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1.
NH 2 profiles were measured in a discharge flow reactor at ambient temperature by monitoring reactants and products with an electron impact mass spectrometer. At the low pressures used (0.7 and 1.0 mbar) the gas-phase self-reaction is dominated by a ‘bimolecular’ H 2-eliminating exit channel with a rate coefficient of k3b(300 K) = (1.3 ± 0.5) × 10 −12 cm 3 molecule −1 s −1 and leading to N 2H 2 + H 2 or NNH 2 + H 2. Although the wall loss for NH 2 radicals is relatively small ( kw ≈ 6–14 s −1), the contribution to the overall NH 2 decay is important due to the relatively slow gas-phase reaction. The heterogeneous reaction yields N 2H 4 molecules. 相似文献
2.
The generality of a two-electron reduction process involving an
mechanism has been established for M 3(CO) 12 and M 3(CO) 12− n(PPh 3) n (M = Ru, Os) clusters in all solvents. Detailed coulometric and spectral studies in CH 2Cl 2 provide strong evidence for the formation of an ‘opened’ M 3(CO) 122− species the triangulo radical anions M 3(CO) 12−· having a half-life of < 10 −6 s in CH 2Cl 2. However, the electrochemical response is sensitive to the presence of water and is concentration dependent. An electrochemical response for “opened” M 3(CO) 122− is only detected at low concentrations < 5 × 10 −4 mol dm −3 and under drybox conditions. The electroactive species ground at higher concentrations and in the presence of water M 3(CO) 112− and M 6(CO) 182− were confirmed by a study of the electrochemistry of these anions in CH 2Cl 2; HM 3(CO) 11− is not a product. The couple [M 6(CO) 18] −/2− is chemically reversible under certain conditions but oxidation of HM 3(CO) 11− is chemically irreversible. Different electrochemical behaviour for Ru 3(CO) 12 is found when [PPN][X] (X = OAc −, Cl −) salts are supporting electrolytes. In these solutions formation of the ultimate electroactive species [μ-C(O)XRu 3(CO) 10] − at the electrode is stopped under CO or at low temperatures but Ru 3(CO) 12−· is still trapped by reversible attack by X presumably as [η 1-C(O)XRu 3(CO) 11] −. It is shown that electrode-initiated electron catalysed substitution of M 3(CO) 12 only takes place on the electrochemical timescale when M = Ru, but it is slow, inefficient and non-selective, whereas BPK-initiated nucleophilic substitution of Ru 3(CO) 12 is only specific and fast in ether solvents particulary THF. Metal---metal bond cleavage is the most important influence on the rate and specificity of catalytic substitution by electron or [PPN]-initiation. The redox chemistry of M 3(CO) 12 clusters (M = Fe, Ru, Os) is a consequence of the relative rates of metal---metal bond dissociation, metal-metal bond strength and ligand dissociation and in many aspects resembles their photochemistry. 相似文献
3.
The collisional quenching of electronically excited germanium atoms, Ge[4p 2( 1S 0)], 2.029 eV above the 4p 2( 3P 0) ground state, has been investigated by time-resolved atomic resonance absorption spectroscopy in the ultraviolet at λ = 274.04 nm [4d( 1P 10) ← 4p 2( 1S 0)]. In contrast to previous investigations using the ‘single-shot mode’ at high energy, Ge( 1S 0) has been generated by the repetitive pulsed irradiation of Ge(CH 3) 4 in the presence of excess helium gas and added gases in a slow flow system, kinetically equivalent to a static system. This technique was originally developed for the study of Ge[4p 2( 1D 2)] which had eluded direct quantitative kinetic study until recently. Absolute second-order rate constants obtained using signal averaging techniques from data capture of total digitised atomic decay profiles are reported for the removal of Ge( 1S 0) with the following gases ( kR in cm 3 molecule −1 s −1, 300 K): Xe, 7.1 ± 0.4 × 10 −13; N 2, 4.7 ± 0.6 × 10 −12; O 2, 3.6 ± 0.9 × 10 −11; NO, 1.5 ± 0.3 × 10 −11; CO, 3.4 ± 0.5 × 10 −12; N 2O, 4.5 ± 0.5 × 10 −12; CO 2, 1.1 ± 0.3 × 10 −11; CH 4, 1.7 ± 0.2 × 10 −11; CF 4, 4.8 ± 0.3 × 10 −12; SF 6, 9.5 ± 1.0 × 10 −13; C 2H 4, 3.3 ± 0.1 × 10 −10; C 2H 2, 2.9 ± 0.2 × 10 −10; Ge(CH 3) 4, 5.4 ± 0.2 × 10 −11. The results are compared with previous data for Ge( 1S 0) derived in the single-shot mode where there is general agreement though with some exceptions which are discussed. The present data are also compared with analogous quenching rate data for the collisional removal of the lower lying Ge[4p 2( 1D 2)] state (0.883 eV), also characterized by signal averaging methods similar to that described here. 相似文献
4.
