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1.
The reaction: F + HCl→ HF ( v 3) + Cl (1), has been initiated by photolysing F 2 using the fourth-harmonic output at 266 nm from a repetitively pulsed Nd: YAG laser By analysing the time-dependence of the HF(3,0) vibrational chemiluminescence, rate constants have been determined at (296 ± 5) K for reaction (1), k1 = (7.0 ± 0.5) × 10 −12 cm 3 molecule −1 s −1, and for the relaxation of HF( v = 3) by HCl, CO 2, N 2O, CO, N 2 and O 2: kHCl = (1.18 ±0.14) × 10 −11 kCO2 = (1.04 ± 0. 13) × 10 −12, kN2O = (1.41 ± 0.13) × 10 −11 kCO = (2.9 ± 0.3) × (10 −12, kN2 = (7.1 ± 0.6) × 10 −14 and kO2 = (1.9 ± 0.6) × 10 −14 cm 3molecule −1s −1. 相似文献
2.
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
3.
Rate constants for the reactions of OH with CH 3CN, CH 3CH 2CN and CH 2=CH-CN have been measured to be 5.86 × 10 −13 exp(−1500 ± 250 cal mole −1/ RT), 2.69 × 10 −13 exp(−1590 ± 350 cal mole −1/ RT and 4.04 × 10 −12 cm 3 molecule −1 s −1, respectively in the temperature range 298–424 K. These results are discussed in terms of the atmospheric lifetimes of nitrfles. 相似文献
4.
The state-selected reaction of CH(X 2Πν″ = 0, 1) with H 2 has been studied, in which CH was generated by IRMPD of a precursor gas, CH 3OH. The subsequent evolution of CH (ν″ = 0, 1) was monitored by the sensitive LIF technique. For the ground state and vibrationally excited state CH, the reaction with H 2 is found to depend on the total pressure in the sample cell at room temperature, which suggests that the reaction proceeds through an intermediate adduct, CH 3. The backward dissociation process is found to depend on the buffer pressure, which can be rationalized via a collision-induced backward dissociation. The decay rates of CH (ν″ = 0, 1) due to collisions with H 2 and Ar at a buffer pressure of 10 Torr are kH2 (ν″ = 1) = (2.3±0.1) × 10 −1 cm 3 molecule −1 s −1 and kAr (ν″ = 1) = (4.4±0.1) × 10 −13 cm 3 molecule −1 s −1. Possible effects of the vibrational excitation on the reaction rate of CH (ν″ = 1) are discussed. 相似文献
5.
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
6.
The rate coefficients for the reactions of C 2H and C 2D with O 2 have been measured in the temperature range 295 K T 700 K. Both reactions show a slightly negative temperature dependence in this temperature range, with kC2H+O2 = (3.15 ± 0.04) × 10 −11 ( T/295 K) −(0.16 ± 0.02) cm 3 molecule −1 s −1. The kinetic isotope effect is kC2H/ kC2D = 1.04 ± 0.03 and is constant with temperature to within experimental error. The temperature dependence and the C 2H + O 2 kinetic isotope effect are consistent with a capture-limited metathesis reaction, and suggest that formation of the initial HCCOO adduct is rate-limiting. 相似文献
7.
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
8.
This survey begins with the photochemistry at 254 nm and 298 K in the system H 2O 2COO 2RH, the primary objective of which is to determine the rate constants for the reaction OH + RH → H 2O + R relative to the well-known rate constant for the reaction OH + CO → CO 2 + H. Inherent in the scheme is that the reaction HO 2+CO→OH+CO 2 is negligible compared with the OH reaction, and a literature consensus gives kHO2 < 10 −19 cm 3 molecule −1 s −1, or some 10 6 less than kOH at 298 K. Theoretical calculations establish that the first stage in the HO 2 reaction is the formation of a free radical intermediate HO 2 + CO → HOOCO (perhydroxooxomethyl) which decomposes to yield the products, and that the rate of formation of the intermediate is equal to the rate of formation of the products. The structure of the intermediate and a reaction profile are shown. High temperature rate data reported subsequent to the data in the consensus and theoretical calculations lead here to a recommendation that, in the range 250–800 K, kHO2 = 3.45 × 10−12T1/2 exp(1.15 × 104/T) cm3 molecule−1 s−1, the hard-sphere-collision Arrhenius modification. This yields kHO2(298) = 1.0 × 10−27 cm3 molecule−1 s−1 or some 1014 slower than kOH(298). 相似文献
9.
