Detection of Voigt Spectral Line Profiles of Hydrogen Radio Recombination Lines toward Sagittarius B2(N)

We report the detection of Voigt spectral line profiles of radio recombination lines (RRLs) toward Sagittarius B2(N) with the 100 m Green Bank Telescope (GBT). At radio wavelengths, astronomical spectra are highly populated with RRLs, which serve as ideal probes of the physical conditions in molecular cloud complexes. An analysis of the Hn alpha lines presented herein shows that RRLs of higher principal quantum number (n > 90) are generally divergent from their expected Gaussian profiles and, moreover, are well described by their respective Voigt profiles. This is in agreement with the theory that spectral lines experience pressure broadening as a result of electron collisions at lower radio frequencies. Given the inherent technical difficulties regarding the detection and profiling of true RRL wing spans and shapes, it is crucial that the observing instrumentation produce flat baselines as well as high-sensitivity, high-resolution data. The GBT has demonstrated its capabilities regarding all of these aspects, and we believe that future observations of RRL emission via the GBT will be crucial toward advancing our knowledge of the larger-scale extended structures of ionized gas in the interstellar medium (ISM).

An efficient recyclable peroxometalate-based polymer-immobilised ionic liquid phase (PIILP) catalyst for hydrogen peroxide-mediated oxidation

A linear cation-decorated polymeric support with tuneable surface properties and microstructure has been prepared by ring-opening metathesis polymerisation (ROMP) of a pyrrolidinium-functionalised norbornene-based monomer with cyclooctene. The derived peroxophosphotungstate-based polymer-immobilised ionic liquid phase (PIILP) catalyst is an efficient and recyclable system for the epoxidation of allylic alcohols and alkenes, with only a minor reduction in performance on successive cycles.

Solubility of carbon dioxide, ethane, methane, oxygen, nitrogen, hydrogen, argon, and carbon monoxide in 1-butyl-3-methylimidazolium tetrafluoroborate between temperatures 283 K and 343 K and at pressures close to atmospheric

Experimental values for the solubility of carbon dioxide, ethane, methane, oxygen, nitrogen, hydrogen, argon and carbon monoxide in 1-butyl-3- methylimidazolium tetrafluoroborate, [bmim][BF4] - a room temperature ionic liquid - are reported as a function of temperature between 283 K and 343 K and at pressures close to atmospheric. Carbon dioxide is the most soluble gas with mole fraction solubilities of the order of 10-2. Ethane and methane are one order of magnitude more soluble than the other five gases that have mole fraction solubilities of the order of 10-4. Hydrogen is the less soluble of the gaseous solutes studied. From the variation of solubility, expressed as Henry's law constants, with temperature, the partial molar thermodynamic functions of solvation such as the standard Gibbs energy, the enthalpy, and the entropy are calculated. The precision of the experimental data, considered as the average absolute deviation of the Henry's law constants from appropriate smoothing equations is of 1%. © 2005 Elsevier Ltd. All rights reserved.

Thermophysical properties, low pressure solubilities and thermodynamics of solvation of carbon dioxide and hydrogen in two ionic liquids based on the alkylsulfate anion

Densities and viscosities of the ionic liquid 1-butyl-3-methylimidazolium octylsulfate, [C4C1Im][C8SO4] were measured as a function of temperature between 313 K and 395 K. Solubilities of hydrogen and carbon dioxide were determined, between 283 K and 343 K, and at pressures close to atmospheric in [C4C1Im][C 8SO4] and in another ionic liquid based on the alkylsulfate anion-1-ethyl-3-methylimidazolium ethylsulfate, [C 2C1Im][C2SO4]. Density and viscosity were measured using a vibrating tube densimeter from Anton Paar and a rheometer from Rheometrics Scientific with accuracies of 10-3 g cm -3 and 1%, respectively. Solubilities were obtained using an isochoric saturation technique and, from the variation of solubility with temperature, the partial molar thermodynamic functions of solvation, such as the standard Gibbs energy, the enthalpy, and the entropy, are calculated. The precision of the experimental data, considered as the average absolute deviation of the Henry's law constants from appropriate smoothing equations, is better than ±1%. © The Royal Society of Chemistry.

