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Extramural Research

Grantee Research Project Results

Grantee Research Project Results

The Photolysis of Nitric Acid

EPA Grant Number: U914750
Title: The Photolysis of Nitric Acid
Investigators: Myers, Tanya L.
Institution: University of Chicago
EPA Project Officer: Broadway, Virginia
Project Period: January 1, 1995 through January 1, 1996
Project Amount: $102,000
RFA: STAR Graduate Fellowships (1995)
Research Category: Academic Fellowships , Engineering and Environmental Chemistry , Fellowship - Chemistry



The objective of this research project is to use photofragment translational energy spectroscopy to study photodissociation reactions in which nonadiabatic effects at the transition state influence the branching among energetically allowed product channels.


The dissociation of nitric acid on pinb,oright arrowpi*NO2 excitation at 193 nm has been studied in a crossed laser-molecular beam apparatus. The primary reaction channels are OH + NO2 and O + HONO. We measure the branching ratio between these two competing processes and determine (OH + NO2)/(O + HONO) = 0.50 ± 0.05. Our experiments provide evidence of a minor O + HONO pathway, which we assign to O(3P) and HONO in its lowest triplet state. The dominant pathway correlates to O(1D) + HONO (X1A). The translational energy distributions reveal two distinct pathways for the OH + NO2 channel. One pathway produces stable NO2 fragments in the 12B2 electronic state. The second pathway produces unstable NO2 fragments, which undergo secondary dissociation to NO + O. We examine the influence of nonadiabaticity along the OH + NO2 reaction coordinate to explain the significant branching to this other channel. Finally, we introduce a new method for generating correlation diagrams for systems with electronic transitions localized on one moiety in which we restrict the changes allowed in remote molecular orbitals along the reaction coordinate. Analysis of previously measured X + NO2 photofragment pathways in nitromethane and methyl nitrate provide further support for using a restricted correlation diagram to predict the adiabatic and nonadiabatic product channels.

Supplemental Keywords:

fellowship, nitric acid, reaction coordinate, methyl nitrate, nitromethane, correlation diagram, photolysis, adiabatic and nonadiabatic effects., Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Chemical Engineering, Environmental Chemistry, Ecosystem/Assessment/Indicators, Chemistry, photodissociation reaction, photofragment translational energy spectroscopy, photolysis, reaction coordination, dissociation of nitirc acid

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The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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