- Oxidation of peroxynitrite by inorganic radicals: A pulse radiolysis study
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Reactivity of the peroxynitrite ion toward a number of inorganic radicals was determined by using the pulse radiolysis technique. The rate constants for the oxidation of the ONOO- ion by CO3·-, ·N3, and ClO2· radicals were determined from their decay kinetics to be (7.7 ± 1.2) x 106 (I = 0.6 M), (7.2 ± 0.9) x 108, and (3.2 ± 0.3) x 104 M-1 s-(l), respectively. For the ·OH radical, the rate constant of (4.8 ± 0.8) x 109 M-1 s-1 was obtained by using competition kinetic analysis. The oxidation potential of the ONOO- ion was estimated as 0.8 V from the kinetic data. Although thermodynamically favorable, oxidation of ONOO- by the °NO2 radical was not observed; an upper limit of 2.5 x 104 M-1 s-1 could be set for this reaction. Contribution from some of these reactions to the decomposition of peroxynitrite in the presence and absence of CO2 is discussed.
- Goldstein, Sara,Saha, Abhijit,Lymar, Sergei V.,Czapski, Gidon
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- Reduction potentials of so3·- , so5·- , and S4O6·3- radicals in aqueous solution
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Reduction potentials of the SC3·- , SO5·- , and S4O63·- radicals in aqueous solutions are measured by pulse radiolysis at 294 K. These radicals are produced by reaction of ·OH or N3· radicals with sulfite, peroxymonosulfate, and thiosulfate anions, respectively. The potentials for the couples SO3·-/SO32- and SO5·-/ SO52- are determined from equilibrium constants with three reference couples of the phenoxyl/phenoxide type, i.e., those derived from phenol, 3-cresol, and tyrosine. The potential for PhO·/PhO- is redetermined against ClO2·/ClO2- and confirms the published value. The potentials for the other two phenols are determined against PhO·/PhO-. The potential for the SO3·-/SO32- couple is found to be 0.73 ± 0.01 V vs·NHE. The potential for SO5·-/SO52- is found to be 0.81 ± 0.02 V. The reduction potential of the radical formed from the one-electron oxidation of thiosulfate, which exhibits a λmax at 375 nm, is also determined. This radical was identified before as either the monomeric S2O3·- or the dimeric S4O6·3-. Equilibrium measurements for this species, using N3· and the 4-cyanophenoxyl radical as references, support the dimeric assignment and yield a value of 1.07 ± 0.03 V for the reduction potential for the couple S4O6·3- /2S2O32-.
- Das, Tomi Nath,Huie, Robert E.,Neta
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- Photodetachment of the Azide Anion in the Gas Phase. Electron Affinity of the Azide Radical
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We report the formation of the azide anion, N3-, in the gas phase using azidotrimethylsilane as the source.The azide anion is formed as a product of a fast ion-molecule reaction between the trimethylsilylnitrene anion, (CH3)3SiN-, and azidotrimethylsilane.A photodetachnemt treshold for N3- is obtained which can be equated with the adiabatic electron affinity of the azide radical, N3, giving EA = 62.1 +/- 2.8 kcal/mol.
- Jackson, Robert L.,Pellerite, Mark J.,Brauman, John I.
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- Velocity modulation infrared laser spectroscopy of negative ions: The (011)- (001) band of azide (N3-)
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We have measured 43 transitions centered at 1972 cm-1 in the (011)-(001 ) bending hot band of the azide ion (N3-) using diode laser velocity modulation spectroscopy of an NH3/N20 discharge.The data, ranging from P(32) to R (40), were fit to a standard l-type doubling Hamiltonian through quartic terms.The I splittings in the spectrum were unusually large compared with similar molecules.Intensity measurements indicate that the vibrational and rotational degrees of freedom are equilibrated, unlike the case for isoelectronic NCO-.Additional lines of the ν3 fundamental have also been measured, which further refine the values of the ground state parameters.
