- 308 nm laser photodissociation of HN3 adsorbed on Si(111)-7×7
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The photodissociation of HN3 adsorbed on Si(111)-7×7 at 308 nm was investigated using HREELS and XPS. Species such as NHx N2, and N3 were identified on the surface with comparable concentrations after the irradiation with 1×1020 photons of a 10 L HN3 dosed Si(111) surface. The N3 species showed two stretching modes at 178 and 255 meV, while that of the N2 appeared at 206 meV in HREELS. The formation of these products was also corroborated by the corresponding XPS results. Further laser irradiation caused the dissociation and partial desorption of the adsorbates with NHx left on the surface. Annealing the post-irradiated sample to 500 and 800 K resulted in the breaking of the NH bond and the desorption of the H-species, while the atomic N remained on the surface forming silicon nitride. The possibility of using HN3 for laser-induced chemical vapor deposition of Si3 N4 and group-III nitrides at low temperatures is suggested.
- Bu, Y.,Lin, M. C.
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- Photodecomposition of cis-azidoamminebis(2,4-pentanedionato)cobalt(III). The photoactive state
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The photodecomposition of cis-Co(acac)2N3NH3 (acac = 2,4-pentanedionate) occurs with the formation of Co(acac)2 and azide radicals. This reaction has been effected with the use of exciting radiations throughout the 250-580-nm region, and in the 250-470-nm region the quantum efficiency for this reaction is surprisingly wavelength independent. Examination of the optical spectra of Co(acac)2N3NH3 and Co(acac)3 and the respective optical electronegativities of the azide and 2,4-pentanedionate ligands suggests that photooxidation of the 2,4-pentanedionato group should be favored over that of the azido group. Yet photooxidation of the azido group is the only observed reaction. This observation, the relative constancy of the quantum efficiency, and the energy of the threshold for the onset of redox photodecomposition ((21.3-17.2) × 103 cm-1) suggest that the photoactive state is a triplet charge-transfer state involving the azido group. The photoreaction has an apparent activation energy of 11.7 kcal/mol, and solvent assistance in the loss of the azide radical is implicated.
- Reed, James L.
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- Role of Azide Concentration in Pulse Radiolysis Studies of Oxidation: 3,4-Dihydroxyphenylalanine
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The radiolysis of aqueous solutions of 3,4-dihydroxyphenylalanine (dopa) using N3 as a one-electron oxidant leads to the formation of dopasemiquinone and, successively, dopaquinone and dopachrome.It is now shown that under pH conditions where significant protonation of N3(1-) to HN3 occurs, dopachrome formation is supressed, probably due predominantly to addition of HN3 to dopaquinone.The possibility of such nucleophilic reactions occuring needs to be considered in studies of quinone intermediates generated using N3 as oxidant.
- Lambert, Chris,Truscott, T. George,Land, Edward J.,Riley, Patrick A.
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- Design and characterization of a synthetic electron-transfer protein
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A 30-residue polypeptide [H21(30-mer)] with the sequence Ac-K(IEALEGK)2(IEALEHK)-(IEALEGK)G-NH2 was synthesized. The circular dichroism (CD) spectrum of the peptide shows minima at 208 and 222 nm and θ222/θ208 = 1.06, which indicates the formation of a self-assembled coiled-coil when dissolved in aqueous solution. The concentration dependence of the CD data can be fit to an expression that describes a two-state monomer - dimer equilibrium for the apopeptide(K(d) = 1.5 ± 0.4 μM and θ(max) = -23 800 ± 130 deg cm2 dmol-1), showing that it has a maximum helicity of 69%. A [MTSL-C21(30-mer)] dimer was also prepared in which MTSL is the thiol-specific nitroxide spin label 1-oxyl-2,2,5,5-tetramethyl-Δ3-pyrroline-3-methyl-methanethiosulfonate attached to C21 of the 30-mer. Fourier deconvolution analysis of the dipolar line broadening of the electron paramagnetic resonance (EPR) spectrum yields a measure of the interchain Cα - Cα distance of 13.5 ± 0.9 A at position 21 of the coiled-coil, which is nearly identical to those distances observed for the isostructural family of bZip proteins. Two metallohomodimers, [Ru(trpy)(bpy)-H21(30-mer)]2 and [Ru(NH3)5-H21(30-mer)]2, in which the ruthenium complexes were coordinated with the H21 site of the 30-mer, were prepared. Sodium dodecyl sulfate - polyacrylamide gel electrophoresis (SDS - PAGE), chemical cross-linking studies, and analytical ultracentrifugation show that the peptides exist as a dimeric coiled-coil with a molecular weight of ~ 7.5 kDa. The electron transfer (ET) heterodimer, [Ru(trpy)(bpy)-H21 (30-mer)]/ [Ru(NH3)5-H21(30-mer)], was prepared, and molecular modeling shows that the two metal complexes are separated by a metal-to-metal distance of ~ 24 A across the noncovalent peptide interface. Pulse radiolysis was used to measure an ET rate constant of k(et) = 380 ± 80 s-1 for the intracomplex electron transfer (ΔG°= -1.11 eV) from the Ru(II)(NH3)5-H21 donor to the Ru(III)(trpy)(bpy)-H21 acceptor. The value for k(et) falls within the range reported for modified proteins over comparable distances and supersedes the one reported in an earlier communication.
