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At least 739 records · Page 41
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NASA NTRS1985

On the production of N(+) by energetic electrons

Calculations of the ratio of N(+) to total N2 ion production for auroral electrons which give a value of 0.16 compared to the value of 0.22 that has been assumed in a recent publication is presented. The corresponding ratio for photoelectron production is 0.05, which makes photoelectron production of N(+) negligible compared to photodissociative production. The ratio of 3914-A to total ion production is found to be 0.07 for auroral electrons and a similar 0.06 for photoelectrons. The 3371-A ratio to total N2 ion production is 0.09. This calculation also reveals that the secondary electrons in auroras, with energies less than 100 eV, produce only about one third of the total number of ions produced. Only one quarter of the N(+) ions are created by secondary electrons.

Richards, P. G.↗
NASA NTRS1985

Physical state of volatiles on the surface of triton

Several possible configurations for volatiles on Triton are assessed. It is concluded that the simplest volatile configuration which best satisfies the constraints with the least number of ad hoc assumptions is N2 and CH4 both in solid forms, perhaps partly as a microscopic mixture, but more probably as a disequilibrium assemblage, nonuniformly distributed. Thermodynamic equilibrium is then limited by seasonal transport and the finite diffusion time of CH4 in crystalline N2. Although a nitrogen ocean cannot be excluded, it requires very restrictive assumptions.

Lunine, J. I.↗
NASA NTRS1985

The photochemistry of the early atmosphere

The composition of the earth's present atmosphere is described. The formation of the earth from the coalescence and accretion of the refractory elements of the solar nebula is examined. Two possible compositions of the prebiological paleoatmosphere, which are a reducing atmosphere of CH4, NH3, and H2 or a mildly reducing atmosphere of H2O, CO2, and N2, and their photochemistry are analyzed. General photochemical and chemical processes are reviewed. The use of the coupled continuity-transport equation to calculate the vertical distribution of each species is discussed. A study of the photochemical process of CH4 and NH3 reveals that the reducing atmosphere could not possibly exist. An analysis of the photochemistry and chemistry of the H2O, CO2, and N2 atmosphere reveals that the photodissociation of H2O and CO2 results in a prebiotic source of O2, H2CO, and HCN, which are the components for the evolution of photosynthetic organisms and a strongly oxidizing atmosphere. The reactions which produce O2 and H2CO from H2O and CO2, and the relation between H2O and CO2 concentrations and O2 levels are investigated. The formation of O3 photochemically from O2 is explained.

Levine, J. S.↗
NASA NTRS1986

Titan's latitudinal temperature distribution and seasonal cycle

Voyager IRIS brightness temperature measurements of Titan at a wavelength of 530/cm are crudely indicative of ground or lower tropospheric temperatures and indicate 93 K for the equator and 91 K for both northern and southern high latitudes. The symmetry between north and south is unexpected for the time of Voyager encounter (Northern Titan spring). It is shown that this near-symmetry can arise naturally in a model where the poles are 'pinned' year-round at the dew point of CH4-N2 lakes or, more probably, a CH4-N2 rich surface layer on a deep ethane-rich ocean. For a polar temperature of 91 K, the model implies that the atmosphere contains somewhat less than 8 percent mole fraction of CH4.

Stevenson, D. J.↗
NASA NTRS1986

Photochemistry of methane and the formation of hydrocyanic acid (HCN) in the earth's early atmosphere

A one-dimensional photochemical model is used to analyze the photochemistries of CH4 and HCN in the primitive terrestrial atmosphere. CH4, N2, and HCN photolysis are examined. The background atmosphere and boundary conditions applied in the analysis are described. The formation of HCN as a by-product of N2 and CH4 photolysis is investigated; the effects of photodissociation and rainfall on HCN is discussed. The low and high CH4 mixing ratios and radical densities are studied.

Zahnle, K. J.↗
NASA NTRS1986

Diode laser measurements of line strengths and widths in the 4.5-micron bands of N2O

Line-strength measurements in the N2O nu3-fundamental region using a tunable diode-laser spectrometer. From these measurements and the Herman-Wallis factor determined by Boissy et al. (1975), the nu-3-fundamental band strength is found to be 1203 + or - 22 per sq cm atm at 297 K. Line-broadening parameters for two nu-3-fundamental lines were determined using nitrogen (N2) as the broadening gas. Measured strengths and N2 line-broadening parameters for several hot-band lines are also presented.

