- REACTIONS OF METAL-CLUSTER CARBONYLS IN PILLARED CLAY GALLERIES: SURFACE COORDINATION CHEMISTRY AND FISCHER-TROPSCH CATALYSIS.
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A new method is reported for introducing transition-metal centers in the galleries of a thermally stable pillared clay. The authors approach focuses on the reactions of metal-cluster carbonyl complexes with protons and surface hydroxyl groups of an alumina pillared montmorillonite, henceforth abbreviated APM. The surface chemistry of tri- and tetranuclear ruthenium, osmium, and iridium carbonyls is examined in comparison to the chemistry of these species on the surfaces of bulk oxides. Also, we report the formation of supported ruthenium aggregates in the intracrystalline environment of the clay and describe the Fischer-Tropsch (FT) product selectivity of this new catalyst system.
- Giannelis,Rightor,Pinnavaia
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- Preferential oxidation of CO in H2 by aqueous polyoxometalates over metal catalysts
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Stream cleaning: CO in CO/H2 mixtures is oxidized preferentially at room temperature with an aqueous polyoxometalate (POM) solution over gold catalysts (see scheme). The rate of H2 oxidation is slow and is inhibited by CO. This process can be used to remove CO efficiently from H 2 gas streams. The solution containing protons and reduced POM can be used to produce electrical energy at a fuel-cell anode through re-oxidation of the reduced POM.
- Kim, Won Bae,Voitl, Tobias,Rodriguez-Rivera, Gabriel J.,Evans, Steven T.,Dumesic, James A.
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- Temperature dependence of adlayers on Pt(1 1 1) and Au(1 1 1) in a sulfuric acid solution studied by in situ IRAS
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Temperature dependence studies of adsorption of sulfuric acid species on Pt(111) and Au(111) electrodes were carried out using in situ infrared reflection absorption spectroscopy. A temperature-dependent shift of the interconversion potential between HSO4-/H3O+ and H2SO4 on a Pt(111) electrode was observed. A temperature-dependent frequency shift of the absorption bands of HSO4- was also observed on both Pt(111) and Au(111) electrodes in the potential region where a √3×√7 structure evolved. Modelling experiments in ultrahigh vacuum revealed that ordering of the overlayer water molecules played an important role in the frequency of the absorption bands of HSO4-.
- Shingaya,Ito
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- Chemistry and Structure of the CH3O2(+) Product of the O2(+) + CH4 Reaction
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The CH3O2(+) product ion of the thermal energy reaction between O2(+) and CH4 has been studied in reaction with a number of neutral molecules.The reactivity pattern demonstrates very convincingly that the structure of the ion is methylene hydroperoxy cation, CH2OOH(+), in contrast to previous reports that the ion is protonated formic acid, HC(OH)2(+) or HC(O)OH2(+).From these and other data the heat of formation of this ion is determined to be between 182 and 188 kcal/mol.
- Doren, J. M. Van,Barlow, S. E.,DePuy, C. H.,Bierbaum, V. M.,Dotan, I.,Ferguson, E. E.
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- Electrochemical reduction of bisulfite in mildly acidic buffers: Kinetics of sulfur dioxide - Bisulfite interconversion
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The reduction of bisulfite on a bismuth rotating disk electrode (RDE) was studied in aqueous buffered electrolytes over the pH range 3-6. Clearly defined limiting currents were observed in all solutions examined; however, their magnitudes were not only smaller than those expected for a process limited by the diffusion of bisulfite from the bulk solution, but were also found to decrease as the media became less acidic. This behavior was attributed to a preceding homogeneous process that generates sulfur dioxide, the actual electroactive species. UV - visible absorption - reflection spectroscopy measurements at a RDE showed that in the potential region in which such limiting currents are observed, dithionite is produced with 100% faradaic efficiency, Results of rotation rate staircase scan amperometric RDE experiments were found to be consistent with the conversion of bisulfite into SO2 proceeding via a general acid catalysis mechanism, and allowed values for the rate constants for the following reactions to be determined: SO2 + H2O → HSO3- + H3O+, kb = (1.6 ± 0.2) 107 s-1; HSO3- + H3O → SO2 + H2O, kfH = (1.2 ± 0.15) 109 M-1 s-1; HSO3- + CH3COOH → SO2 + H2O + CH3COO-, kfHA = (1.7 ± 0.5) 104 M-1 s-1. On this basis, and assuming diffusion-controlled rates for proton transfer from strong acids to oxygen bases, a more detailed mechanism involving formation of sulfurous acid as an intermediate is discussed and some thermodynamic and kinetic properties of the latter are estimated.
