High-resolution mid-infrared spectroscopy of buffer-gas-cooled methyltrioxorhenium molecules

We demonstrate cryogenic buffer-gas cooling of gas-phase methyltrioxorhenium (MTO).This molecule is closely related to chiral organometallic molecules where the parity-violating energy differences between enantiomers is measurable.The molecules are produced with a rotational temperature of approximately 6 K by laser ablation of an MTO pellet inside a cryogenic helium buffer gas cell.Facilitated by the low temperature, we demonstrate absorption spectroscopy of the 10.2 μm antisymmetric Re=O stretching mode of MTO with a resolution of 8 MHz and a frequency accuracy of 30 MHz.We partially resolve the hyperfine structure and measure the nuclear quadrupole coupling of the excited vibrational state.Our ability to produce dense samples of complex molecules of this type at low temperatures represents a key step towards a precision measurement of parity violation in a chiral species.