Lowenstein, M.↗
NASA NTRS1986

The reactive thermal conductivity of air at high temperatures

This paper presents the thermal conductivity of air from the dissociation and ionization reactions of the nitrogen and oxygen species in air from 1000 K to 25,000 K. The results for nitrogen are compared with results for the nonreactive (frozen) contribution to the thermal conductivity of the 'nitrogen system' (N2, N, N/+/, and the electron, e). At 6000 K, the contribution to the thermal conductivity from the dissociation of N2 is more than an order of magnitude greater than the frozen thermal conductivity and, at 15,000 K, the contribution to the thermal conductivity from the ionization of nitrogen atoms is about as large as the contribution from the frozen thermal conductivity.

Biolsi, L.↗
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 NTRS1987

The catalysis of hydrazines

Hydrazine sulfate in a hot aqueous solution can be catalyzed in the direction of 3 N2H4 = 4 NH3 + N2. Free hydrazine in a hot aqueous solution dissociates in the presence of platinum in the following direction: 2 N2H4 = 2 NH3 + N2 + H2. In the presence of sodium hydroxide, the catalytic dissociation of hydrazine takes a third direction: 3 N2H4 = 2 NH3 + 2 N3 + 3 H2.

Tanatar, S.↗
NASA NTRS1986

Pressure and temperature dependences of the reaction of OH with nitric acid

Rate constants for the reaction of OH with HNO3 have been measured by using a laser flash photolysis resonance absorption technique at 298 and 248 K in the presence of 10-730 Torr of He, N2, and SF6. A dependence on total pressure was observed with rate constant values increasing at 298 K from 1.11 x 10 to the -13th cu cm/molecule/s at 10 Torr to 1.45 x 10 to the -13th cu cm/molecule/s at 730 Torr, and at 248 K from 1.87 x 10 to the -13th cu cm/molecule/s at 10 Torr to 3.07 x 10 to the -13th cu cm/molecule/s at 730 Torr with helium as the diluent gas. Falloff behavior occurred at lower pressures with SF6 or N2 as the diluent gas. Extrapolated zero pressure rate constants were determined and correspond to an Arrhenius activation energy of E/R = -710 K.

Stachnik, R. A.↗
NASA NTRS1987

Energetic He(+) precipitation in a mid-latitude aurora

Ground-based spectral observations of a midlatitude aurora on Sept. 22, 1982 indicated that the observed emissions were caused by either O(+) or H(+) energetic ions. In this paper, the model of Ishimoto et al. (1986) is used to simulate the interaction between precipitating energetic He(+) and a neutral atmosphere of He, O, and N2, computing the atmospheric impacts in terms of heating, ionization, and excitation of certain emissions and comparing the results with those obtained earlier with O(+) as the energetic flux. It was found that, of the total energy influx, approximately 50 percent goes into ionization, compared with 2 percent in the case of O(+), and 40 percent is backscattered or escapes, compared with 16 percent in the case of O(+). By contrast, He(+) is much less efficient at heating the atmosphere and does not excite the N2 2P system. It is concluded that the aurora observed on Sept. 22 is well explained by an influx of energetic O(+) together with a 6 percent admixture of He(+).

Ishimoto, M.↗
NASA NTRS1987

Tunable diode laser measurements of formaldehyde foreign-gas broadening parameters and line strengths in the 9-11-micron region

A tunable diode laser spectrometer has been used to determine pressure broadening coefficients due to collision with the foreign gases air, H2, O2, and N2 in the nu4 and nu6 bands of H2CO between 9 and 11 microns. Absolute line strengths for twenty-eight transitions have also been determined. The broadening coefficients are very similar to theoretical literature values in the cases of air, N2, and O2. The H2-H2CO values are in good agreement with earlier experimental millimeter-wave results.

Nadler, Shachar↗
NASA NTRS1987

Spectral determination of nitrogen vibrational temperatures

A technique for determining the vibrational temperature of nitrogen molecules is found from the emission of the N2 first positive spectrum. The technique involves calculating wavelength integrals of portions of the emission spectrum associated with transitions from the ststes B3Pi(g)(v-prime) to A3 Sigma(u +)(v-double prime) where Delta = 2, 3, etc. Ratios of the integrated intensities are then correlated with vibrational temperature. The dependence of the technique on rotational temperature is considered and less dependence is obtained if the overlap between Delta v-regions is accounted for. The technique is applied to the shock layer of a blunt body in an arc jet flow. The N2(1+) spectrum is measured in the shock layer to obtain the intensity integral ratios. From these ratios estimates of the vibrational temperature are found from the correlation which agree quite well with calculated temperatures in the shock layer flow.

