Isothiocyanic Acid and Related Compunds: Understanding the Photoinduced Dynamics of Prebiotic Molecules

• Applicant: Professor Dr. Ingo Fischer
• Subject Area: Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 539340449

The characteristic feature of this project is the focus on a small group of related molecules, isothiocyanic acid HNCS, its isomers and radicals derived from it. A variety of different experimental and computational methods are applied to characterize the electronic structure of HNCS and its dynamics upon interaction with high energy radiation from the ultraviolet (UV) to the soft X-ray regime. The work is motivated by the relevance of HNCS and related compounds in astrochemistry, in particular its possible role as a precursor to sulfur-containing biomolecules.At the energy of the first intense absorption band of HNCS around 250 nm, several close-lying dissociation pathways are expected to compete. We will identify the main reaction products and determine the dissociation mechanism. The main tool will be the photoionization of the reaction products and their detection by Velocity map imaging (VMI) . To obtain a full picture of the excited-state dynamics, we will carry out time-resolved experiments at free-electron laser (FEL) facilities using X-ray probe methods. In the vacuum ultraviolet (VUV) region we will record valence photoelectron spectra, characterize the ground and excited electronic states of HNCS+ as well as NCS+ and investigate the dissociative photoionization to obtain ionization and appearance energies that in turn allow to extract thermochemical information. The fragmentation dynamics upon X-ray excitation and ionization will be investigated with the goal to identify possible site-selectivity and the differences upon replacing Oxygen by Sulfur. Finally, we will address the photochemistry of HNCS isomers and possibly other sulfur-containing reactive molecules of astrochemical interest.All experiments are complemented by theory. As the different experimental methods require different computational tools, we will cooperate with several theory groups, who add their specific expertise to the individual work packages. With all groups, we have successfully cooperated in the past. However, most computations will be carried out by the graduate students involved in the project.

• DFG Programme: Research Grants