The electrical characterization and response to hydrogen of Schottky diodes with a resistive metal electrode—rectifying an oversight in Schottky diode investigation

Schottky-barrier structures with a resistive metal electrode are examined using the 4-point probe method where the probes are connected to the metal electrode only. The observation of a significant decrease in resistance with increasing temperature (over a range of similar to 100 K) in the diode resistance-temperature (R(D)-T) characteristic is considered due to charge carrier confinement to the metal electrode at low temperature (high resistance), with the semiconductor progressively opening up as a parallel current carrying channel (low resistance) with increasing temperature due to increasing thermionic emission across the barrier. A simple model is constructed, based on thermionic emission at quasi-zero bias, that generates good fits to the experimental data. The negative differential resistance (NDR) region in the R(D)-T characteristic is a general effect and is demonstrated across a broad temperature range for a variety of Schottky structures grown on Si-, GaAs- and InP-substrates. In addition the NDR effect is harnessed in micro-scaled Pd/n-InP devices for the detection of low levels of hydrogen in an ambient atmosphere of nitrogen.

Density Functional Theory Study on the Cleavage Mechanism of the Carbonyl Bond in Amides on Flat and Stepped Ru Surfaces: Hydrogen-Induced or Direct C-O Bond Breaking?

We have performed density functional theory (DFT) calculations to investigate the reaction mechanism of the cleavage of the carbonyl bond in amides on both flat and stepped Ru surfaces. The simplest amide molecule, N,N-dimethylacetamide (DMA), was used as the exemplar model molecule. Through the calculations, the most stable transition states (TSs) in all the pathways on both flat and stepped Ru surfaces are identified. Comparing the energy profiles of different reaction pathways, we find that a direct cleavage mechanism is always energetically favored as compared with an alternative hydrogen-induced mechanism on either the flat or stepped Ru surface. It is easier for the dissociation process to occur on the stepped surface than on the flat surface. However, as compared with the terrace, the superiority of step sites boosting the C-O bond dissociation is not as evident as that on CO dissociation.

Hydrogen adsorption on functionalized nanoporous activated carbons

There is considerable interest in hydrogen adsorption on carbon nanotubes and porous carbons as a method of storage for transport and related energy applications. This investigation has involved a systematic investigation of the role of functional groups and porous structure characteristics in determining the hydrogen adsorption characteristics of porous carbons. Suites of carbons were prepared with a wide range of nitrogen and oxygen contents and types of functional groups to investigate their effect on hydrogen adsorption. The porous structures of the carbons were characterized by nitrogen (77 K) and carbon dioxide (273 K) adsorption methods. Hydrogen adsorption isotherms were studied at 77 K and pressure up to 100 kPa. All the isotherms were Type I in the IUPAC classification scheme. Hydrogen isobars indicated that the adsorption of hydrogen is very temperature dependent with little or no hydrogen adsorption above 195 K. The isosteric enthalpies of adsorption at zero surface coverage were obtained using a virial equation, while the values at various surface coverages were obtained from the van't Hoff isochore. The values were in the range 3.9-5.2 kJ mol(-1) for the carbons studied. The thermodynamics of the adsorption process are discussed in relation to temperature limitations for hydrogen storage applications. The maximum amounts of hydrogen adsorbed correlated with the micropore volume obtained from extrapolation of the Dubinin-Radushkevich equation for carbon dioxide adsorption. Functional groups have a small detrimental effect on hydrogen adsorption, and this is related to decreased adsorbate-adsorbent and increased adsorbate-adsorbate interactions.