The overall conformational order of the alkyl tail of the lyotropic lamellar phase of the dimethyldodecyl amineoxide, (CH 3) 2ON +(CH 2) 11CH 3 (DDAO)---H 2O system (75.7 wt.%) has been studied by using Fourier transform infrared spectroscopy. The spectral region 1000–1400 cm −1, covering the CH 2 wagging modes and the methyl umbrella modes of DDAO, has been recorded in the temperature interval 3–60°C and at different mole fractions of gramicidin-D with respect to DDAO ( Xg = 0.03, 0.05 and 0.1) for both DDAO-H 2O and DDAO-D 2O systems. It has been shown that the DDAO amphiphile molecules of the lamellar phase reorganise in a phase-like transition near 25–30°C. The DDAO-water system does not show any significant bands corresponding to a double gauche conformation at 1355 cm −1 nor to a gauche-transgauche (kinked) conformation at 1367 cm −1. These bands are probably present but hidden in the broad low-frequency side of the CH 3 umbrella band at 1377 cm −1. Upon incorporation of gramicidin into the lamellar phase both head group and acyl chain spectra of the lipid change in such a way as to indicate a decreased “ordering” of the molecules, as judged by comparison with spectra of the same molecule in a micellar environment, and with increased fluidity of the acyl chains. 相似文献
5.
The enthalpy and entropy of sublimation of N-ethylthiourea were obtained from the temperature dependence of its vapour pressure measured by both the torsion–effusion and the Knudsen effusion method in the temperature range 360–380 K. The compound undergoes no solid-to-solid phase transition or decomposition below 380 K. The pressure against reciprocal temperature resulted in lg( p, kPa) = (13.40 ± 0.27) − (6067 ± 102) / T(K). The molar sublimation enthalpy and entropy at the mid interval temperature were Δ subHm(370 K) = (116.1 ± 2.0) kJ mol −1 and Δ subSm(370 K) = (218.0 ± 5.2) J mol −1 K −1, respectively. The same quantities derived at 298.15 K were (118.8 ± 2.1) kJ mol −1 and (226.1 ± 5.5) J mol −1 K −1, respectively. 相似文献
6.
The low temperature heat capacities of N-(2-cyanoethyl)aniline were measured with an automated adiabatic calorimeter over the temperature range from 83 to 353 K. The temperature corresponding to the maximum value of the apparent heat capacity in the fusion interval, molar enthalpy and entropy of fusion of this compound were determined to be 323.33 ± 0.13 K, 19.4 ± 0.1 kJ mol −1 and 60.1 ± 0.1 J K −1 mol −1, respectively. Using the fractional melting technique, the purity of the sample was determined to be 99.0 mol% and the melting temperature for the tested sample and the absolutely pure compound were determined to be 323.50 and 323.99 K, respectively. A solid-to-solid phase transition occurred at 310.63 ± 0.15 K. The molar enthalpy and molar entropy of the transition were determined to be 980 ± 5 J mol −1 and 3.16 ± 0.02 J K −1 mol −1, respectively. The thermodynamic functions of the compound [ HT − H298.15] and [ ST − S298.15] were calculated based on the heat capacity measurements in the temperature range of 83–353 K with an interval of 5 K. 相似文献
7.
The second-order rate constants of gas-phase Lu( 2D 3/2) with O 2, N 2O and CO 2 from 348 to 573 K are reported. In all cases, the reactions are relatively fast with small barriers. The disappearance rates are independent of total pressure indicating bimolecular abstraction processes. The bimolecular rate constants (in molecule −1 cm 3 s −1) are described in Arrhenius form by k(O 2)=(2.3±0.4)×10 −10exp(−3.1±0.7 kJmol −1/ RT), k(N 2O)=(2.2±0.4)×10 −10exp(−7.1±0.8 kJmol −1/ RT), k(CO 2)=(2.0±0.6)×10 −10exp(−7.6±1.3 kJmol −1/ RT), where the uncertainties are ±2σ. 相似文献
8.
