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1.
Saddle point geometries and barrier heights have been calculated for the H abstraction reaction HO 2( 2A″)+H( 2S) → H 2( 1Σ +g)+O 2( 3Σ −g) and the concerted H approach-O removing reaction HO 2 ( 2A″)+H( 2S) → H 2O( 1A 1)+O( 3P) by using SDCI wavefunctions with a valence double-zeta plus polarization basis set. The saddle points are found to be of C s symmetry and the barrier heights are respectively 5.3 and 19.8 kcal by including size consistent correction. Moreoever kinetic parameters have been evaluated within the framework of the TST theory. So activation energies and the rate constants are estimated to be respectively 2.3 kcal and 0.4×10 9 ℓ mol −1 s −1 for the first reaction, 20.0 kcal and 5.4.10 −5 ℓ mol −1 s −1 for the second. Comparison of these results with experimental determinations shows that hydrogen abstraction on HO 2 is an efficient mechanism for the formation of H 2 + O 2, while the concerted mechanism envisaged for the formation of H 2O + O is highly unlikely. 相似文献
2.
A mixture of NF 3 and Ar is passed through an rf discharge in a flow-system to produce, among other species, F and NF 2. When H 2, D 2, or CH 4 are added downstream, reactions with F atoms produce vibrationally excited HF or DF together with H, D, or CH 3. The latter free radicals can react with NF 2, probably by an elimination reaction to produce electronically excited NF: NF 2( 2B 1) + H(D, CH 3) → HF *(DF * + NF(a 1Δ). A vibrational-to-electronic energy transfer process between the products of this reaction then produces the next higher state of NF: HF(ν 2) + NF(a 1Δ) → HF(ν−2) + NF(b 1Σ +). A similar transfer process has also been found between the electronically excited a 1Δ states of O 2 and NF: O 2(a 1Δ) + NF(a 1Δ) → O 2(X 3Σ −) + NF(b 1Σ +). The H or D atoms but not the CH 3 radicals are then found to react with either NF(a 1Δ) or NF(X 3Σ −) to produce electronically excited N( 2D) atoms, which in turn react with the NF(a 1Δ) molecules to produce N 2(B 3Π g). The observed nitrogen first positive radiation has been demonstrated to be produced entirely by this reaction mechanism rather than by the N( 4S) recombination that accounts for the Rayleigh afterglow. In addition, the occurrence of the reaction N( 2D) + N 2O → NO(B 2Π r) + N 2 (X 1Σ +g) has been verified. Finally we have observed emission at 3344 Å, which we attribute to the NF(A 3Π), which has not been previously reported. 相似文献
3.
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
4.
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
5.
The rate constants at which oxidizing and reducing radicals react with the dinuclear iron(III) complex Fe 2O(ttha) 2− were measured in neutral aqueous solution. The rate constants for reduction of the complex by ·CO 2.− CH 3.CHOH and O 2.− were found to be comparable with rate constants previously measured in mononuclear iron(III) polyaminocarboxylate systems. Fe 2O(ttha) 2− reacts slowly with O 2.− ( k8 = (1.2 ± 0.2) × 10 4 dm 3 mol −1 s −1) and, hence, is a relatively poor catalyst for the dismutation of superoxide radical. The hydrated electron reduces the complex at a diffusion-controlled rate in a process which consumes one proton: e aq− + Fe 2O(ttha) 2− → Fe 2III,IIO(ttha) 3− The reduction by carbon-centered radicals produces a (III,II) mixed-valence complex with an absorption spectrum different from that of the Fe 2(II,III) species produced from reduction by the hydrated electron. The oxidizing radicals .OH and ·CO 3− appear to act as reductants of the complex via ligand oxidation rather than by oxidation of the Fe 2IIIO core to Fe 2III,IVO. In the former case ligand attack appears to occur mainly at the methylene carbon of a glycinate group. The decarboxylation product, CO 2, was detected by its aquation reaction in the presence of a pH sensitive dye, bromthymol blue. 相似文献
6.
