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Über dieses Buch

This thesis examines various aspects of excess excitation energy dissipation via dynamic changes in molecular structure, vibrational modes and solvation. The computational work is carefully described and the results are compared to experimental data obtained using femtosecond spectroscopy and x-ray scattering. The level of agreement between theory and experiment is impressive and provides both a convincing validation of the method and significant new insights into the chemical dynamics and molecular determinants of the experimental data. Hence, the method presented in the thesis has the potential to become a very important contribution to the rapidly growing field of femtosecond x-ray science, a trend reflected in the several free-electron x-ray lasers (XFELs) currently being built around the world.

Light-induced chemical processes are accompanied by molecular motion of electrons and nuclei on the femtosecond time scale. Uncovering these dynamics is central to our understanding of the chemical reaction on a fundamental level.

Asmus O. Dohn has implemented a highly efficient QM/MM Direct Dynamics method for predicting the solvation dynamics of transition metal complexes in solution.



Introduction and Background


Chapter 1. Introduction

The work presented in this thesis is focused on describing how the dynamics behind nuclear motion play out on the stage of femtochemistry.
Asmus Ougaard Dohn

Chapter 2. The Systems of This Project

There are two overall groups of complexes in this study: Members of the d\(^8\)-metal complexes, known for the debated nature of the ‘d\(^8\)–d\(^8\)-interactions’[1], that can cause oligomerisation [2, 3]. This entails having two (or more) electron-rich elements close to each other, but weaker bound than in the covalent case, such that large changes in molecular geometry are very likely to occur if the system is perturbed; an opportune model system for dynamics measurable with the XDS-pump-probe method.
Asmus Ougaard Dohn

Preliminary Studies


Chapter 3. Treating Relativistic Effects in Transition Metal Complexes

Working with transition metal complexes in a computational environment presents itself with a set of added considerations.
Asmus Ougaard Dohn

Chapter 4. X-Ray Scattering from Purely Classical MD

At the beginning of this project, the already established method within our group for fitting experimentally recorded XDS signals to molecular geometries was (very) simply put to (1) use DFT calculations to optimize geometries, (2) systematically modify important interatomic distances.
Asmus Ougaard Dohn

Direct Dynamics


Chapter 5. Background

This work is mostly focused on application, which is why this chapter is intended as a guide for future users, with only a brief theoretical outline of the methods employed in this part of the project.
Asmus Ougaard Dohn

Chapter 6. Direct Dynamics Simulations of Ir $$_2$$ 2 (dimen) $$_4^{2+}$$ 4 2 +

As described in Chap. 2, the dimen ligand provides the optimal compromise between flexibility and rigidity for large, but controllable structural changes e.g. by electronic excitation.
Asmus Ougaard Dohn

Chapter 7. Direct Dynamics Simulations of the Ru=Co Complex

This section describes the ongoing work on simulating structural- and solvation changes in the bi-centered Ru=Co complex described in Sect. 2.​4.
Asmus Ougaard Dohn



Chapter 8. Summarising Discussion and Outlook

The investigation of transient dynamics in transition metal complexes and their surroundings through simulations has led to the observations presented in this thesis. The following is an attempt to condense the discoveries, discuss future strategies, and return to the initially posed questions on how excess excitation energy dissipates in solvated systems.
Asmus Ougaard Dohn


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