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At least 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Rocket observation of the N II 2143 A emission in an aurora

Using a rocket-mounted spectrometer with a multichannel detector, the existence of the N II 2143 A doublet in the auroral ultraviolet spectrum was confirmed. The measured intensity is in agreement with previous auroral observations and is consistent with a peak electron-impact cross section of 1-2 x 10 to the -18th sq cm. By comparing an altitude profile of the 2143 A emission to the N2(+) 3914 A emission, a deactivation rate for the N(+)(5S) state was obtained. The most likely quencher is N2, although the possibility of a reaction with O2 cannot be ruled out. For N2, the deduced value of the quenching coefficient equals 5.5 x 10 to the -10th cu cm/s.

Siskind, David E.↗
NASA NTRS1987

Chemical processes in Triton's atmosphere and surface

The Neptune moon Triton may have an appreciable atmosphere; the preliminary calculations of Delitsky (1983) have suggested that there should be a significant resultant chemistry in a possible N2 ocean with dissolved CH4, given charged-particle radiolysis of gaseous mixtures and gamma radiolysis of N2-CH4 solutions. The latter will yield substantial quantities of organic products which will be partially soluble in any N2-CH4 liquid present. Attention is presently given to the energy sources available for Triton, in order to estimate rates of synthesis and ascertain the possible history of such simple and complex organic products on Triton's surface.

Delitsky, M. L.↗
NASA NTRS1986

Current status of the prebiotic synthesis of small molecules

Experiments designed to simulate conditions on the primitive earth and to demonstrate how the organic compounds that made up the first living organisms were synthesized are described. Simulated atmospheres with CH4, N2, NH3, and H2O were found to be most effective for synthesis of small prebiotic molecules, although atmospheres with H2, CO, N2, and H2O, and with H2, CO2, N2, and H2O also give good yields of organic compounds provided the H2/CO and H2/CO2 ratios are above 1 and 2, respectively. The spark discharge (which is a good source of HCN) and UV light are also important. Reasonable prebiotic syntheses were worked out for the amino acids that occur in proteins (with the exception of lysine, arginine, and histidine), and for purines, pyrimidines, sugars, and nicotinic acid. Many of the molecules that have been produced in these simulated primitive-earth experiments are found in carbonaceous chondrites.

Miller, Stanley L.↗
NASA NTRS1988

Method of producing high T(subc) superconducting NBN films

Thin films of niobium nitride with high superconducting temperature (T sub c) of 15.7 K are deposited on substrates held at room temperature (approx 90 C) by heat sink throughout the sputtering process. Films deposited at P sub Ar 12.9 + or - 0.2 mTorr exhibit higher T sub c with increasing P sub N2,I with the highest T sub c achieved at P sub n2,I= 3.7 + or - 0.2 mTorr and total sputtering pressure P sub tot = 16.6 + or - 0.4. Further increase of N2 injection starts decreasing T sub c.

Thakoor, Sarita↗
NASA NTRS1988

Spectral signature of the beam plasma discharge

The effect of the beam current on the spectrum of a beam plasma discharge (BPD) in N2 at 50, 100, or 400 microtorr is investigated experimentally in the 2.6-m chamber described by Bernstein et al. (1983). The results are presented graphically and discussed in detail. An increase in the ratio of first positive N2 emissions to first negative N2(+) emissions at BPD onset is shown to disappear at currents above the BPD threshold and is attributed to a large population of suprathermal electrons.

Hallinan, T. J.↗
NASA NTRS1988

Spectra of van der Waals complexes (dimers) with applications to planetary atmospheres

Spectral features observed in the atmosphere of Titan by the Voyager IR experiment have been attributed to weakly bound complexes of N2 and H2, dominant and minor constituents, respectively. The abundance of H2-N2 dimers there was computed. Current calculations include quantitative spectral line positions and intensities for N2-Ar and CO2-CO2 relating to Titan and Earth, and to Mars and Venus, respectively. This work suggests applications to spectra of planetary atmospheres obtained in spacecraft missions.

