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

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 stabilization 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

High resolution spectroscopy of methyltrioxorhenium: towards the observation of parity violation in chiral molecules

Originating from the weak interaction, parity violation in chiral molecules has been considered as a possible origin of the biohomochirality. It was predicted in 1974 but has never been observed so far. Parity violation should lead to a very tiny frequency difference in the rovibrational spectra of the enantiomers of a chiral molecule. We have proposed to observe this predicted frequency difference using the two photon Ramsey fringes technique on a supersonic beam. Promising candidates for this experiment are chiral oxorhenium complexes, which present a large effect, can be synthesized in large quantity and enantiopure form, and can be seeded in a molecular beam. As a first step towards our objective, a detailed spectroscopic study of methyltrioxorhenium (MTO) has been undertaken. It is an ideal test molecule as the achiral parent molecule of chiral candidates for the parity violation experiment. For the 187Re MTO isotopologue, a combined analysis of Fourier transform microwave and infrared spectra as well as ultra-high resolution CO2 laser absorption spectra enabled the assignment of 28 rotational lines and 71 rovibrational lines, some of them with a resolved hyperfine structure. A set of spectroscopic parameters in the ground and first excited state, including hyperfine structure constants, was obtained for the antisymmetric Re=O stretching mode of this molecule. This result validates the experimental approach to be followed once a chiral derivative of MTO will be synthesized, and shows the benefit of the combination of several spectroscopic techniques in different spectral regions, with different set-ups and resolutions. First high resolution spectra of jet-cooled MTO, obtained on the set-up being developed for the observation of molecular parity violation, are shown, which constitutes a major step towards the targeted objective.Comment: 20 pages, 6 figure

Spectroscopie à très haute résolution de molécules sublimées en jet supersonique : vers une observation de la non conservation de la parité dans les molécules chirales par spectroscopie laser

The work presented in this manuscript consisted in the elaboration and optimisation of an experimental set up dedicated to the observation of parity violation (PV) in a supersonic beam of chiral molecules. Remarkably enough, the molecules considered which are currently being synthesized are in the solid phase at 300 K. We thus built a set up which enables to obtain a vapour phase of the molecules of interest by heating to realise a supersonic expansion via a pickup method with helium as a carrier gas. Furthermore, we used a time of flight technique to detect and estimate the amount of seeded molecules. We tested our set up with methyltrioxorhenium (MTO), a molecule from which chiral derivatives are being synthesized. We built up an experimental procedure to obtain the spectral characteristics and molecular parameters of the studied molecule. For that purpose we used saturated absorption spectroscopy in a cell at 300 K. Then a supersonic expansion of MTO in helium was obtained showing very good results. Indeed a ~10% molar fraction of MTO could be reached. Finally we recorded linear absorption spectra of MTO in beam on the experimental set up dedicated to the PV observation using a multi pass cell. The experimental data analysis enabled to simulate the theoretical spectrum of MTO. These results are very promising results with respect to the future experiments planned with chiral molecules.Le travail, présenté dans ce manuscrit, a consisté en l'élaboration et l'optimisation d'un dispositif expérimental dédié à la mesure de la violation de la parité (VP) dans les molécules chirales en jet supersonique. Les molécules envisagées qui sont en cours de synthèse, ont la propriété d'être à l'état solide à 300 K. Afin de pouvoir les mettre en jet, nous avons construit un dispositif permettant de réaliser la mise en phase vapeur par chauffage et leur ensemencement dans un gaz porteur. De plus, nous avons utilisé une technique de détection par temps de vol, afin d'estimer la quantité de molécules ensemencées. Nous avons testé notre dispositif avec le méthyltrioxorhénium (MTO) dont des dérivés chiraux sont en cours de synthèse. Nous avons mis au point une procédure expérimentale afin de déterminer les caractéristiques spectrales et les paramètres moléculaires du MTO. Pour cela, nous avons mesuré le spectre d'absorption saturée en cellule à 300 K. Puis, nous avons réalisé la mise en jet du MTO dans de l'hélium par chauffage et obtenu de très bons résultats, puisqu'une fraction molaire de MTO de ~10% a été mesurée. Enfin, nous avons enregistré le spectre d'absorption linéaire du MTO en jet sur le dispositif expérimental dédié à la mesure de la VP, notamment grâce à l'utilisation d'une cellule multi-passages. L'analyse des données nous a permis d'obtenir une simulation du spectre théorique. Ces résultats sont très prometteurs en vue des expériences sur les molécules chirales

