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Two different interpretations of measured dissociation rate constants and effects on coupled vibrational dissociational flows of oxygen over wedge
Resonance theory for three body recombination kinetics for calculating recombination rate constant of deuterium atom
The degradation of the LM193 dual voltage comparator has been studied at different TID dose rate profiles, including several different constant dose rates and a variable dose rate that simulates the behavior of a solar flare. A comparison of results following constant dose rate vs. variable dose rates is made to explore how well the constant dose rates used for typical part testing predict the performance during a simulated space-like mission. Testing at a constant dose rate equal to the lowest dose rate seen during the simulated flare provides an extremely conservative estimate of the overall amount of degradation. A constant dose rate equal to the average dose rate is also more conservative than the variable rate. It appears that, for this part, weighting the dose rates by the amount of total dose received at each rate (rather than the amount of time at each dose rate) results in an average rate that produces an amount of degradation that is a reasonable approximation to that received by the variable rate.
Calculation of recombination rate constants of diatomic molecules according to Mach number of flow at supersonic nozzle exit
Chemical kinetics measurements on 82 gas phase reactions of chlorine containing species are reviewed. Recommended rate constants are given. The principal species of interest are Cl, Cl2, ClO, Cl2O, ClOO, OClO, CINO, HCl and halo derivatives of methane and ethane. Absorption spectra are given for 21 species. In addition the chemical kinetics methods used to obtain these data are discussed with regard to their applicability and reliability.
Mechanical-feedback regulated modulating valve maintains pressure in bag equal to that within bellows, causing fluid to be expelled at a constant rate. Adaptable to systems where bellows are replaced by cylinders, bladders, or diaphragms.
The objective of the present report is to survey the various values of forward and backward reaction rate constants used by investigators in the field of high-temperature (T greater than 2000 K) gas reactions involving nitrogen and oxygen only. The objective is to find those values that correlate well so that they can be used for the studies of hypersonic flow and supersonic combustion with reasonable confidence. Relatively good agreement among these various values is observed for temperatures lower than 10,000 K.
A steady-state flow apparatus, shown earlier to be suitable for the study of rapid gas reactions, has been used to determine the pressure dependence of the relative quasi-bimolecular rate constants for the reactant pairs ammonia (AM)-trimethylamine (TMA) and dimethylamine (DMA)-trimethylamine in reaction with boron trifluoride. The pressure dependence of the former was determined in the range 0.03-75 torr and that of the latter in the range 0.02-720 torr.
Reaction rate constants of ion-molecule interchange reaction as function of temperature, flow velocity, activation energy and constant part of steric factor P
In low-temperature flash photolysis of NH 3 /O 2 /N 2 mixtures, the NH 2 consumption rate and the product distribution is controlled by the reactions NH 2 + HO 2 → products (R1), NH 2 + H (+M) → NH 3 (+M) (R2), and NH 2 + NH 2 (+M) → N 2 H 4 (+M) (R3). In the present work, published flash photolysis experiments by, among others, Cheskis and co-workers, are re-interpreted using recent direct measurements of NH 2 + H (+N 2 ) and NH 2 + NH 2 (+N 2 ) from Altinay and Macdonald. To facilitate analysis of the FP data, relative third-body collision efficiencies compared to N 2 for R2 and R3 were calculated for O 2 and NH 3 as well as for other selected molecules. We report results were in good agreement with the limited experimental data. Based on reported NH 2 decay rates in flash photolysis of NH 3 /O 2 /N 2 , a rate constant for NH 2 + HO 2 → NH 3 + O 2 (R1a) of $k_{1\text{a}}$ = 1.5(±0.5) × 10 14 cm 3 mol –1 s –1 at 295 K was derived. This value is higher than earlier determinations based on the FP results but in good agreement with recent theoretical work. Kinetic modeling of reported N 2 O yields indicates that NH 2 + HO 2 → H 2 NO + O (R1c) is competing with R1a, but perturbation experiments with addition of CH4 indicate that it is not a dominating channel. Measured HNO profiles indicate that this component is formed directly by NH 2 + HO 2 → HNO + H 2 O (R1b), but theoretical work indicates that R1b is only a minor channel. Based on this analysis, we estimate $k_{1\text{c}}$ = 2.5 × 10 13 cm 3 mol –1 s –1 and $k_{1\text{b}}$ = 2.5 × 10 12 cm 3 mol –1 s –1 at 295 K, with significant uncertainty margins.
A new global potential energy hypersurface for H2 + H2 is constructed and quasiclassical trajectory calculations performed using the resonance complex theory and energy transfer mechanism to estimate the rate of three body recombination over the temperature range 100 to 5000 K. The new potential is a faithful representation of ab initio electron structure calculations, is unchanged under the operation of exchanging H atoms, and reproduces the accurate H3 potential as one H atom is pulled away. Included in the fitting procedure are geometries expected to be important when one H2 is near or above the dissociation limit. The dynamics calculations explicitly include the motion of all four atoms and are performed efficiently using a vectorized variable-stepsize integrator. The predicted rate constants are approximately a factor of two smaller than experimental estimates over a broad temperature range.
