Carboxylic acid aggregation: From anharmonic benchmarks to chemical imaging

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Formic acid dimer is among the best studied model systems for hydrogen bonds and the simplest organic representative featuring two of these molecular connections. By combining extensive new results from high sensitivity infrared and Raman studies at low temperature in supersonic vacuum expansions, there is hope to characterize its vibrational states in unprecedented completeness. In this way, an extensive experimental database for the intermolecular dynamics at the limits of current quantum dynamical capabilities of theoretical chemistry can be established. In particular, the splitting of the monomeric vibrational states through their interactions remains insufficiently understood. An international workshop is designed to bring together leading experimentalists and theoreticians in the field towards the end of the project to define the state of knowledge and to identify remaining gaps.Equally important is the characterization of weaker interactions of formic acid molecules with these dimers because of their key role in further aggregation, for the condensed phase and also for highly excited dimer states. Systematic variation of substituents and optimization of technical constraints promises an experiment-based understanding. For this purpose, a spatial characterization of supersonic jets with respect to the distribution of monomers, dimers and trimers is crucial. It is now in reach for the first time by virtue of a hyperspectral imaging FTIR technique, in which two-dimensional gas expansions are probed by infrared absorption in a cluster-, isotope- and molecule-specific way.The final goal of this project is a high level characterization of the vibrational dynamics of an enigmatic molecular pair known for over 1.5 centuries, together with the firm establishment of a new direct absorption technique for the vibrational characterization of two-dimensional gas flows.