Exploring the Influence of Non-Covalent Interactions on Tunneling Phenomena via Cryogenic Ion Vibrational Spectroscopy

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In recent years, Johnson and co-workers have developed an experimental setup that allows for the observation of internal rearrangements of ions in the gas phase under cryogenic conditions. Their approach disturbs the equilibrium between rapidly interconverting isomers via infrared excitation and then monitors if the equilibrium is re-established within the given spectroscopic timeframe. While they were able to qualitatively determine the occurrence of such fast equilibrations within a small binary water complex and even observed a profound influence of the presence of D2, the extraction of quantitative kinetic parameters remains a challenge. The goal of this research project is to apply this methodology to the rapid OH rotamerisation of phenols, facilitated via quantum mechanical tunneling. Thus the scope of these experiments will be extended to biologically and industrially relevant organic compounds. In order to provide insights into the scarcely investigated influence of non-covalent interactions on tunneling phenomena, vibrational spectroscopic measurements will be performed both on the bare ions as well as on complexes with different tags like Ar or D2. The experimental work will be complemented by quantumchemical calculations of vibrational spectra, potential energy surfaces of the rotamerisation and interaction energies of phenol with the weakly coordinating tags. The investigation of multiple phenol derivatives will then provide an extensive dataset to improve the extraction of kinetic parameters from cryogenic ion vibrational measurements. Ultimately, the insights into the rotamerisation of phenols in gas phase gained by such experiments will deepen our understanding of tunneling processes in general.