摘要:

AbstractThe kinetics of the reactionshave been studied in a discharge flow system under pseudo‐first‐order conditions. The OH concentration was monitored by laser induced fluorescence and helium was used as the carrier gas. Values ofk1= (8.1 ± 1.7) × 10−13,k2= (1.31 ± 0.26) × 10−11,k3= (2.6 ± 0.5) × 10−11, andk4= (2.5 ± 0.4) × 10−11cm3molecule−1s−1, at 298 K and 1 torr total pressure, were obtained.To validate the newly constructed system the rate constant for the reactionwas determined in a similar manner. The value ofk5= (6.7 ± 0.9) × 10−12cm3molecule−1s−1at 298 K and 1 torr total pressure is in very good agreement with other literature values.The mechanisms for the atmospheric degradation of these compounds have been constructed to allow their incorporation in a photochemical trajectory computer model, to assess their impact on photochemical ozone creation in the troposphe

ISSN:0538-8066    

DOI:10.1002/kin.550260112

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractGaAs (100) wafers were etched in mixtures of hydrogen atoms and methyl radicals. The atoms were formed in a remote hydrogen plasma, and a fraction of these were converted into methyl radicals by introducing methane into the flow system upstream from the semiconductor surface. The flux of hydrogen atoms into the reaction chamber was determined by isothermal calorimetry. The methyl radical flux passing over the substrate was then calculated using previously determined rate parameters for the reaction between atomic hydrogen and methane, and a simple modeling program. The GaAs etch rates were about an order of magnitude faster when methyl radicals were present in the hydrogen atom stream, and were found to follow a first‐order dependence on the partial pressure of methyl radicals. Absolute rate constants were determined and an Arrhenius activation energy of 1.2 kcal mol−1was calculated. The values ofkandEaare consistent with a diffusion‐controlled process. SEM photographs of the surface revealed small crystallographic features that made the surface appear very rough. XPS analysis indicated that these surfaces were arsenic deficient. A mechanism is proposed for the etching of GaAs by a combination of methyl radicals and hydrogen atoms. © 1994 John Wiley&Son

ISSN:0538-8066    

DOI:10.1002/kin.550260113

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe pyrolysis of isobutane has been studied at 500°C in a “Pyrex” static reactor packed with platinum. It is shown that both dehydrogenation and demethanat on rates are strongly depressed by the metal packing. The reaction rates are very sensitive to the amount of cabonaceous coating which is deposited on the walls. As this amount increases, both rates first increase, go through a maximum and decrease. These observations are compared with those previously made on propane pyrolysis in a “Pyrex” reactor packed with stainless steel. The present results are interpreted on the basis of a hetero‐homogeneous chain mechanism in which the selectivity of the free‐radical reaction is not altered referring to the unpacked reactor. © 1994 John Wi

ISSN:0538-8066    

DOI:10.1002/kin.550260114

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractMultiphoton decomposition of 1‐bromo 2‐fluoroethane (CH2BrCH2F, BFE) with a two‐color CO2infrared laser is reported as a function of number of laser pulses. For single color irradiation at a wavelength chosen to excite BFE, the decomposition product, vinyl fluoride, which accumulates during the many‐pulse MPD experiment, is found to deactivate BFE decomposition. When a second laser, tuned to a vinyl fluoride absorption is introduced, coincident with the first, the vinyl fluoride is found to activate further BFE decomposition. These results are accounted for in terms of a pressure‐dependent model. Changes in model parameters, upon addition of the second laser, are shown to be consistent with interpretations in terms of collision‐dependent reaction schemes. © 1994 John Wil

ISSN:0538-8066    

DOI:10.1002/kin.550260115

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractRate constants are calculated for CH3(+ Ar) ⇄ CH2+ H (+ Ar) at the limiting low‐pressure, the limiting high‐pressure, as well as the intermediate fall‐off ranges. The results show that published experimental rate constants for methyl dissociation correspond to the fall‐off region close to the low‐pressure limit. At the low‐pressure limit the activation energy is less than the bond dissociation energy, in agreement with experimental results. Forward and backward rate coefficients at the high‐pressure limit are compared with other theoretical calculations. More theoretical and experimental work is necessary to understand the reverse reaction and its competing reactions, as well as the decomposition channel leading to CH + H2. © 1994 John

