Enantiopure beams of chiral molecules

Chirality plays an important role in many chemical reactions and biological processes. A large class of biologically and pharmaceutically relevant molecules are chiral and exist in one of two mirror-image versions, or enantiomers. The left- or right-handed enantiomers often exhibit dramatically different effects when they are placed in biological environments. Most biomolecules in our bodies occur almost exclusively with one handedness, a phenomenon known as the homochirality of life. Despite the high abundance of chirality in nature, detecting and quantifying the handedness of a sample remains challenging. We propose an experiment that synthesizes elements from the fields of chiral analysis, microwave spectroscopy, and molecular beam manipulation methods, yielding a cold, state-selected, species- selected, high flux beam of neutral molecules. The technique is applicable to any molecular species of which cold beams in the gas phase are available. We will demonstrate this broadly applicable technique with a chirality-selected molecular beam. Recently, a new method for sensitive chiral analysis via microwave spectroscopy of gas phase molecules was demonstrated at Harvard University. Here, chiral enantiomers can clearly be distinguished by recording a phase-resolved microwave signal. Enantiomeric excess levels of nearly racemic samples can be determined at the 1% level. However, it still remains an open challenge to extract pure, state-selected samples from mixtures using controlled, field-mediated methods. We propose to combine enantiomer-specific state preparation with a so-called Moiré deflectometer to produce state- and species selected molecular beams. A Moiré deflectometer for atomic or molecular beams combines high signal throughput with periodic narrow beam collimation resulting in a high force sensitivity. It consists of three equally spaced identical gratings where the resulting molecular fringe pattern at the position of the third grating is a shadow image of the illuminated structures. We propose to combine the state-selectivity of microwaves and the sensitivity to small accelerations of Moiré deflectometers to realize a state-selective Moiré Selector. We will introduce an additional electric deflection field within the selector which acts mainly on the chosen enantiomer. The frequency of the electric field can be tuned to the chosen state and leads to the transmission of only the selected enantiomer. The resulting species-selected beams of molecules with a well-defined quantum state are of great interest for a wide range of applications across the sciences, from cold chemistry and physical chemistry to tests of the foundations of quantum mechanics.

During the course of the Schrödinger Project Enantiopure Beams of Chiral Molecules experiments on the investigation and control of so-called chiral molecules were performed. Chirality in molecules is also called handedness, originating from the fact, that like hands they can exist in two mirror images (enantiomers) that cannot be transformed into each other by mere rotation or translation. They are of high importance in many biological and chemical reactions, also in the human body. In many ways these enantiomers behave in an almost identical way, making them intrinsically hard to be distinguished and separated from a mixture of different enantiomers. The most striking result of the project is the successful development and demonstration of a method to manipulate the internal rotational state of chiral molecules enantiomer-specifically. This new scheme opens up the path for future experiments in fundamental physics as well as physical chemistry. Our result has been published in Physical Review Letters. Another interesting result of our experiments is the use of microwave spectroscopy in a cryogenic buffer gas cell to study the reaction of ozone molecules with isoprene molecules. Isoprene is the most abundant, non-methane hydrocarbon emitted into the atmosphere by vegetation. Its reaction with ozone involves reactive intermediate species of which not all have been measured directly previously. Our work has the potential to contribute towards the ability to isolate, identify, and quantify new reactive intermediates in the ozonolysis. This work has been published in Physical Chemistry Chemical Physics. Other research within the project and related to it involved time-resolved studies of conformational relaxation dynamics, and structural investigation of the previously not unambiguously determined structure of the molecule butadiene. Both results are published as separate articles in Angewandte Chemie International Edition. In summary we could demonstrate new techniques that lay the path to a multitude of future studies and scientific investigations.