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Journal ArticleDOI

Absolute rate constants for the reaction of atomic hydrogen with ketene from 298 to 500 K

01 Jun 1979-Journal of Chemical Physics (American Institute of Physics)-Vol. 70, Iss: 11, pp 5222-5227
TL;DR: In this article, the rate constants for the reaction of atomic hydrogen with ketene have been measured at room temperature by two techniques, flash photolysis-resonance fluorescence and discharge flow resonance fluorescence.
Abstract: Rate constants for the reaction of atomic hydrogen with ketene have been measured at room temperature by two techniques, flash photolysis-resonance fluorescence and discharge flow-resonance fluorescence. The measured values are (6.19 + or - 1.68) x 10 to the -14th and (7.3 + or - 1.3) x 10 to the -14th cu cm/molecule/s, respectively. In addition, rate constants as a function of temperature have been measured over the range 298-500 K using the FP-RF technique. The results are best represented by the Arrhenius expression k = (1.88 + or - 1.12) x 10 to the -11th exp(-1725 + or - 190/T) cu cm/molecule/s, where the indicated errors are at the two standard deviation level.
Citations
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Book ChapterDOI
01 Jan 1984
TL;DR: In this article, a critical survey of reaction rate coefficient data important in describing high-temperature combustion of H2, CO, and small hydrocarbons up to C4 is presented.
Abstract: This chapter is a critical survey of reaction rate coefficient data important in describing high-temperature combustion of H2, CO, and small hydrocarbons up to C4. A recommended reaction mechanism and rate coefficient set is presented. The approximate temperature range for this mechanism is from 1200 to 2500 K, which therefore excludes detailed consideration of cool flames, low-temperature ignition, or reactions of organic peroxides or peroxy radicals. Low-temperature rate-coefficient data are presented, however, when they contribute to defining or understanding high-temperature rate coefficients. Because our current knowledge of reaction kinetics is incomplete, this mechanism is inadequate for very fuel-rich conditions (see Warnatz et al., 1982). For the most part, reactions are considered only when their rates may be important for modeling combustion processes. This criterion eliminates considering many reactions among minor species present at concentrations so low that reactions of these species cannot play an essential part in combustion processes. The philosophy in evaluating the rate-coefficient data was to be selective rather than exhaustive: Recent results obtained with experimental methods capable of measuring isolated elementary reaction rate parameters directly were preferred, while results obtained using computer simulations of complex reacting systems were considered only when sensitivity to a particular elementary reaction was demonstrated or when direct measurements are not available. Theoretical results were not considered.

547 citations

Journal ArticleDOI
TL;DR: In this article, a method to calculate the first-order sensitivities of the mole fractions and temperature with respect to the rate constants is discussed and applied to nitric oxide production in the presence of hydrocarbons.

410 citations

Journal ArticleDOI
TL;DR: Dimethyl ether reaction kinetics at high temperature were studied in two different flow reactors under highly dilute conditions, with the equivalence ratio varying from 0.32 ≤ ϕ ≤ 3.4 as discussed by the authors.
Abstract: Dimethyl ether reaction kinetics at high temperature were studied in two different flow reactors under highly dilute conditions. Pyrolysis of dimethyl ether was studied in a variable-pressure flow reactor at 2.5 atm and 1118 K. Studies were also conducted in an atmospheric pressure flow reactor at about 1085 K. These experiments included trace-oxygen-assisted pyrolysis, as well as full oxidation experiments, with the equivalence ratio (ϕ) varying from 0.32 ≤ ϕ ≤ 3.4. On-line, continuous, extractive sampling in conjunction with Fourier Transform Infra-Red, Non-Dispersive Infra-Red (for CO and CO2) and electrochemical (for O2) analyses were performed to quantify species at specific locations along the axis of the turbulent flow reactors. Species concentrations were correlated against residence time in the reactor and species evolution profiles were compared to the predictions of a previously published detailed kinetic mechanism. Some changes were made to the model in order to improve agreement with the present experimental data. However, the revised model continues to reproduce previously reported high-temperature jet-stirred reactor and shock tube results. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet: 32: 713–740, 2000

