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1.
The photoexcited triplet state of phenazine in toluene glasses at 35 K is investigated by light modulation-EPR spectroscopy. From the transient EPR spectra and the kinetics in the three canonical orientations (p = x, y, z) the rate parameters are determined. Thus, the depopulation rate constants kp, the anisotropic spin lattice relaxation rate constants Wp, and the ratios between the population constants Ap are calculated: kx = (2.2 ± 0.3) × 102 s?1, ky = (0.21 ± 0.04) × 102 s?1, kz = (0.06 ± 0.03) × 102 s?1, Wx = (8.6 ± 0.9) × 103 s?1, Wy = (11.0 ± 1.0) × 103 s?1, Wz = (14.0 ± 1.4) × 103 s?1, and Ax: Ay:Az ≈ 1:0.04:0.02. It is concluded therefore that the in-plane spin state |τx > is the active one.  相似文献   

2.
Fourier transform infrared (FTIR) smog chamber techniques were used to investigate the atmospheric chemistry of the isotopologues of methane. Relative rate measurements were performed to determine the kinetics of the reaction of the isotopologues of methane with OH radicals in cm3 molecule−1 s−1 units: k(CH3D + OH) = (5.19 ± 0.90) × 10−15, k(CH2D2 + OH) = (4.11 ± 0.74) × 10−15, k(CHD3 + OH) = (2.14 ± 0.43) × 10−15, and k(CD4 + OH) = (1.17 ± 0.19) × 10−15 in 700 Torr of air diluent at 296 ± 2 K. Using the determined OH rate coefficients, the atmospheric lifetimes for CH4–xDx (x = 1–4) were estimated to be 6.1, 7.7, 14.8, and 27.0 years, respectively. The results are discussed in relation to previous measurements of these rate coefficients.  相似文献   

3.
Abstract

The kinetics and stability constants of l-tyrosine complexation with copper(II), cobalt(II) and nickel(II) have been studied in aqueous solution at 25° and ionic strength 0.1 M. The reactions are of the type M(HL)(3-n)+ n-1 + HL- ? M(HL)(2-n)+n(kn, forward rate constant; k-n, reverse rate constant); where M=Cu, Co or Ni, HL? refers to the anionic form of the ligand in which the hydroxyl group is protonated, and n=1 or 2. The stability constants (Kn=kn/k-n) of the mono and bis complexes of Cu2+, Co2+ and Ni2+ with l-tyrosine, determined by potentiometric pH titration are: Cu2+, log K1=7.90 ± 0.02, log K2=7.27 ± 0.03; Co2+, log K1=4.05 ± 0.02, log K2=3.78 ± 0.04; Ni2+, log K1=5.14 ± 0.02, log K2=4.41 ± 0.01. Kinetic measurements were made using the temperature-jump relaxation technique. The rate constants are: Cu2+, k1=(1.1 ± 0.1) × 109 M ?1 sec?1, k-1=(14 ± 3) sec?1, k2=(3.1 ± 0.6) × 108 M ?1 sec?1, k?2=(16 ± 4) sec?1; Co2+, k1=(1.3 ± 0.2) × 106 M ?1 sec?1, k-1=(1.1 ± 0.2) × 102 sec?1, k2=(1.5 ± 0.2) × 106 M ?1 sec?1, k-2=(2.5 ± 0.6) × 102 sec?1; Ni2+, k1=(1.4 ± 0.2) × 104 M ?1 sec?1, k-1=(0.10 ± 0.02) sec?1, k2=(2.4 ± 0.3) × 104 M ?1 sec?1, k-2=(0.94 ± 0.17) sec?1. It is concluded that l-tyrosine substitution reactions are normal. The presence of the phenyl hydroxyl group in l-tyrosine has no primary detectable influence on the forward rate constant, while its influence on the reverse rate constant is partially attributed to substituent effects on the basicity of the amine terminus.  相似文献   