A new global potential energy hypersurface for H2 + H2 is constructed and quasiclassical trajectory calculations performed using the resonance complex theory and energy transfer mechanism to estimate the rate of three body recombination over the temperature range 100 to 5000 K. The new potential is a faithful representation of ab initio electron structure calculations, is unchanged under the operation of exchanging H atoms, and reproduces the accurate H3 potential as one H atom is pulled away. Included in the fitting procedure are geometries expected to be important when one H2 is near or above the dissociation limit. The dynamics calculations explicitly include the motion of all four atoms and are performed efficiently using a vectorized variable-stepsize integrator. The predicted rate constants are approximately a factor of two smaller than experimental estimates over a broad temperature range.
Studies of the formation and loss processes for GeH4 are required in order to provide data to help determine the major chemical form in which germanium exists in the atmospheres of Jupiter and Saturn. The reaction of hydrogen atoms with germane is one of the most important of these reactions. The absolute rate constant for this reaction as a function of temperature and pressure is studied. Flash photolysis of dilute mixtures of GeH4 in argon, combined with time-resolved detection of H atoms via Lyman alpha resonance fluorescence, is employed to measure the reaction rate. The reaction is shown to be moderately rapid, independent of total pressure, but possessing a positive temperature dependence.
Recent concern about the depletion of stratospheric ozone by chlorine species from the decomposition of chlorofluoromethanes has emphasized the need for laboratory studies of the first reaction steps involved, especially those which control the concentration of the OH and ClO radicals in the stratosphere. Rate constants for the reactions of OH with ClO, Cl2, and Cl2O at 298 K have been determined in a discharge flow system using resonance fluoresence detection. The results are (9.1 + or - 1.3) x 10 to the -12th, (5.5 + or - 0.3) x 10 to the -14th, and (6.5 + or - 0.5) x 10 to the -12th (all in units of cu cm/sec), respectively.
The reaction of N(4S) atoms with ozone was examined at 298 K using discharge flow and flash photolysis techniques, both coupled with resonance fluorescence detection of N(4S). No reaction was detected in either system, and an upper limit of 5 x 10 to the -16th cu cm/molecule/s was estimated for the rate constant. This is 1000 times lower than the presently accepted value of 5.7 x 10 to the -13th cu cm/molecule/s which is based on a discharge flow-mass spectrometric study of the reaction. Potential complications in the latter experiment are discussed.
In recent years, considerable attention has been given to the role of chlorine compounds in the catalytic destruction of stratospheric ozone. However, while some reactions have been studied extensively, the kinetic data for the reaction of Cl with C2H2 is sparse with only three known determinations of the rate constant k3. The reactions involved are Cl + C2H2 yields reversibly ClC2H2(asterisk) (3a) and ClC2H2(asterisk) + M yields ClC2H2 + M (3b). In the present study, flash photolysis coupled with chlorine atomic resonance fluorescence have been employed to determine the pressure and temperature dependence of k3 with the third body M = Ar. Room temperature values are also reported for M = N2. The pressure dependence observed in the experiments confirms the expectation that the reaction involves addition of Cl to the unsaturated C2H2 molecule followed by collisional stabilization of the resulting adduct radical.
The column abundances of CH3 observed by the Infrared Space Observatory (ISO) satellite on Saturn and Neptune were lower than predicted by atmospheric photochemical models, especially for Saturn. It has been suggested that the models underestimated the loss of CH3 due to poor knowledge of the rate constant k of the CH3 + CH3 self-reaction at the low temperatures and pressures of these atmospheres. Motivated by this suggestion, we undertook a combined experimental and photochemical modeling study of the CH3 + CH3 reaction and its role in determining planetary CH3 abundances. In a discharge flow-mass spectrometer system, k was measured at T = 155 K and three pressures of He. The results in units of cu cm/molecule/s are k(0.6 Torr) = 6.82 x 10(exp -11), k(1.0 Torr) = 6.98 x 10(exp -11), and k(1.5 Torr) = 6.91 x 10(exp -11). Analytical expressions for k were derived that (1) are consistent with the present laboratory data at T = 155 K, our previous data at T = 202 K and 298 K, and those of other studies in He at T = 296-298 K and (2) have some theoretical basis to provide justification for extrapolation. The derived analytical expressions were then used in atmospheric photochemical models for both Saturn and Neptune. These model results reduced the disparity with observations of Saturn, but not with observations of Neptune. However, the disparity for Neptune is much smaller. The solution to the remaining excess CH3 prediction in the models relative to the ISO observations lies, to a large extent, elsewhere in the CH3 photochemistry or transport, not in the CH3 + CH3 rate.
Electron-attachment cross sections are reported in the electron energy range 0-150 MeV, at an energy resolution of 6.5 MeV (full width at half maximum) for the molecules HI and DI. Use is made of the Kr photoionization method to obtain cross sections for HI, and a signal intercomparison technique to obtain cross sections and the thermal-attachment rate constant for DI. Attachment properties of the two molecules are very similar. The ratio of attachment cross sections is discussed in terms of the reduced-mass dependence of the dissociation width and the survival probability, and in terms of spectroscopic thresholds and rotational populations for attachment at 300 K. Approximate potential-energy curves for the lowest states of the neutral molecule and negative ion are given.