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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Radiometric observations of the 752.033-GHz rotational absorption line of H2O from a laboratory jet

With the aid of a high-resolution two-stage heterodyne radiometer, spectral absorption measurements of the 752.033 GHz line of water vapor were carried out, using a blackbody continuum as a background radiation source for investigating the absorptive properties of the H2O content of high altitude rocket plumes. To simulate this physical situation in a laboratory environment, a small steam jet was operated within a large high-vacuum chamber, with the H2O jet plume traversing the radiometer line of sight. The experiments verified that this rotational line is optically thick, with excitation temperatures below 100 K, in the downstream part of the plume, as predicted by theoretical modelling.

Dionne, G. F.↗
NASA NTRS1980

Experimental study of cluster formation in binary mixture of H2O and H2SO4 vapors in the presence of an ionizing radiation source

Molecular clusters formed in pure nitrogen containing H2O and H2SO4 vapors and exposed to a 3 mCi Ni63 beta source were studied in the mass range 50 to 780 amu using a quadrupole mass spectrometer. Measurements were made under several combinations of relative humidity and relative acidity ranging from 0.7 to 7.5 percent and 0.00047 to 0.06333 percent, respectively. The number of H2SO4 molecules in the clusters observed ranged from 1 to 7 whereas the number of H2O molecules ranged from 1 to 16. The experimental cluster spectra differ considerably from those calculated using the classical nucleation theory. First order calculations using modified surface tension values and including the effects of multipole moments of the nucleating molecules indicate that these effects may be enough to explain the difference between the measured and the calculated spectra.

Singh, J. J.↗
NASA NTRS1981

Far-infrared observations of the H2O masers in NGC 281, NGC 2175, and S255/257

The H2O masers in NGC 281, NGC 2175, and S255/257 have been observed in four far-infrared bands from 40-140 microns with 30 arcsec and 50 arcsec beams. The far-IR positions are consistent with the H2O positions. The far-IR sources have luminosities of 10 to the 4 + or 0.5 solar luminosities, dust temperatures of 36-50 K, H densities greater than 10 to the 4.5, and apparent masses of 12-120 solar masses.

Wright, E. L.↗
NASA NTRS1982

The tropospheric gas composition of Jupiter's north equatorial belt (NH3, PH3, CH3D, GeH4, H2O) and the Jovian D/H isotropic ratio

The gas composition of the troposphere of Jupiter in the clearest regions of the North Equatorial Belt (NEB) was derived from the Voyager 1 IRIS data. The infrared spectrum for this homogeneous cloud free region was modeled to infer altitude profiles for NH3, PH3, GeH4 and H2O. The Profiles for NH3 and PH3 were found to be depleted in the upper troposphere but otherwise in agreement with their solar values at the 1 bar level. The mole fraction for CH3D was determined to be 3.5(+1.0 or -1.3) x 10 to the minus 7th power. The GeH4 mole fraction of 7+ or -2 x 10 to the minus 10th power at the 2 to 3 bar level is a factor of 10 lower than the solar value. The H2O mole fraction is approximately 1 x 0.00001 at the 2.5 bar level and is increasing to approximately 3 x 0.00001 at 4 bars where it is a factor of 30 lower than solar. Using IRIS infrared values for the mole fractions of CH3D and CH4 a value of D/H = 3.6(+1.0 or -1.4)x 0.00001 is derived. Assuming this Jovian D/H ratio is representative of the protosolar nebula, and correcting for chemical galactic evolution, yields a value of 5.5 - 9.0 x 0.00001 for the primordial D/H ratio and an upper limit of 1.8 to 2.4 x 10 to the minus 31st power cu cm for the present day baryon density.

Kunde, V.↗
NASA NTRS1982

Calculation of composition distribution of ultrafine ion-H2O-H2SO4 clusters using a modified binary ion nucleation theory

Thomson's ion nucleation theory was modified to include the effects of curvature dependence of the microscopic surface tension of field dependent, nonlinear, dielectric properties of the liquid; and of sulfuric acid hydrate formation in binary mixtures of water and sulfuric acid vapors. The modified theory leads to a broadening of the ion cluster spectrum, and shifts it towards larger numbers of H2O and H2SO4 molecules. Whether there is more shifting towards larger numbers of H2O or H2SO4 molecules depends on the relative humidity and relative acidity of the mixture. Usually, a broadening of the spectrum is accompanied by a lowering of the mean cluster intensity. For fixed values of relative humidity and relative acidity, a similar broadening pattern is observed when the temperature is lowered. These features of the modified theory illustrate that a trace of sulfuric acid can facilitate the formation of ultrafine, stable, prenucleation ion clusters as well as the growth of the prenucleation ion clusters towards the critical saddle point conditions, even with low values of relative humidity and relative acidity.

