The photocurrent kinetics in acid solutions have been investigated. The diffusion coefficients of atoms H?((7±2)×10?5cm2s?1) and D?((4±1)×10?5cm2s?1) and OH? and OD? radicals ((1±0.3)×10?5cm2s?1) are found. The rate constants of capture of solvated electrons by H3O+ and D3O+ ions are identical and equal to (8±1)×109M?1s?1. From the shape of the kinetic curves it follows that electrochemical desorption of atomic hydrogen occurs from the adsorbed state. The rate constant of this process has been measured. It is shown that the rate constant of electrochemical desorption depends only slightly on the potential. 相似文献
The decay of prompt fluorescence in crystalline naphthalene at 300 K, excited by a picosecond 266 nm pulse, has been studied as a function of excitation intensity. Experimental decay curves can be fitted only when the exponential distribution in depth of excitation and the radial (gaussian) intensity profile of the excitation are both taken into account. From an analysis of the decay at early time (?5 ns) a best fit value of the singlet—singlet annihilation rate constant is found γSS = (4 ± 1) × 10?10 cm3 s?1. If the reaction is diffusion-limited, this rate implies an average singlet diffusivity DS = (2 ± 1) × 10?4 cm2 s?1. 相似文献
The rate constant of the gas-phase reaction Fe(a5D4) + CO2 at 1180–2380 K and a total gas density of (7.0–10.0) × 10?6 mol/cm3 behind incident shock waves is k(Fe + CO2) = 1.4 × 1014.0 ± 0.3exp[?(14590 ± 1100)/T] cm3 mol?1 s?1, as determined by resonance atomic absorption photometry. Using thermochemical data available from the literature, the rate constant of the reverse reaction was calculated to be k(Fe + CO) = 9.2 × 1011.0 ± 0.3 (T/1000)0.57exp[?(490 ± 1100)/T] cm3 mol?1 s?1. The results are compared with data reported earlier. 相似文献
Triplet vinylidene radicals, produced in the vacuum-ultraviolet photolysis of acetylene, are observed in absorption at 137.4 nm. The lifetime in the presence of helium, for both the protonated and deuterated species, has been determined. Expressed as a bimolecular rate constant the values are kHeH = (1.3 ± 0.3) × 10?14 cm3 molecule?1 s?1 and kHeD = (2.4 ± 0.4 × 10?15 cm3 molecule?1 s?1. An upper limit for removal by acetylene has been deduced. 相似文献
A jet-stream kinetic technique and the resonance fluorescence method applied to detection of iodine atoms were used to measure the rate constants of the reactions of the IO· radical with the halohydrocarbons CHFCl-CF2Cl (k = (3.2 ± 0.9) × 10?16 cm3 molecule s?1) and CH2ClF (k = (9.4 ± 1.3) × 10?16 cm3 molecule s?1), the hydrogen-containing haloethers CF3-O-CH3 (k = (6.4 ± 0.9) × 10?16 cm3 molecule s?1) and CF3CH2-O-CHF2 (k = (1.2 ± 0.6) × 10?15 cm3 molecule s?1), and hydrogen iodide (k = (1.3 ± 0.9) × 10?12 cm3 molecule s?1) at 323 K. 相似文献
Chlorophyll-b in glassy solution has a spin-polarized lowest triplet state at and above 77 K. The magnitude of the effect is different for MTHF and ethanol as solvents, in contrast to what is found for the porphin free base. Chlorophyll-a does not exhibit spin-polarization under identical conditions as for chlorophyll-b. Zero-field parameters are found to be:chlorophyll-a (MTHF) D = (281 ± 6) × 10?4 cm?1; E = (39 ± 3) × 10?4 cm?1;chlorophyll-b (MTHF) D = (289 ± 4) × 10?4 cm?1; E = (49 ± 3) × 10?4 cm?1,From ESR signal kinetics it follows that for chlorophyll-b, population and depopulation mainly involve the spin level y?, describing a spin moving in a plane perpendicular to the molecular plane:Py ? Px ? Pz; kx = 240 ± 40 s?1; ky = 600 ± 120 s?1; kz ? 75 s?1,where Pi and ki denote populating and decay rates. Thus, the kinetic scheme for the chlorophyll triplet is different from that of porphyrins with heavier metal ions, but very similar to that of the porphin free base. The spin-lattice relaxation time is found to be anisotropic and shorter than the decay rates of individual spin levels. Nevertheless, spin polarization can be observed, essentially because the ESR signal amplitude depends on population differences. 相似文献
