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1.
UV spectra and kinetics for the reactions of alkyl and alkylperoxy radicals from methyl tert-butyl ether (MTBE) were studied in 1 atm of SF 6 by the pulse radiolysis-UV absorption technique. UV spectra for the radical mixtures were quantified from 215 to 340 nm. At 240 nm. σ R = (2.6 ± 0.4) × 10 −18 cm 2 molecule −1 and σ RO2 = (4.1 ± 0.6) × 10 −18 cm 2 molecule −1 (base e). The rate constant for the self-reaction of the alkyl radicals is (2.5 ± 1.1) × 10 −11 cm 3 molecule −1 s −1. The rate constants for reaction of the alkyl radicals with molecular oxygen and the alkylperoxy radicals with NO and NO 2 are (9.1 ± 1.5) × 10 −13, (4.3 ± 1.6) × 10 −12 and (1.2 ± 0.3) × 10 −11 cm 3 molecule −1 s −1, respectively. The rate constants given above refer to reaction at the tert-butyl side of the molecule. 相似文献
2.
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
3.
The reactive Kr +F 2− potential energy surface is probed by two-photon, laser-induced chemical bond formation during a Kr+F 2 collision. This is compared with the pulsed laser excitation (two-photon) of Kr(2p 9) followed by collision with F 2 leading to the formation of KrF(B, C). In addition to reporting the excitation spectrum for the two-phonon-induced collision process, these techniques were used to determine quenching rate constants of Kr 2F *. Quenching by Xe gives XeF(B, C) with rate constant (1.5±0.2)×10 −10 cm 3 s −1; the quenching rate constant for F 2 is (1.5±0.2)×10 −10 cm 3 s −1, and the radiative lifetime of Kr 2F * is 240±35 ns. The quenching rate constant for the coupled Kr(2p 8) and Kr(2p 9) levels by F 2 is (13±2)×10 −10 cm 3 s −1. 相似文献
4.
The collisionless lifetime of a flourescent excited state of tetramethylethylene (TME) vapor when excited at 235 nm is 20.8±0.9 ns and the self-quenching rate constant is (2.97±0.01) × 10 −10 cm 3 molecule −1 s −1. The rate constants for quenching of TME vapor by O 2, benzene. CCl 4, Xe, N 2 and CH 4 are also repeated. In the vapor phase, the lifetime strongly depends on the excitation energy. The lifetime of liquid TME is 10±2 ns at 25±2°C. 相似文献
5.
The acidity constants of benzidine (Bz) in aqueous solutions determined potentiometrically at 25° were Ka1 = (1.11 ± 0.08) × 10 −5, Ka2 = (1.45 ± 0.12) × 10 −4. The apparent mixed constants in 0.1 M sodium nitrate are Ka1 = (5.37 ± 0.28) × 10 −6 and Ka2 = (1.14 ± 0.09) × 10 −4. The ultraviolet spectra were recorded as a function of pH and analysed with these constants to obtain the absorption spectra of H 2Bz 2+, HBz + and Bz; the corresponding wavelengths of maximal absorption are 247, 273 and 278 nm, and molar absorptivities 1.63 × 10 4, 1.76 × 10 4 and 2.26 × 10 4 1.mole −1.cm −1. 相似文献
6.
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
7.
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
8.
The spectrum of SO (X 3Σ −) has been observed following the flash excitation of sulphur dioxide with radiation above 250 nm. Sulphur monoxide is produced via an excited molecule mechanism involving triplet SO 2. The rate constant for the reaction 3SO 2 + SO 2 was measured as (3.1 ± 1) × 10 8 M −1 sec −1. 相似文献
9.
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
10.
Vitamin A,dissolved in liquid paraffin, is stable below room temperature, but suffers oxidative decomposition at 80°, giving its epoxide as the main product. The rate of decomposition of vitamin A (V A) at 80° in the presence of oxygen (partial pressure of p) and a small amount of cobaltous stearate (Co) is expressed as: d[V A]/d t = 3·15 × 10 −1:[V A][Co] p1·48 + 1·51 × 10 −5[V A] p0·33 + 0·33 × 10 −5[V A], where the last term represents the spontaneous thermal decomposition. 相似文献
11.
