Electron-Impact Excitation and Ionization in Air

Winifred Huo
2008 46th AIAA Aerospace Sciences Meeting and Exhibit   unpublished
In a partially ionized hypersonic flow field, electron collision plays a significant role in energy re-distribution and in the production of excited states of atoms and molecules that can subsequently radiate. Thus electron collision data is part of the database used in modelling high speed entry flows. First principles computational methods for the calculation of electron-impact data are reviewed. Their merits are discussed, based on the requirements of reliability and the ability to handle
more » ... bility to handle high-lying excited states. Three processes are considered: the production of electrons by electron-impact ionization, the removal of electrons by radiative recombination and dielectronic recombination, and the production of electronic excited states by electron impact. Electronnitrogen atom collisions are used as an illustrative example. The study clarifies the role of high-lying electronic excited states in the ionization process. It shows that the recombination processes can produce sizable radiative heat load in the VUV region. It also shows examples using a scaling method to improve the frequently used Born approximation for electron-impact excitations. Report Documentation Page Form Approved OMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. 1. REPORT DATE re-distribution and in the production of excited states of atoms and molecules that can subsequently radiate. Thus electron collision data is part of the database used in modelling high speed entry flows. First principles computational methods for the calculation of electron-impact data are reviewed. Their merits are discussed, based on the requirements of reliability and the ability to handle high-lying excited states. Three processes are considered: the production of electrons by electron-impact ionization, the removal of electrons by radiative recombination and dielectronic recombination, and the production of electronic excited states by electron impact. Electron-nitrogen atom collisions are used as an illustrative example. The study clarifies the role of high-lying electronic excited states in the ionization process. It shows that the recombination processes can produce sizable radiative heat load in the VUV region. It also shows examples using a scaling method to improve the frequently used Born approximation for electron-impact excitations. 15 . SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT SAR 18. NUMBER OF PAGES 22 19a. NAME OF RESPONSIBLE PERSON a. REPORT unclassified b. ABSTRACT unclassified c. THIS PAGE unclassified Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18
doi:10.2514/6.2008-1207 fatcat:hqfvoeu2gfefplu5cww2vljiuq