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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 1,207 records · Page 67
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NASA NTRS1974

Measurements of ion-molecule reactions of He/+/, H/+/, and HeH/+/ with H2 and D2

Drift tube-mass spectrometer measurements of several ion-molecule reactions believed to be prominent in the hydrogen-helium upper atmosphere of Jupiter are described. The total rate constant at 300 K of the reaction of He(+) with H2 is about 1.1 x 10 to the neg 13 cu cm/sec. The reaction proceeds mainly by dissociative charge transfer to produce H(+), with a small portion going by charge transfer to H2(+) and by atom rearrangement to HeH(+). The rate coefficient increases slowly with ion mean energy to a value of 2.8 x 10 to the neg 13 at 0.18 eV. The rate of the corresponding reaction with deuterium, He(+) + D2, has the rate coefficient of about 5 x 10 to the neg 14 at 300 K. Measurements of the three-body reaction of H' and the two-body reaction of HeH' with H2 to form H3(+) ions are described.

Johnsen, R.↗
NASA NTRS1974

Interstellar molecules - Origin by catalytic reactions on grain surfaces

To determine the compound distribution formed by surface catalysis, mixtures of CO, D2, and ND2 were heated with nickel-iron or montmorillonite clay catalysts for 49-214 hours at 250 to 300 C. Compounds identified include most of the known polyatomic interstellar molecules, as well as homologous series of acetylenes, dienes, alcohols, aldehydes, ketones, ethers, esters, nitriles, amines, etc., and cyclic compounds such as furans and pyrroles. These homologous series are uniquely characteristic of surface catalysis. A search for the heavier members of these series, predicted to occur at 1/10th to 1/1,000th the abundance of the lightest members, thus comprises a crucial test of this mechanism.

Anders, E.↗
NASA NTRS1974

Vibration-translation energy transfer in anharmonic diatomic molecules. 1: A critical evaluation of the semiclassical approximation

The semiclassical approximation is applied to anharmonic diatomic oscillators in excited initial states. Multistate numerical solutions giving the vibrational transition probabilities for collinear collisions with an inert atom are compared with equivalent, exact quantum-mechanical calculations. Several symmetrization methods are shown to correlate accurately the predictions of both theories for all initial states, transitions, and molecular types tested, but only if coupling of the oscillator motion and the classical trajectory of the incident particle is considered. In anharmonic heteronuclear molecules, the customary semiclassical method of computing the classical trajectory independently leads to transition probabilities with anomalous low-energy resonances. Proper accounting of the effects of oscillator compression and recoil on the incident particle trajectory removes the anomalies and restores the applicability of the semiclassical approximation.

Mckenzie, R. L.↗
NASA NTRS1974

Rotational-vibrational coupling in the theory of electron-molecule scattering

The adiabatic-nuclei approximation of vibrational-rotational excitation of homonuclear diatomic molecules can be simply augmented to describe the vibrational-rotational coupling by including the dependence of the vibrational wave function on j. Appropriate formulas are given, and the theory, is applied to e-H2 excitation, whereby it is shown that deviations from the simple Born-Oppenheimer approximation measured by Wong and Schultz can be explained. More important, it can be seen that the inclusion of the j-dependent centrifugal term is essential for transitions involving high-rotational quantum numbers.

Temkin, A.↗
NASA NTRS1974

The ethynyl radical C2H - A new interstellar molecule

Four new interstellar lines have been detected near 87.3 GHz. Based on laboratory ESR data these lines have been positively defined as hyperfine components of the lowest rotational transition of the ethynyl radical C2H. The observations gave precise values for the C2H rotation, spin-doubling, and hyperfine constants. C2H is probably one of the most abundant interstellar polyatomic molecules yet detected.

Tucker, K. D.↗
NASA NTRS1975

Theoretical description of the diimide molecule

The N2H2 molecule is only metastable and as a consequence is not well characterized experimentally. Therefore, we have carried out extensive Hartree-Fock calculations in order to determine equilibrium geometries, one-electron properties, and the relative energies of the cis and trans isomers. In addition, Hartree-Fock and multiconfiguration calculations were carried out to determine the mechanism for isomerization. The trans isomer was found to be 6.6 kcal/mole more stable than the cis form using a basis set which included polarization functions. The lowest energy path found for isomerization occurred by inversion about one nitrogen (rather than rotation about the NN bond) with an activation energy of 47 kcal/mole. Excitation energies for the lowest singlet and triplet excited states are also presented.

