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Results for “ATOMIC EXCITATION”

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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Results from the UCSD magnetic monopole search

The energy loss mechanism for slowly moving magnetic monopoles in helium provides a means of extending the search for such particles by ionization techniques to velocities approximately 3 X 1 million cm/sec (beta approximately equals 0.0001). Other gases (e.g., CH2 or CO2) mixed with helium will be ionized with high efficiency by collisions with excited helium atoms, thus allowing the use of large proportional chamber systems for the detection of the monopoles. The first reported results utilizing this mechanism was the experiment of Kajino, et al., using a detector with an area-solid angle product alpha time delta alpha of 24.7 square meters sr. They set a limit on the flux of monopoles of 7.2 x 10 to the 13th power cm(-2) sr(-1) sec(-1) at a 90% confidence level for beta 3x 0.0001. Here, the results of a He:CH2 proportional tube array designed to extend the velocity limit down to beta approximately 0.0001 are reported. The detector which has been operating at the University of California, San Diego (UCSD) since last summer, is a prototype for a larger array currently under construction at UCSD. The data presented here is from 200 days of live time with the prototype detector.

Masek, G. E.↗
NASA NTRS1985

Theoretical studies of dissociative recombination

The calculation of dissociative recombination rates and cross sections over a wide temperature range by theoretical quantum chemical techniques is described. Model calculations on electron capture by diatomic ions are reported which illustrate the dependence of the rates and cross sections on electron energy, electron temperature, and vibrational temperature for three model crossings of neutral and ionic potential curves. It is shown that cross sections for recombination to the lowest vibrational level of the ion can vary by several orders of magnitude depending upon the position of the neutral and ionic potential curve crossing within the turning points of the v = 1 vibrational level. A new approach for calculating electron capture widths is reported. Ab initio calculations are described for recombination of O2(+) leading to excited O atoms.

Guberman, S. L.↗
NASA NTRS1985

Heat balance of the ionosphere - Implications for the International Reference Ionosphere

Theoretical considerations can be helpful tools in modeling ionospheric parameters in regions and for times where not enough experimental data are available. This study asks whether results of heat balance calculations should be introduced to supplement the data base for the International Reference Ionosphere. The present status of the theoretical understanding is discussed and the influence of the following unresolved or neglected times are examined: (1) electron heating rate, (2) electron cooling by fine structure excitation of atomic oxygen, and (3) height-dependent Coulomb Logarithm. The ambiguity introduced by these terms leads to up to 30 percent uncertainty in the electron temperature of the lower ionosphere. The electron temperature in the upper ionosphere is largely determined by heat conduction from above and depends critically on the conditions assumed at the boundary between ionosphere and plasmasphere.

Bilitza, D.↗
NASA NTRS1989

Ionization by line photons and its effect on hydrogen line ratios

Inside a line-emitting cloud the density of trapped photons could be so high that they ionize hydrogen atoms from excited levels far more efficiently than electronic collisions. Such ionizations can reduce the population of high-level hydrogen and consequently reduce the Balmer line emissivity by a factor of 3 or more. As a result, the Balmer line emission is not enhanced as significantly in the partially ionized zone as predicted by current models unless an exceptionally large column density is assumed.

Zheng, Wei↗
NASA NTRS1991

Investigation of the excited state iodine lifetime in the photodissociation of perfluoroalkyl iodides

An evaluation of prospective laser materials for a space-based solar pumped laser system over the past decade has resulted in the identification of the iodine photodissociation laser as that system best suited to solar-pumped high energy operation. The active medium for the solar-pumped iodine photodissociation laser is from the family of perfluoroalkyl iodides. These lasants have the general form C(n)F(2n + 1)I, often abbreviated as RI. These iodides are known to exhibit photodissociaiton of the C-I bond when irradiated by near UV photons. The focus was on the experimental determination of the lifetime of the excited iodine atom following photodissociation of C4F9I, and also to monitor fluorescence from the iodine molecule at 500 nm to determine if I2 is being produced in the process. Photodissociation is achieved using an XeCl excimer laser with an output wavelength of 308 nm. The XeCl beam is focused into the middle of a cylindrical quartz cell containing the lasant. The laser pulse is detected with a fast risetime photomultiplier tube as it exits the cell. Other aspects of the investigation are discussed.

