Bulletin of the American Physical Society
42nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 56, Number 5
Monday–Friday, June 13–17, 2011; Atlanta, Georgia
Session K5: UItrafast Molecular Dynamics |
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Chair: Arvinder Sandhu, University of Arizona Room: A705 |
Wednesday, June 15, 2011 2:00PM - 2:12PM |
K5.00001: Multiphoton dissociation of H$_{2}$S by intense x-ray pulses from the Linac Coherent Light Source FEL Brendan Murphy, Li Fang, Matthias Hoener, Edwin Kukk, Elliot Kanter, John Bozek, Nora Berrah We will report on sequential multiphoton ionization of H$_{2}$S by intense pulses of x-rays from the LCLS free electron laser. Following L-shell excitation, fragmentation of the molecule is observed by Auger electron, photoelectron, and ion time-of-flight spectroscopy. Intensity dependent features in these spectra shed light on the dynamics of the dissociation process. [Preview Abstract] |
Wednesday, June 15, 2011 2:12PM - 2:24PM |
K5.00002: Studying Ultrafast Internal Conversion Dynamics in Ethylene using ultrafast VUV-XUV pulses Champak Khurmi, Tom Allison, Travis Wright, Adam Stooke, Roger Falcone, Ali Belkacem This talk will present our recent efforts to better understand ultrafast internal conversion dynamics in \textit{ethylene }(C$_{2}$H$_{4})$. \textit{Ethylene} is a prototypical double bond molecule. Theoretical calculations predict that after $\pi \quad \to $ $\pi $* excitation (161nm), \textit{ethylene} relaxes to its ground state through two conical intersections. Our recent time resolved photoion yield experiments provide confirmation of these two distinct non-radiative decay paths and their branching ratio in agreement with theoretical predictions. To further understand the elimination channels of molecular hydrogen from the vibrationally hot ground state of C$_{2}$H$_{4}$, our efforts to develop time resolved photoelectron spectroscopy in the VUV-XUV domain will also be discussed. [Preview Abstract] |
Wednesday, June 15, 2011 2:24PM - 2:36PM |
K5.00003: Attosecond pump-probe of doubly excited states in helium Johannes Feist, Stefan Nagele, Joachim Burgd\"orfer, Christopher Ticknor, Lee A. Collins, Barry I. Schneider Pump--probe experiments using two attosecond light pulses promise to provide unprecedented temporal resolution of electronic wave packet dynamics and have thus been called the ``holy grail'' of attosecond physics. Their experimental realization has up to now been out of experimental reach because of the limited intensity of attosecond sources. We study such setups for probing doubly excited states of helium, which present a prototypical example for correlated electron dynamics. We will present schemes to achieve sufficient yields for the experimental realization of such a setup. Furthermore, we will discuss the novel information that can be gained about the dynamics of the system and that is not available in conventional spectroscopy. [Preview Abstract] |
Wednesday, June 15, 2011 2:36PM - 2:48PM |
K5.00004: Laser enabled Auger decay in argon atoms and dimers Predrag Ranitovic, Xiao-Min Tong, Craig W. Hogle, N. Toshima, M.M. Murnane, H.C. Kapteyn In rare-gas atoms, Auger decay in which an inner-valence shell ns hole is filled is normally not energetically allowed. However, in the presence of a strong laser field, a new laser-enabled Auger decay channel can open up to increase the double-ionization yield. This process is efficient at high laser intensities, and an ns hole can be filled within a few femtoseconds of its creation. This novel laser-enabled Auger decay (LEAD) process is of fundamental importance for controlling electron dynamics in atoms, molecules, and materials. We then use LEAD to investigate charge transfer in a Coulomb exploding Ar dimer. We can selectively double-ionize either the Ar dimer (threshold $\sim $ 36 eV) or Ar atoms (threshold $\sim $ 43.5 eV) using combined laser (1.5 eV) and XUV photons (36 eV) in a time-resolved fashion, and then comparing the kinetic energy releases. The Ar dimer can be double ionized when the 3s hole is filled by a 3p electron from either one of the two Ar atoms through LEAD. Theoretical calculation will support data taken using COLTRIMS and HHG. [Preview Abstract] |
Wednesday, June 15, 2011 2:48PM - 3:00PM |
K5.00005: Dynamic imaging a relaxed chemical bond using Infrared laser pulses Junliang Xu, Cosmin I. Blaga, Anthony D. DiChiara, Emily Sistrunk, Kaikai Zhang, Pierre Agostini, Louis F. DiMauro, Chii-Dong Lin According to the quantitative rescattering (QRS) theory, the high-energy ATI (HATI) electron spectra from a molecule M can be used to extract the backscattering differential cross section (DCS) for e$^{-}$+M$^{+}$ collisions. In this talk, we will present our analysis of experimental HATI data with MIR lasers for N$_{2}$ and O$_{2}$. The N-N bond length retrieved from the HATI spectra agrees with that for N$_{2}$ to within 5{\%}. For O$_{2 }$the retrieved bond length is consistently much smaller than the known O-O bond length, 1.21{\AA}. Instead, it is much closer to the bond length of O$_{2}^{+}$, 1.12{\AA}. We interpret this result in terms of bond relaxation of O$_{2}$ following tunneling ionization. O$_{2}^{+}$ has a vibrational period of 17 fs while the returning time for a 2000 nm laser is about $\sim $5-6 fs, thus allowing the two O atoms to relax from its initial separation of 1.21 {\AA} to the new separation of 1.12 {\AA} of O$_{2}^{+}$. [Preview Abstract] |
Wednesday, June 15, 2011 3:00PM - 3:12PM |
