solvent desorption rates of acetone, acetonitrile, ethyl acetate and tetrahydrofuran multilayers from ? and ? tegafur were approximately 30 times higher than those of solvent monolayers. Scanning electron micrographs showed that sample storage in solvent vapor atmosphere promotes small tegafur particles recrystallization to larger particles. PMID:24060368

Bobrovs, Raitis; Acti?š, Andris

2013-11-30

396

Hydrogen on Pd(100)-S: the effect of sulfur on precursor mediated adsorption and desorption  

NASA Astrophysics Data System (ADS)

The influence of adsorbed sulfur on the adsorption and desorption of H 2 on Pd(100) was studied using temperature programmed desorption (TPD) for sulfur coverages (? S) from 0.00 to 0.35 ML. The saturation coverage (? H,sat) drops linearly with sulfur coverage, and above 0.28 ML of sulfur no hydrogen adsorbs. Direct site blocking is implied by the linear fall of ? H,sat with ? S, with each sulfur atom effectively blocking 3.7 ± 0.5 sites for hydrogen adsorption. The adsorption of H 2 on the sulfur free Pd(100) surface is best described by a second-order precursor model. When sulfur is added to the surface, however, the effect of the precursor state is diminished, and for ?S ? 0.15 hydrogen uptake is adequately modeled by secondrder direct adsorption. For low hydrogen coverages values for the activation energy and the preexponential factor for hydrogen adatom recombination drop in compensatory fashion from 85 {kJ}/{mol} and 10 -2.5{cm 2}/{s} on the sulfur free surface to 49 {kJ}/{mol} and 10 -6.8{cm 2}/{s} at ?S = 0.15, respectively. The effect of sulfur on the desorption kinetics of hydrogen suggests that the influence of adsorbed sulfur is more complex than simple site blocking. The compensation effect between the preexponential factor and the activation energy from surfaces with sulfur adlayers may arise from a more constrained transition state for desorption on sulfur covered surfaces or from a distribution of activation energies for desorption.

Burke, M. L.; Madix, R. J.

1990-11-01

397

140 H/D isotopomers identified by long-range NMR hyperfine shifts in ruthenium(III) ammine complexes. Hyperconjugation in Ru-NH3 bonding.  

PubMed

(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

Laidlaw, W Michael; Denning, Robert G; Green, Jennifer C; Boyd, Jonathan; Harmer, Jeffrey; Thompson, Amber L

2013-06-17

398

Mechanical properties of hybrid organic-inorganic CH3NH3BX3 (B = Sn, Pb; X = Br, I) perovskites for solar cell absorbers  

NASA Astrophysics Data System (ADS)

The crystal structures, elastic and anisotropic properties of CH3NH3BX3 (B = Sn, Pb; X = Br, I) compounds as solar cell absorber layers are investigated by the first-principles calculations. The type and strength of chemical bond B-X are found to determine the elastic properties. B-X bonds and the organic cations are therefore crucial to the functionalities of such absorbers. The bulk, shear, Young's modulus ranges from 12 to 30 GPa, 3 to 12 GPa, and 15 to 37 GPa, respectively. Moreover, the interaction among organic and inorganic ions would have negligible effect for elastic properties. The B/G and Poisson's ratio show it would have a good ductile ability for extensive deformation as a flexible/stretchable layer on the polymer substrate. The main reason is attributed to the low shear modulus of such perovskites. The anisotropic indices AU, AB AG, A1, A2, and A3 show ABX3 perovskite have very strong anisotropy derived from the elastic constants, chemical bonds, and symmetry.

Feng, Jing

2014-08-01

399

DIAL with heterodyne detection including speckle noise: Aircraft/shuttle measurements of O3, H2O, and NH3 with pulsed tunable CO2 lasers  

NASA Technical Reports Server (NTRS)

Atmospheric trace constituent measurements with higher vertical resolution than attainable with passive radiometers are discussed. Infrared differential absorption lidar (DIAL), which depends on Mie scattering from aerosols, has special advantages for tropospheric and lower stratospheric applications and has great potential importance for measurements from shuttle and aircraft. Differential absorption lidar data reduction involves comparing large amplitude signals which have small differences. The accuracy of the trace constituent concentration inferred from DIAL measurements depends strongly on the errors in determining the amplitude of the signals. Thus, the commonly used SNR expression (signal divided by noise in the absence of signal) is not adequate to describe DIAL measurement accuracy and must be replaced by an expression which includes the random coherent (speckle) noise within the signal. A comprehensive DIAL computer algorithm is modified to include heterodyne detection and speckle noise. Examples for monitoring vertical distributions of O3, H2O, and NH3 using a ground-, aircraft-, or shuttle-based pulsed tunable CO2 laser DIAL system are given.

Brockman, P.; Hess, R. V.; Staton, L. D.; Bair, C. H.

1980-01-01

400

Solid organic residues produced by irradiation of hydrocarbon-containing H2O and H2O/NH3 ices: infrared spectroscopy and astronomical implications.  

