Neutral Nitrogen Atoms Research Articles

INNER-SHELL PHOTOIONIZATION STUDIES OF NEUTRAL ATOMIC NITROGEN

ABSTRACT Inner-shell ionization of a 1s electron by either photons or electrons is important for X-ray photoionized objects such as active galactic nuclei and electron-ionized sources such as supernova remnants. Modeling and interpreting observations of such objects requires accurate predictions for the charge state distribution (CSD), which results as the 1s-hole system stabilizes. Due to the complexity of the complete stabilization process, few modern calculations exist and the community currently relies on 40-year-old atomic data. Here, we present a combined experimental and theoretical study for inner-shell photoionization of neutral atomic nitrogen for photon energies of 403–475 eV. Results are reported for the total ion yield cross section, for the branching ratios for formation of N+, N 2 + ?> , and N 3 + ?> , and for the average charge state. We find significant differences when comparing to the data currently available to the astrophysics community. For example, while the branching ratio to N 2 + ?> is somewhat reduced, that for N+ is greatly increased, and that to N 3 + ?> , which was predicted to be zero, grows to ≈ 10 % ?> at the higher photon energies studied. This work demonstrates some of the shortcomings in the theoretical CSD data base for inner-shell ionization and points the way for the improvements needed to more reliably model the role of inner-shell ionization of cosmic plasmas.

Single-molecule imaging of activated nitrogen adsorption on individual manganese phthalocyanine.

An atomic-scale understanding of gas adsorption mechanisms on metal-porphyrins or metal-phthalocyanines is essential for their practical application in biological processes, gas sensing, and catalysis. Intensive research efforts have been devoted to the study of coordinative bonding with relatively active small molecules such as CO, NO, NH3, O2, and H2. However, the binding of single nitrogen atoms has never been addressed, which is both of fundamental interest and indeed essential for revealing the elementary chemical binding mechanism in nitrogen reduction processes. Here, we present a simple model system to investigate, at the single-molecule level, the binding of activated nitrogen species on the single Mn atom contained within the manganese phthalocyanine (MnPc) molecule supported on an inert graphite surface. Through the combination of in situ low-temperature scanning tunneling microscopy, scanning tunneling spectroscopy, ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, and density functional theory calculations, the active site and the binding configuration between the activated nitrogen species (neutral nitrogen atom) and the Mn center of MnPc are investigated at the atomic scale.

Temporally and spatially resolved plasma spectroscopy in pulsed laser deposition of ultra-thin boron nitride films

Physical vapor deposition (PVD) has recently been investigated as a viable, alternative growth technique for two-dimensional materials with multiple benefits over other vapor deposition synthesis methods. The high kinetic energies and chemical reactivities of the condensing species formed from PVD processes can facilitate growth over large areas and at reduced substrate temperatures. In this study, chemistry, kinetic energies, time of flight data, and spatial distributions within a PVD plasma plume ablated from a boron nitride (BN) target by a KrF laser at different pressures of nitrogen gas were investigated. Time resolved spectroscopy and wavelength specific imaging were used to identify and track atomic neutral and ionized species including B+, B*, N+, N*, and molecular species including N2*, N2+, and BN. Formation and decay of these species formed both from ablation of the target and from interactions with the background gas were investigated and provided insights into fundamental growth mechanisms of continuous, amorphous boron nitride thin films. The correlation of the plasma diagnostic results with film chemical composition and thickness uniformity studies helped to identify that a predominant mechanism for BN film formation is condensation surface recombination of boron ions and neutral atomic nitrogen species. These species arrive nearly simultaneously to the substrate location, and BN formation occurs microseconds before arrival of majority of N+ ions generated by plume collisions with background molecular nitrogen. The energetic nature and extended dwelling time of incident N+ ions at the substrate location was found to negatively impact resulting BN film stoichiometry and thickness. Growth of stoichiometric films was optimized at enriched concentrations of ionized boron and neutral atomic nitrogen in plasma near the condensation surface, providing few nanometer thick films with 1:1 BN stoichiometry and good thicknesses uniformity over macroscopic areas.

