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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Effect of adsorbed films on friction of Al2O3-metal systems

The kinetic friction of polycrystalline Al2O3 sliding on Cu, Ni, and Fe in ultrahigh vacuum was studied as a function of the surface chemistry of the metal. Clean metal surfaces were exposed to O2, Cl2, C2H4, and C2H3Cl, and the change in friction due to the adsorbed species was observed. Auger electron spectroscopy assessed the elemental composition of the metal surface. It was found that the systems exposed to Cl2 exhibited low friction, interpreted as the van der Waals force between the Al2O3 and metal chloride. The generation of metal oxide by oxygen exposures resulted in an increase in friction, interpreted as due to strong interfacial bonds established by reaction of metal oxide with Al2O3 to form the complex oxide (spinel). The only effect of C2H4 was to increase the friction of the Fe system, but C2H3Cl exposures decreases friction in both Ni and Fe systems, indicating the dominance of the chlorine over the ethylene complex on the surface

Pepper, S. V.↗
NASA NTRS1977

Effect of trichlorofluoromethane and molecular chlorine on ozone formation by simulated solar radiation

Mixtures of air with either Cl2 or CFCl3 were photolyzed in a reaction chamber by simulated solar radiation. Ozone formation was temporarily inhibited by Cl2 and permanently inhibited by CFCl3. A chemical mechanism including gas phase and wall reactions is proposed to explain these results. The CFCl3 is assumed to be adsorbed on the chamber walls and to poison the sites for Cl destruction.

Bittker, D. A.↗
NASA NTRS1978

Effect of nitric oxide on photochemical ozone formation in mixtures of air with molecular chlorine and with trichlorofluoromethane

Ozone formation in a reaction chamber at room temperature and atmospheric pressure were studied for the photolysis of mixtures of NO with either Cl2 or CFCl3 in air. Both Cl2 + NO and CFCl3 + NO in air strongly inhibited O3 formation during the entire 3 to 4 hour reaction. A chemical mechanism that explains the results was presented. An important part of this mechanism was the formation and destruction of chlorine nitrate. Computations were performed with this same mechanism for CFCl3-NO-air mixtures at stratospheric temperatures, pressures, and concentrations. Results showed large reductions in steady-state O3 concentrations in these mixtures as compared with pure air.

Bittker, D. A.↗
NASA NTRS1978

Infrared vibration-rotation spectra of the ClO radical using tunable diode laser spectroscopy

Tunable diode laser spectroscopy is used to measure the infrared vibration-rotation spectra of the ClO radical. The radical is generated in a flow system where a Cl2-He mixture passes through a microwave discharge to dissociate the Cl2. An O3-O2 mixture from an ozone generator is injected into the system downstream of the microwave discharge where O3 combines with Cl to form ClO. By adjusting the gas flow rates to yield an excess of Cl atoms, all the ozone is combined. ClO concentration is measured with UV absorption at 2577 and 2772 A and a deuterium lamp as a continuous source. Total cell pressure is 5.5 torr. The diode laser spectrometer is calibrated with ammonia lines as a reference where possible. The frequency of vibration-rotation lines is expressed as a function of rotational quantum number, fundamental vibrational frequency, and the rotational constants of the upper and lower vibrational states.

Rogowski, R. S.↗
NASA NTRS1979

Launch vehicle effluent measurements during the August 20, 1977, Titan 3 launch at Air Force Eastern Test Range

Airborne effluent measurements within the launch cloud and visible and infrared measurements of cloud physical behavior are discussed. Airborne effluent measurements include concentrations of HCl, Cl2, NO, NOX, and particulates as a function of time during each sampling pass through the exhaust cloud. The particle size distribution was measured for each pass through the cloud. Mass concentration as a function of particle diameter was measured over the size range of 0.05- to 25 micron diameter, and particle number density was measured as a function of diameter over a size range of 0.5 to 7.5 micron. Effluent concentrations in the cloud ranged from about 30 ppm several minutes after launch to about 1 to 2 ppm at 100 minutes. Maximum Cl2 concentrations were about 40 to 55 ppb and by 20 minutes were less than 1.0 ppb. A tabulated listing of the airborne data is given in the appendix. Usable cloud imaging data were limited to the first 16 minutes after launch.

