Chiral Control of Gas‐Phase Molecules using Microwave Pulses

Abstract

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.

Towards detection of molecular parity violation by microwave spectroscopy of CpRe(CH$_{3}$)(CO)(NO)

“…Furthermore, enantiomerselective population transfer experiments based on advanced microwave pulse schemes can selectively populate or depopulate certain rotational states of interests by just changing the phase of one microwave pulse in the scheme, which can be highly advantageous for such experiments. [49,50] Alternative approaches to perform microwave spectroscopy with perspectively even higher resolution are Ramsey type arrangements using the method of separated oscillatory fields. [51] We note in passing that we also attempted to predict parity violating wavenumber splittings in the CO and NO stretching fundamental using our recently described perturbative approach that uses finite differences of analytic PV potential gradients together with cubic parity conserving potentials to take multi-mode effects into account [23].…”

The influence of microwave pulse conditions on enantiomer-specific state transfer

“…In early ESST studies, these two factors significantly limited the transfer efficiency of ESST [16,21]. By using an elaborate MW scheme, this has recently been improved upon [22].…”

Microwave Three-Wave Mixing Spectroscopy of Chiral Molecules in Weakly Bound Complexes

“…A decade ago, the first M3WM experiment was successfully accomplished using 1,2-propanediol cooled with a cryogenic helium buffer gas [rotational temperature ( T rot ) ∼ 7 K], demonstrating that this method is capable of identifying enantiomers. , Later on, our laboratory performed experiments using a microwave spectrometer with a supersonic jet, which cooled the gas-phase sample to a lower T rot of ∼1–2 K . As rotational spectroscopy is sensitive to isomers and conformers, this approach can be used to analyze complex chemical samples containing multiple chiral species and molecules with multiple stereogenic centers. , In addition to chiral analysis, it can further be applied to separate the two enantiomers in a specific rotational state with the inclusion of an additional excitation at the listen transition of the M3WM cycle, also known as enantiomer-specific state transfer. − In this study, we present the results of an extended experiment in which we applied the M3WM method to investigate a weakly bound gas-phase complex, limonene–H 2 O (Figure ). We also highlight the advantages of preparing chiral molecular complexes, particularly in cases in which the target molecule lacks sufficient electric dipole moment components.…”

“…This highlights the potential of M3WM spectroscopy to be extended to a broader range of chiral systems, offering a promising strategy for investigating their chirality. In addition, the produced chiral complexes can be enantio-separated in a specific rotational state using an enantiomer-selective state transfer scheme, − which has been developed on the basis of the M3WM approach, preparing the enantio-enriched or enantio-purified samples for advanced precision experiments and further investigations.…”

“… 20 , 30 In addition to chiral analysis, it can further be applied to separate the two enantiomers in a specific rotational state with the inclusion of an additional excitation at the listen transition of the M3WM cycle, also known as enantiomer-specific state transfer. 31 − 34 In this study, we present the results of an extended experiment in which we applied the M3WM method to investigate a weakly bound gas-phase complex, limonene–H 2 O ( Figure 1 ). We also highlight the advantages of preparing chiral molecular complexes, particularly in cases in which the target molecule lacks sufficient electric dipole moment components.…”