Computer Science – Sound
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt........29c&link_type=abstract
Thesis (PH.D.)--THE UNIVERSITY OF NORTH CAROLINA AT CHAPEL HILL, 1995.Source: Dissertation Abstracts International, Volume: 57
Computer Science
Sound
Jupiter, Ammonia, Hydrazine, Earth
Scientific paper
Infrared spectroscopy has been used as a tool for elucidating the spectroscopic and physical properties of cryogenic aerosols. Ammonia and hydrazine aerosols have been studied using this technique under conditions designed to mimic those found in the atmosphere of Jupiter. Aerosols of water ice, nitric acid and water, and sulfuric acid and water were also studied under temperature conditions similar to those found in the Earth's stratosphere. Aerosols are generated in low temperature flow cells via homogeneous and heterogeneous nucleation of the gas phase. The technique affords information on the size, composition, number density, and in some cases shape, of the particles created. Both ammonia and hydrazine aerosols were studied over the temperature range from 180 K to 110 K. Mie theory can adequately describe the observed particle spectra in most cases. Under conditions designed to enhance particle aggregation, shape effects in the 9.4 mu m absorption band of the ammonia aerosols become apparent which can be modeled well using the Discrete Dipole Approximation. Both substances can exist as supercooled liquid droplets. Ammonia particles freeze distinctly at 155 K, while hydrazine particles freeze over the temperature range from 180 K to 170 K. Spectra of aerosols which are of mixtures of ammonia and hydrazine reveal that the inclusion of hydrazine into ammonia particles affects the spectrum of the ammonia very little, while the hydrazine absorptions are strongly perturbed. Hydrazine is not very soluble in the ammonia particles, even at very low concentrations. A new technique for determining complex refractive indices from aerosol spectra has been developed and applied to water ice and crystalline hydrazine. Comparisons with previous data indicate that the method is sound and accurate. The temperature dependence of the water ice complex refractive index has been quantified and compares well with previous results as a function of temperature. No temperature dependence of the complex refractive index of crystalline hydrazine was found over the temperature range of study. Water/nitric acid aerosols were observed to form crystalline hydrates under a wide range of compositions and temperatures. Both the di- and the trihydrate were observed. The spectra agree relatively well with thin -film spectra of the hydrates, although there are some differences. Water/sulfuric acid particles were also studied. In the dilute particles (<40 wt%), water ice was the first material to freeze. The observed freezing point as a function of composition agreed well with theoretical calculations by other researchers.
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