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Electron-nuclear dynamics and its control by external electromagnetic fields

Golubev, Nikolay V.

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Abstract

In recent years, the rapid development of attosecond pulse techniques opened the door for studying and eventually controlling electronic dynamics. Due to strong coupling between the electronic and nuclear motion, control over the pure electronic step offers the extremely interesting possibility to steer the succeeding chemical reactivity by predetermining the reaction outcome at a very early stage. Using the electron dynamics and quantum coherence to induce a particular chemical process is the new paradigm in the emerging field of "attochemistry".

One example of physical phenomena, where an electronic dynamics significantly affect on reactivity is the process of an ultrafast charge migration. The positive charge created upon ionization of a molecule can migrate throughout the system on a few-femtosecond time scale solely driven by the electron correlation and electron relaxation. Charge migration triggered by ionization appeared to be a general phenomenon taking place both after inner- and outer-valence ionization of molecules.

This thesis is devoted to the theoretical investigation of the fascinating interplay between the faster electron and the slower nuclear dynamics appearing upon ionization of a molecular system in the presence of an external electromagnetic field. The possibilities to manipulate quantum molecular dynamics by applying specifically tailored ultrashort laser pulses are inspected and analyzed. In particular, the focus is made on the role which the coherent electronic dynamics plays and how the control of the electronic movement influences the outcomes of induced processes. We present here both analytical and numerical approaches allowing one to design laser pulses which can force the evolution of a quantum system in a predefined way. We demonstrate by fully ab initio calculations on experimentally interesting molecules that simple pulses can be used to control the charge-migration oscillations. It is further shown how the correlated treatment of electronic and nuclear dynamics affects the coherence of the electronic wave packet. Our full-dimensional calculations on the propiolic acid molecule show that the electronic decoherence time can be long enough to allow one to observe several oscillations of the charge before nuclear dynamics eventually traps it. Utilizing the strong coupling between the electronic and the nuclear motion, we exemplify the key idea of the attosecond control of molecular reactivity. We demonstrate on a simple model of molecular fragmentation that the nuclear rearrangement can be guided by a manipulation of the electronic dynamics only. We argue that this example clearly illustrates the concept of attochemistry and thus can be used as a starting point to deepen our understanding of the possibilities to control chemical reactions.

Item Type: Dissertation
Supervisor: Kuleff, PD Dr. Alexander
Date of thesis defense: 14 December 2017
Date Deposited: 03 May 2018 12:59
Date: 2018
Faculties / Institutes: Fakultät für Chemie und Geowissenschaften > Institute of Physical Chemistry
Subjects: 530 Physics
540 Chemistry and allied sciences
Controlled Keywords: ultrafast electronic dynamics, quantum control, electron-nuclear dynamics
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