A5023995585- Advanced Chemical Physics Studies
- Atomic and Molecular Physics
- Laser-Matter Interactions and Applications
- Mass Spectrometry Techniques and Applications
- Spectroscopy and Quantum Chemical Studies
- Photochemistry and Electron Transfer Studies
- Spectroscopy and Laser Applications
- Electron and X-Ray Spectroscopy Techniques
- Cold Atom Physics and Bose-Einstein Condensates
- Laser-induced spectroscopy and plasma
- X-ray Spectroscopy and Fluorescence Analysis
- Quantum, superfluid, helium dynamics
- Laser Design and Applications
- Quantum optics and atomic interactions
- Particle accelerators and beam dynamics
- Ion-surface interactions and analysis
- Nuclear Physics and Applications
- Atomic and Subatomic Physics Research
- Photocathodes and Microchannel Plates
- Molecular Junctions and Nanostructures
- Atmospheric Ozone and Climate
- Quantum chaos and dynamical systems
- Atmospheric and Environmental Gas Dynamics
- Distributed and Parallel Computing Systems
- Electrochemical Analysis and Applications
University of California, Davis
2016-2025
Lawrence Berkeley National Laboratory
2016-2025
NOAA Chemical Sciences Laboratory
2025
University of California System
2014-2025
Berkeley College
2018-2020
Czech Academy of Sciences, J. Heyrovský Institute of Physical Chemistry
2018
Charles University
2018
Auburn University
2008-2015
University of California, Berkeley
1977-2014
Universidad Autónoma de Madrid
2005-2009
Semiclassical scattering theory has been used to investigate interference effects in rotational state distributions for inelastic atom–diatom collisions. The Δj=even selection rule homonuclear molecules is seen semiclassically be an effect, and when this symmetry weakly broken—i.e., ’’almost homonuclear’’ molecule, one which the odd anisotropy much smaller than even anisotropy—the persists form of a propensity rule, σ (odd Δj) ≪σ (even Δj). If sufficiently large, however, can see inversion...
Although valence electrons are clearly delocalized in molecular bonding frameworks, chemists and physicists have long debated the question of whether core vacancy created a homonuclear diatomic molecule by absorption single x-ray photon is localized on one atom or over both. We been able to clarify this with an experiment that uses Auger electron angular emission patterns from nitrogen after inner-shell ionization as ultrafast probe hole localization. The experiment, along accompanying...
We consider the extension of complex-coordinate technique to problem locating molecular resonances. suggest a method which uses complex normalizable functions and becomes equivalent usual dilatation transformation asymptotically, but is different for small values electronic coordinates. The illustrated by application bound states ${\mathrm{H}}_{2}^{+}$ model nonspherical resonance problem.
A theoretical model of electronically nonadiabatic collision processes is proposed which describes all degrees freedom, electronic and heavy particle (translation, rotation, vibration), by classical mechanics. The advantage such an approach that since freedom are treated on the same dynamical footing (i.e., via mechanics), effects described correctly (even resonance in to vibrational/rotational energy transfer). Calculations can be carried out within framework standard quasiclassical...
The multiconfiguration time-dependent Hartree-Fock (MCTDHF) method is formulated for treating the coupled electronic and nuclear dynamics of diatomic molecules without Born-Oppenheimer approximation. treats full dimensionality motion, uses no model interactions, in principle capable an exact nonrelativistic description diatomics electromagnetic fields. An expansion wave function terms configurations orbitals whose dependence on internuclear distance only that provided by underlying prolate...
Despite decades of progress in quantum mechanics, electron correlation effects are still only partially understood. Experiments which both electrons ejected from an oriented hydrogen molecule by absorption a single photon have recently demonstrated puzzling phenomenon: The ejection pattern the depends sensitively on bond distance between two nuclei as they vibrate their ground state. Here, we report complete numerical solution Schrödinger equation for double photoionization H 2 . results...
Difficulties in the straightfoward application of complex-coordinate method to calculation resonance states many-electron systems are examined. For case shape resonances, it is shown that many these difficulties can be avoided by using complex coordinates only after reduction system an effective one-electron problem. Further simplifications achieved use inner-projection technique facilitate computation Hamiltonian matrix elements. The first illustrated a model-potential Its suitability for...
A time-dependent formulation of the boomerang model for resonant electron–molecule scattering is presented in terms a wave packet propagating on complex potential surface metastable anion. The results calculations using efficient semiclassical techniques are found to be excellent agreement with full quantum-mechanical vibrational excitation cross sections e−–N2 scattering. application as computational and conceptual approach problem collisions polyatomic molecules discussed light recent...
We present accurate cross sections for two-photon double ionization of helium at photon energies above and below the threshold sequential ionization. Above this $(54.4\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$, competes with nonsequential Remarkably, even $54.4\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, leaves a clear signature in magnitude shape both total energy-sharing sections---even though these it is only virtual process.
