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At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1929

The Gaseous Explosive Reaction : A Study of the Kinetics of Composite Fuels

This report deals with the results of a series of studies of the kinetics of gaseous explosive reactions where the fuel under observation, instead of being a simple gas, is a known mixture of simple gases. In the practical application of the gaseous explosive reaction as a source of power in the gas engine, the fuels employed are composite, with characteristics that are apt to be due to the characteristics of their components and hence may be somewhat complex. The simplest problem that could be proposed in an investigation either of the thermodynamics or kinetics of the gaseous explosive reaction of a composite fuel would seem to be a separate study of the reaction characteristics of each component of the fuel and then a study of the reaction characteristics of the various known mixtures of those components forming composite fuels more and more complex. (author)

Stevens, F W↗
NASA NTRS1987

Carbon kinetic isotope effect in the reaction of CH4 with HO

The carbon kinetic isotope effect in the CH4 + HO reaction is measured experimentally and the use of carbon isotope ratios to diagnose atmospheric methane is examined. The chemical, photolysis, and analytical experimental conditions and procedures are described. It is determined that the CH4 + HO reaction has a carbon kinetic isotope effect of 1.010 + or 0.007 for k(12)k(13) (rate constants ratio) at 297 + or - 3 K. This value is compared with the data of Rust and Stevens (1980). Causes for the poor correlation between the data at high methane conversions are discussed. It is supposed that the difference between the k(12) and k(13) values is due to a difference in the activation energy of the two reactions.

Davidson, J. A.↗
NASA NTRS1981

Kinetics study of the reactions of NO with FO, ClO, BrO, and IO at 298 K

The kinetics of the four considered reactions were studied by means of the discharge flow/mass spectrometric technique. The discharge flow/mass spectrometer has been described by Sander et al. (1981). The flow velocity in the investigation was varied in the range from 750 to 2100 cm/s, while total pressures in the range from 1.0 torr to 2.1 torr were employed. The results of the study are compared to the values of current literature. With minor exceptions, the new results are in excellent agreement with the data of the previous studies. It is pointed out that the reported results will have a minimal impact on the predictions of atmospheric photochemical model calculations as they have confirmed prior expectations.

Ray, G. W.↗
NASA NTRS1980

A laser flash photolysis-resonance fluorescence kinetics study of the reaction Cl/2P/ + CH4 yields CH3 + HCl

The technique of laser flash photolysis-resonance fluorescence is employed to study the kinetics of the reaction Cl(2P) + CH4 yields CH3 + HCl over the temperature range 221-375 K. At temperatures less than or equal to 241 K the apparent bimolecular rate constant is found to be dependent upon the identity of the chemically inert gases in the reaction mixture. For Cl2/CH4/He reaction mixtures (total pressure = 50 torr) different bimolecular rate constants are measured at low and high methane concentrations. For Cl2/CH4/CCl/He and Cl2/CH4/Ar reaction mixtures, the bimolecular rate constant is independent of methane concentration, being approximately equal to the rate constant measured at low methane concentrations for Cl2/CH4/He mixtures. These rate constants are in good agreement with previous results obtained using the discharge flow-resonance fluorescence and competitive chlorination techniques. At 298 K the measured bimolecular rate constant is independent of the identity of the chemically inert gases in the reaction mixture and in good agreement with all previous investigations. The low-temperature results obtained in this investigation and all previous investigations can be rationalized in terms of a model which assumes that the Cl(2P 1/2) state reacts with CH4 much faster than the Cl(2P 3/2) state. Extrapolation of this model to higher temperatures, however, is not straightforward.

Ravishankara, A. R.↗
NASA NTRS1997

A Competitive Kinetics Study of the Reaction of Cl with CS2 in Air at 298 K

The relative rate technique has been used to investigate the kinetics of the reaction of Cl atoms with carbon disulfide, CS2, at 700 Torr total pressure of air at 298 K. The decay rate of CS2 was measured relative to CH4, CH3Cl and CHF2CL. For experiments using CH4 and CH3Cl references, the decay rate of CS2 was dependent on the ratio of the concentration of the reference to that of CS2. We ascribe this behavior to the generation of OH radicals in the system leading to complicated secondary chemistry. From experiments using CHF2Cl we are able to assign an upper limit of 4 x 10(exp -15) cu cm/(molecule s) for the overall reaction, Cl + CS2 yields products.

Wallington, Timothy J.↗
NASA NTRS1986

Kinetic study of the reaction CH (X 2Pi) + H2 yields CH2 (X 3B1) + H in the temperature range 372 to 675 K

The kinetics of the reversible reaction CH (X 2Pi) + H2 yields CH2 (X 3B1) + H at 372-675 K and total pressure 100 torr (mainly Ar) is investigated experimentally. The ground-state CH radicals are produced by photolysis of CHBr3 using 10-mJ 266-nm laser pulses (repetition rate 10 Hz) and monitored by measuring the fluorescence induced by a 429.8-nm dye laser, in the apparatus described by Berman et al. (1982) and Berman and Lin (1984). The results are presented in tables and graphs and characterized. The absolute rate constants for the forward and reverse reactions are determined, and their temperature dependence is given by Arrhenius expressions and formulas obtained in transition-state-theory calculations. The heat of formation of CH2 at 0 K is estimated (assuming that the recombination reaction CH2 + H has zero activation energy) as 92.6 + or - 0.5 kcal/mol.

