Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (8 results)

  • Article
LBL Publications (2003)
We present a non-empirical potential model for studying threshold vibrational excitation of polar moleculesby electron impact. This work builds on the zero-range potential virtual state model of Gauyacq and Herzenberg (J.P. Gauyacq and A. Herzenberg, Phys. Rev. A 25, 2959 (1982)), using known analytic properties of the S-matrix for a dipole potential to predict the analytic continuation of the negative ion potential curve into the continuum. We derive an equation that determines the nuclear dynamics which can be solved without the need for an expansion in target vibrational states. The model is applied to e{sup -} - HCl and is found to capture the essential features of the observed excitation cross sections, including both the threshold peaks as well as oscillatory structures at energies above threshold.
    Cover page: Scattering of slow electrons by polar molecules: Application of effective-range potential theory to HC1
    • Article
    LBL Publications (2003)
    Threshold structures, reminiscent of those seen in the polar hydrogen halides, have recently been observed in the cross sections for electron impact excitation of certain vibrational levels of the non-polar CO2 molecule. These structures occur at energies outside the range where shape resonances dominate the dynamics. We propose a virtual state model that describes the multi-dimensional nuclear dynamics during the collision and explains quantitatively the selectivity observed in the excitation of the Fermi dyad, as well as the pattern of threshold peaks and oscillations seen in the upper levels of the higher polyads.
      Cover page: Threshold vibrational excitation of CO{sub 2} by slow electrons
      • Article
      • Peer Reviewed
      Lawrence Berkeley National Laboratory (2005)

      Despite decades of progress in quantum mechanics, electron correlation effects are still only partially understood. Experiments in which both electrons are ejected from an oriented hydrogen molecule by absorption of a single photon have recently demonstrated a puzzling phenomenon: The ejection pattern of the electrons depends sensitively on the bond distance between the two nuclei as they vibrate in their ground state. Here we report a complete numerical solution of the Schrodinger equation for the double photoionization of H2. The results suggest that the distribution of photoelectrons emitted from aligned molecules reflects electron correlation effects that are purely molecular in origin.

        Cover page: Complete Photo-Induced Breakup of the H2 Molecule as a Probe of Molecular Electron Correlation
        • Article
        • Peer Reviewed
        Lawrence Berkeley National Laboratory (2006)

        We present converged, completely ab initio calculations of the triple differential cross sections for double photoionization of aligned H2 molecules for a photon energy of 75.0 eV. The method of exterior complex scaling, implemented with both the discrete variable representation and B-splines, is used to solve the Schroedinger equation for a correlated continuum wave function corresponding to a single photon having been absorbed by a correlated initial state. Results for a fixed internuclear distance are compared with recent experiments and show that integration over experimental angular and energy resolutions is necessary to produce good qualitative agreement, but does not eliminate some discrepancies. Limitations of current experimental resolution are shown to sometimes obscure interesting details of the cross section.

          Cover page: Double Photoionization of Aligned Molecular Hydrogen
          • Article
          • Peer Reviewed
          Lawrence Berkeley National Laboratory (2008)

          Exterior complex scaling provides a practical path for first-principles studies of atomic and molecular ionization problems since it avoids explicit enforcement of asymptotic boundary conditions for 3-body Coulomb breakup. We have used the method of exterior complex scaling, implemented with both the discrete variable representation and B-splines, to obtain the first-order wave function for molecular hydrogen corresponding to a single photon having been absorbed by a correlated initial state. These wave functions are used to construct converged triple differential cross sections for double photoionization of aligned H2 molecules.

            Cover page: First Principles Study of Double Photoionization of H2 Using Exterior Complex Scaling
            • Article
            Lawrence Berkeley National Laboratory (2005)
              Cover page: First Principles Calculations of the Double Photoionization of Atoms and Molecules using B-splines and Exterior Complex Scaling
              • Article
              • Peer Reviewed
              LBL Publications (2008)
                Cover page: The Role of Nuclear Motion in the Photo-Double Ionization of Molecular Hydrogen
                • Article
                • Peer Reviewed
                LBL Publications (2015)
                Classical iterative methods for tomographic reconstruction include the class of Algebraic Reconstruction Techniques (ART). Convergence of these stationary linear iterative methods is however notably slow. In this paper we propose the use of Krylov solvers for tomographic linear inversion problems. These advanced iterative methods feature fast convergence at the expense of a higher computational cost per iteration, causing them to be generally uncompetitive without the inclusion of a suitable preconditioner. Combining elements from standard multigrid (MG) solvers and the theory of wavelets, a novel wavelet-based multi-level (WMG) preconditioner is introduced, which is shown to significantly speed-up Krylov convergence. The performance of the WMG-preconditioned Krylov method is analyzed through a spectral analysis, and the approach is compared to existing methods like the classical Simultaneous Iterative Reconstruction Technique (SIRT) and unpreconditioned Krylov methods on a 2D tomographic benchmark problem. Numerical experiments are promising, showing the method to be competitive with the classical Algebraic Reconstruction Techniques in terms of convergence speed and overall performance (CPU time) as well as precision of the reconstruction.
                  Cover page: A multi-level preconditioned Krylov method for the efficient solution of algebraic tomographic reconstruction problems
                  Top