Cobb, Stephen H.↗
NASA NTRS1992

The complete UV spectrum of SO2 by electron impact. I - The vacuum ultraviolet spectrum

Measurements of the VUV emission cross sections of SO2 from 40 to 200 nm in the laboratory in a crossed beam experiment are reported. The wavelength range comprised the EUV spectrum, from 40 to 120 nm, and the FUV spectrum, from 120 to 200 nm. The studies included the measurement of excitation functions of the strongest multiplets from 0 to 1 keV impact energy and the identification of dissociation processes from the analysis of the threshold excitation function. It is shown that the FUV emission cross sections for dissociative excitation of atomic multiplets are generally much larger in the FUV than in the EUV. The emission cross sections measured are important for the preparation and data analysis of spacecraft observations of Io to be obtained for the 1990s.

Ajello, Joseph M.↗
NASA NTRS1992

An in Situ Technique for Elemental Analysis of Lunar Surfaces

An in situ analytical technique that can remotely determine the elemental constituents of solids has been demonstrated. Laser-Induced Breakdown Spectroscopy (LIBS) is a form of atomic emission spectroscopy in which a powerful laser pulse is focused on a solid to generate a laser spark, or microplasma. Material in the plasma is vaporized, and the resulting atoms are excited to emit light. The light is spectrally resolved to identify the emitting species. LIBS is a simple technique that can be automated for inclusion aboard a remotely operated vehicle. Since only optical access to a sample is required, areas inaccessible to a rover can be analyzed remotely. A single laser spark both vaporizes and excites the sample so that near real-time analysis (a few minutes) is possible. This technique provides simultaneous multielement detection and has good sensitivity for many elements. LIBS also eliminates the need for sample retrieval and preparation preventing possible sample contamination. These qualities make the LIBS technique uniquely suited for use in the lunar environment.

Kane, K. Y.↗
NASA NTRS1993

Plume characteristics of an arcjet thruster

An experimental investigation is conducted of the plume of a 1.5 kW hydrogen-fueled arcjet thruster. The velocity and translational temperature are measured by laser induced fluorescence of excited-state atomic hydrogen at a variety of locations and operating conditions. The peak velocity and temperature at the center of the exit plane of 14.7 km/s and 5000 K lead to a Mach number of 1.9. Evidence is presented which demonstrates the extent to which viscous forces dominate the flow, such as the exit plane Reynolds number of 18. Data taken in the plume suggest a transition from supersonic to subsonic flow via viscous dissipation. In addition, the results suggest that high tank pressures (0.4 to 1.5 Torr) limit the ability to simulate space environments for different portions of the plume.

Liebeskind, John G.↗
NASA NTRS1995

Analysis of hydrogen Lyman-alpha observations of the coma of Comet P/Halley near the perihelion

The pioneer Venus Orbiter Ultraviolet Spectrometer measurements of the Lyman-alpha intensity of atomic hydrogen excited by solar resonance scattering in the coma of Comet P/Halley acquired from December 28, 1985, to January 6, 1986, and from January 31, 1986, to March 6, 1986, are simulated with the Monte Carlo Particle Trajectory Model corrected for optical depth effects. Spatially detailed comparisons between data and model show excellent agreement and are used to infer that the highest cometary activity may not be at perihelion, but about 2 1/2 weeks before. An improved set of H2O production rates is presented for the period of time that the spectrometer was observing and is found to be consistent with the rates from other types of measurements. The apparent discrepancy between Stewart (1987) in early March and International Ultraviolet Explorer OH derived rates is resolved. The problem with the conversion of 18-cm OH radio brightness to H2O production rates is also discussed.

Smyth, William H.↗
NASA NTRS2002

HALOE Observations of Perturbations in High Northern Latitude NO and O3 During the April 2002 Solar Storm Episode

The April 2002 solar storm event provides a unique opportunity to study the resulting effects on upper atmospheric constituents such as NO and O3. Two sources may perturb these constituents. For a magnetic-storm-source, energetic particles collide with and dissociate N2 in the lower thermosphere to produce excited nitrogen atoms which then combine with O to produce NO. The NO subsequently is transported down to lower altitudes where it reacts with and thus destroys mesospheric and possibly stratospheric ozone. For a solar-particle-event-source, high energy particles penetrate directly into the mesosphere, break apart N2 and water vapor, creating NOx and HOx to destroy ozone in the middle atmosphere. We present perturbations in high northern latitude NO and O3 as measured by the Halogen Occultation Experiment (HALOE) aboard the Upper Atmosphere Research Satellite between April 20-27. HALOE observations show an order of magnitude increase in mesospheric NO and a factor of approximately 2 decrease in mesospheric O3. We will also compare these observations with NASA GSFC 2D model computations.

