Probing The Unimolecular Decay Of Atmospherically

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Probing The Unimolecular Decay Of Atmospherically

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University of Pennsylvania
ScholarlyCommons
Publicly Accessible Penn Dissertations 2019
Probing The Unimolecular Decay Of Atmospherically Important Criegee Intermediates
Victoria Paige Barber University of Pennsylvania
Follow this and additional works at: https://repository.upenn.edu/edissertations Part of the Physical Chemistry Commons, Special Education Administration Commons, and the
Special Education and Teaching Commons Recommended Citation Barber, Victoria Paige, "Probing The Unimolecular Decay Of Atmospherically Important Criegee Intermediates" (2019). Publicly Accessible Penn Dissertations. 3611. https://repository.upenn.edu/edissertations/3611
This paper is posted at ScholarlyCommons. https://repository.upenn.edu/edissertations/3611 For more information, please contact [email protected]

Probing The Unimolecular Decay Of Atmospherically Important Criegee Intermediates
Abstract Ozonolysis of alkenes is an important source of hydroxyl (OH) radicals, key oxidants in the Earth’s troposphere. Alkene ozonolysis proceeds via carbonyl oxide species known as Criegee intermediates. Infrared (IR) action spectroscopy is used to study OH production from jet-cooled, stabilized Criegee intermediates. IR activation drives the rate-limiting 1,4 H-atom transfer from a syn-alkyl substituent to the terminal oxygen of the carbonyl oxide group, followed by rapid unimolecular decay to OH, which is detected by ultraviolet (UV) laser-induced fluorescence (LIF). IR action spectra provide spectral fingerprints of the Criegee intermediates. OH appearance rates are measured following IR activation by varying the IR-UV time delay. This technique is applied to two prototypical Criegee intermediates, synCH3CHOO and (CH3)2COO, in three different energy regimes, including at energies significantly below the calculated transition state (TS) barrier, indicating the importance of quantum mechanical tunneling in the H-atom transfer reaction. The role of tunneling is further confirmed by a significant observed kinetic isotope effect for the D-atom transfer reaction of syn-CD3CHOO. The IR action spectroscopy technique is also extended to more complex Criegee intermediates. Methyl vinyl ketone oxide (MVK-oxide) is an unsaturated four-carbon Criegee intermediate formed from the ozonolysis of isoprene, the most abundant non-methane volatile organic compound in the atmosphere. MVK-oxide was generated via a novel synthetic method and identified by its IR action spectrum. OH appearance rate measurements validate the calculated TS barrier for the H-atom shift reaction, and provide insight into an alternative unimolecular decay mechanism. The methyl-ethyl substituted Criegee intermediate (MECI) is a saturated four-carbon Criegee intermediate and is unique among Criegee intermediates studied by IR action spectroscopy because multiple conformational forms can undergo H-atom transfer to OH. Comparisons among the Criegee intermediates studied provides insight into substituent effects on unimolecular decay. The experimental OH appearance rates across many systems are in good agreement with statistical RRKM rate calculations incorporating tunneling, validating the unimolecular decay mechanism. Finally, UV LIF is used to detect vinoxy radicals, a coproduct in the H-atom transfer reaction. LIF detection of vinoxy radicals may be a probe for alternative unimolecular chemistry of vinyl-substituted Criegee intermediates from isoprene ozonolysis.
Degree Type Dissertation
Degree Name Doctor of Philosophy (PhD)
Graduate Group Chemistry
First Advisor Marsha I. Lester
Keywords Criegee intermediate, Hydroxyl radical, Infrared Spectroscopy, Kinetics
Subject Categories Chemistry | Physical Chemistry | Special Education Administration | Special Education and Teaching
This dissertation is available at ScholarlyCommons: https://repository.upenn.edu/edissertations/3611

PROBING THE UNIMOLECULAR DECAY OF ATMOSPHERICALLY IMPORTANT CRIEGEE INTERMEDIATES Victoria P. Barber A DISSERTATION in Chemistry
Presented to the Faculties of the University of Pennsylvania in
Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy 2019
Supervisor of Dissertation ____________________ Dr. Marsha I. Lester, Edmund J. Khan Distinguished Professor
Graduate Group Chairperson ____________________ Dr. David Christianson, Roy and Diana Vagelos Professor in Chemistry and Chemical Biology
Dissertation Committee Dr. Jessica M. Anna, Assistant Professor of Chemistry Dr. Zahra Fakhraai, Associate Professor of Chemistry Dr. Abraham Nitzan, Donner Professor of Physical Sciences