- Polak, Mark,Gruebele, Martin,Peng, Grace S.,Saykally, Richard J.
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- Primary photochemical processes for Pt(IV) diazido complexes prospectIVe in photodynamic therapy of tumors
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Diazide diamino complexes of Pt(iv) are considered as prospective prodrugs in oxygen-free photodynamic therapy (PDT). Primary photophysical and photochemical processes for cis,trans,cis-[Pt(N3)2(OH)2(NH3)2] and trans,trans,trans-[Pt(N3)2(OH)2(NH3)2] complexes were studied by means of stationary photolysis, nanosecond laser flash photolysis and ultrafast kinetic spectroscopy. The process of photolysis is multistage. The first stage is the photosubstitution of an azide ligand to a water molecule. This process was shown to be a chain reaction involving redox stages. Pt(iv) and Pt(iii) intermediates responsible for the chain propagation were recorded using ultrafast kinetic spectroscopy and nanosecond laser flash photolysis. The mechanism of photosubstitution is proposed.
- Shushakov, Anton A.,Pozdnyakov, Ivan P.,Grivin, Vjacheslav P.,Plyusnin, Victor F.,Vasilchenko, Danila B.,Zadesenets, Andrei V.,Melnikov, Alexei A.,Chekalin, Sergey V.,Glebov, Evgeni M.
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p. 9440 - 9450
(2017/08/03)
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- Acid-base equilibrium dynamics in methanol and dimethyl sulfoxide probed by two-dimensional infrared spectroscopy
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Two-dimensional infrared (2DIR) spectroscopy, which has been proven to be an excellent experimental method for studying thermally-driven chemical processes, was successfully used to investigate the acid dissociation equilibrium of HN3 in methanol (CH3OH) and dimethyl sulfoxide (DMSO) for the first time. Our 2DIR experimental results indicate that the acid-base equilibrium occurs on picosecond timescales in CH3OH but that it occurs on much longer timescales in DMSO. Our results imply that the different timescales of the acid-base equilibrium originate from different proton transfer mechanisms between the acidic (HN3) and basic (N3-) species in CH3OH and DMSO. In CH3OH, the acid-base equilibrium is assisted by the surrounding CH3OH molecules which can directly donate H+ to N3- and accept H+ from HN3 and the proton migrates through the hydrogen-bonded chain of CH3OH. On the other hand, the acid-base equilibrium in DMSO occurs through the mutual diffusion of HN3 and N3- or direct proton transfer. Our 2DIR experimental results corroborate different proton transfer mechanisms in the acid-base equilibrium in protic (CH3OH) and aprotic (DMSO) solvents.
- Lee, Chiho,Son, Hyewon,Park, Sungnam
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p. 17557 - 17561
(2015/07/07)
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- Kinetic and spectroscopic observations on the azidyl, N3{radical dot}, radical oxidation of fac-(Lspectator)ReI(CO)3(Lacceptor ) to fac-(Lspectator)ReII(CO)3(Laccepto r), Lspectator = 4,4′-bpy; Lacceptor ...
