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At least 523 records · Page 29
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NASA NTRS1986

Detection of OH from Comet Halley in the far-infrared

The 2 Pi 3/2 (J = 5/2 yields 3/2 + yields - parity) transition of OH was detected in comet Halley at 119.44 microns. The upper limit to the line intensity of the - yields + parity transition is 119.23 microns. The ratio of these lines is consistent with radiative pumping of the rotational levels through absorption of near ultraviolet solar photons which excite the low lying vibrational levels of OH. The far-infrared lines probe the inner regions of the coma where OH is produced through photodissociation of a parent molecule (presumably H2O). Hence, these lines complement the 18 cm radio measurements which are sensitive to the outer regions of the comet coma. The OH production rate is highly model dependent but is of the order 2 to 4 times 10 to the 29th power molecules/sec.

Stacey, Gordon J.↗
NASA NTRS1986

Spatial distribution of 6300A emission determined from narrow-band images of Halley's Comet

In March 1986 the Wisconsin dual-etalon Fabry-Perot spectrometer was adapted for use with an intensified CCD imaging detector and good quality images of OI 6300A emission from a 10 arcmin field centered on Halley's comet head were obtained in April and May 1986. The 10 km/sec bandpass was adequate to eliminate spectral contamination from cometary NH2 and, with appropriate Doppler shifts, terrestrial airglow. The observed distribution of OI emission indicates O(sup 1)D production from 2 sources, presumably photodissociation of H2O and OH. Scale lengths are determined for the distributions of these sources in the coma.

Roesler, F. L.↗
NASA NTRS1987

Absolute 1* quantum yields for the ICN A state by diode laser gain versus absorption spectroscopy

Absolute I* quantum yields were measured as a function of wavelength for room temperature photodissociation of the ICN A state continuum. The temperature yields are obtained by the technique of time-resolved diode laser gain-versus-absorption spectroscopy. Quantum yields are evaluated at seven wavelengths from 248 to 284 nm. The yield at 266 nm is 66.0 +/- 2% and it falls off to 53.4 +/- 2% and 44.0 +/- 4% at 284 and 248 respectively. The latter values are significantly higher than those obtained by previous workers using infrared fluorescence. Estimates of I* quantum yields obtained from analysis of CN photofragment rotational distributions, as discussed by other workers, are in good agreement with the I* yields. The results are considered in conjunction with recent theoretical and experimental work on the CN rotational distributions and with previous I* yield results.

Hess, Wayne P.↗
NASA NTRS1986

A model of the Schumann-Runge continuum of O2

Ab initio calculations of the B3Sigma sub u(-) potential energy curve of O2 are reported together with the transition moment connecting the B3Sigma sub u(-) and the ground electronic states. Photodissociation cross sections are presented over the wavelength region 127-152 nm. Small adjustments to the potential energy curve and the transition moment lead to a model of the absorption which agrees well with the experimental cross sections and which reproduces the structural features observed on the high-energy edge. The shoulder at 135.6 nm is attributed to the lowest 3Pi sub u state and the auxiliary maxima to transitions into the B3Sigma sub u(-) state.

Allison, A. C.↗
NASA NTRS1985

Rocket observation of the ultraviolet spectrum of Comet Halley

An ultraviolet sounding rocket telescope/spectrograph experiment observed Comet Halley on Feb. 26, 1986, 17 days after perihelion. From the long-slit spectra, the production rates of O, C, and CO are calculated. The derived water production rate is a lower limit of 5.0 x 10 to the 29th/s and the volume mixing ratio of CO to H2O is 21 percent. The predicted brightness distribution from a radial outflow model with H2O and CO as parent molecules are in accordance with the measured spatial profiles of O I and CO emissions. The ratio of the production rates of CO to C is 2.7 which is consistent with the carbon source being the photodissociation of CO. However, the radial outflow model which best fits the CO data predicts significantly weaker C I emissions than was observed. A better fit to the carbon data is found when an inner coma source of C at a rate of 3 percent of the water production rate is included in the model.

Woods, T. N.↗
NASA NTRS1986

Solar pumped laser technology options for space power transmission

An overview of long-range options for in-space laser power transmission is presented. The focus is on the new technology and research status of solar-pumped lasers and their solar concentration needs. The laser options include gas photodissociation lasers, optically-pumped solid-state lasers, and blackbody-pumped transfer lasers. The paper concludes with a summary of current research thrusts.