DEDICATION
This dissertation is dedicated to my family and friends
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ACKNOWLEDGMENTS
I would first like to acknowledge my advisor, Marsha Lester, for her guidance throughout my time at Penn. Marsha has been an extraordinary mentor. She has pushed me to think hard about difficult problems and helped me grow tremendously as a scientist. Graduate school has at times been a challenging journey, but I have never regretted joining Marsha’s group. She has been a thoughtful, encouraging teacher, and I am profoundly grateful to her.
I’d also like to acknowledge my committee members, Jessica Anna, Zahra Fahkraai, and Abraham Nitzan, for their thoughtful engagement with my work over my years at Penn. I’d also like to thank our collaborators, Stephen Klippenstein and Anne McCoy, who have helped me learn and grow as a scientist.
To my past and present lab mates in the Lester group: thank you for your comradery and friendship. I am proud to have been a member of such a collaborative, smart, and supportive group of scientists. I began in the group working alongside Yi Fang and Fang Liu, two remarkable researchers who answered my endless questions and tried to impart as much of their expertise on me as possible before they moved on from Penn. I later had the privilege to work with Amy Green, Shubhrangshu Pandit, and Anne Reinholdt, all of whom were wonderful mentors, coworkers, and friends. Along the way, I crossed paths with Nathan Kidwell, Hongwei Li, Barbara Marchetti, and Greg Drozd, each of whom was wonderful to work with and get to know. Guanghan Wang, Trisha Bhagde, Vincent Esposito, Tianlin Liu, Ziao Liu, and Trent McHenry are all wonderful lab mates, and I can’t wait to hear about their future research in the group. Finally, Michael Vansco, who has been my cohort buddy from the very beginning of my time at Penn (despite the fact that we’ve never actually worked on a project together), has been a wonderful and supportive friend. He has read every piece of writing I wanted a second set of
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eyes on, spotted me when I didn’t have cash for the lunch cart, let me bounce ideas off him in the office, and was always in to grab an after-work drink. I look forward to hearing about each other’s science, and lives, for a long time to come.
Thank you to my lovely friends here in the chemistry department, who have listened to every rant, congratulated me on every success, explored Philadelphia, eaten late night pizza in the library, grabbed evening beers at New Deck, and assured me that none of us were going through graduate school alone. Thank you to my non-chemistry friends, who may not have always understood exactly what I was doing here, but who supported me nonetheless. Thank you to my family, who have been my cheerleaders long before I started graduate school, and who I’m sure will be long after I finish.
Finally, thank you to my husband, Josh, who has somehow managed to strike the balance between understanding how important my work is to me, and reminding me that work isn’t everything. He has welcomed me home with food ready after late night study sessions, taken me on weekend adventures, bragged about my accomplishments, put failures into perspective, and loved me throughout. He has been unfailingly supportive, and, while I could have done it without him, it would have been a whole lot harder.
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ABSTRACT
PROBING THE UNIMOLECULAR DECAY OF ATMOSPHERICALLY IMPORTANT CRIEGEE INTERMEDIATES Victoria P. Barber Marsha I. Lester
Ozonolysis of alkenes is an important source of hydroxyl (OH) radicals, key oxidants in the Earth’s troposphere. Alkene ozonolysis proceeds via carbonyl oxide species known as Criegee intermediates. Infrared (IR) action spectroscopy is used to study OH production from jetcooled, stabilized Criegee intermediates. IR activation drives the rate-limiting 1,4 H-atom transfer from a syn-alkyl substituent to the terminal oxygen of the carbonyl oxide group, followed by rapid unimolecular decay to OH, which is detected by ultraviolet (UV) laser-induced fluorescence (LIF). IR action spectra provide spectral fingerprints of the Criegee intermediates. OH appearance rates are measured following IR activation by varying the IR-UV time delay. This technique is applied to two prototypical Criegee intermediates, syn-CH3CHOO and (CH3)2COO, in three different energy regimes, including at energies significantly below the calculated transition state (TS) barrier, indicating the importance of quantum mechanical tunneling in the H-atom transfer reaction. The role of tunneling is further confirmed by a significant observed kinetic isotope effect for the D-atom transfer reaction of syn-CD3CHOO. The IR action spectroscopy technique is also extended to more complex Criegee intermediates. Methyl vinyl ketone oxide (MVK-oxide) is an unsaturated four-carbon Criegee intermediate formed from the ozonolysis of isoprene, the most abundant non-methane volatile organic compound in the atmosphere. MVK-oxide was generated via a novel synthetic method and identified by its IR action spectrum. OH appearance rate measurements validate the calculated TS barrier for the H-atom shift reaction, and provide insight into an alternative unimolecular decay mechanism. The methyl-ethyl substituted Criegee
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intermediate (MECI) is a saturated four-carbon Criegee intermediate and is unique among Criegee intermediates studied by IR action spectroscopy because multiple conformational forms can undergo H-atom transfer to OH. Comparisons among the Criegee intermediates studied provides insight into substituent effects on unimolecular decay. The experimental OH appearance rates across many systems are in good agreement with statistical RRKM rate calculations incorporating tunneling, validating the unimolecular decay mechanism. Finally, UV LIF is used to detect vinoxy radicals, a coproduct in the H-atom transfer reaction. LIF detection of vinoxy radicals may be a probe for alternative unimolecular chemistry of vinyl-substituted Criegee intermediates from isoprene ozonolysis.
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TABLE OF CONTENTS
DEDICATION ....................................................................................................... II ACKNOWLEDGMENTS ..................................................................................... III ABSTRACT .......................................................................................................... V TABLE OF CONTENTS .....................................................................................VII LIST OF TABLES ............................................................................................. XV LIST OF ILLUSTRATIONS ............................................................................... XX CHAPTER 1 INTRODUCTION............................................................................. 1
1. Unimolecular Reactions of and OH Production from Criegee intermediates .. 4 2. Bimolecular Reactions of Stabilized Criegee Intermediates ............................. 9 3. Understanding the Reactions of more Complex Criegee Intermediates ........ 18 4. Summary of this Thesis....................................................................................... 26 References ....................................................................................................................... 32
CHAPTER 2 REAL TIME OBSERVATION OF UNIMOLECULAR DECAY OF CRIEGEE INTERMEDIATES TO OH RADICAL PRODUCTS........................... 37
Acknowledgments .......................................................................................................... 51 References ....................................................................................................................... 51
CHAPTER 3 DEEP TUNNELING IN THE UNIMOLECULAR DECAY OF CH3CHOO CRIEGEE INTERMEDIATES TO OH RADICAL PRODUCTS......... 53
I. Introduction .................................................................................................................. 54 vii

