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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Heterogeneous reactions of HNO3(g) + NaCl(s) yields HCl(g) + NaNO3(s) and N2O5(g) + NaCl(s) yields ClNO2(g) + NaNO3(s)

The heterogeneous reactions of HNO3(g) + NaCl(s) yields HCl(g) + NaNO3(s) (eq 1) and N2O5(g) + NaCl(s) yields ClNO2(g) + NaNO3(S) (eq 2) were investigated over the temperature range 223-296 K in a flow-tube reactor coupled to a quadrupole mass spectrometer. Either a chemical ionization mass spectrometer (CIMS) or an electron-impact ionization mass spectrometer (EIMS) was used to provide suitable detection sensitivity and selectivity. In order to mimic atmospheric conditions, partial pressures of HNO3 and N2O5 in the range 6 x 10(exp -8) - 2 x 10(exp -6) Torr were used. Granule sizes and surface roughness of the solid NaCl substrates were determined by using a scanning electron microscope. For dry NaCl substrates, decay rates of HNO3 were used to obtain gamma(1) = 0.013 +/- 0.004 (1sigma) at 296 K and > 0.008 at 223 K, respectively. The error quoted is the statistical error. After all corrections were made, the overall error, including systematic error, was estimated to be about a factor of 2. HCl was found to be the sole gas-phase product of reaction 1. The mechanism changed from heterogeneous reaction to predominantly physical adsorption when the reactor was cooled from 296 to 223 K. For reaction 2 using dry salts, gamma(2) was found to be less than 1.0 x 10(exp -4) at both 223 and 296 K. The gas-phase reaction product was identified as ClNO2 in previous studies using an infrared spectrometer. An enhancement in reaction probability was observed if water was not completely removed from salt surfaces, probably due to the reaction of N2O5(g) + H2O(s) yields 2HNO3(g). Our results are compared with previous literature values obtained using different experimental techniques and conditions. The implications of the present results for the enhancement of the hydrogen chloride column density in the lower stratosphere after the El Chichon volcanic eruption and for the chemistry of HCl and HNO3 in the marine troposphere are discussed.

Leu, Ming-Taun↗
NASA NTRS1987

Quantification of HCl from High Resolution Infrared Solar Spectra Obtained at the South Pole in December 1986

Ground-based infrared solar spectra at 0.02/ cm resolution obtained at the Amundsen-Scott South Pole station in December 1986 have been analysed for the atmospheric content of HCl. Nonlinear least-squares spectral fitting applied to the spectra yields a total HCl column amount of (6.4 +/- 0.8) x 10(exp 15) molec/sq cm, most being stratospheric. This amount is larger than that extrapolated from earlier results on the latitudinal distribution of atmospheric HCl.

Goldman, A.↗
NASA NTRS1972

Line shape parameters for HCl and HF in a CO2 atmosphere.

Results of high-resolution (0.1 cm/cm) on several CO2-broadened lines in the fundamentals of HCl35 and HCl37. Line intensities, half-widths, and shapes were determined at room temperature. Half-widths in HCl-CO2 collisions were computed for several temperatures, employing Anderson's (1949) theory. The measured shapes of HCl lines broadened by CO2 are described by a semiempirical super-Lorentzian shape. The curve-of-growth for this line shape is derived in terms of a function similar to the Ladenburgh-Reiche function. Absorption between R(0) and P(1) is affected by the appearance of several pressure-induced Q-branch lines, at the pressures from 1 to 10 atm used in the present study.

Varanasi, P.↗
NASA NTRS1973

Vapor phase growth of group 3, 4, and 5 compounds by HCl transport of elements

Technique has been devised for vapor-phase epitaxial growth of group 3, 4, and 5 binary, ternary, or quaternary compounds by HCl transport of the constituent elements or dopants. Technique uses all the constituents of the alloy system in their elemental form. Transport of these elements by an HCl + H2 carrier gas facilitates their transport as subchlorides.