- Tolmachev, Yuriy V.,Scherson, Daniel A.
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- Ion-Molecule Reactions Involving H3O+, H2O+, and OH+ at Thermal Energy
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The rate coefficients for a variety of reactions involving OH+, H2O+, and H3O+ with CS2, H2S, SO2, NO, NO2, N2O, N2, O2, CH4, CO2, CO, NH3, and H2 are obtained with a selected ion flow tube.The product channels include proton transfer, charge transfer, atom abstraction, and association.Most of the reaction rates are fast and have high reaction efficiencies.Reaction of OH+ with NO2 is found to produce both NO2+ and NO+; even though both reaction channels are also exothermic with H2O+, only NO2+ is produced.H3O+ is found to undergo association reactions with SO2 and N2O and H2O+ does so with CO2 and N2O.The reaction of H2O+ with N2O also involves a second-order process in addition to the association pathway.
- Shul, R. J.,Passarella, R.,DiFazio, L. T.,Keesee, R. G.,Castleman, A. W.
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- Orthorhombic B2CN crystal synthesized by high pressure and temperature
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B0.54C0.28N0.18 precursor powder with turbostratic structure was prepared by using melamine and boric acid. The precursor was transformed into orthorhombic B2CN under definite high pressure and temperature conditions. The composition of the orthorhombic B2CN powder is B0.47C0.23N0.30. Its lattice parameters are a=0.4776 nm, b=0.4585 nm and c=0.3629 nm. A strong absorption band from 1088 to 1385cm-1 of orthorhombic B2CN was observed by infrared measurement. In the photoluminescence (PL) spectrum of orthorhombic B2CN powder measured at room temperature, a broad peak corresponding to its band-edge emission centers at 374 nm.
- He,Tian,Yu,Wang,Liu,Guo,Li,Jia,Chen,Zou,Yanagisawa
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- Thermal decomposition of hydrogen peroxide in the presence of sulfuric acid
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Hydrogen peroxide (H2O2) is popularly employed as a reaction reagent in cleaning processes for the chemical industry and semiconductor plants. By using differential scanning calorimetry (DSC) and vent sizing package 2 (VSP2), this study focused on the thermal decomposition reaction of H2O2 mixed with sulfuric acid (H 2SO4) with low (0.1, 0.5 and 1.0 N), and high concentrations of 96 mass%, respectively. Thermokinetic data, such as exothermic onset temperature (T 0), heat of decomposition (ΔH d), pressure rise rate (dP/dt), and self-heating rate (dT/dt), were obtained and assessed by the DSC and VSP2 experiments. From the thermal decomposition reaction on various concentrations of H2SO4, the experimental data of T 0, ΔH, dP/dt, and dT/dt were obtained. Comparisons of the reactivity for H2O2 and H2O2 mixed with H2SO4 (lower and higher concentrations) were evaluated to corroborate the decomposition reaction in these systems.
- Wu,Chen,Cheng,Lee,Shu
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- Interaction between the ion dipole and the ion-induced dipole in reactions of the polar ion ArH+3
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The reactions of the highly polar ion ArH+3 with the nonpolar neutrals Xe, Kr, CH4, CO, NO, O2, and N2 and with the polar neutrals SO2, H2O, NH3, CH3I, and C2H5I have been investigated in a selected ion flow drift tube experiment at near thermal conditions.The rate coefficients obtained have typically 15percent-35percent larger values than the collisional limiting values kL and kADO obtained by the Langevin and ADO (average dipole orientation) theory, respectively.These data are explained on the basis of the interaction between the dipole of ArH+3 and the ion-induced dipole and the permenent dipole, respectively, of the neutral reactants.Rate coefficients for the reactions of H+3 with the above neutrals were also obtained for comparison, as well as the zero field mobility of ArH+3 in helium being (18.5+/-1.5) cm2/V s.The ion KrD+3 (KrH+3) was detected unambiguously for the first time.Its dissociation energy is larger than 0.29 eV which is the lower limit of the dissociation energy of ArH+3.
- Praxmarer, C.,Hansel, A.,Lindinger, W.