Fox, Kenneth↗
NASA NTRS1989

Measurements of argon broadened Lorentz width and pressure-induced line shift coefficients in the nu4 band of (C-12)H4

Room temperature argon broadened halfwidth and pressure-induced line shift coefficients have been determined for 118 transitions in the nu4 band of (C-12)H4 from analysis of high resolution laboratory absorption spectra recorded with the McMath Fourier transform spectrometer operated on Kitt Peak by the National Solar Observatory. Transitions up to J-double-prime = 12 have been measured using a nonlinear least-squares spectral fitting procedure. The variation of the measured halfwidth coefficients with symmetry type and rotational quantum number is very similar to that measured previously for N2 and air broadening, but the absolute values of the argon broadening coefficients are all smaller. On average, the ratio of the argon broadened halfwidth coefficient to the corresponding N2 broadened halfwidth coefficient is 0.877 + or - 0.017 (2 Sigma). More than 95 percent of the pressure-induced shifts are negative with values ranging from -0.0081 to +0.0055/cm atm. The pressure shifts in argon are nearly equal to corresponding values measured previously in N2 and air.

Rinsland, Curtis P.↗
NASA NTRS1989

Biological nitrogen fixation under primordial Martian partial pressures of dinitrogen

One of the most striking differences between the conditions on early Mars and earth was a low (18 mb) partial pressure of N2 (pN2) on early Mars, as opposed to 780 mb N2 on earth. To investigate the possibility of biological nitrogen fixation under conditions of early Mars, experiments were carried out on the growth of Azotobacter vinelandii and Azomonas agilis in nitrogen-free synthetic medium under various partial pressures of N2 (ranging from 780 to 0 mb). It was found that, although the biomass, cell number, and growth rate of these bacteria decreased with decreasing pN2 values below pN2 of 400 mb, both microorganisms were capable of growing at pN2 as low as 5 mb (but not at of below 1 mb), indicating that biological fixation of nitrogen could have occurred on primordial Mars.

Klingler, J. M.↗
NASA NTRS1990

Electron energy spectrum and magnetic interactions in high-T(sub c) superconductors

The character of magnetic interactions in La-Sr-Cu-O and Y-Ba-Cu-O systems is of primary importance for analysis of high-T(sub c) superconductivity in these compounds. Neutron diffraction experiments showed the antiferromagnetic ground state for nonsuperconducting La2CuO4 and YBa2Cu3O6 with the strongest antiferromagnetic superexchange being in the ab plane. The nonsuperconducting '1-2-3' system has two Neel temperatures T sub N1 and T sub N2. The first one corresponds to the ordering of Cu atoms in the CuO2 planes; T sub N2 reflects the antiferromagnetic ordering of magnetic moments in CuO chains relatively to the moments in the planes T sub N1 and T sub N2 depend strongly on the oxygen content. Researchers describe magnetic interactions in high-T superconductors based on the Linear Muffin-Tin Orbitals (LMTO) band structure calculations. Exchange interaction parameters can be defined from the effective Heisenberg hamiltonian. When the magnetic moments are not too large, as copper magnetic moments in superconducting oxides, J sub ij parameters can be defined through the non-local magnetic susceptibility of spin restricted solution for the crystal. The results of nonlocal magnetic susceptibility calculations and the values of exchange interaction parameters for La CuO and YBa2Cu3O7 systems are given in tabular form. Strong anisotropy of exchange interactions in the ab plane and along the c axis in La2CuO4 is obviously seen. The value of Neel temperature found agrees well with the experimental data available. In the planes of '1-2-3' system there are quite strong antiferromagnetic Cu-O and O-O interaction which appear due to holes in oxygen subbands. These results are in line with the magnetic model of oxygen holes pairing in high-T(sub c) superconductors.