Group 1 Complexes of an (Amido-amino)silane and Their Use in the Synthesis of the Bi(III) Amide, Bi(Me2Si{NAr}{N(H)Ar})Cl2 (Ar = 2,6-i-Pr2C6H3)

The synthesis of sodium and potassium salts of the monoanionic, (amido-amino)silane, [Me2Si{NAr}{N(H)Ar}]− (Ar = 2,6-i-Pr2C6H3), and their use as ligand transfer reagents to bismuth are presented. Initial attempts to form Li(Me2Si{NAr}{N(H)Ar) (2) using equimolar amounts of n-BuLi and the neutral compound Me2Si{N(H)Ar}2 (1) gave mixtures of the unreacted di(amino)silane and the known dianion, Li2(Me2Si{NAr}2), on workup. Reaction of 1 with NaH and KH, however, afforded the desired anion in the soluble, crystalline compounds Na(Me2Si{NAr}{N(H)Ar})(THF)3 (3(THF)3) and K(Me2Si{NAr}{N(H)Ar}) (4). The crystal structure of 4 shows a cyclic hexamer [4]6, containing intra- and intermolecular K···π-aryl interactions. Reaction of 3 or 4 with BiCl3 demonstrated that both compounds are effective ligand transfer reagents, affording the bismuth compound Bi(Me2Si{NAr}{N(H)Ar})Cl2 (5). The crystal structure of 5 showed a primary monodentate κ1-N-bonding mode for the ligand with a close Bi···N contact to the neutral amino nitrogen atom. Long range Bi···Cl interactions associate these molecules into dimers, [5]2.

Trend of Nitriding on Chromium-Molybdenum Steel via Low Temperature Screen Plasma Technology

Low temperature screen plasma technology, a high plasma density, through using a low energy supply, shows excellent effects on a low alloy chromium-molybdenum steel for plastic molds because it does not show a compound layer and a high surface hardness without a deterioration in matrix hardness. For interest about hardening depth, both the screen plasma nitriding and plasma nitro-carburizing processes were tested including nitrogen, hydrogen and a methane mixed gas environmental at 653 K, 713 K. The optical emission spectroscopy (OES) has been analyzed during screen plasma nitriding (SPN) and a nitro-carburizing process (SPNC) was proceeded at 713 K and the same pressure. I find it difficult to dissociate nitrogen molecules perfectly with neutral nitrogen atoms via the DC-plasma nitriding process. Therefore, the SPN and SPNC process have shown a high density of plasma species even though low temperature plasma conditions have a high peak intensity of Hβ and Hγ in the results of the analysis by OES. The hardness value was measured with the micro-Vickers hardness tester after the SPN, SPNC process and the chemical composition of nitriding layers were traced by GDOES. The screen nitriding layer via the screen plasma technology has shown excellent properties with a thickness depth of about 850 ~ 900 HV without the deterioration of matrix hardness value.

Radiative lifetime measurement of excited neutral nitrogen atoms by time resolved laser-induced breakdown spectroscopy

Lifetimes of the excited 2P2 (3P) 3p 4S3/2 level of a nitrogen atom for transitions to lower states were measured by time-resolved laser-induced breakdown spectroscopy.

Luminescence lifetimes of neutral nitrogen-vacancy centres in synthetic diamond containing nitrogen

The decay time of luminescence from neutral nitrogen-vacancy (NV 0) centres in synthetic diamond is reported. The intrinsic luminescence lifetime of NV 0 is measured as τr = 19 ± 2 ns. Neutral substitutional nitrogen atoms are shown to quench luminescence from NV0 by dipole–dipole resonant energy transfer at a rate such that the transfer time would equal τr if one atom was ∼3 nm from the NV0. In chemical-vapour-deposited diamonds grown with a small nitrogen content, that are brown as a result of vacancy-cluster defects, the decay time of NV0 equals τr in the as-grown material. However, after annealing at ≥1700 °C to remove the brown colour, luminescence from the NV0 centres is severely quenched. This effect is suggested to be a result of the destruction of NV0 centres and the creation of new NV0 centres localized in vacancy-rich regions of the crystals.

