Evidence for speed-dependent effects in NH3 self-broadened spectra: towards a new determination of the Boltzmann constant

In this paper we present an accurate analysis of the shape of an isolated rovibrational ammonia line from the strong nu2 band around 10 $\mu$m, recorded by laser absorption spectroscopy. Experimental spectra obtained under controlled temperature and pressure, are confronted to various models that take into account Dicke narrowing or speed-dependent effects. Our results show clear evidence for speed-dependent broadening and shifting, which had never been demonstrated so far in NH3. Accurate lineshape parameters of the nu2 saQ(6,3) line are obtained. Our current project aiming at measuring the Boltzmann constant, kB, by laser spectroscopy will straight away benefit from such knowledge. We anticipate that a first optical determination of kB with a competitive uncertainty of a few ppm is now reachable.Comment: 13 pages, 5 figures, 1 tabl

Determination of the Boltzmann constant by laser spectroscopy as a basis for future measurements of the thermodynamic temperature

In this paper, we present the latest results on the measurement of the Boltzmann constant kB, by laser spectroscopy of ammonia at 10 ?m. The Doppler absorption profile of a ro-vibrational line of an NH3 gas sample at thermal and pressure equilibrium is measured as accurately as possible. The absorption cell is placed inside a large 1m3 thermostat filled with an ice-water mixture, which sets the temperature very close to 273.15 K. Analysing this profile, which is related to the Maxwell-Boltzmann molecular speed distribution, leads to a determination of the Boltzmann constant via a measurement of the Doppler width (proportional tosqrt(kBT)). A spectroscopic determination of the Boltzmann constant with an uncertainty as low as 37 ppm is obtained. Recent improvements with a new passive thermostat lead to a temperature accuracy, stability and homogeneity of the absorption cell better than 1 ppm over a day

A revised uncertainty budget for measuring the Boltzmann constant using the Doppler Broadening Technique on ammonia

We report on our on-going effort to measure the Boltzmann constant, kB, using the Doppler Broadening Technique. The main systematic effects affecting the measurement are discussed. A revised error budget is presented in which the global uncertainty on systematic effects is reduced to 2.3 ppm. This corresponds to a reduction of more than one order of magnitude compared to our previous Boltzmann constant measurement. Means to reach a determination of kB at the part per million accuracy level are outlined

Measurement of the Boltzmann constant by the Doppler broadening technique at a 3,8x10-5 accuracy level

In this paper, we describe an experiment performed at the Laboratoire de Physique des Lasers and dedicated to an optical measurement of the Boltzmann constant. With the proposed innovative technique, determining comes down to an ordinary frequency measurement. The method consists in measuring as accurately as possible the Doppler absorption profile of a rovibrational line of ammonia in thermal equilibrium. This profile is related to the Maxwell-Boltzmann molecular velocity distribution along the laser beam. A fit of the absorption line shape leads to a determination of the Doppler width proportional to sqrt(kT) and thus to a determination of the Boltzmann constant. The laser source is an ultra-stable CO2 laser with a wavelength . The absorption cell is placed in a thermostat keeping the temperature at 273.15 K within 1.4 mK. We were able to measure with a relative uncertainty as small as 3.8x10-5, which represents an improvement of an order of magnitude for an integration time comparable to our previous measurement published in 2007 [1

Accurate determination of the Boltzmann constant by Doppler spectroscopy: Towards a new definition of the kelvin

proceedings of the ICAP 2012 conference (23rd International Conference on Atomic Physics)International audienceAccurate molecular spectroscopy in the mid-infrared region allows precision measurements of fundamental constants. For instance, measuring the linewidth of an isolated Doppler-broadened absorption line of ammonia around 10 µm enables a determination of the Boltzmann constant k B. We report on our latest measurements. By fitting this lineshape to several models which include Dicke narrowing or speed-dependent collisional effects, we find that a determination of k B with an uncertainty of a few ppm is reachable. This is comparable to the best current uncertainty obtained using acoustic methods and would make a significant contribution to any new value of k B determined by the CODATA. Furthermore, having multiple independent measurements at these accuracies opens the possibility of defining the kelvin by fixing k B , an exciting prospect considering the upcoming redefinition of the International System of Units

Mesure de la constante de Boltzmann par spectroscopie laser : vers une contribution au futur Système International d'unités

