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Type of Document	Dissertation
Author	Thomson, J. Alex
URN	etd-01232006-143205
Persistent URL	http://resolver.caltech.edu/CaltechETD:etd-01232006-143205
Title	Emissivities and absorptivities of gases
Degree	PhD
Option	Engineering and Applied Science
Advisory Committee	Advisor Name Title S. S. Penner Committee Chair
Keywords	none
Date of Defense	1958-01-01
Availability	unrestricted
Abstract Equilibrium emissivities and absorptivities of heated gases have been computed from spectroscopic data. Several problems have been studied: (1) The relation between equilibrium absorptivities and equilibrium emissivities for diatomic and polyatomic molecules has been investigated. Our theoretical results provide a satisfactory correlation of available experimental data for heated water vapor but not for carbon dioxide. The origin of the failure of the theory for carbon dioxide is discussed in detail. (2) The available, empirically determined, emissivity data for water vapor have been correlated in terms of a statistical model for the distribution of spectral lines within well-defined wavelength regions corresponding to the stronger vibration-rotation bands. This correlation provides a useful framework for the extrapolation of measured emissivity data to temperatures and pressures somewhat different from those used to obtain the experimental data. (3) The equilibrium emissivity of heated NO has been calculated for the conditions under which this molecule exists in high-temperature air during reentry of hypersonic missiles. An extension of the Mayer-Goody statistical model was used for emissivity calculations on NO. Our semi-analytical results are in acceptable agreement with a simpler numerical analysis of Kivel, Mayer and Bethe. The original investigations of gas absorptivities and emissivities are introduced with a brief survey of basic theoretical results. An attempt has also been made to calculate the dipole moments and low energy transition probabilities for HF, HCl, and HBr. In this study it was found that the intensities of lines lying in the infrared are very sensitive to the details of the approximating wavefunctions. A considerably more detailed description of the wavefunctions than is available at present is required to make confident predictions of absolute intensities from first principles.
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