Orientation of doubly excited states in N2

We have measured the total fluorescent intensity and circular polarization of light emitted in $3p{\phantom{\rule{0.16em}{0ex}}}^{4}\phantom{\rule{-0.16em}{0ex}}{P}^{o}\ensuremath{\rightarrow}3s{\phantom{\rule{0.16em}{0ex}}}^{4}\phantom{\rule{-0.16em}{0ex}}P$ transitions of excited neutral nitrogen atoms created by the photofragmentation of the N${}_{2}$ molecule with circularly polarized light having energies between 21 and 26 eV. The intensity measurements show the effect of predissociation of the ${\text{N}}_{2}$ Rydberg series $R$($C$) ${}^{1}\phantom{\rule{-0.16em}{0ex}}{\ensuremath{\Sigma}}_{u}^{+}$ states by non-Rydberg doubly excited resonances (NRDERs), while nonzero values of circular polarization allow us to unambiguously identify the presence of a directly excited NRDER with ${}^{1}\phantom{\rule{-0.16em}{0ex}}{\ensuremath{\Pi}}_{u}$ symmetry in this energy range.

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K-Shell X-Ray Spectroscopy of Atomic Nitrogen

Absolute K-shell photoionization cross sections for atomic nitrogen have been obtained from both experiment and state-of-the-art theoretical techniques. Because of the difficulty of creating a target of neutral atomic nitrogen, no high-resolution K-edge spectroscopy measurements have been reported for this important atom. Interplay between theory and experiment enabled identification and characterization of the strong 1s → np resonance features throughout the threshold region. An experimental value of 409.64±0.02 eV was determined for the K-shell binding energy.

Temperature dependence of Raman scattering from 4H-SiC with hexagonal defects

Noncontact temperature measurements based on Raman scattering were performed on 4H-SiC with hexagonal defects. These measurements show that the four-phonon process makes a greater contribution to the E2(TO) mode than to the E1(TO) mode. The longer lifetimes of E2(TO) and E1(TO) phonons in hexagonal defects demonstrate that there are fewer possible decay channels than in the defect free zone. The absence of electronic Raman peaks in the hexagonal defects suggests that hexagonal defects seriously limit the uniformity of the nitrogen distribution. The intensity of electronic Raman spectra is related to the density of neutral nitrogen atoms.

Metal complexes of an amine bisphenol with a thiophene side-arm

Dioxomolybdenum(VI) and oxotungsten(VI) complexes with a new amine bisphenol ligand (H2L) are reported. The ligand which carries a neutral nitrogen atom, two phenolic oxygen atoms and a thiophene side-arm was synthesized by a simple one-pot Mannich reaction. Further reaction with [MoO2(acac)2] yielded a monomeric molybdenum complex [MoO2(L)(MeOH)] (2a) or a dimeric complex [Mo2O2(μ-O)2(L)2] (2b), depending on the reaction conditions. The reaction with a tungsten trisglycolate [W(eg)3] led to the formation of a monomeric compound [WO(eg)(L)] (3). In these complexes, the potentially tetradentate amine bisphenolate dianion coordinates as a tridentate O,N,O donor while the sulfur side-arm donor remains intact. The solid-state structure of 2a was investigated by X-ray crystallography.

Comparison of TALIF and catalytic probes for the determination of nitrogen atom density in a nitrogen plasma afterglow

The density of neutral nitrogen atoms in a glass reactor was measured by two absolute methods: two-photon absorption laser induced fluorescence (TALIF) and catalytic probes. The source of N atoms was nitrogen plasma created in a quartz tube by surfatron microwave generator operating at 2.45 GHz and adjustable output power up to 300 W. The TALIF measurements were performed using a dye laser which was pumped by a YAG laser. At the exit of the dye laser, the beam frequency was doubled through a KDP crystal and then mixed in a BBO crystal. The wavelength of the output laser beam was chosen at 206.65 nm so two-photon absorption was suitable to excite nitrogen atoms from the ground state to the 5d 2D state. Absolute N density was determined by using calibration with krypton. Simultaneously, the N atom density was measured with a fiber optics catalytic probe (FOCP) with a well-activated iron catalytic tip. Measurements were performed by both methods at nitrogen flows between 0.2 and 2 l min−1, and discharge powers between 60 and 300 W. At rather high nitrogen flows, the N atom density increased monotonically with increasing discharge power, while at lower flow saturation was observed. TALIF showed somewhat higher values than FOCP which was attributed to the accuracy of both methods. The main advantage of TALIF is a broader detection range, while FOCP is an extremely simple and inexpensive technique.

