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 S04: Photoionization, Photodetachment, and PhotodissociationLive
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Chair: Jan Rost, Max Planck Institute for the Physics of |
Thursday, June 3, 2021 10:30AM - 10:42AM Live |
S04.00001: Molecular Frame Photoionization Time Delays in a Shape Resonance Robert R Lucchese, F. Holzmeier, J. Joseph, J. Houver, D. Dowek Characterizing time delays in molecular photoionization as a function of the photoelectron emission direction relative to the orientation of the molecule provides unprecedented insights into the attosecond dynamics induced by extreme ultraviolet or X-ray one-photon absorption. The scrutiny of this fundamental process, including the role of continuum resonant states, is of crucial interest for the control of chemical reactions on the attosecond time scale. Here we report single-photon ionization experiments and calculations providing photoionization time delays angle-resolved in the molecular frame, obtained as the energy derivative of the phases of the photoionization amplitudes. For valence ionization of NO across a shape resonance, the observed time delays varying over a few hundreds of attoseconds are modeled using a multichannel Fano formalism which describes the interfering resonant and non-resonant contributions to the dynamics of the ejected electron. Comparing these results with computed e-NO+ scattering highlights the connection of photoionization time delays with Wigner scattering time delays. |
Thursday, June 3, 2021 10:42AM - 10:54AM Live |
S04.00002: Electron and ion spectroscopies of core-hole decays1 Stephen Southworth, Dimitris Koulentianos, Gilles Doumy, Anne Marie March, Adam E Fouda, Phay J Ho, Linda Young, Lan Cheng, Marc Simon, John Bozek, Denis Ceolin, Ralph Puettner, Maria Novella Piancastelli K-shell x-ray absorption by heavy atoms triggers multi-step decay processes via emission of x rays and Auger electrons as vacancies are transferred from core to valence shells. This results in ranges of final charge states, e.g., 2+ to 8+ for Kr, due to different decay pathways [1]. When the core hole is produced in a heavy atom of a molecule, electrons from neighboring atoms participate in the decay cascade and result in ion fragmentation [1]. We are using high-resolution electron spectroscopy and coincidence ion-momentum spectroscopy to characterize core-hole decays. Tunable x rays at the Advanced Photon Source excite K-shell electrons to pre-edge resonances and to the ionization continuum. Recent results include excitation and ionization of the Br K-shell of CF3Br. The electron spectrometer provides photoelectron and Auger electron spectra that are complementary to ion-ion coincidence measurements. Understanding core-hole decays offers challenges to theory, including treatments of relativistic, electron correlation, and wave function relaxation effects [1] and molecular dynamics simulations of dissociative ionization processes [2]. |
Thursday, June 3, 2021 10:54AM - 11:06AM Live |
S04.00003: Considerations of natural orbital decompositions of H2 for double photoionization investigations Frank L Yip, Roger Bello, Thomas N Rescigno, Robert Luccese, C W McCurdy Recently, we have investigated the role of electron correlation in double photoionization studies using a natural orbital decomposition of fundamental two-electron systems: atomic helium and molecular H2 [1]. The latter molecular target reveals much more sensitivity to the natural orbitals accounted for in the description of the intitial state, requiring substantially more correlating configurations be included compared to helium. Here we will further explore the consequences of basis set accuracy and completeness in representing the H2 bound state, paying particular attention to the gauge dependence of the double photoionization cross sections and the resulting angular distributions. |
Thursday, June 3, 2021 11:06AM - 11:18AM Live |
S04.00004: Photoionization fine structure in dilute ultracold gases Panagiotis Giannakeas, Matthew Eiles, Francis J Robicheaux, Jan M Rost The above-threshold photoionization of alkali atoms in the presence of a dilute environment, such as an ultracold gas, is investigated. |
Thursday, June 3, 2021 11:18AM - 11:30AM Live |
S04.00005: Bond dissociation energies of transition metal and lanthanide borides with resonant two photon ionization spectroscopy Dakota Merriles, Kimberly Tomchak, Christopher Nielson, Erick Tieu, Michael D Morse Metal boride compounds have unique properties that make them as chemically interesting as they are relevant in a multitude of disciplines. As more applications are discovered for metal borides, improved chemical models are needed to accurately predict the behavior of these species. To assist in this effort, we have developed a method for the precise and accurate measurement of bond dissociation energies (BDEs) and have applied it to the diatomic transition metal borides (MB), triatomic transition metal diborides (MB2), and triatomic lanthanide metal borides (LnB2). For the vast majority of these species, none have had their BDEs experimentally studied previously before. |
