ISSN:0538-8066    

DOI:10.1002/kin.550260102

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550260103

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractA procedure to calculate the quantum mechanical transition probability of a unimolecular primary chemical process,A−→A+e−is investigated for the circumstance whereA−andAhave different numbers of vibrational and rotational degrees of freedom (one is linear, the other not). A procedure is introduced to deal with the coupling between the vibrational and rotational motions. The proposed method was applied to calculating the lifetimes of CO2˙−and N2O˙−in the gas phase. The geometry optimizations and frequency calculations for CO2, CO2˙−, N2O, and N2O˙−are performed at HF, MP2, and QCISD(T) levels with 6‐31G* or 6–31+G* basis sets, in order to obtain reliable geometric and spectroscopic information on these systems. Lifetimes are calculated for several of the lower vibrational–rotational states of the anions, as well as for the Boltzmann distribution of states at 298K. The lifetime of the lowest vibrational–rotational state of CO2˙−, is 1.03 × 10−4s, and of the lowest vibrational state with rotational levels weighted by Boltzmann distribution at 298 K, 1.50 × 10−4s. These values are in good agreement with the experimental number, 9.0 ± 2.0 × 10−5s, and support the experimental evidence that CO2˙−was formed in its ground vibrational level by the techniques used. The lifetime of CO2˙−calculated with Boltzmann distribution over its vibrational and rotational levels at 298K, is 1.51 × 10−5s. There are no direct measurements of the lifetime of N2O˙−, but it was estimated to be greater than 10−4s from experimental evidence. The predicted lifetimes of N2O˙−, at its lowest vibrational–rotational state (0K) and lowest vibrational state with rotational levels weighted by the Boltzmann distribution at 298K, are 238 and 19.1 s, respectively. The lifetime of N2O˙−at thermal equilibrium at 298Kis 6.66 × 10−2s, indicating that electron loss from the excited vibrational states of N2O˙−is significant. This study represents the first theoretical i

ISSN:0538-8066    

DOI:10.1002/kin.550260104

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe flash photolysis of aqueous solutions of rhodizonic and croconic acids has been studied in the presence and absence of electron acceptors. No transient absorption which could be identified with an excited state was observed with either anion. The rate of recovery of the ground state in the absence of additives was a first‐order process with both acids and gave rate constants for deactivation of the excited state,kD, of 2.4 × 105s−1for rhodizonate and 2.8 × 105s−1for croconate. With croconate dianion in the presence of three acceptors, 4‐nitrobenzylbromide, methylviologen, and biacetyl, a transient absorption was detected, with a maximum absorbance at 500 nm, and was tentatively identified with the monoanion radical, formed following electron transfer to the acceptor. From the rate of growth of the transient, rate constants for the rate of electron transfer to the acceptor were measured as follows: 4‐nitrobenzylbromide: 2.8 × 109M−1s−1; methyl viologen: 3.7 × 1010M−1s−1; and biacetyl: 2.0 × 108M−1s−1. The significance of the measurements is discussed in relation to the mechanism proposed for the photochemical reactions of these dianions.

ISSN:0538-8066    

DOI:10.1002/kin.550260105

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe kinetics of the gas‐phase reactions of O3with a series of alkenes and two α,β‐unsaturated ketones have been investigated at atmospheric pressure (ca. 740 torr) of air and 296 ± 2 K, using a relative rate method in the presence of sufficient cyclohexane to scavenge OH radicals generated in these reactions. Combined with our previous relative rate measurements (Int. J. Chem. Kinet.,24,803 (1992)), the rate constants obtained relative tok(O3+ propene) = 1.00 were: 3‐penten‐2‐one, 3.62 ± 0.16; 2‐cyclohexen‐1‐one,<0.19; bicyclo[2.2.2]‐2‐octene, 7.44 ± 0.48; 1,3‐cycloheptadiene, 16.1 ± 1.1; cycloheptene, 23.7 ± 1.6; 1,3‐cyclohexadiene, 134 ± 13; bicyclo[2.2.1]‐2‐heptene, 170 ± 16; and bicyclo[2.2.1]‐2,5‐heptadiene, 390 ± 36. The resulting rate constants then lead to a self‐consistent set of room temperature data for the reactions of O3with these alkenes and α,β‐unsaturated ketones. These rate constants are compared with the literature data, and the effects of r

