摘要:

AbstractTime‐resolved investigations of the atomic resonance fluorescence Sr(53P1→ 51S0) and the molecular chemiluminescence from SrCl(A2Π1/2,3/2, B2Σ+→ X2Σ+) are reported following the reaction of the electronically excited strontium atom, Sr(5s5p(3PJ)), 1.807 eV above its 5s2(1S0) electronic ground state, with CH2Cl2. The optically metastable strontium atom was generated by pulsed dye‐laser excitation of ground state strontium vapor to the Sr(53P1) state at λ = 689.3 nm (Sr(53P1← 51S0)) at elevated temperature (850 K) in the presence of excess helium buffer gas in which rapid Boltzmann equilibration within the 53PJmanifold takes place. Sr(53PJ) was then monitored by time‐resolved atomic fluorescence from Sr(53P1) at the resonance wavelength together with chemiluminescence from electronically excited SrCl resulting from reaction of the excited atom with CH2Cl2. The molecular systems recorded in the time‐domain were SrCl(A2Π1/2→ X2Σ+) (Δν = 0, λ = 674 nm), SrCl(A2Π3/2→ X2Σ+) (Δν = 0, λ = 660 nm), and SrCl(B2Σ+→ X2Σ+) (Δν = 0, λ = 636 nm). Both the A2Π (179.0 kJ mol−1) and (B2Σ+(188.0) kJ mol−1) states of SrCl are energetically accessible on collision between Sr(3P) and CH2Cl2. Exponential decay profiles for both the atomic and molecular (A,B – X) chemiluminescence emission are observed and the first‐order decay coefficients characterized in each case. These are found to be equal under identical conditions and hence SrCl(A2Π, B2Σ+) are shown to arise from direct Cl‐atom abstractions on reaction with this halogenated species. The combination of integrated molecular and atomic intensity measurements, coupled with optical sensitivity calibration, yields estimations of the branching ratios into the A1/2,3/2, B, and X states arising from Sr(53PJ) + CH2Cl2which are found to be as follows: A1/2, 3.0 × 10−3; A3/2, 1.7 × 10−3; B, 4.4 × 10−4yielding ΣSrCl(A1/2+ A3/2+ B) = 5.1 × 10−3. As only the X, A and B states of SrCl are accessible on reaction, this indicates an upper limit for the branching ratio into the ground state of 0.995. The present results are compared with previous time‐resolved measurements on SrF, Cl, Br(A2Π,B2Σ+− X2Σ+) that we have reported on various halogenated species and with analogous chemiluminescence studies on Sr(3P) with other halides obtained from molecular beam measurements. The results are further compared with those from a series of previous analogous investigations in the time‐domain we have presented of molecular emissions from CaF, Cl, Br, I (A,B – X) arising from the collisions of Ca(43PJ) with appropriate halides and with branching ratio

ISSN:0538-8066    

DOI:10.1002/kin.550270802

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe kinetics of the degradation ofN‐amino‐3‐azabicyclo[3,3,0]octane by chloramine has been studied by GC and HPLC in stoichiometric conditions in a solution buffered with NaOH/KH2PO4and Na2B4O7.10 H2O between pH = 10.5 and 13.5. The second‐order reaction exhibits specific acid catalysis which indicates competitive oxidation between the haloamine and the neutral and ionic forms of the bicyclic hydrazine. The enthalpy and entropy of activation were determined at pH = 12.89.In a nonbuffered solution, the interaction is autocatalyzed due to acidification of the mixture by the ammonium ions. In basic medium, the reaction forms an endocyclic hydrazone. A mathematical treatment based on an implicit equation allows a quantitative interpretation of all the phenomena observed over the above pH interval. This takes both the acid/base dissociation equilibria and the alkaline hydrolysis of the chloro‐derivative into account. © 1995 John Wiley

ISSN:0538-8066    

DOI:10.1002/kin.550270803

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe production and reactions of vinyl radicals and hydrogen atoms from the photolysis of vinyl iodide (C2H3I) at 193 nm have been examined employing laser photolysis coupled to kinetic‐absorption spectroscopic and gas chromatographic product analysis techniques. The time history of vinyl radicals in the presence of hydrogen atoms was monitored using the 1,3‐butadiene (the vinyl radical combination product) absorption at 210 nm. By employing kinetic modeling procedures a rate constant of 1.8 × 10−10cm2molecule−1s−1for the reaction C2H3+ H has been determined at 298 K and 27KPa (200 torr) pressure. A detailed error analysis for determination of the C2H3+ H reaction rate constant, the initial C2H3and H concentrations are performed. A combined uncertainty of ±0.43 × 10−10cm2molecule−1s−1for the above measured rate constant has been evaluated by combining the contribution of the random errors and the systematic errors (biases) due to uncertainties of each known parameter used in the modeling. © 1995 J

