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At least 73 records · Page 4

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NASA NTRS1979

Refinement of the aeronomically determined rate coefficient for the reaction of N2/+/ with O

An earlier aeronomic determination of the rate coefficient for the reaction N2(+) + O yields NO(+) + N using Atmosphere Explorer data indicated a small increase in the rate coefficient with ion temperature, contrary to laboratory observations. This was incorrectly attributed to neglect of an increase in the N2(+) recombination rate with vibrational excitation. Recent aeronomical results have shown that the rate coefficient for charge exchange of O(+)(2D) with N2 is about an order of magnitude smaller at thermal temperatures than at energies greater than 0.5 eV (i.e., energies at which laboratory measurements have been made). It is shown that the use of the smaller charge exchange rate coefficient coupled with recent results on N2 quenching of O(+)(2D) yields a temperature dependence in excellent agreement with the laboratory results for the rate coefficient.

Torr, D. G.↗

NASA NTRS1979

An experimental and theoretical study of the mean diurnal variation of O/+/, NO/+/, O2/+/, and N2/+/ ions in the mid-latitude F1 layer of the ionosphere

A theoretical model of the diurnal variations in the compositions of the ions O(+), NO(+), O2(+) and N2(+) in the midlatitude F1 layer is presented and compared with measurements made by AE-C. The theoretical model includes the rate coefficients and branching ratios for the dissociative recombination of NO(+), O2(+) and N2(+) with electrons and the ion-atom interchanges of O(+) with N2 and N2(+) with O. Input parameters to the model comprise measurements of ion and electron temperatures, neutral atmosphere composition, the solar EUV flux and the photoelectron spectrum. In general, model calculations are found to agree with satellite measurements, confirming the major ion sources and sinks of the photochemical model, which has an accuracy of + or - 60%.

Torr, D. G.↗

NASA NTRS1980

Comparison of the N2/+/ photochemistry at different phases of the solar cycle

Thermospheric and ionospheric data obtained on 12 orbits throughout 1978 are analyzed using the chemical scheme established during 1974 when the solar EUV intensities were less than half of those encountered in 1978. It is shown that this scheme, with some modification, applies to the more active period. Photoionization of N2 is found to be the major source of N2(+) in the F2 layer, by contrast with the charge exchange reaction of O+(2D) with N2, which was dominant for the lower solar activity. The results confirm the laboratory measurements of the dissociative recombination rate coefficient for N2 with electrons, as well as the theoretically calculated rate coefficient for the quenching of O+(2D) by electrons.

Torr, M. R.↗

NASA NTRS1983

Photochemistry of N2(+) in the daytime F region

The photochemistry of N2(+) in the daytime F region continues to be a source of concern due primarily to the uncertain roles of the metastable O+(2D) ion and possible vibrational excitation. This investigation adopts a unique subset of data from the Atmospheric Explorer C satellite that spans distinct regions near the low-latitude F peak wherein either chemical reactions or electron processes alternatively control the N2(+) abundances. Concentrations of N2(+) calculated according to current theory and including recent laboratory data for O+(2D) losses via N2 are found to exceed ionospheric observations between 220 and 400 km by a factor near 2. Relevant characteristics of the basic molecular ion concentration measurements are described, along with an analysis for select orbits conducted according to current photochemical equilibrium theory. Possible simple modifications of this theory are discussed in terms of the constraints suggested by the nature of the observations.

Breig, E. L.↗

NASA NTRS1984

Results of a comprehensive study of the photochemistry of N2(+) in the ionosphere

The improved match that can be obtained between the Atmospheric Explorer (AE) data on the ionospheric F layer N2(+) abundance and theoretical predictions by changing the dissociative recombination rate coefficient is demonstrated. Historically, models have overestimated the N2(+) concentration. It is shown that the calculated enhancement is due to charge exchange between 0(+)(2D) with N2. Increasing alpha by a factor of 2-3, at least in the orbits examined, can augment the destruction of vibrationally excited N2(+) ions. However, the validity of the correction is dependent on the availability of further laboratory data.

