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Editorial on the Research Topic: Computational Methods for the Description of Intermolecular Interactions and Molecular Motion in Confining Environments

Das Ionisierungsverhalten kleiner Moleküle (insbesondere H2 und NH3) in intensiven, ultrakurzen Laserfeldern wird theoretisch untersucht. Das Hauptaugenmerk liegt dabei auf dem Einfluss der Kerndynamik. Zunächst wird das Ionisierungsverhalten des H2-Moleküls bei eingefrorener Kernschwingung untersucht. Bereits im Rahmen dieser Näherung kann im Mehrphotonenregime ein zuvor beobachteter Zusammenbruch der Näherung im Gleichgewichtsabstand festgehaltener Kerne erklärt werden. Weiterhin wird der Übergang vom Mehrphotonen zum quasistatischen Ionisierungsregime für 800-nm-Laserfelder untersucht. Eine neuartige Methode zur Beschreibung der korrelierten Schwingungs- und Elektronendynamik des H2-Moleküls (7D) wird entwickelt. Mit dieser Methode wird schließlich der Einfluss der Kernbewegung während des Laserfeldes auf das Ionisierungsverhalten untersucht. Es wird ein sichtbarer Einfluss auf den zuvor diskutierten Zusammenbruch der Näherung festgehaltener Kerne beobachtet. Dies gilt ebenfalls für einen vor kurzem experimentell beobachteten Isotopeneffekt in der Ionisierung der Moleküle H2 vs. D2 untersucht. Im zweiten Teil der Arbeit wird das Ionisierungsverhalten des NH3-Moleküls untersucht. Die Möglichkeit, die Kerngeometrieabhängigkeit zur Erzeugung und Messung von Schwingungswellenpaketen im neutralen NH3-Molekül mittels Lochfraß auszunutzen, wird untersucht. Das erwartete Schwingungsverhalten und die dafür optimalen Laserparameter werden aufgezeigt. Zusätzlich wird die Möglichkeit des Filmens eines tunnelnden Kernwellenpakets im Doppelmuldenpotential entlang der Schwingungskoordinate untersucht. In der Tat sollte die Verwendung extrem kurzer Laserfelder das Drehen eines Echtzeit-Filmes dieses quantenmechanischen Tunnelprozesses ermöglichen. Abschließend werden die Winkelabhängigkeit der Ionisierungswahrscheinlichkeit von NH3 (ähnelt Orbitalgeometrie) sowie elliptisch polarisierte Laserfelder untersucht., The ionization behavior of small molecules (especially H2 and NH3) exposed to intense, ultrashort laser fields is investigated theoretically. The focus lies on the influence of nuclear dynamics on this ionization behavior. The ionization behavior of the H2 molecule is first examined within the frozen-nuclei approximation. A previously reported pronounced breakdown of the fixed-nuclei approximation can be explained already within this level of approximation. Furthermore, the transition from the multiphoton to the quasistatic ionization regime is studied for 800 nm laser pulses. A novel approach for the correlated description of the electronic-vibrational motion of the H2 molecule (7D) is developed. The influence of vibrational dynamics during the laser field on the ionization behavior is investigated using this method. A pronounced difference on the previously discussed breakdown of the fixed-nuclei approximation is observed. The vibrational dynamics also lead to a notable change for a recently experimentally observed isotope effect in the ionization of the molecular isotopes H2 vs. D2. The ionization behavior of the NH3 molecule is studied in the second part of this thesis. The possibility to exploit the geometry dependence of the ionization yield in order to create and measure vibrational wave packets in the neutral NH3 molecule via Lochfraß is explored. The expected vibrational dynamics and the optimal laser parameters to observe this effect are demonstrated. Furthermore, the possibility to shoot a "movie" of a tunneling wave packet in the double-well potential along the vibrational coordinate is investigated. Indeed, extremely short laser fields should allow creating a real-time movie of the quantum-mechanical tunneling process. Finally, the orientation dependence of the ionization yield of the NH3 molecule (reflecting the orbital shape) and elliptically polarized laser fields are studied.

Fermosecond dynamics has been recently observed by resonant X-ray Raman scattering (RXRS) after excitation along the dissociative Cl 1s -> 6 sigma* resonance of gas phase HCl. In this paper, we show a method to take into account and correct for self-absorption of the elastic peak, in order to allow for quantitative comparison with theory. We have performed measurements on the DCl molecule exhibiting ultrafast nuclear motion. A comparison between HCl and DCl is presented., Conference: International Symposium on Scattering, Coincidence and Absorption Studies of Molecules. Fed Univ Rio de Janeiro, Rio de Janeiro, BRAZIL. SEP 04-06, 2006

The principles that form the basis of all quantum mechanics were first introduced in 1926 by Schroedinger. Since that time these principles have been extended to become the framework of the theory used today. Although the simplicity of the theory cannot be questioned, practical implementation of the basic concepts has often proven difficult. For certain applications, including the hydrogen atom as well as other one electron systems, the Schroedinger Theory allows exact analytic solution. For larger systems, approximations are necessary. The first approximation that is generally incorporated into the Schroedinger Theory is known as the Born Oppenheimer Approximation. The use of this approximation allows the separation of electronic and nuclear motions. Further simplification can be achieved through a method for dealing with the electron-electron interaction potential. This approach was first suggested by Hartree, and was subsequently extended by Fock to include exchange effects. In molecular orbital theory, an electron orbital is replaced by a one-electron wave function delocalized over the whole molecule. This concept, together with the Pauli principle and the work of Hartree and Fock allow the wavefunction to be expressed in a single Slater determinant.