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• Atomic, Molecular and Optical Physics  (92)
• Physical Chemistry  (61)
• 1990-1994
• 1970-1974  (153)
• 1972  (153)
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• 1990-1994
• 1970-1974  (153)
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• 1
Electronic Resource
New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Effects of deuterium substitution in propylene on the relative rates of H(D) atom abstraction from and addition to the olefin, and on the orientation of H(D) atom addition, have been studied in the gas phase at room temperature. Effects of isotopic substitution of the olefinic hydrogen atoms on abstraction could not be observed, but abstraction is reduced five- to tenfold by deuteration of the methyl group. Deuteration of either olefinic position enhances the rate of addition to the substituted carbon atom. Disproportionation-combination ratios for deuterium-substituted propyl radicals are not greatly different from those for unsubstituted radicals, the largest effect being for C3D7 radicals, for which the overall kd/kc is reduced 10-15%.
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• 2
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Measurements of the D(R—NO) bond strength in some C-nitrosocompounds have been made using an electron impact method. The appearance potential of the radical ion (R+) has been determined, the D(R—NO) bond energy being obtained from the relation \documentclass{article}\pagestyle{empty}\begin{document}$$D{\rm (R} - {\rm NO) = }AP{\rm (R}^{\rm + } {\rm)} - IP({\rm R}.)$$\end{document} The values obtained are: D(C6H5—NO) = 41 kcal/mole, D(t-C4H9—NO) = 34 kcal/mole, D(t-C5H11—NO) = 36 kcal/mole and D(i-C3H7—NO) = 36.5 kcal/mole. These values are in good agreement with the numerous estimations of Benson and coworkers and confirm that the C—N bond strength in C-nitrosocompounds is very much less than in nitrocompounds or in amines.
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• 3
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: A general computational method for obtaining complete solutions of time-dependent kinetic equations has been developed and applied to free radical-initiated reactions of alkanes with oxygen. The method has been applied to the low-temperature, peroxide-initiated oxidations of isobutane and isopentane. Using available independently measured and estimated values for the rate constants and activation parameters for each of the 20 proposed reaction steps for the oxidation of isobutane, the rates and products have been calculated for both the liquid phase and gas phase in the range of 100°-155°C. The calculated rates and products of oxidation agree with published experimental values. The oxidation of isopentane was examined by a 32-reaction model. The rate constants were estimated using values for the appropriate rate steps in the oxidation of n-butane and isobutane. The calculation of the oxidation rate and products agree with our experiments.
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• 4
Electronic Resource
New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
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• 5
Electronic Resource
New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
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• 6
Electronic Resource
New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The flash photolysis-resonance fluorescence technique has been used to measure the reaction of ground-state sulfur atoms with molecular oxygen as a function of both temperature and total pressure. The most suitable source of S(3P) for this study was found to be COS in the presence of CO2, as a diluent gas and with the photolysis flash filtered so as to remove all radiation of wavelengths below 1650 Å. Under these conditions, it was found that over the temperature range of 252-423°K the rate data could be fit to a simple Arrhenius-type equation of the form \documentclass{article}\pagestyle{empty}\begin{document}$$k_1 = (2.24 \pm 0.27) \times 10^{ - 12} {\rm exp}\left({\frac{{{\rm - 0}{\rm .00} \pm {\rm 0}{\rm .10 kcal/mole}}}{{RT}}} \right)$$\end{document} Units are cm3 molec-1 s-1. The small A-factor for this reaction, the lack of any pressure dependence, and the direct observation of the production of O(3P) with increasing reaction time suggest that the S(3P) atom attacks the O2(3Σ) molecule end-on forming SOO which rapidly falls apart to form SO (3Σ) and O(3P).
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• 7
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Absolute rate constants for the reaction of S(3P) with ethylene were measured over an ethylene concentration range of 7, a total pressure of 50 to 400 torr, and a flash intensity range of 10. At 298°K, the bimolecular rate constant was found to be invariant over this range of variables and had a measured value of 4.96 × 10-13 cm3 molec-1 s-1. Over the temperature range of 218° to 442°K, the rate data could be fit to a simple Arrhenius equation of the form \documentclass{article}\pagestyle{empty}\begin{document}$$k_1 = (7.13 \pm 0.74) \times 10^{ - 12} {\rm exp}\left({\frac{{{\rm - 1}{\rm .58} \pm {\rm 0}{\rm .08 kcal/mole}}}{{RT}}} \right)$$\end{document} Units are cm3 molec-1 s-1. The dependence of the measured value of k1 on the concentration of the reaction product ethylene episulfide is discussed.
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• 8
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The reaction of C2F5 radicals with H2S \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {(2)} & {{\rm C}_{\rm 2} {\rm H}_{\rm 5} + {\rm H}_{\rm 2} {\rm S} \to {\rm C}_{\rm 2} {\rm F}_{\rm 5} {\rm H} + {\rm HS}} & {k_H } \\ \end{array}$$\end{document} was studied over the range 1°-123°C using C2F5 radicals generated by photolysis of perfluoropropionic anhydride. The rate constant kH for reaction (2) is given by \documentclass{article}\pagestyle{empty}\begin{document}$$\log {\rm }k_H ({\rm cm}^{\rm 3} {\rm mole}^{ - 1} \sec ^{ - 1}) = (11.70 \pm 0.19) - (4260 \pm 290)/\theta$$\end{document} where θ = 2.303RT/cal mole-1. The relevance of this result to conflicting published data on the analogous reaction between CF3 radicals and H2S is discussed. It is concluded that there is little difference in the Arrhenius parameters for reaction of CF3 and C2F5 radicals with H2S.
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• 9
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: A metathetical reaction between carbon tetrachloride and toluene to give benzyl chloride and chloroform occurs at temperatures above 200°C (k = 4.8 × 1010 e-32,900/RT cc mole-1sec-1). The reaction does not involve free radicals, as is shown by the kinetic behavior of the system, by the lack of effect of added free-radical chain inhibitors, and by the absence of the expected chain termination product, hexachloroethane. The reaction is one of a general type between carbon tetrachloride and alkanes or alkylaromatics, but at the temperatures required it is often obscured by dehydrohalogenation of the product to the highly reactive olefin. At high temperatures, benzyl chloride reacts with toluene to give bibenzyl and hydrogen chloride, apparently also by a metathetical reaction. The transition state is postulated to be four-center, in which the carbon-chlorine and carbon-hydrogen bonds are broken and reformed: The experimental preexponential factor is in good agreement with that calculated from transition-state theory.
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• 10
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The kinetics of the “a” and “b” band emissions arising from the 1Σg+ ← 3Ou and 1Σg+ ← 3lu transitions of the diatomic mercury molecule at λmax ∼ 4850 Å and 3350 Å, respectively, have been studied at low concentrations of mercury in the presence of N2, C2H6, C3H8, and N2O. Rate constant values have been obtained for the following reactions of the excimer molecule: Hg2(3lu) + N2 → Hg2(3Ou) + N2 and Hg2(3Ou) + RH → Hg2(1Σg+) + RH, where RH = C2H6 or C3H8. From a consideration of the detailed kinetics of band emissions, it was also possible to derive rate constants for the quenching reactions of Hg(3P0) atoms. These values are in reasonable agreement with those obtained previously from monitoring atom concentrations directly by 4047 Å absorbiometry.
