High resolution spectroscopy of methyltrioxorhenium: towards the observation of parity violation in chiral molecules†

Originating from the weak interaction, parity violation in chiral molecules has been considered as a possible origin of the biohomochirality. It was predicted in 1974 but has never been observed so far. Parity violation should lead to a very tiny frequency difference in the rovibrational spectra of the enantiomers of a chiral molecule. We have proposed to observe this predicted frequency difference using the two photon Ramsey fringes technique on a supersonic beam. Promising candidates for this experiment are chiral oxorhenium complexes, which present a large effect, can be synthesized in large quantity and enantiopure form, and can be seeded in a molecular beam. As a first step towards our objective, a detailed spectroscopic study of methyltrioxorhenium (MTO) has been undertaken. It is an ideal test molecule as the achiral parent molecule of chiral candidates for the parity violation experiment. For the 187Re MTO isotopologue, a combined analysis of Fourier transform microwave and infrared spectra as well as ultra-high resolution CO2 laser absorption spectra enabled the assignment of 28 rotational lines and 71 rovibrational lines, some of them with a resolved hyperfine structure. A set of spectroscopic parameters in the ground and first excite