A cw laser absorption diagnostic for methyl radicals

Davidson, David F.; Chang, Albert Y.; Rosa, Massimiliano; Hanson, Ronald K.

doi:10.1016/0022-4073(93)90067-r

Cited by 63 publications

(32 citation statements)

References 25 publications

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“…The value of the absorption Coefficient given in ref. [22] was confirmed in each of the azomethane traces used in this study. Data for several pressure regimes, 0.50, 1.20, and 1.45 atm, are summarized in Table I1 and in Figure 5 .…”

Section: Resultsmentioning

confidence: 96%

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A shock tube study of methyl‐methyl reactions between 1200 and 2400 K

Davidson

Rosa

Chang

et al. 1995

Int J of Chemical Kinetics

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The methyl-methyl reaction was studied in a shock tube using uv narrowline laser absorption to measure time-varying concentration profiles of CH3. Methyl radicals were rapidly formed initially by pyrolysis of various precursors, azomethane, ethane, or methyl iodide, dilute in argon. The contributions of the various product channels, C~H I ; , C2H5 + H, CzH4 + Hz, and CH2 + CH4, were examined by varying reactant mixtures and temperature.The measured rate coefficients for recombination to CzHfi between 1200 and 1800 K are accurately fit using the unimolecular rate coefficients reported by Wagner and Wardlaw (1988). The rate coefficient for the CzH5 + H channel was found to be 2.4 (+0.5) X 10'" exp (-6480/Tj [cm3/mol-sl between 1570 and 1780 K, and is in agreement with the value reported by Frank and Braun-Unkhoff (1988). No evidence of a contribution by the C2H4 + Ha channel was found in ethane/methane/argon mixtures, although methyl profiles in these mixtures should be particularly sensitive to this channel. An upper limit of approximately 10l1 [cm3/mol-sl over the range 1700 to 2200 K was inferred for the rate coefficient of the CzH4 + Hz channel. Between 1800 and 2200 K, methyl radicals are also rapidly removed by CHs + H * 'CHz + Ha.In this temperature range, the reverse reaction was found to have a rate coefficient of 1.3 ( 2 0.3) X 1014 [cm3/mol-s], which is 1.8 times the room-temperature value. 0 1995 John Wiley & Sons, Inc.

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Section: Resultsmentioning

confidence: 96%

“…kA, has been determined previously at A = 216.615 nm in the temperature range T = 1300 to 2400 K with an uncertainty of 212% [21,22], and is given by the following expression …”

Section: Experimental Methodsmentioning

confidence: 99%

A shock tube study of methyl‐methyl reactions between 1200 and 2400 K

Davidson

Rosa

Chang

et al. 1995

Int J of Chemical Kinetics

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“…Davidson and co-workers, who used shock tube experiments, compiled results of other groups in this field and derived the absorption cross section of the methyl absorption in the ultraviolet spectral range at 216 nm [47,48]. In the first broadband ultraviolet absorption measurements for quantitative detection of methyl radicals in a hot filament reactor containing hydrocarbons Childs et al [49] used the absorption cross section reported by Arthur [50].…”

Section: Measurements By Uv Absorptionmentioning

confidence: 97%

“…In the first broadband ultraviolet absorption measurements for quantitative detection of methyl radicals in a hot filament reactor containing hydrocarbons Childs et al [49] used the absorption cross section reported by Arthur [50]. In succeeding papers the studies were extended [51,52]. Based on the re-measured absorption cross section of Davidson et al [53] Cappelli and co-workers used the method of broadband ultraviolet absorption at 216 nm for quantitative detection of the methyl radical in plasmas of a supersonic arc jet [54] and in a microwave bell jar reactor [55], both utilized for diamond deposition (comp.…”

Section: Measurements By Uv Absorptionmentioning

confidence: 98%

On the Reaction Kinetics of Chemically Active Molecular Microwave Plasmas

Stancu

Pipa

Lombardi

et al. 2005

Contrib. Plasma Phys.