The thiolactic acid (TLA) self-assembled monolayer modified gold electrode (TLA/Au) is demonstrated to catalyze the electrochemical response of norepinephrine (NE) by cyclic voltammetry. A pair of well-defined redox waves were obtained and the calculated standard rate constant ( ks) is 5.11×10 −3 cm s −1 at the self-assembled electrode. The electrode reaction is a pseudo-reversible process. The peak current and the concentration of NE are a linear relationship in the range of 4.0×10 −5–2.0×10 −3 mol l −1. The detection limit is 2.0×10 −6 mol l −1. By ac impedance spectroscopy the apparent electron transfer rate constant ( kapp) of Fe(CN) 3−/Fe(CN) 4− at the TLA/Au electrode was obtained as 2.5×10 −5 cm s −1. 相似文献
12.
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
13.
Rate coefficients for the reactions of cyclohexadienyl ( c-C 6H 7) radicals with O 2 and NO were measured at 296 ± 2 K. The c-C 6H 7 radicals were detected selectively by laser-induced fluorescence. The rate coefficient for the reaction of c-C 6H 7 with O 2, (4.4 ± 0.5) × 10 −14 cm 3 molecule −1 s −1, was independent of the bath-gas (He) pressure (13–80 Torr). In the reaction of c-C 6H 7 with NO, thermal equilibrium among c-C 6H 7, NO, and C 6H 7NO was observed. The forward and reverse reactions were in the falloff region, and the equilibrium constant was (1.5 ± 0.6) × 10 −15 cm 3 molecule −1. 相似文献
14.
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
15.
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
16.
A UV spectrometric method was developed to determine the molar absorptivity ( C) and formation constant ( Kc) of the association complex of unsubstituted chalcone in cyclohexane, in the concentration range from 4.00·10 −4 to 2.00·10 −2 mol dm −3. The thermodynamic and spectroscopic magnitudes such as Kc and C contribute to the understanding of the physicochemical behavior of several , β-unsaturated carbonylic compounds, of low solubility in water, as it is the case of numerous flavonoids of chemical and biological importance. The studied association complex, formed by two chalcone molecules, is characterized by the constants C (300.8 nm)=4.98·10 4 dm 3 mol −1 cm −1 and Kc=5.58·10 3. The method proposed is convenient for the study of solute–solute molecular associations particularly those due to dipole–dipole interactions. 相似文献
17.
The singlet exciton quenchings due to SS and ST interactions in crystalline anthracene have been separated by considering the kinetics of the two interactions. The corresponding rate constants are γSS = (1 ± 0.5) × 10 −8 and γST = (f ± 3) × 10 −9 cm 3 sec −1. 相似文献
18.
Two flow injection analyses (FIA) methods for the determination of diffusion coefficients in a straight single tube FIA system were developed. Based on the analytical solution of the convection-diffusion equation, linear relationships of the logarithmic values of the dispersion coefficient ( D) and the half-peak width ( W1/2) with the diffusion coefficient ( Dm) were obtained. Experiments were designed to verify these methods. For example, for potassium hexacyanoferrate (III) a Dm value of 0.72 × 10 5 cm2 s−1 was found versus a literature value of 0.76 × 10 5 cm2 s−1 (error, 5%). For potassium hexacyanoferrate (II) a Dm value of 0.67 × 10 5 cm2 s−1 was obtained versus a literature value of 0.63 × 10 5 cm2 s−1 (error, 6%). The diffusion coefficients of some important biomedical compounds, such as dopamine, epinephrine, norepinephrine and ascorbic acid, were then determined. The values of 10 5 Dm/ cm2 s−1 are 0.60 ± 0.03, 0.44 ± 0.02, 0.60 ± 0.01 and 0.68 ± 0.06, respectively. 相似文献
19.
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
20.
The behavior of the ciprofloxacin (CPFX) complex with copper, Cu(II)L 2, at a mercury electrode has been investigated in borax–boric acid buffer. The adsorption phenomena were observed by linear sweep voltammetry. The mechanism of the electrode reaction was found to be reduction of Cu(II)L 2 adsorbed on the surface of the electrode by an irreversible charge transfer to metal amalgam, Cu(0)(Hg). In the presence of DNA, the formation of the electrochemically non-active complexes Cu(II)L 2–DNA results in the decrease of the equilibrium concentration of Cu(II)L 2 and its peak current. Under the optimum conditions, the decrease of the peak current is proportional to DNA concentration. The linear ranges are 6.67×10 −8 to 1.20×10 −5 g ml −1 for calf thymus DNA (ctDNA), 3.30×10 −8 to 2.33×10 −6 g ml −1 for fish sperm DNA (fsDNA) and 1.0×10 −8 to 1.2×10 −6 g ml −1 for yeast RNA. The detection limits are 5.00×10 −9, 3.00×10 −9 and 2.50×10 −9 g ml −1, respectively. This method exhibits good recovery and high sensitivity. 相似文献
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