Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session U58: Ultrafast Spectroscopies and Coherent Phenomena in the X-ray Domain IIFocus
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Sponsoring Units: DCP DAMOP DLS DCMP Chair: Michael Schuurman, Natl Research Council-Canada Room: Mile High Ballroom 3B |
Thursday, March 5, 2020 2:30PM - 3:06PM |
U58.00001: Ultrafast X-ray Molecular Dynamics Invited Speaker: Stephen R. Leone Transient absorption in the extreme ultraviolet and X-ray spectral regimes is used to probe molecular dynamics on both femtosecond and attosecond timescales. Laser-produced high-order harmonics are generated to use as the probe, while ultraviolet or visible pulses excite the molecular system by well-defined transitions. The method is used to investigate dissociating molecules, ring opening, passage through curve crossings and conical intersections, singlet-to-triplet transitions, and electronic and vibrational coherences. By extending the probe photon energies to 300 eV in the soft X-ray, carbon species are investigated to reveal atom-specific electronic orbitals during electronic transformations of organic molecules. Time domain measurements provide an assessment of multiple excited state products and key points along the reaction trajectories. Passage through curve crossings and conical intersections reveal distinct changes in electronic state character at the crossings, and shifts in core level spectroscopic features provide information on the changes in orbital energetics and occupancies, such as when bonds break. X-ray spectroscopic transitions of transient intermediate states are directly characterized. On ultrashort timescales, electronic and vibrational wave packet coherent dynamics are also observed. The results form the basis of an X-ray spectroscopic revolution in molecular dynamics, sensitive to electron state character. |
Thursday, March 5, 2020 3:06PM - 3:18PM |
U58.00002: Probing the ultrafast intermediate states of a divalent cobalt-manganese complex with femtosecond M-edge XANES Elizabeth Ryland, Kaili Zhang, Josh Vura-Weis In this work we perform ultrafast transient M-edge XANES on divalent Cobalt-Manganese(N,N,N-tri(2-(2-pyridylamino)ethyl)amine)Cl, a heterobimetallic system with directly-interacting dual metal centers held within a non-innocent ligand scaffold. The strong metal-metal interaction facilitated by the ‘double-decker’ type ligand scaffold leads to a highly multiconfigurational electronic structure with relaxation pathways unavailable in monometallic analogues. With the ultrashort broadband probe pulse used in transient high-harmonic generation spectroscopy, we are able to perform M-edge XANES on both metal edges simultaneously with high specificity for each metal center and ligand environment. By combining transient XANES with transient UV-visible spectroscopy we can compile a full picture of the ultrafast electronic relaxation dynamics of this complex molecule. Photoinduced MM’CT is followed by distinct electronic dynamics at both metal edges and within the ligand scaffold, suggesting complex interplay of the Co, Mn, and ligand redox centers. Increased understanding of the relation of function to metal-specific photodynamics will help lay essential groundwork for the development of multimetallic catalysts with efficiencies comparable to those found in nature. |
Thursday, March 5, 2020 3:18PM - 3:54PM |
U58.00003: Ultrafast spin cross-over dynamics in heme proteins Invited Speaker: Majed Chergui Heme proteins are essential for respiration, neural transmission and biological signaling. The binding |
Thursday, March 5, 2020 3:54PM - 4:30PM |
U58.00004: Ultrafast X-Ray Absorption Spectroscopy as a Probe of Conical Intersection-Mediated Dynamics: Theoretical Tools and Studies Invited Speaker: Simon Neville Ultrafast time-resolved X-ray absporption spectroscopy (TRXAS) has emerged as a powerful tool for probing excited-state non-adiabatic molecular dynamics. Of particular interest is the sensitivity of TRXAS to the changes in valence electron density that occur as an excited-state wavepacket approaches a region of conical intersection between electronic states. In particular, the mixing of state characters in these high-coupling regions can be expected to modulate the amount of localisation of the valence electron density around the individual atomic centres, resulting in shifts in the core-orbital energies. Resultantly, shifts in the peaks in the TRXAS are expected to occur, which may be directly related to the non-adiabatic nuclear dynamics. |
Thursday, March 5, 2020 4:30PM - 4:42PM |
U58.00005: RIXS within the coupled-cluster framework reveals the hidden transitions of transient species in ionized liquid water Kaushik Nanda, Ludvig Kjellsson, Jan-Erik Rubensson, Gilles Doumy, Stephen Southworth, Phay J Ho, Anne M March, Andre Al Haddad, Yoshiaki Kumagai, Ming-Feng Tu, Muhammad Shafiq Mohd Yusof, Tushar Debnath, Caroline Arnold, Ralph Welsch, Ludger Inhester, Robin Santra, Marc Simon, William F Schlotter, Stefan Moeller, Giacomo Coslovich, Jake Korelek, Daniel DePonte, Zhi-Heng Loh, Anna Krylov, Linda Young X-ray spectroscopies such as resonant inelastic X-ray scattering (RIXS) expand our ability to investigate the chemical structure and dynamics; in particular, when augmented with reliable theoretical tools. Computing the RIXS spectra, however, is challenging; primarily due to the difficulties in computing the underlying core-excited virtual states that are embedded inside the valence-ionization continuum in a converged fashion. We will present a novel electronic structure method within the equation-of-motion coupled cluster framework that facilitates converged calculations of the RIXS spectra for both closed- and open-shell species. We will illustrate the capabilities of our approach by measuring its performance in modeling the RIXS spectrum of the transient aqueous OH radical formed in ionized liquid water against experiments. We will provide orbital characterization of the distinct peaks in the RIXS spectrum of the OH radical for absorption below water’s absorption edge. We will provide ab initio explanation of why the intermolecular charge-transfer transitions of aqueous OH radical, that are dominant in UV-visible spectrum, are suppressed in RIXS revealing the hidden localized valence transition. |
Thursday, March 5, 2020 4:42PM - 5:18PM |
U58.00006: Simulating Time-resolved X-ray Spectroscopy: Progress and Challenges Invited Speaker: Tom Penfold The emergence of X-FELs has meant that our ability to probe ultrafast structural dynamics is becoming increasingly common. Importantly, the combined structural, electronic and spin information contained within X-ray spectroscopy offers new perspectives for understanding the correlated dynamics of these degrees of freedom within the femtosecond regime. However, the complex nature and high information content of this class of techniques means that detailed theoretical studies are often essential to provide a firm link between the spectroscopic observables and the underlying molecular structure and dynamics. |
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