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• 11
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The room-temperature photolysis of N2O (10-100 torr) at 2139 Å to produce O(1D) has been studied in the presence of CH4 (10-891 torr). The reactions of O(1D) with CH4 were found to be \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {(4)} & {{\rm O(}^{\rm 1} D{\rm)} + {\rm CH}_{\rm 4} } & \to & {{\rm HO + CH}_{\rm 3} } & {0.95 \pm 0.05} \\ {(8)} & {} & \to & {{\rm O(}^{\rm 3} P{\rm)} + {\rm CH}_{\rm 4} } & {{\rm 0}{\rm .05} \pm {\rm 0}{\rm .05}} \\ {} & {} & \to & {{\rm CH}_{\rm 2} + {\rm H}_{\rm 2} {\rm O}} & {{\rm 〈 0}{\rm .03}} \\ {} & {} & \to & {{\rm CH}_{\rm 3} {\rm OH}} & {{\rm 〈 0}{\rm .01}} \\ {} & {} & \to & {{\rm CH}_{\rm 2} {\rm O + H}_{\rm 2}} & {{\rm 〈 0}{\rm .002}} \\\end{array}$$\end{document} The method of chemical difference was used to measure the rate constant ratio k4/(k2 + k3), where reactions (2) and (3) are \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {(2)} & {{\rm O(}^{\rm 1} D{\rm)} + {\rm N}_{\rm 2} {\rm O}} & { \to {\rm N}_{\rm 2} + {\rm O}_{\rm 2} } \\ {(3)} & {} & { \to 2{\rm NO}} \\\end{array}$$\end{document} The CH3 radicals produced in reaction (4) react with the O2 and NO produced in reactions (2) and (3). Thus, near the endpoint of the internal titration, φ{C2H6} gives an accurate measure of k4/(k2 + k3). For the translationally energetic O(1D) atoms produced in the photolysis, k4/(k2 + k3) = 2.28 ± 0.20. However, if He is added to remove the excess translational energy, then k4/(k2 + k3) drops to 1.35 ± 0.3.
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• 12
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The self-radiolysis of CO2 in excess tritium (3H2) has been studied at pressures of 0.1 to 1.0 atm, temperatures of -80° to +100°C, and in the presence of added H2O, He, or Ar. The primary products of decomposition are CO and 3H2O. Secondary products are C3H4, C23H4, and a white polymer. The rates of disappearance of CO2 and formation of products and G-;values were measured. The disappearance of CO2 initially obeys first-order kinetics, then slows down with time at a rate depending upon the initial pressure of 3H2. The initial rates are proportional to pressures of CO2 and 3H2. They are independent of temperature, decreased by addition of H2O vapor, and increased by addition of He or Ar. The proposed mechanism of decomposition of CO2 and formation of products involves ionization of CO2 followed by dissociative recombination forming CO and O. Then the O reacts with a hydrogen-containing species forming OH and H2O, and a back reaction forms CO2 from CO and OH.
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• 13
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The rate constants (kuni) for the first-order disappearance of the title molecules have been determined under VLPP conditions. The kuni are not the rate constants of ultimate interest since they reflect the fact that energy transfer competes with the chemical decomposition. Use of the Rice-Ramsperger-Kassel-(Marcus) [RRK(M)] theory allows the determination of the high-pressure rate constants (kα), if the mode of decomposition is known. The heats of formation of the radicals NH2, CH3NH, and (CH3)2N are known. These values should be usable for prediction of the activation energy for N—N bond homolysis in the hydrazines. Measured rate constants for UDMH and TMH bear this out, but the rate constant for MMH does not. This and other evidence lead to the conclusion that MMH decomposes via molecular concerted elimination of NH3 and H2 not and by N—N bond scission. The following values are preferred from this work (θ = 2.303RT in kcal/mole). Mode of decomposition is N - N bond scission unless noted otherwise in parenthesis: \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{ll} \underline{{{{\rm Molecule}}}}& \underline{{{{\rm log }k_\infty /\sec ^{ - 1} (298^\circ {\rm K})}}}\\ {{{{\rm MMH}}}}&{{{13.2{\rm - }54/\theta (- {\rm NH}_{\rm 3});}}}\\ {} & {13.5{\rm - }57/\theta (- {\rm H}_{\rm 2})} \\ {{\rm UDMH}} & {17.0{\rm - }63/\theta } \\ {{\rm SDMH}} & {{\rm 13}{\rm .5 - 57/}\theta {\rm (} - {\rm H}_{\rm 2} {\rm)}} \\ {{\rm TMH}} & {{\rm 17}{\rm .4 - 54/}\theta } \\\end{array}$$\end{document}.
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• 14
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
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• 15
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Products of the radical reactions arising from t-Bu2O2, CF3I, and CH3I at 146°C in the vapor phase have been measured over a 33-fold range of CH3I/CH3I ratios and shown to be governed by the rapidly established equilibrium \documentclass{article}\pagestyle{empty}\begin{document}$${\rm Me} \cdot + {\rm CF}_{\rm 3} {\rm I}\mathop {{\rm \rightleftharpoons}}\limits^K {\rm MeI} + {\rm CF}_{\rm 3} \cdot$$\end{document} Together with K estimated by thermochemical methods, the results yield, for the rate of recombination for CF3· radicals, kr = 109.7 ± 0.5 M-1 sec-1.
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• 16
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The kinetics of the reactions of H atoms with H2S and with COS were measured at 298deg;K in a flow system using mass-spectrometric detection. The rate constants were found to be 3.8 × 10-13 and 2.2 × 10-14 cm3 part-1 sec-1, respectively, with an estimated accuracy of 25%. At high flow rates of H2S, 0.5 molecules of H2S are consumed per H atom originally present. At all flow rates of COS, H2S is a major product, CO production equals COS consumption, and 0.5 molecules of COS are consumed per H atom. The results are consistent with the reaction HS + HS → H2S + S being the dominant process for thiyl radicals, and evidence is presented to indicate that its reaction rate is close to collisional frequency.
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• 17
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
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• 18
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The thermal decomposition of 1,1,1-trifluoro-2-chloroethane has been investigated in the single-pulse shock tube between 1120° and 1300deg;K at total reflected shock pressures from ∼2610 to 3350 torr. Under these conditions, the major reaction is the α,α-elimination of hydrogen chloride, \documentclass{article}\pagestyle{empty}\begin{document}$${\rm CF}_{\rm 3} {\rm CH}_{\rm 2} {\rm Cl}\mathop {{\rm \rightarrow}}\limits^{k_1 } {\rm CF}_{\rm 2} {\rm CHF} + {\rm HCl}$$\end{document} with \documentclass{article}\pagestyle{empty}\begin{document}$${\rm log(}k_1^\infty {\rm, sec}^{ - {\rm 1}} {\rm) = 13}{\rm .3} \pm {\rm 0}{\rm .4} - (65.5 \pm 2.2{\rm kcal})/2.303RT$$\end{document} The decomposition also involves the slower α,β-elimination of hydrogen fluoride, \documentclass{article}\pagestyle{empty}\begin{document}$${\rm CF}_{\rm 3} {\rm CH}_{\rm 2} {\rm Cl}\mathop {{\rm \rightarrow}}\limits^{k_2 } {\rm CF}_{\rm 2} {\rm CHCl} + {\rm HF}$$\end{document} with the first-order rate constant given by \documentclass{article}\pagestyle{empty}\begin{document}$${\rm log(}k_2^\infty {\rm, sec}^{ - {\rm 1}} {\rm) = 12}{\rm .7} \pm {\rm 0}{\rm .5} - (67.6 \pm 2.7{\rm kcal})/2.303RT$$\end{document} At temperatures above 1270°K, two additional minor products were observed. These were identified as CF2CFCl and CF3CHCl2 and suggest C—Cl rupture as a third reaction channel leading to complicated kinetics.