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Full title: Kinetic and spectroscopic observations on the azidyl, N3{radical dot}, radical oxidation of fac-(Lspectator)ReI(CO)3(Lacceptor ) to fac-(Lspectator)ReII(CO)3(Laccepto r), Lspectator = 4,4′-bpy; Lacceptor = dipyridyl[3,2-a:2′3′-c]phenazine or Lspectator = Cl-; Lacceptor = bathocuproindisulfonate: A revisitation to the self-exchange rate constants of the N3{radical dot} / N3- and Re(II)/Re(I) couples and to the redox potential of the N3{radical dot} radical The oxidation of two triscarbonyl fac-(Lspectator)ReI(CO)3(Lacceptor )z complexes (Lspectator = 4,4′-bpy; Lacceptor = dipyridyl[3,2-a:2′3′-c]phenazine (dppz) and z = + or Lspectator = Cl-; Lacceptor = bathocuproinedisulfonate (bcds2-) and z = 2-) by azidyl radicals, N3{radical dot}, was investigated by pulse radiolysis. Reaction rate constants were determined for the electron transfer reactions between the Re(II) products and reductants, Ru (bipy)33 + and Ni(Me6-[14]dieneN4)2+, and used for the calculation of the self-exchange rate constant of the Re(II)/Re(I) couples. The self-exchange rate constants, k ~ 107 M-1 s-1, were one order of magnitude larger than the constant, k ~ 106 M-1 s-1, communicated in the literature for the [Re(DMPE)3]+/2+ (DMPE = 1,2-bis(dimethylphosphine)ethane). The larger rate constants of the triscarbonyl complexes are in agreement with the smaller inner sphere reorganization energy of the complexes relative to [Re(DMPE)3]+/2+. Moreover, the study demonstrated that the redox potential of the azidyl radicals is EN3{radical dot} / N3-0 = 1.70 V versus NHE, a value larger than one communicated earlier, and that the self-exchange rate constant of the N3{radical dot} / N3- couple is kN3{radical dot} / N3- = 2.7 × 106 M- 1 s- 1. The small value of the N3{radical dot} / N3- self-exchange rate constant has been related to the large solvent reorganization energy of the reaction.
- Ruiz,Juliarena,Wolcan,Ferraudi
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p. 3681 - 3687
(2008/10/09)
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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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- Reactions of laser-ablated aluminum atoms with nitrogen atoms and molecules. Infrared spectra and density functional calculations for the AlN2, Al2N, Al2N2, AlN3, and Al3N molecules
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Laser-ablated aluminum atoms react with dinitrogen on condensation at 10 K to form N3 radical and the subject molecules, which are identified by nitrogen isotopic substitution, further reactions on annealing, and comparison with isotopic frequencies computed by density functional theory. The major AlN3 product is identified from three fundamentals and a statistically mixed nitrogen isotopic octet pattern. The aluminum rich Al2N and Al3N species are major products on annealing to allow diffusion and further reaction of trapped species. This work provides the first experimental evidence for molecular AlxNy species that may be involved in ceramic film growth.
- Andrews, Lester,Zhou, Mingfei,Chertihin, George V.,Bare, William D.,Hannachi, Yacine
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p. 1656 - 1661
(2007/10/03)
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- Substitution kinetics of the aqua ligand in [Re(NO)(H2O)(CN)4]2- by the monodentate nucleophiles SCN-, N3- and thiourea and the X-ray crystal structure of (AsPh4)2[Re(NO)(SC(NH2)2)(CN) 4]
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The substitution reactions between [Re(NO)(H2O)(CN)4]2- and the nucleophiles SCN-, N3- and thiourea revealed that both the aqua and the hydroxo ligands are substituted with respective rate constants of 3.6(1) × 10-3 and 1.57(5) × 10-3 M-1 s-1 at 40°C in the case of SCN-. The pKa1 was spectrophotometrically determined as 9.90(2) at 25°C and kinetically as 9.50(4) at 40°C with NCS- as the incoming nucleophile. The (AsPh4)2[Re(NO)(SC(NH2)2)(CN) 4] complex was isolated as the product for the reaction between [Re(NO)(H2O)(CN)4]2- and thiourea and its X-ray crystal structure determined. The Re - NO and N - O bond lengths are 1.736(11) and 1.146(13) A, respectively, while the Re - S bond distance is 2.503(4) A. The thiourea is bonded cis with respect to the nitrosyl group.
