Engineering topics
Graedel, T. E.
Publications and source records attributed to Graedel, T. E..
Carbon and oxygen isotope fractionation in dense interstellar clouds
It is pointed out that isotope fractionation as a result of chemical reactions is due to the small zero-point energy differences between reactants and products of isotopically distinct species. Only at temperatures near absolute zero does this energy difference become significant. Favorable conditions for isotope fractionation on the considered basis exist in space within dense interstellar clouds. Temperatures of approximately 10 K may occur in these clouds. Under such conditions, ion-molecule reactions have the potential to distribute isotopes of hydrogen, carbon, oxygen unequally among the interstellar molecules. The present investigation makes use of a detailed model of the time-dependent chemistry of dense interstellar clouds to study cosmological isotope fractionation. Attention is given to fractionation chemistry and the calculation of rate parameters, the isotope fractionation results, and a comparison of theoretical results with observational data.
The kinetic chemistry of dense interstellar clouds
A model of the time-dependent chemistry of dense interstellar clouds is formulated to study the dominant chemical processes in carbon and oxygen isotope fractionation, the formation of nitrogen-containing molecules, and the evolution of product molecules as a function of cloud density and temperature. The abundances of the dominant isotopes of the carbon- and oxygen-bearing molecules are calculated. The chemical abundances are found to be quite sensitive to electron concentration since the electron concentration determines the ratio of H3(+) to He(+), and the electron density is strongly influenced by the metals abundance. For typical metal abundances and for H2 cloud density not less than 10,000 molecules/cu cm, nearly all carbon exists as CO at late cloud ages. At high cloud density, many aspects of the chemistry are strongly time dependent. Finally, model calculations agree well with abundances deduced from observations of molecular line emission in cold dense clouds.
Photochemistry in planetary atmospheres
Widely varying paths of evolutionary history, atmospheric processes, solar fluxes, and temperatures have produced vastly different planetary atmospheres. The similarities and differences between the earth atmosphere and those of the terrestrial planets (Venus and Mars) and of the Jovian planets are discussed in detail; consideration is also given to the photochemistry of Saturn, Uranus, Pluto, Neptune, Titan, and Triton. Changes in the earth's ancient atmosphere are described, and problems of interest in the earth's present troposphere are discussed, including the down wind effect, plume interactions, aerosol nucleation and growth, acid rain, and the fate of terpenes. Temperature fluctuations in the four principal layers of the earth's atmosphere, predicted decreases in the ozone concentration as a function of time, and spectra of particles in the earth's upper atmosphere are also presented. Finally, the vertical structure of the Venus cloud system and the thermal structure of the Jovian planets are shown graphically.
Dynamic spectra of type III solar bursts from 4 to 2 MHz observed by OGO-III
Dynamic spectra of type 3 solar bursts from OGO-3 antenna/radiometer observations
The association of solar optical flares with type III solar bursts from 4 to 2 MHz observed by OGO-III
Solar optical flares association with type 3 bursts from OGO-3 observations, suggesting temporary creation or enhancement of electron stream propagation by filament or sunspot structure change
Dynamic Spectra of 4-2 Mhz Solar Bursts - Results from Orbiting Geophysical Observatory 3 Final Report, Part 1 - Scientific
Data collected by OGO-3 in detecting solar bursts
OGO 3 data analysis - Dynamic spectra of solar bursts Final scientific report
Solar burst time profiles and dynamic spectra for calculating theoretical values for Type 3 burst characteristics