摘要:

AbstractMolecular modulation spectroscopy combined with ultraviolet spectroscopic techniques have been used to observe the behavior of the CH3O2radicals generated in the gas phase by near‐ultraviolet modulated photolysis of flowing Cl2CH4O2mixtures. The kinetics of the disproportionation reaction (1)and the absorption cross‐sections of CH3O2were measured by computer fitting of the modulated absorption traces obtained in the wavelength range 220 to 270 nm at 300 K and 240 torr. The rate constant for the elementary self‐reaction

ISSN:0538-8066    

DOI:10.1002/kin.550220802

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractA treatment of ionic‐atmosphere effects upon symmetrical electron‐transfer reactions resulting from added electrolyte is outlined. Relationships are derived on the basis of the extended Debye‐Huckel model for the increase in the activation free energy, ΔGia*, associated with reorganization of the ionic atmosphere for homogeneous‐phase reactions involving a pair of spherical reactants with varying internuclear distanceR. Similar relationships apply to the energetics of symmetrical optical electron transfer, since the increase in the optical transition energy, ΔE opia, should equal the corresponding ionic atmosphere reorganization energy,E ria; under the anticipated linear response conditions,E ria= 4ΔGia*. The predicted ΔGia* (and hence ΔE opia) values increase sharply with increasingR, as a consequence of the diminished “sharing” of the ionic cloud surrounding the donor and acceptor sites under these conditions. Outer‐sphere electrochemical reactions, featuring a single “near‐isolated” reactant, are predicted to feature substantially larger ΔGia* values than for homogeneous processes proceeding with the reaction partners in contact. The influence of more specific “ionic atmosphere” effects upon ΔGia*, especially involving reactant‐electrolyte ion pairing, is also discussed. Unlike that of the nonspecific ionic atmosphere, the nuclear reorganization process associated with counterion transport between donor and acceptor sites coupled with electron transfer is nonlinear in nature, so thatE ria≠ 4ΔGia*. Some recent experimental data for electrolyte effects upon the rate constants for ferrocenium‐ferrocene self exchange and related systems ar

ISSN:0538-8066    

DOI:10.1002/kin.550220803

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe fast reaction of O atoms with NO2has been used in measurements of absolute concentrations of O atoms. Similarly, the reaction of H with NO2can be used to generate OH radicals in known concentrations. Relative concentrations of both O atoms and OH radicals have frequently been measured by resonance fluorescence determinations in the ultra‐violet. It will be shown that the stoichiometry of these reactions is strongly dependent on the initial concentration of reactants and on the contact time (in the case of OH on secondary reactions as well), making it impossible to equate directly the loss of NO2with the loss of O atoms or the production of OH radicals.In the first part of this work a simple analytical mathematical method for the determination of the concentration of atomic oxygen will be developed. The method is based on the integrated second order kinetic equation, and the effect of the experimental conditions on the results is discussed.In the second part, the production of OH as a function of contact time and of the initial concentrations of H and NO2is examined using a five reaction mechanism. By careful choice of the initial concentrations of reactants it is possible to reproduce the experimental results using simplified analytical expressions for the concentration of OH and hence to calculate a calibration factor.The importance of carrying out the calibration measurements under the same experimental conditions as those employed in kinetic experiments is highlighte

ISSN:0538-8066    

DOI:10.1002/kin.550220804

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractMixtures of NO and NO/H2in Ar were shock‐heated and photolyzed with an ArF excimer laser. Measurements in these experiments of N‐atom profiles using atomic resonance absorption spectrophotometry (ARAS) permitted the determination of two rate coefficients. The rate coefficient for the reactionwas found to be 4.29 × 1013exp(−787/T) cm3mol−1sec−1(±20% at 1400 K to ±10% at 3500 K). This is the first direct high temperature measurement of this rate coefficient in the exothermic direction. The rate coefficient for the reactionwas found to be 1.60 × 1014exp(−12650/T) (±35% from 1950 to 2850 K). To our knowledge, this is the first direct measurement of this rate coefficient.A study of the N‐atom ARAS absorption behavior revealed a noticeable pressure dependence, as well as a weak temperature dependence, in the Beer‐Lambert law absorption coefficient. Proper consideration of these effects is important when the N‐atom ARAS diagnostic is used for absolute conc

ISSN:0538-8066    

DOI:10.1002/kin.550220805

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe kinetics of the oxidation of water with bismuth(V) in presence of silver(I) has been investigated in a mixture of HClO4(1.0 mol dm−3) and HF (1.5 mol dm−3). The reaction is second order, viz., first order with respect to bismuth(V) and silver(I), each, and the second order rate constant is (6.6 ± 0.7) × 10−3dm3mol−1s−1. However, rate is independent of hydrogen ion concentration. A comparative analysis of these results with the results obtained for pdp, pds, and Ce(IV), reactions with silver(I) has also been made to correlate the rate constants and the redox‐potentials of the ox

ISSN:0538-8066    

DOI:10.1002/kin.550220806

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractRate constants for the gas‐phase reactions of O3with a series of monoterpenes and related compounds have been determined at 296 ± 2 K and 740 torr total pressure of air or O2using a combination of absolute and relative rate techniques. Good agreement between the absolute and relative rate data was observed, and the rate constants obtained (in units of 10−17cm3molecule−1s−1) were: α‐pinene, 8.7; β‐pinene, 1.5; Δ3‐carene, 3.8; 2‐carene, 24; sabinene, 8.8;d‐limonene, 21; γ‐terpinene, 14; terpinolene, 140; α‐phellandrene, 190; α‐terpinene, 870; myrcene, 49;trans‐ocimene, 56;p‐cymene,<0.005; and 1,8‐cineole,<0.015. While these rate constants for α‐ and β‐pinene and sabinene are in good agreement with recent absolute and relative rate determinations, those for the other monoterpenes are generally lower than the literature data by factors of ca. 2–10. The measured rate constants for the monoterpenes are reasonably consistent with predictions based upon the number and positions of the

ISSN:0538-8066    

DOI:10.1002/kin.550220807

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550220801

出版商:John Wiley&Sons, Inc.    

年代:1990

数据来源: WILEY