Computational Inorganic Photochemistry: From Ultrafast Photodissociation to Photostereochemistry

The interaction between light and molecules containing a transition metal center gives rise to a fascinating multitude of chemistry in many different fields, from biochemistry to semi-conductor technology. Some fundamental reactions within this field of inorganic photochemistry will be investigated using state of the art computational techniques. This will allow us to understand the basic processes at the level of the electrons and atomic nuclei after light absorption. For example when a transition metal carbonyl absorbs a photon it may dissociate a carbonyl ligand in the order of a few tens of femtoseconds. It then relaxes in such a way that only certain motions of the atomic nuclei are observed in cutting-edge spectroscopic experiments. In order to model such phenomena we need to use quantum mechanics at both the level of electrons and the nuclei. We evaluate the electronic wavefunctions and related potential energy surfaces on which nuclear motion takes place, including appropriate coupling to allow the molecules to 'switch' surfaces. The nuclear wavefunction is then propagated and this simulates the actual dynamics induced by light absorption. Transition metal complexes can contain many atoms and modelling the motion of multiple vibrational modes, over several coupled potential energy surfaces is a real challenge. However such realistic modelling is essential if we are to understand the basic processes with a view to designing materials with specific applications in mind.In this proposal we aim to study two fundamental classes of inorganic photochemical reactions from first-principles using high-level electronic structure theory combined with advanced methods of nuclear dynamics. One proptotypical system is transition metal carbonyl photodissociation, an extremely important photoinduced process. In particular the photodissociation dynamics of Fe(CO)5 will be studied; this system is expected to show the importance of coupling between 3 or more potential energy surfaces and a significant number of vibrational modes. The other type of effect to be investigated is the photostereochemistry of certain open-shell Chromium(III) complexes. These systems have different stereo-isomers, which can be created (or interchanged) via the application of light. If we understand such processes we can then design complexes for use in applications such as fast light-switching and solar energy conversion. Such complexes have an odd number of electrons and therefore spin-orbit coupling between states with different spin-multiplicites is expected to be important.In summary we wish to use state of the art computational techniques to investigate what happens after certain inorganic molecules absorb light. We plan to study both the electronic rearrangements after absorption and the subsequent (ultrafast) nuclear motion using advanced methods that will give us a detailed understanding of inorganic photochemistry at the molecular level.