Woods, D. C.↗
NASA NTRS1979

Launch vehicle effluent measurements during the September 5, 1977, Titan 3 launch at Air Force eastern test range

Airborne effluent measurements and cloud physical behavior data are presented. The monitoring program included airborne effluent measurements in situ in the launch cloud, visible and infrared photography of cloud growth and physical behavior, and limited surface collection of rain samples. Effluent measurements included concentrations of HCl, Cl2, NO, nitric oxide, and particles as a function of time in the exhaust cloud. In situ particle mass concentration and number density were measured as a function of time and size in the range of 0.05 micron m to 30 micron m diameter. Measurement results were similar to those of previous launch monitorings. Maximum HCl and nitric oxide concentrations of Cl2 were maximum about 2 minutes after launch and by 10 to 15 minutes had decayed to less than 10 ppb (detection limit). Particle measurements showed most of the particles present to be below about 3-micron m diameter. Postlaunch analyses of collected particle samples showed significant amounts of Al (some cases Cl) from about 3-micron m to 0.04-micron m diameter.

Wornom, D. E.↗
NASA NTRS1985

Rate constants for the quenching of metastable O2 (1Sigma g +) molecules

The O2 (1Sigma g +) rates for CO2, H2, N2, Cl2, CO, O3, and 2,3 DMB-2 are determined by monitoring the 762-nm emission in a fast-flow-discharge chemiluminescence detection system (Leu, 1984; Leu and Smith, 1981). The results are presented in tables and graphs and briefly characterized. The rate constants (in cu cm/s x 10 to the -16th) are 4600 + or - 500 for CO2, 7000 + or - 300 for H2, 17 + or - 1 for N2, 4.5 + or - 0.8 for Cl2, 45 + or - 5 for CO, 220,000 + or - 30,000 for O3, and 6000 + or - 100 for 2,3 DMB-2. The temperature dependence of the CO2 and O3 quenching reactions at 245-362 K is found to be negligible.

Kwang, Y. C.↗
NASA NTRS1988

Laboratory studies of sticking coefficients and heterogeneous reactions important in the Antarctic stratosphere

Laboratory studies of sticking coefficients of H2O, HCl, Cl2, and HNO3 on ice and heterogeneous reactions of ClONO2 with ice or HCl/ice have been performed in a fast flow reactor. A quadrupole mass spectrometer with electron impact ionization was used as a detector. Measured sticking coefficients are: 0.3 (+0.7, -0.1) for H2O, 0.4 (+0.6, -0.2) for HCL, less than 0.0001 for Cl2, and 0.3 (+0.7, -0.1) for HNO3 at 200 K. The reaction probability of ClONO2 on ice was found to be 0.06 (+ or - 0.03) while HOCl was observed as a sole product in the gas phase. With HCl present in ice, the reaction probability of ClONO2 is greatly enhanced, approaching 0.27 (+0.73, -0.13) while molecular chlorine was found to be the major product in the gas phase. Another reaction product was nitric acid which remained in the solid phase. Since the polar stratospheric clouds contain ice particles or possibly HCl/ice particles on the surface, the present results should be a major factor in producing the observed springtime ozone depletion in the Antarctic stratosphere.

Leu, Ming-Taun↗
NASA NTRS1988

Laboratory studies of sticking coefficients and heterogeneous reactions important in the stratosphere

The discovery of ozone depletion during spring in the Antarctic stratosphere has received wide spread attention. Both meteorological and chemical mechanisms have been used in attempts to explain this observation. The chemical theory focused on the chlorofluoromethanes released into the atmosphere. However, gas-phase, homogeneous reactions alone in the model can not adequately explain such a depletion. Heterogeneous reactions on ice surfaces could be important in the Antarctic stratosphere. These reactions are thought to convert ClONO2 and N2O5 into HNO3 in the solid phase while Cl2, HOCl, and ClNO2 are released into the stratosphere as gas-phase products. The photolysis of Cl2, HOCl, and ClNO2, then produces active chlorine which subsequently removes ozone through several catalytic cycles, including the Cl2O2 mechanism. The polar stratospheric clouds are thought to consist of mixtures of water ice, nitric acid, and sulfuric acid. Condensation of HCl onto the PSC's could provide active surfaces for heterogeneous reactions.