Hysteretic adsorption and desorption of hydrogen by nanoporous metal-organic frameworks

Adsorption and desorption of hydrogen from nanoporous materials, such as activated carbon, is usually fully reversible. We have prepared nanoporous metal-organic framework materials with flexible linkers in which the pore openings, as characterized in the static structures, appear to be too small to allow H-2 to pass. We observe hysteresis in their adsorption and desorption kinetics above the supercritical temperature of H-2 that reflects the dynamical opening of the "windows" between pores. This behavior would allow H-2 to be adsorbed at high pressures but stored at lower pressures.

High-capacity hydrogen and nitric oxide adsorption and storage in a metal-organic framework

Gas adsorption experiments have been carried out on a copper benzene tricarboxylate metal-organic framework material, HKUST-1. Hydrogen adsorption at 1 and 10 bar (both 77 K) gives an adsorption capacity of 11.16 mmol H-2 per g of HKUST-1 (22.7 mg g(-1), 2.27 wt %) at 1 bar and 18 mmol per g (36.28 mg g(-1), 3.6 wt %) at 10 bar. Adsorption of D-2 at 1 bar (77 K) is between 1.09 (at 1 bar) and 1.20(at < 100 mbar) times the H-2 values depending on the pressure, agreeing with the theoretical expectations. Gravimetric adsorption measurements of NO on HKUST-1 at 196 K (1 bar) gives a large adsorption capacity of similar to 9 mmol g(-1), which is significantly greater than any other adsorption capacity reported on a porous solid. At 298 K the adsorption capacity at 1 bar is just over 3 mmol g(-1). Infra red experiments show that the NO binds to the empty copper metal sites in HKUST-1. Chemiluminescence and platelet aggregometry experiments indicate that the amount of NO recovered on exposure of the resulting complex to water is enough to be biologically active, completely inhibiting platelet aggregation in platelet rich plasma.

Nanoporous metal organic framework materials for hydrogen storage

Hydrogen is expected to play an important role in future transportation as a promising alternative clean energy source to carbon-based fuels. One of the key challenges to commercialize hydrogen energy is to develop appropriate onboard hydrogen storage systems, capable of charging and discharging large quantities of hydrogen with fast enough kinetics to meet commercial requirements. Metal organic framework (MOF) is a new type of inorganic and organic hybrid nanoporous particulate materials. Its diverse networks can enhance hydrogen storage through tuning the structure and property of MOFs. The MOF materials so far developed adsorb hydrogen through weak dispersion interactions, which allow significant quantity of hydrogen to be stored at cryogenic temperatures with fast kinetics. Novel MOFs are being developed to strengthen the interactions between hydrogen and MOFs in order to store hydrogen under ambient conditions. This review surveys the development of such candidate materials, their performance and future research needs. (C) 2009 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

Adsorption properties of HKUST-1 toward hydrogen and other small molecules monitored by IR

Among microporous systems metal organic frameworks are considered promising materials for molecular adsorption. In this contribution infrared spectroscopy is successfully applied to highlight the positive role played by coordinatively unsaturated Cu2+ ions in HKUST-1, acting as specific interaction sites. A properly activated material, obtained after solvent removal, is characterized by a high fraction of coordinatively unsaturated Cu2+ ions acting as preferential adsorption sites that show specific activities towards some of the most common gaseous species (NO, CO2, CO, N-2 and H-2). From a temperature dependent IR study, it has been estimated that the H-2 adsorption energy is as high as 10 kJ mol(-1). A very complex spectral evolution has been observed upon lowering the temperature. A further peculiarity of this material is the fact that it promotes ortho-para conversion of the adsorbed H-2 species.

High sensitivity (1 ppm) hydrogen detection using an unconventional Pd/n-InP Schottky device

Hydrogen is detected using a Pd/n-InP Schottky diode in which the elongated, very thin Pd electrode is of greater resistance than the underlying semiconductor substrate. Four-probe measurements of the device resistance, as a function of hydrogen concentration, are made by contacting only the Pd electrode, with a sensitivity of 1 ppm being achieved. On hydrogen exposure the device resistance drops from an initial high value, characteristic of the Pd electrode alone, to a lower value due to a hydrogen-induced lowering of the Schottky barrier that opens up the InP substrate as a parallel current carrying channel.