Theoretical modeling of molecules in weakly interacting environments: trifluoride anions in argon

Experimental observation of quantum mechanical fluorine tunnelling

Quantum mechanical tunnelling occurs when a molecule transforms between two states separated by a finite energy barrier that cannot be overcome thermally. To date, it has been observed for elements up to oxygen. Efforts to go one element further are hindered by the strong bonds formed by fluorine with other elements, which suppress tunnelling. In this work, laser ablation is used to create fluorine-only species and trap weakly-bound polyfluorides in a neon matrix at cryogenic temperatures. Spectroscopic investigations reveal a temperature-dependent doublet-splitting, providing experimental evidence for heavy-atom quantum mechanical tunnelling. Theoretical modelling attributes the signal to tunnelling of the central fluorine atom in a quasi-linear [F2 ⋯  F ⋯  F2]- complex through a rotational barrier caused by steric hindrance and electronic effects in the neon matrix. The present study offers new insights into chemical interactions in polyfluorides and, more generally, of quantum phenomena in confined environments.

From the Automated Calculation of Potential Energy Surfaces to Accurate Infrared Spectra

Advances in the development of quantum chemical methods and progress in multicore architectures in computer science made the simulation of infrared spectra of isolated molecules competitive with respect to established experimental methods. Although it is mainly the multidimensional potential energy surface that controls the accuracy of these calculations, the subsequent vibrational structure calculations need to be carefully converged in order to yield accurate results. As both aspects need to be considered in a balanced way, we focus on approaches for molecules of up to 12-15 atoms with respect to both parts, which have been automated to some extent so that they can be employed in routine applications. Alternatives to machine learning will be discussed, which appear to be attractive, as long as local regions of the potential energy surface are sufficient. The automatization of these methods is still in its infancy, and the generalization to molecules with large amplitude motions or molecular clusters is far from trivial, but many systems relevant for astrophysical studies are already in reach.