4.
The kinetics of C2H5O2 and C2H5O2 radicals with NO have been studied at 298 K using the discharge flow technique coupled to laser induced fluorescence (LIF) and mass spectrometry analysis. The temporal profiles of C2H5O were monitored by LIF. The rate constant for C2H5O + NO → Products (2), measured in the presence of helium, has been found to be pressure dependent: k2 = (1.25±0.04) × 10?11, (1.66±0.06) × 10?11, (1.81±0.06) × 10?11 at P (He) = 0.55, 1 and 2 torr, respectively (units are cm3 molecule?1 s?1). The Lindemann-Hinshelwood analysis of these rate constant data and previous high pressure measurements indicates competition between association and disproportionation channels: C2H5O + NO + M → C2H5ONO + M (2a), C2H5O + NO → CH3CHO + HNO (2b). The following calculated average values were obtained for the low and high pressure limits of k2a and for k2b : k = (2.6±1.0) × 10?28 cm6 molecule?2 s?1, k = (3.1±0.8) × 10?11 cm3 molecule?1 s?1 and k2b ca. 8 × 10?12 cm3 molecule?1 s?1. The present value of k, obtained with He as the third body, is significantly lower than the value (2.0±1.0) × 10?27 cm6 molecule?2 s?1 recommended in air. The rate constant for the reaction C2H5O2 + NO → C2H5O + NO2 (3) has been measured at 1 torr of He from the simulation of experimental C2H5O profiles. The value obtained for k3 = (8.2±1.6) × 10?12 cm3 molecule?1 s?1 is in good agreement with previous studies using complementary methods. © 1995 John Wiley & Sons, Inc.  相似文献   

5.
The photophysical properties of bonellin, a free-base chlorin, were studied in ethanolic solution. For the singlet excited state the following data were determined: an energy level, EBS= 187 ± 2kJ mol-1, a lifetime, τf= 6.3± 0.1ns at 298 K, and fluorescence quantum yields, φr= 0.07 ± 0.02 (298 K) and 0.20 ± 0.04 (77 K). The S1→ T intersystem crossing quantum yield was φisc= 0.85 ± 0.1. No phosphorescence was observed at 298 K and 77 K. Based on quenching experiments the triplet state energy level was determined to be EBT= 180 ± 20 kJ mol-1. A unimolecular decay rate constant, k1= (2.3 ± 0.5)· 103 s-1 at room temperature, and a molar absorption coefficient, εT443= 9500 ± 500 M-1 cm-1, were obtained for the triplet state. This species was quenched by O2 with ko2= (1.7 ±0.3)· 108M-1 s-1, and by benzoquinone with kq= (5.2 ± 0.3)-109M-1 s-1. The latter value, as well as the high value determined for the triplet annihilation rate constant, k2= (2 ± 0.5)· 109M-1 s-1, might reflect an electron transfer mechanism. Copper bonellin had a shorter triplet lifetime (>20 ns), which offers a possible explanation for its lack of photodynamic action.  相似文献   

6.
Spectrophotometric methods have been used to obtain rate laws and rate parameters for the following reactions: with ka, kb, Ea, Eb having the values 85±5 l./mole · s, 5.7±0.2 s?1 (both at 298.2°K), and 56±4 and 66±2 kJ/mole, respectively. with kc=0.106±0.004 l./mole ·s at 298.2°K and Ec=67±2 kJ/mole. with kd=(3.06 ±; 0.15) × 10?3 l./mole ·s at 298.2°K and Ed=66±2 kJ/mole. Mechanisms for these reactions are discussed and compared with previous work.  相似文献   

7.
Using a relative rate method, rate constants for the gas-phase reactions of 2-methyl-3-buten-2-ol (MBO) with OH radicals, ozone, NO3 radicals, and Cl atoms have been investigated using FTIR. The measured values for MBO at 298±2 K and 740±5 torr total pressure are: kOH=(3.9±1.2)×10−11 cm3 molecule−1 s−1, kO3=(8.6±2.9)×10−18 cm3 molecule−1 s−1, k=(8.6±2.9)×10−15 cm3 molecule−1 s−1, and kCl=(4.7±1.0)×10−10 cm3 molecule−1 s−1. Atmospheric lifetimes have been estimated with respect to the reactions with OH, O3, NO3, and Cl. The atmospheric relevance of this compound as a precursor for acetone is, also, briefly discussed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 589–594, 1998  相似文献   