- Kornilova, Anna Y.,Wishart, James F.,Xiao, Wenzhong,Lasey, Robin C.,Fedorova, Anna,Shin, Yeon-Kyun,Ogawa, Michael Y.
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- Engineered Regulon to Enable Autonomous Azide Ion Biosensing, Recombinant Protein Production, and in Vivo Glycoengineering
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Detection of azide-tagged biomolecules (e.g., azido sugars) inside living cells using "click"chemistry has been revolutionary to the field of chemical biology. However, we currently still lack suitable synthetic biology tools to autonomously and rapidly d
- Bandi, Chandra Kanth,Skalenko, Kyle S.,Agrawal, Ayushi,Sivaneri, Neelan,Thiry, Margaux,Chundawat, Shishir P. S.
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- The Redox Potential of the Azide/Azidyl Couple
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Pulse radiolysis experiments were carried out with neutral aqueous solutions containing azide with iodide, bromide, or thiocyanate to examine possible one-electron transfer rates and equilibria involving the N3 radical/N3(1-) couple.The N3 radical was found to oxidize I(1-) with a rate constant of 4.5E8/M*s.No reaction was observed between I2(1-) radical and N3(1-).With Br(1-), however, the system reached equilibrium, Br2(1-) radical + N3(1-)->f = 4.0E8/M*s and kr = 7.3E3/M2*s.From the equilibrium constant K = 5.5E4 M and the redox potential E(Br2(1-) radical/2Br(1-)) = 1.63 V we calculated E(N3 radical/N3(1-)) = 1.35 +/- 0.02 V vs.NHE.Cyclic voltammetry experiments with N3(1-) showed a single peak on the anodic scan and no peak on the cathodic scan due to the rapid decay of the N3 radicals.From the dependence of peak potential on scan rate we derived E1/2 for the N3 radical/N3(1-) couple, 1.32 /- 0.03 V vs.NHE.
- Alfassi, Zeev B.,Harriman, Anthony,Huie, Robert E.,Mosseri, S.,Neta, P.
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- Time resolved resonance Raman observation of the extreme protonation forms of a radical zwitterion in water
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The reactions of the aqueous proton with the zwitterionic p-aminophenoxyl radical in strongly basic to extremely acidic aqueous solutions have been investigated using time-resolved resonance Raman spectroscopy. The dynamic stability of the different protonation forms of the radical, observed on the microsecond time scale in this work, has been achieved by controlling the proton exchange rate in water. In strongly acidic solutions we observe a rare ring-H+ bonded dication species, a key intermediate in the amine hydrolysis. The neutral p-aminophenoxyl radical undergoes NH2- deprotonation in strongly basic aqueous solutions, which has no analogues in closed-shell amines.
- Tripathi
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- Observation of N3 by Laser-Induced Fluorescence
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Gas-phase N3 was generated by the F + NH3 reaction and detected by using laser-induced fluorescence in a flow reactor.The and the excitations were investigated.Evidence was obtained for an upper-state lifetime of level or the smaller spin-orbit splitting in the level can be utilized for monitoring of N3 by the LIF technique using a monochromator to disperse the fluorescence.Very weak transitions were identified, and these could be useful for monitoring the laser-induced fluorescence of N3 with an interference filter.
- Beaman, R. A.,Nelson, T.,Richards, D. S.,Setser, D. W.
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- Photodissociation of HN3 at 248 nm and Longer Wavelength: A CASSCF Study
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In the present work, photodissociation of HN3 at 248 nm and longer wavelength is investigated with the complete active space SCF (CASSCF) molecular orbital method. The stationary points on the ground- and excited-state potential energy surfaces are fully optimized at the CASSCF level with cc-pVDZ and cc-pVTZ basis sets. The potential energy profiles, governing HN3 dissociation to NH + N2 and H + N3, are characterized with the multireference MP2 (CASPT2) algorithm. The pathways leading to different products are determined on the basis of the obtained potential energy surfaces of dissociation and their crossing points. A comparison is made among the present and previous theoretical results and experimental findings. The present study provides an insight into the mechanism of the UV photodissociation of HN3 at a wavelength range from 355 to 248 nm.