A laser pulse-and-probe method has been used to determine the nascent vibrational populations in NO( v=0–4) and O 2( v=6–11) formed in the thermal reaction: O( 3P) + NO 2 → O 2( v) + NO( v). A frequency-tripled Nd: YAG laser is used to photolyse NO 2, diluted tenfold in Ar, and laser-induced fluorescence spectroscopy in the NO A 2Σ +-X 2Π and O 2 B 3Σ −u -X 3Σ −g electronic band system is used both to follow the kinetics of individual vibrational states and to determine the nascent vibrational distributions. The majority of the NO product is formed in v = 0 and the average vibrational yield is ≈ 4.6%. The O 2 populations fall monotonically from v = 6 to 11 in a distribution close to what is expected on prior grounds. Based on a surprisal analysis, the average vibrational energy yield in O 2 is ≈ 26%. The nature of the reaction dynamics is discussed. 相似文献
7.
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
8.
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
9.
The one-electron oxidation of Mitomycin C (MMC) as well as the formation of the corresponding peroxyl radicals were investigated by both steady-state and pulse radiolysis. The steady-state MMC-radiolysis by OH-attack followed at both absorption bands showed different yields: at 218 nm G i (-MMC) = 3.0 and at 364 nm G i (-MMC) = 3.9, indicating the formation of various not yet identified products, among which ammonia was determined, G(NH 3) = 0.81. By means of pulse radiolysis it was established a total κ (OH + MMC) = (5.8 ± 0.2) × 10 9 dm 3 mol −1 s −1. The transient absorption spectrum from the one-electron oxidized MMC showed absorption maxima at 295 nm (ε = 9950 dm 3 mol −1 cm t-1), 410 nm (ε = 1450 dm 3 mol −1 cm −1) and 505 nm ( ε = 5420 dm 3 mol −1 cm −1). At 280–320 and 505 nm and above they exhibit in the first 150 μs a first order decay, κ 1 = (0.85 ± 0.1) × 10 3 s −1, and followed upto ms time range, by a second order decay, 2κ = (1.3 ± 0.3) × 10 8 dm 3 mol -1 s −1. Around 410 nm the kinetics are rather mixed and could not be resolved. The steady-state MMC-radiolysis in the presence of oxygen featured a proportionality towards the absorbed dose for both MMC-absorption bands, resulting in a Gi (-MMC) = 1.5. Among several products ammonia-yield was determined G(NH3) = 0.52. The formation of MMC-peroxyl radicals was studied by pulse radiolysis, likewise in neutral aqueous solution, but saturated with a gas mixture of 80% N2O and 20% O2. The maxima of the observed transient spectrum are slightly shifted compared to that of the one-electron oxidized MMC-species, namely: 290 nm (ε = 10100 dm3 mol−1 cm−1), 410 nm (ε = 2900 dm3 mol−1 cm−1) and 520 nm (ε = 5500 dm3 mol−1 cm−1). The O2-addition to the MMC-one-electron oxidized transients was found to be at 290 to 410 nm gk(MMC·OH + O2) = 5 × 107 dm3 mol−1 s−1, around 480 nm κ = 1.6 × 108 dm3 mol−1 s−1 and at 510 nm and above, κ = 3 × 108 dm3 mol−1 s−1. The decay kinetics of the MMC-peroxyl radicals were also found to be different at the various absorption bands, but predominantly of first order; at 290–420 nm κ1 = 1.5 × 103 s−1 and at 500 nm and above, κ = 7.0 × 103 s−1. The presented results are of interest for the radiation behaviour of MMC as well as for its application as an antitumor drug in the combined radiation-chemotherapy of patients. 相似文献
10.
Pulse radiolysis of epicatechin in aqueous solution has been done to investigate the reactions of epicatechin derived phenoxy radical (EpO) at neutral pH. EpO was generated by N 3 reacting toward EpOH, the rate constant was measured to be 3 × 10 8 dm 3 mol −1 s −1. The biomolecular termination of EpO is rather slow ((2 k < × 10 6 dm 3 mol −1 s −1) and results in products exhibiting strong visible absorption around 450 nm. No reactions have been observed for EpO with O 2 and O 2 in the time scale of pulse radiolysis (0.01 s), suggesting the bimolecular rate constant are less than 10 4 and 5 × 10 6 dm 3 mol −1 s −1, respectively. 相似文献
11.
