Bulletin of the American Physical Society
51st Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 65, Number 4
Monday–Friday, June 1–5, 2020; Portland, Oregon
Session T05: Photoionization, photodetachment and photodissociationLive

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Chair: Arvinder Sandhu, University of Arizona Room: D139140 
Friday, June 5, 2020 10:30AM  10:42AM Live 
T05.00001: Angleandtime resolved photoionization of neutral Rydberg wave packets in Argon Alexander Plunkett, Dakota Waldrip, Chris H. Greene, Arvinder Sandhu We studied dynamics of spinorbit split Rydberg wave packets in Argon and conducted multichannel quantum defect analysis of the ionization pathways. Using extreme ultraviolet attosecond pulse trains, we excite a Rydberg wavepacket in Argon and ionize it with a delayed IR probe pulse to produce photoelectrons that are analyzed in a time and angle resolved fashion with a velocity map imaging spectrometer. We focus on two ionization channels, corresponding to the spinorbit split ionic ground state. We observed quantum beating in each channel with distinct phase relationship between the two channels. The timeevolution of energy dependent angular distributions is also analyzed. Experimental results are compared with multichannel quantum defect theory calculations to highlight the importance of manyelectron interactions in photoionization. [Preview Abstract] 
Friday, June 5, 2020 10:42AM  10:54AM Live 
T05.00002: Photodouble ionization of water at 20 eV above threshold at the unequal energy regime. Juan Martin Randazzo, Giorgio Turri, Paola Bolognesi, John Mathis, Lorenzo Ugo Ancarani, Lorenzo Avaldi While the photo double ionization (PDI) of two electron atoms and simple molecules has been deeply studied, the progress for complex molecules has been rather slow over the last years. Triple differential cross section (TDCS) for water PDI at 20 eV above threshold have been recently measured, at equal energy regime and a particular geometry of the outgoing electrons. Further experimental results where presented considering different emission angles, together with a first theoretical step in the very difficult problem of completely modeling this highly complex process. Basically, it reduces the tenelectron degrees of freedom to the ones corresponding to a twoelectron system, and decouple the initial states in partial waves, ending in a set of systems which is solved by means of the Generalized Sturmian Method. In this contribution we extend the analysis to the unequal energy regime for the outgoing electrons, based on new experimental and theoretical results. The experimenttheory comparison is fair, considering the theoretical approximations. [Preview Abstract] 
Friday, June 5, 2020 10:54AM  11:06AM Live 
T05.00003: Electronion Recombination and Photoionization of Ca~XV Sultana Nahar Characteristic features of the inverse processes of photoionization and electronion recombination of Ca`XV, Ca~XV + h$\nu \leftrightarrow$ Ca~XVI + e, studied using the unified method of Nahar and Pradhan (1992) will be presented. Particular focus is on the high temperature plasmas where the ion is more available. The study includes excitation to 28 LS states belonging to n=2,3 complex of the core ion. The resonant features arising from core ion excitation to states of n=3 complex are much stronger than those from n=2 complex and introduce a third DR bump at temperature of 1.6 MK enhancing recombination rates at high temperature region. The statespecific features in photoionization and electron recombination of 582 bound states of Ca XV have been obtained. The computations were carried out in the Rmatrix method using a 29 term close coupling expansion for the core ion. [Preview Abstract] 
Friday, June 5, 2020 11:06AM  11:18AM Live 
T05.00004: Validity of the staticexchange approximation for innershell photoionization of polyatomic molecules C. Marante, L. Greenman, C. S. Trevisan, T. N. Rescigno, C. W. McCurdy, R. R. Lucchese The singlechannel staticexchange approximation, which completely ignores correlation between the continuum and molecular ion electrons, is demonstrated to fail seriously for molecules with symmetry equivalent atoms whose core shells are being ionized when delocalized symmetry orbitals are used. We present cross sections and molecular frame photoelectron angular dependences (MFPADs) with both uncoupled and coupled ionization channels together with an analysis of the validity of the singlechannel approximation to explain why and how it breaks down and the degree of channel coupling required to recover an accurate description of the physics of innershell photoionization. When localized core hole wave functions are used, the photoionization calculations as a singlechannel computations then give accurate results, when the MFPADs with the hole in the different symmetry equivalent locations are summed. A gridbased variational method, relying on a central grid and offcenter subgrids on the nuclear positions is described, that makes such calculations possible on larger systems. [Preview Abstract] 
Friday, June 5, 2020 11:18AM  11:30AM Live 
