Probing weak force-induced parity violation by high-resolution mid-infrared molecular spectroscopy

Abstract

To date no experiment has reached the level of sensitivity required to observe weak nuclear force-induced parity violation (PV) energy differences in chiral molecules. In this paper, we present the approach, adopted at Laboratoire de Physique des Lasers (LPL), to measure frequency differences in the vibrational spectrum of enantiomers. We review different spectroscopic methods developed at LPL leading to the highest resolutions, as well as 20 years of CO₂ laser stabilisation work enabling such precise measurements. After a first attempt to observe PV vibrational frequency shifts using sub-Doppler saturated absorption spectroscopy in a cell, we are currently aiming at an experiment based on Doppler-free two-photon Ramsey interferometry on a supersonic beam. We report on our latest progress towards observing PV with chiral organo-metallic complexes containing a heavy rhenium atom.

Keywords:

• parity violation
• mid-infrared
• high-resolution spectroscopy
• fundamental physics
• frequency metrology

Acknowledgements

The authors acknowledge financial support from Centre National de la Recherche Scientifique (CNRS), Région Île-de-France and Université Paris 13. This work is part of the project NCPCHEM 2010 BLAN 724 3 funded by the Agence Nationale de la Recherche (ANR, France). We would like to thank its co-ordinator Trond Saue and participants (Jeanne Crassous, Nidal Saleh, Laure Guy, Radovan Bast, Thérèse R. Huet, Pierre Asselin, Pascale Soulard,…) for valuable discussions. O. Lopez is gratefully acknowledged for his contribution to this project.

Notes

^gIn these experimental conditions, only the mean velocity V was roughly measured.

^hUncertainty given by the TOF fit.

ⁱUncertainty is dominated by that on γ_MTO, the unknown effective MTO Poisson coefficient during the supersonic expansion, assumed to be between 1.11 and 1.33.

1. The transverse velocity is defined as the velocity component that is perpendicular to the laser beam.

2. OsO₄ being very reactive, the absorption cell has to be pumped and filled again after a few hours in order to maintain best stabilities. On the contrary, when using SF₆, the cell is filled only once a day.

3. There has been quite a significant activity in the quantum chemical community in the past years with important contributions from the groups of M. Quack, R. Berger, P. Lazzeretti, P. Schwerdtfeger, P. Manninen and T. Saue that have been summarised in recent reviews [61,62].

4. Note that isotopically chiral MTO (CH₃Re¹⁶O¹⁷O¹⁸O) had already been suggested by Quack [67].

5. v_long means the velocity component along the molecular beam axis, which is usually almost perpendicular to the laser beam and thus close to v _⊥, the speed transverse to the laser beam axis introduced in the Section on molecular ultra-high resolution spectroscopy.

6. Note that this probably leads to slightly underestimated T_long .