ISSN:0538-8066    

DOI:10.1002/kin.550260116

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe forward rate constant,k1, and the equilibrium constant,Kp, for the association reaction of the benzyl radical with oxygen have been determined. The rate constantk1was measured as a function of temperature (between 298 and 398 K) and pressure (at 20 and 760 torr of N2) by two different techniques, argon‐lamp flash photolysis and excimer‐laser flash photolysis, both of which employed UV absorption spectroscopy (at 253 nm and 305 nm, respectively) to monitor the benzyl radical concentration. Over the range of conditions studied, we find that the reaction is independent of pressure and is almost independent of temperature, which is in accord with two early studies of the reaction but in apparent disagreement with more recent work. For our results in 760 torr of N2and for 298

ISSN:0538-8066    

DOI:10.1002/kin.550260117

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe photolysis of mixtures of acetone and propylene at 308 nm has been studied kinetically from approximately 300 K to 580 K. Rate constants were calculated for the reactionsat total pressures ranging from 110 torr to 750 torr and for [C3H6]/[(CH3)2CO] ratios in the range 0.03 to 3.3. No dependence of the rate constants on total pressure or on this concentration ratio could be detected within this range of conditions. The temperature dependence of the rate constants is given by\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} k_{\rm 1} = 7.2 \times 10^7 \left({\pm 22\%} \right)\exp \left({{{- 3260 \pm 40} \mathord{\left/ {\vphantom {{- 3260 \pm 40} T}} \right. \kern-\nulldelimiterspace} T}} \right){\rm M}^{- 1} {\rm s}^{- 1} \\ k_{\rm 2} = 1.6 \times 10^8 \left({\pm 32\%} \right)\exp \left({{{- 4440 \pm 90} \mathord{\left/{\vphantom {{- 4440 \pm 90} T}} \right. \kern-\nulldelimiterspace} T}} \right){\rm M}^{- 1} {\rm s}^{- 1} \\ \end{array} $$\end{document}© 1994 John Wiley&Sons, Inc

ISSN:0538-8066    

DOI:10.1002/kin.550260118

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe pulsed CO2laser‐induced decompositions of propan‐2‐ol, butan‐2‐ol, pentan‐2‐ol, pentan‐3‐ol, and hexan‐2‐ol in the gas phase have been investigated. Like ethanol which we examined previously [1] the absorption cross section of propan‐2‐ol for pulsed 9R14 radiation increases with pressure at low pressures, an effect attributed to rotational hole‐filling. In contrast the absorption cross section of butan‐2‐ol (10R24) has only a small pressure dependence and those of pentan‐2‐ol (9R26), pentan‐3‐ol (10R14), and hexan‐2‐ol (9P20) show little or no variation with pressure in the range 0.1–5.0 torr.Decomposition products have been investigated at low pressure where the excitation of the alkanols was essentially collision free. The observed products for all the alkanols can be rationalized on the basis of primary dehydration and CC fission channels, with minor contributions from other mole

ISSN:0538-8066    

DOI:10.1002/kin.550260119

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractBond dissociation energies are frequently derived from values of the high pressure activation energy for bond scission reactions. The value derived depends on the transition state structure chosen for the reaction. We consider several models of the transition state and show that the variation in derived BDE values can be quite substantial, 3 to 6 kcal/mol at the high temperatures of pyrolysis kinetics. Application of the restricted Gorin model of the transition state results in BDE values in good agreement with current thermochemistry, while the other models tested result in lower to much lower values. © 1994 John Wiley&Sons, Inc

ISSN:0538-8066    

DOI:10.1002/kin.550260120

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe yields of CO2and CO formed from the gas‐phase photolysis at 222 nm of very low pressures of formic acid where the monomer predominates have been determined using FTIR spectroscopy. The observed ratio of CO2/CO approaches unity as the formic acid pressure approaches zero. Previous studies have shown that the quantum yield for HCOOH +hv→ OH + HCO (or H + CO) is 0.70 at 298 K. The present experimental results indicate that the ratio of the quantum yields of the possible molecular photolysis channels forming H2+ CO2(ϕ1b) and H2O + CO (ϕ1c) is ca. 1. Including this result in an analysis of previously reported quantum yields of CO and CO2determined at higher pressures of formic acid, where both monomer and dimer contribute significantly to the products, indicates that ϕ1b= ϕ1c= 0. © 1994 John Wiley&S

ISSN:0538-8066    

DOI:10.1002/kin.550260121

出版商:John Wiley&Sons, Inc.    

年代:1994

数据来源: WILEY