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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.

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At least 343 records · Page 19
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NASA NTRS1988

Atmospheric Trace Molecule Spectroscopy (ATMOS)

The Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment is a space-borne investigation designed to obtain fundamental information related to the chemistry and physics of the earth's upper atmosphere (20 to 120 km altitude). The instrument, a high resolution (0.01/cm) interferometric spectrometer, measures the atmospheric absorption of solar radiation over the wavelength range from 2 to 16 micrometers, a spectral band which encompasses active transitions of all of the molecular species of current importance in upper atmospheric studies. There are two major aspects to the experiment: (1) the determination of the detailed compositional structure of the stratosphere and mesosphere, and its global, seasonal, and long-term variability; and (2) the study of the partitioning of absorbed solar energy at levels in the atmosphere characterized by dissociation of many of the constituents and by the breakdown of thermodynamic equilibrium. Characteristics of ATMOS are given. This experiment will be part of the atmospheric science research payload flown on the Atmospheric Laboratory for Applications and Science (ATLAS 1) NASA mission planned for late 1990.

Farmer, C. B.↗
NASA NTRS1995

Rotational And Rovibrational Energy Transfer In Electron Collisions With Molecules

Air flows around a hypervelocity reentry vehicle undergo dissociation, rovibrational excitation and ionization. More specifically the air, initially 80% N2 and 20% O2, in the shock layer consists of species such as N, O, N2, O2, NO, N+, O+, N+, O+, NO+ and 2 free electrons. It was pointed out in multi temperature models'' that the temperature of the rotational energy modes and the gas-kinetic translational temperature are quickly equilibrated by a few collisions and rise rapidly to high temperatures as 50000K before falling off to equilibrium value of 10000K. Contrary, the electronic and vibrational temperatures state energy distributions remain low (less than 15000K) because of the slow equilibration. Electron vibrational energy transfer is thought to play a crucial role in such a ionizing flow regime since chemical reaction rates and dissociation depend strongly on the vibrational temperatures. Modeling of these flowfields in principle require the rovibrational excitation and de-excitation cross section data for average electron energies from threshold up to several eV (leV=11605.4 K). In this lecture we focus on theoretical description of rotational effects i.e. energy transfer of electrons to molecules such that the molecular rotational (vojo goes to voj) or vibrational and rotational (v(sub 0)j(sub 0) goes to vj) states are changed. Excitation and de-excitation of electronic states was discussed in a previous talk at this conference.

Thuemmel, Helmar T.↗
NASA NTRS1975

Relative quantum yield for the production of O-atom and S-atom from the photodissociation of OCS in the vacuum UV

The relative efficiencies for two dissociative channels in the vacuum UV photolysis of carbonyl sulphide have been determined using the flash photolysis-resonance fluorescence technique to measure initial yields of atomic oxygen and atomic sulphur. At wavelengths above 105 nm, the dissociation of OCS to form atomic sulphur exceeded that for the formation of atomic oxygen to such an extent that only an upper limit could be placed on the minor process. In addition, the flash photo-excitation of carbonyl sulphide produced a long-lived spontaneous emission in the UV and vacuum UV that might be due to molecular fluorescence from OCS.

Klemm, R. B.↗
NASA NTRS1995

KWIC imaging of the Orion Nebula

We present the first results obtained with our new imaging Fabry-Perot spectrometer, KWIC. We obtained a fully sampled 9.8 sec. spatial resolution image of the inner 8 min. x 12 min. region of the Orion Nebula in the 37 micro m continuum and a somewhat smaller scale image in the (SiII) 35 micro m line. The continuum image traces out the structure of the interface region between the molecular cloud and the Orion A HII region, as well picking out embedded sources such as the BN-KL star cluster. The continuum directly yields the luminosity of the sources and is used to deduce dust mass and grain parameters. Our (SiII) image both reveals the clumpy structure of the interface region and signals the presence of a dissociative J-shock in the high velocity outflow from IRc2.

Stacey, G. J.↗
NASA NTRS1985

The sublimation temperature of the cometary nucleus Observational evidence for H2O snows

It is shown that information on the chemical composition of cometary snows can be inferred from the distance r(0) between sublimating states in the cometary nucleus. Consideration is given to three techniques for measuring r(0): estimation of the dependence on distance of non-gravitational forces (NGF); estimation of the dependence on distance of molecular emissions; and (3), analysis of the cometary light curve. The dependence on distance of the NGFs suggests that the observed sublimations of short-period coments are determined by water snow. Light curves of newly discovered comets appear to confirm this result. The large production rates of H and OH in cometary atmospheres suggest that they are due to dissociation of H2O in the vapor states. Estimates of r(0) for eleven different comets are given in a table.