Conway, E. J.↗
NASA NTRS1986

A search for the millimeter-wave transitions of CO(+) in Comet P/Halley

Although no detection was obtained in the present search for the N = 2-1, J = 5/2-3/2, and J = 3/2-1/2 mm-wave transitions of CO(+) in Comet P/Halley, a 2-sigma upper limit of 8 x 10 to the 11th/sq cm was determined for the beam-averaged column density of this specie. Upon comparison of this upper limit estimate with model predictions involving the variation of such parameters as the chemical composition and ionization mechanisms, it appears that H2O may be the main nucleus constituent of the comet. If, in addition, photodissociation ionization is active in the coma, then the origin of the CO(+) is more likely to be in CO2 than in CO.

Baum, S.↗
NASA NTRS1986

Detection of silicon in the Galactic center

The detection of the forbidden Si II 34.815 micron line in the Galactic center region is reported. It is demonstrated that, in the case of the Galactic center, the emission arises mainly from the photodissociation region and not the shocked molecular component seen via H2, CO, and OH lines. It is also shown that significant Si II emission is not expected from the ionized gas even though the Galactic center is a rather low excitation H II region.

Hertier, T.↗
NASA NTRS1986

Reaction rate constant of HO2+O3 measured by detecting HO2 from photofragment fluorescence

A room-temperature discharge-flow system investigation of the rate constant for the reaction 'HO2 + O3 yields OH + 2O2' has detected HO2 through the OH(A-X) fluorescence produced by photodissociative excitation of HO2 at 147 nm. A reaction rate constant of 1.9 + or - 0.3 x 10 to the -15th cu cm/molecule per sec is obtained from first-order decay of HO2 in excess O3; this agrees well with published data.

Manzanares, E. R.↗
NASA NTRS1986

Meteoric material and the behavior of upper stratospheric polar zone

Ozone mixing ratios as a function of pressure level and time are presented based on data obtained with the Nimbus-7 SBUV instrument between 1979 and 1984, and implications of this data for the explanations of the spring Antarctic ozone depletion are considered. It is suggested that meteoric atoms react with the atmosphere to bond to OH, and subsequently react with HCl to form salts, resulting in the accumulation of chlorine during polar winter. The sudden release of this chlorine from photodissociation of these salts during spring could account for the loss of ozone in the upper atmosphere.

Aikin, A. C.↗
NASA NTRS1986

A rapid and accurate method for calculation of stratospheric photolysis rates with molecular scattering

A method for calculating the photodissociation rates needed for photochemical modeling of the stratosphere, which includes the effects of molecular scattering, is described. The procedure is based on Sokolov's method of averaging functional correction. The radiation model and approximations used to calculate the radiation field are examined. The approximated diffuse fields and photolysis rates are compared with exact data. It is observed that the approximate solutions differ from the exact result by 10 percent or less at altitudes above 15 km; the photolysis rates differ from the exact rates by less than 5 percent for altitudes above 10 km and all zenith angles, and by less than 1 percent for altitudes above 15 km.

Boughner, Robert E.↗
NASA NTRS1986

Climatic consequences of very high carbon dioxide levels in the earth's early atmosphere

The possible consequences of very high carbon dioxide concentrations in the earth's early atmosphere have been investigated with a radiative-convective climate model. The early atmosphere would apparently have been stable against the onset of a runaway greenhouse (that is, the complete evaporation of the oceans) for carbon dioxide pressures up to at least 100 bars. A 10- to 20-bar carbon dioxide atmosphere, such as may have existed during the first several hundred million years of the earth's history, would have had a surface temperature of approximately 85 to 110 C. The early stratosphere should have been dry, thereby precluding the possibility of an oxygenic prebiotic atmosphere caused by photodissociation of water vapor followed by escape of hydrogen to space. Earth's present atmosphere also appears to be stable against a carbon dioxide-induced runaway greenhouse.

Kasting, James F.↗
NASA NTRS1986

The interstellar medium in the central 1 kiloparsec of M82

The spatial distribution of the 158 micron forbidden C II emission in the central 1 kiloparsec of the infrared galaxy M82 is discussed, and the detection of two fine-structure lines of forbidden O I and forbidden O III at 146 and 52 microns is reported. Within 500 pc of the nucleus, the far-infrared emission lines contain about 200 million solar luminosities. The neutral gas in the inner disk is in dense, relatively small clouds, thin filaments, or sheets of very low volume filling factor, associated with a lower density ionized medium of moderately high filling factor. Within 500 pc of the nucleus, about 30 million solar masses is contained in H II regions and 30 million solar masses in photodissociation regions. There is a component of ionized and neutral gas near LSR of roughly 150 km/s centered near the compact radio source 41.9 + 58 and elongated along the minor axis of M82. The gas is especially dense in this region and appears to be associated with X-ray emission and the inner H-alpha filaments.