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Key words Microwave plasmas, reaction kinetics, degree of dissociation, hydrogen, methyl radical, quantum cascade laser, boron monoxide. PACS 52. 20, 52.25, 52.75, 52.80 Recent studies of phenomena in molecular non-equilibrium microwave plasmas, which have been performed within the framework of the DFG-Sonderforschungsbereich 198, project A12, are presented in this review article. Special attention is devoted to the properties and kinetics of transient molecular species. The experimental methods used were optical emission and absorption spectroscopy. The main objectives of this contribution were threefold: (i) the determination of the degree of dissociation of hydrogen in plasmas, (ii) the quantitative detection of the methyl radical, and (iii) plasma process monitoring using quantum cascade lasers.

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“…Another key combustion radical and shock tube diagnostic is CH 3 . The primary wavelength of interest is 216.615 nm, corresponding to the Hertzberg ßt band at high temperature [53]. Assuming the pressure dependence at HPST conditions is small, the absorption coefficient of methyl at 216.615 nm given by Davidson et al [53] is assumed herein to be valid at elevated pressures:…”

Section: (13)mentioning

confidence: 99%

Nonideal Effects Behind Reflected Shock Waves in a High-Pressure Shock Tube

Mathieu¹,

Hanson²

1999

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044REPORT Public reporting burden for this collection ot information is estimated to average 1 hour per response, including the time for review ng instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection information. Send comment regarding this burden estimates or any aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for information Operations and reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and Shock tubes often experience temperature and pressure nonuniformities behind the reflected shock wave that cannot be neglected in chemical kinetics experiments. Because of increased viscous effects, smaller tube diameters, and nonideal shock formation, the reflected-shock nonidealities tend to be greater in higher-pressure shock tubes. Since the increase in test temperature (AT 5 ) is the most significant parameter for chemical kinetics, experiments were performed in the Stanford High Pressure Shock Tube using infrared emission from a known amount of CO in Argon. From the measured change in vibrationally equilibrated CO emission with time, the corresponding dT 5 /dt (or AT5 for a known time interval) of the mixture was inferred assuming an isentropic relationship between post-shock temperature and pressure changes. For a range of representative conditions in Argon (20-530 Atm, 1240-1900, the test temperature 2 cm from the endwall increased 3-8 K after 100 )J,s and 15-40 K after 500 u,s, depending on the initial conditions. Separate pressure measurements using a shielded piezoelectric transducer confirmed the isentropic assumption. An analytical model of the reflected-shock gas dynamics was also developed. The measured incident-shock axial velocity profile and a model of the boundary layer growth provide the upstream boundary conditions needed to define the properties behind the moving reflected shock. The calculated AT 5 's agree well with those obtained from experiment. The analytical model was used to estimate the effects of temperature and pressure nonuniformities on typical chemical kinetics measurements. When the kinetics are fast and occur in less than 300 |is, the temperature increase is typically negligible, although some correction is suggested for kinetics experiments lasting longer than 500 (xs. The temperature increase, however, has a negligible impact on the measured absorption profiles of OH and CH 3 when using laser absorption diagnostics at 306 and 216 nm, respectively, validating the use of a constant absorption coefficient. Infrared emission experiments are more sensitive to temperature and pressure changes, so T 5 nonuniformities should be taken into account when interpreting IR-emission data. NONIDEAL EFFECTS BEHIND REFLECTED SHOCK WAVES IN A HIGH-PRESSURE SHOCK TUBEEric L. Petersen f and Ronald K. Hanson AbstractShock tubes often experience temperature and pressure nonuniformities behind the reflecte...

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A cw laser absorption diagnostic for methyl radicals

Cited by 63 publications

References 25 publications

A shock tube study of methyl‐methyl reactions between 1200 and 2400 K

A shock tube study of methyl‐methyl reactions between 1200 and 2400 K

On the Reaction Kinetics of Chemically Active Molecular Microwave Plasmas

Nonideal Effects Behind Reflected Shock Waves in a High-Pressure Shock Tube

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