Abdou, W. A.↗

NASA NTRS1986

Effects of vibrational enhancement of N2 on the cooling rate of ionospheric thermal electrons

It is shown that the cooling rate of ionospheric thermal electrons by molecular nitrogen may be reduced by more than a factor of 3 as a result of the enhanced vibrational excitation of N2 from a number of chemical sources. Furthermore, under conditions of enhanced F region electron densities (greater than 10 to the 6 per cubic centimeter), N2 may act as a small net source rather than as a sink of electron thermal energy. The object of the study is to use results of the Atmospheric Explorer program and improved laboratory reaction rate measurements to evaluate the impact of N2 vibrational on the transfer of energy between N2 and thermal electrons.

Richards, P. G.↗

NASA NTRS1988

High-temperature shock formation of N2 and organics on primordial Titan

Theoretical models suggest that the initial form of nitrogen in Titan's atmosphere may have been NH3. The possible importance of strong shocks produced during high-velocity impacts accompanying the late stages of accretion are investigated as a method for converting NH3 to N2, of which Titan's atmosphere is now primarily composed. The focused beam of a high-power laser is used to simulate the effects of an impact in Titan's atmosphere. For mixtures of 10, 50, and 90 percent NH3, yields of 0.25, 1, and 6 x 20 to the 17th molecules of N2 per joule, respectively, were obtained. It is also found that the yield of HCN is comparable to that for N2. Several other hydrocarbons are produced, many with yields in excess of theoretical high-temperature-equilibrium models. The above yields, when combined with models of the satellite's accretion, result in a total N2 production comparable to that present in TItan's atmosphere and putative ocean.

Mckay, Christopher P.↗

NASA NTRS1989

Effects of H2O, CO2, and N2 Air Contaminants on Critical Airside Strain Rates for Extinction of Hydrogen-Air Counterflow Diffusion Flames

Coaxial tubular opposed jet burners (OJB) were used to form dish shaped counterflow diffusion flames (CFDF), centered by opposing laminar jets of H2, N2 and both clean and contaminated air (O2/N2 mixtures) in an argon bath at 1 atm. Jet velocities for flame extinction and restoration limits are shown versus wide ranges of contaminant and O2 concentrations in the air jet, and also input H2 concentration. Blowoff, a sudden breaking of CFDF to a stable ring shape, occurs in highly stretched stagnation flows and is generally believed to measure kinetically limited flame reactivity. Restore, a sudden restoration of central flame, is a relatively new phenomenon which exhibits a H2 dependent hysteresis from Blowoff. For 25 percent O2 air mixtures, mole for mole replacement of 25 percent N2 contaminant by steam increased U(air) or flame strength at Blowoff by about 5 percent. This result is consistent with laminar burning velocity results from analogous substitution of steam for N2 in a premixed stoichiometric H2-O2-N2 (or steam) flame, shown by Koroll and Mulpuru to promote a 10 percent increase in experimental and calculated laminar burning velocity, due to enhanced third body efficiency of water in: H + O2 + M yields HO2 + M. When the OJB results were compared with Liu and MacFarlane's experimental laminar burning velocity of premixed stoichiometric H2 + air + steam, a crossover occurred, i.e., steam enhanced OJB flame strength at extinction relative to laminar burning velocity.

Pellett, G. L.↗

NASA NTRS1991

Production of N(+)-asterisk from N2 + hnu - Effective EUV emission yields from laboratory and dayglow data

Photodissociative ionization of N2 into the unbound N2(+) H 2Sigma-g(+) state is identified as the parentage of a number of N(+) and N-excited states that contribute to the u.v. dayglow. Yields have been obtained for the production of extreme ultraviolet emission lines of N(+) and N from a laboratory experiment using a broadband synchrotron radiation source with fluorescence spectroscopy. The yields are termed 'effective', in that they are constant percentages of the H state cross section. These are compared wih effective yields needed to reproduce N II 1085 and 916 A lines from four dayglow observations using a model of solar energy deposition and photoelectron production and loss in the earth's thermosphere. The 1085 A effective yield measured in the laboratory (18 percent) agrees with that from the dayglow data (average of 17 percent) to well within experimental uncertainties. Thus, it is concluded that photodissociative ionization of N2 is the primary source of the N II 1085 A dayglow. However, there is an order of magnitude discrepancy among the various dayglow observations of the 1085/916 intensity ratio, only one of which is consistent with the laboratory observation of 4.4. Neither contamination by other dayglow features nor atmospheric extinction can account for the disparities. Laboratory measurements of N2 and O2 absorption cross sections at these wavelengths are also reported.