Turshevski, S. A.↗
NASA NTRS1990

Single pulse vibrational Raman scattering by a broadband KrF excimer laser in a hydrogen-air flame

Spontaneous vibrational Raman scattering (VRS) is produced by a broadband excimer laser at 248 nm (KrF) in a H2-air flame, and VRS spectra are recorded for lean, stoichiometric, and rich flames. Except at very lean flame conditions, laser-induced fluorescence (LIF) processes interfere with VRS Stokes lines from H2, H2O, and O2. No interference is found for the N2 Stokes and N2 anti-Stokes lines. In a stoichiometric H2/air flame, single-pulse measurements of N2 concentration and temperature (by the VRS Stokes to anti-Stokes ratio) have a relative standard deviation of 7.7 and 10 percent, respectively. These single pulse measurement errors compare well with photon statistics calculations using measured Raman cross sections.

Pitz, Robert W.↗
NASA NTRS1990

Preliminary plume characteristics of an arcjet thruster

An experimental program initiated to characterize the near field of an arcjet plume is described. The complete emission spectrum from 3200 to 7200 A at the nozzle exit plane detected the electronically excited species N2, N2(+), NH, and H, indicating excitation, dissociation, ionization, and recombination in the nozzle. Axial intensity profiles indicated an exponential decay in excited state population for H(alpha), H(beta), and NH. The rate of axial decay indicated lower velocities for NH than H in the plume and population of the third excited energy state of hydrogen from the decay of higher energy levels. Rotational temperatures ranged from 750 K for N2 to 2500 K for NH. Based on these results, the arcjet plume is found to be a highly nonequilibrium plasma. Anode electrical configuration is found to have a large effect on the spectral intensities measured in the plume.

Manzella, David H.↗
NASA NTRS1990

Plasma puff initiation of high Coulomb transfer switches

The plasma-puff triggering mechanism based on a hypocycloidal pinch geometry was investigated to determine the optimal operating conditions for the azimuthally uniform surface flashover which initiates plasma-puff under wide range of fill gas pressure of Ar, He and N2. The optimal fill gas pressure for the azimuthally uniform plasma-puff was about 120 mTorr and 450 Torr for He and N2, and between 120 mTorr and 5 Torr for Ar. The inverse pinch switch was triggered with the plasma-puff and the switching capability under various electrical parameters and working gas pressures of Ar, He and N2 was determined. It was also shown that the azimuthally uniform switching discharges were dependent on the type of fill gas and its fill pressure. A new concept of plasma-focus driven plasma-puff was also discussed in comparison with the hypocycloidal pinch plasma-puff triggering. The main discharge of inverse pinch switch with plasma-focus driven plasma-puff trigger is found to be more azimuthally uniform than that with hypocycloidal pinch plasma-puff trigger in a gas pressure region between 80 mTorr and 1 Torr.

Venable, D. D.↗
NASA NTRS1990

LIF and emission studies of copper and nitrogen

A technique is developed to determine the rotational temperature of nitrogen molecular ion, N2(+), from the emission spectra of B-X transition, when P and R branches are not resolved. Its validity is tested on simulated spectra of the 0-1 band of N2(+) produced under low resolution. The method is applied to experimental spectra of N2(+) taken in the shock layer of a blunt body at distances of 1.91, 2.54, and 3.18 cm from the body. The laser induced fluorescence (LIF) spectra of copper atoms is analyzed to obtain the free stream velocities and temperatures. The only broadening mechanism considered is Doppler broadening. The temperatures are obtained by manual curve fitting, and the results are compared with least square fits. The agreement on the average is within 10 percent.

Akundi, Murty A.↗
NASA NTRS1991

Vibrational relaxation in very high temperature nitrogen

Vibrational relaxation of N2 molecules is considered at temperatures up to 40,000 K in gas mixtures that contain electrons as well as heavy collision partners. The theory of vibrational relaxation due to N2-N2 collisions is fit to experimental data to 10,000 K by choice of the shape of the intermolecular potential and size of the collision cross section. These values are then used to extrapolate the theory to 40,000 K.