We detail in this manuscript the experiment developed in the MMTF team of the Laboratoire de Physique des Lasers, whose aim is to contribute to the redefinition of the International System of units through the measurement of the Boltzmann constant, kB, by laser spectroscopy. The method used is based on the linear absorption spectroscopy of an ammonia gas maintained at constant temperature. The Boltzmann constant is deduced from the gas temperature measurement and the width of the recorded absorption profile. First and second generation experiments already led to a 38x10-6 statistical uncertainty on the measurement of kB. In this manuscript, we describe how we improved the experimental set-up to reduce the measurement uncertainty to a fewx10-6 level. We make profit of these experimental improvements and fit the data in a new way to reduce the measurement statistical uncertainty to a 6.4x10-6 level. Then, we carry out a complete study of systematic effects that could affect the Boltzmann constant measurement. We notably describe the experimental set-up built to analyze NH3 hyperfine structure. Among other things, we evaluate the impact of the gas composition, the transition saturation, and the laser beam modulation. Finally, we deeply study how to model collisions between molecules. In the end, the global uncertainty budget on systematic effects is reduced to a 2.1x10-6 level. All the obtained results and future prospects pave the way to an optical measurement of kB with an accuracy of a few 10-6.Ce manuscrit présente l'expérience développée dans l'équipe MMTF du Laboratoire de Physique des Lasers avec pour objectif de contribuer à la redéfinition du Système International d'unités en mesurant la constante de Boltzmann, kB, par spectroscopie laser. La méthode utilisée est fondée sur la spectroscopie d'absorption linéaire d'un gaz d'ammoniac maintenu à température constante. La constante de Boltzmann est déduite de la mesure de température du gaz et de la largeur du profil d'absorption enregistré. Des expériences de 1ère et 2ème génération ont d'ores et déjà permis d'atteindre une incertitude statistique de 38x10-6 sur la mesure de kB. Dans ce mémoire, nous décrivons les améliorations apportées au dispositif expérimental pour réduire l'incertitude de mesure au niveau de quelques 10-6. Nous mettons à profit ces développements expérimentaux et utilisons une nouvelle procédure d'ajustement des données expérimentales pour réduire l'incertitude statistique de mesure au niveau de 6,4x10-6. Nous effectuons par la suite une étude complète des effets systématiques susceptibles d'affecter la mesure de kB. Nous décrivons notamment le dispositif expérimental mis en place pour analyser la structure hyperfine de NH3. Nous évaluons entre autres l'impact de la composition du gaz, de la saturation de la transition, et de la modulation du faisceau laser. Enfin, nous menons une étude poussée de la modélisation des collisions entre molécules. Au final, le budget d'incertitude global sur les effets systématiques est réduit au niveau de 2,1x10-6. L'ensemble des résultats obtenus et les perspectives envisagées ouvrent la voie vers une mesure optique de kB avec une incertitude de quelques 10-6

Mesure de la constante de Boltzmann par spectroscopie laser (vers une contribution au futur Système International d unités)

Ce manuscrit présente l expérience développée dans l équipe MMTF du Laboratoire de Physique des Lasers avec pour objectif de contribuer à la redéfinition du Système International d unités en mesurant la constante de Boltzmann, kB, par spectroscopie laser. La méthode utilisée est fondée sur la spectroscopie d absorption linéaire d un gaz d ammoniac maintenu à température constante. La constante de Boltzmann est déduite de la mesure de température du gaz et de la largeur du profil d absorption enregistré. Des expériences de 1ère et 2ème génération ont d ores et déjà permis d atteindre une incertitude statistique de 38x10 sur la mesure de kB. Dans ce mémoire, nous décrivons les améliorations apportées au dispositif expérimental pour réduire l incertitude de mesure au niveau de quelques 10 . Nous mettons à profit ces développements expérimentaux et utilisons une nouvelle procédure d ajustement des données expérimentales pour réduire l incertitude statistique de mesure au niveau de 6,4x10 . Nous effectuons par la suite une étude complète des effets systématiques susceptibles d affecter la mesure de kB. Nous décrivons notamment le dispositif expérimental mis en place pour analyser la structure hyperfine de NH3. Nous évaluons entre autres l impact de la composition du gaz, de la saturation de la transition, et de la modulation du faisceau laser. Enfin, nous menons une étude poussée de la modélisation des collisions entre molécules. Au final, le budget d incertitude global sur les effets systématiques est réduit au niveau de 2,1x10 . L ensemble des résultats obtenus et les perspectives envisagées ouvrent la voie vers une mesure optique de k avec une incertitude de quelques 10 .We detail in this manuscript the experiment developed in the MMTF team of the Laboratoire de Physique des Lasers, whose aim is to contribute to the redefinition of the International System of units through the measurement of the Boltzmann constant, kB, by laser spectroscopy. The method used is based on the linear absorption spectroscopy of an ammonia gas maintained at constant temperature. The Boltzmann constant is deduced from the gas temperature measurement and the width of the recorded absorption profile. First and second generation experiments already led to a 38x10 statistical uncertainty on the measurement of kB. In this manuscript, we describe how we improved the experimental set-up to reduce the measurement uncertainty to a fewx10 level. We make profit of these experimental improvements and fit the data in a new way to reduce the measurement statistical uncertainty to a 6.4x10 level. Then, we carry out a complete study of systematic effects that could affect the Boltzmann constant measurement. We notably describe the experimental set-up built to analyze NH3 hyperfine structure. Among other things, we evaluate the impact of the gas composition, the transition saturation, and the laser beam modulation. Finally, we deeply study how to model collisions between molecules. In the end, the global uncertainty budget on systematic effects is reduced to a 2.1x10 level. All the obtained results and future prospects pave the way to an optical measurement of kB with an accuracy of a few 10 .PARIS13-BU Sciences (930792102) / SudocSudocFranceF

Could the palatalization or affrication of plosive dental consonants be an ongoing process of phonetic change in metropolitan French?

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Existe-t-il une signification sociale stable et univoque de la palatalisation/affrication en français ? Étude sur la perception de variantes non standard

International audiencePrevious socio-phonetic studies showed that palatalization and/or affrication of plosive dental consonants, often considered by phoneticians to be non-standard and working class variants, are widespread in contemporary French, suggesting an on-going phonetical change process. We investigate whether the use of these variants in a sizeable speech sample induces any particular conscious or unconscious evaluational reaction in ordinary young listeners from two different French big cities. Using broadcast news as a formal context for this study, a perceptual experiment was conducted. Results suggest that the mere presence of a high degree of palatalization/ affrication is not sufficiently salient to trigger off a stigmatizing reaction, and that perception is very dependent on the global context; a complex correlation with other co-occurring features could be inferred from our data