Meier, R. R.↗

NASA NTRS1991

The absorption coefficient of the liquid N2 2.15-micron band and application to Triton

The present measurements of the temperature dependence exhibited by the liquid N2 2.15-micron 2-0 collision-induced band's absorption coefficient and integrated absorption show the latter to be smaller than that of the N2 gas, and to decrease with decreasing temperature. Extrapolating this behavior to Triton's nominal surface temperature yields a new estimate of the N2-ice grain size on the Triton south polar cap; a mean N2 grain size of 0.7-3.0 cm is consistent with grain growth rate calculation results.

Grundy, William M.↗

NASA NTRS1993

Constraints on N2 in Neptune's atmosphere from Voyager measurements

It is shown that N2 may be present in the troposphere of Neptune in an amount difficult to evaluate but which could easily be as high as 0.003, while there is no evidence that it is present in the atmosphere of Uranus. The estimate of the helium abundance depends on the assumed value for N2. If there is no N2 in the observed region of the atmosphere of Uranus and an N2 mole fraction of 0.003 on Neptune, the central value of the estimates of the helium abundance are equal to 0.26 by mass in both planets, which is close to the protosolar value of 0.28. This would imply that the He/H2 ratios measured in the outer atmospheres of Uranus and Neptune are representative of the ratio in the primitive solar nebula and thus were not modified during planetary formation.

Conrath, B. J.↗

NASA NTRS1997

Temperature Dependence of the Collisional Removal of O2(A(sup 3)Sigma(sup +)(sub u), upsilon=9 ) with O2 and N2

The temperature dependence of the collisional removal of O2 molecules in the upsilon = 9 level of the A(sup 3)Sigma(sup +)(sub u) electronic state has been studied for the colliders O2 and N2, over the temperature range 150 to 300 K. In a cooled flow cell, the output of a pulsed dye laser excites the O2 to the upsilon = 9 level of the A(sup 3)Sigma(sup +)(sub u) state, and the output of a time-delayed second laser monitors the temporal evolution of this level via a resonance-enhanced ionization. We find the u thermally averaged removal cross section for O2 collisions is constant (approx. 10 A(sup 2)) between room temperature and 200 K, then increases rapidly with decreasing temperature, doubling by 150 K. In contrast, the N2 cross section at 225 K is approx. 8% smaller and gradually increases to a value at 150 K that is approx. 60% larger than the room temperature value. The difference between the temperature dependence of the O2 and N2 collision cross section implies that the removal by oxygen becomes more important at the lower temperatures found in the mesosphere, but removal by N2 still dominates.

Hwang, Eunsook S.↗

NASA NTRS1996

High Resolution UV Spectroscopy of H2 and N2 Applied to Observations of the Planets by Spacecraft

The next generation of high resolution UV imaging spacecraft are being prepared for studying the airglow and aurora of the Earth, the other terrestrial planets and the Jovian planets. To keep pace with these technological improvements we have developed a laboratory program to provide electron impact collision cross sections of the major molecular planetary gases (H2, N2, CO2, O2, and CO). Spectra under optically thin conditions have been measured with a high resolution (lambda/delta(lambda) = 50000) UV spectrometer in tandem with electron impact collision chamber. High resolution spectra of the Lyman and Wemer band systems of H2 have been obtained and modeled. Synthetic spectral intensities based on the J-dependent transition probabilities that include ro-vibronic perturbations are in very good agreement with experimental intensities. The kinetic energy distribution of H(2p,3p) atoms resulting from electron impact dissociation of H2 has been measured. The distribution is based on the first measurement of the H Lyman-alpha (H L(alpha)) and H Lyman-beta (H L(beta)) emission line Doppler profiles. Electron impact dissociation of H2 is believed to be one of the major mechanisms leading to the observed wide profile of H L-alpha from Jupiter aurora by the Hubble Space Telescope (HST). Analysis of the deconvolved line profile of H L-alpha reveals the existence of a narrow line peak (40 mA FWHM) and a broad pedestal base (240 mA FWHM). The band strengths of the electron excited N2 (C(sup 3) Pi(sub(upsilon) - B(sup 3)Pi(sub g)) second positive system have been measured in the middle ultraviolet. We report a quantitative measurement of the predissociation fraction 0.15 +/- 01(sup .045, sub .01) at 300 K in the N2 c'(sub )4 (1)sigma(sup +, sub g) - x(1)sigma(sup +, sub g)(00) band, with an experimental determination of rotational line strengths to be used to understand N2 EUV emission from Titan, Triton and the Earth.