8.
The overall rate constants for H-abstraction (kH) from tetrahydrofuran and D-abstraction (kD) from fully deuterated tetrahydrofuran by chlorine atoms in the temperature range of 298-547 K were determined. In both cases, very weak negative temperature dependences of the overall rate constants were observed, described by the expressions: kH = (1.55 ± 0.13) × 10−10 exp(52 ± 28/T) cm3 molecule−1 s−1 and kD = (1.27 ± 0.25) × 10−10exp(55 ± 62/T) cm3 molecule−1 s−1. The experimental results show that the value of the kinetic isotope effect (kH/kD), amounting to 1.21 ± 0.10, is temperature independent at 298-547 K.  相似文献   

9.
Smog chamber/Fourier transform infrared (FTIR) techniques were used to measure the kinetics of the reaction of n‐CH3(CH2)xCN (x = 0–3) with Cl atoms and OH radicals: k(CH3CN + Cl) = (1.04 ± 0.25) × 10−14, k(CH3CH2CN + Cl) = (9.20 ± 3.95) × 10−13, k(CH3(CH2)2CN + Cl) = (2.03 ± 0.23) × 10−11, k(CH3(CH2)3CN + Cl) = (6.70 ± 0.67) × 10−11, k(CH3CN + OH) = (4.07 ± 1.21) × 10−14, k(CH3CH2CN + OH) = (1.24 ± 0.27) × 10−13, k(CH3(CH2)2CN + OH) = (4.63 ± 0.99) × 10−13, and k(CH3(CH2)3CN + OH) = (1.58 ± 0.38) × 10−12 cm3 molecule−1 s−1 at a total pressure of 700 Torr of air or N2 diluents at 296 ± 2 K. The atmospheric oxidation of alkyl nitriles proceeds through hydrogen abstraction leading to several carbonyl containing primary oxidation products. HC(O)CN, NCC(O)OONO2, ClC(O)OONO2, and HCN were identified as the main oxidation products from CH3CN, whereas CH3CH2CN gives the products HC(O)CN, CH3C(O)CN, NCC(O)OONO2, and HCN. The oxidation of n‐CH3(CH2)xCN (x = 2–3) leads to a range of oxygenated primary products. Based on the measured OH radical rate constants, the atmospheric lifetimes of n‐CH3(CH2)xCN (x = 0–3) were estimated to be 284, 93, 25, and 7 days for x = 0,1, 2, and 3, respectively.  相似文献   

10.
The reduction of Fe(CN)5L2? (L = pyridine, isonicotinamide, 4,4′‐bipyridine) complexes by ascorbic acid has been subjected to a detailed kinetic study in the range of pH 1–7.5. The rate law of the reaction is interpreted as a rate determining reaction between Fe(III) complexes and the ascorbic acid in the form of H2A(k0), HA?(k1), and A2? (k2), depending on the pH of the solution, followed by a rapid scavenge of the ascorbic acid radicals by Fe(III) complex. With given Ka1 and Ka2, the rate constants are k0 = 1.8, 7.0, and 4.4 M?1 s?1; k1 = 2.4 × 103, 5.8 × 103, and 5.3 × 103 M?1 s?1; k2 = 6.5 × 108, 8.8 × 108, and 7.9 × 108 M?1 s?1 for L = py, isn, and bpy, respectively, at μ = 0.10 M HClO4/LiClO4, T = 25°C. The kinetic results are compatible with the Marcus prediction. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 126–133, 2005  相似文献   