Quantitative IR solution data in carbon tetrachloride and chloroform are recorded for the CO and OH regions of 31 chromones. In the 1580–1700 cm −1 region, 5-hydroxychromones show three main maxima, the two of highest frequency, at 1663 ± 3 cm −1 and 1630 ± 5 cm −1 in CCl 4 (1661 ± 2 cm −1 and 1627 ± 5 cm −1 in CHCl 3), being sufficiently intense as to possess high CO character. Typically, 5-alkoxychromones exhibit two intense maxima in this region, 1663 ± 3 cm −1 and 1613 ± 7 cm −1 in CCl 4 (1657 ± 2 cm −1 and 1608 ± 12 cm −1 in CHCl 3). Diagnostically useful changes in contour and principal peak positions can be seen for substituted and annellated 5-hydroxychromones. In the 2500–3650 cm −1 region, the stretching frequencies of OH groups at the most commonly encountered positions (C-5, C-7, and 2-CH 2OH) in natural chromones, are identified. 相似文献
9.
The effect of temperature on fracture behaviour of isotactic polypropylene films has been studied on two PP samples of molecular weights M W=270 kg mol −1 and M W=150 kg mol −1, using the Essential Work of Fracture method. Two ductile-brittle transitions as a function of temperature are in evidence at respectively 10 and 60 °C. The former transition occurs for the highest molecular weight and the latter one for the lowest molecular weight. Three processes are involved in the temperature effect on PP toughness: (1) The decrease of yield stress with temperature according to Eyring’s law; (2) The role of cooperative motions in the amorphous phase: the ductile-brittle transition of the sample of highest MW corresponds to the glass transition; and (3) The role of the mobility of the crystalline phase: the ductile-brittle transition of the sample of lowest MW corresponds to the C transition. 相似文献
10.
The Gibbs energy of formation of IrO 2(s) has been measured by means of oxygen dissociation pressure measurements, and by EMF measurements using ZrO 2 (+ CaO) as the solid electrolyte. In addition, high-temperature enthalpy increments of IrO 2 have ben measured from 416 to 940 K using a drop calorimeter. A “third law” evaluation of the experimental results and data from literature has been made. For the enthalpy of formation of IrO 2(s) the value Δ H° f (298.15 K) - −(59.60 ± 0.03) kcal mole −1 has been selected. The thermodynamic functions of IrO 2(s) have been calculated in the temperature range 298–1200 K. 相似文献
11.
The rate coefficients of the reactions: (1) CN + H 2CO → products and (2) NCO + H 2CO → products in the temperature range 294–769 K have been determined by means of the laser photolysis-laser induced fluorescence technique. Our measurements show that reaction (1) is rapid: k1(294 K) = (1.64 ± 0.25) x 10 −11 cm 3 molecule −1 s −1; the Arrhenius relation was determined as k1 = (6.7 ± 1.0) x 10 −11 exp[(−412 ± 20)/T] cm 3 molecule −1 s −1. Reaction (2) is approximately a tenth as rapid as reaction (1) and the temperature dependence of k2 does not conform to the Arrhenius form: k2 = 4.62 x 10 −17T1.71 exp(198/ T) cm 3 molecule −1 s −1. Our values are in reasonable agreement with the only reported measurement of k1; the rate coefficients for reaction (2) have not been previously reported. 相似文献
12.
The hydrothermal reactions of vanadium oxide starting materials with divalent transition metal cations in the presence of nitrogen donor chelating ligands yield the bimetallic cluster complexes with the formulae [{Cd(phen 2) 2V 4O 12]·5H 2O (1) and [Ni(phen) 3] 2[V 4O 12]·17.5H 2O (2). Crystal data: C 48H 52Cd 2N 8O 22V 4 (1), triclinic.
a=10.3366(10), b=11.320(3), c=13.268(3) Å, =103.888(17)°, β=92.256(15)°, γ=107.444(14)°, Z=1; C 72H 131N 12Ni 2O 29.5V 4 (2), triclinic.
a=12.305(3), b=13.172(6), c=15.133(4), =79.05(3)°, β=76.09(2)°, γ=74.66(3)°, Z=1. Data were collected on a Siemens P4 four-circle diffractometer at 293 K in the range 1.59° <θ<26.02° and 2.01°<θ<25.01° using the ω-scan technique, respectively. The structure of 1 consists of a [V 4O 12] 4− cluster covalently attached to two {Cd(phen) 2} 2+ fragments, in which the [V 4O 12] 4− cluster adopts a chair-like configuration. In the structure of 2, the [V 4O 12] 4− cluster is isolated. And the complex formed a layer structure via hydrogen bonds between the [V 4O 12] 4− unit and crystallization water molecules. 相似文献
13.