Winter, N. W.↗
NASA NTRS1975

Inelastic scattering in atom-diatomic molecule collisions. II - Effect of rotation on vibrational transition

Rotational and vibrational transitions in a diatomic molecule caused by collisions with an atom are analyzed by a semiclassical method for conditions where the rotational transitions can be handled well by the sudden approximation and the vibrational transitions belong to the adiabatic regime. The contribution to the vibrational transition probability from the correction, which takes the finite value of the spacing between rotational energy levels into account, is examined.-

Stallcop, J. R.↗
NASA NTRS1975

Production of organic molecules in the outer solar system by proton irradiation - Laboratory simulations

Preliminary experiments to investigate the formation of colored polymers and other interesting molecules by the irradiation of gas mixtures with protons are discussed. As in previous experiments, colored polymers were produced. An important feature of the present work is the presence or absence of absorption at 5 microns in the different materials produced; Titan is quite dark at this wavelength and Io is fairly bright. Such features may provide criteria for accepting or rejecting various materials produced in these experiments as reasonable coloring agents for the outer solar system.

Scattergood, T.↗
NASA NTRS1975

Vibration-translation energy transfer in anharmonic diatomic molecules. I - A comparative evaluation of the semiclassical approximation

The semiclassical approximation (quantum oscillator, classical path) is applied to anharmonic diatomic oscillators in excited initial states. Multistate numerical solutions giving the vibrational transition probabilities for collinear collisions with an inert atom are compared with equivalent, exact quantum-mechanical calculations. Several symmetrization methods are shown to correlate accurately the predictions of both theories for all initial states, transitions, and molecular types tested, but only if coupling of the oscillator motion and the classical trajectory of the incident particle is considered. In anharmonic heteronuclear molecules, the customary semiclassical method of computing the classical trajectory independently leads to transition probabilities with anomalous low-energy resonances. Proper accounting of the effects of oscillator compression and recoil on the incident particle trajectory removes the anomalies and restores the applicability of the semiclassical approximation.

Mckenzie, R. L.↗
NASA NTRS1975

Scattering of 4.5 eV electrons by ground /x 3 Sigma g minus/ state and metastable /a 1 Delta g/ oxygen molecules

The paper reports on differential and integral cross sections for scattering of 4.5 eV electrons by ground state (x 3 Sigma g minus) and metastable (a 1 Delta g) oxygen molecules in the -2.0 eV to plus 2.0 eV energy loss range. The cross section for the (a 1 Delta g to b 1 Sigma g plus) transition was found to be more than an order of magnitude larger than that of the excitation of the b state from the ground state. It was found that the principle of detailed balance can be applied to the rotationally unresolved inelastic and superelastic electronic transitions between the (x 3 Sigma g minus) and (a 1 Delta g) states, which indicates that for this transition one may neglect the very different rotational level structure of the two states in estimating superelastic cross section from inelastic data to an accuracy of about 15 per cent.

Hall, R. I.↗
NASA NTRS1975

Fluorescence detection of organic molecules in the Jovian atmosphere

A search for fluorescent emission due to the presence of possible organic molecules in the Jovian atmosphere is described. We first consider natural Jovian fluorescent emission excited by precipitating auroral particles. Due to our lack of knowledge of the Jovian precipitating particle energies and fluxes we next consider fluorescent emission excited by a laser system aboard a Jupiter spacecraft. Laser-induced fluorescence is routinely used to monitor trace constituents and pollutants in the terrestrial atmosphere. Several spacecraft laser systems are currently under development. Our calculations indicate that laser-induced fluorescent detection is approximately two orders of magnitude more sensitive than rocket ultraviolet measurements of possible Jovian absorption features at 2600 A that have been attributed to the presence of adenine or benzene.

