Search NASA⌕ Search

SEARCH · Search NASA

Results for “photoelectrons”

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.

At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Conjugate photoelectron excitation of O I 4368 airglow emission.

Conjugate photoelectron fluxes are shown to be mainly responsible for the excitation of O I 4368 radiation observed with a grille spectrometer located at Langmuir Laboratory, New Mexico (L equals 1.7). On the basis of observations of O I 7774 and 4368 tropical emissions at Agulhas, Negras, Brazil (L equals 1.1), the contribution of radiative recombination to the New Mexico intensity is shown to be small. Conjugate photoelectron excitation at the Brazilian site has not been observed.

Christensen, A. B.↗
NASA NTRS1973

Thermalization and transport of photoelectrons - A comparison of theoretical approaches.

Three methods of studying ionospheric photoelectron thermalization, in which transport effects are evaluated in different ways, are outlined and compared. One method uses a diffusion equation formulation, the second proceeds from a two-stream approximation to the general particle transfer equation, and the third employs a Monte Carlo technique to simulate electron paths. The methods are compared by applying them to identically prepared models. The methods are in close agreement for altitudes in the region of local energy loss, but higher altitudes reveal a discrepancy of as much as a factor of 2 in the net flux of photoelectrons. The discrepancy is removed by appropriately modifying the computational techniques.

Cicerone, R. J.↗
NASA NTRS1973

Investigation of photoelectron spectroscopy

The problem of obtaining true and meaningful branching ratios from the photoelectron spectra is investigated. The problem consists of understanding the transmission of an electron energy analyzer for electrons with different energies, understanding the effects of using partially polarized radiation from different vacuum monochromators, and in understanding the effects of the angular distribution of photoelectrons ejected from different orbitals. An analysis of the degree of polarization of monochromatic radiation and of the problem of varying angular distributions led to the construction of a cylindrical mirror electron energy analyzer set at the special angle of 54 deg 44 min so that no discrimination would occur for electrons of different angular distributions. With the analyzer properly calibrated for transmission of electrons of different energies, data were taken at several wavelengths and for several atmospheric gases.

Samson, J. A. R.↗
NASA NTRS1973

Measurement of the lunar photoelectron layer in the geomagnetic tail

Stable photoelectron fluxes (with energies between 40 and 200 eV) were observed by the Apollo 15 Charged Particle Lunar Environment Experiment (CPLEE). These observations, made in the magnetotail under near vacuum conditions, are compared with numerically calculated photoemission spectra to determine the approximate potential difference between ground and CPLEE'S apertures (a distance of 26 cm). Numerically calculated density and potential distributions are compared with the measured values to provide an estimate of the photoelectron yield function of the dust layer covering the moon.

Reasoner, D. L.↗
NASA NTRS1974

Angular distribution of photoelectrons from atomic oxygen, nitrogen and carbon

The angular distributions of photoelectrons from atomic oxygen, nitrogen, and carbon are calculated. Both Hartree-Fock and Hartree-Slater (Herman-Skillman) wave functions are used for oxygen, and the agreement is excellent; thus only Hartree-Slater functions are used for carbon and nitrogen. The pitch-angle distribution of photoelectrons is discussed, and it is shown that previous approximations of energy-independent isotropic or sin squared theta distributions are at odds with the authors' results, which vary with energy. This variation with energy is discussed, as is the reliability of these calculations.

Manson, S. J.↗
NASA NTRS1975

Theory of photoelectron thermalization and transport in the ionosphere

A new theoretical approach for calculating the equilibrium photoelectron flux energy and pitch angle distribution in the ionosphere is presented. Photoelectron transport, secondary electron production, and energy degradation by the excitation of the discrete energy states of the neutral atmospheric constituents and by continuous energy transfer to the ambient thermal electron gas are included in a manner consistent with the Boltzmann equation which constitutes the foundation of the theory. A difference equation, suitable for numerical solution, is given, and a numerical method for the solution of this equation is discussed in detail.

Mantas, G. P.↗
NASA NTRS1975

Effects of anisotropic electron-ion interactions in atomic photoelectron angular distributions

A summary of the angular momentum transfer formulation of the differential photoionization cross section is presented and photoionization amplitudes in LS coupling are considered. The application of the theoretical concepts and relations developed is illustrated with the aid of an example involving the calculation of the angular distribution of photoelectrons ionized from atomic sulfur according to a certain reaction. The investigation shows that anisotropic electron-ion interactions in atomic sulfur lead to measurable differences between photoelectron angular distribution asymmetry parameters corresponding to alternative ionic term levels.

Dill, D.↗
NASA NTRS1975

Angular distribution of photoelectrons at 584A using polarized radiation

Photoelectron angular distributions for Ar, Xe, N2, O2, CO, CO2, and NH3 were obtained at 584 A by observing the photoelectrons at a fixed angle and simply rotating the plane of polarization of a highly polarized photon source. The radiation from a helium dc glow discharge source was polarized (84%) using a reflection type polarizer.

Hancock, W. H.↗
NASA NTRS1976

High resolution daytime photoelectron energy spectra from AE-E

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.