Delsemme, A. H.↗
NASA NTRS2020

Detection of Interstellar HC4NC and an Investigation of Isocyanopolyyne Chemistry under TMC-1 Conditions

Abstract We report an astronomical detection of HC4NC for the first time in the interstellar medium with the Green Bank Telescope toward the TMC-1 molecular cloud with a minimum significance of 10.5σ. The total column density and excitation temperature of HC4NC are determined to be 3.29+8.60 ´ 1011 cm−2 and 6.7+0.3 K, respectively, using -1.20 -0.3 Markov chain Monte Carlo analysis. In addition to HC4NC, HCCNC is distinctly detected whereas no clear detection of HC6NC is made. We propose that the dissociative recombination of the protonated cyanopolyyne, HC5NH+, and the protonated isocyanopolyyne, HC4NCH+, are the main formation mechanisms for HC4NC while its destruction is dominated by reactions with simple ions and atomic carbon. With the proposed chemical networks, the observed abundances of HC4NC and HCCNC are reproduced satisfactorily.

Astrochemistry↗
NASA NTRS1977

Far ultraviolet atomic and molecular nitrogen emissions in the dayglow

A scanning spectrophotometer was used to observe the far ultraviolet day airglow between 1130 and 1520 A at 4.4-A spectral resolution. Fourteen bands of the N2 Lyman-Birge-Hopfield (LBH) system are clearly resolved and suggest a total LBH system zenith column emission rate of 3810 plus or minus 520 R extrapolated to the subsolar point. A photoelectron flux model (based on recent photoelectron flux measurements and the observed LBH altitude profile) is used to derive the direct and dissociative excitation contributions to the atomic nitrogen emissions. The calculated atomic nitrogen density agrees with other measurements, although it is an order of magnitude greater than previous photochemical model results.

Takacs, P. Z.↗
NASA NTRS1991

Formation of ions and radicals from icy grains in comets

Ion and radical formation in comets are thought to occur primarily by photodissociation of gas phase molecules. Experimental evidence and theoretical calculations are presented that show that some of the radical and ions can come directly from ice grains. The experimental evidence suggest that if the frozen molecules on the surface of grains undergo direct dissociation then they may be able to release radicals directly in the gas phase. If the molecules undergo predissociation it is unlikely that they will release radicals in the gas phase since they should be quenched. Calculations of this direct photodissociation mechanism further indicate that even if the parent molecule undergoes direct dissociation, the yield will not be high enough to explain the rays structure in comets unless the radicals are stored in the grains and then released when the grain evaporates. Calculations were also performed to determine the maximum number of ions that can be stored in an icy grain's radius. This number is compared with the ratio of the ion to neutral molecular density. The comparison suggests that some of the ions observed near the nucleus of the comet could have originally been present in the cometary nucleus. It is also pointed out that the presence of these ions in icy grains could lead to radical formation via electron recombination. Finally, an avalanche process was evaluated as another means of producing ions in comets.

Jackson, William M.↗
NASA NTRS2002

Assembly of Colloidal Materials Using Bioadhesive Interactions

We have pursued the use of biological crosslinking molecules of several types to make colloidal materials at relatively low volume fraction of colloidal particles. The objective is to make binary alloys of colloidal particles, made of two different colloidal particles coated with complementary biological lock-and-key binding molecules, which assemble due to the biological specificity. The long-term goal is to use low affinity lock-and-key biological interactions, so that the can anneal to form crystalline states. We have used a variety of different surface chemistries in order to make colloidal materials. Our first system involved using selectin-carbohydrate (sialyl-Lewis) interactions; this chemistry is derived from immune system. This chemical interaction is of relatively low affinity, with timescales for dissociation of several seconds. Furthermore, the adhesion mediated by these molecules can be reversed by the chelation of calcium atoms; thus assembled structures can be disassembled reversibly. Our second system employed avidin-biotin chemistry. This well-studied system is of high affinity, and is generally irreversible on a laboratory time-scale. Thus, we would expect selectin-carbohydrate interactions at high molecular density and avidin-biotin interactions to give kinetically-trapped structures; however, at low densities, we would expect significant differences in the structure and dynamics of the two materials, owing to their very different release rates. We have also begun to use a third chemistry - DNA hybridization. By attaching single stranded DNA oligonucleotide chains to beads, we can drive the assembly of colloidal materials by hybridization of complementary DNA chains. It is well known that DNA adenosine-thymine (A-T) and guanine-cytosine (G-C) bases hybridize pairwise with a Gibbs free energy change of 1.7 kcal/mol per base; thus, the energy of the assembly can be modulated by altering the number of complementary bases in the DNA chains. Using these different crosslinking molecules, we have assembled colloidal materials from different-sized colloidal particles, A and B. In the first sets of experiment, we used high densities of adhesion molecules, and 0.96 micron (A) and 5.5 micron (B) diameter particles. The high density of adhesion molecules means that the structures are kinetically trapped in nonequilibrium configurations. The structure of the suspension can be varied by changing the number ratio of the two types of colloidal particles, NA and NB, where A is the smaller particle. With carbohydrate-selectin or avidin-biotin interactions, large NA/NB leads to the formation of colloidal micelles, with the large center B particle surrounded by many smaller A particles. As the ratio NA/NB decreases, the structures become more extended, approaching the formation of macro-Rouse polymers - extended linear chains where A beads are connected with intervening small B linkers.

