Mass Spectrometric Studies of Ionization in Shock Heated Gas Mixtures

Citation

Wang, Charles Chang-Ping (1967) Mass Spectrometric Studies of Ionization in Shock Heated Gas Mixtures. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/GN3Q-Y356. https://resolver.caltech.edu/CaltechETD:etd-11142005-104254

Abstract

The initial stage of thermal ionization in gas mixtures behind strong normal shock waves has been studied using a mass spectrometer. The sampling process, the unique role of mass spectrometric analysis, the ionization mechanism and the effect of impurities on the ionization relaxation time of the inert gases are discussed. A detailed analysis of ion diffusion through the end wall thermal boundary layer to investigate the effect of the sampling process on the reaction and reaction products are described. The experiments were conducted in argon and xenon at temperatures of from 10,000 ºK to 30,000 ºK and pressures from 15 mmHg to 80 mmHg. A large number of different ions were detected in "pure" (the estimated level of naturally occurring impurities was 50 ppm) argon. H+ and O+ were found in much greater amounts than any of the other products. The roles of H and O were studied further by mixing a small amount of H2 or O2 in argon. The activation energy and the effective cross section for ionization were obtained from the measured ionization rate. For argon, the activation energy agrees within experimental accuracy with the result of Kelly (1966). For hydrogen the activation energy is about 10 ev, and this value coincides with its first excited state. The effective cross section is a thousand times larger than the corresponding effective cross section for the ionization of argon. This explains why small amounts of hydrogen affect the argon ionization relaxation time.

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