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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 235 records · Page 13
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NASA NTRS1972

Laboratory CO2 photolysis studies related to planetary atmospheres

The CO(a 3II) state, the upper state of the Cameron bands, was characterized with respect to its average radiative lifetime and its quenching coefficients for a series of simple molecules. The CO2 recombination reaction (O(3P) + CO + M yields CO2 + M) was studied as a function of temperature. For M = CO, the rate constant can be expressed as k = 6.5 x 10/33 exp(-4340 plus or minus 550/RT) cm to the 6th power molec/2 sec/1, whereas the rate for M = CO2, the pertinent species in the planetary atmospheres, is 1.6 times greater. The quantum yield for CO2 photodissociation was measured in the 1200-1500 A region, using atomic line sources. The yield throughout this spectral region was much lower than that measured at 1470 A, the lowest value obtained being 8% at 1304 A.

Slanger, T. G.↗
NASA NTRS1972

Photochemistry and lifetimes of interstellar molecules

A quantitative discussion is presented of the lifetime against photodecomposition, or the probability of photodecomposition, of interstellar molecules. In addition to photodissociation, molecules can also be destroyed by interaction with high energy radiation and energetic particles. These processes are much less effective than destruction by ultraviolet radiation. However, when the ultraviolet is highly attenuated in clouds, the energetic radiation and particles will persist and will become relatively more important and the ultimate lifetimes in clouds may depend upon these processes.

Stief, L. J.↗
NASA NTRS1972

The diurnal heat budget of the thermosphere

Detailed numerical calculations of thermospheric heat sources and sinks are presented and their relative importance is discussed in reference to the energy balance phenomena of the neutral atmosphere. It is shown that the thermal energy available from the absorption in the Schumann-Runge continuum leading to photodissociation of O2 is by far the largest energy source in the lower thermosphere. Other sources of varying importance in different altitude ranges are: (1) energy from photoelectrons, (2) energy exchange from thermal plasma, (3) chemical reactions (ion-electron dissociative recombination) energy gain, and (4) kinetic and dissipative energy associated with the neutral wind. The energy sinks of importance are thermal conduction at the lower boundary (120 km) and radiative cooling of atomic oxygen. It is shown that the combined energy from processes 2 to 4 constitute only a small fraction of the total energy available from photoelectrons and are in phase with the latter. It is suggested that a choice of a lower boundary much below 120 km, e.g. near the mesopause level (90 km), should be more appropriate for general thermospheric studies.

Chandra, S.↗
NASA NTRS1972

A discussion of CO and O on Venus and Mars

The absorption of solar ultraviolet radiation in the wavelength range 2000 to 2200 A by CO2 strongly reduces the dissociation rate of HCl on Venus. The Cl catalytic reaction for the rapid recombination of O and CO and the yellow coloration of the Venus haze by OCl(-) and Cl3(-) appears to be unlikely. At the time of the Martian dust storm, the dissociation of H2O in the vicinity of the surface may vanish. The increase of dissociation at high altitudes, however, can be the source of H atoms in the upper atmosphere. The H atoms from the dissociation of hydrides may catalyze the recombination of CO and O in the lower atmospheres of these planets according to the following scheme: H + CO + M yields HCO + M, and HCO + O yields H + CO2. In the case of Venus, there may be other kinds of sinks for the photodissociation products, and its chemical environment might be more complex than that of Mars.

Shimizu, M.↗
NASA NTRS1972

The chemistry of neutral species in the D and E regions.

The photodissociation of molecular species such as oxygen, nitrogen, and water vapor in the upper atmosphere leads to the formation of a reservoir of chemical energy consisting of highly reactive atomic gases. The reactions of these with each other, and with the rest of the atmosphere, give a complex neutral chemistry involving many species and reactions. Local equilibrium can rarely be assumed for these reactions; transport by the horizontal and vertical mean flow, by eddy diffusion, and by molecular diffusion has quite different effects on the various constituents, depending on the time constants. The entire subject of the neutral chemistry in the D and E regions (between 50 and 160 km altitude) is reviewed, and related to existing experimental results. Needs for further research on the subject are indicated.

