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

TL;DR

This study demonstrates cryogenic buffer-gas cooling of methyltrioxorhenium molecules, enabling high-resolution mid-infrared spectroscopy that reveals hyperfine structure and nuclear quadrupole coupling, advancing molecular control and measurement techniques.

Contribution

The paper introduces a method for cooling MTO molecules to cryogenic temperatures and performing high-resolution spectroscopy, which was not previously achieved for this molecule.

Findings

MTO molecules cooled to ~6 K via buffer-gas cooling.

Resolved hyperfine structure in the vibrational spectrum.

Measured nuclear quadrupole coupling of excited state.

Abstract

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 may be 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~$\mu$m 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.