II. Methods ....................................................................................................................... 59 III. Results ........................................................................................................................ 60
A. IR spectrum .............................................................................................................. 61 B. Unimolecular decay rate ........................................................................................... 64
IV. Discussion.................................................................................................................. 74 V. Conclusions ................................................................................................................ 83 Acknowledgments .......................................................................................................... 85 References ....................................................................................................................... 85
CHAPTER 4 TUNNELING EFFECTS IN THE UNIMOLECULAR DECAY OF (CH3)2COO CRIEGEE INTERMEDIATES TO OH RADICAL PRODUCTS ....... 89
I. Introduction ................................................................................................................. 90 II. Methods ....................................................................................................................... 95 III. Results ........................................................................................................................ 97
A. IR action spectrum ............................................................................................. 98 B. Unimolecular decay rates................................................................................. 101
IV. Discussion................................................................................................................ 111 V. Conclusions .............................................................................................................. 121 Acknowledgments ........................................................................................................ 122 References ..................................................................................................................... 123
CHAPTER 5 SELECTIVE DEUTERATION ILLUMINATES THE IMPORTANCE OF TUNNELING IN THE UNIMOLECULAR DECAY OF CRIEGEE INTERMEDIATES TO HYDROXYL RADICAL PRODUCTS ........................... 126
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Criegee IntermediatesUnimolecular DecayTunnelingAtmosphericallyPenn