Leu, Ming-Taun↗
NASA NTRS1989

Ozone minimum occurs in Antarctica in the springtime

Observations on the formation of the Antarctic ozone hole in the upper atmosphere are summarized, and the mechanism responsible for the ozone depletion in the spring is examined. It is shown that the sequence of events begins with the absorption of H2O, N2O5, HCl, and ClONO2 on the cloud ice particles in the winter and chemical reactions among absorbed chemicals which release (HNO3)s, Cl2, HOCl, and ClNO2. With the return of sunlight in the spring, the clouds evaporate, and the Cl2, HOCl, and ClONO2 molecules are destroyed by sunlight to form Cl atoms. These attack ozone, producing a reduction of ozone that accounts for the bulk of the ozone decrease observed by the ground-based ozone monitors. Data on the ozone concentration for the period between 1957 through 1987 indicate that the southern ozone hole has been intensifying since 1975 as the amount of man-made chlorine increases.

Aikin, Arthur C.↗
NASA NTRS1991

Heterogeneous processes: Laboratory, field, and modeling studies

The efficiencies of chemical families such as ClO(x) and NO(x) for altering the total abundance and distribution of stratospheric ozone are controlled by a partitioning between reactive (active) and nonreactive (reservoir) compounds within each family. Gas phase thermodynamics, photochemistry, and kinetics would dictate, for example, that only about 1 percent of the chlorine resident in the lower stratosphere would be in the form of active Cl or ClO, the remainder existing in the reservoir compounds HCl and ClONO2. The consistency of this picture was recently challenged by the recognition that important chemical transformations take place on polar regions: the Airborne Antarctic Ozone Experiment (AAOE) and the Airborne Arctic Stratospheric Expedition (AASA). Following the discovery of the Antarctic ozone hole, Solomon et al. suggested that the heterogeneous chemical reaction: ClONO2(g)+HCl(s) yields Cl2(g)+HNO3(s) could play a key role in converting chlorine from inactive forms into a species (Cl2) that would rapidly dissociate in sunlight to liberate atomic chlorine and initiate ozone depletion. The symbols (s) and (g) denote solid phase, or adsorbed onto a solid surface, and gas phase, respectively, and represent the approach by which such a reaction is modeled rather than the microscopic details of the reaction. The reaction was expected to be most important at altitudes where PSC's were most prevalent (10 to 25 km), thereby extending the altitude range over which chlorine compounds can efficiently destroy ozone from the 35 to 45 km region (where concentrations of active chlorine are usually highest) to lower altitudes where the ozone concentration is at its peak. This chapter will briefly review the current state of knowledge of heterogeneous processes in the stratosphere, emphasizing those results obtained since the World Meteorological Organization (WMO) conference. Sections are included on laboratory investigations of heterogeneous reactions, the characteristics and climatology of PSC's, stratospheric sulfate aerosols, and evidence of heterogeneous chemical processing.

Poole, Lamont R.↗
NASA NTRS1993

Thermodynamic data for fifty reference elements

This report is a compilation of thermodynamic functions of 50 elements in their standard reference state. The functions are C(sub p)(sup 0), (H(sup 0)(T) - H(sup 0)(0)), S(sup 0)(T), and -(G(sup 0)(T) - H(sup 0)(O)) for the elements Ag, Al, Ar, B, Ba, Be, Br2, C, Ca, Cd, Cl2, Co, Cr, Cs, Cu, F2, Fe, Ge, H2, He, Hg, I2, K, Kr, Li, Mg, Mn, Mo, N2, Na, Nb, Ne, Ni, O2, P, Pb, Rb, S, Si, Sn, Sr, Ta, Th, Ti, U, V, W, Xe, Zn, and Zr. Deuterium D2 and electron gas e(sup -) are also included. The data are tabulated as functions of temperature as well as given in the form of least-squares coefficients for two functional forms for C(sub p)(sup 0) with integration constants for enthalpy and entropy. One functional form for C(sub p)(sup 0) is a fourth-order polynomial and the other has two additional terms, one with T(exp -1) and the other with T(exp -2). The gases Ar, D2, e(sup -), H2, He, Kr, N2, Ne, O2, and Xe are tabulated for temperatures from 100 to 20,000 K. The remaining gases Cl2 and F2 are tabulated from 100 to 6000 K and 1000 to 6000 K. The second functional form for C(sub p)(sup 0) has an additional interval from 6000 to 20,000 K for the gases tabulated to 20,000 K. The fits are constrained so that the match at the common temperature endpoints. The temperature ranges for the condensed species vary with range of the data, phase changes, and shapes of the C(sub p)(sup 0) curves.