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• 19
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: An e×tensive table is given of the Kassel integral \documentclass{article}\pagestyle{empty}\begin{document}$$I(S,B,D) = \Gamma \mathop {(S)}\limits^1 \int_0^\infty {\frac{{x^{S - 1} e^{ - x} dx}}{{1 + 10^D \left({\frac{x}{{B + x}}} \right)^{S - 1} }}}$$\end{document} that occurs in the Rice-Ramsperger-Kassel theory of unimolecular gas reactions.
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• 20
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Electron transfer involving triplet molecules of anthraquinone sulfonates has been studied by flash photolysis. It was revealed that semiquinone radicals were formed in one-electron oxidation of carbonate anions. Absorption spectra and the kinetics of decay transients in aqueous and aqueous-alcoholic solutions have been studied.
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• 21
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The thermal decompositions of 1-chloro-1-fluoroethane and 1-chloro-1,1-difluorethane at atmospheric pressure have been studied in the temperature range 500-600°C in a flow system. The dehydrochlorinations are homogenous in a carbonaceous reactor and unimolecular. The rate constants are given by \documentclass{article}\pagestyle{empty}\begin{document}$$k_{\rm I} = 10^{13.94 \pm 0.05} \exp (- 57,015 \pm 200/RT)^{\sec - 1}$$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$$k_{{\rm II}} = 10^{14.35 \pm 0.12} \exp (- 60,200 \pm 500/RT)^{\sec - 1}$$\end{document} The criteria for molecular or chain processes in thermal dehydrochlorinations are discussed.
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• 22
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The reaction of NO2 with C2F4 was studied at 30°, 68°, 114°, and 157°C by in situ monitoring the infrared absorption bands of the products. The major primary products of the reaction are O2NCF2CFO and FNO. Smaller amounts of CF2O (and presumably NO) are also produced. There was no evidence for other primary products, though they may have been produced in minor amounts. The rate laws for the production of both O2NCF2CFO and CF2O are first order in both [NO2] and [C2F4]. CF2O production is at least partly heterogeneous as demonstrated by packing the quartz reaction vessel with Pyrex beads and by using a Monel cell. The homogeneous rate constant obtained from the high-temperature results gives a rate constant of 3.4 × 108 exp (minus;17000/RT) M-1sec-1 for CF2O production. Actually these Arrhenius parameters represent lower limits, since the heterogeneous reaction may still be playing a significant role. The production rate of O2NCF2CFO is not much affected by changing the nature of the surface or the surface to volume ratio. However the reaction may be heterogeneous, since the rate constant for its formation of 1.3 × 104 e×p (-7500/RT) M-1sec-1 has an abnormally low pree×ponential factor. E×periments in the presence of NO indicate that the mechanism for O2NCF2CFO formatlon is \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{l} \begin{array}{*{20}c} {(11)} & {{\rm NO}_{\rm 2} + {\rm C}_{\rm 2} {\rm F}_{\rm 4} \to {\rm O}_{\rm 2} {\rm NCF}_{\rm 2} {\rm CF}_{\rm 2} } \\ \end{array} \\ \begin{array}{*{20}c} {(12)} & {{\rm O}_{\rm 2} + {\rm NCF}_{\rm 2} {\rm CF}_{\rm 2} + {\rm NO}_{\rm 2} \to {\rm O}_{\rm 2} {\rm NCF}_{\rm 2} {\rm CFO} + {\rm FNO}} \\ \end{array} \\ \end{array}$$\end{document} The intermediate can also react with NO: \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {(13)} & {{\rm O}_{\rm 2} {\rm NCF}_{\rm 2} {\rm CF}_{\rm 2} + {\rm NO} \to {\rm O}_{\rm 2} {\rm NCF}_{\rm 2} {\rm CF}_{\rm 2} {\rm NO}} \\ \end{array}$$\end{document} with k13/k12 = 1.3.
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• 23
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Study of n-butane pyrolysis at high temperature in a flow system allows measurement of the sum of the rate constants of the initiation reactions \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{l} \begin{array}{*{20}c} {(1)} & {{\rm C}_{\rm 4} {\rm H}_{{\rm 10}} \to {\rm 2C}_{\rm 2} {\rm H}_{\rm 5} ^{\rm .} } \\ \end{array} \\ \begin{array}{*{20}c} {(2)} & {{\rm C}_{\rm 4} {\rm H}_{{\rm 10}} \to {\rm CH}_{\rm 3} ^{\rm .} } \\ \end{array} + {\rm C}_{\rm 3} {\rm H}_{\rm 7} ^{\rm .} \\ \end{array}$$\end{document} and of the Arrhenius parameters of the reactions \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{l} \begin{array}{*{20}c} {(3)} & {{\rm CH}_{\rm 3} ^{\rm .} + {\rm C}_{\rm 4} {\rm H}_{{\rm 10}} \to {\rm CH}_{\rm 4} + {\rm C}_{\rm 4} {\rm H}_{\rm 9} ^{\rm .} } \\ \end{array} \\ \begin{array}{*{20}c} {(4)} & {{\rm C}_{\rm 2} {\rm H}_{\rm 5} ^{\rm .} + {\rm C}_{\rm 4} {\rm H}_{{\rm 10}} \to {\rm C}_{\rm 2} {\rm H}_{\rm 6} } \\ \end{array} + {\rm C}_{\rm 4} {\rm H}_{\rm 9} ^{\rm .} \\ \end{array}$$\end{document} Established data for k1/k2 allow estimation of k1 for 951°K and this, with recent thermochemical data, yields the result log k-1 (l.mole s-1) = 8.5, in remarkable agreement with a recent measurement [20] but over si×ty times smaller than conventional assumption. The product k3k4 (l.2mole-2s-2) is found to be associated with the Arrhenius parameters log (A3A4) = 21.90 ± 0.6 and (E3 + E4) = 38.3 ± 2.7 kcal/mole. These values are much higher than would be e×pected on the basis of low temperature estimates. Independent evaluation gives log A4 = 10.5 ± 0.4 (l.mole-1s-1) and E4 = 20.1 ± 1.7 kcal/mole, hence log A3 = 11.4 ± 0.8 (l.mole-1s-1) and E3 = 18.2 ± 3.2 kcal/mole. These values are shown to be entirely consistent with a wide range of results from pyrolytic studies, and it is argued that they further confirm the view that Arrhenius plots for alkyl radical-alkane metathetical reactions are strongly curved, in part due to tunneling and, appreciably, to other as yet unidentified effects. Since there is published evidence that metathetical reactions involving hydrogen atoms show even greater curvature, it is suggested that this may be a characteristic of many metathetical reactions.
