Bulletin of the American Physical Society
52nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 66, Number 6
Monday–Friday, May 31–June 4 2021; Virtual; Time Zone: Central Daylight Time, USA
Session K01: Focus Session: Charge Migration & Electronic CoherenceFocus Live
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Chair: James Cryan, SLAC National Lab |
Wednesday, June 2, 2021 10:30AM - 11:00AM Live |
K01.00001: Electron dynamics in biorelevant- and chiral molecules Invited Speaker: Francesca Calegari Attosecond science is nowadays a well-established research field, which offers formidable tools for the realtime investigation of electronic processes. In this context, we have recently demonstrated that attosecond pulses can initiate electronic beatings in aromatic amino-acids [1]. Still, there is a long path towards attochemistry and the full control of the molecule via electronic coherences. |
Wednesday, June 2, 2021 11:00AM - 11:12AM Live |
K01.00002: Probing Electronic Coherence with Pulse Shape Spectroscopy Brian M Kaufman, Philipp Marquetand, Tamás Rozgonyi, Thomas Weinacht Electronic coherence decays much more rapidly in molecules than atoms as a consequence of averaging over the different rates of phase advance for different internuclear separations associated with nonlocal nuclear wave functions. We make use of an ultrafast pulse shaper to produce few cycle phase locked pulse pairs with independent control over the phase and delay between pulses and show via interference that the electronic coherence of a wave function in a molecule that undergoes internal conversion via nonadiabatic (non-Born-Oppenheimer) coupling between electronic states is maintained. We show that this coherence can be used to control the population of different electronic states and determine the electronic coherence times for two similar molecules. |
Wednesday, June 2, 2021 11:12AM - 11:24AM Live |
K01.00003: Decoherence and Revival in Attosecond Charge Migration Driven by Non-adiabatic Dynamics Danylo T Matselyukh, Nikolay Golubev, Victor Despré, Alexander I Kuleff, Hans Jakob Woerner Charge migration is driven by a coherent superposition of electronic states and evolves on the single-femtosecond time scale. A key open question concerns the effect of nuclear motion and electronically non-adiabatic dynamics on charge migration. This work represents the first experimental characterization of both. We report the measurement of a series of quantum beats with a half-period of only 690 as in strong-field excited neutral silane using attosecond transient absorption spectroscopy at the silicon L-edge. With the help of Multi-Configurational Time-Dependent Hartree simulations, these beats are interpreted to be caused by the coherent excitation of multiple valence-excited states and a 3-eV-higher-lying Rydberg state. These beats are observed to decohere due to nuclear motion within 10 fs and to display a revival after 50 fs in both theory and experiment. The recoherence is found to result from the concentration of the valence-state population in the lowest electronically excited states due to non-adiabatic population transfer, as well as the electronically adiabatic dynamics in the valence and Rydberg excited states. By showing that electronic coherence in molecules can be created through strong-field electronic excitation, maintained through non-adiabatic population transfer and have the possibility of reviving after being initially decohered by nuclear motion, these experimental and theoretical results give unprecedented insight into the intriguing mechanisms of attochemistry. |
Wednesday, June 2, 2021 11:24AM - 11:54AM Live |
K01.00004: Molecular Modes of Attosecond Charge Migration Invited Speaker: Kenneth J Schafer We discuss recent progress in understanding molecular charge migration (CM), the rapid movement of positively charged holes in a molecule following localized excitation or ionization. We focus our theoretical calculations on questions that are relevant to successful CM experiments. These include: Which molecules are most likely to support CM? Does the manner in which CM is initiated influence how it proceeds? Does CM manifest in generic ways so that its periodicity and visibility can be predicted to follow simple rules? |
Wednesday, June 2, 2021 11:54AM - 12:06PM Live |
K01.00005: Attosecond charge migration in model carbon chains studied with nonlinear dynamics Francois Mauger, Aderonke Folorunso, Kyle A Hamer, Cristel Chandre, Mette B Gaarde, Kenneth Lopata, Kenneth J Schafer Ultrafast charge migration, where the coherent motion of electrons and holes in molecules are followed in real time, is currently attracting much theoretical and experimental interest. In this presentation I will discuss recent theoretical investigations of attosecond charge migration in model carbon chains that employs tools from nonlinear dynamics [1]. I will show that, following ionization, the mean-field interaction drives synchronization of the electron motion and gives rise to a variety of migration dynamics. Notably, this synchronization can support several modes of current-like charge-migration in a molecule, with periods varying by several hundred attoseconds. I will also discuss how functionalization and hybridization can play an important role in synchronizing migration dynamics. These results shed new light on the mechanisms that regulate charge-migration dynamics in complex molecules using nonlinear collective effects. [1] F. Mauger et al., “Nonlinear dynamics of attosecond charge migration in model carbon chains,” arXiv:2007.08007 (2021) |
Wednesday, June 2, 2021 12:06PM - 12:18PM Live |
K01.00006: Coherent electron dynamics of core-excited molecules at an x-ray free-electron laser Taran Driver, Siqi Li, Elio G Champenois, Philipp Rosenberger, Philip H Bucksbaum, Louis F DiMauro, Matthias F Kling, Jonathan Marangos, Agostino Marinelli, James P Cryan A new generation of x-ray free-electron lasers (XFELs) offers the possibility to initiate and probe sub-femtosecond electron dynamics in molecules with atomic site specificity. We demonstrate the production of a core-excited electronic wavepacket using isolated attosecond soft x-ray pulses at the Linac Coherent Light Source. We time-resolve the subsequent Auger-Meitner decay process with sub-femtosecond resolution and observe that the evolution of the core-excited wavepacket maps to quantum interference in the emitted Auger-Meitner electron current. Sub-femtosecond precision is achieved by angular streaking and a novel self-referencing scheme. Control of the coherent electron dynamics is achieved by tuning the central photon energy of the exciting XFEL pulse. Mapping the time evolution of the core-excited state to the Auger-Meitner current offers a unique testbed for probing coherent electron dynamics in molecules on the attosecond timescale. |
Wednesday, June 2, 2021 12:18PM - 12:30PM Live |
K01.00007: Angular Momentum Coherences in Molecular Dynamics Margaret Gregory, Simon Neville, Michael S Schuurman, Albert Stolow, Varun S Makhija With the advent of attosecond science ultrafast probes of excited state dynamics have recently achieved unprecedented time resolution, now sufficient to resolve molecular electronic dynamics. A number of different methods have been proposed to probe physical processes of chemical interest, such as charge migration and passage through conical intersections, using this technology. However, many of these methods rely on the molecule being fixed in space. Here we examine instead the full dimensional, laboratory frame, time evolving probability distribution generated by resonant excitation of an isolated molecule. We find that the excited state molecular dynamics induce time dependent anisotropy in this probability distribution, the moments of which are directly observable by ultrafast scattering experiments. These observable Molecular Angular Distribution Moments (MADMs) are related to density matrix elements in the lab frame, and fully characterize the molecular dynamics. Furthermore, higher order moments, which can be experimentally isolated, exclusively contain the off diagonal electronic density matrix elements, in other words the electronic coherences, allowing separation of these from population dynamics. As a demonstrative example we compute the MADMs and lab frame density matrix elements for the case of an excited state electronic wavepacket in 4-amino-4’-nitrostilbene, a molecule thought to exhibit charge migration in the molecular frame. |
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