Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session J26: DCP Prize SessionInvited Live Prize/Award Undergrad Friendly
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Sponsoring Units: DCP Chair: Amy Mullin, University of Maryland, College Park |
Tuesday, March 16, 2021 3:00PM - 3:36PM Live |
J26.00001: Irving Langmuir Award in Chemical Physics (2021): Confining water: from biolubrication to nano-cavitation Invited Speaker: Jacob Klein The persistent fluidity of water when confined down to sub-nanometer films between solid surfaces [1], which is in striking contrast to non-polar liquids whose viscosity diverges when so confined [2], extends also to water confined to hydration layers [3]. In such cases the tenacious attachment of the water of hydration to the charges it surrounds, together with its fluidity, act as a ‘molecular ball bearing’ under confinement and shear, and thus constitute remarkable lubrication vectors, particularly in aqueous and biological environments [4-6]. Such hydration lubrication plays a crucial role in biolubrication and homeostasis of human tissues that slide past each other, especially in joints [7] and biomedical devices [8]. A very different behavior is seen when the confining surfaces are highly hydrophobic; when such surfaces approach across water, nano-cavities nucleate spontaneously between them and expand rapidly before collapsing. This effect may account for the long-known but still puzzling observations of long-ranged attraction between such surfaces [9]. |
Tuesday, March 16, 2021 3:36PM - 4:12PM Live |
J26.00002: JCP-DCP Future of Chemical Physics Lectureship: Spectroscopic probes of plasmon-molecule dynamics Invited Speaker: Renee Frontiera Plasmonic nanomaterials show great promise as highly selective photocatalysts, however their efficiency is currently limited by a lack of understanding of the mechanisms relevant in the ability to convert light to chemical energy. We have developed ultrafast and steady-state surface- enhanced Raman spectroscopic (SERS) techniques to probe plasmon-molecule dynamics relevant to plasmon-driven chemistry. This talk will discuss our use of ultrafast SERS to probe the contributions of plasmon-generated hot electron transfer, heating, and vibrational energy transfer on timescales relevant to photocatalysis. Specifically, we probe plasmon to molecular carrier transfer on the picosecond timescale by quantitating the growth of radical molecular species. We probe the effects of temperature on chemical reactivity by monitoring transient Stokes and anti-Stokes Raman intensities to quantify vibrational kinetic energy in adsorbates, finding that heating is not a major contributor to plasmonic photocatalysis. Finally, I’ll discuss our discovery of a highly selective plasmon-driven methyl migration reaction in which the plasmonic substrate can provide nanoscale spatial control of reactivity. These efforts in developing a fundamental understanding of plasmon-mediated processes in molecules will ultimately aid in the rational design of cost-effective plasmonic materials capable of driving industrially relevant chemistries using solar radiation. |
Tuesday, March 16, 2021 4:12PM - 4:36PM Live |
J26.00003: Probing and controlling chemical reactions at sub-microkelvin temperatures Invited Speaker: Yu Liu Advances in AMO physics techniques led to the creation of ultracold samples of molecules and opened opportunities to explore chemistry in the ultralow temperature regime. While many prior studies investigated how long-range forces influence ultracold reactions, we extend the exploration into the short-range where the particle rearrangment takes place. To this end, we developed an experimental apparatus that combines production of state-controlled ultracold molecules with highly efficient and universal ion-based detection. This allowed us to probe the exchange reaction between ultracold KRb molecules, and eventually gain control over its various aspects. In this talk, I will describe the identification of an unusually long-lived intermediate complex, steering the reaction pathway with light, and controlling the quantum state occupation of the reaction products via an external magnetic field. Finally, I will present our recent results on a complete pair-correlated map of the product quantum state distribution. I will compare our result to the celebrated statistical theory, and test one of its central tenets: in an energy-rich intermediate complex, is there a complete redistribution of energy prior to its dissociation? |
Tuesday, March 16, 2021 4:36PM - 5:00PM Live |
J26.00004: Developing new, multidimensional pump-probe spectroscopies for investigating semiconductors Invited Speaker: Darien Morrow Optical harmonic generation and sum-frequency methods are largely used to provide |
Tuesday, March 16, 2021 5:00PM - 5:36PM Live |
J26.00005: Earle K. Plyler Prize for Molecular Spectroscopy & Dynamics: Hyperspectral Imaging with ultrafast 2D spectroscopies : Principles And Applications To Biological And Materials Systems Invited Speaker: Martin T Zanni This talk will cover recent efforts to turn ultrafast multidimensional spectroscopies into microscopies. Experiments will be shown using far-field techniques, like 2D IR spectra collected with a new MCT camera, confocal techniques images are generated by tightly focusing the 2D pulse sequences, and new detection methods using action spectroscopies. The principles behind the techniques will be given and applications shown that range from singlet fission microcrystals to transgenic animals tissues to human lenses. |
Tuesday, March 16, 2021 5:36PM - 6:00PM Live |
J26.00006: Justin Jankunas Dissertation Award in Chemical Physics: Carotenoid-Mediated Light Harvesting in Plants Uncovered with Ultrabroadband Two-Dimensional Electronic Spectroscopy Invited Speaker: Minjung Son Plants absorb across the visible solar spectrum and rapidly funnel the energy downhill to power growth. In excess sunlight, they dissipate harmful energy as heat to protect against photodamage. Previous measurements have been limited to the two lowest-energy, exclusively chlorophyll transitions of their light-harvesting machinery, leaving the carotenoid-mediated pathways unexplored. We report the development of an ultrabroadband two-dimensional (2D) electronic spectrometer that enables us to map energy flow in the major light-harvesting protein of plants, LHCII, across the visible range. Using this apparatus, we uncover two previously inaccessible pathways of light harvesting as well as dissipation in LHCII, both mediated by carotenoids. By analyzing the vibrational wavepackets in the 2D spectra, we identify a debated dark state (SX) specific to a single carotenoid, lutein 2, that serves as a key mediator for efficient light harvesting. On a second carotenoid, lutein 1, we resolve a dissipative energy transfer from the chlorophyll to its dark S1 state. The distinct photophysics revealed for these two chemically identical pigments highlight the capability of the protein binding pocket to control the electronic structure, and in turn, function of carotenoids in photosynthesis. |
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