Structure and dynamics in solutions – the core electron perspective Ida Josefsson c Ida Josefsson, Stockholm University 2015 ISBN 978-91-7649-258-1 Printed in Sweden by Holmbergs, Malmö 2015 Distributor: Department of Physics, Stockholm University List of Papers The following papers, referred to in the text by their Roman numerals, are included in this thesis. − − PAPER I: Solvent Dependence of the Electronic Structure of I and I3 Susanna K. Eriksson, Ida Josefsson, Niklas Ottosson, Gunnar Öhrwall, Olle Björneholm, Hans Siegbahn, Anders Hagfeldt, Michael Odelius, and Håkan Rensmo, The Journal of Physical Chemistry B, 118, 3164–3174 (2014). DOI: 10.1021/jp500533n PAPER II: Collective hydrogen-bond dynamics dictates the electronic − structure of aqueous I3 Ida Josefsson, Susanna K. Eriksson, Niklas Ottosson, Gunnar Öhrwall, Hans Siegbahn, Anders Hagfeldt, Håkan Rensmo, Olle Björneholm, and Michael Odelius, Physical Chemistry Chemi- cal Physics, 15, 20189–20196 (2013). DOI: 10.1039/c3cp52866a − PAPER III: Solvent-Dependent Structure of the I3 Ion Derived from Pho- toelectron Spectroscopy and Ab Initio Molecular Dynamics Simulations Naresh K. Jena, Ida Josefsson, Susanna K. Eriksson, Anders Hagfeldt, Hans Siegbahn, Olle Björneholm, Håkan Rensmo, and Michael Odelius. Chemistry – A European Journal, 21, 4049–4055 (2015). DOI: 10.1002/chem.201405549 PAPER IV: Solvation Structure Around Ruthenium(II) Tris(bipyridine) in Lithium Halide Solutions Ida Josefsson, Susanna K. Eriksson, Håkan Rensmo, and Michael Odelius. In manuscript. PAPER V: Ab Initio Calculations of X-ray Spectra: Atomic Multiplet and Molecular Orbital Effects in a Multiconfigurational SCF Approach to the L-Edge Spectra of Transition Metal Com- plexes Ida Josefsson, Kristjan Kunnus, Simon Schreck, Alexander Föh- lisch, Frank de Groot, Philippe Wernet, and Michael Odelius, The Journal of Physical Chemistry Letters, 3, 3565–3570 (2012). DOI: 10.1021/jz301479j PAPER VI: From Ligand Fields to Molecular Orbitals: Probing the Lo- cal Valence Electronic Structure of Ni2+ in Aqueous Solu- tion with Resonant Inelastic X-ray Scattering Kristjan Kunnus, Ida Josefsson, Simon Schreck, Wilson Quevedo, Piter S. Miedema, Simone Techert, Frank M. F. de Groot, Michael Odelius, Philippe Wernet, and Alexander Föhlisch, The Journal of Physical Chemistry B, 117, 16512–16521 (2013). DOI: 10.1021/jp4100813 PAPER VII: Orbital-specific mapping of the ligand exchange dynamics of Fe(CO)5 in solution. Philippe Wernet, Kristjan Kunnus, Ida Josefsson, Ivan Rajkovic, Wilson Quevedo, Martin Beye, Simon Schreck, Sebastian Grü- bel, Mirko Scholz, Dennis Nordlund, Wenkai Zhang, Robert W. Hartsock, William F. Schlotter, Joshua J. Turner, Brian Kennedy, Franz Hennies, Frank M. F. de Groot, Kelly J. Gaffney, Simone Techert, Michael Odelius, and Alexander Föhlisch. Nature, 520, 78–81 (2015). DOI: 10.1038/nature14296 PAPER VIII: Mechanistic insight into the ultrafast ligand addition and spin crossover reactions following Fe(CO)5 photodissocia- tion in ethanol. Kristjan Kunnus, Ida Josefsson, Ivan Rajkovic, Simon Schreck, Wilson Quevedo, Martin Beye, Christian Weniger, Sebastian Grübel, Mirko Scholz, Dennis Nordlund, Wenkai Zhang, Robert W. Hartsock, Kelly J. Gaffney, William F. Schlotter, Joshua J. Turner, Brian Kennedy, Franz Hennies, Frank M. F. de Groot, Simone Techert, Michael Odelius, Philippe Wernet, and Alexan- der Föhlisch. Submitted to Structural Dynamics. Reprints were made with permission from the publishers. Comments on my own contribution Paper I: I participated in designing the study, carried out all the calculations and part of the analysis, and wrote parts of the manuscript. Paper II: I participated in designing the study, performed the spectrum calcu- lations, wrote the program for geometry sampling, and had the main responsi- bility for the manuscript. Paper III: I participated in formulating the problem, performed calibrating cal- culations, and participated in writing the manuscript. Paper IV: I participated in designing the study, had the main responsibility for the calculations, analysis, and writing of the manuscript. Paper V and VI: I participated in the development of the computational scheme, carried out part of the calculations and analysis, and wrote parts of the manuscript for Paper V. Paper VII and VIII: I performed the bulk of the calculations for the spectrum simulations and energetics and participated in the analysis and writing of the manuscript. Paper I, II, and V were included in my licentiate thesis [1] and parts of the background and results in this thesis were described there also. Contents List of Papers iii Comments on my own contribution v Abbreviations ix 1 Introduction 11 1.1 Energy from the sun . 11 1.2 Core-level spectroscopy . 13 1.3 Calculations of core-level spectra . 14 1.4 Aim of this thesis . 14 2 Computational framework 17 2.1 The Born–Oppenheimer approximation . 17 2.2 Electronic structure methods . 18 2.2.1 Solving the electronic Schrödinger equation . 19 2.2.2 Molecular orbitals and the basis set approximation . 20 2.2.3 Electron correlation . 21 2.3 Multiconfigurational theory . 