The oxidation reaction of 2-aminophenol (OAP) to 2-aminophenoxazin-3-one (APX) initiated by 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) has been investigated in methanol at ambient temperature. The oxidation of OAP was followed by electronic spectroscopy and the rate constants were determined according to the rate law −d[OAP]/d t= kobs[OAP][TEMPO]. The rate constant, activation enthalpy and entropy at 298 K are as follows: kobs (dm 3 mol −1 s −1)=(1.49±0.02)×10 −4, Ea=18±5 kJ mol −1, Δ H‡=15±4 kJ mol −1, Δ S‡=−82±17 J mol −1 K −1. The results of oxidation of OAP show that the formation of 2-aminophenoxyl radical is the key step in the activation process of the substrate. 相似文献
14.
The Raman spectra of F 3PBH 3 and F 3PBD 3 have been recorded (2500-10 cm −1) of the liquids (−80°C) and solids (−196°C) as well as the infrared spectra (4000-33 cm −1) of the solids. In the spectrum of the solid state many of the 10B and 11B fundamentals were clearly defined and it was also possible to assign the BH 3 torsional frequency from the infrared and Raman spectra of the solids. A complete vibrational assignment is proposed and a normal coordinate calculation carried out. The force constant of 2.46 mdyn Å −1 for the P-B stretching mode is consistent with the short P-B bond; this constant is compared to the similar quantity for several other phosphorus-boron compounds. All of the E modes for the “free” molecule are shown to be split by the site symmetry which indicates that the molecules occupy C s or C 1 sites. The large number of observed lattice modes is consistent with two or more molecules per primitive cell. The torsional frequency was observed at 224 cm −1 and 167 cm −1 in hydrogen and deuterium compounds in the solid, respectively. These frequencies gave a periodic barrier of 4.15 kcal mole −1 for F 3PBH 3 and 4.31 kcal mole −1 for F 3PBD 3. CNDO/2 calculations have been carried out for F 3PBH 3 and the isoelectronic F 3SiCH 3 molecule in both the staggered and eclipsed forms and the dipole and barrier origins are discussed. 相似文献
15.
Equilibria between aluminium(III), pyrocatechol (1,2-dihydroxybenzene, H 2L) and OH − were studied in 0.6 M Na(Cl) medium at 25°C. The measurements were performed as emf titrations (glass electrode) within the limits 1.5 ≤ − log[H +] ≤ 9; 0.0005 ≤ B ≤ 0.015 M; 0.006 ≤ C ≤ 0.03 M and 2 ≤ C/B ≤ 30 ( B and C stand for the total concentrations of aluminium(III) and pyrocatechol respectively). All data can be explained with a main series of complexes: A1L +, log β −2,1,1 = − 6.337 ± 0.005; A1L 2−, log β −4,1,2 = −15.44 ± 0.017 and A1L 33−, log β −6,1,3 = − 28.62 ± 0.024 together with two minor species: Al(OH)L 22−, log β −5,1,2 = − 23.45 ± 0.079 and Al 3(OH) 3L 3, log β −9,3,3 = − 29.91 ± 0.066. Of the two, the latter probably is a type of average composition complex principally occurring at low C/B quotients. The first acidity constant for pyrocatechol as determined in separate experiments is log β −1,0,1 = − 9.198 ± 0.001. The standard deviations given are 3σ(log β p,q,r). Data were analyzed with the least squares computer program LETAGROPVRID. In a model calculation using kaolinite as solid phase, we compared the complexation ability of this system with that of the system Al 3+-OH −-salicylic acid, reported earlier in this series. 相似文献
16.
The e.m.f. of the galvanic cells Pt,C,Te(l),NiTeO 3,NiO/15 YSZ/O 2 ( Po2 = 0.21 atm),Pt and Pt,C,NiTeO 3,Ni 3TeO 6,NiO/15 YSZ/O 2 ( Po2 = 0.21 atm),Pt (where 15 YSZ=15 mass% yttria-stabilized zirconia) was measured over the ranges 833–1104 K and 624–964 K respectively, and could be represented by the least-squares expressions E(1)±1.48 (mV) = 888.72 − 0.504277 (K) and E(II) ±4.21 (mV) = 895.26 − 0.81543 T (K). After correcting for the standard state of oxygen in the air reference electrode, and by combining with the standard Gibbs energies of formation of NiO and TeO2 from the literature, the following expressions could be derived for the ΔG°f of NiTeO3 and Ni3TeO6: ΔGf°(NiTeO3) ± 2.03 (kJ mol−1) = −577.30 + 0.26692T (K) and ΔG°f(Ni3TeO6)±2.54 (kJ mol−1) = −1218.66 + 0.58837T (K). 相似文献
17.
