Detection of the Elusive Triazane Molecule (N3H5) in the Gas Phase

We report the detection of triazane (N₃H₅) in the gas phase. Triazane is a higher order nitrogen hydride of ammonia (NH₃) and hydrazine (N₂H₄) of fundamental importance for the understanding of the stability of single‐bonded chains of nitrogen atoms and a potential key intermediate in hydrogen–nitrogen chemistry. The experimental results along with electronic‐structure calculations reveal that triazane presents a stable molecule with a nitrogen–nitrogen bond length that is a few picometers shorter than that of hydrazine and has a lifetime exceeding 6±2 μs at a sublimation temperature of 170 K. Triazane was synthesized through irradiation of ammonia ice with energetic electrons and was detected in the gas phase upon sublimation of the ice through soft vacuum ultraviolet (VUV) photoionization coupled with a reflectron‐time‐of‐flight mass spectrometer. Isotopic substitution experiments exploiting [D₃]‐ammonia ice confirmed the identification through the detection of its fully deuterated counterpart [D₅]‐triazane (N₃D₅).     

Syntheses,Crystal Structures,and Vibrational Properties of Two Lead Azide Halides PbN3X (X = Cl,Br)

Abstract: Two new lead azide halides, PbN₃X (X = Cl, Br), were precipitated from aqueous solutions and structurally analyzed by both X-ray single-crystal/powder diffraction and vibrational spectroscopy, in addition to density-functional theory calculations. PbN₃Cl crystallizes in the monoclinic space group P2₁/m (no. 11) with a = 5.5039(11), b = 4.3270(9), c = 7.6576(15) Å, β = 101.28(3)° and adopts a structure with alternating layers of cations and anions. PbN₃Br crystallizes in the orthorhombic space group Pnma (no. 62) with a = 7.9192(2), b = 4.2645(1), c = 11.1396(3) Å, and the cations and anions are alternating crosswise. Within PbN₃Cl, a Pb²⁺ cation is surrounded by five azide and four chloride anions whereas, in PbN₃Br, the coordination consists of five azide and three bromide anions. Both structures contain chain-like [Pb₂X₂]²⁺ units with Pb–Cl = 2.95–3.21 Å and Pb–Br = 3.03–3.38 Å, and the N₃^– dumbbell is capped by five Pb²⁺ with Pb–N = 2.79–2.91 Å in PbN₃Cl and with Pb–N = 2.69–2.89 Å in PbN₃Br. The infrared and Raman spectra show the typical frequencies of a slightly asymmetric N₃^– unit, in good agreement with DFT phonon calculation. Thermal analyses reveal PbN₃Cl to be stable up to 290 °C before it explodes to yield PbCl₂, metallic Pb, and gaseous N₂.     

Ammonothermal Synthesis,Crystal Structure,and Vibrational Properties of the Doubly Deprotonated Calcium Guanidinate,CaC(NH)3

We report the synthesis of the doubly deprotonated calcium guanidinate, CaC(NH)₃, from liquid ammonia and its crystal structure as determined from powder X-ray and neutron diffraction, and confirmed using CNH elemental analysis and infrared (IR) spectroscopy data. CaC(NH)₃ crystallizes in the hexagonal system with space group P6₃/m (no. 176) with Z = 2 and a = 5.2666(13) Å, c = 6.5881(6) Å and V = 158.25(4) ų. We also compare the structural similarities and differences of this phase with the isotypical strontium and ytterbium compounds.     

A Free-Radical Prompted Barrierless Gas-Phase Synthesis of Pentacene

A representative, low-temperature gas-phase reaction mechanism synthesizing polyacenes via ring annulation exemplified by the formation of pentacene (C₂₂H₁₄) along with its benzo[a]tetracene isomer (C₂₂H₁₄) is unraveled by probing the elementary reaction of the 2-tetracenyl radical (C₁₈H₁₁^.) with vinylacetylene (C₄H₄). The pathway to pentacene—a prototype polyacene and a fundamental molecular building block in graphenes, fullerenes, and carbon nanotubes—is facilitated by a barrierless, vinylacetylene mediated gas-phase process thus disputing conventional hypotheses that synthesis of polycyclic aromatic hydrocarbons (PAHs) solely proceeds at elevated temperatures. This low-temperature pathway can launch isomer-selective routes to aromatic structures through submerged reaction barriers, resonantly stabilized free-radical intermediates, and methodical ring annulation in deep space eventually changing our perception about the chemistry of carbon in our universe.     

