Bulletin of the American Physical Society
48th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 62, Number 8
Monday–Friday, June 5–9, 2017; Sacramento, California
Session J4: Photoioniozation, Photodetachment, and Photodissociation |
Hide Abstracts |
Chair: Ilya Fabrikant, University of Nebraska--Lincoln Room: 309 |
Wednesday, June 7, 2017 2:00PM - 2:12PM |
J4.00001: K-shell Photodetachment of C$_n^-$ Anions Samantha Fonseca dos Santos, Nicolas Douguet, A. E. Orel, T. N. Rescigno The cross section for inner-shell ionization of the C$^-$ anion is known to be characterized by a single, prominent 1s $\rightarrow$ kp shape resonance just above the K-edge.\footnote{C. W. Walter {\it et al.}, Phys. Rev. A 73, 062702 (2006)} More recently, Berrah and coworkers \footnote {R. Bilodeau {\it et al.}, meetings.aps.org/link/BAPS.2015.DAMOP.K1.140} have found similar behavior in the heavier carbon anion chains C$_n^-$, $n=2,3,...8$, but with the added feature that in the longer chains the single peak seen in C$^-$ inner-shell photodetachment splits into multiple peaks, depending on the length of the chain. To understand this finding, we have undertaken a theoretical study of inner-shell photodetachment of the molecular anions using the complex Kohn variational method. Our preliminary results for photodetachment of C$_2^-$ and C$_3^-$ are found to be in good agreement with experiment and exhibit both bound resonances below threshold and shape resonances above the K-edge. We will also discuss the basic physical mechanism underlying the splitting of the observed shape resonances in these systems. [Preview Abstract] |
Wednesday, June 7, 2017 2:12PM - 2:24PM |
J4.00002: Single Photon Double Ionization of Atomic Oxygen Madhushani Wickramarathna, Thomas Gorczyca, Connor Ballance, Wayne Stolte Single photon double ionization cross sections are calculated using an R-matrix with pseudostates (RMPS) method (P. G. Burke, R-matrix Theory of Atomic Collisions, Springer 2011) which was recently applied by Gorczyca et al. (JPB, 46, 195201, 2013) for the double photoionization of helium. With the convergence of these theoretical calculations for the simple case of helium, we extend this methodology to consider the more complex case of oxygen double photoionization. We compare our calculated results with recent measurements at the Advanced Light Source, as well as earlier experimental measurements (Angel and Sampson, PRA, 38, 5578, 1988). Our RMPS results agree well, qualitatively, with the experimental measurements, but there exist outstanding discrepancies to be addressed. [Preview Abstract] |
Wednesday, June 7, 2017 2:24PM - 2:36PM |
J4.00003: Double photoionization of H$_2$ using a hybrid Gaussian-discrete variable representation basis for molecular continuum processes Frank L. Yip, C. William McCurdy, Thomas N. Rescigon A hybrid basis that combines Gaussian basis functions typically used in bound-state molecular electronic structure calculations with a grid-based discrete variable representation (DVR) suitable for continuum processes involving one or more electrons is used to fully describe the double ionization of molecular H$_2$ by a single photoabsorption. Comparison will be made with the most detailed information that has been calculated and measured for this Coulomb explosion: the triply differential cross sections that relate the angular distribution and energy sharing of all of the particles in the frame of the molecule. The advantages of utilizing this hybrid basis for double ionization processes beyond this simplest molecular target will be highlighted. [Preview Abstract] |
Wednesday, June 7, 2017 2:36PM - 2:48PM |
J4.00004: Photodetachment microscopy in time-dependent fields Harindranath Ambalampitiya, Ilya Fabrikant Photodetachment microscopy studies spatial distribution of photodetached electrons in static electric fields. The theory of this phenomenon was recently extended [1] to time-dependent electric fields in the terahertz range. In the present paper we use the semiclassical propagator (time-dependent Green's function) for investigation of temporal and spatial interference of classical electron trajectories in ac fields within a broad frequency range from radio to terahertz frequencies. The chosen length scale corresponds to the geometry of a traditional photodetachment microscopy experiment [2]. The propagator approach allows us to treat singularities in temporal and spatial distributions due to bifurcations, when the trajectories emerge in pairs from the complex space-time domain. $^1$ B. C. Yang and F. Robicheaux, Phys. Rev. A {\bf 92}, 063410 (2015). $^2$ C. Blondel, C. Delsart, and F. Dulieu, Phys. Rev. Lett. {\bf 77}, 3755 (1996). [Preview Abstract] |
Wednesday, June 7, 2017 2:48PM - 3:00PM |
J4.00005: Molecular Simulations of Multi-Photon Dissociation of CaH$^{+}$ and CaD$^{+}$ Smitha Janardan, Aaron Calvin, John Condoluci, Rene Rugango, Gang Shu, Kenneth Brown The vibronic and rovibronic $1^{1}\Sigma, \nu = 0 \rightarrow 2^{1}\Sigma, \nu' = 0, 1, 2, 3$ transitions are measured using molecular simulations of resonance enhanced multi-photon dissociation (REMPD) of CaH$^{+}$ and CaD$^{+}$. These measurements are vital for measuring rotational state preparation of CaH$^{+}$. The simulation method comes in two flavors: simple and full simulations, where the simple model ignores dissociation and full simulations take dissociation into account. Both methods convolute a tunable laser with an underlying rovibronic spectrum to find corresponding transition rates. By fitting the simulated spectrum to the experimental spectrum, physical constants and information, such as transition frequency, transition dipole moments, rotational constants, and dissociation pathway, is extracted. Assuming the Born-Oppenheimer Approximation (BOA), the vibronic transitions require a 687 cm$^{-1}$ shift from their theoretically predicted values to match both CaH$^{+}$ and CaD$^{+}$. Both transition dipoles and rotational constants match relatively relatively well with theory, and we will describe possible dissociation paths through excited $\Sigma$ and $\Pi$ states. [Preview Abstract] |