Hansen, C. Frederick↗
NASA NTRS1991

Collisional excitation and radiative properties of N II - The strong intercombination (1D - 3P0) transition at 748 A

Laboratory measurements of EUV emission from electron-excited N2 have been obtained at medium resolution, providing N II EUV emission cross section measurements and allowing the confirmation of recent calculations by Fawcett (1987) indicating the presence of a strong intercombination line in N II at 748.37 A. The most recently available data are used to predict the basic collisional and radiative properties of N II, the plasma diagnostic properties are briefly explored, and radiative cooling coefficients are given. Some basic properties of electron-excited N II and N2 are examined in the EUV in order to diagnose emission spectra of the earth and Titan. The N II emissions in the earth dayglow, particularly at 916 A, are much brighter than current estimates of source rates. The N II 1085 A line in the dayglow contains a significant component from dissociative photoionization excitation. The N II 1085 A, 916 A, and 670 A lines in the Titan dayglow spectrum appear to be compatible with direct electron excitation of N2.

Tripp, T. M.↗
NASA NTRS1991

Vibrational relaxation and dissociation in nitrogen

Calculations of the vibrational and dissociation transition probabilities are made for N2-N2 and N2-N collisions by means of a semiclassical N-state approximation. The flaws in previous techniques are reviewed, with special attention given to the prediction of overtones. The method presented ignores the effects of molecular rotation and employs a revised extended Rydberg intermolecular potential to describe diatom-diatom and diatom-atom collisions. The collision velocities investigated exhibit probabilities of less than unity by means of the N-state method. The continuum is quantized to treat dissociation, and the collision results demonstrate probability enhancements for V-V-T transitions in both bound-bound and bound-free transitions. The technique is of particular interest for the theoretical modeling of reentry flows such as those encountered in aerobraking maneuvers.

Varghese, Philip L.↗
NASA NTRS1991

Electron energy spectrum and magnetic interactions in high-Tc superconductors

The character of magnetic interactions in La-Sr-Cu-O and Y-Ba-Cu-O systems is of primary importance for analysis of high-T(sub c) superconductivity in these compounds. Neutron diffraction experiments showed the antiferromagnetic ground state for nonsuperconducting La2CuO4 and YBa2Cu3O6 with the strongest antiferromagnetic superexchange being in the ab plane. The nonsuperconducting '1-2-3' system has two Neel temperatures T(sub N1) and T(sub N2). The first one corresponds to the ordering of Cu atoms in the CuO2 planes; T(sub N2) reflects the antiferromagnetic ordering of magnetic moments in CuO chains relatively to the moments in the planes T(sub N1) and T(sub N2) which depend strongly on the oxygen content. Researchers describe magnetic interactions in high-T superconductors based on the Linear Muffin-Tin Orbitals (LMTO) band structure calculations. Exchange interaction parameters can be defined from the effective Heisenberg Hamiltonian. When the magnetic moments are not too large, as copper magnetic moments in superconducting oxides, J(sub ij) parameters can be defined through the non-local magnetic susceptibility of spin restricted solution for the crystal. The results of nonlocal magnetic susceptibility calculations and the values of exchange interaction parameters for La CuO and YBa2Cu3O7 systems are given in tabular form. Strong anisotropy of exchange interactions in the ab plane and along the c axis in La2CuO4 is obviously seen. The value of Neel temperature found agrees well with the experimental data available. In the planes of '1-2-3' system there are quite strong antiferromagnetic Cu-O and O-O interaction which appear due to holes in oxygen subbands. These results are in line with the magnetic model of oxygen holes pairing in high-T(sub c) superconductors.

Turshevski, S. A.↗
NASA NTRS1992

Rate calculations for the simultaneous vibrational relaxation and dissociation of nitrogen

Experimental data on vibrational relaxation and dissociation rates in highly nonequilibrium gases are scarce. Recently there have been several attempts at generating these rates by direct calculation of inelastic collision cross-sections. Some issues that need to be considered if such calculations are to be used as a basis for analysis and design are examined. In particular, the following are examined: (1) collinear vs 3D scattering models, (2) accurate intermolecular potentials, (3) closed channels and acceleration schemes, (4) thermal averaging and thermal rates, and (5) code validation. It has been necessary to confront these issues during the course of N2-N2 and N2-N inelastic cross-section calculations.

Gonzales, David A.↗