The thermal decomposition of CaOsO 3 by differential thermal analyses, thermogravimetry and X-ray powder diffraction has been studied. In nitrogen CaOsO 3 decomposes at 880 ± 10°C into CaO, osmium metal and oxygen due to the reaction CaOsO 3 → CaO + Os + O 2. In static air the decomposition occurs in three stages: 2CaOsO 3 + 1/2O 2 → Ca 2Os 2O 7 (in region 775–808°C), Ca 2Os 2O 7 → Ca 2Os 2O 6,5 + 1/4O 2 (at a temperature interval of 850–1000°C) and in the third stage Ca 2Os 2O 6,5 → 2CaO + OsO 4 ÷ 1/4 O 2 (at 1005 ± 5°C). The first intermediate Ca 2Os 2O 7 is isostructural with orthorhombic Ca 2Nb 2O 7 and its cell parameters are: a0 = 3.745 Å, b0 = 25.1 Å, c0 = 5.492 Å, Z = 4, space group Cmcm or Cmc2. Ca 2Os 2O 7 exhibits metallic conductivity and its electrical resistivity is 4.6 × 10 −2 ohm-cm at 296K. 相似文献
12.
Measurements of electron stimulated desorption (ESD) yields of O −, at incident electron energies below 20 eV, from 0.15 monolayers (ML) of O 2 physisorbed at 20 K on a variety of molecular solids have been performed. It is observed that for O 2 condensed on 4 ML of H 2O, the O − signal from dissociative electron attachment (DEA) to O 2 is entirely absent. We attribute this to a complete quenching of the dissociative 2Π u, 2Σ +g, and 2Σ +u, resonances of O −2 by the adjacent water molecules. 相似文献
13.
The fraction FΣ of excited-state oxygen formed as b 1Σ g+ was determined for a series of triplet-state photosensitizers in CCl 4 solutions. FΣ was determined by monitoring the intensities of (a) O 2(b 1Σ g+) fluorescence at 1926 nm (O 2(b 1Σ g+)→O 2(a 1Δ g) and (b) O 2(a 1 Δ g) phosphorescence at 1270 nm (O 2(a 1Δ g) → O 2(X 3Σ g−)). Oxygen excited states were formed by energy transfer from substituted benzophenones and acetophenones. The data indicate that FΣ depends on several variables including the orbital configuration of the lowest triplet state and the triplet-state energy. The available data indicate that the sensitizer-oxygen charge transfer (CT) state is not likely to influence FΣ strongly by CT-mediated mixing of various sensitizer-oxygen states. 相似文献
14.
The electronic quenching rates of NO(A 2Σ +, v′=0–2) are measured for the gases He, Ar, Xe, N 2, O 2, CO 2, N 2O, and SF 6. The variations of the fluorescence intensity were measured for the (0,0), (1,0), and (2,0) bands of the γ band system when the quencher gases were added. The quenching rates were determined by using the Stern–Volmer plots with the known radiative lifetimes of the excited states. The electronic quenching rate constants are fast for the group of gases of O 2, CO 2, N 2O, and SF 6, whose quenching rate constants are in the order of 10 −10 cm 3/s. The quenching rate constants are slow for the group of gases including He, Ar, Xe, and N 2 whose rate constants are in the order of 10 −14 cm 3/s. For the slow group, the quenching rate constants increase rapidly for v′=2 compared with those of v′=0 and 1. The charge transfer model and collision complex model are used to understand the quenching mechanism. For the fast group which mainly consists of gases with positive electron affinities, the charge transfer model adequately describes the mechanism. For the slow quenching group, a theoretical background is provided by consider the coupling of initial and final states in the complex potential surfaces. 相似文献
15.