Blackwell, Harvel E.↗
NASA NTRS1987

Precision ozone calibration system based on vapor pressures of ozone

A precision ozone calibration system for stratospheric research has been developed and evaluated. Vapor pressures above solid ozone are mixed with a carrier gas (N2) to produce stratospheric ozone mixing ratios at total pressures of 1 to cover 20 torr. The uncertainty in the ozone mixing ratios is approximately + or - 1.5 percent, the stability of ozone is + or - 0.3 percent. Experiments to be calibrated may sample the gas mixture over a wide range of flow rates; the maximum throughput of gas with corrections of less than 1 percent to ozone is about 200 torr 1/min. A mass spectrometer system continuously monitors the purity and stability of the N2-O3 gas mixture.

Mauersberger, K.↗
NASA NTRS1987

The production of excited molecular species by electron impact in high temperature nonequilibrium air

Low-energy electron-impact excitation cross sections of N2 and CO are calculated using the Schwinger multichannel formulation, and calculations are extended to the important threshold region where experimental measurement becomes difficult. Cross sections are used to determine the excitation rate coefficients for the production of the important radiative states of N2 at a variety of electronic, rotational, and vibrational temperatures. Excitation of these states requires at least 6.2 eV, and the rate coefficients increase with the electronic temperature. The dependence on the vibrational temperature is mainly determined by the shape of the potential function for the vibrational motion. A strong resonance feature near threshold is found for the excitation of CO, in agreement with previous measurements.

Huo, Winifred M.↗
NASA NTRS1987

Compatability of dispersion-strengthened platinum with resistojet propellants

Resistojets for the Space Station require long life and multipropellant capability. The choice of available materials to meet these requirements is limited. Dispersion-strengthened platinum was selected. Past results indicated that it should be suffieiently inert in candidate propellant environments and should be capable of operating at moderate temperatures for extended periods. A series of propellant compatibility tests was done with platinum strengthened with either yttria or zirconia. Data presented included the results of 1000-hr tests in CO2, H2, ammonia (NH3), N2, steam, hydrazine (N2H4), and methane (CH4); and 2000-hr tests in H2 and NH3. The platinum samples were tested at 1400 C in CO2, H2, NH3, N2, steam, and N2H4; at 500 C in CH4; and at 800 C in N2H4. The mass-loss results indicated material life, exptrapolated from experimental mass-loss data, in excess of 100 000 hr in all environments except steam and N2H4, where it was greater than or =45000 hr. Generally, on the basis of mass loss, there were no compatibility concerns in any of the environments considered. Optical and scanning electron microscopy were used to determine the effect of propellants on the material surface and to evaluate material stability.

Whalen, Margaret V.↗
NASA NTRS1987

Effects of microgravity on tissue perfusion and the efficacy of astronaut denitrogenation for EVA

A potentially flight-applicable, breath-by-breath method for measuring N2 elimination from human subjects breathing 100 percent O2 for 2-3 hr periods has been developed. The present report describes this development with particular emphasis on required methodological accuracy and its achievement in view of certain properties of mass spectrometer performance. A method for the breath-by-breath analysis of errors in measured N2 elimination profiles is also described.

Gerth, Wayne A.↗
NASA NTRS1987

Nonlinear effects in coplanar GaAs/InGaAs strained-layer superlattice directional couplers

The performance characteristics of InGaAs/GaAs strained-layer superlattice coplanar ridge-type directional couplers realized by molecular beam epitaxy are reported. The measured power transfer characteristics with 1.15 micron incident photoexcitation demonstrate nonlinear coupling due to absorption associated with the tails of the excitonic resonances in the quantum wells. From a theoretical fit of the measured data, the nonlinear refractive index coefficient, n2, of the multiquantum well is found to be 2.25 x 10 to the -7th sq cm/W. This agrees very well with a value of n2 = 1.9 x 10 to the-7th sq cm/W obtained independently on the same material from interferometric measurents.

Das, Utpal↗