Bis(3-methyl-2-pyridyl)ditelluride and pyridyl tellurolate complexes of zinc, cadmium, mercury: Synthesis, characterization and their conversion to metal telluride nanoparticles

Treatment of an acetonitrile solution of metal chloride with bis(3-methyl-2-pyridyl)ditelluride, [Te(2)(pyMe)(2)], in the same solvent yielded complexes of composition [MCl(2){Te(2)(pyMe)(2)}] (M = Zn or Cd) whereas reactions of [MCl(2)(tmeda)] with NaTepyR (R = H or Me) gave tellurolate complexes of the general formula [M(TepyR)(2)] (M = Cd or Hg). When the cadmium complex [Cd(Tepy)(2)] was crystallized in the presence of excess tmeda, [Cd(Tepy)(2)(tmeda)] was formed exclusively. These complexes were characterized by elemental analyses, uv-vis, (1)H NMR data. The crystal structures of [ZnCl(2){Te(2)(pyMe)(2)}] and [Cd(Tepy)(2)(tmeda)] were established by single crystal X-ray diffraction. In the former zinc is coordinated to nitrogen atoms of the pyridyl group, while in the latter the coordination environment around tetrahedral cadmium is defined by the two neutral nitrogen atoms of tmeda, and two pyridyl tellurolate ligands. Thermal behavior of some of these complexes was studied by thermogravimetric analysis. Pyrolysis of [M(Tepy)(2)] in a furnace or in coordinating solvents such as hexadecylamine/tri-n-octylphosphine oxide (HDA/TOPO) at 350 and 160 degrees C, respectively gave MTe nanoparticles, which were characterized by uv-vis, photoluminiscence, XRD, EDAX and TEM.

Modification of PET surface by nitrogen plasma treatment

A study on nitrogen plasma functionalization of polyethyleneterephthalate (PET) is presented. The samples of PET foils were exposed to a weakly ionized, highly dissociated RF nitrogen plasma with an electron temperature of 5 eV, a density of positive ions of the order of 1015 m-3 and a density of neutral nitrogen atoms of the order of 1021 m-3. The pressure was 75 Pa and a discharge power was 200 W. The PET-samples were exposed to plasma and its afterglow from 3 s to 10 s. After the treatment the surface was analysed by XPS (X-ray photoelectron spectroscopy). XPS results showed appearance of new functional groups like amine and amide.

Hyperthermal (1–100eV) nitrogen ion scattering damage to D-ribose and 2-deoxy-D-ribose films

Highly charged heavy ion traversal of a biological medium can produce energetic secondary fragment ions. These fragment ions can in turn cause collisional and reactive scattering damage to DNA. Here we report hyperthermal (1-100 eV) scattering of one such fragment ion (N(+)) from biologically relevant sugar molecules D-ribose and 2-deoxy-D-ribose condensed on polycrystalline Pt substrate. The results indicate that N(+) ion scattering at kinetic energies down to 10 eV induces effective decomposition of both sugar molecules and leads to the desorption of abundant cation and anion fragments. Use of isotope-labeled molecules (5-(13)C D-ribose and 1-D D-ribose) partly reveals some site specificity of the fragment origin. Several scattering reactions are also observed. Both ionic and neutral nitrogen atoms abstract carbon from the molecules to form CN(-) anion at energies down to approximately 5 eV. N(+) ions also abstract hydrogen from hydroxyl groups of the molecules to form NH(-) and NH(2) (-) anions. A fraction of OO(-) fragments abstract hydrogen to form OH(-). The formation of H(3)O(+) ions also involves hydrogen abstraction as well as intramolecular proton transfer. These findings suggest a variety of severe damaging pathways to DNA molecules which occur on the picosecond time scale following heavy ion irradiation of a cell, and prior to the late diffusion-limited homogeneous chemical processes.