Kinetic study of the reaction of chlorine atoms with hydroxyacetone in gas-phase

International audienceIn this letter the kinetics of the reaction of hydroxyacetone CH3C(O)CH2OH with Cl atoms is investigated using the relative rate technique. Experiments are carried out in a 65 L multipass photoreactor in the temperature range of 281–350 K. A mid-infrared spectrometer based on a quantum cascade laser in external cavity emitting at 9.5 μm is used to analyze the reactants. The determined rate coefficient for the investigated reaction is (1.7 ± 0.3) × 10−11exp(381.5 ± 57.3/T). The results are presented and discussed in terms of precision and compared with those obtained previously. The impact of Cl atoms on the atmospheric life time of hydroxyacetone is also discussed

Intercomparison of in situ water vapor balloon-borne measurements from Pico-SDLA H2O and FLASH-B in the tropical UTLS

International audienceIn this paper we compare water vapor mixing ratio measurements from two quasi-parallel flights of the Pico-SDLA H2O and FLASH-B hygrometers. The measurements were made on 10 February 2013 and 13 March 2012, respectively, in the tropics near Bauru, Sao Paulo St., Brazil during an intense convective period. Both flights were performed as part of a French scientific project, TRO-Pico, to study the impact of the deep-convection overshoot on the water budget. Only a few instruments that permit the frequent sounding of stratospheric water vapor can be flown within a small volume weather balloons. Technical difficulties preclude the accurate measurement of stratospheric water vapor with conventional in situ techniques. The instruments described here are simple and lightweight, which permits their low-cost deployment by non-specialists aboard a small weather balloon. We obtain mixing ratio retrievals which agree above the cold-point tropopause to within 1.9 and 0.5 % for the first and second flights, respectively. This level of agreement for measured stratospheric water mixing ratio is among the best ever reported in the literature. Because both instruments show similar profiles within their combined uncertainties, we conclude that the Pico-SDLA H2O and FLASH-B datasets are mutually consistent

Overview of the TRO-pico campaign aiming at studying of the impact of convective overshooting on the stratospheric water budget

Two processes are competing in the control of water vapor concentration in the tropical stratosphere: i) The socalled cold trap that is the slow ascent of water vapour in the TTL followed by ice crystal freezing and sedimentation leading to the drying of air entering the stratosphere and ii) convective overshooting that injects ice crystals sublimating in the stratosphere, eventually followed by further condensation and sedimentation. In contrast with the large-scale cold trap mechanism, overshooting towers are small-size and fast, but relatively frequent processes. Even if the first is frequently thought to be the main process controlling the amount of water in the stratosphere, the importance of overshooting, highly dependent on the frequency of the events, is still unknown. The aim of the TRO-pico project, supported by the French ANR, is to characterize the variability and frequency of convective water injections, its contribution at the regional wet season timescale, and to improve the understanding of their role with respect to the cold trap at a wider scale. The project is based on a small balloon campaign in Bauru (22.3 S) in S-E Brazil, including different phases during the wet season : March 2012 at the end of the most active convective season, a transition phase in November-December 2012 before the most active season, and January-February 2013, which corresponds to the peak of the convective activity. The campaign involves a series of light-weight payloads, including Pico-SDLA laser (H2O, CO2 or CH4) and FLASH Lyman alpha hygrometers, a mini-SOAZ spectrometer for O3, NO2, H2O and BrO, an AICEP (Electric field and Lightning) sensor, and COBALD, LOAC and micro-lidar aerosol instruments, combined with ground based radar and lidar measurements, satellite observations from CALIPSO, MLS and adequate modeling tools, that is to say all parameters that are sensitive to convective intensity. TRO-pico is a two time-scale campaign: i) a Six Month Observation Period (SMOP) covering one complete wet season during which water vapour profiles are measured regularly for studying their seasonal variability, and ii) an intensive observation period (IOP) during the most convectively intense summer period when measurements of all above parameters are performed close to or above thunderstorms. After a short presentation of objectives and instrumentation involved, the main results from the complete TRO-pico campaign will be shown, including the most intense period of convection and the transition period between the dry and the wet seasons