- Smith, John,Purcell, Walter,Lamprecht, Gert J.,Roodt, Andreas
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p. 1389 - 1395
(2008/10/09)
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- Decrease in the Oxidation Potential of the Tris-2,2'-bipyridyl Ruthenium(II) Complex Upon Electrostatic Binding to Colloidal Silica as Evidenced on the Basis of the Reaction with the Azidyl Radical
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The azidyl radical which is otherwise unreactive towards the Ru(bpy)32+ complex reacts with this complex in aqueous solution provided negatively charged colloidal silica particles are present.The increase in reactivity is explained in terms of ion binding, i.e.Ru(bpy)32+ complexes becoming rather firmly attached to the negatively charged particles.The attachment causes a decrease in the redox potential of the system Ru(bpy)33+/Ru(bpy)32+ from E0 = 1.27 V vs.NHE (in the absence of colloidal silica) to E0 = 1.17 V vs.NHE (in the presence of colloidal silica).This value was obtained on the basis of E0 = 1.35 V vs.NHE for the system .N3/N3-. - Keywords: Colloides / Complex Compounds /Radiation Chemistry / Radicals
- Naik, Devidas B.,Schnabel, Wolfram
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p. 1559 - 1562
(2007/10/02)
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- Temperature Dependence of the Rate Constants for Reaction of Dihalide and Azide Radicals with Inorganic Reductants
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Rate constants for several reactions of inorganic radicals with inorganic reductants in aqueous solutions have been measured by pulse radiolysis as a function of temperature, generally between 5 and 75 deg C.The reactions studied were of the dihalide radicals, Cl2.-, Br2.-, and I2.-, the (SCN).- radical, and the neutral radical N3., reacting with the substitution-inert metal complexes, Fe(CN)6(4-), Mo(CN)8(4-), and W(CN)8(4-), and with the anions SO3(2-), HSO3(1-), NO2(1-), and ClO2(1-).The rate constants measured were in the range of 1E6 to 5E9 M-1 s-1and the calculated Arrhenius activation energies ranged from 5 to 35 kJ mol-1.The preexponential factors also varied considerably, with log A ranging from 8.9 to 13.1.The temperature dependence of the reaction rate constant is correlated to the reaction exothermicity for the metal complexes, which apparently react by outer-sphere electron transfer.The simple anions, however, have lower activation energies, which do not correlate well with the exothermicities, suggesting that these anions probably react by inner-sphere mechanism.
- Shoute, L. C. T.,Alfassi, Z. B.,Neta, P.,Huie, R. E.
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p. 3238 - 3242
(2007/10/02)
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- Kinetics and mechanism of the sulfite-induced autoxidation of cobalt(II) in aqueous azide medium
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The autoxidation of Co(II) in azide medium is accelerated by sulfur(IV) oxides at a concentration level of 10-5 M. The formation of Co(III) was followed spectrophotometrically under the following conditions: [Co(II)] = 5 × 10-4 M; initial [Co(III)] = (0-3.6) × 10-5 M; [total S(IV)] = (1-4) × 10-5 M; 4 3-] = 0.1-0.5 M; temperature = 25°C; ionic strength = 1.0 M. The autoxidation reaction exhibits typical autocatalytic behavior in which the induction period depends on the Co(III) concentration. A detailed kinetic study of both the autoxidation step and the reduction of Co(III) by sulfur(IV) oxides demonstrates that the same rate-determining step is operative in both cases. This step involves the reduction of Co(III) by sulfur(IV) oxide to produce the SO3- radical, which reacts with dissolved oxygen to produce SO5- and rapidly oxidizes Co(II) in at least two consecutive steps. The observed rate constant depends on the pH and azide concentration, since these control the speciation of the sulfur(IV) oxides and cobalt(II/III) azide complexes. The proposed mechanism is discussed in reference to available literature information.
