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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 1,261 records · Page 70
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Ion-molecule reactions in unsaturated hydrocarbons - Allene, propyne, diacetylene, and vinylacetylene

Ion-molecule reactions in allene, propyne, diacetylene, and vinylacetylene (1-buten-3-yne) have been studied at near-thermal energies by the technique of ion cyclotron resonance mass spectrometry. Rate coefficients and branching ratios are reported for the reactions of C3Hn(+) (n = 1-4) with allene and propyne and for the reactions of C4Hn(+) (n = 0-5) with diacetylene and vinylacetylene. Branching ratios are also given for the reactions of C4Hn(+), C5Hn and C6Hn(+) with propyne and for reactions of C6Hn(+) with diacetylene and vinylacetylene. More than 90 percent of the reactive channels lead to product ions having a larger carbon skeleton than the reactant ion. Evidence for ions with the same m/e ratio having differing reactivities was obtained for C3Hn(+), C6H7(+), and C7H7(+). Ion reaction sequences in allene and propyne were followed at higher pressures (0.0001 torr) to investigate secondary, tertiary, and higher order processes.

Anicich, V. G.↗
NASA NTRS1984

Ejection of atoms and molecules from Io by plasma-ion impact

The directions and energy distributions of neutral atoms and molecules ejected from Io are modeled analytically. The particles are emitted from the Io exosphere by collisions of incident plasma ions. Some of the Io atmosphere is attributed to particles sputtered off the surface by incoming plasma ions, while other departing particles originate at the top of volcanic plumes. Account is taken of the thermal motion of incident plasma and Io's gravitational field when calculating the distribution of the ejected particles. The distributions associated with each type of ejection force are projected to be different and highly dependent on the inclusion of realistic cross-sections. Attention is focused on Na-rich species and defining ejection processes which can be verified with ground-based observations. It is, however, concluded that no particles are ejected directly from the surface by Jean's escape.

Sieveka, E. M.↗
NASA NTRS1985

Inclusion of exact exchange in the noniterative partial-differential-equation method of electron-molecule scattering - Application to e-N2

The noniterative partial-differential-equation (PDE) approach to electron-molecule scattering of Onda and Temkin (1983) is modified to account for the effects of exchange explicitly. The exchange equation is reduced to a set of inhomogeneous equations containing no integral terms and solved noniteratively in a difference form; a method for propagating the solution to large values of r is described; the changes in the polarization potential of the original PDE method required by the inclusion of exact static exchange are indicated; and the results of computations for e-N2 scattering in the fixed-nuclei approximation are presented in tables and graphs and compared with previous calculations and experimental data. Better agreement is obtained using the modified PDE method.

Weatherford, C. A.↗
NASA NTRS1985

Energy transfer mechanisms between molecules

Reliable rate coefficients for energy transfer and relaxation phenomena are needed in order to do the theoretical modeling which is necessary for accomplishing the following objectives: understanding and justifying proposed laser systems, determining limitations, identifying control parameters, and scaling to space-power requirements. Modeling also establishes the criteria to be followed for lasant selection. Lack of knowledge of rate coefficients is invariably the biggest obstacle to successful modeling. Existing theoretical methods are discussed, sources of error are identified, and transfer laser criteria suggested by the theory are listed. The emphasis is on vibrational-vibrational (V-V) energy transfer caused by both short range and long range interactions between molecules. Special attention is given to the importance of near-resonant collisional and dipole-dipole transfer. A technique is proposed for significantly improving the theoretical predictions of rate coefficients.

Meador, W. E.↗
NASA NTRS1984

A vectorized molecule code

The vectorization of the computational chemistry code, MOLECULE, is discussed. Computational simplifications of molecular integrals, memory management, and contraction schemes are addressed and a brief guide for users is included.

Almloef, J.↗
NASA NTRS1985

Collisional excitation of molecules in dense interstellar clouds

State transitions which permit the identification of the molecular species in dense interstellar clouds are reviewed, along with the techniques used to calculate the transition energies, the database on known molecular transitions and the accuracy of the values. The transition energies cannot be measured directly and therefore must be modeled analytically. Scattering theory is used to determine the intermolecular forces on the basis of quantum mechanics. The nuclear motions can also be modeled with classical mechanics. Sample rate constants are provided for molecular systems known to inhabit dense interstellar clouds. The values serve as a database for interpreting microwave and RF astrophysical data on the transitions undergone by interstellar molecules.