Wednesday, June 7, 2017 3:00PM - 3:12PM |
J4.00006: Intermolecular Coulombic Decay (ICD) Occuring in Triatomic Molecular Dimer Wael Iskandar, Averell Gatton, Bishwanath Gaire, Elio Champenois, Kirk Larsen, Niranjan Shivaram, Ali Moradmand, Travis Severt, Joshua Williams, Daniel Slaughter, Thorsten Weber For over two decades, the production of ICD process has been extensively investigated theoretically and experimentally in different systems bounded by a week force (ex. van-der-Waals or Hydrogen force). Furthermore, the ICD process has been demonstrated a strong implication in biological system (DNA damage and DNA repair mechanism) because of the production of genotoxic low energy electrons during the decay cascade. Studying large complex system such as triatomic molecular dimer may be helpful for further exploration of ``Auger electron driven cancer therapy". The present experiment investigates the dissociation dynamics happened in collision between a photons and CO$_2$ dimer. We will focus more specifically on the CO$_2$$^+$+CO$_2$$^+$ fragmentation channel and the detection in coincidence of the two ionic fragments and the two electrons will be done using a COld Target Recoil Ion Momentum Spectroscopy (COLTRIMS). The measurements of the Kinetic Energy Release of the two fragments and the relative angular distribution of the electrons in the molecular frame reveal that the ICD is the only mechanism responsible for the production of this fragmentation channel. [Preview Abstract] |
Wednesday, June 7, 2017 3:12PM - 3:24PM |
J4.00007: Photoionization and Recombination of Astrophysically Important ION Cl II Sultana Nahar Photoionization of Cl II $\rightarrow$ e + Cl III is of importance in nebular models since it determines the fractional abundance of [Cl III]. Intensity ratios of collisionally excited forbidden [Cl III] lines are electron density diagnostics, analogous to the prominent [S II] lines. I will present extensive relativistic calculations using Breit-Pauli R-Matrix (BPRM) method aimed at obtaining photoionization cross section up to high energies, and unified recombination cross sections including radiative and di-electronic components (RR and DR). The configuration interaction expansion of the target wavefunctions comprise of $3s^22p^3$, $3s3p^4$, $3s^23p^23d$, $3s^23p^24s$, $3s^23p^24p$, $3s^23p^24d$, $3s^23p^25s$, $3p^33d$, $3s^23p3d^2$, $3p^5$. The preliminary photoionization cross sections of the 8 lowest levels, $3s^23p^4(^3P_{0,1,2},^1D_2, ^1S_0$, $3s3p^3(^3P_{0,1,2}$ of Cl II are compared with the existing measured values at ALS and found to reproduce all features in the observed spectrum. [Preview Abstract] |
Wednesday, June 7, 2017 3:24PM - 3:36PM |
J4.00008: New Calculations for Plasma Opacities: Atomic Processes, Equation-of-State, and Astrophysical Models Anil Pradhan, Sultana Nahar, Lianshui Zhao, Chris Orban, Werner Eissner, Regner Trampedach Existing plasma opacities have been brought into question by recent experimental results from the Sandia Z-pinch facility and theoretical works [1,2]. Opacities calculations are complex and entail a nexus of fundamental issues in atomic physics, plasma physics and astrophysics. We report new calculations for iron ions, including ab initio treatment of autoionizing resonances and electron impact broadening for the first time, that result in significant opacity enhancements, as measured experimentally and required to reconcile solar abundances with helioseismic models. We discuss related issues of the equation-of-state in the ``chemical picture" with realistic atomic description, perturbed by the plasma environment and dissolution of excited levels. We also note important astrophysical applications in stellar interior models and observable parameters. \\ 1. J. Bailey, et al., Nature Lett. 517, 56 (2015)\\ 2. S.N. Nahar and A.K. Pradhan, Phys. Rev. Lett. 116, 235003 (2016) [Preview Abstract] |
(Author Not Attending)
|
J4.00009: Strong-Field Molecular Ionization: Suppression Induced by Dimensionality Youliang Yu, Brett Esry For highly non-perturbative strong-field dynamics such as tunneling ionization induced by a long-wavelength laser field, reduced-dimensional models are tempting when it comes to numerically solving the time-dependent Schr\"odinger equation~(TDSE). Although such models can often be useful for qualitative predictions, their validity should always be examined. We study the impact of dimensionality for strong-field molecular ionization by solving the TDSE for H$_2^+$ with both a one-dimensional model and a full-dimensional Hamiltonian. We observe in both cases that the fixed-$R$ ionization yield is suppressed relative to the atomic yield to fairly large internuclear distances for a range of laser wavelengths. Similar observations of suppression at 800\,nm have been explained as frustrated tunneling ionization. Surprisingly, we find that the suppression is much stronger in one dimension than in three with the result that the one-dimensional ionization yield asymptotes to within 1\% of the atomic yield only when $R$ approaches about 250\,a.u. for 800\,nm. In three dimensions, this agreement is reached already at $R$=90\,a.u. We will explore these and other dependencies on dimensionality for this problem. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700