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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 91 records · Page 5
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NASA NTRS1973

Evidence from spectra of bright fireballs

Spectral data with dispersions from 11 to 94 A/mm on 4 fireballs of actual brightness of -4 to -12 magnitude and with velocities of about 30 km/s at 70 to 80 km heights are used for studies of meteor radiation problems. The radiation of fireballs is found to be strongly affected by self absorption. But if the emission curve of growth is used for correction of the self absorption of Fe I lines, a great discrepancy between spectral data and efficiency data for total Fe I light is found. If one assumes that the self absorption is superposed on another effect, a decrease of the dimensions of the radiating volume with increasing lower potential, the spectral data on Fe I lines will be in agreement with the luminous efficiency of total Fe I meteor radiation. Formulas for emission curve of growth and Boltzmann distribution including this effect are derived. This effect is important for fireballs brighter than about -1 or -2 magnitude, while self absorption seems to be important even for fainter meteors.

Ceplecha, Z.↗
NASA NTRS1973

Investigation of gas temperature measurements using ultraviolet excitation

A high resolution spectrographic study has been made of the nitrogen first negative system as induced by ultraviolet radiation. The radiation used in this experiment was the neutral helium resonance radiation at 584 A. Nitrogen molecules at approximately 300 K and at a pressure of one torr were ionized by the ultraviolet radiation with the aid of a windowless experimental configuration. The resulting nitrogen fluorescence was analyzed with sufficient resolution to enable study of the intensities of the R branch rotational lines of the 0-0 vibrational band of the first negative system. The data indicate that the induced population of the upper levels approximates a Boltzmann Distribution at the ambient temperature of the gas.

Ofelt, G. S.↗
NASA NTRS1974

Observation of a driver gas-tangential discontinuity

A complete analysis of an interplanetary disturbance of Nov. 19, 1970 using the Apollo 12-SIDE (Suprathermal Ion Detector Experiment) is presented. The SIDE detectors were pointing at 26.3 degrees from the normal solar-wind direction during the observations. The data were least-squares fitted (using a parabolic hypersurface approximation) to a convected Maxwell-Boltzmann distribution function. The results of the fit combined with two other experiments showed a drastic change in the wind speed (from an steady 352 km/sec down to 219 km/sec), direction, and temperature. Except for a delta-function increase at the onset, the density remained constant. There was a considerable enhancement in the abundance of He and probably of heavier elements. The interplanetary magnetic field exhibited a jump of 21 gamma with a change in latitude from -56 to -76 degrees in solar ecliptic coordinates. It is concluded that the disturbance was due to the driver gas-tangential discontinuity of a solar flare-induced shock wave. The characteristic of the tangential discontinuity fit well with theoretical prediction.

Medrano, R. A.↗
NASA NTRS1976

Monte Carlo calculations of diatomic molecule gas flows including rotational mode excitation

The direct simulation Monte Carlo method was used to solve the Boltzmann equation for flows of an internally excited nonequilibrium gas, namely, of rotationally excited homonuclear diatomic nitrogen. The semi-classical transition probability model of Itikawa was investigated for its ability to simulate flow fields far from equilibrium. The behavior of diatomic nitrogen was examined for several different nonequilibrium initial states that are subjected to uniform mean flow without boundary interactions. A sample of 1000 model molecules was observed as the gas relaxed to a steady state starting from three specified initial states. The initial states considered are: (1) complete equilibrium, (2) nonequilibrium, equipartition (all rotational energy states are assigned the mean energy level obtained at equilibrium with a Boltzmann distribution at the translational temperature), and (3) nonequipartition (the mean rotational energy is different from the equilibrium mean value with respect to the translational energy states). In all cases investigated the present model satisfactorily simulated the principal features of the relaxation effects in nonequilibrium flow of diatomic molecules.

Yoshikawa, K. K.↗
NASA NTRS1975

A search for chemical laser action in low pressure metal vapor flames

Optical emissions were studied from low pressure (approximately 1 torr) dilute diffusion flames of Ca and Mg vapor with O2, N2O and mixtures of CCl4 and O2. The Ca flames with O2 and N2O revealed high vibrational excitation of the product CaO molecule (up to v=30). The flames with CCl4 revealed extreme nonequilibrium metal atom electronic excitation, up to the metal atom ionization limit (6.1 eV for Ca, 7.6 eV for Mg). The metal atom excited electronic state populations did not follow a Boltzmann distribution, but the excitation rates ('pumping rate') were found to obey an Arrhenius-type expression, with the electronic excitation energy playing the role of activation energy and a temperature of about 5000 K for triplet excited states and 2500 K for singlets (vs. approximately 500 K translational temperature).