Green, S.↗
NASA NTRS1987

High resolution infrared spectroscopy from space: A preliminary report on the results of the Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment on Spacelab 3

The ATMOS (Atmospheric Trace Molecule Spectroscopy) experiment has the broad purpose of investigating the physical structure, chemistry, and dynamics of the upper atmosphere through the study of the distributions of the neutral minor and trace constituents and their seasonal and long-term variations. The technique used is high-resolution infrared absorption spectroscopy using the Sun as the radiation source, observing the changes in the transmission of the atmosphere as the line-of-sight from the Sun to the spacecraft penetrates the atmosphere close to the Earth's limb at sunrise and sunset. During these periods, interferograms are generated at the rate of one each second which yield, when transformed, high resolution spectra covering the 2.2 to 16 micron region of the infrared. Twenty such occultations were recorded during the Spacelab 3 flight, which have produced concentration profiles for a large number of minor and trace upper atmospheric species in both the Northern and Southern Hemispheres. Several of these species have not previously been observed in spectroscopic data. The data reduction and analysis procedures used following the flight are discussed; a number of examples of the spectra obtained are shown, and a bar graph of the species detected thus far in the analysis is given which shows the altitude ranges for which concentration profiles were retrieved.

Farmer, Crofton B.↗
NASA NTRS1987

Experimental Resonance Enhanced Multiphoton Ionization (REMPI) studies of small molecules

Resonance enhanced multiphoton ionization (REMPI) utilizes tunable dye lasers to ionize an atom or molecule by first preparing an excited state by multiphoton absorption and then ionizing that state before it can decay. This process is highly selective with respect to both the initial and resonant intermediate states of the target, and it can be extremely sensitive. In addition, the products of the REMPI process can be detected as needed by analyzing the resulting electrons, ions, fluorescence, or by additional REMPI. This points to a number of exciting opportunities for both basic and applied science. On the applied side, REMPI has great potential as an ultrasensitive, highly selective detector for trace, reactive, or transient species. On the basic side, REMPI affords an unprecedented means of exploring excited state physics and chemistry at the quantum-state-specific level. An overview of current studies of excited molecular states is given to illustrate the principles and prospects of REMPI.

Dehmer, J. L.↗
NASA NTRS1986

Ion-molecule reactions of hydrocarbon ions in C2H2 and HCN

Rate coefficients and product distributions have been determined for reaction of the ions C(x)H(y)+ (x ranging from 1 to 4, and y ranging from 0 to 4) with C2H2 and HCN. The measurements were obtained using the ion cyclotron resonance technique at 298 K. In several reactions an association product was observed at pressures as low as 0.000001 torr, and in these cases stabilization of the intermediate was assumed to be by photon emission. Most of the reaction studied yield ions having a larger carbon skeleton than the reactant ion. These reactions provide routes for building large organic and organonitrogen molecules in combustion zones of unsaturated hydrocarbon flames and in astrochemical environments.

Anicich, V. G.↗
NASA NTRS1987

Oscillator strengths for visible and ultraviolet observations of interstellar molecules

Optical observations of molecules in diffuse interstellar clouds are discussed. The role of oscillator strengths in determining cloud properties such as densities, temperatures, and particle and photon fluxes is examined. The use of an emission technique, molecular and atomic lifetime measurements, and absorption measurements to estimate oscillator strengths is described. It is noted that the lifetime and absorption measurements are more advantageous than the emission technique to estimate oscillator strengths.

Smith, Peter L.↗
NASA NTRS1987

Infrared observations of circumstellar molecules

A current listing of IR observations of circumstellar molecules is presented. These observations were performed using Fabry-Perot, Fourier transform, and laser heterodyne spectroscopy. The most abundant species were CO, SiO, and HCN, while trace species included NH3, CH4, SiH4, and CS. Among the undetected species were H2, HCl, and CH2.

Betz, Albert↗
NASA NTRS1987

Evidence for chain molecules enriched in carbon, hydrogen, and oxygen in comet Halley

In situ measurements of the composition and spatial distribution of heavy thermal positive ions in the coma of comet Halley were made with the heavy-ion analyzer RPA2-PICCA aboard the Giotto spacecraft. Above 50 atomic mass units an ordered series of mass peaks centered at 61, 75, 91, and 105 atomic mass units were observed. Each peak appears to be composed of three or more closely spaced masses. The abundances decrease and the dissociation rates increase smoothly with increasing mass. These observations suggest the presence of chain molecules that are enriched in carbon, oxygen, and hydrogen, such as polyoxymethylene (polymerized formaldehyde), in comet Halley.