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• 24
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
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• 25
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The pyrolyses of trimethylethylene and tetramethylethylene have been investigated in the presence and absence of nitric oxide. It appears that apart from a unimolecular split, e.g., a disproportionation reaction such as may play an important role in initiation. Nitric oxide had no effect on H2 production, which is probably a molecular process. There was similar behavior of both compounds in the presence of NO, indicating that the olefinic hydrogen atom does not play a decisive role. Other aspects of the mechanisms are discussed.
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• 26
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The rate of the isotope exchange reaction between iron(II) and iron(III) perchlorates has been measured in a solvent mixture containing a 3:2 mole ratio of water to dimethyl sulfoxide over the temperature range from 25° to -98°C. In this temperature range, the reactants can diffuse together faster than they can undergo isotope exchange. The activation enthalpy and entropy for the acid-independent reaction were 6.0 ± 1.2 kcal/mole and -38 ± 17 cal/deg mole, respectively. Below -22°C, the acid-dependent exchange reaction did not contribute significantly to the exchange. In liquid media at -112° and -117°C and in a solid glass at -136°C, no isotope exchange was observed over the period of a calculated half-life for the reaction. At these temperatures, the rate at which the reactants diffuse together is slower than the calculated rate of isotope exchange. In a solid glass at -196°C, no isotope exchange was observed over the period of one week.
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Notes: The total decomposition rates of the chemically activated alkanes n-butane, n-pentane, isopentane, and neohexane were measured using an internal comparison technique. Chemical activation was by the C—H insertion reaction of excited singlet-state methylene radicals. A total of ten rate constants ranging from 4.6 × 105 to 2.3 × 107 sec-1 were measured for these alkanes at different excitation energies. These rates correlate via RRKM theory calculations with thermal A-factors in the range of 1016.1 to 1017.1 sec-1 for free rotoractivated complex models and in the range of 1016.4 to 1017.8 sec-1 for vibrator-activated complex models. It was found that high critical energies for decomposition, “tight” radical models, and activated complex models with free internal rotations were required to correlate the decomposition rates of these alkanes with estimated alkyl radical recombination rates. The correlation is just barely possible even for these favorable extremes, indicating that there may be a basic discrepancy between the recombination rate and decomposition rate data for alkanes.
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Notes: The thermal decomposition of 3-chloro-3-trichloromethyldizairine in carbon tetrachloride and iso-octane has been investigated over the temperature range 75-115°C. The products, tetrachloroethylene and nitrogen, are formed quantitatively by a first-order reaction which is probably unimolecular: The results yielded the following Arrhenius equations: \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{l} k({\rm CCl}_{\rm 4} {\rm)} = {\rm 10}^{{\rm 13}{\rm .8} \pm {\rm 0}{\rm .2}} \exp (- 29,200 \pm 200/RT)\sec ^{ - 1} \\ k(iso - {\rm octane)} = {\rm 10}^{{\rm 13}{\rm .8} \pm {\rm 0}{\rm .2}} \exp (- 29,000 \pm 150/RT)\sec ^{ - 1} \\ \end{array}$$\end{document}.
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Notes: A comparative study of the kinetics of the N-nitrosation of sulfanilamide by cyclohexyl nitrite and by nitrous acid has been made, using an automated technique. The results indicate that a common nitrosating species is effective in analogous reactions involving cyclohexyl nitrite or nitrous acid. The N-nitrosation reaction has been followed spectrophotometrically by coupling the diazotized product with 1-naphthol. Under certain conditions a competitive reaction takes place in which coupling occurs with unreacted sulfanilamide.
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• 33
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• 34
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Notes: The pyrolysis of ethyl acetate has been studied by the very low-pressure pyrolysis (VLPP) technique. The results obtained agree well with the previously determined high-pressure Arrhenius parameters where log k∞ = 12.6 - 48.0/θ. The rate constants given by these parameters have also been shown to be consistent with the predictions of the RRK and RRKM theories and demonstrate the applicability of the technique to the study of thermal decompositions.
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• 35
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Notes: Values of the rate constants for allyl-radical abstraction from toluene and allyl-radical recombination have been recalculated in the light of recent data on butene-1 decomposition. The rate of recombination is in good agreement with that found by Van den Bergh and Callear [13] and the cross-combination ratio for the allyl + methyl system has a “normal” value of almost 4. It is concluded that allyl radicals behave like alkyl radicals in respect of their rates of reaction with other radicals.
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• 36
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Notes: An analysis of the atmospheric observations of O2(1δg) in the dayglow and twilight confirms the crude experimental assessments of Brown [1] and the conclusions that can be made from recent work of Westenberg, Roscoe, and DeHaas [2] that the reaction \documentclass{article}\pagestyle{empty}\begin{document}$${\rm H} + {\rm O}_{\rm 2} (^1 \Delta g) \to {\rm OH} + {\rm O}$$\end{document} is relatively slow, much slower than was expected or can be explained easily in theoretical terms. Using a value for the concentration of atomic hydrogen at 85 km, an upper limit rate of 3×10-13 cm3 molecule-1 sec-1 would be compatible with current atmospheric models. An evaluation of the available data for the rates of several reactions involving ground state or electronically excited species, for which the values are reasonably well established, is included to better analyze the general effects of an electronically excited reactant. This further illustrates the unusual slowness of the H + O2(1Δg) reaction.
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• 37
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Notes: Previous studies by Buckler and Norrish of the second limit of CO and O2 mixtures containing small amounts (0.25-10%) of H2 have been used to obtain the velocity constant of the reaction \documentclass{article}\pagestyle{empty}\begin{document}$${\rm O} + {\rm CO} + {\rm M = CO}_{\rm 2} + {\rm M}$$\end{document} These estimates of k33 = 3.9 × 108 and 3.5 × 108 liter2 mole-2 sec-1 (M = H2) at 500° and 560°C, respectively, have been combined with other estimates over the range 300°-3500°K to give k33 = 3.0 × 108 exp (-3000/RT) for M = Ar; the considerable scatter in the available points does not encourage any great confidence in this expression and may be attributed at least partly to the different molecules used as M by different workers. For KCl-coated and CsCl-coated vessels at 540°C, studies of the second limit of H2 + O2 mixtures, to which CO has been added, have indicated that with both the surfaces, the effect of CO on the limit is masked by changes in the surface nature. In the case of CsCl, the results have enabled a lower limit of about 0.6 to be obtained for the efficiency of CO relative to H2 in the reaction \documentclass{article}\pagestyle{empty}\begin{document}$${\rm H} + {\rm O}_{\rm 2} + {\rm M = HO}_{\rm 2} + {\rm M}$$\end{document} Use of a computer treatment to interpret the second limit of CO + H2 + O2 mixtures in aged boric-acid-coated vessels at 500°C gives a value of mCO = 0.74 ± 0.04 together with an estimate of k32 (H + CO + M″ = HCO + M″)/k4 = 0.022 ± 0.003, which leads to k32 = 2.3 × 108 liter2 mole-2 sec-1 (M = H2) at 500°C.