The rate constants 〈σ · υ〉 for collisional de-excitation of the metastable 5D states of Ba+ ions have been determined in an ion trap experiment. TheD-states are selectively populated by pulsed laser excitation of the 6P1/2 or 6P3/2 state and the decay at different background pressures is monitored by the change in fluorescence intensity of the excited ions. From the pressure dependence of the decay constants we calculate the de-excitation rate constants for different collision partners, averaged over the velocity distribution of the trapped ion cloud. For He, Ne, H2 and N2 we obtain in the c.m. energy range of 0.1–0.5 eV: 〈σ·υ〉 (He)=3.0±0.2·10?13cm3/s, 〈σ·υ〉 (Ne)=5.1±0.4·10?13cm3/s, 〈σ·υ〉 (H2)=3.7±0.3·10?11cm3/s, 〈σ·υ〉 (N2)=4.4±0.3·10?11cm3/s. The results can be understood qualitatively by a consideration of the ion-atom and ion-molecules interaction potential. 相似文献
The absolute rate constants of the reactions F + H2CO → HF + HCO (1) and Br + H2CO → HBr + HCO (2) have been measured using the discharge flow reactor-EPR method. Under pseudo-first-order conditions (¦H2CO¦?¦F¦or¦Br¦), the following values were obtained at 298 K: k1 = (6.6 ± 1.1) × 10?11 and k2 = (1.6± 0.3) × 10?12, Units are cm3 molecule?1s?1. The stratospheric implication of these data is discussed and the value obtained for k makes reaction (2) a possible sink for Br atoms in the stratosphere. 相似文献
The rate coefficients of the reactions of CN and NCO radicals with O2 and NO2 at 296 K: (1) CN + O2 → products; (2) CN + NO2 → products; (3) NCO + O2 → products and (4) NCO + NO2 → products have been measured with the laser photolysis-laser induced fluorescence technique. We obtained k1 = (2.1 ± 0.3) × 10?11 and k2 = (7.2 ± 1.0) × 10?11 cm3 molecule?t s?1 which agree well with published results. As no reaction was observed between NCO and O2 at 297 K, an upper limit of k3 < 4 × 10?17 cm3 molecule?1 S?1 was estimated. The reaction of NCO with NO2 has not been investigated previously. We measured k4 = (2.2 ± 0.3) × 10?11 cm3 molecule?1 s?1 at 296 K. 相似文献
Absolute rate constants for the reaction of O(3P) atoms with n-butane (k2) and NO(M Ar)(k3) have been determined over the temperature range 298–439 K using a flash photolysis-NO2 chemiluminescence technique. The Arrhenius expressions obtained were k2 = 2.5 × 10?11exp[-(4170 ± 300)/RT] cm3 molecule?1 s?1, k3 = 1.46 × 10?32 exp[940 ± 200)/ RT] cm6 molecule?2 s?1, with rate constants at room temperature of k2 = (2.2 ± 0.4) × 10?14 cm3 molecule?1 s?1 and k3 = (7.04 ± 0.70)×10?32 cm6 molecule?2 s?1. These rate constants are compared and discussed with literature values. 相似文献
A method of measuring the kinetics of currents arising at the electron photoemission from a metal into electrolyte solution when affected by the u.v. laser pulses for 10?8 s at the frequency of repetitions 10–25 Hz is described. Measurements have been taken in solutions without acceptors and in those containing N2O and NO2?, NO3? ions as electron acceptors. The rate constants of capture of the solvated electrons by N2O ((6±1)×09 mol?1 s?1) and NO2? ((4.5±1)×109 mol?1 s?1) and the diffusion coefficients of OH-radicals ((1.0±0.3)×10?5 cm2 s?1) and of NO ((1.2±0.3)×10?5 cm2 s?1) are found. The oxidation rate of NO32? has been shown to decrease from 40 cm s?1 in the range of potentials ?0.55 to ?1.0 V. The rate constant of bimolecular recombination of the solvated electrons ((1.3±0.4)×1010 mol?1 s?1) has been found from the dependence of the emitted charge on the light intensity. 相似文献
A combined EPR/LMR spectrometer and fast-flow system has been used to investigate the reactions HO2 + NO(k1), HO2 + OH(k2), HO2 + HO2(k3) at room temperature. The rate constants have been measured: k1 = (7.0 ± 0.6) × 10?12 cm3 s?1 (P = 7–10 Torr);k2 = (5.2 ± 1.2) × 10?11 cm3 s?1 (P = 8–10 Torr);k3 = (1.65 ± 0.3) × 10?12 cm3 s?1 (P = 2.1–24.9 Torr). The conclusion is drawn from analysis of the literature and the present work that k2 and k3 do not depend on pressure up to 1 atm. 相似文献
Rate constants for the reaction of OH radicals with OCS and CS2 have been determined at 296 K using the flash photolysis resonance fluorescence technique. The values derived from this study are kOH + OCS = (5.66 ± 1.21) × 10?14 cm3 molecule?1 s?1 and kOH + CS2 = (1.85 ± 0.34) × 10?13 cm3 molecule?1 s?1, where the uncertainties are 95% confidence limits making allowance for possible systematic errors. 相似文献