Mitchell, D. L.↗
NASA NTRS1986

The diffusion of individual molecules within a gas

The Direct Simulation Monte Carlo method is used to study the positional history of the individual molecules in a gas that is homogeneous at the macroscopic level and is in Maxwellian equilibrium at the microscopic level. The behavior at small times is characterized by 'persistence of velocity' effects, and a 'random walk' type of dispersal occurs over a longer timescale. It is shown that the rate of dispersal can be directly related to the self-diffusion coefficient. In addition, the diffusion coefficients are obtained directly from one-dimensional calculations, and the local Knudsen number at which the Chapman-Enskog theory breaks down is determined. Results are presented for both simple gases and gas mixtures.

Bird, G. A.↗
NASA NTRS1987

Concentrations of ethane (C2H6) in the lower stratosphere and upper troposphere and acetylene (C2H2) in the upper troposphere deduced from Atmospheric Trace Molecule Spectroscopy/Spacelab 3 spectra

This paper reports the results of the spectroscopic analysis of C2H6 and C2H2 absorption spectra obtained by the Atmospheric Trace Molecule Spectroscopy (ATMOS) instrument flown on the Shuttle as part of the Spacelab 3 mission. The spectra were recorded during sunset occultations occurring between 25 deg N and 31 deg N latitudes, yielding volume-mixing ratio profiles of C2H6 in the lower stratosphere and the upper troposphere, and an upper tropospheric profile of C2H2. These results compare well with previous in situ and remote sounding data obtained at similar latitudes and with model calculations. The results demonstrate the feasibility of the ATMOS instrument to sound the lower atmosphere from space.

Rinsland, C. P.↗
NASA NTRS1987

Molecular line parameters for the atmospheric trace molecule spectroscopy experiment

During its first mission in 1985 onboard Spacelab 3, the ATMOS (atmospheric trace molecule spectroscopy) instrument, a high speed Fourier transform spectrometer, produced a large number of high resolution infrared solar absorption spectra recorded in the occultation mode. The analysis and interpretation of these data in terms of composition, chemistry, and dynamics of the earth's upper atmosphere required good knowledge of the molecular line parameters for those species giving rise to the absorptions in the atmospheric spectra. This paper describes the spectroscopic line parameter database compiled for the ATMOS experiment and referenced in other papers describing ATMOS results. With over 400,000 entries, the linelist catalogs parameters of 46 minor and trace species in the 1-10,000/cm region.

Brown, L. R.↗
NASA NTRS1987

Some diatomic molecules from comet P/Halley's UV spectra near spacecraft flybys

The abundances of diatomic molecules seen in the UV both give clues to the parent compounds and help unravel the gas and ion mass spectrometry. From IUE spectra of comet Halley, upper limits on SH and CS(+) column densities and estimates of probable NO, S2, and SO are found. In particular, judged from the 226-nm gamma band, NO was relatively abundant at 2-8 x 10 to the 13th/sq cm on March 9-14. The production rate of S2 was around 1 x 10 to the 27th molecules/s at that time, but both showed day-to-day variability by 2-3 times.

Wallis, Max K.↗
NASA NTRS1988

A computational study of the TiO2 molecule

A computational investigation of the ground 1A1 and lowest energy B2 states of the titanium dioxide molecule has been carried out. The treatment utilized SCF calculations in an extended basis followed by a CI treatment for each geometry. The ground state geometry agrees well with experiment, while the agreement between the computed vibrational frequency nu1 and the experimental value for a matrix isolated TiO2 is less satisfactory. Population analysis for the ground state indicates less than one excess electron on each oxygen atom. The first excited state has a linear geometry and the singlet and triplet are essentially degenerate.

Ramana, M. V.↗
NASA NTRS1988

Vibrational-excitation cross sections of water molecules by electron impact

A crossed-beam technique was used to measure absolute differential cross sections for the vibrational excitation of water-vapor molecules. The energy and angular range were from 2.2 to 20 eV and from 30 to 150 deg. Vibrational-excitation cross sections were determined for the bending (010) and stretching (100 and 001) modes of the electronic ground state. It is shown that the integral cross sections are generally larger than those of Seng and Linder (1976) by 10-20 percent for both the bending and stretching modes. It is noted that the results obtained are of interest in connection with the theoretical modeling of cometary ionospheres.

Shyn, T. W.↗