Experimental and theoretical studies of interstellar grains
Steady state vibrational populations of SiO and CO in dilute black body radiation fields have been calculated as a function of total pressure, kinetic temperature and chemical composition of the gas. Approximate calculations for polyatomic molecules have also been presented. Vibrational disequilibrium becomes increasingly significant as total pressure and radiation density decrease. Many regions of postulated grain formation are found to be far from thermal equilibrium before the onset of nucleation. Calculations based upon classical nucleation theory or equilibrium thermodynamics are expected to be of dubious value in such regions. Laboratory measurements of the extinction of small iron and magnetite grains were made from 195nm to 830nm and found to be consistent with predictions based upon published optical constants. This implies that small iron particles are not responsible for the 220nm interstellar extinction feature. A feature which begins near 160nm in the extinction spectrum of HD44179 is identified as due to water ice. Measurements have been made of the critical partial pressure of SiO (P/(sub c/) necessary to initiate avalanche nucleation in the SiO-H/sub 2/ system as a function of temperature (750K < T < 1000K). The condensate produced by this process is Si/sub 2/O/sub 3/ rather than SiO/sub 2/. Analysis of P/(sub c)/ versus T using classical nucleation theory yields a value of 500 ergs/cm/sup 2/ for the surface free energy of the initial clusters. Despite the fact that this value is in reasonable agreement with those from the literature, numerous inconsistencies in the analysis are noted.
- Research Organization:
- Maryland Univ., College Park (USA)
- OSTI ID:
- 5987995
- Resource Relation:
- Other Information: Thesis (Ph. D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
INTERSTELLAR GRAINS
NUCLEATION
CARBON MONOXIDE
COSMIC GASES
EQUILIBRIUM
HIGH TEMPERATURE
HYDROGEN
INFRARED SPECTRA
IRON
MAGNESIUM
MAGNETITE
PRESSURE MEASUREMENT
SILICON OXIDES
TEMPERATURE DEPENDENCE
THERMODYNAMICS
ALKALINE EARTH METALS
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
ELEMENTS
FLUIDS
GASES
IRON COMPOUNDS
IRON ORES
IRON OXIDES
METALS
MINERALS
NONMETALS
ORES
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PARTICLES
SILICON COMPOUNDS
SPECTRA
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
640105* - Astrophysics & Cosmology- Galaxies