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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Theoretical characterization of the minimum energy path for the reaction H + O2 to HO2(asterisk) to HO + O

The potential energy surface for the H + O2 to HO2(asterisk) to HO + O reaction has been investigated in the region of the minimum energy path using CASSCF/contracted CI (CCI) calculations with a large basis set. The results show no barrier for the addition of an H atom to O2, in agreement with previous studies. A crossing between the surface for electrostatic (OH dipole-O quadrupole) interaction and that for the formation of an O-O chemical bond, at r(infinity) of about 5.5 a(0), results in a small (about 0.5 kcal/mol) barrier.

Walch, Stephen P.↗
NASA NTRS1988

The excitation of the O(1S) state by the dissociative recombination of O2(+) ions - Electron temperature dependence

The rate coefficient for the excitation of the O(1S) state due to the dissociative recombination of O2(+) (v of not greater than 3) ions has been determined as a function of the electron temperature from 300-3500 K. In agreement with the work of Guberman (1987), the results suggest that the absolute magnitude of alpha(1S) is nearly the same for a wide variety of O2(+) vibrational distributions over the electron temperature range normally encountered in the nocturnal F-region. It is noted that previous studies which modeled 5577-A airglow data using a fixed value for f(1S) may be misleading.

Zipf, Edward C.↗
NASA NTRS1988

Transport properties for the oxygen system - O2, O, O(+), and e

The transport properties of the oxygen system, O2, O, O(+), and the electron, e, are calculated and their applications are discussed. The possible two-body interactions in the oxygen system are examined and the exponential repulsive potential is used to determine collision integrals for these interactions. Values are presented for the viscosity of the pure gases, the self-diffusion coefficient of the pure gases at 1 atm pressure, the translational thermal conductivity of the pure gases, and the internal thermal conductivity of O2.

Biolsi, Louis↗
NASA NTRS1988

The measurement of absolute absorption of millimeter radiation in gases - The absorption of CO and O2

An apparatus is described that will measure absolute absorption of millimeter radiation in gases. The method measures the change in the quality factor of a Fabry-Perot resonator with and without gas present. The magnitude of the change is interpreted in terms of the absorption of the lossy medium inside the resonator. Experiments have been performed on the 115-GHz CO line and the 119-GHz O2 line at two different temperatures to determine the linewidth parameter and the peak absorption value. These numbers can be combined to give the integrated intensity which can be accurately calculated from results of spectroscopy measurements. The CO results are within 2 percent percent of theoretically predicted valves. Measurements on O2 have shown that absorption can be measured as accurately as 0.5 dB/km with this technique. Results have been obtained for oxygen absolute absorption in the 60-80-GHz region.

Read, William G.↗
NASA NTRS1988

Manganese oxidation in pH and O2 microenvironments produced by phytoplankton

This paper reports on the oxidation of Mn(II) by pure cultures of Chlorella. It is shown that these cultures establish strong microgradients of pH and O2 concentration due to their photosynthetic activity, and it is demonstrated that Mn oxidation in the pelagic zone of Oneida Lake, New York, is limited to a microzone of high pH and O2 associated with the near-surface aggregates of phytoplankton cells. The data suggest that visible light is important in catalyzing Mn oxidation by driving the photosynthetic removal of CO2 with concomitant increases in pH.

Richardson, Laurie L.↗
NASA NTRS1989

Imaging observations of lower thermospheric O(1S) and O2 airglow emissions from STS 9 - Implications of height variations

The lower thermospheric nightglow in the Southern Hemisphere was observed with the Atmospheric Emissions Photometric Imager during the Spacelab 1 mission in December, 1983. Observations of emission from O(1S) at 2972 and 5577A, O2 at 7620 A, OH near 6300 A, and the combined emission from the three upper states of O2 which lead to the Herzberg I and II and Chamberlain band emissions in B and near UV are discussed. The altitudes of peak emission heights are determined, showing that the peak heights are not constant with latitude. It is found that airglow heights varied with latitude by as much as 8 km. The observed airglow height pattern near the equator is similar to that of Wasser and Donahue (1979).

Swenson, G. R.↗
NASA NTRS1989

Theoretical characterization of the potential energy surface for H + O2 yields HO2(asterisk) yields HO + O. II - The potential for H atom exchange in HO2

The results of CASSCF multireference contracted CI calculations with large ANO basis sets are presented for the exchange region of the HO2 potential-energy surface. The saddle point for H atom exchange is about 13 kcal/mol below the energy of H + O2; therefore, this region of the surface should be accessible during H + O2 recombination and methathesis reactions.