Mcbride, Bonnie J.↗
NASA NTRS1993

Laser flash photolysis studies of atmospheric free radical chemistry using optical diagnostic techniques

Some recent studies carried out in our laboratory are described where laser flash photolytic production of reactant free radicals has been combined with reactant and/or product detection using time-resolved optical techniques to investigate the kinetics and mechanisms of important atmospheric chemical reactions. Discussed are (1) a study of the radical-radical reaction O + BrO yields Br + O2 where two photolysis lasers are employed to prepare the reaction mixture and where the reactants O and BrO are monitored simultaneously using atomic resonance fluorescence to detect O and multipass UV absorption to detect BrO; (2) a study of the reaction of atomic chlorine with dimethylsulfide (CH3SCH3) where atomic resonance fluorescence detection of Cl is employed to elucidate the kinetics and tunable diode laser absorption spectroscopy is employed to investigate the HCl product yield; and (3) a study of the aqueous phase chemistry of Cl2(-) radicals where longpath UV absorption spectroscopy is employed to investigate the kinetics of the Cl2(-) + H2O reaction.

Wine, Paul H.↗
NASA NTRS1973

Strength of Chemical Bonds

Students are not generally made aware of the extraordinary magnitude of the strengths of chemical bonds in terms of the forces required to pull them apart. Molecular bonds are usually considered in terms of the energies required to break them, and we are not astonished at the values encountered. For example, the Cl2 bond energy, 57.00 kcal/mole, amounts to only 9.46 x 10(sup -20) cal/molecule, a very small amount of energy, indeed, and impossible to measure directly. However, the forces involved in realizing the energy when breaking the bond operate over a very small distance, only 2.94 A, and, thus, f(sub ave) approx. equals De/(r - r(sub e)) must be very large. The forces involved in dissociating the molecule are discussed in the following. In consideration of average forces, the molecule shall be assumed arbitrarily to be dissociated when the atoms are far enough separated so that the potential, relative to that of the infinitely separated atoms, is reduced by 99.5% from the potential of the molecule at the equilibrium bond length (r(sub e)) for Cl2 of 1.988 A this occurs at 4.928 A.

Christian, Jerry D.↗
NASA NTRS1997

Can Chlorine Anion Catalyze the Reaction fo HOCl with HCl?

The reaction of HOCl + HCl -> Cl2 + H20 in the presence of Cl has been studied using ab initio methods. This reaction has been shown to have a high activation barrier of 46.5 kcal/mol. The chlorine anion, Cl- is found to catalyze the reaction, viz. two mechanisms. The first involves Cl- interacting through the concerted four-center transition state of the neutral reaction. The other mechanism involves the formation of a HCl-HOCl-Cl- intermediate which dissociates into Cl2 + Cl- + H20. The steps are found to have no barriers. The overall exothermicity is 15.5 kcal/mol.

