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Photochemical and dynamics studies of oxygen isotope exchange reactions of carbon dioxide

Citation

Yeung, Laurence Y. (2010) Photochemical and dynamics studies of oxygen isotope exchange reactions of carbon dioxide. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:12222009-120450275

Abstract

This dissertation describes laboratory studies of three oxygen isotope exchange reactions — O(1D) + CO2, O2 + CO2, and O(3P) + CO2 — and their importance to oxygen cycling in the upper atmosphere. First, we studied the isotope exchange reaction O(1D) + CO2, which is believed to govern the oxygen-isotope budget of CO2 in the stratosphere. Our combined field, laboratory, and modeling study of the exceptionally rare 16O13C18O isotopologue revealed that O(1D) + CO2 explains only part of the stratospheric CO2 isotopologue budget, not all of it as previously thought: O(1D) + CO2 could not explain the large enrichments of 16O13C18O (i.e., of the "Δ47" tracer) at high Northern latitudes. Mesospheric and heterogeneous chemistry of CO2 were proposed as possible sources of this meridional variation in 16O13C18O. Therefore, we performed crossed-molecular-beam experiments to investigate the chemistry of CO2 at hyperthermal collision energies; this class of reaction could be important in the upper atmosphere, where low gas densities and high rates of photochemistry increase the relative probability of hyperthermal reactions. Our experimental and theoretical study of the O2 + CO2 isotope exchange reaction showed that the reaction can occur through a short-lived CO4 reaction complex, which leads to O2 + CO2 products that are highly internally excited, but possibly still in their ground electronic state. Our study of O(3P) + CO2 collisions at hyperthermal energies showed that O(3P) + CO2 isotope exchange can occur in the upper atmosphere, proceeding through a short-lived CO3 reaction complex. The O(3P) + CO2 → O2 + CO reaction was also observed, and our data suggest that it can proceed through a 'stripping' mechanism or a CO3 complex. These reactions demonstrate new ways in which oxygen can be cycled through CO2 in the atmosphere; their isotope effects, manifest in the isotopic composition of atmospheric CO2, may impose independent constraints on atmospheric transport and biosphere-atmosphere interactions.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Stable isotopes, clumped isotopes, stratosphere, mesosphere, polar stratospheric cloud, carbon dioxide, crossed molecular beam, CO3, CO4, quasiclassical trajectory
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Thesis Availability:Mixed availability, specified at file level
Research Advisor(s):
  • Okumura, Mitchio (co-advisor)
  • Eiler, John M. (co-advisor)
Thesis Committee:
  • Beauchamp, Jesse L. (chair)
  • Marcus, Rudolph A.
  • Blake, Geoffrey A.
  • Chen, Pin
Defense Date:10 December 2009
Author Email:lyeung (AT) caltech.edu
Funders:
Funding AgencyGrant Number
Davidow FundUNSPECIFIED
National Science FoundationUNSPECIFIED
Missile Defense AgencyHQ0006-05-2-0001
Air Force Office of Scientific ResearchFA955D-07-1-0095
National Aeronautics and Space AdministrationUNSPECIFIED
Record Number:CaltechTHESIS:12222009-120450275
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:12222009-120450275
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:5474
Collection:CaltechTHESIS
Deposited By: Laurence Yeung
Deposited On:05 Feb 2010 17:15
Last Modified:26 Dec 2012 03:20

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PDF (Chapter 1: Introduction) - Final Version
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PDF (Chapter 2: Large and unexpected enrichment in stratospheric 16O13C18O) - Final Version
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PDF (Chapter 3: A hyperthermal O-atom exchange reaction, O2 + CO2) - Final Version
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[img] PDF (Chapter 4: Dynamics of O(3P) + CO2 collisions at hyperthermal energies) - Final Version
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PDF (Chapter 5: Summary and outlook) - Final Version
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PDF (Front matter: Acknowledgements, abstract, table of contents, lists of figures and tables) - Final Version
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