The rate constants, k1 and k2 for the reactions of C 2F 5OC(O)H and n-C 3F 7OC(O)H with OH radicals were measured using an FT-IR technique at 253–328 K. k1 and k2 were determined as (9.24 ± 1.33) × 10 −13 exp[−(1230 ± 40)/ T] and (1.41 ± 0.26) × 10 −12 exp[−(1260 ± 50)/ T] cm 3 molecule −1 s −1. The random errors reported are ±2 σ, and potential systematic errors of 10% could add to the k1 and k2. The atmospheric lifetimes of C 2F 5OC(O)H and n-C 3F 7OC(O)H with respect to reaction with OH radicals were estimated at 3.6 and 2.6 years, respectively. 相似文献
10.
At 25°C, I = 1.0 M (CF 3SO 3−Li ++CF 3SO 3H), [H +] = 0.034–0.274 M and λ = 453 nm, the rate equation for the oxidation of Ti(H 2O), 63+ by bromine was found to be: −d/[Br 2] T/d t= kK/[Br 2][Ti III]/[H +]+ K+ kK/[Br 3−][Ti III]/[H ++ K, where k = 9.2 × 10 −3 M −1 s −1 and K = 4.5 × 10 −3 M. At [H +] = 1.0 M, [Br −] = 0.05–0.4 M, the apparent second-order rate constant decreases as [Br −] increases. The pH-dependence of the oxidation of TiIII-edta by bromine is interpreted in terms of the change in identity of the TiIII-edta species as the pH of the reaction medium changes. The second-order rate constants were fitted using a non-linear least-square computer program with (1/k0edta)2 weighting into an equation of the form: k0edta =k1+k2K1[H+]−1+k3K1K2[H+]−2/1+K1[H+[H+−1+K1K2[H+]−2, with K1 and K2 fixed as earlier determined at 9.55 × 10−3 and 2.29 × 10−9 M, respectively, for the oxidation of bromine. k1=k2=(3.1±0.32)×103M−1s−1 k3=(2.3±0.45)×106N−1s−1. It is proposed that these electron transfer reactions proceed by univalent changes with the production of Br2.− as a transient intermediate. An outer-sphere mechanism is proposed for these reactions. The homonuclear exchange rate for TiIII-edta+TiIV-edta is estimated at 32 M−1 s−1. 相似文献
11.
Pentaerythrityl tetraethylenediamine (PETEDA) dendrimer was synthesized from pentaerythrityl tetrabromide and ethylenediamine. Its molecular structure was characterized by elemental analysis, Fourier transform infrared resonance (FT-IR) and hydrogen nuclear magnetic resonance ( 1H NMR) spectroscopy. The composite membranes for selectively permeating CO 2 were prepared by using PETEDA-PVA blend polymer as the active layer and polyethersulfone (PES) ultrafiltration membrane as the support layer and their permselectivity was tested by pure CO 2 and CH 4 gases and the gas mixture containing 10 vol.% CO 2 and 90 vol.% CH 4, respectively. For pure gases, the membrane containing 78.6 wt% PETEDA and 21.4 wt% PVA in the blend has a CO 2 permeance of 8.14 × 10 −5 cm 3 (STP) cm −2 s −1 cmHg −1 and CO 2/CH 4 selectivity of 52 at 143.5 cmHg feed gas pressure. While feed gas pressure is 991.2 cmHg, CO 2 permeance reaches 3.56 × 10 −5 cm 3 (STP) cm −2 s −1 cmHg −1 and CO 2/CH 4 selectivity is 19. For the gas mixture, the membrane has a CO 2 permeance of 6.94 × 10 −5 cm 3 (STP) cm −2 s −1 cmHg −1 with a CO 2/CH 4 selectivity of 33 at 188.5 cmHg feed gas pressure, and a CO 2 permeance of 3.29 × 10 −5 cm 3 (STP) cm −2 s −1 cmHg −1 with a CO 2/CH 4 selectivity of 7.5 at a higher feed gas pressure of 1164 cmHg. A possible gas transport mechanism in the composite membranes is proposed by investigating the permeating behavior of pure gases and the gas mixture and analyzing possible reactions between CO 2/CH 4 gases and the PETEDA-PVA blend polymer. The effect of PETEDA content in the blend polymer on permselectivity of the composite membranes was investigated, presenting that CO 2 permeance and CO 2/CH 4 selectivity increase and CH 4 permeance decreases, respectively with PETEDA content. This is explained by that with increasing PETEDA content, the carrier content increases, and the crystallinity and free volume of the PETEDA-PVA blend decrease that were confirmed by the experimental results of X-ray diffraction spectra (XRD) and positron annihilation lifetime spectroscopy (PALS). 相似文献
12.