Walch, Stephen P.↗
NASA NTRS1989

Comment on predissociation of O2 in the B state

Theoretical models and experimental data on the predissociation of O2 in the B state are analyzed, with a focus on the results reported by Wodtke et al. (1988). Absorption cross sections in the (11,0) Schumann-Runge band of O2 at 79 K (Yoshino et al., 1987) are matched to curves synthesized from lower fine-structure components for 5Pi(u) and 3Pi(u) predissociative mechanisms. It is concluded that the 3Pi(u) predominance proposed by Wodtke et al. is not justified by the data. In a reply by Wodtke and Huwel, the need for further studies to clarify the apparent discrepancies between absorption and emission spectroscopy is indicated.

Freeman, D. E.↗
NASA NTRS1990

Parameterizations for the absorption of solar radiation by O2 and CO2 with application to climate studies

Simple and accurate parameterizations have been developed for computing the absorption of solar radiation due to O2 and CO2. The parameterizations are based on the findings that temperature has a minimal effect on the absorption and that the one-parameter scaling can be applied to take into account the effect of pressure variation along a path. Overlapping of the absorption due to CO2 and water vapor is treated accurately in the parameterizations. Simulations with a zonally averaged multilayer energy balance model show that the absorption of solar radiation due to O2 and CO2 has a small, albeit nonnegligible, effect on climate. The global surface solar radiation is reduced by 2.2 W/sq m, and the warming of the surface temperature due to a doubled CO2 concentration is reduced by 10 percent in the Northern Hemisphere.

Chou, Ming-Dah↗
NASA NTRS1989

'Design of CO-O2 recombination catalysts for closed-cycle CO2 lasers'

Pulsed CO2 lasers have many applications in aeronautics, space research, weather monitoring and other areas. Full exploitation of the potential of these lasers is hampered by the dissociation of CO2 that occurs during laser operation. The development of closed-cycle CO2 lasers requires active CO-O2 recombination (CO oxidation) catalysts and design methods for implementation of catalysts inside lasers. This paper will discuss the performance criteria and constraints involved in the design of monolith catalyst configurations for use in a closed-cycle laser and will present a design study performed with a computerized design program that had been written. Trade-offs between catalyst activity and dimensions, flow channel dimensions, pressure drop, O2 conversion and other variables will be discussed.

Guinn, K.↗
NASA NTRS1991

CW laser strategies for multi-parameter measurements of high-speed flows containing either NO or O2

Measurements of gasdynamic quantities were performed using a rapid-tuning CW dye laser to resolve Doppler-shifted spectral features in either the O2 Schumann-Runge bands or the NO gamma band near 225 nm. With the rapid-tuning capability, spectral features were acquired at a repetition rate of 4 kHz. Monitoring O2 transitions provided estimates of velocities while monitoring collision-broadened NO line pairs provided simultaneous measurements of velocity, temperature and pressure. Experiments were first performed in absorption within the transient one-dimensional flows generated in a shock tube. Agreement between measured and theoretical values, as calculated from one-dimensional shock relations, was typically better than 5 percent. The method was extended to fluorescence detection of NO in a static cell. Temperature and pressure were extracted from recorded profiles, and the results agreed well with expected values.

Dirosa, M. D.↗
NASA NTRS1991

Relative contributions of discrete and continuum absorption to the photodissociation of vibrationally excited O2 (v = 12-20)

In order to test the proposal that photodissociation of highly vibrationally excited O2 in the Schumann-Runge (SR) band is a source of upper stratospheric ozone, cross sections for the band and continuum absorption are calculated. Calculated maximum SR cross sections are in the 1-2 x 10 to the -18th sq cm range, with the O2(B) state contributing 2-3 orders of magnitude greater absorption than the 1 3Pi(u) state. For v-double prime = 12, it is shown that the SR band and continuum cross sections merge smoothly at 250 nm. It is shown that numerous processes, the most important of which is nonlinear photoabsorption, ultimately lead to the prediction that narrow laser line absorption in the 248-nm region should generate comparable O atom yields whether absorption is into the bands or the continuum. In the atmosphere, SR band absorption is the dominant process.