Levine, J. S.↗
NASA NTRS1976

IR pumped third-harmonic generation and sum-frequency generation in diatomic molecules

The potential efficiency of using nonlinear up-conversion techniques for the high efficiency type lasers (CO,CO2, and chemical) is assessed. Results indicate that: the small pump photon energy necessitates the use of molecular media for conversion if resonance enhancement is to be used and that molecular systems present several problems. These difficulties include: their levels are complex; their transition probabilities are often unknown; and the oscillator strengths among vibrational levels in the ground electronic state of a molecule are much smaller than those among electronic states of an atom, thus limiting the magnitude of nonlinear interactions. It is shown that this problem can be eliminated by making use of vibronic transitions which, being primarily electronic transitions have much larger matrix elements and efficient conversion can be achieved with molecular systems.

She, C. Y.↗
NASA NTRS1976

Hydrogen molecules in interstellar space

The most important results obtained from Copernicus satellite observations of ultraviolet H2 absorption features are summarized. The properties of the hydrogen molecule are described along with the radiative processes in which it can be involved. Techniques and equipment used in observing H2 absorption features from space are reviewed. The results are discussed in terms of the fraction of hydrogen in molecular form, rotational excitation of H2, physical conditions within interstellar gas clouds, and approaching clouds characterized by high excitation and negative radial velocity. It is shown that: (1) an appreciable fraction of the hydrogen in denser and thicker clouds is molecular, (2) at least some of the interstellar clouds are far from pressure equilibrium, (3) the approaching clouds are apparently dense thick sheets moving toward the sun as viewed in the local standard of rest, (4) these clouds are probably shock waves produced in the interstellar gas by old supernova remnants or expanding H II regions, and (5) the abundances relative to H of such elements as O, Mg, Si, and Cl in these clouds are nearly equal to the solar values, which is in contrast to the depletions observed in many other interstellar clouds.

Spitzer, L.↗
NASA NTRS1977

Indirect observation of unobservable interstellar molecules

It is suggested that the abundances of neutral non-polar interstellar molecules unobservable by radio astronomy can be systematically determined by radio observation of the protonated ions. As an example, observed N2H(+) column densities are analyzed to infer molecular nitrogen abundances in dense interstellar clouds. The chemistries and expected densities of the protonated ions of O2, C2, CO2, C2H2 and CH4 are then discussed. Microwave transition frequencies fo HCO2(+) and C2H3(+) are estimated, and a preliminary astronomical search for HCO2(+) is described.

Herbst, E.↗
NASA NTRS1977

Energy threshold effects in the collisionless dissociation of polyatomic molecules by ir laser radiation

The threshold for collisionless dissociation of SF6, SiF4, and CF2Cl2 by focused CO2 laser radiation has been measured. This threshold is a laser pulse energy effect and, within experimental error, is found to be the same for all three gases. Provided collisions cannot occur during the laser pulse, the degree of dissociation produced depends only on the energy in the pulse, which is consistent with simple adiabatic vibrational heating of the molecules by the laser.

Gower, M. C.↗
NASA NTRS1977

Indirect observation of unobservable interstellar molecules

It is suggested that the abundances of neutral nonpolar interstellar molecules unobservable by radio astronomy can be systematically determined by radio observation of the protonated ions. As an example, observed N2H(+) column densities are analyzed to infer molecular nitrogen abundances in dense interstellar clouds. The chemistries and expected densities of the protonated ions of O2, C2, CO2, C2H2, and CH4 are then discussed. Microwave transition frequencies for HCO2(+) and C2H3(+) are estimated, and a preliminary astronomical search for HCO2(+) is described.

Herbst, E.↗
NASA NTRS1977

Rotational excitation of linear molecules by collisions with atoms - Comparison of classical and quantum methods

Exact quantum results for the rotational excitation of rigid linear molecules by collisions with atoms are compared with classical trajectory results. The systems studied are CO-He, CS-H2, OCS-H2, HCl-He, and HCl-Ar at collision energies up to 500/cm. Total cross sections and state to state rate constants are compared. The classical results are found to be in good agreement with the quantum results on the average. Differences arising from the existence of purely quantum effects are clearly evident, but consistent and predictable. Two methods of extracting state selective information from moments of the classical distribution are examined and found to be less reliable than the usual histogram method. In conjunction with previous comparisons of classical and quantum results these calculations provide a useful measure of the limitations and reliability of classical trajectories.

Chapman, S.↗