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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
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NASA NTRS1971

Twilight and nighttime ionospheric temperatures from oxygen wavelengths 6300 and 5577 spectral line profiles

Fabry-Perot interferometer measurements of atomic oxygen 6300 A and 5577 A line profiles from twilight and nightglow are used to determine the neutral temperatures in F2 and E regions of the earth's ionosphere. The exospheric temperatures T sub n (infinity) determined from the 6300 A profiles are usually somewhat higher than those calculated from Jacchia's model, with differences as large as approximately 300 K noted when T sub n (infinity) = 1500 to 1600 K. The post-sunset and pre-dawn rate of change of T sub n (infinity) is often substantially larger than the Jacchia prediction. The 5577 A (E-region) measured temperatures range from 200 to 220 K on quiet nights to 500 to 600 K during geomagnetic storms.

Feibelman, W. A.↗
NASA NTRS1971

Ion thruster diagnostics using spectral line amplitudes

The optical radiation from the plasma discharge of an electron bombardment mercury ion thrustor was investigated. Using the measured ratio of the Hg I line amplitude at 3655 A to that at 3650 A, a theory incorporating a bimodal electron distribution (Maxwell electrons plus primary electrons) was used to obtain the average electron temperature and primary electron fraction in the thruster ion chamber. The electron temperature ranged from about 1.2 eV to 6.6 eV; whereas the primary electron fraction varied from zero percent to about 5 percent. These values depended upon the discharge voltage and the radial location of the measurement. The percentage of doubly ionized mercury produced in the chamber was also determined as a function of discharge voltage.

Milder, N. L.↗
NASA NTRS1972

Ion thruster diagnostics using spectral line amplitudes.

The optical radiation from the plasma discharge of an electron bombardment mercury ion thruster was investigated. This work extends and refines earlier measurements, correcting certain ambiguities that arose in the analysis of line amplitudes. Using the measured ratio of the Hg I line amplitude at 3655 A to that at 3650 A, a theory incorporating a bimodal electron distribution (Maxwell electrons plus primary electrons) was used to obtain the average electron temperature and primary electron fraction in the thruster ion chamber. The electron temperature ranged from about 1.2 eV to 6.6 eV; whereas the primary electron fraction varied from zero percent to about 5 percent. These values depended upon the discharge voltage and the radial location of the measurement. The percentage of doubly ionized mercury produced in the chamber was also determined as a function of discharge voltage.

Milder, N. L.↗
NASA NTRS1972

Formation of spectral lines in a planetary atmosphere. II - Spectroscopic evidence for the structure of the visible Venus clouds.

We demonstrate in this article that there is spectroscopic evidence for the structure of the visible Venus cloud layers. From physically realistic models of the lower Venus atmosphere, we have shown that only observations of the phase variations of the CO2 bands in the Venus spectrum can provide the information for a unique identification of the structure of the cloud layers. It is proved that Venus cannot have a single dense cloud layer, but must have two scattering layers; a thin aerosol layer situated in the lower stratosphere, overlying a dense cloud deck. The aerosol plays an important role in the scattering of radiation, so that its identification provides an explanation of the reflecting layer-scattering model controversy for the interpretation of spectra formed in a cloudy planetary atmosphere.

Hunt, G. E.↗
NASA NTRS1972

Twilight and nighttime ionospheric temperatures from oxygen 6300- and 5577-A spectral-line profiles.

Use of Fabry-Perot interferometer measurements of atomic-oxygen 6300- and 5577-A line profiles from twilight and nightglow to determine the neutral temperatures in the F2 and E regions of the earth's ionosphere. The exospheric temperatures determined from the 6300-A profiles are usually somewhat higher than the temperatures calculated from Jacchia's model, and differences as large as about 300 K are noted when the exospheric temperature equals 1500 to 1600 K. The postsunset and predawn rate of change of the exospheric temperature is often substantially larger than the Jacchia prediction. The 5577-A (E region) measured temperatures range from 200 to 220 K on quiet nights to 500 to 600 K during geomagnetic storms.

Feibelman, W. A.↗
NASA NTRS1972

Formation of spectral lines in planetary atmospheres. III - The use of analytic scattering diagrams in computations of synthetic spectra for cloudy atmospheres.

Results of some comparisons that have been made of line profiles and equivalent widths computed from atmospheric models where the scattering has been represented by the Mie theory and a simple analytic expression, the Heyney-Greenstein function. These results show that the spectroscopic features for these models are indistinguishable and demonstrate the value of using this simple analytic function in terms of the great saving in computer time when computing synthetic spectra for any cloudy planetary atmosphere.

