SEARCH · Engineering Papers
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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Particle densities, elastic and inelastic scattering, electron diffraction patterns, and adsorbate influence on surface structure and work function changes on crystalline surfaces
Equipment and capabilities developed in investigation of K and L shell ionization cross sections, X ray intensity ratios, bremsstrahlung spectrum, coincidence, and inelastic electron scattering
The daytime photoelectron energy spectrum has been measured at altitudes above 154 km by the photoelectron-spectrometer experiment on the Atmosphere Explorer-E satellite. Below 200 km, well-resolved peaks are observed in the spectrum corresponding to production of O(+) and N2(+) in various electronic states from photoionization of N2 and O by solar He II (304A) radiation. Vibration-rotation excitation of N2 by inelastic electron scattering is observed at 2.5 eV. The features due to nitrogen disappear from the spectrum at altitudes above 200 km.
Experimental studies concerning elastic and inelastic electron scattering by coherently ensembles of Ba (...6s6p (sub 1)P(sub 1)) atoms with various degrees of alignment will be described. An in-plane, linearly-polarized laser beam was utilized to prepare these target ensembles and the electron scattering signal as a function of polarization angle was measured for several laser geometries at fixed impact energies and scattering angles. From these measurements, we derived cross sections and electron-impact coherence parameters associated with the electron scattering process which is time reverse of the actual experimentally studied process. This interpretation of the experiment is based on the theory of Macek and Herte. The experimental results were also interpreted in terms of cross sections and collision parameters associated with the actual experimental processes. Results obtained so far will be presented and plans for further studies will be discussed.
Symmetric excited state electron capture cross sections in ion-atom inelastic scattering, using two state approximation formulas
A complex study of the electron-phonon interaction in thin NbC films with electron mean free path l=2-13 nm gives strong evidence that electron scattering is significantly modified due to the interference between electron-phonon and elastic electron scattering from impurities.
Resonances below inelastic threshold of electron hydrogen scattering examined by projection operator technique of Feshbach
Inelastic scattering of electrons by surface plasma oscillation for low energy electron diffraction and photoemission, interpreting surface plasmon excitation
Nanowire electron scattering spectroscopy (NESS) has been proposed as the basis of a class of ultra-small, ultralow-power sensors that could be used to detect and identify chemical compounds present in extremely small quantities. State-of-the-art nanowire chemical sensors have already been demonstrated to be capable of detecting a variety of compounds in femtomolar quantities. However, to date, chemically specific sensing of molecules using these sensors has required the use of chemically functionalized nanowires with receptors tailored to individual molecules of interest. While potentially effective, this functionalization requires labor-intensive treatment of many nanowires to sense a broad spectrum of molecules. In contrast, NESS would eliminate the need for chemical functionalization of nanowires and would enable the use of the same sensor to detect and identify multiple compounds. NESS is analogous to Raman spectroscopy, the main difference being that in NESS, one would utilize inelastic scattering of electrons instead of photons to determine molecular vibrational energy levels. More specifically, in NESS, one would exploit inelastic scattering of electrons by low-lying vibrational quantum states of molecules attached to a nanowire or nanotube.
High energy electron ionization cross section for hydrogen, noting high quantum number correspondence to classical expression
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The goal of this research grant was to calculate accurate oscillator strengths and electron collisional excitation strengths for inelastic transitions in atomic species of relevance to Planetary Atmospheres. Large scale configuration-interaction atomic structure calculations have been performed to obtain oscillator strengths and transition probabilities for transitions among the fine-structure levels and R-matrix method has been used in the calculations of electron-ion collision cross sections of C II, S I, S II, S III, and Ar II. A number of strong features due to ions of sulfur have been detected in the spectra of Jupiter satellite Io. The electron excitation cross sections for the C II and S II transitions are studied in collaboration with the experimental atomic physics group at the Jet Propulsion Laboratory. There is excellent agreement between experiment and theory which provide an accurate and broad-base test of the ability of theoretical methods used in the calculation of atomic processes. Specifically, research problems have been investigated for: electron impact excitation cross sections of C II: electron impact excitation cross sections of S III; energy levels and oscillator strengths for transitions in S III; collision strengths for electron collisional excitation of S II; electron impact excitation of inelastic transitions in Ar II; oscillator strengths of fine-structure transitions in neutral sulfur; cross sections for inelastic scattering of electrons from atomic nitrogen; and excitation of atomic ions by electron impact.
The experimental problems are summarized for measurement of inelastic differential cross sections (DCSs) for electron scattering from gases at electron impact energies near the threshold. A procedure is described and demonstrated with an example of CO.
Differential cross sections for electron scattering by hydrogen with and without vibrational excitation, discussing inelastic processes
Numerical coefficients required to express the angular distribution for the rotationally elastic or inelastic scattering of electrons from a diatomic molecule were tabulated for the case of nitrogen and in the energy range from 0.20 eV to 10.0 eV. Five different rotational states are considered.
Inelastic and superelastic scattering of 30- and 100-eV electrons by laser-excited 6s 6p 1P and subsequent cascade-populated 6s 6p 3P, 6s 5d 1D, and 6s 5d 3D Ba atoms have been observed. Absolute differential cross sections for the singlet and relative scattering intensities for the triplet species have been determined in the 5 to 20 deg angular region. Under the present conditions excitations dominate over deexcitations.
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