Lugten, J. B.↗
NASA NTRS1986

Rocket ultraviolet spectroscopy of comet Halley and abundance of carbon monoxide and carbon

Two far ultraviolet observations of comet Halley made on 26 February, 1986 and 13 March, 1986 with a sounding rocket experiment are reported. The observed CO spatial profiles can be modelled by a radial outflow model for a parent molecule and suggest that the CO is produced directly from the nucleus of the comet. Using the observed O I emission profile to deduce the H2O production rate, the abundance of CO relative to H2O is found to be 20 percent + or - 5 percent for the first flight and 17 percent + or - 4 percent for the second flight, making CO the second most abundant parent molecule in the coma. The derived production rate of atomic carbon is consistent with that expected from the photodissociation of carbon monoxide.

Woods, T. N.↗
NASA NTRS1987

Observations of Comet Halley at H-alpha and 6300 A

High spectral resolution measurements of Comet Halley at H-alpha and OD-1 were obtained in March, 1986 using a small aperture telescope with the Fabry-Perot interferometer at the Arecibo Observatory. It is suggested that the highly structured spectral signature observed at H-alpha is due to collimation of atomic hydrogen in the inner hydrogen corona, following photodissociation of parent species, and that the emission is due to resonance fluorescence of solar Lyman-beta radiation. A feature at 6300.8 A accompanying the OD-1 emission at 6300.3 A is attributed to NH2. For a 6-arcmin field of view, a brightness for the OD-1 emission of 260 + or - 50 rayleighs is found for both March 15 and 17.

Kerr, R. B.↗
NASA NTRS1986

Transient gain-versus-absorption laser probing of spin-orbit states, kinetics and dynamics

The spin-orbit populations of excited (2P1/2) and ground (2P3/2) state Br atoms at 2714 nm and I atoms at 1315 nm are examined using a tunable F-center laser and a diode laser. The transient laser gain-versus-absorption measurements are utilized to estimate quantum yields of the spin-orbit states in the photodissociation of Br- and I-containing compounds; the continuum yields for Br2 are investigated in terms of temperature. The collisional release, Doppler velocity effects, and differing reactivity of the spin-orbit excited and ground state atoms are studied. It is noted that the transient gain versus absorption technique is applicable to the analysis of kinetic phenomena due to its high sensitivity and excellent time resolution.

Smedley, John E.↗
NASA NTRS1987

New lines of ethylene and a search for methylene in IRC + 10216

Seven new lines in the 10 micron nu7 band of C2H4 have been detected in the highly obscured carbon star IRC + 10216. The line intensities cannot be well described by a single rotational temperature, in contrast to the lines of CH4 and SiH4 previously observed in this source. There are at least three interpretations: the line intensities are variable on a time scale of months and years, C2H4 lines are formed over a region less homogeneous than that of CH4 and SiH4, or ethylene is somewhat nonthermally excited. Regardless, the line intensities indicate an average rotational temperature of 100 K and a column density of about 4 x 10 to the 15th/sq cm, which is approximately 2 x 10 to the -5th times the CO abundance. A search was also made for infrared transitions of CH2, the methylene radical. No lines were detected, but the observational limits are compared with the abundance and radial distribution for CH2 predicted by a model invoking the photodissociation of CH4.

Goldhaber, D. M.↗
NASA NTRS1987

Absolute I(asterisk) quantum yields for the ICN A state by diode laser gain-vs-absorption spectroscopy

Absolute I(asterisk) quantum yields have been measured as a function of wavelength for room temperature photodissociation of the ICN A state continuum. The yields are obtained by the technique of time-resolved diode laser gain-vs-absorption spectroscopy. Quantum yields are evaluated at seven wavelengths from 248 to 284 nm. The yield at 266 nm is 66.0 + or - 2 percent and it falls off to 53.4 + or - 2 percent and 44.0 + or - 4 percent at 284 and 248 nm, respectively. The latter values are significantly higher than those obtained by previous workers using infrared fluorescence. Estimates of I(asterisk) quantum yields obtained from analysis of CN photofragment rotational distributions, as discussed by other workers, are in good agreement with the I(asterisk) yields reported here. The results are considered in conjunction with recent theoretical and experimental work on the CN rotational distributions and with previous I(asterisk) quantum yield results.

Hess, Wayne P.↗