Hunt, G. E.↗
NASA NTRS1972

Spectral-line structures of saturated parametric instabilities.

The nonlinear saturation spectrum of parametric instabilities is shown to be restricted to discrete values of the propagation vector if spontaneous emission is neglected and a one-dimensional analysis is used. The purely growing instability is not excited for equal ion and electron temperatures if the power is less than 3.5 times the threshold power. The inadequacy of the present one-dimensional treatment is pointed out, and it is shown that waves with propagation vectors that are not parallel to the pump field must be present even if spontaneous emission is neglected.

Kuo, Y.-Y.↗
NASA NTRS1973

An analysis of the unified and scalar additivity theories of spectral line broadening

The qualities of the unified and scalar theories proposed by various authors for describing the static and dynamic characteristics of a radiation perturber interaction are discussed. The regions of validity of these theories and the properties of the approximations applied by them are considered. New derivation procedures are proposed for the unified and scalar additivity theories of line broadening. These procedures do not require the use of an elaborate projection operator, of Green's function techniques in contrast to previous methods.

Smith, E. W.↗
NASA NTRS1974

Effect of a progressive sound wave on the profiles of spectral lines. 2: Asymmetry of faint Fraunhofer lines

The absorption coefficient profile was calculated for lines of different chemical elements in a medium with progressive sound waves. Calculations show that (1) the degree and direction of asymmetry depend on the atomic ionization potential and the potential of lower level excitation of the individual line; (2) the degree of asymmetry of a line decreases from the center toward the limb of the solar disc; and (3) turbulent motions 'suppress' the asymmetry.

Kostyk, R. I.↗
NASA NTRS1977

Precision measurements of NH3 spectral lines near 11 microns using the infrared heterodyne technique

Absolute line-center frequencies for eleven lines of ammonia in near coincidence with CO2-laser transitions have been determined to accuracies of + or -3 MHz by infrared heterodyne detection. These results were obtained by heterodyning a blackbody with a stable grating-tuned CO2 gas laser. A discussion of the apparatus and method of calculation, including error analysis, is presented. With these accurately determined line-center positions, the ammonia molecule will be a useful secondary-frequency standard for diode-laser spectroscopy in the 11-micron wavelength region.

Hillman, J. J.↗
NASA NTRS1978

On the detectability of millimeter wavelength spectral lines from planetary atmospheres

This paper adopts a simple line-formation model to estimate detection limits on the fractional absorption produced by molecular lines in the spectra of the planets, when observed with the 14-m antenna and low-noise receivers of the Five College Radio Astronomy Observatory. The results, which can readily be adjusted for receiver and telescope characteristics of other observatories, indicate that three kinds of observing programs may prove fruitful: (1) programs to monitor temporal variations of the strong CO absorption in the spectrum of Venus and Mars; (2) searches for weak absorption lines of other molecules, which are particularly promising for Venus: and (3) efforts to measure broad features in the continuous spectra of Venus, and possibly Jupiter, produced by molecules deep in the planetary atmospheres. Except for delineation of broad features of NH3 and possibly H2O near 25 GHz, hardly any useful observations can be made at frequencies less than 60 GHz.

White, R. E.↗
NASA NTRS1979

Redistribution of scattered radiation by collisions in the nonimpact region of the spectral line profile

The scattering of radiation in the presence of collisions can be described quantum-mechanically in terms of essentially two processes. The first may be thought of as an absorption to the excited state followed subsequently (after propagating in the excited state) by emission. This gives rise to radiation redistributed about the transition frequency. The effects of m-degeneracy are particularly interesting for this first process. As an example a case is considered in which the incident frequency is in the quasi-static line wing, while the scattered frequency is close to the line center. It is found that under these circumstances the dominant contribution from this process in the scattered spectrum is obtained for an absorption of the incident frequency taking place during a strong (close) collision and reemission of the scattered frequency when the atom is essentially unperturbed

Cooper, J.↗
NASA NTRS1980

Effective depth of spectral line formation in planetary atmospheres

The effective level of line formation for spectroscopic absorption lines has long been regarded as a useful parameter for determining average atmospheric values of the quantities involved in line formation. The identity of this parameter was recently disputed. The dependence of this parameter on the average depth where photons are absorbed in a semi-infinite atmosphere is established. It is shown that the mean depths derived by others are similar in nature and behavior.

Lestrade, J. P.↗