K5.00006: Dissociation dynamics of O$_{2}^{+}$ in intense laser fields M. Magrakvelidze, S. De, C.L. Cocke, U. Thumm We investigated the nuclear dynamics of the electronically and vibrationally excited O$_{2}^{+}$ molecules by applying intense ultrashort IR probe pulses and measuring the fragment kinetic energy release (KER) spectra as a function of the pump-probe delay. To analyze these spectra, we performed vibrational-wave-packet-propagation calculations on adiabatic O$_{2}^{+}$ potential curves. First, to identify relevant transiently populated electronic states of O$_{2}^{+}$, we modeled the pump step in Franck-Condon approximation and calculated the time evolution of initial O$_{2}^{+}$ vibrational wave packets separately for selected molecular potential curves. The comparison of calculated KER spectra as a function of delay, quantum beat frequency, and vibrational revival times for one adiabatic curve at a time with experimental spectra serves as a guide for selection of relevant O$_{2}^{+}$ electronic states. Next, we included probe-laser-induced dipole couplings between the relevant molecular potential curves and compared the improved calculated KER spectra with the experiment, in an attempt to reveal non-adiabatic effects in measured KER spectra that are due to the coupled motion of vibrational wave packets in different electronic states. [Preview Abstract] |
Wednesday, June 15, 2011 3:12PM - 3:24PM |
K5.00007: Carrier-Envelope Phase Effects for Long Wavelength Dissociation of $\mathbf{HeH^{+}}$ D. Ursrey, B.D. Esry Much emphasis has been placed on using intense, short laser pulses for coherent control of molecular dissociation. Due to their accessibility to theorists, the majority of these studies have focused on $\mathrm{H_{2}^{+}}$ and its isotopes. Control over the spatial asymmetry of the dissociating fragments has been demonstrated in experiments starting from $\mathrm{D_{2}}$ by varying the carrier envelope phase (CEP)~[1]. Theoretical interpretations of the control mechanisms have been provided within a Floquet-like picture~[2-3]. We desire to extend the theoretical study of the coherent control of dissociation to heteronuclear systems. Here, we present results on the response of $\mathrm{HeH^{+}}$, the simplest heteronuclear species with an electronic asymmetry in the standard Born-Oppenheimer approximation, to an intense laser pulse. We study the CEP dependence of the spatial asymmetry and dissociation probability for the system in intense fields with long wavelengths ($\lambda=800$ to $4000$ nm). [1] M. F. Kling {\it et~al.}, Science {\bf 312}, 246 (2006). [2] V. Roudnev, B. D. Esry, and I. Ben-Itzhak, Phys. Rev. Lett. {\bf 93}, 163601 (2004). [3] J.~J. Hua and B.~D. Esry, J. Phys. B {\bf 42}, 085601 (2009). [Preview Abstract] |
Wednesday, June 15, 2011 3:24PM - 3:36PM |
K5.00008: Breakup of the H$_2$ molecule by xuv laser pulses: A time-dependent treatment in prolate spheroidal coordinates Xiaoxu Guan, Klaus Bartschat, Barry I. Schneider We report calculations of the triple-differential cross section for one-photon double ionization of molecular hydrogen, based on a fully {\it ab initio}, non\-perturbative approach to solve the time-dependent Schr\"odinger equation in prolate spheroidal coordinates. The spatial coordinates $\xi$ and $\eta$ are discretized in a finite-element discrete-variable representation. The wave packet of the laser-driven two-electron system is propagated in time through an effective short iterative Lanczos method. For both symmetric and asymmetric energy sharing, the present results agree to a satisfactory level with most earlier predictions for the absolute magnitude and the shape of the angular distributions, except for the recent time-independent calculations based on the exterior complex scaling method in prolate spheroidal coordinates~[1]. Extensive tests of the numerical implementation were performed, including the effect of truncating the Neumann expansion for the dielectronic interaction on the description of the initial bound state and the predicted cross sections.\\[4pt] [1] L. Tao, C. W. McCurdy, and T. N. Rescigno, Phys.~Rev.~A~{\bf 82} (2010) 023423. [Preview Abstract] |
Wednesday, June 15, 2011 3:36PM - 3:48PM |
K5.00009: Theoretical study of femtosecond XUV transparency induced by coherent coupling of helium doubly excited states Michal Tarana, Chris H. Greene Presently there is great interest in the application of light in the X-ray regime, produced by high-order harmonics, to investigate novel coherent X-ray optical phenomena. Loh et al. [1] report the observation of EIT-like behavior in the extreme ultraviolet (XUV) by coherent coupling of 2s2p and 2p2 doubly excited states in He, probing with laser-produced high-order harmonics. The EIT-like phenomenon observed in their work is characterized by an increase in transmission over the entire unperturbed lineshape. It is the aim of our work to extend the phenomenological theoretical treatment of this effect included in [1]. We present calculations based on numerical solution of the time-dependent Schr\"odinger equation in an LS-coupling configuration interaction basis set. The calculations utilize a complex absorbing potential at long range and and permit an analysis of the resulting ionization yield. This approach has the potential to give a more detailed understanding of the underlying physics than the phenomonological treatment adopted in [1]. \\[4pt] [1] Z.H. Loh, C.H. Greene and S.R. Leone, Chem. Phys. 350, 7 (2008). [Preview Abstract] |
Wednesday, June 15, 2011 3:48PM - 4:00PM |
K5.00010: ABSTRACT WITHDRAWN |
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