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
13.
The kinetics of the association reaction of CF 3 with NO was studied as a function of temperature near the low-pressure limit, using pulsed laser photolysis and time-resolved mass spectrometry. CF 3 radicals were generated by photolysis of CF 3I at 248 nm and the kinetics was determined by monitoring the time-resolved formation of CF 3NO. The bimolecular rate constants were measured from 0.5 to 12 Torr, using nitrogen as the buffer gas. The results are in very good agreement with recent data published by Vakhtin and Petrov, obtained at room temperature in a higher pressure range and, therefore, the two studies are quite complementary. A RRKM model was developed for fitting all the data, including those of Vakhtin and Petrov and for extrapolating the experimental results to the low- and high-pressure limits. The rate expressions obtained are the following: k1(0) = (3.2 ± 0.8) × 10 −29 ( T/298) −(3.4±0.6) cm 6 molecule −2 s −1 for nitrogen used as the bath gas and k1(∞) = (2.0 ± 0.4) × 10 −11 ( T/298) (0±1) cm 3 molecule −1 s −1. RRKM calculations also help to understand the differences in reactivity between CF 3 and other radicals, for the same association reaction with NO. 相似文献
14.
Excitation of solutions of Fe(bipy) 2(CN) 2 by a 266-nm laser pulse produces a hydrated electron and the oxidized complex, Fe(bipy) 2 (CN) 2+, in the primary photochemical step, in homogeneous aqueous solution as well as in aqueous solutions containing cetyltrimethylammonium bromide (CTAB) or sodium dodecyl sulfate (SDS) micelles. In all cases nascent hydrated electrons react with ground state Fe(bipy) 2(CN) 2 to form Fe(bipy) 2(CN) 2−, and comparison of the decay constants in the three media (H 2O: k = 2.8 × 10 10 M −1 s −1; CTAB: k = 2.9 × 10 10 M −1 s −1; SDS: k = 5.5 × 10 9 M −1 s −1), shows that the reaction is essentially unaffected by CTAB micelles but is much slower in SDS solution. Similar micellar effects were found for the back reaction between e aq− and Fe(bpy) 2(CN) 2+. Rate constants for the scavenging of the photogenerated hydrated electrons by methyl viologen (MV 2+) cations and NO 3− anions were measured in the three systems, and the results indicate that for scavenging by MV 2+ the rate constants are decreased in the micelle systems ( k in H 2O, 8.4 × 10 10; CTAB, 3.5 × 10 10 and SDS, 1.58 × 10 10 M −1 s −1), whereas for NO 3− the CTAB micelle decreases while the SDS micelle enhances the scavenging compared to water solution ( k in H 2O, 8.3 × 10 9; CTAB, 7 × 10 8; and SDS, 2.05 × 10 10 M −1 s −1). For the comproportionation reaction between Fe(bipy) 2(CN) 2+ and Fe(bipy) 2(CN) 2− both micelles reduce the rate ( k in H 2O, 3.3 × 10 10; CTAB, 2.3 × 10 10; and SDS, 1.05 × 10 10 M −1s −1), but while the reaction of Fe(bipy) 2(CN) 2+ with MV + is increased in CTAB compared to water, it is slowed in SDS ( k in H 2O, 2.4 × 10 10; CTAB, 8.9 × 10 10; and SDS, 1.8 × 10 10 M −1s −1). All effects observed in these microheterogeneous systems can be uniformly interpreted in terms of Coulombic interactions between the actual reactants and the charged surface of the micelles. 相似文献
15.
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
16.
EPR lineshape simulation studies have been performed on a specimen of 80MoO 3–20B 2O 3 glass in the temperature range of 300–77 K. The values of the obtained spin Hamiltonian parameters are: g=1.940, g=1.974, A=150.0×10 −4 cm −1, A=35.6×10 −4 cm −1 and g=1.935, g =1.975, A=141.9×10 −4 cm −1, A=34.5×10 −4 cm −1 at 300 and 77 K, respectively. The paramagnetic site in the specimen is molybdenyl, MoO 3+, ion in which the Mo is in a distorted octahedral environment of six oxygen atoms with C 4v symmetry. The 11-parallel and 11-perpendicular line feature of the EPR lineshape shows that two Mo nuclei are magnetically equivalent in the glassy matrix, in the temperature range 300–77 K. 相似文献
17.
