Electronic States of Gas Phase 3d Transition Metal Complexes

One expression of the quantum nature of the electron is the so-called spin, which can be demonstrated experimentally via the magnetic moment of the electron. In a magnetic field, the magnetic moment and therefore the spin aligns itself with or in the opposite direction to the field; this is referred to as up-spin or down-spin. As neighboring electrons also generate a magnetic field, the electrons in an atom or molecule are aligned collectively, i.e. each electron has either up or down spin. In many stable molecules, there are exactly the same number of up- and down-spin electrons. However, under certain circumstances, and whenever there is an odd number of electrons, there is an excess of one spin direction. The difference between the number of electrons with up- and down-spin results in the spin state of the system. In metals such as iron, the sum of the spin excesses of many individual atoms can lead to a piece of this metal being attracted to a magnet. In metal complexes, i.e. chemical compounds containing one or more metal atoms, local spin centers can arise. Such spin centers are relevant in catalysis, but can also be used in the efficient storage of information. A deeper understanding of the spin states of such centers is therefore of great interest for the application of a metal complex. Even if empirical values and quantum chemical methods often allow a reasonable assumption, there is no method that can be used to reliably predict the spin state of a chemical compound. At the same time, it is known that minute changes in the composition of a compound can have a major influence on the local spin centers. The aim of this project is to deepen our understanding of the spin states of molecular compounds with one spin center and to contribute to the development of reliable methods for the prediction of spin states. For this purpose, small molecules are produced, and their spin states are analyzed. This is done by irradiating the molecules with laser light of different energies. If the energy of the incident light matches the energy required to change the properties of a single electron, this can be detected. In comparison with quantum chemical calculations, this allows direct conclusions to be drawn about the spin state of the molecule. In order to exclude subtle influences of the environment, e.g. a solvent, on the molecules, all experiments take place in a vacuum so that the molecules are completely isolated. These precisely controlled conditions in combination with a well-considered design of the molecules under investigation provide a valuable data set for the systematic investigation and optimization of computational methods for the prediction of spin states. At the end of the project, a generally applicable method for this prediction should be available.