Imido, amino and amido coordination of diaminouracil to rhenium(V)

Reaction of equimolar quantities of cis-[ReO2I(PPh3)2] with 5,6-diamino-1,3-dimethyl-2,4-dioxopyrimidine (H2ddd) in acetonitrile led to the formation of [Re(ddd)(Hddd)I(PPh3)2] (ReO4) (1). A single-crystal X-ray crystal structure shows that ddd is coordinated as a monodentate through the doubly deprotonated amino nitrogen and is therefore present as an imide. The chelate Hddd is coordinated as a bidentate via a neutral amino nitrogen atom, trans to the imido nitrogen, and a singly deprotonated amido nitrogen atom, trans to the iodide.

Copper(II) Complexes of the Tetraazamacrocyclic Tertiary Amide Ligand Alanyl‐Cyclam

AbstractHydrogen bonding to the electrically neutral tertiary carboxamide nitrogen atom of peptidyl‐prolyl groups is known to facilitate the C–N bond rotation during peptide and protein folding. Since metal complexes with nitrogen‐coordinated tertiary amide ligands are formally analogous, they may be used to model this so‐called electrophilic activation. In this paper we report on the synthesis of a monoacylated cyclam complex, [(Boc‐Ala‐cyclam)Cu](CF3SO3)2 (8; Boc: tert‐butyloxycarbonyl, Ala: alanine, cyclam: 1,4,8,11‐tetraazacyclotetradecane). It contains a fully sp3‐hybridized metal‐bound amide nitrogen atom. The resonance is completely cancelled and the observed C–N distance of 147 pm is consistent with a single bond. These features are exceptional among Werner‐type complexes and define the maximal possible electrophilic distortion of an amide bond.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Copper(II) Complexes of the Tetraazamacrocyclic Tertiary Amide Ligand Alanyl‐Cyclam (Eur. J. Inorg. Chem. 12/2006)

AbstractThe cover picture shows the structural changes in tertiary carboxamide groups induced by coordination of the electrically neutral nitrogen atom to a metal ion. Changing the hybridization from sp2 to sp3 results in pyramidalization at the nitrogen atom. This is expressed by the parameter χN which ranges from 0° (sp2) to 60° (sp3). Werner complexes with relatively weak M–Namide bonds are known with χN values between 30° and 47°. Full sp3 hybridization with complete lifting of the resonance and a value of 58° for χN is achieved in a complex in which the copper(II) ion is in the centre of the tetraazamacrocyclic amide ligand tert‐butoxycarbonyl‐alanyl‐cyclam. Details of its synthesis and structure are discussed in the article by R. Alsfasser et al. on p. 2357 ff.

The chemistry of nitrogen coordinated tertiary carboxamides: a spectroscopic study on bis(picolyl)amidecopper(ii) complexes

Metal coordination of the electrically neutral nitrogen atom of a tertiary carboxamide reduces the barrier to C-N-bond rotation and activates the amide towards methanolysis. X-Ray crystallographic studies indicate that this reactivity is correlated to a lifting of the amide resonance structure and concurrent pyramidalization at nitrogen. However, mechanistic data in solution have not been obtained. It became evident that structural mobility is characteristic of the complexes and the crystallographic data do not fully account for relevant reactive species. In this report we summarize IR, UV-vis, and EPR spectra of amide nitrogen coordinated bis(picolyl)amide complexes with copper(II) triflate and copper(II) chloride. A comparison between spectra sampled in the aprotic solvents dichloromethane and acetonitrile, as well as under methanolysis conditions reveals the nature of several species formed in solution. The key reactions are (I) ligand exchange involving either CH3CN or CH3OH, or, in IR experiments, bromide ions from KBr, (II) coordination-dissociation equilibria involving the urethane protecting groups of amino acid substituted ligands Boc-Xaa-bpa (Boc = tert-butoxycarbonyl, Xaa = glycine, alanine, and leucine, respectively, bpa = bis(picolyl)amine), (III) dissociation of a chloro ligand from LCuCl2 complexes and formation of square-pyramidal complex cations [LCuCl]+, and finally (IV) complete dissociation of the polydentate tertiary amide ligand to produce free copper ions in solution. Taken together, the results provide a fairly detailed qualitative picture of the processes which accompany the amide bond methanolysis.