Zabarnick, S.↗
NASA NTRS1997

Temperature-Dependent Kinetics Studies of the Reactions Br((sup 2)P(sub 3/2)) + CH3SCH3 reversible reaction CH3SCH2 + HBr. Heat of Formation of the CH3SCH2 Radical

Time-resolved resonance fluorescence detection of Br((sup 2)P(sub 3/2)) atom disappearance or appearance 266 nm laser flash photolysis of CF2Br2/CH3SCH3/H2/N2 and Cl2CO/CH2SCH3/HBr/H2/N2 mixtures has been employed to study the kinetics of the reactions Br((sup 2)P(sub 3/2)) + CH3SCH3 reversible reaction HBr + CH3SCH2 (1,-1) as a function of temperature over the range 386-604 K. Arrhenius expressions in units of cu cm/molecule which describe the results are k3= (9.0 +/- 2.9) x 10 (exp -11) exp[(-2386 +/- 151)/T]; errors are 2 sigma and represent precision only. To our knowledge, these are the first kinetic data reported for each of the two reactions studied. Second and third law analyses of the equilibrium data for reactions 1 and -1 have been employed to obtain the following enthalpies of reaction in units of kcal/mol: Delta-H(298) = 6.11 +/- 1.37 and Delta-H(0) = 5.37 +/- 1.38. Combining the above enthalpies of reaction with the well-known heats of formation of Br, HBr, CH3SCH3 gives the following heats of formation of the CH3SCH2 radical in units of kcal/mol: Delta-H(sub(f,298)) = 32.7 +/- 1.4 and Delta-H(sub (f,0)) = 35.3 +/- 1.4; errors are 2 sigma and represent estimates of absolute accuracy. The C-H bond dissociation energy in CH3SCH3 obtained from our data, 93.7 +/- 1.4 kcal/mol at 298 K and 92.0 +/- 1.4 kcal at 0 k, agrees well with a recent molecular beam photofragmentaion study but is 3 kcal/mol lower than the value obtained from an iodination kinetics study.

Jefferson, A.↗
NASA NTRS1997

Temperature-Dependent Kinetics Studies of the Reactions Br((sup 2)P3/2) + H2S yields SH + HBr and Br((sup 2)P3/2) + CH3SH yields CH3S + HBr. Heats of Formation of SH and CH3S Radicals

Time resolved resonance fluorescence detection of Br(sup 2)P3/2) atom disappearance or appearance following 266-nm laser flash photolysis of CF2Br2/H2S/H2/N2, CF2Br2/CH3SH/H2/N2, Cl2CO/H2S/HBr/N2, and CH3SSCH3/HBr/H2/N2 mixtures has been employed to study the kinetics of the reactions Br((sup 2)P3/2) + H2S = SH + HBr (1,-1) and Br((sup2)P3/2) + CH3SH = CH3S + HBr (2, -2) as a function of temperature over the range 273-431K. Arrhenius expressions in units of 10(exp -12) cu cm/molecule/s which describe the results are k1 = (14.2 +/- 3.4) exp[(-2752 +/- 90)/T],(k-1) = (4.40 +/- 0.92) exp[(-971 +/- 73)/T],k(2) = (9.24 +/- 1.15) exp[(-386 +/- 41)/T], and k(-2) = (1.46 +/-0.21) exp[(-399 +/-41)/T; errors are 2 sigma and represent precision only. By examining Br((sup 2)P3/2) equilibrium kinetics following 355nm laser flash photolysis of Br2/CH3SH/H2/N2 mixtures, a 298 K rate coefficient of (1.7 +/- 0.5) x 10(exp -10) cu cm/molecule/s has been obtained for the reaction CH3S + Br2 yields CH3SBr + Br. To our knowledge, these are the first kinetic data reported for each of the reactions studied. Measured rate coefficients, along with known rate coefficients for similar radical + H2S, CH3SH, HBr,Br2 reactions are considered in terms of possible correlations of reactivity with reaction thermochemistry and with IP - EA, the difference between the ionization potential of the electron donor and the electron affinity of the electron acceptor. Both thermochemical and charge-transfer effects appear to be important in controlling observed reactivities. Second and third law analyses of the equilibrium data for reactions 1 and 2 have been employed to obtain the following enthalpies of reaction in units of kcal/mol: for reaction 1, Delta-H(298) = 3.64 +/- 0.43 and Delta-H(0) = 3.26 +/-0.45; for reaction 2, Delta-H(298) = -0.14 +/- 0.28 and Delta-H(0) = -0.65 +/- 0.36. Combining the above enthalpies of reaction with the well-known heats of formation of Br, HBr, H2S, and CH3SH gives the following heats of formation for the RS radicals in units of kcal/mol: Delta-H(sub f)(sub 0)(SH) = 34.07 +/- 0.72, Delta-H(sub f)(sub 298)(SH) = 34.18 +/- 0.68, Delta-H(sub f)(sub 0)(CH3S) = 31.44 +/- 0.54, Delta-H(sub f)(sub 298)(CH3S) = 29.78 +/- 0.44; errors are 2 sigma and represent estimates of absolute accuracy. The SH heat of formation determined from our data agrees well with literature values but has reduced error limits compared to other available values. The CH3S heat of formation determined from our date is near the low end of the range of previous estimates and is 3-4 kcal/mol lower than values derived from recent molecular beam photofragmentation studies.

Nicovich, J. M.↗
NASA NTRS1981

A laser flash photolysis kinetics study of the reaction OH + H2O2 yields HO2 + H2O

Absolute rate constants for the reaction are reported as a function of temperature over the range 273-410 K. OH radicals are produced by 266 nm laser photolysis of H2O2 and detected by resonance fluorescence. H2O2 concentrations are determined in situ in the slow flow system by UV photometry. The results confirm the findings of two recent discharge flow-resonance fluorescence studies that the title reaction is considerably faster, particularly at temperatures below 300 K, than all earlier studies had indicated. A table giving kinetic data from the reaction is included.

Wine, P. H.↗