ISSN:0538-8066    

DOI:10.1002/kin.550260106

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractTime‐resolved studies of silylene, SiH2, generated by laser‐flash photolysis of phenylsilane, have been employed to obtain rate constants for its bimolecular reactions with C2H2and C2D2. The reactions have been studied in the gas‐phase, in the pressure range 1–100 torr (with SF6bath gas) at five temperatures in the range 291–613 K.Reaction with C2H2is pressure dependent, consistent with a third body assisted association reaction. However the lack of a simple fit to RRKM calculated values suggests a more complex process with another reaction channel. Reaction with C2D2is faster than with C2H2, showing a pressure dependent isotope effect. The data are consistent with a rapid isotopic scrambling mechanism. Further RRKM modeling of a three‐channel decomposition mechanism for the suggested silirene adduct (intermediate) provides a semi‐quantitative fit to the data. Rate constants extracted from the modeling are shown to be consistent with a mechanism leading to formation of both ethynylsilane and vinylsilylene, as previously proposed by O'Neal, Ring et al. from higher temperature studies. An enthalpy surface is shown to be consistent with this mechanism. © 1994 John W

ISSN:0538-8066    

DOI:10.1002/kin.550260107

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe third‐law method is used to assess the authenticity of available equilibrium constants for the thermal dissociation of N2O5⇌ NO2+ NO3. © 1994 John Wiley&Sons,

ISSN:0538-8066    

DOI:10.1002/kin.550260108

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractAn improved method has been used to synthesize perfluoroazo‐2‐propane. Pyrolysis over the temperature range 450–514 K in a static system has been shown to be a homogeneous, first‐order process. No pressure dependence was observed in the presence of excess inert gas (SF6). The only products were nitrogen and perfluoro‐2,3‐dimethylbutane. The rate constant (k) for the decomposition process is given by:\documentclass{article}\pagestyle{empty}\begin{document}$$ \log \left({{k \mathord{\left/{\vphantom {k s}} \right. \kern-\nulldelimiterspace} s}^{- 1}} \right) = 16.7 \pm 0.2 - {{\left({9856 \pm 109} \right)} \mathord{\left/{\vphantom {{\left({9856 \pm 109} \right)} T}} \right. \kern-\nulldelimiterspace} T} $$\end{document}These results lead to a straightforward mechanism for the decomposition processThe results are compared with those for other azo compounds. © 1994 John Wil

ISSN:0538-8066    

DOI:10.1002/kin.550260109

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractReactions of Cu2with several small molecules have been studied in the gas phase, under thermalized conditions at room temperature, in a fast‐flow reactor. They fall into one of two categories. Cu2does not react with O2, N2O, N2, H2, and CH4at pressures up to 6 torr. This implies bimolecular rate constants of less than 5 × 10−15cm3s−1at 6 torr He. Cu2reacts with CO, NH3, C2H4, and C3H6in a manner characteristic of association reactions. Second‐order rate constants for all four of these reagents are dependent on total pressure. The reactions with CO, NH3, and C2H4are in their low pressure limit at up to 6 torr He buffer gas pressure. The reaction with C3H6begins to show fall‐off behavior at pressures above 3 torr. Limiting low‐pressure, third‐order rate constants are 0.66 ± 0.10, 8.8 ± 1.2, 9.3 ± 1.4, and 85 ± 15 × 10−30cm6s−1in He for CO, NH3, C2H4, and C3H6, respectively. Modeling studies of these rate constants imply that the association complexes are bound by at least 20 kcal mol−1in the case of C2H4and C3H6and at least 25 kcal mol−1in the other cases. The implications of these results for Cu‐ligand bonding are developed in comparison with existing work on the interactions of these ligands with Cu atoms, larger clusters, and surfaces

ISSN:0538-8066    

DOI:10.1002/kin.550260110

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe association reactions of atomic nickel with ethene and fully deuterated ethene in carbon dioxide buffer gas at 295 K have been investigated in the pressure range 5–100 torr, using a laser photolysis‐laser fluorescence technique. By comparison with results of ab initio quantum chemistry calculations for the complex Ni[C2H4], the data are shown to be consistent with reaction on both ground and excited state potential energy surfaces. A simple rate equations treatment is described which shows the form of the pressure dependence of the second‐order recombination rate coefficient in this case. Under conditions which are expected to hold for the Ni + C2H4(C2D4) reaction, the pressure dependence has the standard Lindemann‐Hinshelwood form, with the limiting high pressure rate constant given by an apparent value which reflects the degree to which the participating electronic states are coupled by nonadiabatic transitions. The limiting high pressure behavior of the recombination rate coefficient for Ni + C2H4is not strongly affected by deuterium isotope substitution. However, the effect on the low pressure rate constant is large and consistent with RRKM unimolecular reaction theory. This validates the use of RRKM calculations for estimating the binding energy of the complex from kinetic data. The binding energy of Ni[C2H4] is estimated to be 35.2 ± 4.2 kcal mol−1. © 1994 John Wile

ISSN:0538-8066    

DOI:10.1002/kin.550260111

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY