SEARCH · Search NASA
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Deoxygenation of benzoyl cyanide, studies of vinyl nitrenes and diene isocyanates, and other aspects of nitrogen chemistry significant to primordial biological systems
Density profiles of N(4S), NO, N(2D), NO(+), and N(+) are calculated for the thermosphere of Venus. The results show that N(4S) is the dominant odd nitrogen species throughout the thermosphere and has a maximum density of 18 million atoms/cu cm at 132 km. The calculated NO(+) density agrees well with recent Pioneer Venus measurements, but the calculated N(+) densities are a factor of two to five less than the measurements. The production of N(4S) atoms generated in the model is adequate to explain recent measurements of the nitric oxide chemiluminescent emission on the night side of Venus.
Observations of N2(+) and NH2 in Comet Halley and N2H(+) and NH3 in nine Galactic star-forming regions are used to determine the average N2/NH3 abundance ratio in these objects. For Comet Halley, N2/NH3 of about 0.1 is found, and for the quiescent gas in a sample of star-forming regions, N2/NH3 of about 170 +/- 100. The cometary N2/NH3 ratio corrected for gas-phase elemental nitrogen depletion in Comet Halley indicates that the gas component in the comet-forming region of the solar nebula was N2/NH3 of about 4. It is concluded that more realistic models which include condensation fractionation effects are required before the N2 and NH3 abundances in comet volatiles can be related to star-forming regions.
A one-dimensional model is utilized to study the role of nonmethane hydrocarbons (NMHCs) in tropospheric chemistry. The effects of NMHCs on tropospheric peroxyacetyl nitrate (PAN) formation are analyzed; the global distribution and seasonal variability of PAN in the troposphere of the Northern and Southern Hemispheres are examined. The NMHC-PAN measurements obtained by model simulations are compared to the photochemical theory. The seasonal cycles in NMHC abundances are predicted, and their effects on other tropospheric species are investigated.
In Titan's upper atmosphere N2 is dissociated to N by solar UV and high energy electrons. This flux of N provides for interesting organic chemistry in the lower atmosphere of Titan. Previously the main pathway for the loss of this N was thought to be the formation of HCN, followed by diffusion of this HCN to lower altitudes leading ultimately to condensation. However, recent laboratory simulations of organic chemistry in Titan's atmosphere suggest that formation of the organic haze may be an important sink for atmospheric N. Because estimates of the eddy diffusion profile on Titan have been based on the HCN profile, inclusion of this additional sink for N will affect estimates for all transport processes in Titan's atmosphere. This and other implications of this sink for the N balance on Titan are considered.
Based on the conservation of chemical elements in chemical reactions, a rule is proved that the number of boundary conditions given by densities and/or nonzero velocities should not be less than the number of chemical elements in the system, and the boundary conditions for species given by densities and velocities should include all elements in the system. Applications of this rule to Mars are considered. It is shown that the problem of the CO2-H2O chemistry in the lower and middle atmosphere of Mars, say, in the range of 0-80 km does not have a unique solution, if only CO2 and H2O densities are given at the lower boundary, and the remaining boundary conditions are fluxes. Two examples of models of this type are discussed. Two models of the photochemistry of the Martian atmosphere, with and without nitrogen chemistry, are considered. The oxygen nonthermal escape ratio of 1.2 x 10(exp 8)/cu cm/s is given at 240 km and is balanced with the total hydrogen escape rate within an uncertainty of 1% for both models. Both models fit the measured O2 and CO mixing ratios, the O3 abundance, and the O2 1.27-micrometer dayglow almost within the uncertainties of the measured values, though the model without nitrogen chemistry fits better. The importance of nitrogen chemistry in the lower and middle atmosphere of Mars depends on a fine balance between production of NO and N in the upper atmosphere which is not known within the required accuracy.
Ozone plays a central role in the chemistry of the atmosphere both as an ultraviolet shield and as a source of hydroxyl radicals (OH), a potent initiator of atmospheric chemistry. There is evidence to suggest that the ozone abundance in the troposphere (0-10 km) has doubled since the industrial revolution and continues to increase to date. The principle reason for this increase is thought to be the increasing emissions of nitrogen oxides (NO(x)) from anthropogenic activities. Although NO(x) is highly reactive and its products such as HN03 are easily removed by deposition, it now appears that its chemistry is quite complex and it can be transported over long distances via its conversion to a variety of nitrates and penetrates. The sources of atmospheric NO(x) include free tropospheric sources such as lightning and subsonic aircraft, as well as surface emissions which are transported to the free troposphere via convective processes. Recent experimental and theoretical studies have tried to unravel the chemistry of reactive nitrogen species, its sources, and their role in ozone formation. In this presentation we shall describe the results from these studies.
Based on the conservation of chemical elements in chemical reactions, a rule is proved that the number of boundary conditions given by densities and/or non-zero velocities should not be less than the number of chemical elements in the system, and the components given by densities and velocities should include all elements in the system. Applications of this rule to Mars are considered. It is proved that a problem of CO2-H2O chemistry in the lower and middle atmosphere of Mars, say, in the range of 0-80 km does not have an unique solution, if only CO2 and H2O densities are given at the lower boundary, while all other boundary conditions are fluxes. Two models of this type are discussed. These models fit the same boundary conditions, are balanced with a relative uncertainty of 10(exp -4) for H2, and predict the O2, CO, and H2 mixing ratios which differ by order of magnitude. One more species density, e.g. that of O2, should be specified at the boundary to obtain the unique solution. The situation is better if the upper boundary is extended to the exobase where thermal escape velocities of H and H2 can be specified. However, in this case, either oxygen nonthermal escape rate or the O2 density at the surface should be given as the boundary condition. Two models of Mars' photochemistry, with and without nitrogen chemistry, are considered. The oxygen nonthermal escape rate of 1.2 x 10(exp 8) cm(exp -2) s(exp -1) is given at 240 km and is balanced with the total hydrogen escape rate within uncertainty of 1 percent for both models. Both models fit the measured O2 and CO mixing ratios, the O3 line absorption at 9.6 microns, and the O2 1.27 microns dayglow within the uncertainties of the measured values; although, the model without nitrogen chemistry fits better.
The use of images acquired by the Airborne Imaging Spectrometer, an experimental high-spectral resolution imaging sensor developed by NASA, to estimate the lignin concentration of whole forest canopies in Wisconsin is reported. The observed strong relationship between canopy lignin concentration and nitrogen availability in seven undisturbed forest ecosystems on Blackhawk Island, Wisconsin, suggests that canopy lignin may serve as an index for site nitrogen status. This predictive relationship presents the opportunity to estimate nitrogen-cycling rates across forested landscapes through remote sensing.
A 2-Dimensional zonally-averaged thermospheric model and the global University College London (UCL) thermospheric model have been used to investigate the seasonal, solar activity and geomagnetic variation of atomic oxygen and nitric oxide. The 2-dimensional model includes detailed oxygen and nitrogen chemistry, with appropriate completion of the energy equation, by adding the thermal infrared cooling by O and NO. This solution includes solar and auroral production of odd nitrogen compounds and metastable species. This model has been used for three investigations; firstly, to study the interactions between atmospheric dynamics and minor species transport and density; secondly, to examine the seasonal variations of atomic oxygen and nitric oxide within the upper mesosphere and thermosphere and their response to solar and geomagnetic activity variations; thirdly, to study the factor of 7 to 8 peak nitric oxide density increase as solar F sub 10.7 cm flux increases from 70 to 240 reported from the Solar Mesospheric Explorer. Auroral production of NO is shown to be the dominant source at high latitudes, generating peak NO densities a factor of 10 greater than typical number densities at low latitudes. At low latitudes, the predicted variation of the peak NO density, near 110 km, with the solar F sub 10.7 cm flux is rather smaller than is observed. This is most likely due to an overestimate of the soft X-ray flux at low solar activity, for times of extremely low support number, as occurred in June 1986. As observed on pressure levels, the variation of O density is small. The global circulation during solstice and periods of elevated geomagnetic activity causes depletion of O in regions of upwelling, and enhancements in regions of downwelling.
Prompted by the ongoing interest in Spitzer Infrared Spectrometer spectra of carbon stars in the Large Magellanic Cloud, we have investigated the circumstellar chemistry of carbon stars in low-metallicity environments. Consistent with observations, our models show that acetylene is particularly abundant in the inner regions of low metallicity carbon-rich asymptotic giant branch stars - more abundant than carbon monoxide. As a consequence, larger hydrocarbons have higher abundances at the metallicities of the Magellanic Clouds than in stars with solar metallicity. We also find that the oxygen and nitrogen chemistry is suppressed at lower metallicity, as expected. Finally, we calculate molecular line emission from carbon stars in the Large and Small Magellanic Cloud and find that several molecules should be readily detectable with the Atacama Large Millimeter Array at Full Science operations.
The atomic nitrogen in the thermosphere, which is produced either in its ground term or in a highly reactive metastable term, reacts with molecular oxygen to form nitric oxide and atomic oxygen. However, nitric oxide is destroyed in reactions with atomic nitrogen in which molecular nitrogen and atomic oxygen is formed. Adopted reactions and rate coefficients for odd nitrogen chemistry are listed in a table. An analysis is conducted of the temperature distribution below 150 km and its effect on the odd nitrogen chemistry. The latitudinal distribution of nitric oxide is discussed. Satellite measurements have shown that nitric oxide concentrations at high latitudes are highly variable in both time and space. Their average concentrations are 3-4 times higher than at mid-latitudes. The measured variation of nitric oxide density as a function of latitude is shown in a graph.
In Titan's atmosphere, composed mainly of N2 (95-98%) and CH4 (2-5%), a complex chemistry occurs at low temperature, and leads to the production of heavy organic molecules and subsequently solid aerosols. Here, we used the Titan Haze Simulation (THS) experiment, an experimental setup developed at the NASA Ames COSmIC simulation facility to study Titan's atmospheric chemistry at low temperature. In the THS, the chemistry is simulated by plasma in the stream of a supersonic expansion. With this unique design, the gas is cooled to Titan-like temperature ( approximately 150K) before inducing the chemistry by plasma, and remains at low temperature in the plasma discharge (approximately 200K). Different N2-CH4-based gas mixtures can be injected in the plasma, with or without the addition of heavier precursors present as trace elements on Titan, in order to monitor the evolution of the chemical growth. Both the gas- and solid phase products resulting from the plasma-induced chemistry can be monitored and analyzed using a combination of complementary in situ and ex situ diagnostics. A recent mass spectrometry[1] study of the gas phase has demonstrated that the THS is a unique tool to probe the first and intermediate steps of Titan's atmospheric chemistry at Titan-like temperature. In particular, the mass spectra obtained in a N2-CH4-C2H2-C6H6 mixture are relevant for comparison to Cassini's CAPS-IBS instrument. The results of a complementary study of the solid phase are consistent with the chemical growth evolution observed in the gas phase. Grains and aggregates form in the gas phase and can be jet deposited on various substrates for ex situ analysis. Scanning Electron Microscopy images show that more complex mixtures produce larger aggregates. A mass spectrometry analysis of the solid phase has detected the presence of aminoacetonitrile, a precursor of glycine, in the THS aerosols. X-ray Absorption Near Edge Structure (XANES) measurements also show the presence of imine and nitrile functional groups, showing evidence of nitrogen chemistry. These complementary studies show the high potential of THS to better understand Titan's chemistry and the origin of aerosol formation.
Odd-nitrogen chemistry and transport are analyzed using a two-dimensional model and Nimbus 7 data. The Nimbus 7 data include: measurements of O3, NO2, HNO3, H2O, and temperature by the LIMS instrument; N2O, CH4, and temperature measurements by the SAMS instrument; and O3 data from the SBUV instrument. The characteristics of the two-dimensional model used in the study, a modified Guthrie et al. (1984) model, are described. NO2 and HNO3 are calculated using the two-dimensional model, and the computed data are compared with the LIMS NO2 and HNO3 measurements. The model uncertainties are computed based on the photochemical equilibrium assumption, and the role of stratospheric dynamics in determining NO2 and HNO3 is discussed. It is observed that there is good correlation between the LIMS and model data in the upper stratosphere; however, the data do not correspond in the lower stratosphere. The effect of nitrogen sources, such as lightning, on the stratospheric odd nitrogen distribution is examined.
D-region ion chemistry, nitrogen oxides and oxygen allotropes in mesosphere, and ionization sources
A model developed for the aeronomy of odd nitrogen in the thermosphere is used to analyze rocket measurements of N(4S) and NO densities. Data from Atmosphere Explorer were used to develop a consistent reaction kinetics model for odd nitrogen chemistry. It is concluded that most NO(+) dissociative recombination events must produce N(2D), that N(2D) is quenched by O at a rate of 1 trillionth cu cm per sec, and that the atmospheric O2 quenching rate of N(2D) is consistent with the laboratory rate. The major quenching agent of N(2D) between 140 and 220 km is atomic oxygen, and this reaction is the major source of N(4S). Peak N(4S) densities of about (20-60) million per cu cm at 140-150 km are predicted, with the variability being indicative of the model sensitivity to a factor of 2 change in the O/O2 ratio in the thermosphere.
In situ measurements taken over midlatitudes by the Dynamics Explorer 2 spacecraft during a geomagnetic substorm show that a direct correlation exists between depletions in the O/N2 density ratio and in the topside electron density, Ne. On the basis of this correlation, it is concluded that, for the storm of September 1982, losses of free electrons via oxygen and nitrogen chemistry near the F2 peak dominate over wind-induced plasma transport in determining the observed stormtime variations of topside Ne at higher latitudes. However, the appearance of an enhancement in topside Ne along 20-deg invariant latitude indicates that an equatorial wind did develop and was effective in increasing gas temperatures and in generating topside Ne enhancement at lower latitudes.