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 Q03: Ultrafast Molecular DynamicsInvited Live
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Chair: Daniel Rolles, Kansas State University |
Thursday, June 3, 2021 8:00AM - 8:30AM Live |
Q03.00001: Non-adiabatic Excited State Molecular Dynamics Invited Speaker: Thomas Weinacht Following the coupled dynamics of electrons and nuclei in molecules on femtosecond timescales is key to under-standing many fundamental processes in physics, chemistry and biology. I will discuss a combination of experiments that probe such coupled (non-adiabatic) dynamics with a variety of approaches, including pulse shape spectroscopy, time resolved photoelectron spectroscopy and ultrafast electron diffraction. The measurements are compared with high level calculations of the measurement observables, allowing for detailed insight into the non-adiabatic dynamics. |
Thursday, June 3, 2021 8:30AM - 9:00AM Live |
Q03.00002: Understanding UV-Induced Photochemistry Involving Isomerization and Ring-Opening in Thiophenone Invited Speaker: Shashank Pathak Photoinduced isomerization reactions are the driving force behind many chemical processes in nature. We report the results of a combined experimental and theoretical study of the photoinduced ring-opening and isomerization reaction in thiophenone. To visualize the ultrafast structural changes as well as the underlying potential energy landscape, the same reaction was studied by time-resolved photoelectron spectroscopy (TRPES) using a seeded free-electron laser and by Mega-electron-volt ultrafast electron diffraction (MeV-UED). Both methods reveal detailed insights into the ring opening dynamics as well as the formation of three major open-ring photoproducts along with vibrationally hot ground state thiophenone within a timescale of a few hundred femtoseconds. The experiments are complemented by ab initio electronic structure and molecular dynamics calculations of the ground and excited-state molecules. The ring opening is shown to be driven by ballistic S-C bond extension over the timescale of ~100 fs, followed by a redistribution of the energy into several other vibrational degrees of freedom and, in some cases, a subsequent dissociation of the molecule, e.g. by elimination of CO, on a time scale of hundreds of picoseconds. |
Thursday, June 3, 2021 9:00AM - 9:30AM Live |
Q03.00003: Attosecond XUV-induced electron dynamics in molecules Invited Speaker: Alicia Palacios Coherent light sources producing femtosecond and sub-femtosecond laser pulses come with the promise of achieving an actual control on excitation and ionization processes in atoms and molecules. New developments in high-harmonic generation techniques and free electron lasers (FEL) open the way to a real-time imaging of the ultrafast mechanisms that ultimately govern a large extent of charge transfer reactions of interest not only in biology, but also in novel technological applications [1,2]. Attosecond pump-probe spectroscopy has been successfully employed in a manifold of recent experiments pursuing to trace and manipulate molecular fragmentation paths [1]. Most of existing experiments available combine a single or a train of attosecond pulses in the VUV/XUV region to trigger molecular excitation or ionization, whose dynamics is then probed by the time-delayed interaction with an IR field. The ideally pursued scheme is that one using a second VUV/XUV pulse as a probe. This talk will discuss available theoretical methods for a reliable description of ultrafast electron dynamics in ionization processes [2]. The talk will present recent theoretical work to investigate the role of electron-electron correlation in the excitation and/or ionization of molecules when exposed to ultrashort XUV pulses [3-5]. We will then discuss how the coupling of the electronic motion with the nuclear degrees of freedom, in scenarios where they move at comparable time scales or they are tightly coupled, directly affecting the outcome of a reaction. For instance, ultrafast processes such that charge migration, which is predicted to occur prior nuclear rearrangement can be significantly altered when the nuclear degrees of freedom come into play [2,5]. [1] M. Nisoli, P. Decleva, F. Calegari, A. Palacios and F. Martín, Chemical Reviews 117, 10760 (2017) [2] A. Palacios and F. Martín, WIREs Computational Molecular Science 10, 1 (2020) [3] D. Jelovina, J. Feist, F. Martín and A. Palacios, New J. Phys. 20, 123004 (2018) [4] DIR. Boll, O. Fojón, C. W. McCurdy and A. Palacios, Phys. Rev. A 99, 023416 (2019) [5] J. Delgado, M. Lara-Astiaso, J. González-Vázquez, P. Decleva, A. Palacios and F. Martín, Faraday Discussions (https://doi.org/10.1039/D0FD00121J) |
Thursday, June 3, 2021 9:30AM - 10:00AM Live |
Q03.00004: Real-time observation of ultrafast X-ray induced electron and nuclear dynamics in molecules Invited Speaker: Solène Oberli Observing electron and nuclear rearrangements in real-time at specific atoms and without perturbing the system poses a great challenge. Such an achievement is becoming a reality thanks to the capacitites of X-ray Free Electron Lasers of generating ultrashort and intense x-ray pulses. X-ray photons interact mainly with core electrons, whose binding energy is both element-specific and sensitive to the local chemical environment. In order to disentangle the x-ray induced dynamics, we developed quantum models that treat both electron and nuclear motions. Using these tools, we interpret the first Impulsive Stimulated X-ray Raman Scattering experiment in a molecule, nitric oxide, which uses an intense soft x-ray attosecond pulse to induce electronic population transfer and generates a local electronic wavepacket. We also show the possibility to induce selective bond breaking and hydrogen migration in formamide using a two-color x-ray femtosecond pump-probe sequence. Using a similar scheme, we correlate the ultrafast dynamics arising from purely electronic excitation to the local chemical shifts in carbon monoxide. We follow in real-time charge-redistribution accompanying the population transfer from a core-excited state to relaxation via Auger decay, leading ultimately to dissociation and hole trapping at one site of the molecule. Our studies shed light on the most fundamental ultrafast processes taking place in matter, both in linear and nonlinear regimes. |
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