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• 39
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Notes: The gas phase iodination of cyclobutane was studied spectrophotometrically in a static system over the temperature range 589° to 662°K. The early stage of the reaction was found to correspond to the general mechanism \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{l} {\rm RH} + {\rm I} \cdot \mathop {{\rm \rightleftharpoons}}\limits^1 {\rm R} \cdot + {\rm HI} \\ {\rm R} \cdot + {\rm I}_{\rm 2} \mathop {{\rm \rightleftharpoons}}\limits^2 {\rm R} - {\rm I} + {\rm I} \cdot \\ \end{array}$$\end{document} where the Arrenius parameters describing k1 are given by log k1/M-1 sec-1 = 11.66 ± 0.11 - 26.83 ± .31/θ, θ = 2.303RT in kcal/mole. The measured value of E1, together with the fact that E-1 = 1 ± 1 kcal/mole, provides ΔHf,2980(c-C4H7.) = 51.14 ± 1.0 kcal/mole, and the corresponding bond dissociation energy, D(c-C4H7—H) = 96.8 ± 1.0 kcal/mole. A bond dissociation energy of 1.8 kcal/mole higher than that for a normal secondary C—H bond corresponds to one half of the extra strain energy in cyclobutene compared to cyclobutane and is in excellent agreement with the recent value of Whittle, determined in a completely different system. Estimates of ΔHf0 and entropy of cyclobutyl iodide are in very good agreement with the equilibrium constant K12 deduced from the kinetic data. Also in good agreement with estimates of Arrhenius parameters is the rate of HI elimination from cyclobutyl iodide.
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• 40
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Notes: The method of chemical difference was utilized to accurately determine the relative importance of all the reaction steps in the direct photolysis of N2O at 2139 Å (25° and 250°C) and 1849 Å (25° C), as well as in the Hg6(1P1)-sensitized photolysis of N2O at 1849 Å (25°C). In all cases, the primary process is predominantly, if not exclusively, \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {{\rm (1)}} & {{\rm N}_{\rm 2} {\rm O} + hv{\rm or H}_{\rm g} 6(^1 P_1) \to {\rm N}_{\rm 2} + {\rm O(}^{\rm 1} D{\rm)}} \\\end{array}$$\end{document} Experiments with trace amounts of C3H6 added showed a slight, but not significant, difference in product ratios (N2 and O2). From these experiments the quantum yield of O(3P) from all possible sources was estimated as 0.02 ± 0.02. Experiments with excess N2 at 1849 Å indicated that O(1S) was not produced in the direct photolysis. The O(1S) yield is probably zero, and certainly 〈0.05. The O(1D) atom can react with N2O via \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{l} \begin{array}{*{20}c} {{\rm (2)}} & {{\rm O(}^{\rm 1} D{\rm)} + {\rm N}_{\rm 2} {\rm O} \to {\rm N}_{\rm 2} + {\rm O}_2 } \\\end{array} \\ \begin{array}{*{20}c} {{\rm (3)}} & {{\rm O(}^{\rm 1} D{\rm)} + {\rm N}_{\rm 2} {\rm O} \to 2{\rm NO}} \\\end{array} \\ \end{array}$$\end{document} The ratio k2/k3 was found to be 0.69 ± 0.05 in all cases. When combined with other data from our laboratory, the average value is 0.65 ± 0.07. This represents the value for translationally energetic O(1D) atoms. When excess He was added to remove the excess translational energy, k2/k3 rose to 0.83 ± 0.06, which is in reasonable agreement with the value of 1.01 ± 0.06 found in another laboratory. We conclude that for O(1D) atoms with no excess thermal energy, k2/k3 = 0.90 ± 0.10.
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• 41
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Notes: Rate constants for the reactions of atomic oxygen (O3P) with C2H3F, C2H3Cl, C2H3Br, 1,1-C2H2F2, and 1,2-C2H2F2 have been measured at 307°K using a discharge-flow system coupled to a mass spectrometer. The rate constants for these reactions are (in units of 1011 cm3 mole-1 s-1) 2.63 ± 0.38, 5.22 ± 0.24, 4.90 ± 0.34, 2.19 ± 0.18, and 2.70 ± 0.34, respectively. For some of these reactions, the product carbonyl halides were identified.
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• 42
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Notes: NO2 was photolyzed with 2288 Å radiation at 300° and 423°K in the presence of H2O, CO, and in some cases excess He. The photolysis produces O(1D) atoms which react with H2O to give HO radicals \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {{\rm (3)}} & {{\rm O(}^{\rm 1} D{\rm)} + {\rm H}_{\rm 2} {\rm O} \to 2{\rm HO}} \\\end{array}$$\end{document} or are deactivated by CO to O(3P) atoms \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {{\rm (5)}} & {{\rm O(}^{\rm 1} D{\rm)} + {\rm CO} \to {\rm O(}^{\rm 3} P{\rm) + CO}} \\\end{array}$$\end{document} The ratio k5/k3 is temperature dependent, being 0.33 at 300°K and 0.60 at 423°K. From these two points, the Arrhenius expression is estimated to be k5/k3 = 2.6 exp(-1200/RT) where R is in cal/mole - °K. The OH radical is either removed by NO2 \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {{\rm (1)}} & {{\rm OH} + {\rm NO}_{\rm 2} {\rm (+M)} \to {\rm HNO}_{\rm 3} {\rm (+M)}} \\\end{array}$$\end{document} or reacts with CO \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {{\rm (2)}} & {{\rm OH} + {\rm CO} \to {\rm H} + {\rm CO}_{\rm 2} } \\\end{array}$$\end{document} The ratio k2/kα is 0.019 at 300°K and 0.027 at 423°K, and the ratio k2/k0 is 1.65 × 10-5M at 300°K and 2.84 × 10-5M at 423°K, with H2O as the chaperone gas, where kα = k1 in the high-pressure limit and k0[M] = k1 in the low-pressure limit. When combined with the value of k2 = 4.2 × 108 exp(-1100/RT) M-1sec-1, kα = 6.3 × 109 exp (-340/RT)M-1sec-1 and k0 = 4.0 × 1012M-2sec-1, independent of temperature for H2O as the chaperone gas. He is about 1/8 as efficient as H2O.
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• 43
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Notes: Pyrolysis of (CF3)2C(OH)CH2CH=CH2, the reverse of the reaction between perfluoroacetone and propene, has been studied in the gas phase between 475° and 598°K. Even at 573°K, the unimolecular reaction rate constant appears to be in its pressure-independent region at 20.0 torr pressure. In a quartz vessel, the decomposition is homogeneous. The specific unimolecular rate constant is \documentclass{article}\pagestyle{empty}\begin{document}$$k = T^{1/2} 10[^{(10.3 \pm 0.10) - (\frac{{40300 \pm 300}}{{4.575T}})}]\sec ^{ - 1}$$\end{document} where the limits are for one standard deviation. Combining these results with the previously reported results on the reverse reaction, the equilibrium constant for the reaction \documentclass{article}\pagestyle{empty}\begin{document}$${\rm C}_{\rm 3} {\rm H}_{\rm 6} + {\rm CF}_{\rm 3} {\rm COCF}_{\rm 3} {\rm \rightleftharpoons(CF}_{\rm 3} {\rm)}_{\rm 2} {\rm C(OH)CH}_{\rm 2} {\rm CH = CH}_{\rm 2}$$\end{document} is \documentclass{article}\pagestyle{empty}\begin{document}$$k_p = 10[^{(1/4.575)(-34.0 \pm 1.0) + (\frac{{18700 \pm 400}}{T})}]atm^{ - 1}$$\end{document} It is noteworthy that in the temperature range of the study of the forward reaction (448° to 573°K), the percentage of back reaction in the times of the experiments varies from less than 0.1 to 1.5. Using group additivities and the above ΔH0, ΔHf0 of (CF3)2CO is calculated to be -325.2 kcal/mole at 600°K and the average C—C bond is 42.0 kcal/mole.
