Perspective: Tipping the scales: Search for drifting constants from molecular spectra

Abstract

Precision measurement of the rotational energy-level structure of the three-electron molecule He 2 + Transitions in atoms and molecules provide an ideal test ground for constraining or detecting a possible variation of the fundamental constants of nature. In this perspective, we review molecular species that are of specific interest in the search for a drifting proton-to-electron mass ratio μ.In particular, we outline the procedures that are used to calculate the sensitivity coefficients for transitions in these molecules and discuss current searches. These methods have led to a rate of change in μ bounded to 6 × 10 −14 /yr from a laboratory experiment performed in the present epoch. On a cosmological time scale, the variation is limited to | μ/μ| < 10 −5 for look-back times of 10-12 × 10 9 years and to | μ/μ| < 10 −7 for look-back times of 7× 10 9 years. The last result, obtained from high-redshift observation of methanol, translates intoμ/μ = (1.4 ± 1.4) × 10 −17 /yr if a linear rate of change is assumed.

Characterising molecules for fundamental physics: an accurate spectroscopic model of methyltrioxorhenium derived from new infrared and millimetre-wave measurements

“…18 The chiral derivatives of methyltrioxorhenium (MTO) are excellent candidate species for this measurement, because calculations predict relatively large PV energy differences, and because it is possible to synthesize these molecules and bring them into the gas phase. 8,17,19,20 In the present work, we obtain much new spectroscopic information about MTO. A few years ago, a first set of measurements studied the ground and first excited states of the as antisymmetric Re=O stretching mode of MTO.…”

“…For example, precise knowledge of molecular constants is required for modeling atmospheres, whether it be our own 1,2 or those found in exo-planets 3 and in the interstellar medium 4 , for studying collision physics 5,6 , and as crucial groundwork for performing fundamental physics tests 7,8,9,10,11,12,13,14,15,16,17 . One such test is the measurement of the parity-violating (PV) energy difference between opposite enantiomers of a chiral molecule, induced by the weak interaction.…”

Forbidden Vibrational Transitions in Cold Molecular Ions: Experimental Observation and Potential Applications

“…The natural linewidth is estimated to be several orders of magnitude smaller (approximately nanohertz [1] ) and the Doppler width at the temperature of the ions amounts to approximately 1. as a possible variation of fundamental physical constants, [16] the existence of yet unknown fundamental interactions [17] or to constrain the magnitude of the electron's electric dipole moment. [18] Many of these questions can suitably be studied with the rotation-vibration spectra of molecules.…”

Precision spectroscopy comes to the mid-IR

“…From precision molecular vibrational spectra one can derive extremely accurate measurements of fundamental quantities such as the fine-structure constant and the proton-to-electron mass ratio-and perhaps observe those ostensible constants drifting over time. 7 Sensors that detect trace components of a mixture based on their vibrational spectra can be made even more sensitive and specific-with applications to atmospheric, planetary, medical, and industrial sciences. Teams at LNE-SYRTE and the LPL are working on expanding their 43-km fiber-optic link into a continent-wide network so researchers across Europe can benefit from LNE-SYRTE's frequency standards.…”