Medium-resolution spectra of the N 2 b 1Π u-X 1Σ g+ band system were recorded by 1 + 1 multiphoton ionization. In the spectra we found different linewidths for transitions to different vibrational levels in the b 1Π u state: Δν 0 = 0.50 ± 0.05 cm −1, Δν 1 = 0.28 ± 0.02 cm −1, Δν 2 = 0.65 ± 0.06 cm −1, Δν 3 = 3.2 ± 0.5 cm −1, Δν 4 = 0.60 ± 0.07 cm −1, and Δν 5 = 0.28 ± 0.02 cm −1. From these linewidths, predissociation lifetimes τ ν were obtained: τ 0 = 16 ± 3 ps, τ 1 > 150 ps, τ 2 = 10 ± 2 ps, τ 3 = 1.6 ± 0.3 ps, τ 4 = 9 ± 2 ps, and τ 5 > 150 ps. Band origins and rotational constants for the b 1Π uν = 0 and 1 levels were determined for the 14N 2 and 14N 15N molecules. 相似文献
18.
This Letter reports the first kinetic study of 2-butoxy radicals to employ direct monitoring of the radical. The reactions of 2-butoxy with O 2 and NO are investigated using laser-induced fluorescence (LIF). The Arrhenius expressions for the reactions of 2-butoxy with NO ( k1) and O 2 ( k2) in the temperature range 223–311 K have been determined to be k1=(7.50±1.69)×10 −12×exp((2.98±0.47) kJmol −1/RT) cm 3 molecule −1 s −1 and k2=(1.33±0.43)×10 −15×exp((5.48±0.69) kJmol −1/RT) cm 3 molecule −1 s −1. No pressure dependence was found for the rate constants of the reaction of 2-butoxy with NO at 223 K between 50 and 175 Torr. 相似文献
19.
The highly neutralized ethylenediaminetetraacetate (EDTA) titrant (95–99% as Y 4− anion) precipitates with Ag + cations to form the Ag 4Y species, in aqueous medium, which is well characterized from conductometric titration, thermal analysis and potentiometric titration of the silver content of the solid. The precipitate dissolves in excess Y 4− to form a complex, AgY 3−. Equilibrium studies at 25°C and ionic strength 0.50 M (NaNO 3) have shown from solubility and potentiometric measurements that the formation constant (95% confidence level) β 1 = (1.93 ± 0.07) × 10 5 M −1 and the solubility products are KS0 = [Ag +] 4[Y 4−] = (9.0 ± 0.4) × 10 −18 M 5 and KS1 = [Ag +] 3[AgY 3−] = (1.74 ± 0.08) × 10 −12 M4. The presence of Na +, rather than ionic strength, markedly affects the equilibrium; the data at ionic strength 0.10 M are: β 1 = (1.19 ± 0.03) × 10 6 M −1, KS0 = (1.6 ± 0.4) × 10 −19 M 5 and KS1 = (1.9 ± 0.5) × 10 −13 M 4; at ionic strength tending to zero; β 1 = (1.82 ± 0.05) × 10 7 M −1, KS0 = (2.6 ± 0.8) × 10 −22 M 5 and KS1 = (5 ± 1) × 10 −15 M 4. The intrinsic solubility is 2.03 mM silver (I) in 0.50 M NaNO 3. Well-defined potentiometric titration curves can be taken in the range 1–2 mM with the Ag indicator electrode. Thermal analysis revealed from differential scanning calorimetry a sharp exothermic peak at 142°C; thermal gravimetry/differential thermal gravimetry has shown mass loss due to silver formation and a brown residue, a water-soluble polymeric acid (decomposition range 135–157°C), tending to pure silver at 600°C, consistent with the original Ag 4Y salt. 相似文献
20.
A high-resolution emission spectrum of a low-pressure Ar-diluted CO + N 2O → CO 2 + N 2 flame catalyzed by Na metal vapor has been obtained and examined for vibrational disequilibrium. Emission in the 1900-2400 cm −1 spectral region, which includes the fundamental and “hot” bands of CO, CO 2(ν 3), and N 2O(ν 3), was recorded with high resolution and the CO emission was analyzed in detail to determine vibrational and rotational temperatures which were found to be unequal, Tv = 2050°K and TR = 1100°K. An examination of vib-vib and vib-trans energy transfer mechanisms results in the conclusion that an excess of 14% of the chemical energy is preferentially deposited in the resonantly-coupled N 2, CO, CO 2 (ν 3), and N 2O(ν 3) vibrational modes. It is further observed that CO vibrational levels for ν > 4 are excessively populated, presumably due to quenching of Na*(3p) by CO; the flame is accompanied by intense Na D-line chemiluminescence. 相似文献
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