Molecular Spectroscopy

The department is involved in a wide range of advanced spectroscopic experiments that are aimed at obtaining geometric and electronic structure information on stable as well as transient open-shell transition metal species. Apart from standard laboratory equipment UV/vis, IR Raman, Fluorescence and NMR spectroscopy) the department focuses on the following techniques:

(a)  X-ray Absorption and Emission spectroscopy. Modern synchrotron based techniques allow for many exciting, element specific experiments to be performed. The group of Prof. DeBeer is actively involved in the development and application of new X-ray based techniques.[10a-d, 22b, 23a, 34]
Figure 17
Fig. 17: Mößbauer spectroscopy can be used to investigate reaction intermediates. In this example three different intermediates have been observed in the course of an enzymatic reaction.

(b)  Mößbauer spectroscopy is one of the most powerful tools for the investigation of iron containing enzymes, coordination complexes and materials. The group of Dr. Bill has a long term tradition on performing and analyzing Mößbauer spectra with and without an applied external magnetic field.[23b, 25a, 26-27, 35]
Figure 18
Fig. 18: High-resolution EPR combined with modern quantum chemistry provides extended insight into fine structural and electronic details. In this example, the HYSCORE spectra of nitrosyl-myoglobin have been successfully assigned on the basis of QM/MM calculations.

(c)  High resolution electron paramagnetic resonance is the most powerful technique to investigate paramagnetic molecules. In addition to our collaboration with the department of Prof. Lubitz this technique is implemented in our department in the group of Dr. Maurice van Gastel who is exploring novel techniques as well as applications in the fields of bioinorganic chemistry and energy research.[36]
Figure 19
Fig. 19: Resonance Raman spectroscopy provides a detailed electronic structure picture of the excited state that is excited. The vibrational pattern is characteristic for the chromophore and type of excitation.

(d)  Resonance Raman spectroscopy is a particularly powerful technique for the investigation of chromophores. This technique is represented in our department by Dr. Maurice van Gastel who is developing the instrumental as well as theoretical aspects of the technique.[8c, 12, 37] Using resonance Raman spectroscopy one obtains highly and selectively vibrationally resolved information about absorbing species. Besides carrying a wealth of electronic structure information, the enormous enhancement of the inelastic response of a system once excited in the area of an absorption band provides extremely powerful fingerprints that allow for the characterization of elusive species.[37a]
Figure 20
Fig. 20: MCD spectroscopy provides high-resolution electronic structure insight as well as an optical probe of the ground state magnetic properties. In this example the magnetism of an exchange coupled transition metal dimer has been revealed by MCD spectroscopy (right). The MCD spectra are superpositions of the individual ion spectra with the signs being characteristic of the magnetic coupling pattern.

(e)  Magnetic Circular Dichroism spectroscopy is a powerful technique that bridges the fields of optical and magnetic spectroscopy. MCD, as applied to paramagnetic substances, provides a wealth of electronic structure information. In addition, variation of applied field and temperature allows for the optical measurement of the ground state magnetic susceptibility even in the presence of mixtures or impurities. The MCD laboratory is also headed by Dr. Bill using a home-designed setup that allows for spectra to be taken all the way from the deep UV to the near-IR regions.[13, 25a, 25e, 38]

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