11.
The kinetics and mechanism of the following reactions have been studied in the temperature range 230–360 K and at total pressure of 1 Torr of helium, using the discharge‐flow mass spectrometric method: 1a : (1a) 1b : (1b) The following Arrhenius expression for the total rate constant was obtained from the kinetics of OH consumption in excess of ClO radical, produced in the Cl + O3 reaction either in excess of Cl atoms or ozone: k1 = (6.7 ± 1.8) × 10?12 exp {(360 ± 90)/T} cm3 molecule?1 s?1 (with k1 = (2.2 ± 0.4) × 10?11 cm3 molecule?1 s?1 at T = 298 K), where uncertainties represent 95% confidence limits and include estimated systematic errors. The value of k1 is compared with those from previous studies and current recommendations. HCl was detected as a minor product of reaction (1) and the rate constant for the channel forming HCl (reaction (1b)) has been determined from the kinetics of HCl formation at T = 230–320 K: k1b = (9.7 ± 4.1) × 10?14 exp{(600 ± 120)/T} cm3 molecule?1 s?1 (with k1b = (7.3 ± 2.2) × 10?13 cm3 molecule?1 s?1 and k1b/k1 = 0.035 ± 0.010 at T = 298 K), where uncertainties represent 95% confidence limits. In addition, the measured kinetic data were used to derive the enthalpy of formation of HO2 radicals: Δ Hf,298(HO2) = 3.0 ± 0.4 kcal mol?1. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 587–599, 2001  相似文献   

12.
The kinetic and mechanism of the reaction Cl + HO2 → products (1) have been studied in the temperature range 230–360 K and at total pressure of 1 Torr of helium using the discharge‐flow mass spectrometric method. The following Arrhenius expression for the total rate constant was obtained either from the kinetics of HO2 consumption in excess of Cl atoms or from the kinetics of Cl in excess of HO2: k1 = (3.8 ± 1.2) × 10?11 exp[(40 ± 90)/T] cm3 molecule?1 s?1, where uncertainties are 95% confidence limits. The temperature‐independent value of k1 = (4.4 ± 0.6) × 10?11 cm3 molecule?1 s?1 at T = 230–360 K, which can be recommended from this study, agrees well with most recent studies and current recommendations. Both OH and ClO were detected as the products of reaction (1) and the rate constant for the channel forming these species, Cl + HO2 → OH + ClO (1b), has been determined: k1b = (8.6 ± 3.2) × 10?11 exp[?(660 ± 100)/T] cm3 molecule?1 s?1 (with k1b = (9.4 ± 1.9) × 10?12 cm3 molecule?1 s?1 at T = 298 K), where uncertainties represent 95% confidence limits. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 317–327, 2001  相似文献   

13.
Rate coefficients have been determined for the gas‐phase reaction of the hydroxyl (OH) radical with the aromatic dihydroxy compounds 1,2‐dihydroxybenzene, 1,2‐dihydroxy‐3‐methylbenzene and 1,2‐dihydroxy‐4‐methylbenzene as well as the two benzoquinone derivatives 1,4‐benzoquinone and methyl‐1,4‐benzoquinone. The measurements were performed in a large‐volume photoreactor at (300 ± 5) K in 760 Torr of synthetic air using the relative kinetic technique. The rate coefficients obtained using isoprene, 1,3‐butadiene, and E‐2‐butene as reference hydrocarbons are kOH(1,2‐dihydroxybenzene) = (1.04 ± 0.21) × 10−10 cm3 s−1, kOH(1,2‐dihydroxy‐3‐methylbenzene) = (2.05 ± 0.43) × 10−10 cm3 s−1, kOH(1,2‐dihydroxy‐4‐methylbenzene) = (1.56 ± 0.33) × 10−10 cm3 s−1, kOH(1,4‐benzoquinone) = (4.6 ± 0.9) × 10−12 cm3 s−1, kOH(methyl‐1,4‐benzoquinone) = (2.35 ± 0.47) × 10−11 cm3 s−1. This study represents the first determination of OH radical reaction‐rate coefficients for these compounds. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 696–702, 2000  相似文献   

14.
Fourier transform infrared spectroscopy was used to identify and quantify products of the self reaction of ethylperoxy radicals, C2H5O2, formed in the photolysis of Cl2/C2H6 mixtures in 700 torr total pressure of synthetic air at 295 K. From these measurements, branching ratios for the reaction channels (1) of k1a/(k1a + k1b) = 0.68 and k1c/(k1a + k1b + k1c) ? 0.06 were established. Additionally, using the relative rate technique, the rate constant for the reaction of Cl atoms with C2H5OOH was determined to be (1.07 ± 0.07) × 10?10 × cm3 molecule?1 s?1. Results are discussed with respect to the previous kinetic and mechanistic studies of C2H5O2 radicals.  相似文献   