Singh, J. J.↗
NASA NTRS1981

A new search for insterstellar H2O absorption in the spectrum of Zeta Ophiuchi

Intensive Copernicus scans of the 1(11)-0(00) line of the F-X band of H2O were carried out, resulting in a 2 sigma upper limit of 1.04 mA for this line at 1114.225 A. The recently published f-value implies a column density limit of 5.3 x 10 to the 12th/sq cm, marginally above the level expected from recent chemical model calculations. A 1.8 sigma feature appears at the expected position of the H2O line, implying a column density for the ground rotational state of 2.8 x 10 to the 12th/sq cm.

Snow, T. P., Jr.↗
NASA NTRS1984

The EUV spectrum of H2O by electron impact

The vacuum ultraviolet (VUV) spectrum of H2O produced by electron impact at 200 eV is presented. A total of 25 spectral features are identified at a resolution of 0.5 nm over the wavelength range from 40 to 280 nm. Absolute emission cross-sections were obtained for each of the features. The differences of the features are all attributed to the various excited states of the dissociation products, H, O and O(+). The Lyman-alpha feature is the brightest for electron-induced fluorescence of H2O from the UV to the near-IR, and had a cross-section of 6.3 (+ or - 1.0 x 10 to the -18th) sq cm at 200 eV. The Lyman-alpha feature contributed 74 percent of the total measured emission cross-section in the EUV.

Ajello, J. M.↗
NASA NTRS1985

Stratospheric H2O and HNO3 profiles derived from solar occultation measurements

Compact two-channel radiometers for solar occultation experiments have been constructed in order to measure stratospheric trace gases. The instruments can be used as filter- or correlation-type radiometers, depending on the trace gas under investigation. Within the LIMS correlative measurement program, balloon flights were performed with a payload of up to four of these two-channel radiometers. From the filter-type measurements, profiles of the trace gases H2O and HNO3 are inferred for the height region between the tropopause and the balloon float level. The data evaluation also includes a comprehensive analysis of the error sources and their effect on the accuracy of the trace gas profiles. The derived H2O and HNO3 profiles are assessed against the observations of other authors and are discussed in the light of the trace gas distributions calcualted from photochemical models.

Fischer, H.↗
NASA NTRS1985

Comparison of the frequencies of NH3, CO2, H2O, N2O, CO, and CH4 as infrared calibration standards

The absolute accuracies of infrared calibration standards for the line positions have been investigated using a 0.0056-kayser-resolution (unapodized) Fourier-transform spectrum recorded from 550 to 5000 kayser. The spectrum has been obtained using a multicell arrangement containing the various molecular species. Detailed comoparisons reveal that standards for CO2, CH4, and N2O obtained from laser research and NH3 from Fourier-transform spectrometer research are consistent within the accuracies of the present data (+ or 0.0001 kayser). However, certain N2O, H2O, and CO values in the 1100-to 2300 kayser region are systematically high by 0.0001 to 0.0004 kayser. Correction factors for the H2O and CO standards are obtained to bring these into agreement with the laser values. In addition, corrected values for the 2nu-2 and nu-1 bands of N2O at 9 microns are reported.

Brown, L. R.↗
NASA NTRS1986

Picture processing of weak ion-tail emission of H2O in comets P/Crommelin and IRAS-Araki-Alcock

Two-dimensional CCD spectra of P/Crommelin at radius about 0.8 AU and of IRAS-Araki-Alcock at radius of 1.0 AU were obtained at the Kitt Peak National Observatory and Lick Observatory, and the results are discussed. The spectra revealed moderate H2O(+) emission from P/Crommelin predominantly in the antisolar direction, but extending about 6000 km sunward of the nucleus. The H2O(+) emission from IRAS-Araki-Alcock is very weak, appearing only on the antisolar side of the comet's nucleus and extending for at least 2000 km in the tailward direction. The data are interpreted briefly in terms of cometary ionospheric models and are compared with data in the literature.

Spinrad, H.↗
NASA NTRS1987

The excitation function of OH(A2Sigma/+/ - X2Pi) fluorescence produced through photodissociation of H2O

The absolute cross section for production of OH(A2Sigma/+/ X2Pi) fluorescence through photodissociative excitation of H2O was obtained using the University of Wisconsin synchrotron radiation source. The absolute fluorescence cross section function shows three broad features, roughly centered at 710, 400, and 240 A; the maximum value fluorescence cross section was found to be 3.4 x 10 to the -20th sq cm at 703 A. The broad features in the 700-A and 400-A regions are considered to be due to the second and the third excited states of H2O, respectively; it is argued that the broad feature at 240 A may have an origin similar to that of the 400-A broad feature. From present and previous data on quantum yields, it is estimated that part of the yield may be attributable to the production of neutral ground state OH(X) and H(1 2S) fragments. Such a process could provide a significant source of high kinetic energy OH and H observed in cometary atmospheres.