Hammer, Daniel A.↗
NASA NTRS2012

Nitrogen Incorporation in CH4-N2 Photochemical Aerosol Produced by Far UV Irradiation

Nitrile incorporation into Titan aerosol accompanying hydrocarbon chemistry is thought to be driven by extreme UV wavelengths (lambda < 120 nm) or magnetospheric electrons in the outer reaches of the atmosphere. Far UV radiation (120 - 200 nm), which is transmitted down to the stratosphere of Titan, is expected to affect hydrocarbon chemistry only and not initiate the formation of nitrogenated species. We have examined the chemical properties of photochemical aerosol produced at far UV wavelengths using a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS), which allows for elemental analysis of particle-phase products. Our results show that aerosol formed from CH4/N2 photochemistry contains a surprising amount of nitrogen, up to 16% by mass, a result of photolysis in the far UV. The proportion of nitrogenated organics to hydrocarbon species is shown to be correlated with that of N2 in the irradiated gas. The aerosol mass greatly decreases when N2 is removed, indicating that N2 plays a major role in aerosol production. Because direct dissociation of N2 is highly improbable given the immeasurably low cross-section at the wavelengths studied, the chemical activation of N2 must occur via another pathway. Any chemical activation of N2 at wavelengths > 120 nm is presently unaccounted for in atmospheric photochemical models. We suggest that reaction with CH radicals produced from CH4 photolysis may provide a mechanism for incorporating N into the molecular structure of the aerosol. Further work is needed to understand the chemistry involved, as these processes may have significant implications for prebiotic chemistry on the early Earth and similar planets.

Trainer, Melissa G.↗
NASA NTRS1996

A search for HCCN in molecular clouds

We have conducted a deep search for HCCN towards the dark cloud TMC-l and several GMC's via its N(J) = 1(2)-->0(1) transition. HCCN was not detected in any of these sources. Towards TMC-l, assuming optically thin emission, the total column density upper limit is NHCCN < or = 2 x 10(12) cm-2, which corresponds to a fractional abundance upper limit with respect to molecular hydrogen of fHCCN < or = 2 x 10(-10). We find the abundance ratio of HCN:HCCN:HCCCN in TMC-l to be l : <0.01 : 0.3, which suggests that carbon-chain growth by the addition of single carbon atoms may not be efficient under dark cloud conditions. The HCCN abundance limit also places constraints on the branching ratio for the products of the dissociative electron recombination H3C2N+ + e.

Non-NASA Center↗
NASA NTRS1978

Artificially created holes in the ionosphere

The artificial creation of ionospheric holes by the release of highly reactive molecules into the F region is investigated. Through ion-atom interchange or charge transfer reactions, H2 or H2O reacts with O(+) to form OH(+) or H2O(+), respectively, which subsequently dissociatively recombines with electrons at a very rapid rate. The diffusion of H2 is also modified by chemical loss to the ambient atomic oxygen atmosphere. The limited spatial and temporal extent of the hole-making process allows several approximations to be made which permit three-dimensional analytic solutions of the continuity equations for the released particles, the O(+) and e(-) densities, and the intermediary molecular ions. A versatile formalism is developed whereby the hole-making capability of virtually any spatial-temporal configuration of released particles can be determined by convolving a set of destruction operators which can be viewed as Green's functions for the problem. As a specific application of the techniques developed, the modification of a winter nighttime ionosphere is described by simulating the release of 1000 kg of water vapor near a height of 300 km.

Mendillo, M.↗
NASA NTRS1998

Search for Interstellar Water in the Translucent Molecular Cloud Toward HD 154368

We report an upper limit of 9 x 10(exp 12)/sq cm on the column density of water in the translucent cloud along the line of sight toward HD 154368. This result is based on a search for the C-X band of water near 1240 A carried out using the Goddard High-Resolution Spectrograph (GHRS) of the Hubble Space Telescope. Our observational limit on the water abundance, together with detailed chemical models of translucent clouds and previous measurements of OH along the line of sight, constrains the branching ratio in the dissociative recombination of H3O(+) to form water. We find at the 3 sigma level that no more than 30% of dissociative recombinations of H3O(+) can lead to H2O. The observed spectrum also yielded high-resolution observations of the Mg II doublet at 1239.9 A and 1240.4 A, allowing the velocity structure of the dominant ionization state of magnesium to be studied along the line of sight. The Mg II spectrum is consistent with GHRS observations at lower spectral resolution that were obtained previously but allow an additional velocity component to be identified.

