Microwave three-wave mixing has emerged as a novel approach for studying chiral molecules in the gas phase. This technique employs resonant microwave pulses and is a non-linear and coherent approach. It serves as a robust method to differentiate between the enantiomers of chiral molecules and to determine the enantiomeric excess, even in complex chiral mixtures. Besides such analytical applications, the use of tailored microwave pulses allows us to control and manipulate chirality at the molecular level. Here, an overview of some recent developments in the area of microwave three-wave mixing and its extension to enantiomer-selective population transfer is provided. The latter is an important step towards enantiomer separation-in energy and finally in space. In the last section, we present new experimental results on how to improve enantiomer-selective population transfer to achieve an enantiomeric excess of about 40 % in the rotational level of interest using microwave pulses alone.

Mikrowellen Drei‐Wellen Mischen ist ein bemerkenswerter, neuartiger Ansatz für tief gehende Untersuchungen an chiralen Molekülen. Diese nicht‐lineare und kohärente Technik, die auf resonanten Mikrowellenpulsen basiert, dient als robuste Methode zur Unterscheidung von Enantiomeren chiraler Moleküle und zur Bestimmung des Enantiomerenüberschusses, sogar für komplexe Mischungen chiraler Moleküle. Neben solchen analytischen Anwendungen erlaubt uns die Verwendung maßgeschneiderter Mikrowellenpulse die Kontrolle und Manipulation von Chiralität auf der Molekülebene. Der vorliegende Artikel liefert einen Überblick zu jüngsten Entwicklungen im Bereich des Mikrowellen Drei‐Wellen Mischens und seine Erweiterung zu enantiomerenspezifischem Populationstransfer. Letzteres ist ein entscheidender Schritt in Richtung Enantiomerentrennung – energetisch und schließlich auch räumlich. Im letzten Abschnitt präsentieren wir neue experimentelle Ergebnisse zur Verbesserung des enantiomerenspezifischen Populationstransfers, bei denen wir einen Enantiomerenüberschuss von 40 % in dem Rotationsenergieniveau von Interesse allein mit Hilfe von Mikrowellenpulsen erreichen konnten.

Silicon chemistry is an extensive research topic due to its importance for industry and technology, and because of its natural abundance on earth. Silicon is a versatile element, its applications range from pure silicon to compounds. To understand the physical and chemical properties of silicon-containing molecules it is essential to characterize the gas-phase structures.The rotational spectrum and structural analysis of sec-butoxytrimethylsilane (sBT-Si) will be presented. The spectrum of sBT-Si has been recorded using the Hamburg COMPACT spectrometer, which is a chirped-pulse Fourier transform microwave spectrometer, in the 2 -8 GHz frequency range. Quantum-chemical calculations have been carried out to study the conformational flexibility of sBT-Si, and the measured rotational spectrum was examined for the lowest energy conformers. The spectrum is complicated due to the fact that three of the five methyl groups in sBT-Si have a rotational barrier lower than 7 kJ/mol, leading to internal rotation splitting. Despite this, the lowest energy conformer is prominent in the spectrum and has been successfully assigned. Weak signals of the conformer second lowest in energy have also been assigned. In this talk, the conformational flexibility and internal motion of this molecule will be discussed and compared to related molecules.