Configurational forces in crystal plasticity: an analysis of the influence of grain boundaries on crack driving forces

The theory of configurational forces is applied to standard dissipative materials. As a computational example, the method is used to analyze a crystal plastic material law, which assumes flow in the basal and prismatic slip systems of a hexagonally close packed crystal. The material data mimic titanium. Numerical examples include the driving force on a crack interacting with a grain boundary. A simple algorithm is proposed to treat straight crack growth. It is shown how the configurational force at the crack tip is influenced by the presence of the grain boundary.     

Stable isotopes in river waters in the Tajik Pamirs: regional and temporal characteristics

The Gunt River catchment in the Central Pamirs is a representative of the headwater catchments of the Aral Sea Basin. It covers 14,000 km², spanning altitudes between 2000 and 6700 m a.s.l. In a monitoring network, water samples were taken at 30 sampling points every month and analysed for the stable water isotopes (¹⁸O and ²H). Our first results show δ²H values in the range from?131.2 to?94.9 ‰ and δ¹⁸O values from?18.0 to?14.0 ‰. The stable isotope patterns in the catchment seem to follow a systematic way, dominated by an altitude effect with a mean Δ δ²H=?3.6 ‰/100 m. The observed seasonal variations can be explained by geographical aspects such as the influence of different wind systems as well as melting processes.     

13C discriminations of Pinus sylvestris vs. Pinus ponderosa at a dry site in Brandenburg (eastern Germany): 100-year growth comparison

The carbon isotope composition (δ¹³C, ‰) and discrimination (Δ, ‰) of old grown North American Pinus ponderosa Dougl. Ex P. et C. Laws. and European Pinus sylvestris L. were determined using trees grown under almost identical growing conditions in a mixed stand in Bralitz, Northeast Germany. Single-tree δ¹³C analyses of tree-ring cellulose of both species were carried out at a yearly resolution for the period 1901–2001 and the results compared with growth (basal area increment). Annual mean δ¹³C values for P. ponderosa ranged from?21.6 ‰ to?25.2 ‰ and for P. sylvestris from?21.4 ‰ to?24.4 ‰. Accordingly, ¹³C discrimination (Δ) showed higher values for P. ponderosa throughout the investigation period. Five characteristic periods of Δ were identified for both the tree species, reflecting positive and negative influences of environmental factors. Good growing conditions such as after-thinning events had a positive effect on Δ, reflecting higher values, while poor conditions like aridity and air pollution had a negative influence, reflecting lower values. The dynamics of Δ were likewise reflected in the growth (basal area increment, BAI). Higher ¹³C discrimination values of P. ponderosa led to higher BAIs of P. ponderosa in comparison with P. sylvestris. Correlation function analyses confirmed that P. sylvestris was more dependent on precipitation than P. ponderosa, which showed a closer relationship with temperature. The results confirm that under predominantly dry growing conditions, P. ponderosa showed better growth performance than P. sylvestris, indicating better common intrinsic water-use efficiency and, therefore, higher rates of net photosynthesis at a given transpiration. In view of the prospect of climate change, the results are very significant for assessing both trees’ physiological properties and, hence, their potential for coping with future growing conditions.     

First field application of a thermal desorption resonance-enhanced multiphoton-ionisation single particle time-of-flight mass spectrometer for the on-line detection of particle-bound polycyclic aromatic hydrocarbons

The on-line analysis of single aerosol particles with mass spectrometrical methods is an important tool for the investigation of aerosols. Often, a single laser pulse is used for one-step laser desorption/ionisation of aerosol particles. Resulting ions are detected with time-of-flight mass spectrometry. With this method, the detection of inorganic compounds is possible. The detection of more fragile organic compounds and carbon clusters can be accomplished by separating the desorption and the ionisation in two steps, e.g. by using two laser pulses. A further method is, using a heated metal surface for thermal desorption of aerosol particles. If an ultraviolet laser is used for ionisation, a selective ionisation of polycyclic aromatic hydrocarbons (PAH) and alkylated PAH is possible via a resonance-enhanced multiphoton-ionisation process. Laser velocimetry allows individual laser triggering for single particles and additionally delivers information on aerodynamic particle diameters. It was shown that particles deriving from different combustion sources can be differentiated according to their PAH patterns. For example, retene, a C₄-alkylated phenanthrene derivative, is a marker for the combustion of coniferous wood. In this paper, the first field application of a thermal desorption resonance-enhanced multiphoton-ionisation single particle time-of-flight mass spectrometer during a measurement campaign in Augsburg, Germany in winter 2010 is presented. Larger PAH-containing particles (i.e. with aerodynamic diameters larger than 1 μm), which are suspected to be originated by re-suspension processes of agglomerated material, were in the focus of the investigation. Due to the low concentration of these particles, an on-line virtual impactor enrichment system was used. The detection of particle-bound PAH in ambient particles in this larger size region was possible and in addition, retene could be detected on several particles, which allows to identify wood combustion as generic source of these particles. The observed diurnal distribution of these larger particles, however, support the origin by traffic induced re-suspension of sedimented/agglomerated material.     