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- Kinetic study of the complex formation of boric and boronic acids with mono- and diprotonated ligands
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The complex formation reactions of boric and boronic acids (RB(OH)2: R=OH, n-Bu, Ph, and m-NO2Ph) with 4-isopropyltropolone (Hipt) and chromotropic acid (H2cht2-) have been studied kinetically at various pH. The reactions of H2ipt+ with boronic acids were faster than those of Hipt by a factor of 1.5-11, and fully deprotonated ipt- also reacted with m-NO2PhB(OH)2, but slower than Hipt. The tetrahedral m-NO2PhB(OH)3- ion did not react with Hipt. Reaction routes for the complexation of boric acid with chromotropic acid could not be specified because of the unexpected problem of proton ambiguity. Mechanism for the reactions of boronic acids with bidentate ligands was discussed in terms of rate determining chelate ring closure. It was concluded that at least one proton is necessary for the OH- in the tetrahedral intermediates to be eliminated smoothly as water, and a doubly hydrogen-bonded intermediate was proposed for the reactions with diprotic ligands.
- Ito, Hideaki,Kono, Yoko,Machida, Akinori,Mitsumoto, Yoko,Omori, Kenji,Nakamura, Noriko,Kondo, Yuichi,Ishihara, Koji
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- A study of the structure and dynamics of the hydronium ion by high- resolution infrared laser spectroscopy. I. The ν3 band of H316O+
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The results of an extensive study of ν3 (asymmetric stretch) vibration of the H3O+ ion are reported.A total of 86 and 41 transitions were measured with a precision of 0.002 cm-1 for the s-s and a-a inversion subbands, respectively, and least-squares fit to an accurate Hamiltonian.Twenty-four parameters were determined in the analysis.The ν3 frequencies are 3535.974( 11 ) and 3519.397(25) cm-1 for the s-s and a-a inversion components, respectively.
- Begemann, Marianne H.,Saykally, Richard J.
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- Crossed Molecular Beam Studies of Proton Transfer, Unimolecular Decay, and Isotope Scrambling in the Reactions H2+ + H2O, H2+ + D2O, and D2+ + H2O
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We present and experimental study of the title reactions over the collision energy range from 0.7 to 6.9 eV.Over the entire collision energy range, a significant fraction of the products have internal excitation sufficiently high to undergo unimolecular decay to H2O+ or an isotopically substituted water cation.An examination of the reactions D2+ + H2O and H2+ + D2O and observation of H2O+ and HOD+ products of unimolecular decay at 3.0 and 6.3 eV suggest that, at the lower collision energy, the recoil energy distributions are consistent with the results of phase space calculations including all vibrations of the H2O+ or HOD+ product.At this collision energy, the unimolecular decay products have barycentric angular distributions with sharp forward-backward symmetry, suggesting that planar scattering with concomitant angular momentum polarization is an important dynamical feature in these reactions.At the higher collision energy, the complex 'osculates' with a lifetime too short for rapid intramolecular energy transfer.We also present evidence for a direct reaction between H2+ and D2O yielding HOD+ and a bound HD molecule, proceeding through a four-center exchange reaction rather than through unimolecular decay of HD2O+.
- Bilotta, R. M.,Farrar, J. M.
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- Properties of copper(II) hydride formed in the reaction of aquacopper(I) ions with hydrogen atoms. A pulse radiolytic study
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The spectrum of Cu-H+(aq), formed via Cu+ + H → Cu-H+(aq) in aqueous solutions, is reported. In neutral solutions it decomposes via Cu-H+(aq) + H2O → Cu2+(aq) + H2 + OH-(aq) with a rate of 4 × 103 s-1. The properties of Cu-H+(aq) are discussed and compared with those of similar CuII-R compounds.
- Mulac,Meyerstein, Dan
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- Excited state dynamics of liquid water: Insight from the dissociation reaction following two-photon excitation
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The authors use transient absorption spectroscopy to monitor the ionization and dissociation products following two-photon excitation of pure liquid water. The primary decay mechanism changes from dissociation at an excitation energy of 8.3 eV to ionization at 12.4 eV. The two channels occur with similar yield for an excitation energy of 9.3 eV. For the lowest excitation energy, the transient absorption at 267 nm probes the geminate recombination kinetics of the H and OH fragments, providing a window on the dissociation dynamics. Modeling the OH geminate recombination indicates that the dissociating H atoms have enough kinetic energy to escape the solvent cage and one or two additional solvent shells. The average initial separation of H and OH fragments is 0.7±0.2 nm. Our observation suggests that the hydrogen bonding environment does not prevent direct dissociation of an O-H bond in the excited state. We discuss the implications of our measurement for the excited state dynamics of liquid water and explore the role of those dynamics in the ionization mechanism at low excitation energies.