22 2.3.1 Perturbation theory . 24 2.4 Relativistic effects . 25 2.5 Simulations of solutions . 26 2.5.1 Molecular dynamics . 27 2.5.2 Solvation models . 29 3 Concepts in spectroscopy 31 3.1 Core and valence electronic levels . 31 3.2 Photoelectron spectroscopy . 32 3.2.1 Chemical shifts in core-level spectra . 34 3.2.2 Satellites in photoelectron spectra . 35 3.3 X-ray absorption spectroscopy . 35 3.4 Core hole decay . 35 3.5 Peak intensities and spectral line shape . 36 3.5.1 Linewidths and shapes of x-ray spectra . 36 3.6 Resonant inelastic x-ray scattering . 37 3.6.1 Transition probabilities for second order processes . 38 3.7 Time-resolved spectroscopy . 38 4 Summary of results 41 − − 4.1 Solvation and electronic structure of I and I3 ......... 41 4.1.1 Solvent-induced binding energy shifts of I− ...... 42 − 4.1.2 Geometry of I3 in solution . 43 2+ 4.2 [Ru(bpy)3] in lithium halide solution . 47 4.3 Electronic structure of transition metal complexes . 51 4.3.1 Ni2+ in aqueous solution . 53 4.4 Probing changes in the electronic structure of transition metal complexes . 56 5 Conclusions 61 Populärvetenskaplig sammanfattning lxv Acknowledgements lxvii References lxix Abbreviations AO Atomic orbital CASPT2 Second-order perturbation theory with CASSCF reference function CASSCF Complete active space self-consistent field CI Configuration interaction DFT Density functional theory HF Hartree–Fock HOMO Highest occupied molecular orbital LF Ligand field LMCT Ligand-to-metal charge transfer LUMO Lowest unoccupied molecular orbital MD Molecular dynamics MLCT Metal-to-ligand charge transfer MO Molecular orbital NEXAFS Near-edge x-ray absorption fine structure PCM Polarizable continuum model PES Photoelectron spectroscopy RAS Restricted active space RDF Radial distribution function RIXS Resonant inelastic x-ray scattering SCF Self-consistent field SDF Spatial distribution function SIBES Solvent-induced binding energy shift UV–Vis Ultraviolet–visible XAS X-ray absorption spectroscopy XPS X-ray photoelectron spectroscopy 1. Introduction Much effort is spent on the development of clean and inexpensive applications for energy production. Theoretical calculations give the possibility to describe the systems and processes in very fine details and fill an important function for the fundamental understanding of the systems. In this thesis, computational methods are used to study the electronic and solvent structure of model sys- tems, and give insight in the molecular details, which can be of relevance for energy applications. 1.1 Energy from the sun Our society today is entirely dependent on easily accessible energy. Fossil fuels still provide over 80 percent of the energy consumed in the world [2]. The problems associated with this are the substantial impact of the fossil fuels on the environment and the fact that the resources are finite. In order to cover the growing world energy consumption, it is desirable to understand and develop renewable energy sources as a supplement and eventually replacement. The sunlight reaching the Earth’s surface in one hour is more than the world’s entire need for energy over the next year [3], but despite its abundancy, solar energy accounts only for a small fraction of the world energy supply [2]. A chemical system used for solar energy conversion must absorb sunlight irradiating it, and convert the electromagnetic radiation to an energy form that can be used to perform some kind of work. Solar radiation reaching the Earth’s surface has its strongest output range in the visible light region of the electro- magnetic spectrum. At these wavelengths, light interacts the most strongly with the outer shell electrons, called valence electrons, in matter. Sunlight in- teracting with the system changes the valence electronic structure by exciting the absorbing molecule to a higher energy state. When the excited state re- laxes to a lower energy state, reactions important for the energy conversion process can take place. Knowledge of the fundamental chemical processes are essential for the understanding of photochemical applications. Many of these processes take place in electrolyte solutions. Photoelectrochemical systems have been studied as highly interesting ap- plications for solar energy conversion and storage for more than 40 years [4– ∗ + CB/CB− S /S EF hν + Free energy M /M S+/S Figure 1.1: Processes in a photoelectrochemical cell. A molecule is photoex- cited from the ground state S to S∗ by absorption of light with energy hn (red arrow). From the excited state, an electron is injected into the conduction band CB of a semiconductor (green arrow). The oxidized molecule S+ is reduced back to the neutral ground state S by accepting an electron from an electron donating species M at the solution interface (blue arrow). 7]. A photochemical reaction is induced by light irradiating the system and the primary step of the energy conversion process in the photoelectrochemical cell is absorption of sunlight of appropriate wavelength. The absorber may be a solid, or a dye molecule, attached to a semiconductor surface.