The triethylsilane radical R 3•Si, produced by radiolysis in an airfree methanol/silane-system, acts as a specific scavenger for the CH 3•O and •CH 2OH transients with rate constants, k14(R 3•Si + CH 3•O) = 1.1 x 10 8 dm 3 mol -1s -1 and k15(R 3•Si + •CH 2OH) = 0.7 x 10 8 dm 3 mol -1s -1, resulting in R 3Si—OCH 3 (triethylmethoxysilane) and R 3Si—CH 2OH (triethylsilylmethanol). By increasing the silane concentration (range: 10 -2-6 mol dm -3 R 3SiH) the formation of the otherwise major products of methanol radiolysis, formaldehyde and glycol, is successively reduced to nil. The yield of R 3Si—CH 2OH, studied under the same conditions, passes a maximum at about 0.8 mol dm -3 R 3SiH and then also diminishes. On the other hand, the yield of R 3Si—OCH 3 is increased correspondingly and reaches an interpolated value of G = 3.75 ± 0.1 at 4 mol dm -3R 3SiH. This indicates that the radical CH 3•O ( G = 3.75 ± 0.1) is the primary radiolytic transient of methanol in addition to H, e -sol etc., but not •CH 2OH species. The latter one is obviously formed by the secondary reaction: CH 3•O + CH 3OH→ CH 3OH + •CH 2OH. 相似文献
18.
This article gives the degradation rate constants of meso-tetrakis(3,5-disulfonatomesityl)porphinatomanganese(III) X (where X=H 2O and/or OH − depending on pH) (MnTMSP) and its β-brominated analogue (MnTMSPBr 8) toward the oxidants NaOCl, H 2O 2, and (CH 3) 3COOH at various pHs, I=0.2 M and 30°C. In addition, the degradation rate constants of MnTMSP was determined when it was bound to cationic supports — namely, CTAB, a poly(vinylbenzyltrimethylammonium chloride) latex, 2,6-ionene and 2,10-ionene. MnTMSP showed high structural stability toward the peroxides in strong acidic medium and the degradation rate constants were found as low as 10 −4 min −1 at pH<1.50. When NaOCl was employed as the oxidant, the pH dependence of the stability of MnTMSP was vice versa and its degradation rate constant was determined as 1.43×10 −4 min −1 at pH 14.10. In strong acidic solution, the supports CTAB and latex made the stability of MnTMSP toward the peroxides improve significantly. In strong basic solution, only latex-bound MnTMSP showed higher stability toward NaOCl than the homogeneous MnTMSP. Because MnTMSPBr 8 was not stable in solutions having pH higher than 9 and containing no oxidant, its stability was investigated at pH<9 and it showed slightly lower stability toward the peroxides than the non-brominated analogue. 相似文献
19.
The photocatalytic removal of the insecticide fenitrothion (IUPAC name: O, O-dimethyl O-4-nitro- m-tolyl phosphorothioate), C 9H 12NO 5PS, from water suspension of TiO 2, was investigated by following the disappearance of the original substance along with the formation and disappearance of intermediates via recording NMR ( 1H and 31P) and UV spectra, as well as by pH measurements. Based on the obtained data, a possible reaction mechanism was proposed. It was found that 31P-NMR spectrometry can be successfully used to follow the kinetics of transforming organic into inorganic phosphorus in the course of the degradation ( ka=9.2×10 −7 mol dm −3 min −1, r=0.980 for the illumination period after 15 h). The rate of fenitrothion aromatic ring decomposition was followed by UV spectrometry during the illumination ( ka=3.1×10 −6 mol dm −3 min −1, r=0.989). The complete mineralization was attained after about 66 h of irradiation. 相似文献
20.
We have applied cavity ring-down spectroscopy to a kinetic study of the reaction of NO 3 with CH 2I 2 in 25–100 Torr of N 2 diluent at 298 K. The rate constant of reaction of NO 3 + CH 2I 2 is determined to be (4.0 ± 1.2) × 10 −13 cm 3 molecule −1 s −1 in 100 Torr of N 2 diluent at 298 K. The rate constant increases with increasing pressure of buffer gas below 100 Torr. The reaction of CH 2I 2 with NO 3 has the potential importance at nighttime in the atmosphere. 相似文献
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