- Elles, Christopher G.,Shkrob, Ilya A.,Crowell, Robert A.,Bradforth, Stephen E.
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- Interaction of water with GeCl4, SnCl4, and AsCl 3
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The interaction of water with GeCl4, SnCl4, and AsCl3 was studied by IR spectroscopy. The results demonstrate that these chlorides contain molecular water in monomeric form. At water concentrations above 10-2 mol/l, GeCl4 also contains H3O+ ions. The mechanisms of GeCl4 and AsCl3 hydrolysis were studied over a wide range of water concentrations.
- Efremov,Potolokov,Nikolashin,Fedorov
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p. 837 - 846
(2008/10/08)
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- Kinetics of the reaction of O2+ with CH4 from 500 to 1400 K: A case for state specific chemistry
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The temperature dependent rate constants and branching ratios for the reaction of O2+ with CH4 and O2 with CD4 from 500 to 1400 K were determined. By comparing to previous studies, the influence on vibrational excitation in the CH4 reactant was derived.
- Dotan,Viggiano
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p. 6112 - 6118
(2007/10/03)
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- [Ru(II)(hedta)]- complexes of 2,2'-dipyridylamine (dpaH) and a bifunctional tethered analog, N,N,N',N'-tetrakis(2-pyridyl)adipamide (tpada)
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[Ru(II)(hedta)L]- complexes (hedta3- = N-hydroxyethylethylenediamine-N,N,N'-triacetate); L = dpaH (2,2'-dipyridylamine) and tpada (N,N,N',N'-tetrakis(2-pyridyl)adipamide)) have been studied by 1H NMR and electrochemical methods in aqueous solution. The bidentate rings of dpaH and tpada are differentiated as shown by NMR upon coordination to Ru(II) due to differences in the local environment. The dpa-R headgroup of each ligand binds 'in-plane' with the en backbone of hedta3- and with one pyridyl ring being nearer the amine of hedta3- having the pendant glycinato group (matching the known arrangement with bpy (2,2'-bipyridine)). Ru(II/III) E(1/2) values follow the order dpaH (0.32 V) a weaker π-acceptor ligand than bpy, and that the withdrawing carbonyl functionality enhances the π-acceptor capacity for the tpada ligand, approaching the stability imparted by bpy. Only the 1:1 [Ru(II)(hedta)(dpaH)]- complex forms even in the presence of excess dpaH. [Ru(II)(hedta)(dpaH)] has a pK(a) of the dipyridylamine proton of approximately 5.0 with [Ru(II)(hedta)(dpa-)] undergoing aquation (k(H2O)= 1.4 10-2 s-1) and OH--assisted dissociation (k(OH) = 1.33 104 M-1 s-1). The {[Ru(II)-(hedta)]2(tpada)}2- complex serves as a water-soluble model as to how {[ML']2(tpada)} complexes might act as an extended bridge between two metal binding sites, potentially those of metallo-derivatized DNA strands, or between one DNA strand and a protein crosslink. In this model M represents an appropriate metal for DNA derivatization such as Ru(II), Pt(II) or Pd(II) and L' represents the attachments to DNA nucleobase sites, aminocarboxylates/peptide coordination for antitumor purposes. (C) 2000 Elsevier Science S.A.
- Shepherd, Rex E.,Chen, Ya,Kortes, Richard A.,Ward, Matthew S.
