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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Rate constant for the OH + CO reaction - Pressure dependence and the effect of oxygen

The effect of pressure on the rate constant of the OH + CO reaction has been measured for Ar, N2, and SF6 over the pressure range 200-730 torr. All experiments were at room temperature. The method involved laser-induced fluorescence to measure steady-state OH concentrations in the 184.9 nm photolysis of H2O-CO mixtures in the three carrier gases, combined with supplementary measurements of the CO depletion in these same carrier gases in the presence and absence of competing reference reactants. The effect of O2 on the pressure effect was determined. A pressure enhancement of the rate constant was observed for N2 and SF6, but not for Ar, within an experimental error of about 10 percent. The pressure effect for N2 was somewhat lower than previous literature reports, being about 40 percent at 730 torr. For SF6 a factor of two enhancement was seen at 730 torr. In each case it was found that O2 had no effect on the pressure enhancement. The roles of the radical species HCO and HOCO were evaluated.

Demore, W. B.↗
NASA NTRS1986

Reaction rate constant of HO2+O3 measured by detecting HO2 from photofragment fluorescence

A room-temperature discharge-flow system investigation of the rate constant for the reaction 'HO2 + O3 yields OH + 2O2' has detected HO2 through the OH(A-X) fluorescence produced by photodissociative excitation of HO2 at 147 nm. A reaction rate constant of 1.9 + or - 0.3 x 10 to the -15th cu cm/molecule per sec is obtained from first-order decay of HO2 in excess O3; this agrees well with published data.

Manzanares, E. R.↗
NASA NTRS1973

Rate constants for the reactions of hydroxyl and hydroperoxyl radicals with ozone.

Chain decomposition of ozone by hydroxyl and hydroperoxyl radicals has been observed. The rate constant at 300 K for OH + O3 yielding HO2 + O2 is eight times ten to the -14th power cubic centimeters per second. The rate constant for HO2 + O3 yielding OH + 2O2 is three times ten to the -15th power cubic centimeters per second. These results have implications concerning stratospheric ozone.

Demore, W. B.↗
NASA NTRS1979

Rate constant measurements for the reaction Cl + CH2O yields HCl + CHO Implications regarding the removal of stratospheric chlorine

The flash photolysis resonance fluorescence technique was employed to investigate the rate constant for the reaction Cl + CH2O yields HCl + CHO from 223 to 323 K. An Arrhenius fit of the data gives a rate constant equal to (1.09 + or - 0.40) x 10 to the -10th exp/-(131 + or - 98)/T/ in units of cu cm/molecule per sec. The results are compared to two very recent kinetic studies and are assessed in view of the reaction's role in disrupting the Cl-ClO stratospheric ozone depletion chain.

Anderson, P. C.↗
NASA NTRS1979

Rate constant for the reaction H + NO2 from 195 to 400 K with FP-RF and DF-RF techniques

Measurements are made of the rate constant for the reaction H + NO2 yielding OH + NO over significant temperature ranges with the flash photolysis-resonance fluorescence (FP-RF) technique and also with the discharge flow-resonance fluorescence (DF-RF) technique. Since it is important to study chemical reactions with more than one technique, the above reaction is investigated with the FP-RF technique over the temperature range 230-400 K. The results reported do not agree with earlier determinations. Accordingly, a separate set of measurements is made with the DF-RF technique over the temperature range 195-368 K; the results are also reported. The reaction is also considered theoretically, especially with regard to the question of temperature dependence and absolute magnitude of the rate constant.

Michael, J. V.↗
NASA NTRS1990

Rate constant for reaction of atomic hydrogen with germane

Due to the interest in the chemistry of germane in the atmospheres of Jupiter and Saturn, and because previously reported kinetic reaction rate studies at 298 K gave results differing by a factor of 200, laboratory measurements were performed to determine the reaction rate constant for H + GeH4. Results of the study at 298 K, obtained via the direct technique of flash photolysis-resonance fluorescence, yield the reaction rate constant, k = (4.08 + or - 0.22) x 10(exp -12) cu cm/s.

Nava, David F.↗
NASA NTRS1985

Rate constant for the reaction Cl + HO2NO2 yielding products

The rates for the reaction of Cl atoms iwth HO2NO2 were calculated from data obtained by the use of the discharge flow/resonance fluorescence (DF/RF) and the discharge flow/mass spectrometric (DF/MS) techniques. The total rate constant, k1, for the overall reaction: 1a (Cl + HO2NO2 yielding HCl + NO2 +O2), 1b (yielding HO2 + ClNO2), and the two possible additional channels was found to be less than 1.0 x 10 to the -13th cu cm/s at 296 K. The value of (k1a + k1b) was found to be 3.4 + or - 1.4) x 10 to the -14th cu cm/s. Thus, the reaction of Cl with peroxynitric acid is too slow, by a factor of 100, to contribute significantly to the hydrogen abstraction by Cl in the stratosphere.

Simonaitis, R.↗
NASA NTRS1981

Reactions of ethynyl radicals - Rate constants with CH4, C2H6, and C2D6

An experiment to measure ethynyl radical reactivity with other simple molecules is described. Flash photolysis of CF3C2H, a C2H precursor, was kinetically and spectroscopically analyzed for C2H reactions with CH4, C2H6, and C2D6 and rate constants for the abstraction reaction at room temperature were determined. The experimental apparatus is described, and the acetylene feedstock purification procedures are outlined. Rate constants are provided, and additional examination of the effects of added helium showed no alterations over the pressure range 20-700 torr.