Zwillenberg, M. L.↗
NASA NTRS1975

Spectrophotometry of Comet Kohoutek /1973f = 1973XII/

Spectrum scans have been obtained of Comet Kohoutek with a Fourier spectrometer at heliocentric distances from 0.55 to 1.05 AU. The useful spectral range is roughly 3800-8400 A and the resolution is about 10-15 A at 5000 A. Large variations occurred in the gas-to-dust ratio (pre- versus postperihelion) and in the relative strength of the NH2 bands (with heliocentric distance). There is a smaller change in the ratio of CN to C2 emission. The Swan bands of C2 show the customary anomaly in strengths implying highly non-Boltzmann distributions among vibrational levels. The red and violet CN system fluxes are in slightly better agreement with laboratory data on oscillator strengths than results on previous comets. Other species measured include Na, (O I), CH, and C3.

Ahearn, M. F.↗
NASA NTRS1979

Lidar temperature profiling: Performance simulations of Masons method

Several methods of using lasers to measure atmospheric temperature profiles were described. Mason's suggestion was analyzed here to assess its capabilities for various lidar configurations. Temperatures were inferred from a measure of the Boltzmann distribution of rotational states in one of the vibrational bands of O2. Differential absorption was measured using three tunable, narrowband pulsed lasers. The outputs of two were tuned to wavelengths at the centers of absorption lines at either end of a particular branch in the band. The third wave-length was in a region of no absorption; its lidar return measured only the atmospheric backscatter, and therefore allowed calculations of the absorption coefficients at the other two wavelengths as a function of altitude. From the ratio of the two line absorption coefficients plus a priori knowledge of the line parameters, the temperature-altitude profile were calculated.

Schwemmer, G. K.↗
NASA NTRS1979

A search for interstellar glycine

A search has been made for the simplest amino acid - glycine - in Sgr B2, Ori A, and seven other molecular clouds. Six different lines were sought ranging from 83.4 GHz down to 22.7 GHz, and radio telescopes at Parkes, New South Wales, Kitt Peak, Arizona, and Onsala, Sweden, were used. On the assumption of reasonable values for excitation temperature and Boltzmann distributions over rotational energy states, upper limits of column densities for glycine of a few times 10 to the 12th per sq cm to a few times 10 to the 14th per sq cm were typically established in the sources surveyed. Glycine appears to be less abundant than ethanol or ethyl cyanide in molecular clouds such as Sgr B2 and Ori A.

Brown, R. D.↗
NASA NTRS1979

Lidar temperature profiling - Performance simulations of Mason's method

In Mason's method (1975) atmospheric temperatures are inferred from a measure of the Boltzmann distribution of rotational states in one of the vibrational bands of O2. Differential absorption is measured using three tunable, narrowband pulse lasers. The outputs of two are tuned to wavelengths at the centers of absorption lines at either end of a particular branch in the band; the third wavelength is in a region of no absorption. The temperature-altitude profile can be calculated from the ratio of the two line absorption coefficients plus a priori knowledge of the line parameters. In the present paper, computer simulations of various lidar configurations are made, using different line pairs in the atmospheric bands of O2 (approximately 630, 690, and 760 nm). Simulated results are presented for temperature profiles measured from a Space Shuttle lidar.

Schwemmer, G. K.↗
NASA NTRS1981

Modeling of thin-film GaAs growth

A solid Monte Carlo model is constructed for the simulation of crystal growth. The model assumes thermally accommodated adatoms impinge upon the surface during a delta time interval. The surface adatoms are assigned a random energy from a Boltzmann distribution, and this energy determines whether the adatoms evaporate, migrate, or remain stationary during the delta time interval. For each addition or migration of an adatom, potential wells are adjusted to reflect the absorption, migration, or desorption potential changes.

Heinbockel, J. H.↗
NASA NTRS1981

Physics of planetary atmospheres and ionospheres

The traditional atmospheric regions, the distinction between homosphere and heterosphere, and changing atmospheric composition are discussed. The validity of the barometric law based on a Maxwell-Boltzmann distribution, for the major part of a planetary atmosphere and its breakdown in the exosphere due to escape of atmospheric particles is considered. The formation and maintenance of photochemical and diffusion-controlled ionospheric layers are treated. Their applicability to planetary ionospheres is dealt with. The spatial extent of magnetic and nonmagnetic planet ionospheres is investigated. Thermal and nonthermal processes responsible for the mass loss of planetary atmospheres are surveyed.

Bauer, S. J.↗
NASA NTRS1982

Modeling of thin film GaAs growth

A potential scaling Monte Carlo model of crystal growth is developed. The model is a modification of the solid-on-solid method for studying crystal growth in that potentials at surface sites are continuously updated on a time scale reflecting the surface events of migration, incorporation and evaporation. The model allows for B on A type of crystal growth and lattice disregistry by the assignment of potential values at various surface sites. The surface adatoms are periodically assigned a random energy from a Boltzmann distribution and this energy determines whether the adatoms evaporate, migrate or remain stationary during the sampling interval. For each addition or migration of an adatom, the surface potentials are adjusted to reflect the adsorption, migration or desorption potential changes.