400 citations

Journal ArticleDOI
TL;DR: In this paper, a detailed model of the photochemistry of haze formation in the early atmosphere was presented, and the effects of such a haze layer on climate and ultraviolet radiation were examined.
Abstract: The late Archean atmosphere was probably rich in biologically generated CH4 and may well have contained a hydrocarbon haze layer similar to that observed today on Saturn's moon, Titan. Here we present a detailed model of the photochemistry of haze formation in the early atmosphere, and we examine the effects of such a haze layer on climate and ultraviolet radiation. We show that the thickness of the haze layer was limited by a negative feedback loop: A haze optical depth of more than ∼0.5 in the visible would have produced a strong “antigreenhouse effect,” thereby cooling the surface and slowing the rate at which CH4 was produced. Given this climatic constraint on its visible optical depth, the amount of UV shielding provided by the haze can be estimated from knowledge of the optical properties and size distribution of the haze particles. Contrary to previous studies [Sagan and Chyba, 1997], we find that when the finite size of the particles is taken into account, the amount of UV shielding provided by the haze is small. Thus NH3 should have been rapidly photolyzed and should not have been sufficiently abundant to augment the atmospheric greenhouse effect. We also examine the question of whether photosynthetically generated O2 could have accumulated beneath the haze layer. For the model parameters considered here, the answer is “no”: The upper limit on ground level O2 concentrations is ∼10−6 atm, and a more realistic estimate for pO2 during the late Archean is 10−8 atm. The stability of both O2 and NH3 is sensitive to the size distribution and optical properties of the haze particles, neither of which is well known. Further theoretical and laboratory work is needed to address these uncertainties.

268 citations

Journal ArticleDOI
TL;DR: In this article, a one-dimensional photochemical model is used to analyze the photochemistries of CH4 and HCN in the primitive terrestrial atmosphere, and the formation of HCN as a byproduct of N2 and CH4 photolysis is investigated; the effects of photodissociation and rainfall on HCN is discussed.
Abstract: A one-dimensional photochemical model is used to analyze the photochemistries of CH4 and HCN in the primitive terrestrial atmosphere. CH4, N2, and HCN photolysis are examined. The background atmosphere and boundary conditions applied in the analysis are described. The formation of HCN as a by-product of N2 and CH4 photolysis is investigated; the effects of photodissociation and rainfall on HCN is discussed. The low and high CH4 mixing ratios and radical densities are studied.

241 citations

References
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ReportDOI
01 May 1978
TL;DR: In this article, a table of data for gas phase chemical reactions and photochemistry of neutral species is presented, giving preferred values for reaction rate constants, photoabsorption cross sections, and quantum yields of primary photochemical processes.
Abstract: : A table of data for gas phase chemical reactions and photochemistry of neutral species is presented. Specifically, it gives preferred values for reaction rate constants, photoabsorption cross sections, and quantum yields of primary photochemical processes and also cites recent experimental work (to December 1977). It is intended to provide the basic physical chemical data needed as input data for calculations modeling atmospheric chemistry. An auxiliary table of thermochemical data for the pertinent chemical species is given in the appendix. (Author)

159 citations

Journal ArticleDOI
TL;DR: In this paper, a flash photolysis coupled with time resolved detection of H via resonance fluorescence has been used to obtain absolute rate parameters for the reaction of atomic hydrogen with acetylene.
Abstract: The technique of flash photolysis coupled with time resolved detection of H via resonance fluorescence has been used to obtain absolute rate parameters for the reaction of atomic hydrogen with acetylene, i.e., H+C2H2?C2H3* (1); C2H3*+M→C2H3+M (2). The rate constant for the reaction is strongly pressure dependent and was measured over the pressure range 10 to 700 torr. The reaction was also studied as a function of temperature over the range 193 to 400 °K and the high pressure limit of the rate constant at each temperature was used to obtain the Arrhenius expression k1= (9.63±0.60) ×10−12 exp(−2430±30/1.987T) cm3 molecule−1⋅sec−1. The present results are compared with those of previous studies.

97 citations

Journal ArticleDOI
TL;DR: In this article, the authors observed a rather low column density for ketene (approx.10/sup 14/ cm/sup -2/) arising from a high-density region (approximately greater than 10/sup 6/ cm /sup -3/).
Abstract: Interstellar ketene (H/sub 2/C=C=O) has been observed in the source Sgr B2 via its transitions 5/sub 14//sub -/4/sub 13/, 5/sub 15//sub -/4/sub 14/, and 4/sub 13//sub -/3/sub 12/ at frequencies 101981.39, 100094.51, and 81586.19 MHz, respectively. The transitions 5/sub 05//sub -/4/sub 04/, 4/sub 14//sub -/3/sub 13/, and 4/sub 04//sub -/3/sub 03/ have also tentatively been detected. Statistical equilibrium calculations suggest a rather low column density for ketene (approx.10/sup 14/ cm/sup -2/) arising from a high-density region (approximately-greater-than10/sup 6/ cm/sup -3/).

72 citations

Journal ArticleDOI
TL;DR: In this paper, the rate parameters for the reaction of O(3P) with carbonyl sulfide, O (3P + OCS yields CO + SO, and the data were fitted to an Arrhenuis expression with good linearity.
Abstract: The rate parameters for the reaction of O(3P) with carbonyl sulfide, O(3P) + OCS yields CO + SO have been determined directly by monitoring O(3P) using the flash photolysis-resonance fluorescence technique. The value for k sub 1 was measured over a temperature range of 263 - 502 K and the data were fitted to an Arrhenuis expression with good linearity.

61 citations