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Notes: The rate of the thermal reaction of ethylene to form cyclobutane has been measured over the temperature range 723°-786°K and at pressures between 300 and 1300 torr. The equilibrium constant for the system \documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document}$${\rm 2C}_{\rm 2} {\rm H}_{\rm 4}\mathop {\leftrightharpoons}\limits_{kf}^{kr} c - {\rm C}_{\rm 4} {\rm H}_{\rm 8}$$\end{document} was calculated both from the initial rate data and from measurements of the equilibrium concentration of cyclobutane. Agreement with the reported thermodynamic quantities for cyclobutane was satisfactory. The initial rate data gave the following epxression for kf: \documentclass{article}\pagestyle{empty}\begin{document}$${\rm log }k_f {\rm (1}{\rm .mole}^{ - {\rm 1}} {\rm sec}^{ - {\rm 1}} {\rm)} = {\rm 7}{\rm .84} - \frac{{43800}}{{2.3RT}}$$\end{document} while the measurements of the equilibrium concentration of cyclobutane gave the expression for K, \documentclass{article}\pagestyle{empty}\begin{document}$${\rm log }K{\rm (atm}^{ - {\rm 1}} {\rm)} = - \frac{{45.4}}{{2.3R}} + \frac{{20700}}{{2.3RT}}$$\end{document}.
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• 45
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Notes: Dichloromethane, chlorofluoromethane, and dichlorofluoromethane have been brominated competitively with each other and with chloroform and methyl chloride. Using the literature values for the rates of bromination of these latter two compounds, the rate constants for the three former compounds have been determined: \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{l} k_2 ({\rm CH}_{\rm 2} {\rm Cl}_{\rm 2} {\rm)} = (9.77 \pm 1.44) \times 10^9 \exp (- 10,860 \pm 480{\rm cal}/RT) \\ k_2 ({\rm CH}_{\rm 2} {\rm F Cl)} = (7.76 \pm 1.59) \times 10^{10} \exp (- 14,800 \pm 800{\rm cal}/RT) \\ k_2 ({\rm CHF Cl}_{\rm 2} {\rm)} = (1.05 \pm 1.48) \times 10^{10} \exp (- 13,300 \pm 570{\rm cal}/RT) \\ \end{array}$$\end{document} where R is taken to be 1.987 cal deg-1 mol-1 (1 cal = 4.186 J).
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• 46
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Notes: C2F5 radicals were generated in the presence of benzene vapor by the reaction \documentclass{article}\pagestyle{empty}\begin{document}$$({\rm C}_{\rm 2} {\rm F}_{\rm 5} {\rm CO})_2 {\rm O} + hv \to {\rm CO} + {\rm CO}_2 + 2{\rm C}_{\rm 2} {\rm F}_5$$\end{document} The radicals react with the benzene by addition and pseudo H abstraction The rate constant kadd for the addition reaction (7) is given by \documentclass{article}\pagestyle{empty}\begin{document}$$\log k_{add} /k_{c^{1/2} } {\rm cm}^{{\rm 3/2}} {\rm mole}^{ - 1/2} \sec ^{ - 1/2} = (4.49 \pm 0.10) - (4210 \pm 150)/\theta$$\end{document} where θ = 2.303RT cal/mole and kc is the rate constant for combination of C2F5 radicals. The addition becomes reversible above 110°C. The reactions of CF3 and C2F5 radicals with benzene vapor are compared.
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• 47
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Notes: The rate of decomposition of allyl iodide has been measured from 742plusmn;K to 1068±K and from 169 to 1429 torr using a shock tube method in which the disappearance of allyl iodide and the appearance of iodine are followed simultaneously. The kinetics are first order in allyl iodide and probably are slightly dependent upon total pressure. Mathematical modeling shows that they are compatible with a mechanism consisting of three reactions: The experiments yield the rate constant k1, the high-pressure limiting value of which is found to be \documentclass{article}\pagestyle{empty}\begin{document}$$\log _{10} k_\infty (\sec ^{ - 1}) = (14.45 \pm 0.4) - (42.8 \pm 2.4{\rm kcal})/2.3RT$$\end{document} in reasonable agreement with that predicted using the methods of Benson and O'Neal [1].
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• 48
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Notes: The kinetics of the reaction of O + CH3OCH3 were investigated using fast-flow apparatus equipped with ESR and mass-spectrometric detection. The concentration of O(3P) atoms to CH3OCH3 was varied over an unusually large range. The rate constant for reaction \documentclass{article}\pagestyle{empty}\begin{document}$${\rm O} + {\rm CH}_{\rm 3} {\rm OCH}_3 \to {\rm OH} + {\rm CH}_{\rm 2} {\rm OCH}_{\rm 3}$$\end{document} was found to be k = (5.0 ± 1.0) × 1012 exp [(-2850 ± 200/RT)] cm3 mole-1 sec-1. The reaction O + CH3OH was studied using ESR detection. Based on an assumed stoichiometry of two oxygen atoms consumed per molecule of CH3OH which reacts, we obtain a value of k = (1.70 ± 0.66) × 1012 exp [(-2,280 ± 200/RT)] cm3 mole-1 sec-1 for the reaction \documentclass{article}\pagestyle{empty}\begin{document}$${\rm O} + {\rm CH}_{\rm 3} {\rm OH} \to {\rm OH} + {\rm CH}_{\rm 2} {\rm OH}$$\end{document} The results obtained in this study are compared with the results from other workers on these reactions. The observation of essentially equal activation energies in these two reactions is indicative of approximately equal C—H bond strengths in CH3OCH3 and CH3OH. This is in agreement with recent measurements of these bond energies.
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Notes: The gas-phase reaction kinetics of 1,1,2-trimethylcyclopropane have been studied in the temperature range of 700-755°K. First-order unimolecular rate constants for over-all reactant disappearance fit the Arrhenius equation \documentclass{article}\pagestyle{empty}\begin{document}$${\rm log }k_0 {\rm (sec}^{ - {\rm 1}} {\rm)} = {\rm 14}{\rm .47} - \frac{{61.08 \pm 0.51}}{\theta }$$\end{document} Reaction products and the relative rates of their formation are found to be reasonably consistent with the biradical mechanism.