Heinbockel, J. H.↗
NASA NTRS1983

Intensity and extinction irregularities in the H2 emission from Orion

Fourteen lines of the v = 1-0 and v = 2-1 2 micron H2 quadrupole spectrum were measured in a series of ground-based spectroscopic observations of four locations within the Orion molecular cloud-H2 emission complex. Beam sizes of 7 and 10 arcsec were used, with a resolution of 1.8/cm. The results indicate that there are differences in the extinction between regions of as much as 20 mag. In particular there appears to be a ridge of material near the object IRS 2 (= IRc 9), a previously suggested source of activity. The 2-1 S (3) line intensity is substantially stronger at Peak 2 than the present models predict, and this observation is the first indication that there may be a non-Boltzmann distribution within the vibrational levels of shock-excited H2. A detection of the 1-0 Q (6) line is also reported, a feature which was previously absent in spectra of the Orion cloud.

Smith, H. A.↗
NASA NTRS1986

Collisional excitation of interstellar methyl cyanide

Theoretical calculations are used to determine the collisional excitation rates of methyl cyanide under interstellar molecular cloud conditions. The required Q(L,M) as a function of kinetic temperature were determined by averaging fixed energy IOS (infinite order sudden) results over appropriate Boltzmann distributions of collision energies. At a kinetic temperature of 40 K, rates within a K ladder were found to be accurate to generally better than about 30 percent.

Green, Sheldon↗
NASA NTRS1988

Dependence of rate constants on vibrational temperatures - An Arrhenius description

An interpretation of the variation of rate constants with vibrational temperature is proposed which introduces parameters analogous to those of the classical Arrhenius expression. The constancy of vibrational activation energy is studied for the dissociaton of NO, the ion-molecular reaction of O(+) with N2, and the atom exchange reaction of I with H2. It is found that when a Boltzmann distribution for vibrational states is applicable, the variation of the rate constant with the vibrational temperature can be used to define a vibrational activation energy. The method has application to exchange reactions where a vibrational energy threshold exists.

Ford, D. I.↗
NASA NTRS1989

Collisional excitation of interstellar molecules - Deuterated water, HDO

Using an accurate theoretical interacting potential and coupled-channel molecular scattering calculations, excitation rates for deuterated water (HDO) in collisions with He atoms were computed. Data are presented for rates among the 34 rotational levels with energy below 400/cm for temperatures between 50 and 500 K. Excitation rate constants were determined using data from fixed energy cross sections averaged over thermal (Boltzmann) distributions of collision energies. Based on the agreement (for H2O) of rates from two different theoretical potentials and on agreement with the limited experimental data, the larger rates for HDO were estimated to be generally accurate to better than 50 percent.

Green, Sheldon↗
NASA NTRS1991

High temperature electronic excitation and ionization rates in gases

The relaxation times for electronic excitation due to electron bombardment of atoms was found to be quite short, so that electron kinetic temperature (T sub e) and the electron excitation temperature (T asterisk) should equilibrate quickly whenever electrons are present. However, once equilibrium has been achieved, further energy to the excited electronic states and to the kinetic energy of free electrons must be fed in by collisions with heavy particles that cause vibrational and electronic state transitions. The rate coefficients for excitation of electronic states produced by heavy particle collision have not been well known. However, a relatively simple semi-classical theory has been developed here which is analytic up to the final integration over a Boltzmann distribution of collision energies; this integral can then be evaluated numerically by quadrature. Once the rate coefficients have been determined, the relaxation of electronic excitation energy can be evaluated and compared with the relaxation rates of vibrational excitation. Then the relative importance of these two factors, electronic excitation and vibrational excitation by heavy particle collision, on the transfer of energy to free electron motion, can be assessed.

Hansen, Frederick↗
NASA NTRS1992

Estimation of excitation energy of diatomic molecules in expanding nonequilibrium flows

The energy contained in the highly excited vibrational and rotational states in a diatomic gas in a thermochemical nonequilibrium state during expansion is estimated. The estimation is made on the assumption that the populations of the vibrational and rotational states, when normalized by their respective equilibrium values, are describable by simple functions containing no more than four arbitrary parameters. A cubic polynomial, a logarithmic-cubic polynomial, and a bimodal step function are used for this purpose. The four parameters are determined by imposing conditions known at the ground state and the dissociation limit and the mass conservation law. The energy in excess of that accounted for by assuming a Boltzmann distribution of these states, defined here as excess excitation energy, is calculated for N2, O2, NO, CO, OH, and H2. A calculation made for a typical nozzle flow shows that the excess energy may reach 6 percent of the total enthalpy of the flow, and that the flow velocity may decrease by as much as 4 percent due to the nonequilibrium excitation phenomenon.

Park, Chul↗