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

S K Tokunaga,B Darquié,R J Hendricks,M R Tarbutt

doi:10.1088/1367-2630/aa6de4

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 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.

Highlights

There is a demand for precise spectroscopy of increasingly complex molecules
We report the buffer-gas cooling of methyltrioxorhenium
We find that the decay time of the absorption signal decreases much more significantly over this time, which we suggest is the result of changing helium density inside the cell — we observe that the MTO pellet adsorbs significant amounts of helium when at low temperatures, and we speculate that a diminishing amount of this is liberated by successive ablation pulses

Summary

Introduction

There is a demand for precise spectroscopy of increasingly complex molecules. Precise knowledge of molecular constants is required for modelling our atmosphere[1, 2], for the interpretation of spectra of astrophysical and planetary interest[3], for studying collision physics[4, 5], and for performing tests of fundamental physics, ranging from searches for signatures of symmetry breaking[6,7,8,9,10] to measurements of the fundamental constants[11, 12] and their possible variation[13,14,15,16].One such test is the measurement of energy differences between chiral enantiomers induced by parity violation. We demonstrate the first precise spectroscopic measurements of buffer-gas-cooled molecules in the mid-infrared region around 10 μm, obtaining rotational and hyperfine-resolved absorption spectra in the Re=O stretching region of MTO. In a recent experiment at Harvard, MTO has been injected into a cryogenic buffer-gas cell from a heated pulsed valve, and broadband Fourier transform microwave spectroscopy of the molecules was performed[36].

Results

Conclusion