Spaans, Marco↗
NASA NTRS1978

Auroral excitation of optical emissions of atomic and molecular oxygen

The O I 'green line' (1S-1D) at 5577 A and the O2 (0,0) atmosphere band at 7620 A were measured in a steady IBC II(plus) aurora simultaneously with N2 emissions and the auroral electron flux. An empirical model based on these rocket measurements shows that the principal excitation source of O2(b 1 Sigma g plus) is energy transfer from O(1D), with direct electron impact of O2 contributing less than 5 percent. While the altitude profile of the green line emission resembles that which would be produced by electron impact excitation of O2, a dissociative excitation cross section of 10 to the minus 16th power is required for this interpretation. None of the other known O(1S) excitation mechanisms are thought capable of producing the observed emission rate.

Feldman, P. D.↗
NASA NTRS1994

An investigation of the effect of surface impurities on the adsorption kinetics of hydrogen chemisorbed onto iron

The goal of this program has been to develop an understanding of heterogeneous kinetic processes for those molecular species which produce gaseous hydrogen degradation of the mechanical properties of metallic structural materials. During the present program, the interaction of hydrogen with the surfaces of alpha-2 (Ti3Al) titanium aluminide, gamma (TiAl) titanium aluminide, and beryllium were studied. The interaction of low pressure hydrogen with gamma titanium aluminide and beryllium was found to be relatively weak. Weak in the sense that adsorption leads to a low surface concentration of dissociated hydrogen, i.e., the chemisorption process is reversible at room temperature (300 K) for gamma titanium aluminide and the sticking coefficient for chemisorption is extremely small for beryllium. Hydrogen was found to interact readily with alpha-2 titanium aluminide to form a stable surface hydride at 300 K. These results correlate well with other recent studies which show that the mechanical properties for alpha-2 titanium aluminide are readily degraded in hydrogen while gamma titanium aluminide exhibits less degradation and beryllium essentially no degradation. The interaction of oxygen with the surface of several of these materials was studied. More recently, preliminary hydrogen permeation studies were completed for three high temperature alloys, Incoloy 909, Mo-47.5Re (wt. %), and this past year, Haynes 188.

Shanabarger, Mickey R.↗
NASA NTRS2012

Will Organic Synthesis Within Icy Grains or on Dust Surfaces in the Primitive Solar Nebula Completely Erase the Effects of Photochemical Self Shielding?

There are at least 3 separate photochemical self-shielding models with different degrees of commonality. All of these models rely on the selective absorption of (12))C(16)O dissociative photons as the radiation source penetrates through the gas allowing the production of reactive O-17 and O-18 atoms within a specific volume. Each model also assumes that the undissociated C(16)O is stable and does not participate in the chemistry of nebular dust grains. In what follows we will argue that this last, very important assumption is simply not true despite the very high energy of the CO molecular bond.

Nuth, Joseph A., III↗
NASA NTRS1983

Energetic atomic and molecular ions in Saturn's magnetosphere

Voyager 1 and 2 sensor data are analyzed in order to derive the composition, energy spectra, and spatial distribution of energetic ions in the Saturn magnetosphere. In order of abundance, the major species are H, H2(+), He, H3(+), C, and O. The fluxes of all species decreased inside the orbit of Dione, and nearly vanished in the 'slot' region within the orbit of Tethys. Both satellite absorption and precipitation due to pitch angle scattering may be important loss processes in that region. In the outer magnetosphere, photodissociation rapidly destroys a large fraction of the H2(+) ions, but dissociation by impact with neutral H atoms is faster for H2(+) ions in the lowest vibrational state. The ground state lifetime of about 23 days places a limit of about 10-100 days on the mean overall residence time for energetic ions in Saturn's magnetosphere.

Hamilton, D. C.↗
NASA NTRS1989

A study of electron impact excitation of NO. I - The vacuum ultraviolet from 40 to 170 nm. II - The middle ultraviolet from 170 to 270 nm

The electron impact induced fluorescence spectrum of NO at 200 eV was measured for the vacuum UV range (40-170 nm) and the mid-UV range (170-270 nm). The absolute electron impact excitation cross sections are studied by calibrating to the Ly-alpha cross section of H2. The cross section of the N I 120-nm transition by dissociative excitation is found to be 1.73 + or - 0.38 X 10 to the -18th sq cm. Measurements of the cross sections of other features in the vacuum UV and mid-UV are presented. A band model of the far-UV (120-170 nm) is developed. Also, it is found that great care must be taken if NO is the target for relative calibration in the Mid-UV using the molecular branching ratio techniques.

Ajello, J. M.↗