- Fang, Wei-Hai
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- Ultraviolet photodissociation dynamics of HN3: The H+N3 channel
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The H+N3(X 2Πg) channel in the ultraviolet photodissociation of HN3 has been studied at 248.3 and 193.3 nm using the high-n Rydberg H-atom time-of-flight technique. In 248.3 nm photodissociation, center-of-mass translational energy distribution reveals a propensity toward product translation (〈ftrans〉=0.71) and N3 bending and symmetric stretching excitation. An anisotropic product angular distribution (β≈-0.8) indicates a perpendicular electronic transition and rapid dissociation on the excited-state surface. H-N bond energy is estimated: D0(H-N3)≤88.7±0.5 kcal/mol. At 193.3 nm, 〈ftrans〉 is smaller and product angular distribution is energy-dependent, suggesting multiple dissociation pathways via different electronic states.
- Zhang, Jingsong,Xu, Kesheng,Amaral, Gabriel
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- Vibrational and Electronic Spectra of Matrix-Isolated N3. and N3(1-)
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N3. and N3(1-) were formed upon the bombardment of a N2 matrix with kiloelectronvolt-energy fast atoms and/or ions.The vibrational frequencies of N3. in the most stable site, ν2=472.7, ν3=1657.5, and ν1+ν3=2944.9 cm-1 as well as those in two other sites were obtained, and dissociation into N(2D) and N2(1Σg(+)) was observed upon 2Σu(+)g excitation of N3. at 272 nm.The ν3 vibrational frequencies of free and ion-paired N3(1-) in a nitrogen matrix are 2003.5 and 2077.8 cm-1, and their photodetachment thresholds in a mixed nitrogen-argon matrix (ca. 2:1) are 4.5 and 3.4 eV, respectively.The experimental frequencies are compared with the results of Hartree-Fock computations for N3. and N3(1-).The results of similar computations for N3(1+) agree with an extrapolation of the experimental frequencies from N3(1-) and N3. and suggest strongly a value near 1200 cm-1 for ν3.
- Tian, Rujiang,Facelli, Julio C.,Michl, Josef
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- A molecular beam study of the H + N3 reaction. Product NH internal state distribution and electronic state branching ratio
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The H + N3 -> NH(X3Σ-, a1Δ, b1Σ+) + N2 reaction has been studied in a molecular beam-gas scattering arrangement in order to determine the nascent product state distribution.The NH product in specific rovibronic/fine-structure states has been detected by laser fluorescence excitation.The relative cross sections for formation of various vibrational levels in the a1Δ electronic state were determined to equal 1:1.0 +/- 0.3:1.4 +/- 0.3:1.5 for v = 0 through 3, inclusive, while the v = 0 to v = 1 population ratio in the X3Σ- state was found to be 1:0.015 +/- 0.003.The rotational distributions in all vibronic levels were found to be characterized by temperatures near 300 K, suggestive of relaxation of the nascent rotational distributions.By comparison of the populations of a specific pair of X3Σ- and a1Δ state levels and with summation over the derived rovibrational distributions, an electronic state branching ratio of 3.2 +/- 1.3 was obtained for the X3Σ- to a 1Δ electronic state branching ratio.An upper limit of 0.02 was also derived for the ratio of the b1Σ+ v = 0 to a1Δ v = 0 populations.These results are compared with NH fragment distributions observed in the photodissociation of HN3(X1A') and with our expectations based on our fragmentary knowledge of HN3 potential energy surfaces.
- Chen, Jing,Quinones, Edwin,Dagdigian, Paul J.
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- A novel Pt(iv) mono azido mono triazolato complex evolves azidyl radicals following irradiation with visible light
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The platinum(iv) azido complex trans,trans,trans-[PtIV(N3)2(OH)2(py)2] (1) undergoes cycloaddition with 1,4-diphenyl-2-butyne-1,4-dione (2) under mild, catalyst-free conditions, affording a number of mono and bis click products. The major mono click product (3) exists in MeCN as an equilibrium mixture between two species; 3a and 3b rapidly interconvert through nucleophilic attack of the axial Pt-OH group at the adjacent Ph-CO group. The kinetic and thermodynamic parameters for this interconversion have been measured by selective saturation-transfer NMR spectroscopic experiments and are consistent with cyclisation at the Pt centre. Complex 3b was also characterised by X-ray crystallography. Visible light irradiation (440-480 nm) of 3 in d3-MeCN produces azidyl radicals (N3), as demonstrated by EPR spin-trapping with DMPO; no generation of hydroxyl radicals was observed. 1H-195Pt HMBC NMR confirmed that the photoproducts were PtIV rather than PtII species, and HPLC was consistent with these being [3-N3]+ species; no facile photoejection of the triazolato ligand was observed, consistent with MS/MS fragmentation of 3. When 3 was irradiated in the presence of 5′-GMP, no 5′-GMP photoproducts were observed, suggesting that complex 3 is likely to exhibit significantly simplified biological activity (release of azidyl radicals but not DNA binding) compared with complex 1.