Tyagi, R. C.↗
NASA NTRS1975

Auger spectroscopy of HCl interaction with Al at low pressures

The purpose of the present study was to determine some adsorption characteristics of HCl with partially clean polycrystalline Al by Auger electron spectroscopy. The adsorption was found to exhibit a Freundlich-type behavior pattern in which the number of molecules adsorbed varied with HCl pressure linearly on a log-log plot. Assuming that the adsorption behaves according to the Clausius-Clapeyron equation, the isosteric heat of adsorption increases with coverage at low pressures, appearing to approach a constant value of 4-5 kcal/mole.

Lassiter, W. S.↗
NASA NTRS1975

Development of a thin film solid state gaseous HCl sensor

The selection of materials to develop a thin film HCl sensor is discussed. Data were primarily concerned with chemical and physical properties of the film and with electrical properties which exhibit and enhance electrical response when HCl is absorbed on the film surface. Techniques investigated for enhancing electrical response include changing conditions for growing films, adding impurities to the film, changing ambient light intensity, and altering the ambient temperature of the sensing element.

Source record↗
NASA NTRS1976

Spectroscopic detection and vertical distribution of HCl in the troposphere and stratosphere

HCl has been observed in both the troposphere and stratosphere from ground-based and airborne spectroscopic measurements of the 1-0 band at 3-micron wavelength. The results, which are specific to the HCl molecule in the gas phase, show a decreasing mixing ratio with altitude in the lower stratosphere. The stratospheric layer, which commences at about 15 km, reaches its maximum concentration at an altitude above 21 km (the limiting height of the observations to date). The local value for the volume mixing ratio at 21 km is 7 + or - 1 times 10 to the minus 10th. However, the zenith column abundance observed above 21 km implies that the mixing ratios at greater altitudes are unlikely to reach values much in excess of the local value at 21 km.

Farmer, C. B.↗
NASA NTRS1975

Absorption coefficient of HCl in the region 1400 to 2200 A

The results of absorption coefficient measurements of HCl in the region 1400 to 2200 A are reported and compared with those previously published. It is concluded that the present results represent the best compromise of all measurements and should be used for any calculations on the photodissociation rate of HCl in planetary atmospheres.

Inn, E. C. Y.↗
NASA NTRS1977

A gas filter correlation monitor for CO, CH4, and HCl

A fast response instrument for monitoring the atmospheric constituents CO, CH4, and HCl, using a modified nondispersive infrared technique, was designed, assembled, and tested. This gas filter correlation method uses a sample of gas to provide a selective filter for radiation absorbed in a gas mixture containing the specified gas. Depending on the spectral line broadening, temperature, and optical depth of the gas selected, exceptionally high spectral resolution may be attained. A description of the single beam rotating cell system and its specific application is presented along with the signal processing circuit. Calibrations of the instrument show that the technique can be used to measure CO, CH4, and HCl concentrations as small as 5 ppm-m. A field version was employed to measure diurnal variations of CO and CH4 and the interfering effects of other atmospheric gases were analyzed.

Sebacher, D. I.↗
NASA NTRS1978

The reaction Cl + H2CO yields HCl + HCO: Decreased sensitivity of stratospheric ozone to chlorine perturbations

The absolute rate constant for the reaction Cl + H2CO yields HCl + HCO was determined by the flash-photolysis resonance fluorescence method to be 7.5 plus or minus 0.9 (2 sigma) times 10 to the minus 11th power cu cm/molecule sec at 298 K and to have a negligible temperature dependence. This rate which is more than 2000 times faster than the rate of Cl + CH4 indicates that formaldehyde (H2CO) will compete significantly with methane (CH4) for the conversion of active chlorine in the stratosphere to the inactive reservoir HCl. Chlorine will thus be a less efficient destroyer of stratosphere ozone than previously believed. Ambient stratospheric ozone will depend less on the ambient chlorine amount and the predicted response to chlorine perturbations will be lessened. One-dimensional eddy-diffusion photochemical model calculations indicate a factor of 1.1 less sensitivity to chlorine than recently reported. For a steady-state CFM release at 1975 rates (750,000 tons/year) the eventual ozone depletion is now calculated to be 14%.