15.
The rate coefficients for the reaction OH + CH3CH2CH2OH → products (k1) and OH + CH3CH(OH)CH3 → products (k2) were measured by the pulsed‐laser photolysis–laser‐induced fluorescence technique between 237 and 376 K. Arrhenius expressions for k1 and k2 are as follows: k1 = (6.2 ± 0.8) × 10?12 exp[?(10 ± 30)/T] cm3 molecule?1 s?1, with k1(298 K) = (5.90 ± 0.56) × 10?12 cm3 molecule?1 s?1, and k2 = (3.2 ± 0.3) × 10?12 exp[(150 ± 20)/T] cm3 molecule?1 s?1, with k2(298) = (5.22 ± 0.46) × 10?12 cm3 molecule?1 s?1. The quoted uncertainties are at the 95% confidence level and include estimated systematic errors. The results are compared with those from previous measurements and rate coefficient expressions for atmospheric modeling are recommended. The absorption cross sections for n‐propanol and iso‐propanol at 184.9 nm were measured to be (8.89 ± 0.44) × 10?19 and (1.90 ± 0.10) × 10?18 cm2 molecule?1, respectively. The atmospheric implications of the degradation of n‐propanol and iso‐propanol are discussed. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 10–24, 2010  相似文献   

16.
Mixtures of N2O, H2, O2, and trace amounts of NO and NO2 were photolyzed at 213.9 nm, at 245°–328°K, and at about 1 atm total pressure (mostly H2). HO2 radicals are produced from the photolysis and they react as follows: Reaction (1b) is unimportant under all of our reaction conditions. Reaction (1a) was studied in competition with reaction (3) from which it was found that k1a/k31/2 = 6.4 × 10?6 exp { z?(1400 ± 500)/RT} cm3/2/sec1/2. If k3 is taken to be 3.3 × 10?12 cm3/sec independent of temperature, k1a = 1.2 × 10?11 exp {?(1400 ± 500)/RT} cm3/sec. Reaction (2a) is negligible compared to reaction (2b) under all of our reaction conditions. The ratio k2b/k1 = 0.61 ± 0.15 at 245°K. Using the Arrhenius expression for k1a given above leads to k2b = 4.2 × 10?13 cm3/sec, which is assumed to be independent of temperature. The intermediate HO2NO2 is unstable and induces the dark oxidation of NO through reaction (?2b), which was found to have a rate coefficient k?2b = 6 × 1017 exp {?26,000/RT} sec?1 based on the value of k1a given above. The intermediate can also decompose via Reaction (10b) is at least partially heterogeneous.  相似文献   

17.
The photolysis of SO2 at 3130 Å, FWHM = 165 Å, and 22°C has been investigated in the presence of cis- and trans-2-pentene. Quantum yields for the SO2 photosensitized isomerization of one isomer to the other have been made for a variation in the [SO2]/[C5H10] ratio of 3.41–366 for cis-2-C5H10 and of 1.28–367 for trans-2-C5H10. A kinetic analysis of each of these systems permitted new estimates to be made for the SO2 collisionally induced intersystem crossing ratio at 3130 Å from SO2(1B1) to SO2(3B1). The estimates of k1a/(k1a + k1b) obtained are 0.12 ± 0.01 and 0.12 ± 0.02 (two different kinetic analyses in the cis-2-C5H10 study) and 0.20 ± 0.05 and 0.20 ± 0.04 (two different kinetic analyses in the trans-2-C5H10 study). Collisionally induced intersystem crossing ratios of k2a/(k2a + k2b) = 0.51 ± 0.10 and k3a/(k3a + k3b) = 0.62 ± 0.12 were obtained for cis- and trans-2-pentene, respectively. Quenching rate constants at 22°C for removal of SO2(3B1) molecules by cis- and trans-2-C5H10 were estimated as (1.00 ± 0.29) × 1011 l./mole·sec and (0.857 ± 0.160) × 1011 l./mole/sec, respectively. Prolonged irradiations, extrapolated to infinite irradiation times, for mixtures initially containing SO2 and pure isomer, either the cis or trans, yielded a photostationary composition of [trans-2-pentene]/[cis-2-pentene] = 2.1 ± 0.1.  相似文献   

