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

Abstract

Following our first paper about high resolution spectroscopy of methyltrioxorhenium (MTO) [Stoeffler et al. PCCP, 13, 854, (2011)], the present study reports a deeper investigation of the ground state, and Re=O antisymmetric (as) and symmetric (s) stretching excited states of both CH3 187 ReO3 and CH3 185 ReO3 isotopologues, thanks to new devices implemented within our consortium. We carry out high resolution millimeter-wave (MMW) and infrared (IR) spectroscopy in room temperature absorption cells, in a pulsed supersonic jet and in a cryogenic buffer gas cell. This collection of sensitive spectrometers enables us to probe both levels of a vibrational transition in low and room temperature gaseous environments. We thus report a new series of measurements providing particularly accurate rotational and rovibrational data for such a large and heavy organometallic molecule that is solid at room temperature.The combination of the new MMW and IR data leads to an improvement of the rovibrational model of MTO: (i) rotational spectra are extended to the 150-300 GHz range and are analyzed to characterize the ground state rotational and hyperfine structure up to J = 43 and K = 41, resulting in the significant refinement of rotational, quartic and hyperfine parameters, as well as the determination of sextic parameters and a centrifugal distortion correction to the quadrupolar hyperfine constant,(ii) rovibrational data recorded at very different temperatures (between 6 and 300 K) in the 970-1015 cm -1 range, at resolutions down to 8 MHz and frequency accuracies as high as 30 MHz (using the buffer gas technique), are used in a first step to extract more precise excited-state rotational, Coriolis and quartic parameters as well as the ground-state centrifugal distortion parameter of the 187 Re isotopologue, which isn't accessible from rotational spectroscopy alone. In a second step, taking the hyperfine structure into account, the upper state rhenium atom quadrupole coupling constant eQq' is determined from the assignment of partially hyperfine-resolved CO2 laser absorption spectra of a skimmed molecular beam.* now at National Physical Laboratory, Teddington, TW11 0LW, UK. 2 IIntroductionThere is an increasing demand for precision spectroscopy of polyatomic molecules. 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. 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...

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

“…The observed relative line intensities are consistent with the natural isotopic abundances, allowing unambiguous assignments. This improves on two previous spectroscopic studies of supersonic jet-cooled MTO where the resolutions were 150 MHz (Fourier transform infrared spectroscopy [42]) and 120 MHz (laser absorption spectroscopy [43]). Thus, our data improves the accuracy of some of the spectroscopic constants when used in a combined analysis with other datasets at various resolutions [43].…”

“…The figure also shows a fit of the data to a model calculated using a bar spectrum convolved with Lorentzian profiles. In this model, the line centers and intensities are found from an analysis of this vibrational mode of MTO that combines microwave, millimeter-wave and infrared data, as well as the data presented in this paper [43]. We use PGOPHER [44] to simulate spectra and fit the overall shape of the experimental data.…”

“…Using these data, we measure the absolute frequencies of a number of transitions, as listed in table 1. The quantum number assignments are determined with the help of data from Asselin et al [43]. In the data shown in figure 4, we resolve neighbouring rovibrational lines of the 185 Re and 187 Re isotopologues of MTO.…”

“…The hyperfine structure is dominated by the interaction between the rhenium nuclear quadrupole moment and the gradient of the electric field at the nucleus. The spin-rotation interaction between the magnetic field induced by the molecular rotation and the magnetic moment of the rhenium nucleus is much smaller, but large enough that we include it in our analysis [42,43]. Smaller magnetic hyperfine structure resulting from the spins of hydrogen nuclei can be neglected.…”

Mixing Properties of Room Temperature Patch‐Antenna Receivers in a Mid‐Infrared (λ ≈ 9 µm) Heterodyne System

“…In the MIR range and in adverse conditions, such as fog or dusty environment, an electromagnetic signal propagates through the atmosphere much farther than at 1.55 µm securing communications more efficiently . In addition to sensing and communications, few photons coherent nondestructive MIR detection is very promising in quantum metrology, for fundamental researches such as the precise definition of the molecular hyperfine structure and the study of parity violation in molecules …”