Measurement and calculation of CO (7-0) overtone line intensities

Intensities of 14 lines in the sixth overtone (7-0) band of carbon monoxide (12C16O) are measured in the visible range between 14 300 and 14 500 cm-1 using a frequency-stabilized cavity ring-down spectrometer. This is the first observation of such a high and weak overtone spectrum of the CO molecule. A theoretical model is constructed and tested based on the use of a high accuracy ab initio dipole moment curve and a semi-empirical potential energy curve. Accurate studies of high overtone transitions provide a challenge to both experiment and theory as the lines are very weak: below 2 × 10-29 cm molecule-1 at 296 K. Agreement between theory and experiment within the experimental uncertainty of a few percent is obtained. However, this agreement is only achieved after issues with the stability of the Davidson correction to the multi-reference configuration interaction calculations are addressed

Collisional effects in pure D2. Ultra accurate measurements and ab initio calculations

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Collisional effects in pure D2. Ultra accurate measurements and ab initio calculations

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CRDS measurements and ab initio calculations of collisional effects in pure D2

International audienceRecent progress in theoretical calculations of dissociation energies of H2, HD and D2 [1–2] gives predictions of the transition frequencies with uncertainty exceeding the level of 10-3 cm-1 for the first overtone band (2–0) [3]. Such predictions open a way for testing relativistic and quantum electrodynamics corrections. They give also the opportunity for searching for new physics like additional long-range hadron-hadron interactions [4]. At this level of accuracy the uncertainty of the H 2 (or its isotopologues) line position determination in Doppler limit becomes considerably affected by the line-shape effects [5] including asymmetry of the line shapes. Spectral line shapes of D2 transitions are atypical and difficult to model. First strategy for overcoming this problem is measuring the spectra at low pressures, where collisional effects are negligible [3]. However, it is experimentally challenging due to exceptionally low intensities of the quadrupole lines. Another approach is recording them at higher pressures and describe the collisions in a more sophisticated way. Here as an example of the second strategy, we present our preliminary results applied for very weak S(2) transition of deuterium in the 2-0 band, using ab initio calculations. Transition has been measured with the frequency-stabilized cavity ring-down spectroscopy (FS-CRDS) assisted by an optical-frequency comb [6,7], using experimental setup described in [8]. The line positions at high pressures, up to 1000 Torr, were measured with sub-MHz accuracy. Furthermore, to validate ab initio model, we extended our experiments to a wide range of temperatures. We compare it with ab initio quantum scattering calculations, where we obtain the generalized spectroscopic cross sections. The real and imaginary parts provide the speed-dependent collisional broadening γ(ν) and shifting δ(ν). The velocity-changing collisions, in turn, are described by hard-sphere approximation of the ab initio potential which is called the speed-dependent billiard-ball profile (SDBBP) [9]

Ultra accurate measurements and ab initio calculations of collisional effects in pure D2 .

International audienceWe present our experimental spectra of the very weak S(2) transition from the 2–0 band of molecular deuterium, measured with a frequency-stabilized cavity ring-down spectroscopy (FS–CRDS) assisted by the optical frequency comb (OFC). Experimental collisional broadening and shifting are compared with results of ab initio quantum scattering calculations

Cavity ring-down spectroscopy of D2 ro-vibrational line with absolute frequency axis

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COMB-REFERENCED COHERENT RAMAN SPECTROSCOPY ON PURE H2

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Stimulated Raman scattering metrology of molecular hydrogen

International audienceFrequency combs have revolutionized optical frequency metrology, allowing one to determine highly accurate transition frequencies of a wealth of molecular species. These progresses have only marginally benefited infrared-inactive transitions, due to their inherently weak cross-sections. Here we overcome this limitation by introducing stimulated-Raman-scattering metrology, where a frequency comb is exploited to calibrate the frequency detuning between the pump and Stokes excitation lasers. We apply this approach to the investigation of molecular hydrogen, which is a recognized benchmark for tests of quantum electrodynamics and of theories that describe physics beyond the standard model. Specifically, we measure the transition frequency of the Q(1) fundamental line of H-2 around 4155 cm(-1) with few parts-per-billion uncertainty, which is comparable to the theoretical benchmark of ab initio calculations and more than a decade better than the experimental state of the art. Our comb-calibrated stimulated Raman scattering spectrometer extends the toolkit of optical frequency metrology as it can be applied, with simple technical changes, to many other infrared-inactive transitions, over a 50-5000 cm(-1) range that covers also purely rotational bands. Molecular hydrogen has a simple structure that makes it a unique benchmark for molecular quantum physics. The authors determined the transition energy of its fundamental Q(1) vibrational line with an unprecedented parts-per-billion accuracy by a novel spectrometer that combines Stimulated-Raman-Scattering with comb calibration of optical frequencies

Comb-calibrated Raman Spectroscopy of Molecular Hydrogen

International audienceMolecular hydrogen and its isotopologues are key systems to test quantum electrodynamics (QED) at molecular length scales, as their energy levels can be calculated with high accuracy[1]. Comparison of the theoretical values highly accurate experimental determinations transition frequencies allows one QED theories beyond standard model particle physics[2]. Recent measurements rovibrational HD D2, covering mostly second overtone band, have shown a systematic deviation between measured frequencies. Yet, available on H2 characterized by uncertainties order magnitude larger than theory