Thursday, June 3, 2021 11:30AM - 11:42AM Live |
S04.00006: Photoelectron – ion entanglement in streaked and multi-sideband interferometric photoemission: an ab initio approach Hongyu Shi, Uwe Thumm We extended our FE-DVR code for the ab initio calculation of single- and double-ionization [1] to explore the effect of electronic correlation on attosecond time- and emission-angle-resolved photoemission from gaseous helium. Our calculated spectra and relative photoemission time delays for IR streaked direct and shake-up XUV emission to the He+(n=2) channel (i) agree well with experimental and theoretical data in [2] and (ii) allow us to scrutinize the effect of the transient induced dipole moment of the residual excited He+ (n=2,3) ion on photoemission delays. In addition, we ab initio calculated multi-sideband interferometric spectra from helium to reveal the imprint of photoelectron interactions with the residual ion on laser-driven continuum-continuum transitions and relative phase sidebands shifts. |
Thursday, June 3, 2021 11:42AM - 11:54AM Live |
S04.00007: Making non-adiabatic photoionization adiabatic Jonathan Dubois, Ulf Saalmann, Jan M Rost We consider the process of tunnel ionization of atoms driven by circularly-polarized (CP) pulses. For a slowly varying electric field of the laser the intuitive semiclassical picture of adiabatic tunnel ionization pictures the electron passing through the potential barrier induced by a static electric field with constant energy. In reality, however, the laser field alternates in time and the energy of the electron is not conserved in this nonadiabatic tunneling ionization, as the distribution of electron energies at the tunnel exit reveals, with a width of the order of the ponderomotive energy of the laser. Extensive theoretical and experimental studies have been performed to probe and understand these nonadiabatic effects in photoionization. |
Thursday, June 3, 2021 11:54AM - 12:06PM Not Participating |
S04.00008: Analysis of non-linear photo-ionization spectra with deep neural networks trained with synthetic Hamilton matrices Sajal Giri, Ulf Saalmann, Lazaro Alonso, Jan M Rost We have constructed deep neural networks, which can map fluctuating photo-electron spectra obtained from noisy pulses to spectra from noise-free pulses. The network is trained on spectra from noisy pulses in combination with random Hamilton matrices, representing systems which could exist but do not necessarily exist. In [1] we performed a purification of fluctuating spectra, that is, mapping them to those from Fourier-limited Gaussian pulses. Here, we investigate the performance of such neural-network-based maps for predicting spectra of double pulses, pulses with a chirp and even partially-coherent pulses from fluctuating spectra generated by noisy pulses [2]. Secondly, we demonstrate that along with purification of a fluctuating double-pulse spectrum, one can estimate the time-delay of the underlying double pulse, an attractive feature for single-shot spectra from SASE FELs. We demonstrate our approach with resonant two-photon ionization, a non-linear process, sensitive to details of the laser pulse. |
Thursday, June 3, 2021 12:06PM - 12:18PM On Demand |
S04.00009: Convergence strategies for equivalent core hole states in photoionization calculations Cynthia S Trevisan, Carlos Marante, Thomas N Rescigno, C W McCurdy, Robert R Lucchese When photoionization leads to degenerate ion states, coupling between those channels is expected to be large. As a consequence, the single-channel static-exchange approximation fails to describe the physics of inner-shell photoionization when using delocalized orbitals to represent the core-hole states. We have recently shown [PRA 102, 012815 (2020)] that by using localized core orbitals, coupling between core-hole channels is negligible and independent single-channel calculations can achieve results nearly equivalent to those obtained in fully coupled calculations. However, for molecules that involve second-row atoms, additional numerical difficulties are encountered in attempting to converge core photoionization amplitudes with basis set variational methods. The origin of these difficulties lies in the inability of standard contracted Gaussian basis sets to accurately describe core-hole ionization wavefunctions in the region spanned by the core hole. We present a strategy that successfully overcomes these deficiencies. Comparisons of theory and experiment for total cross sections and molecular frame photoelectron angular distributions for inner-shell ionization of the chlorine 2p orbitals in CCl4 are presented. |
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