Wu, C. Y. Robert↗
NASA NTRS1987

Stratospheric O3, H2O, and HDO distributions from balloon-based far-infrared observations

Limb thermal emission spectra of the earth's stratosphere in the FIR obtained as part of the Balloon Intercomparison Campaign (BIC), have been analyzed for retrieval of trace constituent distributions. The observations analyzed here were made with a balloon-borne high-resolution Michelson interferometer operating in the 20-100/cm region, with an unapodized spectral resolution of 0.0033/cm. In this paper the vertical profiles of O3, H2O, and HDO retrieved from the observed spectra are presented and compared with the results from other BIC experiments. The retrieved profiles are found to be in good agreement with other measurements. The measurement of the HDO profile provides information about the sources of stratospheric water vapor. The variation of the D/H ratio of water vapor is derived from an analysis of HDO and H2O lines observed in the FIR spectra and is compared with the available measurements in the literature.

Abbas, M. M.↗
NASA NTRS1987

Sub-kilometer rampart craters in the equatorial region of Mars: Possible implications for the state and distribution of regolith H2O

It was long suspected that Martian rampart crater ejecta morphology originates from an impact into a water or ice-rich crust. If the water-impact hypothesis is correct, then the occurrence of rampart craters at all latitudes, elevations, and in all types of terrain, implies that the distribution of regolith H2O on Mars is global. To test this hypothesis, the occurrence of rampart craters was examined at three locations within the latitude band of + or - 30 degrees (specifically, within the ridged plains unit covered by MC-18). The analysis indicates that while few in number, rampart craters with diameters smaller than 3 km are indeed present at several locations withing the equatorial region of Mars. This finding appears to have significant implications for the inferred state and distribution of subsurface H2O. A more comprehensive analysis of the occurrence of sub-kilometer rampart craters is currently underway.

Clifford, Stephen M.↗
NASA NTRS1987

Simultaneous in situ measurements and diurnal variations of NO, NO2, O3, jNO2, CH4, H2O, and CO2 in the 40- to 26-km region using an open path tunable diode laser spectrometer

Simultaneous in situ measurements of temperature, pressure, and the NO, NO2, O3, jNO2, CH4, H2O, and CO2 concentrations were conducted in the 40- to 26-km region of the stratosphere using the JPL Balloon-borne Laser In Situ Sensor, a tunable diode laser absorption spectrometer. The NO, NO2, CH4, H2O, and CO2 concentration measurements generally show good agreement with previous observations, with a tendency for somewhat lower NO2 amounts. Measured O3 concentrations at 38 km agree well with comparable measurements from in situ UV photometers, but at 28 km they are lower by about 10 percent and agree more closely with the solar backscattered UV data. A decline was found in NO2 during the night over a 5-km altitude range, which implies either lower NO2 postsunset profiles, or an NO2 decay rate that is significantly higher than current model predictions that use N2O5 chemistry.

Webster, Christopher R.↗
NASA NTRS1988

Interactions between HCl, NO(x), and H2O ice in the Antarctic stratosphere - Implications for ozone

The role of PSC particles in determining the distributions of HCl and chlorine radicals is studied. The thermodynamics of HCl in ice is discussed, showing that significant quantities of HCl may be dissolved in ice when PSCs form. It is argued that HCl and HNO3 will be removed from the gas phase early in the condensation process, when only small quantities of H2O have been condensed, reflecting the thermodynamic properties of the solid phases of HCl, HNO3, and H2O. Rapid heterogeneous chemical reactions then volatilize reactive chlorine gases and convert NO(x) to solid-phase nitrates, which can be removed by gravitational settling. Analysis of the suite of heterogeneous chemical processes in the polar stratosphere implies a threshold for HCl concentrations, above which chemical loss rates for ozone increase dramatically.

Wofsy, S. C.↗
NASA NTRS1987

How important is correlation in the description of the Ni-H2O interaction

Using very large basis sets, which can accurately describe the polarizability of Ni and H2O and the dipole moment of H2O, the dipole-induced-dipole interaction is shown to be more than 50 percent of the about 4.8 kcal/mole bonding. Dispersion is found to account for the remainder of the bonding; this is significantly less than in previous estimates. The superposition error at the SCF level is essentially zero, and only 0.5 kcal/mole at the SDCI level, and the binding energy has been corrected for this error.

Bauschlicher, Charles W., Jr.↗
NASA NTRS1990

Photon sputtering of H2O ices: A preliminary report

A preliminary measurement of the total yields of ejected ions and electrons from H2O ices has been carried out using the He I 584 A resonance line as the incident photon beam. The H2O ices were prepared at 77 K in an ultrahigh vacuum system. The total yield of the ejected ion species and electrons was determined to be 8.8x10(exp -5) and 4.2x10(exp -4), respectively.

Wu, C. Y. Robert↗
NASA NTRS1989

H2O masers in star-forming regions

A comprehensive model is presented for the powerful H2O masers observed in star-forming regions. The shocks are the result of interaction of dense, high-velocity clumps with dense shells or clumps in the ambient medium. The shocked material is a thin slab in physical space, but breaks up into a network of filaments in velocity space. These filaments are the individual H2O maser features. The results of maser model calculations are presented which provide the maximum brightness temperatures that can be produced in single-temperature environments of any kind.

Elitzur, Moshe↗