2026-09-19T23:30:53Zhttps://dspace.mit.edu/server/oai/requestoai:dspace.mit.edu:1721.1/1050222026-06-16T18:16:32Zcom_1721.1_7582com_1721.1_7581col_1721.1_131022
Andrei Tokmakoff.
De Marco, Luigi, Ph. D. Massachusetts Institute of Technology
Massachusetts Institute of Technology. Department of Chemistry.
Massachusetts Institute of Technology. Department of Chemistry
2016-10-25T19:49:50Z
2016-10-25T19:49:50Z
2016
2016
http://hdl.handle.net/1721.1/105022
959553462
Thesis: Ph. D. in Physical Chemistry, Massachusetts Institute of Technology, Department of Chemistry, 2016.
Cataloged from PDF version of thesis. Vita
Includes bibliographical references (pages 317-352).
It is no overstatement to claim that hydrogen bonding is the most important intermolecular interaction. On a day-to-day basis, we encounter the peculiar effects of hydrogen bonding in liquid water; however, it is well appreciated that hydrogen bonding is immensely important in many contexts and, in particular, in biological ones. Despite this apparent significance, a general molecular picture of the dynamics of hydrogen-bonding systems is lacking. Over the last two decades, ultrafast multidimensional infrared spectroscopy has emerged as powerful technique for studying molecular dynamics in the condensed phase. By taking advantage of the complex relationship between a molecular oscillator's frequency and its environmental structure, we may understand molecular dynamics from an experimental perspective. However, the study of hydrogen bonding poses a significant technical challenge in that the interaction gives rise to broad resonances in the mid-infrared absorption spectrum. Traditional methods for generating short pulses of mid-infrared light are fundamentally limited in the bandwidth they can produce. Oftentimes, the width of a hydrogen-bonded oscillator's absorption resonance exceeds the broadest bandwidth mid-infrared laser pulse. In this thesis, I describe our development and use of a novel source of short, broadband mid-infrared light pulses that span the entire region of high-frequency molecular vibrations. We use this source as a probe in two-dimensional infrared spectroscopy experiments to study a wide variety hydrogen-bonding systems, including hydrogen-bonded dimers and protein films, with a particular emphasis on liquid water. Across these systems, we observe fascinating trends in the changes in molecular dynamics with increasing complexity of hydrogen bonding. In particular, we find experimental evidence for large deformations of the nuclear potential energy surface, giving rise to extremely anharmonic and collective dynamics. The effect is most dramatic in liquid water, where the rapidly fluctuating hydrogen-bond network results in vibrational excitons wherein O-H stretching motion is delocalized over multiple molecules. In this case, the nuclear potential energy surface is so complex that even simple changes in the mass of the oscillators result in qualitatively different dynamics.
Funding from U.S. Department of Energy DE-FG02-99ER14988 and DE-SC0014305
by Luigi De Marco.
Ph.D. in Physical Chemistry
356 pages
eng
Massachusetts Institute of Technology
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.
http://dspace.mit.edu/handle/1721.1/7582
Chemistry.
The molecular dynamics of hydrogen-bonding explored with broadband two dimensional infrared spectroscopy
Thesis
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<Abstract>It is no overstatement to claim that hydrogen bonding is the most important intermolecular interaction. On a day-to-day basis, we encounter the peculiar effects of hydrogen bonding in liquid water; however, it is well appreciated that hydrogen bonding is immensely important in many contexts and, in particular, in biological ones. Despite this apparent significance, a general molecular picture of the dynamics of hydrogen-bonding systems is lacking. Over the last two decades, ultrafast multidimensional infrared spectroscopy has emerged as powerful technique for studying molecular dynamics in the condensed phase. By taking advantage of the complex relationship between a molecular oscillator's frequency and its environmental structure, we may understand molecular dynamics from an experimental perspective. However, the study of hydrogen bonding poses a significant technical challenge in that the interaction gives rise to broad resonances in the mid-infrared absorption spectrum. Traditional methods for generating short pulses of mid-infrared light are fundamentally limited in the bandwidth they can produce. Oftentimes, the width of a hydrogen-bonded oscillator's absorption resonance exceeds the broadest bandwidth mid-infrared laser pulse. In this thesis, I describe our development and use of a novel source of short, broadband mid-infrared light pulses that span the entire region of high-frequency molecular vibrations. We use this source as a probe in two-dimensional infrared spectroscopy experiments to study a wide variety hydrogen-bonding systems, including hydrogen-bonded dimers and protein films, with a particular emphasis on liquid water. Across these systems, we observe fascinating trends in the changes in molecular dynamics with increasing complexity of hydrogen bonding. In particular, we find experimental evidence for large deformations of the nuclear potential energy surface, giving rise to extremely anharmonic and collective dynamics. The effect is most dramatic in liquid water, where the rapidly fluctuating hydrogen-bond network results in vibrational excitons wherein O-H stretching motion is delocalized over multiple molecules. In this case, the nuclear potential energy surface is so complex that even simple changes in the mass of the oscillators result in qualitatively different dynamics.</Abstract>
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