The Photolysis of Nitric AcidEPA 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) Recipients Lists
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 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.