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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Angular distribution, kinetic energy distributions, and excitation functions of fast metastable oxygen fragments following electron impact of CO2

Dissociative excitation of CO2 by electron impact was studied using the methods of translational spectroscopy and angular distribution analysis. Earlier time of flight studies revealed two overlapping spectra, the slower of which was attributed to metastable CO(a3 pi) fragments. The fast peak is the focus of this study. Threshold energy, angular distribution, and improve time of flight measurements indicate that the fast peak actually consists of five overlapping features. The slowest of the five features is found to consist of metastable 0(5S) produced by predissociation of a sigma u + state of CO2 into 0(5S) + CO(a3 pi). Oxygen Rydberg fragments originating directly from a different sigma u + state are believed to make up the next fastest feature. Mechanisms for producing the three remaining features are discussed.

Misakian, M.↗
NASA NTRS1976

Electron impact excitation coefficients for laboratory and astrophysical plasmas

Electron impact excitation rate coefficients have been obtained for a number of transitions in highly ionized ions of interest to astrophysical and laboratory plasmas. The calculations were done using the method of distorted waves. Results are presented for various transitions in highly ionized Ne, Na, Al, Si, A, Ca, Ni and Fe.

Davis, J.↗
NASA NTRS1986

Differential excitation cross section of atomic oxygen by electron impact - (3P-1D transition)

Results of an electron impact experiment in which a crossed-beam method was used to determine the differential excitation cross sections of atomic oxygen (3P-1D transition) are reported. The measurements cover energies of 7, 10, 15, 20, and 30 eV, with the angular range varying from 30 to 150 deg in 15-deg increments. The results are consistent, both in shape and in magnitude, with theoretical predictions, providing a direct confirmation of the theoretical total excitation cross sections of O(1D) state. Details of the experimental equipment and procedure are given.

Shyn, T. W.↗
NASA NTRS1992

Electron-impact excitation of the n 1P levels of helium - Theory and experiment

New experimental electron-energy-loss data have been used to extract differential and integral cross sections for excitation of the 2 1P level, and for the overlapping (3 1P, 3 1D, 3 3D) levels of helium, at 30-, 50-, and 100-eV incident electron energies. First-order many-body theory (FOMBT) has been used to calculate the differential and integral cross sections for excitation of the n 1P (n = 2,...,6) levels of helium by electron impact, for incident electron energies from threshold to 500 eV. Detailed comparisons between these two new sets of data are made as well as comparisons with appropriate published experimental and theoretical results. A simple scaling relationship is derived from the FOMBT results for n = 2,...,6 that provides differential and integral cross sections for all symmetry final levels of helium with n = 6 or greater.

Cartwright, David C.↗
NASA NTRS1986

Electron-impact excitation of the a3Sigma(+)g, B1Sigma(+)u, c3Pi u, and C1Pi u states of H2

Normilized differential and integral cross sections for electron-impact excitation of the dipole-allowed B1Sigma(+)u, C1Pi u and dipole-forbidden a3Sigma(+)g, c3Pi u states of molecular hydrogen have been determined by analysis of energy-loss spectra obtained with a crossed-beam apparatus at electron-impact energies of 20, 30, 40 and 60 eV and scattering angles ranging from 10 to 120 degrees. Normalization of the data was achieved by utilizing elastic differential cross sections measured previously by (Khakoo and Trajmar, 1986). The cross sections are compared with other available theoretical and experimental data.

Khakoo, M. A.↗
NASA NTRS1975

Nonthermal rotational distribution of CO/A 1Pi/ fragments produced by dissociative excitation of CO2 by electron impact

Measurements were made of the rotational profiles of specific bands of the CO fourth-positive group (4PG). The CO 4PG bands were excited by electron impact dissociative excitation of CO2. The results are applicable to analysis of the Mariner observations of the CO 4PG in the dayglow of Mars. The results indicate that dissociative excitation of CO2 by electron impact leads to CO(A 1Pi) fragments with a rotational distribution that is highly nonthermal. The parent CO2 temperature was about 300 K in the experiment, while the fragment CO(A 1Pi) showed emission band profiles consistent with a rotational temperature greater than about 1500 K. Laboratory measurement of the reduced transmission of the hot bands by thermal CO appears to be the most direct way of determining the column density responsible for the CO(v',0) absorption of Mars.

