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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 91 records · Page 5
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NASA NTRS1987

Collisional excitation of an asymmetric rotor, silicon dicarbide

Rotational excitation rates have been computed for the asymmetric top molecule SiC2 in collisions with low-energy He atoms. The intermolecular forces were obtained from an electron gas model, and collision dynamics were treated within the infinite-order sudden approximation. Total excitation rates, i.e., summed over final levels, are expected to be accurate to about 50 percent, and the larger state-to-state rates are likely to be within a factor of about 2 of the correct values, although some of the smaller (and less important) rates may be less accurate. These rates are also thought to reflect, within this level of accuracy, rates for excitation by collisions with H2 molecules.

Palma, Amedeo↗
NASA NTRS1987

Collisional excitation of interstellar sulfur dioxide

State-to-state rotational excitation rates for the asymmetric top molecule SO2 in collisions with low-energy He atoms have been computed. The intermolecular forces were obtained from an electron gas model, and collision dynamics were treated with the finite-order sudden approximation. The total excitation rate is probably accurate to better than 50 percent; however, individual state-to-state rates may be in error by factors of 2 or 3, and some smaller rates may be accurate only to an order of magnitude. Present results are expected to reflect within the same level of accuracy rates for excitation by collisions with H2 molecules.

Palma, Amedeo↗
NASA NTRS1995

Computing Fluxes Of Molecules On And Near A Spacecraft

Molecular Flux (MOLFLUX) computer code versatile program used to compute following environmental effects induced by spacecraft: fluxes of molecules to, and deposition of molecules on, surfaces; densities and column densities of molecules in surrounding space, and return fluxes of molecules to surfaces caused by both collisions of molecules with ambient atmosphere and by self-scattering. Includes capability to predict buildup in density of ambient gas in front of surfaces exposed to ram conditions by specifying ambient flux rates for all species impinging on surfaces. Surface chemical reactions represented as rates of emission from surfaces. User has option to modify spacecraft configurations and sources of contamination, and to choose which critical surfaces to examine. Written in FORTRAN and C language.

Ehlers, H. K.↗
NASA NTRS1996

Computing Fluxes Of Molecules On And Near A Spacecraft

Molecular Flux (MOLFLUX) computer code is versatile program used to compute following conditions on and near spacecraft: fluxes of molecules to, and deposition of molecules on, surfaces; densities and column densities of molecules in surrounding space, and return fluxes of molecules to surfaces caused by both collisions of molecules with ambient atmosphere and by self-scattering. User has option to modify spacecraft configurations and sources of contamination and to choose which critical surfaces to examine. Written in FORTRAN and C language. Three machine versions available: VAX version (MSC-22260), HP version (MSC-22565), and Cray version (MSC-22566).

Ehlers, H. K.↗
NASA NTRS1973

Calculated dipole moment and energy in collision of a hydrogen molecule and a hydrogen atom

Calculations were carried out using three Slater-type 1s orbitals in the orthogonalized valencebond theory of McWeeny. Each orbital exponent was optimized, the H2 internuclear distance was varied from 7.416 x 10 to the -11th power to 7.673 x 10 to the -11th power m (1.401 to 1.450 bohrs). The intermolecular distance was varied from 1 to 4 bohrs (0.5292 to 2.117 x 10 to the 10th power). Linear, scalene, and isosceles configurations were used. A weighted average of the interaction energies was taken for each intermolecular distance. Although energies are tabulated, the principal purpose was to calculate the electric dipole moment and its derivative with respect to H2 internuclear distance.

Patch, R. W.↗
NASA NTRS1972

Collision integrals for isotopic hydrogen molecules.

The study was undertaken to determine the effects of reduced mass and differences in asymmetry on the collision integrals and thermal diffusion factors of isotopic hydrogen systems. Each system selected for study consisted of two diatoms, one in the j = 0 rotation state and the other in the j = 1 state. The molecules interacted with a Lennard-Jones type potential modified to include angular terms. A set of cross sections and collision integrals were obtained for each system.

Brown, N. J.↗
NASA NTRS1989

Polarization effects in low-energy e-CH4 collisions

Polarization effects on the cross sections for elastic scattering of electrons by the CH4 molecule, for collision energies from 7.5 down to 0.02 eV, are presently studied on the basis of Takatsuka and McKoy's (1981) Schwinger multichannel formulation. While the closed-channel expansion through which polarization effects are encompassed is not fully converged, the cross sections obtained nevertheless exhibit a Ramsauer-Townsend minimum in the 0.1-0.2 eV range; this is about 0.3 lower than the experimentally obtained value. At 7.5 eV, however, the calculated differential cross-sections are in excellent agreement with measured values.

Lima, M. A. P.↗
NASA NTRS1976

Infrared emission from the atmosphere above 200 km

The infrared radiation over the range from 4 to 1000 microns from atoms and molecules in the earth's atmosphere, between 200 and 400 km, was calculated. Only zenith lines of sight were considered. The excitation of the atoms and molecules is due to collisions with other molecules and to absorption of radiation from the earth and sun. In some cases, the abundances of the molecules had to be estimated. The most important lines are the forbidden lines from atomic oxygen at 63.1 and 147 micron, and the vibration-rotation band of nitric oxide at 5.3 micron. These lines can have intensities as high as a few times 0.001 ergs/sq cm/sec/steradian at 200 km altitude. In addition, the vibration-rotation bands of NO(+) at 4.3 micron and CO at 4.7 micron and the pure rotation lines of NO and NO(+) could be detected by infrared telescopes in space.

Simpson, J. P.↗
NASA NTRS1990

New parameter-free polarization potentials in low-energy positron collisions

The polarization potential plays a decisive role in shaping up the cross sections in low energy positron collisions with atoms and molecules. However, its inclusion without involving any adjustable parameter, is still a challenge. Various other techniques employed so far for positron collisions are summarized, and a new, nonadjustable and very simple form of the polarization potential for positron-atom (molecule) collisions below the threshold of positronium formation is discussed. This new recently proposed potential is based on the correlation energy of a single positron in a homogeneous electron gas. The correlation energy was calculated by solving the Schrodinger equation of the positron-electron system and fitted to an analytical form in various ranges of the density parameter. In the outside region, the correlation energy is joined smoothly with the correct asymptotic form. This new positron correlation polarization (PCOP) potential was tested on several atomic and molecular targets such as the Ar, CO, and CH4. The results on the total and differential cross sections on these targets are shown along with the experimental data where available.

Jain, Ashok↗