SEARCH · Search NASA
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
The cross section for the electron-impact excitation of C(+) (2s2 2p 2P0)-(2s2p2 2D) is measured in a colliding-beams apparatus for several collision energies near the threshold for the process. A cross section of (1.1 + or - 0.3) x 10 to the -16th sq cm at threshold is found. Reasonable agreement is found with close-coupling calculations.
Over the past two years several Lyman alpha line profile spectra of Jupiter were obtained using the International Ultraviolet Explorer (IUE) telescope. Several different regions of the planet were observed including the auroral zone, the low and mid latitudes, and the equatorial region which includes the Lyman alpha bulge region. These results have presented a very interesting picture of atomic hydrogen on Jupiter with explanations that range from ion outflow in the auroral zone to large thermospheric winds at low and mid latitudes. New data are needed to address the outstanding questions. Almost certainly, high resolution spectra from the Hubble Space Telescope will play a role in new observations. Better data also require better models, and better models require new laboratory data as inputs. The purpose of this program is two-fold: (1) to introduce a method by which new laboratory electron impact measurements of H2 dissociation can be used to calculate both the slow and fast H(S-2) and H(P-2) fragments in an H2 atmosphere; and (2) to determine the predicted Lyman alpha line shape that would result from electron impact production of these dissociative fragments in the Jovian auroral zone.
The partial and total ionization cross section for the formation of O(+), S(+), SO(+) and SO2(+) from the impact ionization of SO2 are reported, extending the electron impact energies to 200 eV. The relative flow technique is used to determine the cross section values. The threshold potentials for the products are 23.5 eV for O(+), 16.5 eV for S(+), 16.5 eV for SO(+), and 12.5 eV for SO2(+). Good agreement with the literature is found for SO(+) and SO2(+).
Experiments were performed to measure, by electron impact, appearance potentials and the cross sections for ionization, dissociative ionization, and electron attachment for H2S. Results are presented, and discussed individually, for both positive and negative ions. A schematic diagram of the experimental setup is included.
Measurements of the middle ultraviolet (MUV) electron impact induced fluorescence spectrum of SO2 from 200 to 430 nm in a crossed beam experiment are reported. The spectrum is dominated by two features at the experimental resolution of 0.5 nm; these two features are referred to as MUV1 and MUV2. MUV1 is the SO band system extending from 240 to 265 nm produced by dissociative excitation. MUV2 is a blend of the SO2 and SO2(+) molecular band systems in the range 264-430 nm. The excitation function measurements of MUV2 indicate that low-energy electrons effectively prepare SO2 in one or more electronically excited triplet states that involve the SO2 state by direct excitation and/or cascading. The peak cross section for MUV1 occurs at 20 eV with a value of 25.0 +/-5.5 x 10 exp -19 sq cm. The peak cross section for MUV2 arises at 9 eV with a value of 368 +/-81 x 10 exp -19 sq cm. The laboratory results provide a plausible explanation of the Io auroral hot spots observed by Voyager 2.
The doppler profiles of one of the fine structure lines of the NI multiplet and the NII multiplet have been measured. Excitation of the multiplets is produced by electron impact dissociative excitation of N&sub2;
Cyclic ketones containing methoxyl and hydroxyl studied for oxygen rearrangement on electron impact
Kinetic energies of metastable oxygen atoms formed by electron impact dissociation of oxygen and measured in time of flight experiment
Excitation cross sections for resonance states by electron impact on atomic nitrogen and oxygen over aeronomical energy range
Simple group theoretical principles are applied to the consideration of electron scattering off atoms and diatomic and polyatomic molecules. This approach is also used to estimate relative strengths of electron-impact-induced transitions of diatomic and polyatomic molecules.
The analytic characterizations of electron impact cross sections for important atmospheric gases (namely, O2, N2, O, CO, CO2, and He) are updated. With these cross sections it is simple to communicate massive quantities of experimental and theoretical results. In addition, these forms are convenient for applications in energy degradation calculations, including a new approach described in a companion paper.
Emission spectrum of O2 from 115 to 300 nm induced by electron impact at 200 eV was obtained using a crossed-beam configuration under optically thin conditions. The second negative system of O2(+) was observed in the range 186-300 nm. Model calculations were performed to derive the contribution made by the second negative system of O2(+) to auroral spectra in the same wavelength range. Observations of the spectral region from 140 to 185 nm, carried out to verify the report of Erdman and Zipf (1986) on the O or O(+) transitions showed no detectable O or O(+) transitions with a cross section upper limit of 10 to the -21 sq cm.
Low-energy electron impact excitation of the fundamental modes of CO2 has been extensively studied, both experimentally and theoretically. Much attention has been paid to the virtual state feature in the the (100) mode excitation and the (sup 2)II(sub upsilon) resonance feature around 3.8 eV, which is observable in all three fundamental modes. For the excitation of the (010) mode away from the resonance region, the Born dipole approximation was generally considered adequate. The present study employs the Born dipole approximation to treat the long range interaction and the Schwinger multichannel method for the short range interaction. The roles of the two interaction potentials will be compared.
The excitation function of prompt Lyman-alpha radiation, produced by electron impact excitation of atomic hydrogen in the energy range from threshold to 1.8 keV, has been measured in a crossed-beam experiment. The present data are significantly different from earlier experimental results and are in good agreement with recent theoretical convergent close coupling calculations over a two order of magnitude range in impact energy. Multistate coupling affecting the excitation function to 1 keV is apparent in both the present experimental and recent theoretical results.
Time-of-flight techniques have been used to investigate the electron-impact dissociation of H2, HD, and D2 in order to determine the effect of isotopic mass variation in the target molecule on the dissociative excitation process. At incident electron energies near 100 eV, the time-of-flight spectrum produced from each molecule consists of atoms in the metastable 2s state and in high-lying long-lived Rydberg levels. The individual time-of-flight distributions, kinetic-energy spectra, and relative differential cross sections for these two species resulting from each molecule have been measured. The kinetic-energy spectrum of the Rydberg atoms produced from dissociative excitation of H2 was notably dissimilar in shape from the corresponding distributions produced from HD and D2. Also the 2s and Rydberg production cross sections differed between the three molecules. In the dissociation of the heteronuclear HD molecule, the ratio of fast H(2s) atoms to D(2s) atoms was about 1 to 1, while the same ratio comparing the Rydberg atoms was nearly 2 to 1. These differences indicate the influence of the mass variation on the position of the Franck-Condon region in the production of 2s atoms and on the competition between autoionization and dissociation in the formation of Rydberg fragments.
We investigate the ionization of interstellar hydrogen and helium due to electron impact by shock-heated electrons. Taking the electron distributions measured at four interplanetary shocks at 1 AU, we show that the electrons in the downstream region of strong shocks can ionize interstellar atoms at rates matching or exceeding the nominal photoionization or charge-exchange rates. We suggest that this process may explain some puzzling observations of interstellar pickup ions by the Ulysses spacecraft.
Energy required for proton and molecular hydrogen ion production by electron impact in tenuous hydrogen plasma using Maxwellian electron gas model
Mass spectra peaks of N-Acyl-2-indolinols fragmentation processes upon electron impact, noting compounds predominance in open chain tautomer gas phase