Reaction with hydroxyl radicals (OH) is the major pathway for removal of cyclic volatile methyl siloxanes (cVMS) from air. We present new measurements of second‐order rate constants for reactions of the cVMS octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) with OH determined at temperatures between 313 and 353 K. Our measurements were made using the method of relative rates with cyclohexane as a reference substance and were conducted in a 140‐mL gas‐phase reaction chamber with online mass spectrometry analysis. When extrapolated to 298 K, our measured reaction rate constants of D4 and D5 with the OH radical are 1.9 × 10?12 (95% confidence interval (CI): (1.7–2.2) × 10?12) and 2.6 × 10?12 (CI: (2.3–2.9) × 10?12) cm3 molecule?1 s?1, respectively, which are 1.9× and 1.7× faster than previous measurements. Our measured rate constant for D6 is 2.8 × 10?12 (CI: (2.5–3.2) × 10?12) cm3 molecule?1 s?1 and to our knowledge there are no comparable laboratory measurements in the literature. Reaction rates for D5 were 33% higher than for D4 (CI: 30–37%), whereas the rates for D6 were only 8% higher than for D5 (CI: 5–10%). The activation energies of the reactions of D4, D5, and D6 with OH were not statistically different and had a value of 4300 ± 2800 J/mol. 相似文献
The reactions CH3 + and CD3 + have been studied in shoch waves at 1200–1500 K and densities of 2 × 10?6 ?2 × 10?4 mol cm?3 using UV absorption near 216 nm. The rate constants at the highest densities: kH = (1.7 ± 0.6) × 10?11 cm3 s?1 and kD = (2.2 ± 0.9) × 10?11 cm3 s?1 are close to the second order limit. At the lowest densities the rates are lower by a factor of 5. The experimental results agree well with theoretical predictions based on the statistical adiabatic channel model but differ from those of conventional RRKM calculations. A direct observation of the equilibrium C2H6 ? 2CH3 favours the “high” value for ΔH00 (87.76 kcal/mol). 相似文献
The polymer film of N,N‐dimethylaniline (DMA) is deposited on the electrochemically pretreated glassy carbon (GC) electrode by continuous electrooxidation of the monomer. This poly N,N‐dimethylaniline (PDMA) film‐coated electrode can be used as an amperometric sensor of ascorbic acid (AA). The polymer film (thickness (?): 0.3±0.02 μm) having positive charge in its backbone attracts the anionic species AA. Thus, the anodic peak potential (350 mV vs. Ag|AgCl|NaCl(sat)) for the oxidation of AA at the bare electrode is largely shifted to the negative value (150 mV) at this electrode. The PDMA film‐coated electrode is stable in acidic, alkaline and neutral media and can sense AA at different pH's. The diffusion coefficients of AA in solution (D) and in film (Ds) were estimated by rotating disk electrode voltammetry: D=(5.5±0.1)×10?6 cm2 s?1 and Ds=(6.3±0.2)×10?8, (6.0±0.2)×10?8 and (4.7±0.2)×10?8 cm2 s?1 for 0.5, 1.5 and 3.0 mM AA, respectively. A permeability of AA through the PDMA film was found to decrease with increasing the concentration of AA in the solution. In the chronoamperometry, the current response for the oxidation of AA at different times elapsed after potential‐step application is linearly increased with the increase in AA concentration in a wide range of its concentration from 25 μM to 1.65 mM. In the hydrodynamic amperometry, a successive addition of 10 μM AA caused the successive increase in current response with equal amplitude and the sensitivity was calculated as 0.178 μA cm?2 μM?1. So, the fouling of the electrode surface caused by the oxidized product of AA is markedly eliminated at this PDMA film‐coated electrode. A flow injection analysis based on the present electrode was performed to estimate the concentration of vitamin C in fruit juice. 相似文献
Photon-correlation spectroscopy has been used to measure the diffusion coefficient D and first-mode intramolecular relaxation time τ1 of polystyrene in a theta solvent, cyclohexane at 34.5°C. Measurements were made on five narrow fractions (w = 2.88 × 106 to 9.35 × 106) as a function of concentration c, in the dilute regime. D varied linearly with c, D = Do (I + kDc), with Do = (1.4 ± 0.2) × 10?4 cm2 s?1. Although the values obtained for τ1 were reproducible to within 5%, no systematic variation with c was detected. The results are fitted by the relation τ1 = (7.7 ? 0.3) × 10?8 μs, which agrees well with the theoretical expression of Zimm for the non-draining bead-and-spring model, modified for the light-scattering case. 相似文献
The vibrational relaxation of pure HF(υ = 3 and υ = 4) has been studied by pumping HF directly from υ = 0 to υ = 4. The relaxation rates of υ = 3 and υ = 4 were determined to be k3T = (2.8 ± 0.4) × 10?11 cm3 molecule?1 s?1 and k4T = (7.2. ± 0.5) × 10?11 cm3 molecule?1 s?1 at 293 K. It is shown that sigle quantum energy transfer can account for all the vibrational relaxation. 相似文献