Bowhill, S. A.↗
NASA NTRS1972

Origin of C3 in comets.

It is suggested that a potential source of C3 observed in comets is the photodissociation of propyne by solar radiation, most probably in the region of the strong 1216-A Lyman-alpha line. The possibility of a strong correlation between interstellar molecules and the stable parent cometary molecules is also considered.

Stief, L. J.↗
NASA NTRS1972

Mariner 6 and 7 ultraviolet spectrometer experiment - Analysis of the O I 1304- and 1356-A emissions.

Analysis of the O I 1304- and 1356-A data from Mariner 6 and 7, and estimation of the atomic oxygen concentration of the Martian atmosphere. Derived values of the parameters describing the sources of excitation differ considerably from previous estimates. A detailed statistical treatment is used in the analysis. At an exospheric temperature of 350 K the atomic oxygen concentration at 135 km is estimated to be between 0.5 and 1%. The likely source of the 1304-A intensity is resonance scattering of solar 1304-A photons. For the 1356-A emission, the likely source is photodissociation of CO2. There is an indication of a diurnal variation of the Martian upper atmosphere.

Strickland, D. J.↗
NASA NTRS1972

The air afterglow revisited

The air afterglow, 0 + NO2 chemiluminescence, is discussed in terms of fluorescence, photodissociation, and quantum theoretical calculations of NO2. The experimental results presented include pressure dependence, M-dependence, spectral dependence of P and M, temperature dependence, and infrared measurements. The NO2 energy transfer model is also discussed.

Kaufman, F.↗
NASA NTRS1973

Definition Research Study

Data were complied on the physical behavior and characteristics of plasma gas and/or dust in the context of how they relate to the self-contamination of manned orbiting vehicles. A definition is given of a systematic experimental program designed to yield the required empirical data on the plasma, neutral gas, and/or the particulate matter surrounding the orbiting vehicles associated with shuttle missions. Theoretical analyses were completed on the behavior of materials to be released from the orbiting or subsatellite shuttle vehicles. The results were used to define some general experimental design recommendations directly applicable to the space shuttle program requirement. An on-board laser probe technique is suggested for measuring the dynamic behavior, inventory, and physical characteristics of particulates in the vicinity of an orbiting spacecraft. Laser probing of cometary photodissociation is also assessed.

Marmo, F. F.↗
NASA NTRS1972

Neutral hydrogen in cometary comas.

The strong L alpha radiation observed recently in comets Tago-Sato-Kosaka and Bennett can be explained in terms of the resonant scattering of solar L alpha radiation on neutral hydrogen formed by the photodissociation of H2O which is vaporized from a nucleus having an ice core. A complete hydrodynamic description of an atmosphere composed of H2O and its daughter products OH, H and O coupled through frictional interaction as well as production and loss processes is given. Numerical results are computed in a typical case, and it is found that a temperature of about 3000 K for the cometary atmosphere provides the best fit with observation.

Mendis, D. A.↗
NASA NTRS1972

Dayglow forbidden O I 6300 and 5577 A lines in the early morning ionosphere.

Data on a developing morning ionosphere have been obtained by rocket measurement of the atomic oxygen red- and green-line airglow emissions and of the composition of the neutral and ionized constituents of the upper atmosphere. The use of tilting-filter photometers for the optical measurements resulted in reliable and accurate height profiles of the airglow intensity from below 100 to 245 km. The roles of the excitation of both O(super 1 D) and O(super 1 S) atoms by the dissociative recombination of O2(+) and electron impact were studied by using the 6300- and 5577-A data in conjunction with the ion composition measurements. The component of photodissociative excitation of O(super 1 D) by solar radiation in the Schumann-Runge continuum of O2 absorption was assessed as being approximately twice that determined for a previous rocket experiment.

Schaeffer, R. C.↗
NASA NTRS1972

The formation of diatomic molecules in interstellar clouds.

The formation of the classical interstellar molecules CH, CH(+), and CN is investigated, giving attention to the chemistry of moderate-density interstellar clouds. An H I region is considered in the model employed in the study. The major constituents in the region are atoms or ions because of the intensity of the UV radiation field. Aspects of radiative association are discussed together with chemical reactions, the electronic states and optical properties of CH and CH(+), and photodissociation rates.