Polarized absorption spectra of Ba(MnO 4) 2·3H 2O/Ba(ClO 4) 2·3H 2O mixed single crystals are reported at 4.2°K. Previous 1T 2 → 1A 1 assignments for the 5200 Å and 3000 Å absorption bands of MnO 4− are substantiated; further support is provided for the 1T 1 → 1A 1 assignment of the 3600 Å absorption band of MnO 4−. The site-splitting of the 5200 Å 1T 2 state is E( 1E)− E( 1A) ≈ −150 cm −1; that of the 3000 Å 1T 2 state is E( 1E)− E( 1A) ≈ 300 cm −1. A significant e vibronic intensity component is observed in the 5200 Å 1T 2 state. 相似文献
16.
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
17.
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
18.
In addition to the red phosphorescence (T 1( 3 A 2n, π *) → S 0) xanthione exhibits in solution an emission with a maximum at ≈ 23 000 cm −1 and φ f(298°) = 5 × 10 −3. It is shown that this emission is fluorescence from the second excited singlet state (S 2 ( 1A 1 π, π *) → S 0). 相似文献
19.
A superoxochromium(III) ion, Cr aqOO 2+, acts as a catalyst for the co-oxidation of alcohols and nitrous acid with molecular oxygen according to the stoichiometry: CH 3OH+HNO 2+O 2→CH 2O + NO 3− + H 2O+H +. The kinetics are second order in [HNO 2] and independent of the concentrations of the superoxochromium catalyst, substrate, and O 2. The proposed mechanism features the disproportionation of HNO 2 to NO and NO 2, both of which react rapidly with Cr aqOO 2+. The Cr aqOO 2+/NO reaction generates another equivalent of NO 2 and a mole of Cr aqO 2+, the active oxidant. The two-electron oxidation of the alcohol by Cr aqO 2+ produces Cr aq2+, which reacts rapidly with O 2 to regenerate the catalyst, Cr aqOO 2+. The NO 2/Cr aqOO 2+ reaction yields the peroxynitrato complex, Cr aqOONO 22+, in a dead-end equilibrium process that has no effect on the catalytic reaction. The disproportionation of NO 2 yields the final nitrogen-containing product, NO 3−, and regenerates an equivalent of HNO 2. Under a fixed set of conditions, the relative catalytic efficiency (CE) of Cr aqOO 2+ decreases as its concentration increases owing to the competition between O 2 and Cr aqOO 2+ for the intermediate Cr aq2+. 相似文献
20.
采用密度泛函理论研究Au-Pd和Au-Pt 纳米团簇催化解离N 2O. 首先根据计算得到Au 19Pd和Au 19Pt 团簇的最优构型(杂原子均位于团簇的表面). 以Au 19Pd催化解离N 2O为例研究催化解离的反应机理. 对此主要考虑两个反应机理, 分别是Eley-Rideal (ER)和Langmuir-Hinshelwood (LH). 第一个机理中N 2O解离的能垒是1.118 eV, 并且放热0.371 eV. N 2分子脱附后, 表面剩余的氧原子沿着ER路径消除需要克服的能垒是1.920eV, 这比反应沿着LH路径的能垒高0.251 eV. 此外根据LH机理, 氧原子在表面的吸附能是-3.203 eV, 而氧原子在表面转移所需的能垒是0.113 eV, 这表明氧原子十分容易在团簇表面转移, 从而促进氧气分子的生成. 因此, LH为最优反应路径. 为了比较Au 19Pd和Au 19Pt 对N 2O解离的活性, 根据最优的反应路径来研究Au 19Pt 催化解离N 2O, 得到作为铂族元素的铂和钯对N 2O的解离有催化活性, 尤其是钯. 同时, 将团簇与文献中的Au-Pd合金相比较, 得到这两种团簇对N 2O 解离有较高的活性, 尤其是Au 19Pd团簇. 再者, O 2的脱附不再是影响反应的主要原因, 这可以进一步提高团簇解离N 2O的活性. 相似文献
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