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- Deactivation of methylrhenium trioxide - Peroxide catalysts by diverse and competing pathways
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The peroxides from methylrhenium trioxide (MTO) and hydrogen peroxide, CH3ReO2(η2-O2), A, and CH3Re(O)(η2-O2)2(H2O), B, have been fully characterized in both organic and aqueous media by spectroscopic means (NMR and UV-vis). In aqueous solution, the equilibrium constants for their formation are K1 = 16.1 ± 0.2 L mol-1 and K2 = 132 ± 2 L mol-1 at pH 0, μ = 2.0 M, and 25 °C. In the presence of hydrogen peroxide the catalyst decomposes to methanol and perrhenate ions with a rate that is dependent on [H2O2] and [H3O+]. The complex peroxide and pH dependences could be explained by one of two possible pathways: attack of either hydroxide on A or HO2- on MTO. The respective second-order rate constants for these reactions which were deduced from comprehensive kinetic treatments are k(A) = (6.2 ± 0.3) x 109 and k(MTO) = (4.1 ± 0.2) x 108 L mol-1 s-1 at μ = 0.01 M and 25 °C. The plot of log k(ψ) versus pH for the decomposition reaction is linear with a unit slope in the pH range 1.77-6.50. The diperoxide B decomposes much more slowly to yield O2 and CH3ReO3. This is a minor pathway, however, amounting to -4 s-1 at pH 3.21, μ = 0.10 M, and 25 °C. Without peroxide, CH3ReO3 is stable below pH 7, but decomposes in alkaline aqueous solution to yield CH4 and ReO4-. As a consequence, the decomposition rate rises sharply with [H2O2), peaking at the concentration at which [A] is a maximum, and then falling to a much smaller value. Variable-temperature 1H NMR experiments revealed the presence of a labile coordinated water in B, but supported the anhydride form for A. The peroxides from methylrhenium trioxide (MTO) and hydrogen peroxide, CH3ReO2(η2-O2), A, and CH3Re(O)(η2-2)2(H2O), B, have been fully characterized in both organic and aqueous media by spectroscopic means (NMR and UV-vis). In aqueous solution, the values of the equilibrium constants for their formation are given. In the presence of hydrogen peroxide the catalyst decomposes to methanol and perrhenate ions with a rate that is dependent on [H2O2] and [H3O+]. The complex peroxide and pH dependences could be explained by one of two possible pathways: attack of either hydroxide on A or HO2- on MTO. The respective second-order rate constants for these reactions which were deduced from comprehensive kinetic treatments are given. The plot of log k versus pH for the decomposition reaction is linear with the unit slope in the pH range 1.77-6.50. The diperoxide B decomposes much more slowly to yield O2 and CH3ReO3. This is a minor pathway, however, amounting to 3ReO3 is stable below pH 7, but decomposes in alkaline aqueous solution to yield CH4 and ReO4-. As a consequence, the decomposition rate rises sharply with [H2O2], peaking at the concentration at which [A] is a maximum and then falling to a much smaller value. Variable-temperature 1H NMR experiments revealed the presence of a labile coordinated water in B, but supported the anhydride form for A.
- Abu-Omar,Hansen,Espenson
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p. 4966 - 4974
(2007/10/03)
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- Infrared absorption spectroscopy of molecular ions in a corona-dischargeslit expansion
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A new corona slit nozzle has been constructed to study, by means of direct infrared absorption, molecular ions generated in a continuous supersonic expansion. Spectra of the ions H3(+), D2H(+), D3(+), HN2(+), H3O(+) and ArH(+), were detected in the 1900-3600 cm**-1 region using difference frequency and diode laser sources. The new jet source gives a significant improvement in signal-to-noise ratio and a reduction in rotational temperature compared to our previously reported hollow-cathode jet discharge source. The effective rotational and translational temperatures werein the ranges 33-93 and 50-100 K, respectively. The experimental factor s influencing the performance of the source are discussed.
- Xu, Yunjie,Fukushima, M.,Amano, T.,McKellar, A. R. W.
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p. 126 - 131
(2008/10/08)
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- Gas-phase ion chemistry of HP2-, FP2-, and HP2+
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The gas-phase ion-molecule chemistry of the mass-selected ions HP2-, FP2-, and HP2+ has been studied in a tandem flowing afterglow selected-ion flow tube (FA-SIFT). Both HP2- and HP2+ are formed by direct electron impact on phosphine, followed by subsequent ion-phosphine reactions in the first flow tube. The related ion, FP2-, is formed via an ion-molecule reaction between HP2- and hexafluorobenzene. We have observed a number of reactions of HP2-, including hydride transfer and proton abstraction, as well as fluoride transfer and proton abstraction for FP2-. Using bracketing techniques, the gas-phase proton affinity of P2 has been determined as 162 ± 3 kcal mol-1, in good agreement with Nguyen and Fitzpatrick's theoretically predicted value of 158 ± 3 kcal mol-1. The heats of formation of HP2-, HP2+, HPPH, FP2-, and FPPH have been estimated from the experimentally determined hydride, proton and fluoride affinities of P2 and from the gas-phase acidities of HPPH and FPPH.