Ajello, J.↗

NASA NTRS1997

Rotational Energy Transfer of N2 Gas Determined Using a New Ab Initio Potential Energy Surface

Rotational energy transfer between two N2 molecules is a fundamental process of some importance. Exchange is expected to play a role, but its importance is somewhat uncertain. Rotational energy transfer cross sections of N2 also have applications in many other fields including modeling of aerodynamic flows, laser operations, and linewidth analysis in nonintrusive laser diagnostics. A number of N2-N2 rigid rotor potential energy surface (PES) has been reported in the literature.

Huo, Winifred M.↗

NASA NTRS2002

Synthesis of HCN and HNC in Ion-Irradiated N2-Rich Ices

Near-IR observations reveal that N2-rich ice containing small amounts of CH4, and CO, is abundant on the surfaces of Triton, a moon of Neptune, and Pluto. N2-rich ices may also exist, in interstellar environments. To investigate the radiation chemistry of such ices we performed a systematic IR study of ion-irradiated Nz-rich mixtures containing CH4 and CO. Irradiation of N2 + CH4 mixtures at 12 K, showed that HCN, HNC, diazomethane, and NH3 were produced. We also found that UV photolysis of these ices produced detectable HCN and HNC. Intrinsic band strengths, A(HCN) and A(HNC), were measured and used to calculate yields of HCN and HNC. Similar results were obtained on irradiation of N2 + CH4 + CO ices at 12 K, with the main difference being the formation of HNCO. In all cases we observed changes on warming. For example, when the temperature of irradiated Nz + CH4 + CO was raised from 12 to 30 K, HCN, HNC, and HNCO reacted with NH3, and OCN-, CN-, N3-, and NH4+ were produced. These ions, appearing at 30 K, are expected to form and survive on the surfaces of Triton, Pluto, and interstellar grains. Our results have astrobiological implications since some of these radiation products are involved in the syntheses of biomolecules such as amino acids and peptides.

Moore, M. H.↗

NASA NTRS1972

Kinetics and mechanism of the formation of water cluster ions from O2(plus) and H2O in He, Ar, N2, and O2 at 296 K

The reaction sequence leading from O2(+) to H3O(+)-H2O was examined in He, Ar, N2 and O2 carrier gases in a flowing afterglow system. The rate constants for the reactions were measured and the kinetic analysis for their determination is presented. For M = N2, two new steps involving the formation and reaction of O2(+)-N2 were proposed and examined. The rate constants are discussed and compared with other experimental values.

Howard, C. J.↗

NASA NTRS1971

Theoretical N2 vibrational distribution in an aurora.

The N2 vibrational distribution in an aurora is investigated. During the auroral bombardment, the vibrational distribution is non-Boltzmann. The deviation from the Boltzmann distribution increases with increasing altitude. Above 200 km, the loss rate of O(+) due to the reaction O(+) + N2 leading to NO(+) + N is increased by a factor of 1.5 when allowance is made for the non-Boltzmann character of the N2 distribution. This increased loss rate persists for 1000-2000 sec after auroral bombardment commences.

Schunk, R. W.↗

NASA NTRS1972

Resonance scattering of the first positive system of N2 in the dayglow.

Rocket measurements of the differential photoelectron flux and the volume emission rate of the N2(0, 0) second positive band are used to calculate the daytime concentration of metastable A(super 3)Sigma(sub u)+ molecules, and consequently the resonance scattering contribution to the N2 first positive emission in the dayglow. The dominant source of N2 first positive emission is found to be photoelectron impact, with resonance scattering contributing only 10-20 per cent the total emission.

Feldman, P. D.↗