Grantee Research Project Results
The Photolysis of Nitric Acid
EPA Grant Number: U914750Title: The Photolysis of Nitric Acid
Investigators: Myers, Tanya L.
Institution: University of Chicago
EPA Project Officer: Lee, Sonja
Project Period: January 1, 1995 through January 1, 1996
Project Amount: $102,000
RFA: STAR Graduate Fellowships (1995) RFA Text | Recipients Lists
Research Category: Fellowship - Chemistry , Academic Fellowships , Safer Chemicals
Objective:
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.
Approach:
The dissociation of nitric acid on nb,o
*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., Ecosystem Protection/Environmental Exposure & Risk, Scientific Discipline, Chemical Engineering, Chemistry, Environmental Chemistry, Ecosystem/Assessment/Indicators, nitromethane, photofragment translational energy spectroscopy, photodissociation reaction, photolysis, reaction coordinationProgress and Final Reports:
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.