- Yao, Kezi,Bertran, Arnau,Morgan, Jacques,Hare, Samuel M.,Rees, Nicholas H.,Kenwright, Alan M.,Edkins, Katharina,Bowen, Alice M.,Farrer, Nicola J.
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supporting information
p. 6416 - 6420
(2019/05/24)
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- Reactions of laser-ablated osmium and ruthenium atoms with nitrogen. Matrix infrared spectra and density functional calculations of osmium and ruthenium nitrides and dinitrides
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Laser-ablated osmium and ruthenium atoms were reacted with nitrogen molecules; the products were isolated in solid argon and nitrogen and identified by infrared spectroscopy. Both MN and NMN nitrides are observed, and estimates for the triatomic bond angles are made using nitrogen and ruthenium isotopic data. The growth of NOsN on annealing in solid argon suggests that osmium atoms insert into the dinitrogen triple bond at cryogenic temperatures, allowing a lower limit of ~473 kJ/mol to be estimated for the average Os-N bond energy in NOsN. The force constants for MN and NMN (M= Fe, Ru, Os) were calculated using all available isotopic data; force constants increase moving down the metal group, and diatomic MN force constants are larger than those for the corresponding NMN triatomic molecules. DFT calculations for the ruthenium and osmium nitrides give reasonable agreement with experiment. Bonding analyses for these molecules show . that the M-N bonds are largely nonpolar with bond orders in the range 2.5-3.0. Several metal dinitrogen complexes are also observed and assignments are proposed.
- Citra, Angelo,Andrews, Lester
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p. 1152 - 1161
(2007/10/03)
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- One-electron reduction reactions of some inorganic nitrogen radicals in water
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The technique of pulse radiolysis and kinetic absorption spectrophotometry has been used to generate various inorganic nitrogen radicals and follow their one-electron reduction reactions. The method used is based on following the one-electron reduction of these free radicals (R*) by various electron donor compounds (DH) present in solution: the R* + DH → R- (or RH) + D* + H+. The efficiency of this reaction is usually monitored by observing the formation of the D* radicals at the wavelength of their absorption The efficiency of reduction of R* radicals is found to depend upon the known redox potentials (Eo1 at pH 7.0, 25°C) of the donor compounds. Typical titration curves are obtained and from the midpoint (50% electron transfer) the "kinetic potentials" Ek01 of the R* radicals can be derived. The Ek01 values for the one-electron reduction of the following inorganic nitrogen radicals have been determined: *N3 (≥+0.41V), *NH3+ (+0.55V), *NH2 (+0.20V), CH3*NH2+ (+0.06V), CH3*NH (-0.05V), *N2H4+ (+0.034V), *N2H3 (+0.20V), *NHOH (-0.40V), and *NHOCH3 (-0.45V). These values are based on the two-electron redox potentials of the donor compounds. The electron transfer kinetics leading to the formation of D* radicals' are determined and rate constants (≤6.0 × 109 M-1 sec-1) have been obtained. The implications of the results with regard to the reaction mechanism and kinetics of these inorganic nitrogen free radicals are discussed.
- Rao, Parinam S.,Metz, Helene N.,Wilson, David W.,Hayon, Elie M.
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p. 649 - 656
(2007/10/03)
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- Electron transfer between azide and chlorine dioxide: The effect of solvent barrier nonadditivity
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The reaction of chlorine dioxide with excess azide in aqueous media proceeds with complex kinetics and produces N2, N2O, NO3-, Cl-, and ClO2-. In the presence of the spin trap PBN, the reaction is much simpler, and the rate law is -d [ClO2]/dt = k1 [ClO2] [N3-] [PBN]/([PBN] + [ClO2-]k-1/k2), with k1 = 809 M-1 s-1 and k-1/k2 = 19.0 at 25 °C. The inferred mechanism implies that k1 is the rate constant of electron transfer between ClO2 and N3-, k-1 is the reverse rate constant (N3 with ClO2-), and k2 is the rate constant for reaction of N3 with PBN. A dramatically lower value for k1 of 0.62 M-1 s-1 is calculated from the Marcus cross relationship and literature values for the self-exchange rates. The discrepancy is attributed to systematic errors in the literature self-exchange rates that were derived by applying the Marcus cross relationship to reactions of coordination complexes with N3- and ClO2. Such errors develop whenever this method is applied to reactions between species of widely differing size. Correcting for this effect leads to a calculated value of 56 M-1 s-1 for k1, which is in much improved agreement with the observed value. Similar corrections lead to greatly improved correlations for the self-exchange reaction of NO2 with NO2- and the electrontransfer reaction of ClO2 with NO2-.