Saxon, R. P.↗
NASA NTRS1992

Self-, N2, O2, H2, Ar, and He broadening in the nu3 band Q branch of CH4

Self-, N2-, O2-, H2-, Ar-, and He-broadening coefficients, pressure shifts, and integrated intensities have been measured for most transitions in the Q branch of the nu3 fundamental band of methane using a difference-frequency laser spectrometer. A systematic dependence of the broadening coefficients on the tetrahedral symmetry species and order index is observed with striking similarities for N2, O2, and Ar and for H2 and He buffer gases. Comparison with earlier measurements on other bands and branches of methane indicates very little vibrational, branch, or carbon isotope dependence. Dicke narrowing is evident at intermediate pressures, yielding an average narrowing coefficient and an optical diffusion constant for each gas mixture.

Pine, A. S.↗
NASA NTRS1993

Predissociation linewidths in O2 B3Sigma-sub-u(-) (v = 0,2)

Results are presented of measurements of the rotational and fine-structure level-specific linewidths in v = 0 and v = 2 of the O2 B3Sigma-sub-u(-) state, which were carried out using laser-induced fluorescence techniques applied to Schumann-Runge absorption transitions from vibrationally excited O2 X3Sigma-sub-g(-) system. These linewidths represent the first measurements reflecting relative predissociation rates among the B-state levels. The linewidths were found to vary considerably among the various energy levels.

Cosby, P. C.↗
NASA NTRS1993

Variable temperature pressure broadening of the 4(1,4)-3(2,1) transition of H2O by O2 and N2

The O2 and N2 pressure-broadening parameters of the 4(1,4)-3(2,1) rotational transition in the ground vibrational state of H2O have been measured in the temperature range between 100 and 520 K. Above 250 K the measurements were made in an equilibrium cell. Below 250 K a cell, which uses collisional cooling to circumvent the temperature limits imposed by the vapor pressure of the sample gas, was used. The data were fitted to an exponential temperature-dependence for data above 150 K with resultant n values of 0.81(3) for O2 and 0.70(3) for N2, where the entries in parentheses represent the error in the last significant figure of the parameter. Below 150 K the measured pressure-broadening parameters are smaller than those calculated using these values of n.

Goyette, Thomas M.↗
NASA NTRS1993

Reaction of O2(+)(X 2Pi sub g) with H2, D2, and HD - Guided ion beam studies, MO correlations, and statistical theory calculations

Guided ion-beam mass spectrometry is used to examined the reactions of vibrationally cold ground-state O2(+)(X 2Pi sub g) with H2, D2, and HD. The energy dependence of the absolute integral cross sections from thermal energy to over 4 eV are measured in the center-of-mass frame of reference. Results are also presented for internally excited O2(+) ions reacting with D2 and HD. The results are consistent with the dominant state being the a 4Pi sub u electronic state. The experimental excitation functions are analyzed in detail and interpreted by extending the molecular orbital correlation arguments of Mahan (1971) and by comparison with results of statistical phase space theory and with a theory that predicts a tight transition state.

Weber, M. E.↗
NASA NTRS1991

Pressure broadening of the 118.455/cm rotational lines of OH by H2, He, N2, and O2

Tunable far-infrared spectroscopy was used to measure pressure broadening of the 118.455/cm rotational lines of OH by H2, He, N2, and O2. Broadening coefficients of H2 and He were measured for the temperature range of 296 to 80 K, and N2 and O2 broadening coefficients were measured for the 296-210 K temperature range.

Chance, K. V.↗
NASA NTRS1993

Air-, N2-, and O2-broadening and shift coefficients in the nu(3) spectral region of (C-12)H4

Results are presented of an analysis of 29 room-temperature laboratory absorption spectra of a dilute CH4 sample in dry air, N2, and O2 at total pressures ranging from 60 to 550 torr, yielding values of pressure-broadening and pressure-induced-shift coefficients for more than 450 vibration-rotation transitions in the nu(3), nu(2) + nu(4), and 2nu(2)-super-2 bands of (C-12)H4. Comparisons of the present results for the nu(3) and nu(2) + nu(4) bands with previous measurements on other bands and isotopes of CH4 show that, for a given transition, broadening by air and N2 are nearly equal, and broadening by O2 is smaller by less than 10 percent. It is also found that the pressure shift coefficients are more vibrational dependent than the pressure broadening coefficients.

Benner, D. C.↗