Contribution of the First Electronically Excited State of Molecular Nitrogen to Thermospheric Nitric Oxide

The chemical reaction of the first excited electronic state of molecular nitrogen, N₂(A), with ground state atomic oxygen is an important contributor to thermospheric nitric oxide (NO). The importance is assessed by including this reaction in a one-dimensional photochemical model. The method is to scale the photoelectron impact ionization rate of molecular nitrogen by a Gaussian centered near 100 km. Large uncertainties remain in the temperature dependence and branching ratios of many reactions important to NO production and loss. Similarly large uncertainties are present in the solar soft x-ray irradiance, known to be the fundamental driver of the low-latitude NO. To illustrate, it is shown that the equatorial, midday NO density measured by the Student Nitric Oxide Explorer (SNOE) satellite near the Solar Cycle 23 maximum can be recovered by the model to within the 20% measurement uncertainties using two rather different but equally reasonable chemical schemes, each with their own solar soft-xray irradiance parameterizations. Including the N₂(A) changes the NO production rate by an average of 11%, but the NO density changes by a much larger 44%. This is explained by tracing the direct, indirect, and catalytic contributions of N₂(A) to NO, finding them to contribute 40%, 33%, and 27% respectively. The contribution of N₂(A) relative to the total NO production and loss is assessed by tracing both back to their origins in the primary photoabsorption and photoelectron impact processes. The photoelectron impact ionization of N₂ is shown to be the main driver of the midday NO production while the photoelectron impact dissociation of N₂ is the main NO destroyer. The net photoelectron impact excitation rate of N₂, which is responsible for the N₂(A) production, is larger than the ionization and dissociation rates and thus potentially very important. Although the conservative assumptions regarding the level-specific NO yield from the N₂(A)+O reaction results in N₂(A) being a somewhat minor contributor, N₂(A) production is found to be the most efficient producer of NO among the thermospheric energy deposition processes.

Name thesis:degree_name

Ph. D.

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Physics

Department dc:contributor.department

Physics

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

2013

Author dc:creator

• Yonker, Justin David

Chairs dc:contributor.committeechair

• Bailey, Scott M.
• Simonetti, John H.

Committee members dc:contributor.committeemember

• Khodaparast, Giti A.
• Sharpe, Eric R.
• Hagedorn, George A.
• Valeyev, Eduard Faritovich

• Atmospheric Science
• Aeronomy
• Ionosphere
• Thermosphere
• Nitrogen
• Nitric Oxide
• Solar Cycle
• Solar Irradiance
• EUV
• XUV

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Dc Identifier Other

vt_gsexam:947

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/22039