- Awad,Stanbury
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p. 3636 - 3642
(2007/10/02)
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- High Resolution Spectroscopy of N3 by Laser Induced Fluorescence
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The azide radical was generated in the gas-phase photolysis of HN3 and detected by high resolution laser induced fluorescence (LIF) technique.Rotationally resolved spectra of the A2Σu000 2Πg000 and A2Σu010 2Πg010 transitions were obtained.Analysing single rotational lines, the spin splitting constant of the A2Σu000 state was derived to be γ = (1.35 +/- 0.05) * 10-3 cm-1.Evidence was obtained for a lifetime τ of the A2Σu000 state of 0.37 = τ = 20 ns.The observed narrow linewidths are important in other experiments where the determination of scalar und vector properties allows an elucidation of reaction and photodissociation dynamics. Key words: Fluorescence / LIF / Radicals / Spectroscopy, Ultraviolet
- Haas, Tobias,Gericke, Karl-Heinz
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p. 1289 - 1292
(2007/10/02)
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- Elementary Reactions of NH(a1Δ) with Polyatomic Molecules
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The gas phase reactions of NH(a1Δ) with six polyatomic molecules R = HN3, H2O, N2O, NO2, CO2 and C6H6 (benzene) have been studied NH(a1Δ) was generated by laser photolysis of HN3 at λL = 248 nm.The removal of NH(a1Δ) by the reactant R was observed directly with the laser-induced fluorescence (LIF).The removal rate constants k1(R) at room temperature were measured: k1(HN3) = 7.3E13, k1(H2O) = 2.9E13, k1(N2O) = 1.0E12, k1(NO2) = 2.2E13, k1(CO2) = 1.4E11, and k1(C6H6) = 1.0E14 (in cm3/mol s).The contribution of intersystem crossing and of chemical reaction to the reaction products has been investigated quantitatively by the direct detection of the product NH(X3 Σ-) with the LIF.The branching ratios of intersystem crossing are: 6percent, /= 50percent and /= 2percent for H2O and N2O respectively. - Keywords: Chemical kinetics / Elementary reactions / Photochemistry
- Hack, W.,Wilms, A.
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p. 107 - 122
(2007/10/02)
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- Photochemistry of O3/HN3 Mixtures
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Gaseous mixtures of HN3 and O3 were photolyzed with the 249-nm output of a pulsed KrF laser.The photolysis produces O(1D) atoms, which react with HN3 to produce N3 radicals and with the N3 radicals to produce electronically excited NO(A2Σ+).Rate constants for these reactions were determined from comparison of the experimental NO A -> X emission time profiles with NO(A2Σ+) densities calculated from a kinetic model for the system.The rate constants for O(1D) + HN3 and O(1D) + N3 were determined to be (3.2 +/- 1.0)E-10 cm3 s-1 and (1.0 +/- 0.3)E-10 cm3 s-1, respectively.
- Ongstad, A. P.,Coombe, R. D.,Neumann, D. K.,Stech, D. J.
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p. 549 - 552
(2007/10/02)
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- Aspects of the Oxidation of Naphthazarin as studied by Pulse Radiolysis
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The spectroscopic characteristics and kinetic parameters associated with the intermediates formed on reaction of naphthazarin (5,8-dihydroxy-1,4-naphthoquinone) with the oxidising radicals OH., O.-, N3., Br.-.SO
- Mukherjee, Tulsi,Land, Edward J.,Swallow, A. John,Bruce, J. Malcolm,Beaumont, Paul C.,Parsons, Barry J.
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p. 3423 - 3434
(2007/10/02)
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- Reaction of Azide Radicals with Aromatic Compounds. Azide as a Selective Oxidant
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In basic aqueous solution the N3. radical is found to oxidize aromatic systems such as aniline and phenoxide ions and their deivatives at rate constants of (3-5) X 109 M-1s-1.In contrast to the reactions of OH radicals, wh
- Alfassi, Zeev B.,Schuler, Robert H.
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p. 3359 - 3363
(2007/10/02)
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