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Notes: Products of radical combination from the free-radical buffer system \documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document}$${{\rm R}^{\rm .} + {\rm R}^{\rm '} {\rm I}\mathop {\leftrightharpoons}\limits^{{\rm K}_{{\rm RR}}}{\rm RI} + {\rm R}^{'}}$$\end{document}. have been analyzed for the two cases, R = Me, R′ = iPr and R = Et, R′ = iPr. Results are consistent with the previously examined system where R = Me, R′ = Et, and give a value of kP for iPr· combination of 108.6±1.1 M-1 sec-1.
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Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The kinetics of the reaction \documentclass{article}\pagestyle{empty}\begin{document}$${\rm CH}_{\rm 3} + {\rm O}_{\rm 2} (+ {\rm M}) \to {\rm CH}_{\rm 3} {\rm O}_{\rm 2} {\rm (+ M)}$$\end{document} have been studied, using the technique of flash photolysis and kinetic spectroscopy to follow the methyl radical concentration. The order of the reaction lies between 2 and 3 throughout the range of pressure from 25 to 380 torr at 22°C, and the results are consistent with a single reaction sequence: \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{l} {\rm CH}_{\rm 3} + {\rm O}_{\rm 2} \mathop {{\rm \rightleftharpoons}}\limits_{\rm b}^{\rm a} {\rm CH}_{\rm 3} {\rm O}_{\rm 2} ^* \\ {\rm CH}_{\rm 3} {\rm O}_{\rm 2} ^* {\rm } + {\rm M}\mathop {{\rm \rightarrow}}\limits^{\rm c} {\rm CH}_{\rm 3} {\rm O}_{\rm 2} {\rm + M} \\ \\\end{array}$$\end{document} The limiting values of the third-order rate coefficients at low pressures are (3.6±0.3) × 1011 1.2 mole-2 sec-1 when M is neopentane, and (0.94 ± 0.03) × 1011 1.2 mole-2 sec-1 when M is nitrogen. The limiting value of the second-order rate coefficient at high pressures is (3.1 ± 0.3) × 108 1. mole-1 sec-1. The rate constant for the independent second-order reaction \documentclass{article}\pagestyle{empty}\begin{document}$${\rm CH}_{\rm 3} + {\rm O}_{\rm 2} \to {\rm CH}_{\rm 2} {\rm O} \to {\rm OH}$$\end{document} is shown to be not much greater than 2 × 105 1. mole-1 sec-1, so that this reaction does not complete significantly with the combination reaction.This new interpretation is contrary to currently accepted views.
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• 53
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The gas-phase thermal isomerization of N-propylidenecyclopropylamine has been studied in the temerature range of 573° to 635°K. The reaction is homogeneous and kinetically first order and yields 5-ethyl-1-pyrroline as the sole product. The rate constants are independent of pressure in the range of 2.5 to 55 torr and fit the Arrhenius relationship log k(sec-1) = (14.05 ± 0.06) - (47.77 ± 0.16)/θ where θ = 2.303 RT in units of kcal/mole, or log k(sec-1) = (14.05 ± 0.06) - (199.9 ± 0.7)/θ, where θ = 2.303RT in kJ/mole. From considerations of a biradical pathway it is concluded that the resonance stabilization energy of the substituted 2-aza-allyl radical is very similar to that of the methallyl radical.
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• 54
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The kinetics of the gas phase isomerization of 1-chloro-4-bromobicyclo[2.2.0]hexane to 2-chloro-5-bromohexa-1,5-diene have been measured in a static system over the temperature range of 135-215°C, with a variation in the total pressure from 0.6 to 400 torr. For these conditions the rate constants are well represented by the Arrhenius equation: \documentclass{article}\pagestyle{empty}\begin{document}$${\rm log (}k{\rm /sec}^{ - {\rm 1}} {\rm)} = {\rm (13}{\rm .2} \pm {\rm 0}{\rm .2)} - (34.5 \pm 0.4)/\theta$$\end{document} where θ = 2.303RT kcal/mole. Transition state estimates for the biradical mechanism for the isomerization of bicyclo[2.2.0]hexanes are shown to be in good agreement with these Arrhenius parameters. By comparison of the activation energy with that for the isomerization of bicyclo[2.2.0]hexane and 1,4-dichlorobicyclo[2.2.0]hexane, the radical stabilization energy of an α-bromine atom is shown to be 1.0 ± 1.8 kcal/mole. Rates are also reported in the liquid phase at temperatures of 155°C and 175°C with diphenyl ether, nitrobenzene, and dimethylsulfoxide as solvents. The observed rate constants are all faster (by a factor of 1.1-1.7) than those measured in the gas phase and display no correlation between rate and solvent polarity.
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• 55
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Quantum yields of the triplet sulfur dioxide (3SO2)-sensitized phosphoresence (Φsens) in biacetyl (Ac2) have been determined in experiments over a wide range of pressures of SO2 and Ac2. Excited singlet sulfur dioxide (1SO2) was generated using 2650-Å and 28757hyphen;Å light. The values of Φsens were dependent on the [SO2]/[Ac2] ratio, as anticpated theoretically. However, in runs at a fixed [SO2]/[Ac2] ratio, the measured Φsens values were dependent on the total pressure. This theoretically unexpected effect is probably largely the result of biacetyl triplet diffusion with deactivation at the cell wall. Treatment of the quantum yield data in terms of the complete mechanism gave new estimates of the following rate functions: 1SO2 + SO2 → (2SO2) (1), 1SO2 + SO2 → 3SO2 + SO2 (2), k2/(k1 + k2) = 0.082 ± 0.003 (2650 Å), 0.095 ± 0.005 (2875 Å) 3SO2 + Ac2 → SO2 + 3Ac2 (9a), 3SO2 + Ac2 → SO2 + Ac2 (9b), k9a + k9b = (8.4 ± 2.1) × 1010 (2650 Å), (8.1 ± 3.0) × 1010 l./mole-sec (2875 Å) 3SO2 → SO2 + hvp (6), k6 = (7.3 ± 1.3) × 101 sec-1.
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• 56
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The position of abstraction by H atoms from ethylene, propylene, butene-1, and cis- and trans-butene-2 and the rates of abstraction relative to addition have been measured at 25°C. Only allylic abstraction was observed. From ethylene, abstraction relative to addition was ≤3×10-4. For propylene, butene-1, cis-butene-2, and trans-butene-2, abstraction occurred on 0.2%, 1.6%, 1.5%, and 0.9% of the reactive encounters, if dis-proprotionation-combination ratios for allyl and alkyl radicals are similar to those for alkyl-alkyl pairs.
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• 57
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The vibrational excitation of HF and DF and the energy transfer efficiencies for various collision partners were investigated over the temperature and pressure ranges of 1400°K to 4100°K and 0.1 to 0.3 atm, respectively. The extent of excitation was determined as a function of time by continuously monitoring the infrared emission intensity at the center of the 1-0 vibration-rotation band of the molecule. Collisional efficiencies of HF, N2, O2, F, Cl, and DF in relaxing HF and of DF, HF, and N2 in relaxing DF are reported. A comparison with relaxation data for pure HF taken at lower temperature suggests that long-range attractive forces are mechanistically of major importance in the relaxation process. The relatively high efficiency of atomic chlorine in relaxing HF, i.e., (τP)HF-HF/(τP)HF-C1 ≥ 5 at 3000°K is discussed in terms of our previous result for atomic fluorine, i.e., (τP)HF-HF/(τP)HF-F = 18.