- Coichev, Nina,Van Eldik, Rudi
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p. 2375 - 2380
(2008/10/08)
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- Kinetics and Products of the Reactions of NO3 with Monoalkenes, Dialkenes, and Monoterpenes
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Rate constants for the reactions of NO3 with a number of aliphatic mono- and dialkenes and monoterpenes have been determined in a 420 l reaction chamber at 1-bar total pressure of synthetic air by 298 K with a relative kinetic method.The products of these reactions have been investigated also at 1-bar total pressure of synthetic air with in situ FT-IR spectrometry and gas chromatography.In all cases, the initial formation of thermally unstable nitrooxy-peroxynitrate-type compounds containing the difunctional group -CH(OONO2)-CH(ONO2)- has been observed.The experimental results are consistent with a mechanism involving the formation of nitrooxy-alkoxy radicals, -CH(O)-CH(ONO2)-, via the self-reaction of the nitrooxy-peroxy radicals.The further reactions of the nitrooxy-alkoxy radicals then determine the final products.The main reaction pathways are (i) reaction with O2 to form nitrooxy-aldehydes or -ketones and HO2 and (II) thermal decomposition forming aldehydes/ketones and NO2.The mechanisms leading to the final products are discussed, and their possible relevance for the chemistry in the troposphere is considered.
- DeFelippis, Michael R.,Faraggi, M.,Klapper, Michael H.
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p. 2420 - 2424
(2007/10/02)
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- Temperature and pressure effects on the outer-sphere electron-transfer reaction between hexacyanoferrate(II) and pentaamminecobalt(III) complexes in aqueous solution. Comparison of experimental and theoretical volumes of activation
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The kinetics of a series of outer-sphere electron-transfer reactions of the type Co(NH3)4(NH2R)X(3-n)+ + Fe(CN)64- → Co2+ + 4NH3 + NH2R + Xn- + Fe(CN)63- (X = N3-, R = H; X = Cl-, R = H, CH3, i-C4H9) were studied as a function of temperature and pressure. It was possible to separate the ion-pair formation constant and the electron-transfer rate constant in a kinetic way, and the corresponding thermodynamic and activation parameters were determined. For the electron-transfer process, the rate and activation parameters lie in the ranges 0.06 ≤ k × 102 ≤ 20 s-1, 84 ≤ ΔH? ≤ 118 kJ mol-1, +11 ≤ ΔS? ≤ 113 J K-1 mol-1, and +19 ≤ ΔV? ≤ +34 cm3 mol-1. The experimentally observed activation volumes are in good agreement with those predicted theoretically on the basis of an average λ? value of 0.48 ± 0.07. The results are discussed in reference to related studies reported in the literature.
- Krack,Van Eldik
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p. 1700 - 1704
(2008/10/08)
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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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p. 4073 - 4079
(2007/10/02)
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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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p. 2120 - 2122
(2007/10/02)
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- Gas-Phase Synthesis and Reactions of Nitrogen- and Sulfur-Containing Anions
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The flowing afterglow and selected ion-flow tube techniques have been used to study the reactions of H2N- with N2O, CO2, CS2, SO2, and OCS in the gas phase.Thermal energy rate coefficients and product branching ratios have been determined and are discussed in terms of detailed reaction mechanisms.With use of the SIFT-drift technique, the product distribution for the reaction of H2N- with N2O was measured as a function of the center of mass kinetic energy in the range of thermal energy to ca. 15 kcal mol1-.Qualitative studies were made of the reactions of HO-, CH3O-, and (CH3)2N- with N2O, CO2, CS2, SO2, and OCS, and the reactions of a variety of other ions with OCS were also examined.These reactions provide efficient synthetic routes for the gas-phase preparation of a variety of interesting negative ions containing nitrogen and sulfur.The basicities and heats of formation of three of these anions, H2NS-, NSO-, and NCS-, have been bracketed by proton-transfer reactions.The nucleophilicities of these three anions, as well as of H2N-, HO-, HO2-, F-, HS-, CN-, NCO-, N3-, Cl-, and Br- toward CH3I, have been measured.
- Bierbaum, Veronica M.,Grabowski, Joseph J.,DePuy, Charles H.
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p. 1389 - 1393
(2007/10/02)
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