Bulletin of the American Physical Society
54th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 68, Number 7
Monday–Friday, June 5–9, 2023; Spokane, Washington
Session U04: Focus Session: Imaging of Molecular DynamicsFocus
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Chair: Thomas Wolf, SLAC National Accelerator Laboratory Room: Conference Theater |
Thursday, June 8, 2023 2:00PM - 2:30PM |
U04.00001: Pulse Shape Dependent Strong Field Molecular Ionization Studied with Covariance Velocity Map Imaging Invited Speaker: Thomas Weinacht
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Thursday, June 8, 2023 2:30PM - 2:42PM |
U04.00002: UV-induced Ring-opening dynamics investigated using Coulomb Explosion Imaging Keyu Chen, Surjendu Bhattacharyya, Anbu S Venkatachalam, Huynh Van Sa V Lam, Kurtis D Borne, Till Jahnke, Rebecca Boll, Daniel Rolles, Artem Rudenko The UV-induced ring-opening reaction is a widely studied process of significant importance in molecular dynamics. Thiophenone (C4H4OS) has been used as a model ring molecule in these investigations [1]. However, techniques such as time-resolved photoelectron spectroscopy and ultrafast electron diffraction have limitations in providing direct molecular structural information and sub-100 fs temporal resolution, respectively. In this work, we present the results of experiments that employ Coulomb Explosion Imaging with intense X-rays or near-infrared laser pulses . We use a UV pulse at 266 nm to excite the molecule and a high-intensity X-ray or near-infrared (NIR) laser pulse to probe the evolving molecular structure at different time delays. By detecting ionic fragments in coincidence, we are able to capture the dynamics of the ring-opening reaction with high temporal resolution. The experimental results are compared to Coulomb explosion simulations to assist the interpretation. |
Thursday, June 8, 2023 2:42PM - 2:54PM |
U04.00003: Imaging the photophysics of ironpentacarbonyl with ultrafast x-ray scattering Adi Natan, Aviad Schori, Elisa Biasin, Sebastien Boutet, Philip H Bucksbaum, Sergio Carbajo, James M Glownia, Ambar Banerjee, Kelly J Gaffney, Kateryn Ledbetter, Andreas Kaldun, Kristjan Kunnus, Mengning Liang, Michael Minitti, Jordan T O'Neal, Frederic Poitevin, Jennifer Ruddock, Brian M Stankus, Anna Wang, Peter M Weber, Thomas J Wolf, Mattew Ware, Michael Odelius We directly observe the early excited state gas-phase dynamics in the photodissociation of iron pentacarbonyl using ultrafast x-ray scattering. We recorded isotropic and anisotropic difference scattering signals following an ultrashort UV (266 nm) pump and hard x-ray (9.5 keV) probe. Applying the natural scattering kernels method we inverted the scattering signals to real space and recovered the pair density dynamics. We observe coherent periodic motion across several pair distances that is a precursor to the first CO loss, where each period contributes to the dissociation. Using the anisotropic scattering information we obtain evidence that the first CO loss has a preferential axial component. |
Thursday, June 8, 2023 2:54PM - 3:06PM |
U04.00004: Initial-site characterization of hydrogen migration following strong-field double-ionization of ethanol Eleanor Weckwerth, Eric Wells, Travis Severt, Balram Kaderiya, Peyman Feizollah, Bethany C Jochim, Kurtis D Borne, Farzaneh Ziaee, Kanaka Raju P., Kevin D Carnes, Daniel Rolles, Artem Rudenko, ITZHAK BENITZHAK Hydrogen migration in ethanol (CH3CH2OH) can originate from each of the three non-equivalent initial sites of the molecule, leading to hydrogen-rich fragments such as H3+, H2O+, H3O+, and CH4+. Following photofragmentation by intense ultrashort pulses, we measure the momenta of the dissociating fragments using a COLTRIMS technique. By combining measurements of a few different deuterium-tagged isotopologues of ethanol, we determine all the site-specific probabilities for H3+, H2O+, H3O+, and CH4+ ion compositions. The technique can be extended to other dynamical variables, such as the kinetic energy release, and to larger molecules. These measurements provide a new benchmark for molecular dynamics calculations. |
Thursday, June 8, 2023 3:06PM - 3:36PM |
U04.00005: X-ray Induced Coulomb Explosion Imaging of Complex Molecules Invited Speaker: Rebecca Boll Recording images of individual molecules with ultrashort “exposure times” has been a long-standing dream in molecular physics, chemistry, and biology, because this would allow one to follow the motion of atoms on their inherent timescale. While X-ray and electron diffraction have been successfully used for larger molecules, both are very challenging to apply to small gas-phase molecules. Moreover, these techniques are relatively insensitive to hydrogen atoms, which are key to many chemical reactions. |
Thursday, June 8, 2023 3:36PM - 3:48PM |
U04.00006: Direct imaging of coherent bending vibrations in a triatomic molecule Huynh Van Sa V Lam, Anbu S Venkatachalam, Sina Jacob, Surjendu Bhattacharyya, Keyu Chen, Vinod Kumarappan, Daniel Rolles, Artem Rudenko Light-induced vibrational wave packets play a fundamental role in many types of molecular dynamics and have been studied extensively. However, most studies using conventional mass spectrometry provide only indirect information on evolving molecular structures. In this work, we show that one can directly map coherent bending vibrations in a laser-ionized small molecule with excellent temporal resolution using Coulomb explosion imaging (CEI). We use a strong 28-fs near-infrared (NIR) laser pulse to ionize SO2 and induce vibrational wave packets in its cationic states. A second NIR pulse of higher intensity is then used to further ionize and/or dissociate the molecules, and the ionic products are detected in coincidence using a COLTRIMS apparatus. We focus on mapping the O-S-O bending vibrations and find that this motion influences many observables in the multi-dimensional coincidence data. We also show that the bending-mode vibration can be observed directly in the delay-dependent KER spectra and angular distributions of high-charge-states channels. Our observations are supported by classical Coulomb explosion simulations. |
Thursday, June 8, 2023 3:48PM - 4:00PM |
U04.00007: Multi-Particle Cumulant Mapping for Coulomb Explosion Imaging: the Algorithm Chuan Cheng, Leszek J Frasinski, Gönenç Moğol, Felix Allum, Andrew J Howard, Daniel Rolles, Philip H Bucksbaum, Mark Brouard, Ruaridh Forbes, Thomas Weinacht Covariance mapping is widely used to study correlations of different variables in the dataset. The power of the method has been demonstrated in multi-particle imaging, including two- and three-body covariance on molecules of biological relevance and Coulomb explosion imaging (CEI) of molecular dissociation dynamics. While covariance for two particles is rather straightforward, for four-body correlations, one needs to extend covariance mapping to cumulant mapping, which has been tested in recent measurements of strong field ionization of formaldehyde. Here, I will discuss the details of how to compute cumulant mapping for the momentum sum of all four fragments of the formaldehyde molecule, and how one can perform the calculation with a faster and better algorithm. |
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