Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session K43: 2022 DCP Award SessionInvited Live Streamed Prize/Award
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Sponsoring Units: DCP Chair: Michael Heaven, Emory University Room: McCormick Place W-375B |
Tuesday, March 15, 2022 3:00PM - 3:36PM |
K43.00001: Plyler Prize (2022): DC Slice Velocity Map Imaging and My Dalliances with Ozone and Formaldehyde Invited Speaker: Arthur G Suits There are two molecules that hold a special place in my heart: ozone and formaldehyde. Ozone, despite its apparent simplicity, has rich and complex electronic structure and excited state decay pathways. The fascination of formaldehyde lies in accidents of nature that make it a marvelous laboratory for the study of chemical dynamics on its electronic ground state. These molecules have in common the fact that velocity map imaging studies have revealed deep insights into their dynamical properties that also carry general implications. In ozone, these excited state dynamics have been revealed through imaging studies probing both atomic and molecular products in a range of electronic states. One revealing aspect of this has been studies of angular momentum polarization in the O(1D2) product that carry rich information about the nature of the electronic excitation and decay pathways. We will show that coherent orbital orientation in the O(1D2) product must arise from Herzberg-Teller interactions in the excitation step. Furthermore, we show that a novel manifestation of the geometric phase can account for a range of polarization phenomena that have hitherto eluded explanation. In formaldehyde, state-correlated imaging studies reveal deep insight into the behavior and dissociation dynamics involving three distinct continua. We will tell the story of roaming in formaldehyde, in which near-dissociation to radical products leads to an intramolecular reaction with unanticipated consequences. The roaming mechanism is now considered a general aspect of molecular behavior, but has almost always been treated classically. We will present very recent work that shows quantum resonances at the onset of roaming strongly modulate the roaming yield and profoundly impact the molecular and radical channels as well. All this work has been enabled by DC slice velocity map imaging, and we take the opportunity to describe the virtues of this variant of the powerful VMI technique. |
Tuesday, March 15, 2022 3:36PM - 4:00PM |
K43.00002: Justin Jankunas Doctoral Dissertation Award Finalist: Watching the Water Dance: A New Way to Monitor Slow Reaction Kinetics on the Molecular Level with Temperature-controlled Water Clusters Invited Speaker: Nan Yang Cryogenic ion spectroscopy has the unique capability of recording the vibrational spectra of specific isomers and isotopomers of mass selected ions at very low temperature. Such technique provides a new way to identify reaction intermediates and capture clear snapshots of transient structures at the air-water interface. In an exciting recent development, we moved beyond these static pictures by introducing a temperature- and time-dependent ion spectroscopy technique that can follow the kinetics of chemical processes in dynamic equilibrium in a finite system. Think of it as monitoring the kinetics of a reaction in a 20 molecule “nanobeaker” in which the heat required for a chemical process is just another excursion through the phase space volume confined by the free energy landscape. To demonstrate how this method works, we measured the molecular-level trajectories that drive spectral diffusion at the air-water interface. The vibrational spectrum of water in the OH stretching region is very broad because of the wide variations in the H-bond environments. In liquid water, this diffuse spectrum is dynamic in the sense that the frequency of a particular OH oscillator changes rapidly in time and explores the entire envelope in less than 1 ps. Leveraging on our previous understanding of the spectral behavior of H2O molecules in a finite hydrogen bonded network, we tracked the time dependent frequency of a single, isolated OH oscillator in a cage of 20 water molecules. The frequency changes are fascinating because, at the onset of spectral dynamics, the oscillator is observed to “blink” between two widely separated frequencies before undergoing more diffusive excursions with increasing temperature as the cluster melts. With this demonstration of the technique, we open a new and exciting chapter on how we can unravel solvent-mediated chemistry in a regime where every atom counts. |
Tuesday, March 15, 2022 4:00PM - 4:24PM |
K43.00003: Invited Talk: Ezekel Piskulich Invited Speaker: Zeke A Piskulich TBD |
Tuesday, March 15, 2022 4:24PM - 4:48PM |
K43.00004: Nonlinear Spectroscopy in the Extreme Ultraviolet: Probing Ultrafast Dynamics with Attosecond Pulses Invited Speaker: Ashley P Fidler Ultrafast electronic dynamics underlie the most fundamental processes in chemical physics. Nonlinear spectroscopic techniques with extreme ultraviolet (XUV) pulses promise to probe these dynamics on their natural attosecond (10-18 s) to few femtosecond (10-15 s) timescales, but remain under-utilized due to the low photon flux of tabletop attosecond light sources. Recently, the coherent interaction of subfemtosecond XUV pulses and few-cycle near infrared (NIR) pulses have been shown to generate transient wave-mixing signals, extending nonlinear techniques into the XUV regime. Manipulation of the sequence, wavevector, and spectra of these pulses permits selective measurements of excited state evolution with exceptional temporal and spectral resolution. Utilizing a noncollinear geometry between subfemtosecond XUV and two angled NIR pulses, the earliest dynamics of nonlinear signal generation are probed in Rydberg and transient light-induced states in helium gas, revealing few-femtosecond delays in the emergence of higher order signals attributed to the formation of an AC Stark phase grating. This wave-mixing technique is further employed to measure the timescales of ultrafast decay processes in benchmark systems, including the (2P1/2)nd/ns autoionizing states of krypton. Despite pronounced quantum beating due to the XUV-induced coherence, the lifetimes obtained from background-free wave-mixing signals compare favorably with linewidth measurements for the short-lived (2P1/2)nd states. These results illustrate the potential of attosecond nonlinear spectroscopies to elucidate electronic dynamics in diverse systems with unprecedented selectivity. With the continued development of XUV wave-mixing and multidimensional techniques and applications to more complex molecular and solid-state systems, these initial results will provide the foundation for critical insights into the electronic dynamics of chemical reactions. |
Tuesday, March 15, 2022 4:48PM - 5:24PM |
K43.00005: Future of Chemical Physics Lectureship Recepient: Kaifeng Wu Invited Speaker: Kaifeng Wu
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