T05.00005: Multiphoton ionization and RABBITT in H$_2$ studied by the molecular ``Rmatrix with time'' method Jakub Benda, Greg Armstrong, Andrew Brown, Daniel Clarke, Jimena Gorfinkiel, Hugo van der Hart, Zdenek Masin We have developed the molecular Rmatrix method with time [1] (RMT), a variational ab initio multielectron method for solution of the timedependent Schr\"odinger equation for arbitrarily polarized and shaped electric fields. This approach is based on the well established atomic code which has recently undergone a significant upgrade. The molecular strand is interfaced with the mature UKRmol+ [2] timeindependent multiconfigurational Rmatrix codes. The method and the codes are applicable to general polyatomic molecules. As the first application of the molecular RMT code we have decided to study ultrafast laserinduced processes in H$_2$ (multiphoton ionization and RABBITT) for which accurate results are available. In the case of multiphoton ionization of H$_2$ we demonstrate agreement with earlier calculations based on the Rmatrix Floquet approach in the limit of long pulses, as well as with results from perturbation method for weak field limit. For the same molecule we also calculate photoionization time delays for several orientations of the molecule using simulated RABBITT interference and compare our results with other abinitio calculations. [1] A. C. Brown et al, Comput. Phys. Commun., 2020, in press [2] Z. Ma\v{s}\'{\i}n et al, Comput. Phys. Comm. 249 (2020) 1070 [Preview Abstract] 
Friday, June 5, 2020 11:30AM  11:42AM Live 
T05.00006: Energy and angleresolved nonresonant 2photon single valence ionization of N$_2$ using 9.3 eV femtosecond pulses Kirk Larsen, Roger Bello, Robert Lucchese, C. William McCurdy, Daniel Slaughter, Thorsten Weber We present an experimental and theoretical study on the photoionization dynamics of nonresonant 2photon single valence ionization of molecular nitrogen. Using 30 femtosecond 9.3 eV pulses produced via 400 nm driven high harmonic generation and a 3D momentum imaging spectrometer, we detect the photoelectrons and ions produced from 2photon ionization in coincidence. Photoionization populates nitrogenâ€™s X($^2\Sigma_g^+$), A($^2\Pi_u$) and B($^2\Sigma_u^+$) ionic states, where the photoelectron angular distributions of the X($^2\Sigma_g^+$) and A($^2\Pi_u$) states both vary with changes in electron kinetic energy of only a few hundred meV, which we attribute to 2electron resonances. These results are compared against timedependent full ab initio calculations. [Preview Abstract] 
Friday, June 5, 2020 11:42AM  11:54AM On Demand 
T05.00007: Twophoton double photoionization of atomic Mg by ultrashort pulses Frank L Yip, Roger Y Bello, Thomas N Rescigno, Robert R Lucchese, C. William McCurdy We investigate the twophoton double ionization of atomic magnesium induced by ultrashort pulses. Much like for beryllium, and in contrast to helium, the range of photon energies for which nonsequential ionization is the only open pathway is very narrow (less than 1~eV). Thus, sequential ionization pathways feature heavily in these processes. The greater significance of excitedstate correlating configurations in representing the initial state of magnesium has consequences on the resulting angular distributions at photon energies where sequential ionization can access intermediate states that lie nearby in energy, particularly when the pulse length is increased. [Preview Abstract] 
Friday, June 5, 2020 11:54AM  12:06PM On Demand 
T05.00008: DC electric fields in electrodefree glass vapor cell by photoillumination Lu Ma, Eric Paradis, Georg Raithel We demonstrate tunable laser induced DC electric fields in an allglass vapor cell without bulk or thin film electrodes. The fields are generated by a photoelectric effect, and DC field tuning up to 0.8V/cm is shown. The spatial field distribution is mapped by Rydberg electromagnetically induced transparency (EIT) spectroscopy and good spatial homogeneity is demonstrated. We explain the measured data with a boundaryvalue electrostatic model. This work may inspire new approaches for DC electric field control in designing miniaturized atomic vapor cell devices. Limitations and other charge effects will also be discussed. [Preview Abstract] 
Friday, June 5, 2020 12:06PM  12:18PM 
T05.00009: Theoretical predictions of imaging initial vibrational wave functions of H$_2$O$^{++}$ after onephoton double ionization Z. L. Streeter, C. W. McCurdy, R. R. Lucchese Previous analysis of the dissociative dynamics of the H$_2$O$^{++}$ ion following onephoton double ionization for all eight experimentally observed states [Phys. Rev. A 98, 053429 (2018)] provided a clear picture of the breakup mechanisms for H$_2$O$^{++} \rightarrow$ O + H$^+$ + H$^+$ and showed that sampling from the Wigner phase space distribution for the \textit{ground} vibrational state produced classical trajectories that agree extremely well with COLTRIMS observations. The question arises of how different the momentum imaging observations would be for vibrationally \textit{excited} water. Here, we explore this question using the Wigner distributions for excited vibrational states of water in all three modes for classical trajectories on the $2 ^1A_1$, $1 ^1B_1$, and $ 1 ^1A_2$ states of H$_2$O$^{++}$ and the ideas of E. J. Heller and coworkers from the 1970s and 80s. We find that the initial vibrational states, with their nodes, can be imaged in the final momentum plane of the threebody breakup. A separatix dividing $2$ and $3$body dynamics in phase space is revealed for the $2 ^1A_1$ state. For one quantum of excitation of the asymmetric mode the branching ratios for this state flip from $67.3\%$ $3$body to $64.5\%$ $2$body. [Preview Abstract] 
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