Richardson, S. L.↗
NASA NTRS2001

Thermodynamic Data for Fifty Reference Elements

This report is a compilation of thermodynamic functions of 50 elements in their reference state. The functions are: C(sup 0, sub p), {H(T)-H(sup 0)(0)}, S(sup 0)(T), and - {G(sup 0)(T) - H(sup 0)(0)} for the elements Ag, Al, Ar, B, Ba, Be, Br2, C, Ca, Cd, Cl2, Co, Cr, Cs, Cu, F2, Fe, Ge, H2, He, Hg, I2, K, Kr, Li, Mg, Mn, Mo, N2, Na, Nb, Ne, Ni, O2, P, Pb, Rb, S, Si, Sn, Sr, Th, Th, Ti, U, V, W, Xe, Zn, and Zr. Deuterium D, and electron gas e(sup -) are also included. The data are tabulated as functions of temperature as well as given in the form of least-squares coefficients for two functional forms for C(sup 0, sub p) with integration constants for enthalpy and entropy. One functional form for C(sup 0, sub p) is a fourth-order polynomial and the other has two additional terms, one with T(sup -1) and the other with T(sup -2). The gases Ar, D2, e(sup -), H2, He, Kr, N2, Ne, O2, and Xe are tabulated for temperatures from 100 to 20 000 K. The remaining gases Cl2 and F2 are tabulated from 100 to 6000 K. The polynomial functional form for C(sup 0, sub p) for all these gases is split into two temperature intervals of 200 to 1000 K and 1000 to 6000 K. The second functional form for (sup 0, sub p) has an additional interval from 6000 to 20 000 K for the gases tabulated to 20 000 K. The fits are constrained so that the properties match at the common temperature endpoints. The temperature ranges for the condensed species vary with range of the data, phase changes, and shapes of the C(sup 0, sub p) curves.

McBride, Bonnie J.↗
NASA NTRS2001

Studies of Elementary Reactions of Chemical Importance in the Atmospheres of Planets

The methyl self-reaction was studied at T = 298 K and 202 K and at three different pressures, P = 0.5, 1.0, and 2.1 Torr. The experimental measurements were performed in our discharge flow-mass spectrometer (DF-MS) apparatus. The methyl radicals were generated by the reaction of F with methane. Passing a mixture of molecular fluorine, F2, in helium through a microwave cavity generated the atomic fluorine reagent. The atomic F enters the flow tube through a rear port on the flow tube. The methane reagent enters the flow tube through a movable injector located coaxial in the flow tube. The decay of methyl radical signal was monitored at a mass/charge ratio (m/z) of 15 as a function of the injector distance. To minimize secondary chemistry from the reaction CH3 + F to CH2 + HF the initial [CH4](sub 0)/[F](sub 0) was above 37.0 and typically 100. This ensures a 1:1 relationship between initial [F] and [CH3]. A titration of F with excess Cl2 yields the initial [F](sub 0). Our experimental methodology to accurately measure the mass spectrometer scaling factor, i.e., the relationship between initial signal and [CH3](sub 0) has been improved. Now we measure the CH3 signal decay under exponential decay conditions at low initial [F](sub 0), 3x10(exp 11) molecule/cc, in the presence of Cl2. This minimizes the second-order decay contributed by the CH3 self-reaction and a simple extrapolation of the 1n(signal) vs time plot to t = 0 gives the initial signal. This provides the desired relationship between initial signal at 15 amu and [CH3](sub 0). The resulting calibration is then applied to the observed decay of the CH3 signal at high concentrations of CH3 assuming linearity of this scaling factor.

Nesbitt, Fred L.↗
NASA NTRS2003

Studies of Elementary Reactions of Chemical Importance in the Atmospheres of Planets

The paper discusses the following: 1. F + Cl2 Kinetics. Absolute rate constant for the reaction F(P-2) with Cl2 has been measured using the discharge flow kinetics technique coupled to mass spectrometric detection at T = 180 - 360 K and 1 Torr He nominal pressure. 2. Vapor pressure system. The main effort on the vapor pressure system involved the design and construction of an insulated enclosure ("Bakeout Box") to improve the uniformity of heating during the bakeout process. 3. Sunphotometer System. This period saw the completion of the two-channel sunphotometer, its calibration, and two field deployments. 4. Vibrational-to-translation (V-T) transfer rates for light hydrocarbons at low temperatures are important parameters in thermal-structure models of the upper atmospheres of the outer planets and their satellites. However, the required data are either simply not available or do not extend to the low temperatures found in those systems. Because methane is such an important constituent in outer planet atmospheres, we have initiated a program to measure the temperature dependence of (V-T) rates for its relaxation by appropriate collision partners. 5. The central focus of this research has been the vapor phase nucleation and growth of metals/refractory species into small particles and the aggregation of these primary particles into larger structures. These topics are part of the broader goal of understanding the conditions under which interstellar dust grains condense from stellar outflows and how these small dust grains coagulate into larger bodies such as planetesimals or planets.

Nesbitt, Fred L.↗