- O'Hair, Richard A. J.,Krempp, Michèle,Damrauer, Robert,DePuy, Charles H.
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p. 2092 - 2096
(2008/10/08)
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- Deuterium isotope fractionation within protonated water clusters in the gas phase
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Ion product distributions have been analyzed for the collision-activated loss of H2O, HOD, or D2O from the water clusters (L2O)nL+ (L = H, D; n = 2-4). The ionic products of collision-induced dissociation (CID) are observed to be depleted in deuterium with respect to the statistical product distributions predicted for complete randomization of H and D. The measured isotope distributions in the CID product ions are independent of collision energy within experimental error, suggesting that the observed depletion of deuterium is not the result of a kinetic effect in the unimolecular decomposition, but rather a reflection of the individual cluster structures. An equilibrium isotope effect model is proposed wherein the deuterium in the cluster preferentially migrates to the peripheral positions and localizes on the neutral water molecules in the solvent shell, rather than occupying sites in the cluster ion core, such as those on the core hydronium (lyonium) ion. Deuterium enrichment in the neutral water component of each cluster ion results in enhanced loss of deuterated neutral water upon collisional activation. The present isotope fractionation results are compared with literature data for bimolecular gas-phase H/D-exchange reactions and with condensed-phase isotope fractionation data. The observation of isotope fractionation as an equilibrium effect in stabilized gas-phase water cluster ions suggests that isotope fractionation in the bimolecular reactions between (H2O)nH+ ions and D2O results primarily from a nonstatistical distribution of hydrogen and deuterium in the transient reaction intermediates.
- Graul, Susan T.,Brickhouse, Mark D.,Squires, Robert R.
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p. 631 - 639
(2007/10/02)
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- A selected ion flow tube study of the reactions of the PHn+ ions (n=0to 4) with several molecular gases at 300 K
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The reactions of ions in the series PHn+ (n=0 to 4) have been studied at 300 K with CH3NH2, PH3, NH3, CH3CCH, H2S, C2H4, CH3OH, COS, C2H2, O2, H2O, CH4, HCN, CO2, CO, and H2 using a selected ion flow tube (SIFT) apparatus.The majority are fast binary reactions, the measured rate coefficients, k, being close to the respective collisional values, and for reactions involving polyatomic reactant molecules multiple product ions are observed.Most reaction mechanisms are represented in this large number of reactions including charge transfer, proton transfer, atomabstraction and especially evident is phosphorus atom insertion in which product ions such as HnPN+, HnPO+, HnPS+ and HnCmP+ are formed.The reactions of the PHn+ ions (n=0 to 2) with CO2, CO, and H2 proceed by the process of ternary association except for the P+ reaction with CO2, in which PO+ is formed in a fast binary reaction PH4+ reacts only with CH3NH2 and NH3 by fast proton transfer, a process which is always rapid when it is exothermic.Upper limits to the heats of formation of HPO+, H2PO+, PC2H2+ and HCP have also been deduced from their observation as products of some of the reactions.
- Smith, David,McIntosh, Bruce J.,Adams, Nigel G.
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p. 6213 - 6219
(2007/10/02)
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- Multicomponent Cluster Ions. 2. Comparative Stabilities of Cationic and Anionic Hydrogen-Bonded Networks. Mixed Clusters of Water and Hydrogen Cyanide
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The thermocemistry of cluster ions containing nH2O and mHCN molecules,for cluster up to rank r = n + m = 5, was obtained from equilibrium measurements.The clustering of H2O about H3O+ and OH- and the clustering of HCN about HCNH+ show distinct shell filling effects, but the clustering of H2O and HCN about CN- does not.Hydratation by one water molecule eliminates the difference of 5 kcal/mol between the proton affinities of HCN and H2O.Hydration also decreases the difference between the intrinsinc deprotonation energies, i.e., ΔH0acid, of H2O and HCN from 37.7 to 19.8 kcal/mol in the 4-fold hydrated species.In protonated clusters of a given rank r, exchange of H2O by HCN does not significantly affect the total stability of the cluster.This is in contrast to H2O/CH3OH and H2O/CH3CN protonated clusters and H2O/HCN anionic clusters, where increasing nonaqueous content is stabilizing.In the latter, the most stable clusters of any size are the neat CN-.nHCN clusters.
