Theoretical and experimental studies of heterogeneous chemical processes leading to stratospheric ozone depletion

The microscopic chemical mechanisms of heterogeneous reactions involving HC on crystalline ice and nitric acid trihydrate (NAT) are of fundamental interest to physical chemists, because such reactions yield "active" chlorine compounds that are readily photolyzed to yield radicals responsible for the annual destruction of polar stratospheric ozone. Using molecular-orbital and density-functional-based computational methods that are extensively validated, partial dissociation of HCl is shown to be kinetically rapid and thermodynamically favorable on an extended ice Ih surface model with two dangling OH groups in close proximity to adsorbed HCl at a binding site on the surface. Additionally, surface disordering of this ice model is observed at polar stratospheric temperatures when HCl is adsorbed at this site. The partial dissociation of HCl on/atop ice will compete with other proposed mechanisms only if the local density of surface dangling OH groups is high. This alternative mechanism of chlorine activation is not important on NAT, based on the theoretical study of HCl interacting with various low index NAT faces. This is due to the fact that the NAT (001) face (which may be the most prevalent in the polar stratosphere) possesses a low surface density of dangling OH groups. In addition, other selected defect-free low-index NAT faces do not have their dangling OH groups situated favorably for effective partial solvation of HCl. The efficiency of aluminum oxide particulate, which is emitted by solid rocket motors (SRMs), as a catalyst for "activating" chlorine involved in the less dramatic, but still consequential,

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Chemistry.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2002

Author dc:creator

• Mantz, Yves André, 1974-

Advisor dc:contributor.advisor

• Mario J. Molina and Bernhardt L. Trout.

• Chemistry.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/16806

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/16806