ISSN:0538-8066    

DOI:10.1002/kin.550270804

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe primary quantum yield of H‐atom production in the pulsed‐laser photolysis of hydrazine vapor, N2H4+ hν → H + N2H3, was measured to be (1.01 ± 0.12) at 193 nm relative to HBr photolysis, and (1.06 ± 0.16) at 222 nm relative to 248‐nm N2H4photolysis, in excess He buffer gas at 296 K. The H‐atoms were directly monitored in the photolysis by cw‐resonance fluorescence detection of H(2S) at 121.6 nm. The high H‐atom yield observed in the photolysis is consistent with the continuous ultraviolet absorption spectrum of N2H4involving unit dissociation of the diamine from repulsive excited singlet state(s). The laser photodissociation of N2H4was thus used as a ‘clean’ source of H‐atoms in excess N2H4and He buffer gas to study the gas‐phase reaction, H + N2H4→ products; (k1), in a thermostated photolysis reactor made of quartz or Pyrex. The pseudo‐first‐order temporal profiles of [H] decay immediately after photolysis were determined for a range of different hydrazine concentrations employed in the experiments to calculate the absolute second‐order reaction rate coefficient,k1. The Arrhenius expression was determined to bek1= (11.7 ± 0.7) × 10−12exp[−(1260 ± 20)/T] cm3molec−1s−1in the temperature range 222–657 K. The rate coefficient at room temperature was, within experimental errors, independent of the He buffer gas pressure in the range 24.5–603 torr. The above temperature dependence ofk1is in excellent agreement to that we determine in our discharge flow‐tube apparatus in the temperature range 372–252 K and in 9.5 torr of He pressure. The Arrhenius parameters we report are consistent with a metathesis reaction mechanism involving the abstraction of hydrogen

ISSN:0538-8066    

DOI:10.1002/kin.550270805

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe rate constants for the reactions of OH with dimethyl ether (k1), diethyl ether (k2), di‐n‐propyl ether (k3), di‐isopropyl ether (k4), and di‐n‐butyl ether (k5) have been measured over the temperature range 230–372 K using the pulsed laser photolysis‐laser induced fluorescence (PLP‐LIF) technique. The temperature dependence ofk1,k4, can be expressed in the Arrhenius plots form:k1= (6.30 ± 0.10) × 10−12exp[−(234 ± 34)/T] andk4= (4.13 ± 0.10) × 10−12exp[(274 ± 26)/T]. The Arrhenius plots fork2,k3, andk5, were curved and they were fitted to the three parameter expressions:k2= (1.02 ± 0.08) × 10−17T2exp[(797 ± 24)/T],k3= (1.84 ± 0.23) × 10−17T2exp[(767 ± 34)/T], andk5= (6.29 ± 0.74) × 10−18T2exp[(1164 ± 34)/T]. The values at 298 K are (2.82 ± 0.21) × 10−12, (1.36 ± 0.11) × 10−11,(2.17 ± 0.16) × 10−11, (1.02 ± 0.10) × 10−11, and (2.69 ± 0.22) × 10−11fork1,k2,k3,k4, andk5, respectively, (in cm3molecule−1s−1). These result

ISSN:0538-8066    

DOI:10.1002/kin.550270806

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe reaction between Co(en)2(2−pzCO2)2+(bis‐ethylenediamine (2‐pyrazinecarboxylato)cobalt(III)) and Fe(CN)5H2O3−(aquopentacyanoferrate(II)) to form the binuclear complex [(en)2Co( μ‐pzCO2)Fe(CN)5]−has been studied in several isodielectric binary mixtures at 298.2 K (cosolvents: methanol, ethanol, tertbutyl alcohol, ethyleneglycol, and glycerol). Results were rationalized by using a free energy relationship. The importance of correcting the rate constants obtained in the different mixtures from the ionic strength influence has been shown. © 1995 John Wi

ISSN:0538-8066    

DOI:10.1002/kin.550270807

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractA computational study including sensitivity, nondimensional, and stedy‐state analyses of the gas‐phase kinetics associated with Chemical Oxygen‐Iodine Lasers (COIL) was performed to develop a simplified kinetic model and assess kinetic limitations to laser performance. A minimal set of 13 reactions is developed that adequately describes the time evolution of the major chemical constituents of a COIL device. A characteristic time for the dissociation of molecular iodine by singlet oxygen is established in terms of iodine fraction, water content, yield of singlet oxygen, and rate parameters. Finally, an approximate analytic solution to the iodine dissociation problem is established for a broad range of reagent concentrations. The current study is limited in applicability due to the exclusion of chemical heat release and reactive mixing phenomenon. © 1995 John Wiley&Son

ISSN:0538-8066    

DOI:10.1002/kin.550270808

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractMembrance covered oxygen probes are frequently used to monitor the progress of chemical reactions involving dissolved oxygen. For reactions that are comparable in rate to the response of the oxygen probe it is difficult to obtain the correct kinetic constants directly from the probe signal with traditional kinetic data manipulation methods. In this article, we apply the method of impulse response function to describe the probe signal of an oxygen probe for three different types of simple chemical reactions. The impulse response function is obtained experimentally. Using the impulse response function we have obtained the relationships between the probe signal and the kinetic parameters of these reactions. The slow response of the probe has two effects on the kinetic curves of the reaction studied: a time‐lag and distortion of the shape of the kinetic curve throughout the reaction. The latter effect becomes significant when the reaction is fast. Procedures to obtain the correct kinetic information from the oxygen probe signal are described. © 1995 John Wiley&Sons, I

ISSN:0538-8066    

DOI:10.1002/kin.550270809

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550270801

出版商:John Wiley&Sons, Inc.    

年代:1995

数据来源: WILEY