Search for Resolution of Chiral Fluorohalogenomethanes and Parity-Violation Effects at the Molecular Level

The first observation of a parity‐violation effect in molecules induced by weak interactions is still a dream that requires the synthesis and, eventually, the resolution of the enantiomers of well‐chosen simple chiral molecules together with an appropriate experimental set‐up for high‐resolution spectroscopy. Performing IR spectroscopy on highly enantiomerically enriched samples of bromochlorofluoromethane succeeded in giving an upper limit of 10−13 for the relative vibrational energy difference between the two enantiomers. These results led us to conceive a new experimental set‐up based on a supersonic molecular beam and to work on other chiral molecules, such as chlorofluoroiodomethane. A synthesis of (±)‐CHClFI from racemic chlorofluoroiodoacetic acid should, in the near future permit the preparation of optically active samples of this haloform. The development of molecular beam spectroscopy using a two‐photon Ramsey‐fringes experiment should allow us to reach the precision needed to observe parity violation. These experimental challenges, which stimulate a close collaboration between chemists and physicists, are presented. The success of these projects would open the route to new information on the molecular Hamiltonian, a better knowledge of the electroweak interaction, and a better control of the various chirality‐related properties of simple molecules. Left and right are different. The physical and chemical properties of left‐handed and right‐handed enantiomers are often considered to be strictly identical. In fact, the weak interaction, which is extremely weak at the molecular level, is the only force that induces a difference between left and right (see picture). It is responsible for relative frequency differences of the order of 10‐14–10‐19 between the molecular spectra. Despite the very small size of the effect, the authors show that the perspective of its observation is not an inaccessible dream anymore. In this context, the resolution of the enantiomers of the simplest chiral molecules such as fluorohalogenomethanes is of great importance.