PubMed

Methane clathrate (CH4 nH2O)--expected in cometary nuclei, in outer Solar System satellites, and perhaps in interstellar grains--as well as ices prepared from other combinations of CH4, C2H6, or C2H2 with H2O (and sometimes with NH3) were irradiated at 77 degrees K by plasma discharge. CH4 clathrate and other H2O/hydrocarbon ices color and darken noticeably after a dose approximately 10(8) to approximately 10(9) erg cm-2 over a period of 1-10 hr. Upon evaporation of the now yellowish to tan irradiated ices, a colored solid film adheres to the walls of the reaction vessel at room temperature. Transmission measurements of these organic films were made from 2.5 to 50 micrometers wavelength. The residue left after CH4 nH2O irradiation exhibits IR bands which we tabulate and identify with alkane, aldehyde, alcohol, and perhaps alkene and substituted aromatic functional groups. Aldehydes are especially well indicated, and may be related to recent claims of polyoxymethylene (H2CO)n in the coma of Comet Halley. Spectra presented here are compared with previous studies of UV or proton-irradiated, nonenclathrated hydrocarbon-containing ices may be useful for interpreting infrared features found in the spectra of comets and interstellar grains. PMID:11542162

Khare, B N; Thompson, W R; Murray, B G; Chyba, C F; Sagan, C

1989-01-01

401

The effect of the NH2 substituent on NH3: hydrazine as an alternative for ammonia in hydrogen release in the presence of boranes and alanes.  

PubMed

Potential energy surfaces for H(2) release from hydrazine interacting with borane, alane, diborane, dialane and borane-alane were constructed from MP2/aVTZ geometries and zero point energies with single point energies at the CCSD(T)/aug-cc-pVTZ level. With one borane or alane molecule, the energy barrier for H(2)-loss of approximately 38 or 30 kcal mol(-1) does not compete with the B-N or Al-N bond cleavage ( approximately 30 or approximately 28 kcal mol(-1)). The second borane or alane molecule can play the role of a bifunctional catalyst. The barrier energy for H(2)-elimination is reduced from 38 to 23 kcal mol(-1), or 30 to 20 kcal mol(-1) in the presence of diborane or dialane, respectively. The mixed borane-alane dimer reduces the barrier energy for H(2) release from hydrazine to approximately 17 kcal mol(-1). A systematic comparison with the reaction pathways from ammonia borane shows that hydrazine could be an alternative for ammonia in producing borane amine derivatives. The results show a significant effect of the NH(2) substituent on the relevant thermodynamics. The B-N dative bond energy of 31 kcal mol(-1) in NH(2)NH(2)BH(3) is approximately 5 kcal mol(-1) larger than that of the parent BH(3)NH(3). The higher thermodynamic stability could allow hydrazine-borane to be used as a material for certain energetic H(2) storage applications. PMID:19809664

Vinh-Son, Nguyen; Swinnen, Saartje; Matus, Myrna H; Nguyen, Minh Tho; Dixon, David A

2009-08-14

402

Synthesis and characterization of vanadium ions containing chlorocadmiumphosphate CdHPO4Cl·[H3N (CH2)6NH3]0.5 crystals  

NASA Astrophysics Data System (ADS)

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.

Rama Krishna, Ch.; Ravikumar, R. V. S. S. N.

2014-01-01

403

Low-temperature N2 binding to two-coordinate L2Fe(0) enables reductive trapping of L2FeN2(-) and NH3 generation.  

PubMed

The two-coordinate [(CAAC)2Fe] complex [CAAC = cyclic (alkyl)(amino)carbene] binds dinitrogen at low temperature (T<-80?°C). The resulting putative three-coordinate N2 complex, [(CAAC)2Fe(N2)], was trapped by one-electron reduction to its corresponding anion [(CAAC)2FeN2](-) at low temperature. This complex was structurally characterized and features an activated dinitrogen unit which can be silylated at the ?-nitrogen atom. The redox-linked complexes [(CAAC)2Fe(I)][BAr(F)4], [(CAAC)2Fe(0)], and [(CAAC)2Fe(-I)N2](-) were all found to be active for the reduction of dinitrogen to ammonia upon treatment with KC8 and HBAr(F)4?2?Et2O at -95?°C [up to (3.4±1.0)?equivalents of ammonia per Fe center]. The N2 reduction activity is highly temperature dependent, with significant N2 reduction to NH3 only occurring below -78?°C. This reactivity profile tracks with the low temperatures needed for N2 binding and an otherwise unavailable electron-transfer step to generate reactive [(CAAC)2FeN2](-) . PMID:25394570

Ung, Gaël; Peters, Jonas C

2015-01-01

404

Femtosecond time-resolved transient absorption spectroscopy of CH3NH3PbI3 perovskite films: evidence for passivation effect of PbI2.  

PubMed

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

Wang, Lili; McCleese, Christopher; Kovalsky, Anton; Zhao, Yixin; Burda, Clemens

2014-09-01

405

Experimental and Theoretical EPR Study of Jahn-Teller Active [HIPTN3N]MoL Complexes (L = N2, CO, NH3)  

PubMed Central

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