- Meot-Ner, (Mautner) Michael,Speller, Carlos V.
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p. 3663 - 3666
(2007/10/02)
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- Kinetic and Mechanistic Studies on Substitution Reaction of Aquo-ligands from cis-Diaquo-bis(biguanide)cobalt(III)/chromium(III) Ions in Aqueous Medium
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The kinetics of substitution of aguo ligands from cis-diaquo-bis-(biguanide)chromium(III)/cobalt(III) ions by L-histidine in aqueous medium have been studied spectrophotometrically.The following rate law has been established in pH range 3.85 to 5.57 (2+); Complex-I = (3+) and ligand = L-histidine; M = CoIII, CrIII>.In this equation KE is the ion-pair equilibrium constant and ka the rate constant for interchange of outer-sphere complex to inner-sphere complex.The reaction rates are found to be pH dependent in the pH range of 3.85 to 5.57.Values of activation parameters, ΔH and ΔS have been evaluated.The results are consistent with a mechanism involving outer-sphere association of reactants followed by associative interchange of this outer-sphere complex into the product.
- Gangopadhyay, Ashis Kumar,De, G. S.
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p. 778 - 782
(2007/10/02)
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- Studies of the binary reactions of H3O+*(H2O)0,1,2 ions and their deuterated analogues with D2O, H20,and NH3
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The rate coefficients and product ion distributions for the binary of H3O+*(H2O)0,1,2 and D3O+*(D2O)0,1,2 ions with D2O and H2O, respectively, and with NH3 have been studied at 300 K using a selected ion flow tube (SIFT) apparatus.The ions were created in a flowing afterglow ion source and after mass filtering were injected at low energy into the SIFT.All the reactions proceeded at or near the gas kinetic limit.In the D2o and H2O thermoneutral isotopic exchange reactions, the distribution of H and D amongst the product ions and neutrals was seen to be purelystatistical.This implies that these reactions proceed via the formation of an intermediate long-lived association ion in which total randomization of the H and D atoms takes place prior to unimolecular decomposition.No appreciable isotopic exchange occurred in the exothermic NH3 reactions which apparently proceeded via the simpler mechanisms of D+ (or H+) or D3O+ (or H3O+) transfer.The differing mechanisms for the H2O and D2O reactions compared to the NH3 reactions are rationalized in terms of the thermicities of the reactions and the lifetimes of the respective intermediate ions.
- Smith, D.,Adams, N. G.,Henchman, M. J.
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p. 4951 - 4957
(2007/10/02)
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- Studies on trifluoromethanesulfonic acid. Part 2. Conductivities of solutions of metal trifluoromethanesulfonates and other bases in trifluoromethanesulfonic acid
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Electrical conductivity measurements are reported for solutions in trifluoromethanesulfonic acid of a number of simple and complex bases, including univalent and divalent metal trifluoromethanesulfonates.The univalent metal salts, water, aniline, and acetic acid behave as fully dissociated bases, while the alkaline earth metal salts show considerable ion association.The trifluoromethanesulfonate anion appears to have an abnormally high mobility, as compared to the metal cations, and is believed to conduct by a proton-transfer mechanism.Dissociation constants for some weak organic bases and association constants for strontium and barium trifluoromethanesulfonates are estimated.Sulfuric acid behaves as a weak electrolyte, while sulfur trioxide is effectively a non-electrolyte.The conductivities of potassium nitrate and potassium dihydrogenphosphate are consistent with the formation of the nitryl cation and the phocphate acidium ion, respectively.
- Russell, David G.,Senior, John B.
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- Spectra of manganese(III) complexes. I. Aquomanganese(III) ion and hydroxide, fluoride, and chloride complexes
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The absorption spectrum of aqueous manganese(III) is described in the presence and absence of added halide ions. Addition of fluoride to solutions containing aqueous manganese(III) causes a distinct splitting of the 5T2g ← 5Eg (in Oh) to occur. This is shown to be consistent with the formation of MnF2+, Mn3+ + F- = MnF2+ with K ? 106 at ~23°. Jahn-Teller effects are thought to influence the observed spectra.
- Fackler Jr.,Chawla
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p. 1130 - 1134
(2008/10/08)
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