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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS2021

Sputtering of Surfaces by Ion Irradiation: A Comparison of Molecular Dynamics and Binary Collision Approximation Models to Laboratory Measurements

We compare various sputtering simulation methods to experimental results in both the low energy (<1 keV) and high energy (≥1 keV) impact regimes for argon ions impacting a pure copper substrate at normal incidence. Our results indicate that for high energy impacts, both binary collision approximation (BCA) and molecular dynamics methods can be used to generate reasonable predictions for the yield and energy distribution of the sputtered atoms. We also find reasonable agreement between the theoretical and experimental results down to impact energies of 600 eV. However, at 200 eV impact energies, significant discrepancies appear between the experimental and theoretical ejecta energy distributions in the peak position, the width of the energy distribution, and the magnitude of the high energy tail. These discrepancies appear to arise from the experimental results being only for atoms sputtered normal to the substrate surface, whereas the theoretical results are integrated over all 2π solid angles above the surface. Using the BCA code SDTrimSP and limiting the results to only atoms emitted within ±15° of the surface normal brings theory and experiment into reasonable agreement. These results suggest that for low energy impacts, the energy distribution of sputtered atoms is highly dependent on the emission angle of the ejecta.

Solar wind↗
NASA NTRS1972

The atom-molecule reaction D plus H2 yields HD plus H studied by molecular beams

Collisions between deuterium atoms and hydrogen molecules were studied in a modulated crossed beam experiment. The relative signal intensity and the signal phase for the product HD from reactive collisions permitted determination of both the angular distribution and HD mean velocity as a function of angle. From these a relative differential reactive scattering cross section in center-of-mass coordinates was deduced. The experiment indicates that reactively formed HD which has little or no internal excitation departs from the collision anisotropically, with maximum amplitude 180 deg from the direction of the incident D beam in center-of-mass coordinates, which shows that the D-H-H reacting configuration is short-lived compared to its rotation time. Non reactive scattering of D by H2 was used to assign absolute values to the differential reactive scattering cross sections.

Geddes, J.↗
NASA NTRS1982

Stratospheric measurements of collision-induced absorption by molecular oxygen

High-resolution stratospheric solar absorption spectra recorded at sunset with a balloon-borne interferometer, from an altitude of 33 km, are used in a study of collision-induced absorption by the fundamental vibration-rotation band of O2, whose continuum has been identified in the 1400-1700/cm region in spectra obtained at tangent altitudes below 22 km. It is found that transmittance measurements in intervals free of atmospheric line absorption agree with values calculated with the O2 absorption coefficients of Timofeyev and Tonkov (1978), and that the measurements indicate a 20% upper limit for the uncertainty of the available O2 absorption coefficients at lower stratospheric temperatures, on the order of 220 K.

Rinsland, C. P.↗
NASA NTRS1985

Measurement of collision-induced shift and broadening of the ultraviolet transitions of OH

Using a CW tunable laser, absorption measurements were made to determine for the first time the shift and broadening of the ultraviolet transitions of OH induced by collisions with molecular nitrogen and oxygen. Similar measurements were also made for collisions with air and inert gases He, Ne, Ar, and Kr. Both the shift and broadening due to these collisions were found to depend linearly upon pressures in the range from 50 Torr up to 1 atm. The homogeneous linewidth for the P2(2) transition of OH in ambient air is determined to be 0.20 + or - 0.005/cm. Results with Ar and Kr show contributions not accounted for by the polarizability of the colliding species.

Shirinzadeh, B.↗
NASA NTRS1995

The Schwinger Variational Method

Variational methods have proven invaluable in theoretical physics and chemistry, both for bound state problems and for the study of collision phenomena. The application of the Schwinger variational (SV) method to e-molecule collisions and molecular photoionization has been reviewed previously. The present chapter discusses the implementation of the SV method as applied to e-molecule collisions. Since this is not a review of cross section data, cross sections are presented only to server as illustrative examples. In the SV method, the correct boundary condition is automatically incorporated through the use of Green's function. Thus SV calculations can employ basis functions with arbitrary boundary conditions. The iterative Schwinger method has been used extensively to study molecular photoionization. For e-molecule collisions, it is used at the static exchange level to study elastic scattering and coupled with the distorted wave approximation to study electronically inelastic scattering.

Huo, Winifred M.↗