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• 58
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Secondary kinetic isotope effects occur in radical additions to deuterated olefins. Substitution of a deuterium at a carbon undergoing an sp2 to sp3 hybridization-change during reaction, Cβ in eq. (1), leads to an inverse isotope effect of 3-5% (kH/kD = 0.95-0.97). The effect at a carbon going from an olefinic to a radical center, Cα in eq. (1), generally has been assumed to be negligible, since a nominal sp2 hybridization is maintained throughout reaction. Using new, sensitive instrumentation for radioactivity determination and a recently developed quench correction technique, we now find that there is a small, normal isotope effect (kH/kT 1) associated with a change from olefin to radical. Specifically, when R· is the polystyryl radical, X is phenyl, and the α-C bears a tritium, kH/kT = 1.04. This result is discussed in relation to recent data on cycloaddition reactions.
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• 59
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: In polychloro-2,2-difluoropropanes, where a large inductive effect results in relatively low reactivity to chlorination, the presence of additional chlorine causes an increased reactivity of the hydrogens geminal to the chlorine and a reduced reactivity of the remote (third carbon) hydrogens. The ways in which resonance, inductive effect, and steric crowding interact in the rates of chlorination of polar molecules are discussed.
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• 60
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The quantum yields of the sulfur dioxide triplet (3SO2)-sensitized phosphorescence of biacetyl (Φsens) were determined in experiments with N2-SO2-Ac2 and c-C6H12-SO2-Ac2 mixtures excited at 2875 Å at 27°C. The fraction of the biacetyl triplets which reacts homogeneously by radiative or nonradiative decay reactions was determined in a series of runs at constant [SO2]/[M] and [SO2]/[Ac2] ratios but at varied total pressure. A kinetic treatment of the Φsens results and singlet sulfur dioxide (1SO2) quenching rate constant data gave the following new kinetic estimates: 1SO2 + M → (SO2-M) (1b) 1SO2 + M → 3SO2 + M (2b); for 1SO2-N2 collisions, k2b/(k1b + k2b) = 0.033 ± 0.008; for 1SO2-c-C6H12 collisions, k2b/(k1b ± k2b) = 0.073 ± 0.024; previous studies have shown this ratio to be 0.095 ± 0.005 for 1SO2-SO2 collisions. It was concluded that the inter-system crossing ratio in 1SO2 induced by collision is relatively insensitive to the nature of the collision partner M. However, the individual rate constants for the collision-induced spin inversion of 1SO2 (k2b) and the total 1SO2-quenching constants (k1b + k2b) are quite sensitive to the nature of M: k2b/k2a varies from 0.10 ± 0.03 for M = N2 to 1.11 ± 0.37 for M = c-C6H12, and (k1b + k2b)/(k1a + k2a) varies from 0.29 for M = N2 to 1.44 for M = c-C6H12; k1a and k1b are the rate constants for the reactions 1SO2 - SO2 → (2SO2) (1a) and 1SO2 + SO2 → 3SO2 + SO2 (2a), respectively.
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• 61
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The quantum yields of phosphorescence (Φp) of biacetyl have been determined in pure biacetyl, biacetyl-SO2, and biacetyl-c-C6H12 mixtures in experiments using bands of radiation centered at 3450, 3650, 3880, and 4348 Å. It has been shown that the unexpected effect of gas concentration on the quantum yields of the sulfur dioxide triplet-sensitized phosphorescence of biacetyl resulted largely from the significant destruction of biacetyl triplets at the wall of the cell. The kinetics of the variation of Φp with [Ac2], wavelength of the absorbed light, and added gases provide new estimates of the energy relations and the rate constants for the decomposition reaction of vibrationally rich biacetyl molecules in the first excited singlet state (1Ac2
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• 62
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New York, NY : Wiley-Blackwell
ISSN: 0020-7608
Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
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• 63
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New York, NY : Wiley-Blackwell
ISSN: 0020-7608
Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: In order to treat the interaction energy of two molecules a standard Rayleigh-Schrödinger perturbation theory is developed. The Hartree-Fock functions of the separated molecules are used as one particle basis functions, the initial set of states being truncated and non-orthogonal. The non-orthogonality is included into the Hamiltonian by orthogonalization of the basis set. The unperturbed Hamiltonian is chosen so that it possesses the correct symmetry properties with respect to the electron permutations between different molecules. The procedure of this kind automatically results in the appearance of charge transfer states.A graphical technique is elaborated which is a modified version of the Feynman-Goldstone technique and provides a convenient representation of the interaction energy contributions of any order. As an example the first- and the second-order diagrams are considered.A correct expression for the dispersion energy is obtained which differs by a factor from that of the theory using a nonsymmetrical zero approximation.
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• 64
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ISSN: 0020-7608
Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: An exact cluster expansion of many electron wave functions is derived, beginning with a finite linear combination of Slater determinants rather than the more usual single determinant. This general cluster expansion is found to apply both in the case where all possible Slater determinants from a finite set of spin orbitals are included in the linear combination, and in the case where the number of determinants is restricted.The special properties of that finite linear combination of determinants closest to the exact wave function in the least squares sense are studied. These properties lead to the derivation of a general correlated wave functions method, illustrating again the close relationship between methods of this type and cluster expansion theory. Additional approximations, necessary for practical calculations, are set out.
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• 65
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ISSN: 0020-7608
Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: A quasi-relativistic approach to the MO-LCAO method is formulated taking into account the relativistic effects with an accuracy up to (v/c)2 terms, the relativistic part of the electronic interaction in the Hamiltonian being neglected. In the framework of this approximation a set of SCF equations of the Roothaan form is derived; here only the relativistic analogue to the closed shell systems with one-determinant wave functions is considered. In so doing three types of relativistic corrections arise which are quite similar to those of the Pauli equation for one-electron atoms. The new matrix elements appearing due to these corrections can be reduced to some common integrals, which have to be calculated with relativistic radial atomic functions. The method allows a semi-empirical approach to the problem and does not require the Dirac four-component atomic functions (unknown in the most cases), thus making possible approximate quasi-relativistic electronic structure calculations of heavy-atom compounds.
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• 66
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New York, NY : Wiley-Blackwell
ISSN: 0020-7608
Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: An integral formula is derived involving a new type of determinantal function which reproduces the effect of the Young operator θNPN. This result is used to calculate matrix elements between tableau functions of non-orthogonal orbitals. Matrices which transform this representation into the traditional valence-bond scheme are also given.
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• 67
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New York, NY : Wiley-Blackwell
ISSN: 0020-7608
Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: After a brief discussion of progress in the theory of icosahedral molecules, the terms arising from simple electronic configurations are deduced from tables of symmetrized powers of representations previously published by the author.
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• 68
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New York, NY : Wiley-Blackwell
ISSN: 0020-7608
Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Various aspects of Del Re's method, its extension and correlation with important properties such as nuclear quadrupole coupling constants and spin-spin coupling constants are discussed. The Del Re parameters for the C-I bond have been evaluated and those for the C-F bond modified. The bond energies and the heats of formation for several σ-systems have been calculated; the energies of a “bond-orbital” for several alkanes have been found to be related with their ionization potentials.