18.
The Absolute rate constants for the gas-phase reactions of NO3 with HO2 and OH have been determined using the discharge flow laser magnetic resonance method (DF-LMR). Since OH was found to be produced in the reaction of HO2 with NO3, C2F3Cl was used to scavenge it. The overall rate constant, k1, for the reaction, HO2 + NO3 → products, was measured to be k1=(3.0 ± 0.7)×10?12 cm3 molecule?1 s?1 at (297 ± 2) K and P=(1.4 – 1.9) torr. This result is in reasonable agreement with the previous studies. Direct detection of HO2 and OH radicals and the use of three sources of NO3 enabled us to confirm the existence of the channel producing OH:HO2+NO3→OH+NO2+O2 (1a); the other possible channel is HO2+NO3→HNO3+O2 (1b). From our measurements and the computer simulations, the branching ratio, k1a/(k1a + k1b), was estimated to be (1.0). The rate coefficient for the reaction of OH with NO3 was determined to be (2.1 ± 1.0) × 10?11 cm3 molecule?1 s?1. © 1993 John Wiley & Sons, Inc.  相似文献   

19.
Abstract

The EPR spectrum of N, N'-bis-(acetylacetone)ethylenediimino Cu(II), [Cu-en(acac)2], and N, N'-bis-(1,1,1-trifluoroacetylacetone)ethylenediimino-Cu(II), [Cu-en(tfacac)2], have been studied in doped single crystals of the corresponding Ni(II) chelate. The parameters in the usual doublet spin-Hamiltonian are found to be: Cu[en(acac)2], gz =2.183 ± 0.003, gx =2.047 ± 0.004, gy =2.048 ± 0.004, Az =204.8 × 10?4cm?1, Ax =31.5 × 10?4cm?1, Ay =27.1 × 10?4 cm?1, AzN= 12.8 × 10?4 cm?1 and AxN =AyN =14.3 × 10?4 cm?1: Cu[en(tfacac)2], gz =2.192 ± 0.002, gx =2.048 ± 0.004, gy =2.046 ± 0.004, Az =200.8 × 10?4 cm?1, Ax =31.1 × 10?4 cm?1, Ay =28.3 × 10?4 cm?1, AzN =12.8 × 10?4 cm?1 and AxN =AyN =14.6 × 10?4 cm?1. These parameters are related to coefficients in the molecular orbitals of the complex. It is found that the α-bonding is quite covalent and there is significant in-plane σ-bonding. From the nitrogen hyperfine structure it is determined that the hybridization on the nitrogen is sp2.  相似文献   

20.
Cavity ring‐down UV absorption spectroscopy was used to study the kinetics of the recombination reaction of FCO radicals and the reactions with O2 and NO in 4.0–15.5 Torr total pressure of N2 diluent at 295 K. k(FCO + FCO) is (1.8 ± 0.3) × 10−11 cm3 molecule−1 s−1. The pressure dependence of the reactions with O2 and NO in air at 295 K is described using a broadening factor of Fc = 0.6 and the following low (k0) and high (k) pressure limit rate constants: k0(FCO + O2) = (8.6 ± 0.4) × 10−31 cm6 molecule−1 s−1, k(FCO + O2) = (1.2 ± 0.2) × 10−12 cm3 molecule−1 s−1, k0(FCO + NO) = (2.4 ± 0.2) × 10−30 cm6 molecule−1 s−1, and k (FCO + NO) = (1.0 ± 0.2) × 10−12 cm3 molecule−1 s−1. The uncertainties are two standard deviations. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 130–135, 2001  相似文献   

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