Doering, J. P.↗
NASA NTRS1976

Recent progress in photoelectron image detection with CCDs

Intensified CCDs (ICCDs) were built and operated. These ICCDs were electrostatically and magnetically-focussed image tubes which use CCDs as anodes. The ICCDs detected single photoelectrons, and have electron gain very near that which was predicted. The first single-pixel pulse-height distributions were presented, and the leakage current was shown to increase as a function of photoelectron irradiation. The advantages and disadvantages of front- and rear-illuminated designs were discussed in light of differing applications requirements.

Choisser, J. P.↗
NASA NTRS1976

High-resolution threshold photoelectron spectroscopy by electron attachment

A new technique for measuring high-resolution threshold photoelectron spectra of atoms, molecules, and radicals is described. It involves photoionization of a gaseous species, attachment of the threshold, or nearly zero electron to some trapping molecule (here SF6 or CFCl3), and mass detection of the attachment product (SF6/-/ or Cl/-/ respectively). This technique of threshold photoelectron spectroscopy by electron attachment was used to measure the spectra of argon and xenon at 11 meV (FWHM) resolution, and was also applied to CFCl3.

Ajello, J. M.↗
NASA NTRS1977

Photoelectron energy loss and spectral features deduced by the plasma line technique

Plasma line data gathered at the Arecibo Observatory are used to examine relative variations in topside F region differential photoelectron fluxes in the 5- to 20-eV range. A spectral feature not found in present theoretically calculated spectra is noted near 15 eV. A new approach to the interpretation of the measured spectra is taken, which allows a qualitative estimate of the relative importance of different energy loss mechanisms. The altitude variation of the observed photoelectron flux energy spectra at the higher altitudes (above 350 km) and the lower energies (less than 10 eV) agrees quantitatively with the expected variation of the spectrum.

Abreu, V. J.↗
NASA NTRS1976

Angular distribution of photoelectrons at 584 A using polarized radiation

Photoelectron angular distributions for Ar, Xe, N2, O2, CO, CO2, and NH3 have been obtained at 584 A by observing the photoelectrons at a fixed angle and simply rotating the plane of polarization of a highly polarized photon source. The radiation from a helium dc glow discharge source was polarized (84%) using a reflection type polarizer

Hancock, W. H.↗
NASA NTRS1977

Studies of Ar and N2 using threshold photoelectron spectroscopy by electron attachment /TPSA/

Threshold photoelectron spectra of Ar and N2 are studied by a technique called threshold photoelectron spectroscopy by electron attachment, which involves the attachment of the threshold electron to SF6 followed by the detection of SF6(-). Studies on Ar provide a measure of the rejection ratio for nonthreshold electrons of this technique. A rotational propensity rule is given which states that an autoionizing N2 state prefers to decay to N2(+) states with a minimum change in rotational angular momentum.

Chutjian, A.↗
NASA NTRS1977

Measurement of magnetic field aligned potential differences using high resolution conjugate photoelectron energy spectra

Simultaneous high-resolution observations of a distinctive feature in the energy spectrum of conjugate photoelectrons and spacecraft potential relative to the local ionosphere have allowed the net potential difference between magnetic conjugate points at latitudes below the region of low-energy (i.e., lower than 100 eV) auroral electron precipitation to be determined. Measurements made at 300 km from Atmosphere Explorer C show that there is normally no net potential difference between hemispheres in this region, which extended up to invariant latitudes as high as 74 deg. Two types of apparently related anomalous behavior were infrequently observed at high latitudes. During these periods the incident flux of conjugate photoelectrons was either decelerated by about 3 eV or was not detected.

Peterson, W. K.↗
NASA NTRS1978

Photoelectrons and electron temperatures in the Venus ionosphere

Solar wind induced magnetic fields may be present in the dayside ionosphere of Venus. A scale analysis and detailed calculations of the effects of different field line orientations on photoelectron transport and electron temperature show that horizontal magnetic fields considerably alter the profiles of electron heating and temperature and photoelectron flux. Direct injection of solar wind electrons has been considered, and the effects are minor. No evidence is found to support the suggestion that a sharp gradient in electron temperature is the cause of certain features in the Mariner-10 electron density profile.

Butler, D. M.↗
NASA NTRS1979

Photoelectron charge density and transport near differentially charged spacecraft

The effects of photoelectron space charge and current density on differentially charged spacecraft are studied. The steady-state potentials of a sunlit cylinder are calculated using a two-dimensional computer code with a fully self-consistent treatment of space charge and an effective surface conductivity treatment of photoelectron currents. It is found that under conditions of strong differential charging the results do not differ greatly from NASCAP results, which neglect photosheath space charge and currents.

Mandell, M. J.↗
NASA NTRS1985

The ultraviolet dayglow at solar maximum. III - Photoelectron-excited emissions of N2 and O

Rocket observations of the far ultraviolet dayglow spectrum near solar cycle maximum are analyzed using laboratory cross sections, atmospheric composition models, and photoelectron production models. Photoelectron-excited emissions of N2 and O are used to derive a self-consistent description of the atmosphere at solar maximum. Spectral synthesis of the N2 Lyman-Birge-Hopfield bands shows a departure of a 1Pi(q) state vibrational populations from the direct excitation theory. Observations of the N2 second positive (0, 0) 3371-A band and O I 1356-A emission indicate an exospheric temperature of 1600 K, 200 K higher than predicted by empirical models. The empirical models are also found to overestimate the O and O2 densities required to fit the data by a factor of 2 and 1.4, respectively. These results are compared to the results of an analysis of similar observations made in 1978 near solar minimum.

Meier, R. R.↗