Anderson, John↗
NASA NTRS1996

The Electron Excitation Function of H Lyman-(alpha) from Threshold to 1.8 keV

The excitation function of prompt Lyman-(alpha) radiation, produced by electron impact excitation of atomic hydrogen, has been measured for the first time over an extended energy range from threshold to 1.8 keV. Measurments were obtained in a crossed-beams experiment using both magnetically confined and electrostatically focused electrons in collision with atomic hydrogen produced by an intense discharge source.

hydrogen atomic hydrogen Lyman-alpha radiation↗
NASA NTRS2013

Monitoring Temperature in High Enthalpy Arc-heated Plasma Flows using Tunable Diode Laser Absorption Spectroscopy

A tunable diode laser sensor was designed for in situ monitoring of temperature in the arc heater of the NASA Ames IHF arcjet facility (60 MW). An external cavity diode laser was used to generate light at 777.2 nm and laser absorption used to monitor the population of electronically excited oxygen atoms in an air plasma flow. Under the assumption of thermochemical equilibrium, time-resolved temperature measurements were obtained on four lines-of-sight, which enabled evaluation of the temperature uniformity in the plasma column for different arcjet operating conditions.

Martin, Marcel Nations↗
NASA NTRS2022

Vibrational and Rovibrational Spectroscopy Applied to Astrochemistry

The detection of molecules in astrophysical environments almost always requires remote sensing. While radioastronomical observation and associated rotational spectroscopy are powerful astronomical tools, infrared spectral analysis provides a unique means of examining the observable universe, especially for molecules where permanent dipole moments are small or even non-existent. The molecular vibrations of small molecules are now able to be modeled via quantum chemistry and electronic structure theory conjoined to vibrational analysis to within spectroscopic accuracy in many cases. This chapter will showcase this success and build upon it to show how such advances are now being leveraged to describe molecular vibrations for molecules containing dozens of atoms, electronically excited states, "hot bands," exoplanetary atmospheric opacity data, and even emission of polycyclic aromatic hydrocarbons. All of these are required to prune the interstellar spectral garden of its "weeds" in search of "flowers" that will provide the necessary fingerprints for astronomers to be able to probe the heavens for its past, present, and future secrets.

Ryan C. Fortenberry↗
NASA NTRS1977

Rotational excitation of linear molecules by collisions with atoms - Comparison of classical and quantum methods

Exact quantum results for the rotational excitation of rigid linear molecules by collisions with atoms are compared with classical trajectory results. The systems studied are CO-He, CS-H2, OCS-H2, HCl-He, and HCl-Ar at collision energies up to 500/cm. Total cross sections and state to state rate constants are compared. The classical results are found to be in good agreement with the quantum results on the average. Differences arising from the existence of purely quantum effects are clearly evident, but consistent and predictable. Two methods of extracting state selective information from moments of the classical distribution are examined and found to be less reliable than the usual histogram method. In conjunction with previous comparisons of classical and quantum results these calculations provide a useful measure of the limitations and reliability of classical trajectories.

Chapman, S.↗
NASA NTRS1980

The excitation and collisional deactivation of metastable N/2P/ atoms in auroras

The concentration and altitude distribution of metastable N(2P) atoms was measured in a diffuse IBC II(+) auroral arc. The dominant N(2P) source is shown to be the dissociative excitation of N2 by electron impact with a minor contribution from the dissociative recombination of N2(+) ions. The possibility that an ion-molecule process involving atomic oxygen and vibrationally excited N2(+) ions is a significant N(2P) source is examined. Values for the proportional yield of N(+), N(2P), N(2D), and N(4S) atoms from electron-impact dissociation of N2 under optically thick conditions are given.

Zipf, E. C.↗