Differential elastic cross sections for the scattering of electrons by hydrogen molecules are calculated incident momenta \ensuremath{\le}0.7 a.u. Calculations performed using a Gaussian basis-set expansion technique developed previously authors use with nonspherical potentials. With static-exchange model, computed in body-fixed frame and then averaged over molecular orientations. Our results agree well those previous workers. The method is economical has wide applicability to...
It is shown how the classical version of a pseudopotential analysis can be used to obtain models for electronic degrees freedom in molecular collision system. This allows one construct completely model electronically nonadiabatic processes, which has virtue that and heavy particle are described dynamically consistently (i.e., by trajectories). Application this approach fine-structure changing collisions F with H+ Xe gives encouraging agreement quantum mechanical coupled-channel calculations,...
Abstract We publish three Roadmaps on photonic, electronic and atomic collision physics in order to celebrate the 60th anniversary of ICPEAC conference. In Roadmap I, we focus light–matter interaction. this area, studies ultrafast molecular dynamics have been rapidly growing, with advent new light sources such as attosecond lasers x-ray free electron lasers. parallel, experiments established synchrotron radiation femtosecond using cutting-edge detection schemes are revealing scientific...
Exterior complex scaling enables one to solve the time-independent Schr\"odinger equation for three charged particles without explicitly imposing asymptotic boundary condition three-body breakup. We have used this formalism study electron-impact ionization of atomic hydrogen by directly solving radial components scattered wave on a complex, exterior scaled numerical grid. Computational procedures, presented briefly elsewhere [T. N. Rescigno, M. Baertschy, W. A. Isaacs, and C. McCurdy,...
We show that the ``two-potential'' formalism of conventional distorted-wave rearrangement theory, which is formally valid only for short-range interactions, can be used to evaluate amplitudes ionization atomic hydrogen by electron impact. The triply differential cross sections calculated using this method validate earlier results obtained extrapolating quantum mechanical flux. Although it uses same time-independent wave functions, offers significant advantages over flux extrapolation. It...
We examine finite basis set implementations of complex scaling procedures for computing scattering amplitudes and cross sections. While ordinary scaling, i.e., the technique multiplying all interparticle distances in Hamiltonian by a phase factor, is known to provide convergent cross-section expressions only exponentially bounded potentials, we propose generalization, based on Simon's exterior technique, that works long-range potentials as well. establish an equivalence between class...
Hartree–Fock theory is applied to resonance states of an atomic Hamiltonian under the complex coordinate transformation. It concluded that for shape resonances restricted provides a useful and practical approach problem computing energy. Numerical results are presented low-energy 2P in e–Be scattering. With properly chosen basis functions energy obtained these calculations practically independent phase scaling parameter wide range values. Application this technique molecular discussed. The...
The complex Kohn variational method, which is an anomaly-free algebraic procedure, implemented for the case of collisions electrons with polyatomic molecules. method requires only Hamiltonian matrix elements and, in this formulation, does not require any exchange involving continuum functions. Direct scattering potential(s) involve functions are evaluated by adaptive three-dimensional quadrature scheme. entire procedure applied to elastic electron-methane at static-exchange level and proves...
We report the results of accurate time-dependent calculations two-photon ionization helium by ultrashort pulses. Ionization amplitudes and generalized cross sections are extracted from wave function using exterior complex scaling. For photon energies above first threshold, single is enhanced core excited resonances, in processes visible with pulses as short 2 fs, when frequency equal to a transition energy ${\text{He}}^{+}$. explore dependence total section vicinity threshold for sequential...
A method is described for computing scattering amplitudes a cylindrically symmetric potential using square-integrable basis functions. The addition of variational corrections the Kato formula also outlined. Results two-center Gaussian are presented.
The lifetime and level width of the metastable 2Πg state N2− are calculated using restricted Hartree-Fock theory.(AIP)
The decay of highly excited states xenon after absorption extreme ultraviolet light is directly tracked via attosecond transient spectroscopy using a time-delayed near-infrared perturbing pulse. lifetimes the autoionizing 5$s$5${p}^{6}$6$p$ and 5$s$5${p}^{6}$7$p$ channels are determined to be (21.9 \ifmmode\pm\else\textpm\fi{} 1.3) fs (48.4 5.0) fs, respectively. observed values support lifetime estimates obtained by traditional linewidth measurements. experiment additionally obtains...
The method of complex basis functions for computing positions and widths molecular resonances is revisited. An open-ended efficient implementation described. set requirements the are investigated within computationally inexpensive static-exchange approximation, results this investigation lead to a hierarchy sets function calculations on small molecules. These then applied in some larger molecules with multiple low energy shape resonances: carbon tetrafluoride, benzene, pyridine, pyrimidine,...