Laufer, A. H.↗
NASA NTRS1977

Rate constant for formation of chlorine nitrate by the reaction ClO + NO2 + M

The pseudo-first-order decay of ClO in a large excess of NO2 was monitored in a discharge flow/mass-spectrometer apparatus in order to measure the rate constant of the reaction ClO + NO2 + M yields ClONO2 + M for M = He, Ar, and N2 over the temperature range from 248 to 417 K. Numerical results are given for He at 248, 299, 360, and 417 K (1 to 9 torr); for Ar at 298 K (1 to 4 torr); and for N2 at 299, 360, and 417 K (1 to 6 torr). Systematic errors are estimated, and identification of the reaction product is discussed. The results obtained are shown to be in excellent agreement with other recent measurements of the same rate constant.

Leu, M. T.↗
NASA NTRS1982

Rate constant and possible pressure dependence of the reaction OH + HO2

The technique of laser-induced fluorescence is used to measure steady-state OH concentrations in the photolysis of water vapor at 184.9 nm and 298 K, with O2 added in trace amounts. He or Ar is present at total pressures in the range 75-730 torr. The results are used in deriving the rate-constant ratio of k1 to k5 to the 1/2 power, where k1 and k5 are the rate constants for the reactions OH + HO2 = H2O + O2 and HO2 + HO2 = O2, respectively. When available values of k5 are used, the results give k1 = (1.2 + or - 0.4) x 10 to the -10 cu cm/s at 1-atm pressure, with evidence of a decline of k1 at lower pressures. No water-vapor effect on k1 is observed.

Demore, W. B.↗
NASA NTRS1973

Absolute rate constant for the O plus NO chemiluminescence in the near infrared

Infrared chemiluminescence from the process O + NO (+M) NO2 + hv (+M) has been studied between 1.3 and 4.1 micrometer. The wavelength dependence of the continuum between 1.3 and 3.3 micrometer is in fair agreement with previous studies and the measured radiative rate constant at 1.51 micrometer establishes the NO-O glow in this spectral range as a secondary emission standard. Comparison with previous studies of the visible region of the glow implies that the overall radiative rate constant lies in the range (9.4 to 11.2) x 10 to the minus 17 power cu cm sec/1. In the region 3.3 to 4.1 micrometer, the previously observed broad band, peaking at 3.7 micrometer, shows a complex kinetic dependence on O and M.

Golde, M. F.↗
NASA NTRS1974

ICR study of nonreactive ion-molecule collision rate constants for Cl/-/ and Cr/CO/5/-/

Determination of experimental momentum transfer rate constants for systems of Cl(-) and Cr(CO)5(-) ions by means of an ion cyclotron resonance (ICR) line-broadening technique. It is found that in the pure polarization limit of small ion/large neutral collisions the Langevin ion mobility theory gives good agreement with experimental results. A comparison of isotropic and anisotropic neutral systems suggests that a correction for the anisotropic systems is necessary. Beyond the pure polarization limit the Langevin theory gives poor predictions for ion mobilities. The adjustable parameter, gamma, of the Mason-Schamp (12-6-4) potential function permits unique solution of the ion mobility for Cr(CO)5(-) in a wide range of neutral gases. The large values of gamma obtained for most of these systems imply, in terms of the Mason-Schamp theory, that the r to the minus 6th power contribution to the potential function is significant.

Dymerski, P. P.↗
NASA NTRS1978

Rate constant for the reaction ClO + NO yields Cl + NO2

The rate constant for the reaction ClO + NO yields Cl + NO2 has been determined over the temperature range 226.7-415.4 K in a discharge flow system using a mass spectrometer as a detector. The results, expressed in the Arrhenius form, are compared with previous measurements.

Leu, M. T.↗
NASA NTRS1978

Calculated rate constants for the reaction ClO + O yields Cl + O2 between 220 and 1000 deg K

Classical trajectory calculations are presented for the reaction ClO + O yields Cl + O2, a reaction which is an important step in the chlorine-catalyzed destruction of ozone which is thought to occur in the 220 and 1000 K. The calculated rate constant is 4.36 x 10 to the minus 11th power exp (-191/T)cu cm molecule (-1)s(-1) and its value at 300 K is 2.3 plus or minus 10 to the 11th power cu cm molecule (-1)s(-1), about a factor of 2 lower than recent experimental data. The empirical potential energy surface used in the calculations was constructed to fit experimental data for ClO, O2 and ClOO molecules. Other important features of this potential surface, such as the barrier to reaction, were varied systematically and calculations were performed for a range of conditions to determine the best theoretical rate constants. Results demonstrate the utility of classical trajectory methods for determining activation energies and other kinetic data for important atmospheric reactions.

Jaffee, R. L.↗
NASA NTRS1994

The chemistry of bromine in the stratosphere: Influence of a new rate constant for the reaction BrO + HO2

The impact of new laboratory data for the reaction BrO + HO2 yields HOBr + O2 in the depletion of global stratospheric ozone has been estimated using a one-dimensional photochemical model taking into account the heterogeneous reaction on sulphate aerosols which converts N2O5 into HNO3. Assuring an aerosol loading 2 times as large as the 'background' and a reaction probability of 0.1 for the above heterogeneous reaction, the 6 fold increase in the measured rate constant for the reaction of BrO with HO2 increases the computed depletion of global ozone produced by 20 ppt of total bromine from 2.01 percent to 2.36 percent. The use of the higher rate constant increases the HOBr mixing ratio and makes the bromine partitioning and the ozone depletion very sensitive to the branching ratio of the potential channel forming HBr in the BrO + HO2 reaction.

Pirre, Michel↗