Stief, L. J.↗
NASA NTRS1977

The HF:HCl ratio in the 14-38 km region of the stratosphere

A balloon-borne high resolution Michelson interferometer recorded near infrared absorption spectra of the 1-0 fundamental vibration bands of HF and HCl in the stratosphere over Australia in March 1977. The ratio of the number density of HF to that of HCl as a function of stratospheric height was deduced from the measurements. Within estimated experimental error, the ratio is constant, its mean value being 0.1.

Farmer, C. B.↗
NASA NTRS1977

The vertical distribution of HCl in the stratosphere

The vertical distribution of HCl in the stratosphere has been measured from infrared solar absorption spectra recorded with a balloon-borne interferometer. The flights were made in September, 1975, and May, 1976 at float altitudes of 40 km and 37 km, respectively, near Palestine, Texas. Concentration profiles derived from the data show an increase from 0.6 ppbv at 20 km to 1.7 plus or minus .5 ppbv in the region of 37 km. Above 37 km, the data permit only the total abundance to be determined; this value is found to be equivalent to 1.6 plus or minus .6 ppbv if the gas were uniformly mixed. The results from the two flights are closely similar, and no significant seasonal variation in the HCl concentrations can be discerned. The balloon data are consistent with the profile in the 14-21 km altitude region of the stratosphere reported earlier from U-2 observations.

Raper, O. F.↗
NASA NTRS1978

The reaction Cl + H2CO yields HCl + HCO: Decreased sensitivity of stratospheric ozone to chlorine perturbations

The absolute rate constant for the reaction Cl + H2CO yields HCl + HCO has been determined by the flash-photolysis-resonance fluorescence method to be + or - 0.9 (2 sigma) x 10 to the -11th power cu cm/molecule per sec at 298 K and to have a negligible temperature dependence. This rate, which at stratospheric temperatures is more than 2000 times faster than the rate of Cl + CH4 and more than a factor of 2 faster than Cl + HO2, indicates that formaldehyde (H2CO) will compete significantly with methane (CH4) and HO2 for the conversion of active chlorine in the stratosphere to the inactive reservoir HCl. Chlorine will thus be a less efficient destroyer of stratospheric ozone than previously believed. One-dimensional eddy-diffusion photochemical model calculations indicate that the eventual ozone depletion for a steady-state chlorfluoromethane release at 1975 rates (750,000 tons/year) will be lowered from 20% to 18.5% by the inclusion of this reaction.

Stief, L. J.↗
NASA NTRS1981

Temperature dependence of the hydrogen atom abstraction reactions of Cl/+/ and HCl/+/ with H2

Rate constants are reported for the reactions of Cl(+) and HCl(+) with H2 over the temperature range 150-400 K. The Cl(+) reaction has a positive temperature dependence that follows the Arrhenius form k1 = A exp(-169/T). The reaction of HCl(+) has a negative temperature dependence that follows the form k2 = AT to the -0.6 power. The implication of these results for interstellar chemistry is commented on. Schematic potential surfaces for the reactions are suggested.

Cates, R. D.↗
NASA NTRS1984

The rate of the reaction of OH with HCl

Using the techniques of laser/flash photolysis-resonance fluorescence, the absolute rate constant for the OH + HCl reaction is measured from 240 to 295 K. Ultraviolet and infrared spectrophotometry are used to continuously monitor the HCl concentrations. It is shown that the rate constant values obtained in the study are 20-30 percent larger than those recommended by Smith and Zellner (1974) and Ravishankara et al. (1977) for modeling of stratospheric chemistry.

Molina, M. J.↗
NASA NTRS1986

A kinetics study of the homogeneous and heterogeneous components of the HCl + ClONO2 reaction

The kinetics of the reaction HCl + ClONO2 to Cl2 + HNO3 were investigated at 298 K using a flow reactor with FTIR analysis to assess the importance of this reaction for stratospheric chemistry. The observed reaction was characteristic of a heterogeneous process; an upper limit of 5 x 10 to the -18th cu cm/molecule per s was obtained for the homogeneous gas phase rate constant. From calculations of the first order wall rate constant, estimates were made of the reaction rate on stratospheric aerosols. Because both HCl and ClONO2 need to be adsorbed on the particle surface, the reaction will be of negligible importance under most stratospheric conditions.

Friedl, Randall R.↗