Solomon, P. M.↗
NASA NTRS1972

Photochemistry chemical kinetics in the interstellar medium.

Gas phase processes involving interstellar molecules are considered. The primary process is photodissociation in the ambient radiation field. In obscured regions, a combination of Johnson's (1965) and Stecher's (1969) Perseus extinction curves was used to obtain the radiation field as a function of the extinction at 5,500 A. On the basis of laboratory measurements, it is concluded that the molecules of water, ammonia, methane, and formaldehyde have lifetimes less than one hundred years.

Donn, B.↗
NASA NTRS1973

Twilight airglow. I - Photoelectrons and forbidden O I 5577-angstrom radiation.

A payload consisting of a number of experiments to study the earth's atmosphere was launched from White Sands on Feb. 8, 1971. The differential photoelectron flux spectrum was measured as a function of altitude. The energy distribution revealed the N2 vibrational structure appearing at 2.8 V, rising to a maximum at 4 eV, decreasing to an 8-volt-wide plateau at 20 V, and then further decreasing. The ion and electron density distributions were measured simultaneously. An optical measurement of forbidden O I 5577-A radiation was made. Both electron impact on atomic oxygen and dissociative recombination of O2(+) were found to produce this emission above 150 km. The recombination rate for the O(1 S) found from a reported nightglow profile is 2.5 plus or minus 1.5 x 10 to the minus 9th cu cm/sec. Between 140 and 120 km, photodissociation is a source of 5577 radiation. Chapman three-body recombination is dominant below 120 km.

Hays, P. B.↗
NASA NTRS1973

Atomic oxygen transport in the thermosphere.

The photodissociation of oxygen in the lower thermosphere is evaluated to obtain its global average value and the hemispheric imbalance. The observed concentrations of atomic oxygen do not reflect this imbalance in production due to the effect of seasonal wind patterns redistributing the atomic oxygen. The wind system necessary to compensate for the imbalance in solar thermal input into the lower thermosphere is found to transport an amount of atomic oxygen sufficient to compensate for the hemispheric imbalance in production. Ionospheric data indicate a winter enhancement in atomic oxygen concentration; to produce this, a higher degree of oxygen dissociation than that normally accepted (i.e., higher than an atomic to molecular oxygen ratio of unity at 120 km) is needed. The concept that the concentrations of atomic oxygen observed over the winter polar region are maintained by transport from lower latitudes requires that eddy diffusion coefficients derived from vertical transport at low latitudes (ignoring horizontal transport) be reduced by about 25%.

Johnson, F. S.↗
NASA NTRS1973

A first look at atmospheric dynamics and temperature variations on Titan.

Pollack (1973) has used a radiative equilibrium model to match radiometric data for Titan and infers the atmospheric mass, composition, opacity, and gross vertical thermal structure. These results are used to estimate the atmospheric temperature variations by means of scaling analysis, taking into account dynamics both for a baroclinic wave regime and for an axially symmetric circulation regime. Horizontal temperature variations of the atmosphere and surface are found to be very small, and the circulation is found to be weak and probably axially symmetric. The small temperature variations appear to preclude the storage of volatiles in polar caps, so that the present atmospheric methane content may be due to a balance between outgassing and photodissociation.

Leovy, C. B.↗
NASA NTRS1973

Photochemistry of planetary atmospheres

The atmospheric composition of Mars is presented, and the applicability of laboratory data on CO2 absorption cross sections and quantum yields of dissociation is discussed. A summary and critical evaluation are presented on the various mechanisms proposed for converting the photodissociation products CO and O2 back to CO2.

Stief, L. J.↗
NASA NTRS1974

Scientific summary

Methane absorptions are prominent in the Titan atmospheric spectrum; also present are atomic hydrogen and nitrogen bands. Evaluation of the low ultraviolet albedo points to solid methane clouds and photochemical haze. Thermal infrared data indicate solar energy absorption and photodissociation reactions of the gas mixture resulting in the production of organic compounds and free hydrogen atoms.

Hunten, D. M.↗