Phase-resolved real-time breath analysis during exercise by means of smart processing of PTR-MS data

Separation of inspiratory, mixed expired and alveolar air is indispensable for reliable analysis of VOC breath biomarkers. Time resolution of direct mass spectrometers often is not sufficient to reliably resolve the phases of a breathing cycle. To realise fast on-line breath monitoring by means of direct MS utilising low-fragmentation soft ionisation, a data processing algorithm was developed to identify inspiratory and alveolar phases from MS data without any additional equipment. To test the algorithm selected breath biomarkers (acetone, isoprene, acetaldehyde and hexanal) were determined by means of quadrupole proton transfer reaction mass spectrometry (PTR-MS) in seven healthy volunteers during exercise on a stationary bicycle. The results were compared to an off-line reference method consisting of controlled alveolar breath sampling in Tedlar® bags, preconcentration by solid-phase micro extraction (SPME), separation and identification by GC-MS. Based on the data processing method, quantitative attribution of biomarkers to inspiratory, alveolar and mixed expiratory phases was possible at any time during the experiment, even under respiratory rates up to 60/min. Alveolar concentrations of the breath markers, measured by PTR-MS ranged from 130 to 2,600 ppb (acetone), 10 to 540 ppb (isoprene), 2 to 31 ppb (acetaldehyde), whereas the concentrations of hexanal were always below the limit of detection (LOD) of 3 ppb. There was good correlation between on-line PTR-MS and SPME-GC-MS measurements during phases with stable physiological parameters but results diverged during rapid changes of heart rate and minute ventilation. This clearly demonstrates the benefits of breath-resolved MS for fast on-line monitoring of exhaled VOCs.

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Figure Experimental setup showing bicycle ergometer and analytical pathways: Right side PTR-MS: identification of respiratory phases by means of the new algorithm. Left side: confirmation of PTR-MS data for exhaled isoprene by means of GC-MS analysis

     

Flexible and hydrophobic Zn-based metal-organic framework

A zinc-based metal-organic framework Zn(2)(adb)(2)(dabco)·4.5 DMF (K) (DUT-30(Zn), DUT = Dresden University of Technology, adb = 9,10-anthracene dibenzoate, dabco =1,4-diazabicyclo[2.2.2]octane, DMF = N,N-dimethylformamide) was synthesized using a solvothermal route. This MOF exhibits six crystallographic guest dependent phases. Two of them were characterized via single crystal X-ray analysis. The as-synthesized phase K crystallizes in the orthorhombic space group Fmmm, with a = 9.6349(9), b = 26.235(3), and c = 28.821(4) ? and consists of two interpenetrated pillar-layer networks with pcu topology. When the substance loses 0.5 DMF molecules per formula unit, a phase transition from the kinetic phase K to a thermodynamic phase T occurs. Zn(2)(adb)(2)(dabco)·4 DMF (T) crystallizes in the tetragonal space group I4/mmm, with a = 19.5316(8) and c = 9.6779(3) ?. During the evacuation the DUT-30(Zn) undergoes again the structural transformation to A. The activated compound A shows the gate pressure effect in the low pressure region of nitrogen physisorption isotherm and has a BET surface area of 960 m(2 )g(-1) and a specific pore volume of 0.43 cm(3) g(-1). Furthermore, DUT-30(Zn) exhibits a hydrogen storage capacity of 1.12 wt % at 1 bar, a CO(2) uptake of 200 cm(3) g(-1) at -78 °C and 0.9 bar, and a n-butane uptake of 3.0 mmol·g(-1) at 20 °C. The N(2) adsorption process was monitored in situ via X-ray powder diffraction using synchrotron radiation. A low temperature induced transformation of phase A to phase V could be observed if the compound was cooled under vacuum to -196 °C. A further crystalline phase N could be identified if the framework was filled with nitrogen at -196 °C. Additionally, the treatment of activated phase A with water leads to the new phase W.