Ultrafast Nuclear Dynamics Induced by Light from the XUV to the THz Range

Arnold, Caroline; Vendrell Romagosa, Oriol; Welsch, Ralph; Santra, Robin

Book/Dissertation / PhD Thesis

PUBDB-2019-02902

Ultrafast Nuclear Dynamics Induced by Light from the XUV to the THz Range

Arnold, C. (Corresponding author)CFEL*DESY* ; Welsch, R. (Thesis advisor)CFEL*DESY* ; Vendrell Romagosa, O. (Thesis advisor)Extern* ; Santra, R. (Thesis advisor)CFEL*DESY*

2019
Verlag Deutsches Elektronen-Synchrotron Hamburg

Hamburg : Verlag Deutsches Elektronen-Synchrotron, DESY-THESIS 79 pp. (2019) [10.3204/PUBDB-2019-02902] = Dissertation, Universität Hamburg, 2019

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Please use a persistent id in citations: doi:10.3204/PUBDB-2019-02902

Report No.: DESY-THESIS-2019-017

Abstract: With recent advances in the generation of ultrashort laser pulses, electron and nuclear dynamics in molecules can be investigated on their natural, atto- to femtosecond timescale. This opens up the investigation of many interesting phenomena, including primary events in chemistry and biology. The new experimental capabilities are complemented by theoretical investigation to develop a better insight in the nature of ultrafast processes. In this thesis, I will theoretically explore ultrafast nuclear dynamics that are triggered by light over a wide range of the electromagnetic spectrum — from extreme ultraviolet (XUV) to terahertz (THz) radiation. The results are obtained by ab initio methods for both electrons and nuclei. Photoionization using attosecond, coherent, XUV pulses can create coherent superpositions of electronic states of the cation. This initiates coherent electron dynamics, but also nuclear motion, that is often neglected in the interpretation of ultrafast experiments. I use a quantum-dynamical treatment of nuclear motion to show that electronic coherences are affected by the nuclei. Within an adiabatic model, they are destroyed within few femtoseconds. When non-adiabatic couplings are included, electronic coherences may be preserved to some extent. This highlights the importance of considering nuclear motion and nuclear quantum effects even when simulating electron dynamics on the few-femtosecond timescale. The non-adiabatic coupling of electron and nuclear motion allows to control nuclear dynamics through manipulating electronic degrees of freedom. Within a model system of a conical intersection, I explore the possibility of steering nuclei through imprinting a phase difference between electronic states with ultrashort, shaped pulses. Valence ionization triggers electron-hole dynamics that can be observed by time-resolved, transient x-ray absorption spectroscopy. To describe the hole dynamics, I present an expansion to our in-house software XMOLECULE for a mixed quantum-classical treatment of molecular dynamics in electronically excited states. First results on hole dynamics and corresponding x-ray absorption spectra are shown. Ultrafast nuclear motion can also be initiated through strong and short THz pulses, that couple to the intermolecular degrees of freedom of liquids like water. With current THz sources, water can be heated by more than 1000 Kelvin within 100 femtoseconds. I explore the signature of these ultrafast nuclear dynamics in the XUV photoelectron spectrum of liquid water. It is found that the spectral changes are close to the current experimental resolution.

Note: Dissertation, Universität Hamburg, 2019

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