The elemental specificity of X-ray spectroscopy provides unique complimentary information on reaction mechanisms in molecular science when compared vibrational/electronic spectroscopy or scattering techniques. This is particularly useful if elements such as nitrogen and sulfur form dative bonds in transition-metal complexes [1] or are part of functional groups of organic molecules [2] and thereby constitute the site which influences the photochemistry of such molecular systems in a decisive manner. Examples of photo-induced molecular reactions in two types of molecular classes are presented to illustrate, how spectroscopy of ligand- and heteroatoms can (i) unravel the role of ligand-field states in transition-metal complexes and (ii) identify transient molecular species involving sulfur. The latter spectroscopy is illustrated in Fig. 1: Ultraviolet excitation leads to bond fission in disulfides, in C-S and S-S bond cleavage and possibly further secondary reactions to form additional photoproducts due to high thermal excitations or reactions with solvated electrons as generally encountered in protein crystallography where knowledge of radiation damage is crucial for optimal structure analysis. Dimethyl disulfide is the simplest disulfide molecule and not only serves as a model system to investigate the photochemistry of disulfides with time-resolved X-ray spectroscopy but also is relevant in atmospheric and interstellar chemistry as Fig. 1 reveals. There are still many questions to be answered and systematic picosecond studies with high repetition-rates at synchrotron radiation sources as well as femtosecond experiments at X-ray free-electron lasers provide ample future opportunity for core-level spectroscopy of ligand- and heteroatoms.

Photoinduced reaction mechanisms from time-resolved X-ray spectroscopy of ligand- and heteroatoms in ligands and organic molecules

256th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.