Mumma, M. J.↗
NASA NTRS1989

Medium-resolution studies of extreme ultraviolet emission from N2 by electron impact - Vibrational perturbations and cross sections of the c4-prime 1Sigma(+)u and b-prime 1Sigma(+)u states

In a crossed-beam experiment the electron-impact-induced fluorescence spectrum of N2 in the extreme ultraviolet is studied at a spectral resolution of up to 0.03 nm. The optically thin experiment obtained the highest-resolution electron-impact emission spectrum of the Rydberg and valence states of N2. The spectral measurements provide the emission cross sections of each of the vibrational transitions of the Carroll-Yoshino and the Birge-Hopfield-II band systems. Laboratory vibrational-excitation cross sections arising from the mutual perturbation of the c4-prime 1Sigma(+)u and b-prime 1Sigma(+)u states by homogeneous configuration interactions are measured from 10 to 400 eV, and a modified Born approximation analytic model is given for them. The analysis leads to accurate band-system oscillator strengths. The relative emission and excitation cross sections each of the vibrational levels are compared. In addition, low-resolution measurements of the cross section of the atomic dissociation fragments (NI, NII, NIII) from 40 to 102 nm are made, and medium-resolution measurements are made of the emission cross section of the c4 1Pi(u), c5-prime 1Sigma(+)u, c5 1Pi(u), and c6-prime 1Sigma(+)u to X 1Sigma(+)g (0,0) transitions.

Ajello, Joseph M.↗
NASA NTRS1976

Measurement of the 13 to 100 eV electron impact excitation cross section for the X 1Sigma /+/-g yields a 1Pi-g transition in N2

An inelastic scattering technique was used to measure the electron impact excitation cross section for the X 1Sigma (+)-g yields a 1Pi-g transition in N2 in the energy range 13 to 100 eV. The relative excitation cross section was calculated by integration of the relative differential scattering cross sections at various energies and the relative values of the excitation cross section were put on an absolute scale by comparing the relative cross sections to those for excitation of the X 1Sigma (+)-g yields C 3Pi-u transition and those of the electron impact optical emission cross section for the C 3Pi-u yields B 3Pi-g transition as a secondary standard. The excitation cross section was found to vary from a maximum value of 3.6 x 10 to the -17 cu cm between 15 and 18 eV to 5.2 x 10 to the -18 cu cm at 100 eV.

Finn, T. G.↗
NASA NTRS1980

Excitation of the b 3 Sigma u + state of H2 by electron impact - Semiclassical exchange potentials at intermediate energies

Integrated and differential cross sections for the excitation of the b 3 Sigma u + state of H2, from the ground state, by electron impact, are presented. The energy range of interest is 10.5 to 40.0 eV. The close-coupling equations for this process are solved in five different exchange approximations: exact two-electron exchange terms, no orthogonality; exact two-electron exchange terms, orthogonality; semiclassical exchange terms, no orthogonality, with barrier term; semiclassical exchange terms, no orthogonality, no barrier term; and semiclassical exchange terms, orthogonality, with barrier term. The purpose is to judge the reliability of the semiclassical exchange approximation for electronic excitation of molecules by electron impact at intermediate energies. The results are compared with recent theoretical estimates for the same process.

Weatherford, C. A.↗
NASA NTRS1972

Linear momentum transfer effects in molecular dissociation produced by electron impact.

In this study of molecular dissociation produced by electron impact, diatomic systems and polyatomic molecules are considered, and attention is given to the effects of thermal motion and of momentum transfer in the collision process. A procedure is described which makes it possible to 'construct' both the laboratory angular distribution and velocity distribution of the atomic fragments (or, alternatively, the time-of-flight distribution). The calculation assumes that s-wave electron scattering predominates, i.e., that excitation occurs near threshold. The computational procedure may also be reversed to allow construction of possible molecular models to fit given experimental angular and velocity distribution data.

Misakian, M.↗
NASA NTRS1985

The ionization of atomic oxygen by electron impact

Single and double ionization of atomic oxygen by electron impact has been studied experimentally. The energy dependence of the specific ionization cross sections sigma(O+) and sigma(O2+) has been measured in the energy range 40-300 eV using a high-density atomic oxygen source not contaminated by metastable O(D-1) or O(S-1) atoms. The ratios of the measured cross sections to absolute values are given in a table.

Zipf, E. C.↗