Implementing the new Kelvin by molecular precision spectroscopy

Darquie, Benoit

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https://hdl.handle.net/2142/100607 Copy

Description

Title

Implementing the new Kelvin by molecular precision spectroscopy

Author(s)

Darquie, Benoit

Contributor(s)

• Daussy, Christophe
• Briaudeau, Stephan
• Martin, Catherine
• Kozlova, Olga
• Moufarej, Elias

Issue Date

2018-06-22

Keyword(s)

Fundamental interest

Abstract

Next autumn, the redefinition of the international System of Units (SI) will be accepted by the General Conference on Weights and Measures. This major reform will establish a new definition of units in terms of a set of 7 defining constants. The temperature unit, the kelvin, the definition of which is currently based on the triple point of water (TPW), will for example be redefined by fixing the value of the Boltzmann constant kB. For the implementation of the new kelvin, various primary thermometry methods are currently being developed such as Doppler-broadening thermometry (DBT), acoustic gas thermometry, Johnson noise thermometry, dielectric constant gas thermometry, etc... We have previously proposed and developped the DBT method and have used it to demonstrate an accurate determination of kB a,b . Once kB fixed in the new SI, DBT will become a primary spectroscopic method for thermodynamic temperature measurements and thus for the implementation of the new kelvin. DBT is based on the precise measurement of the Doppler broadening of absorption line of a gaz phase atomic or molecular species, an ammonia ro-vibrational transition in the mid-infrared range (∼ 10µm) in our case, combined with some highly accurate modeling of the line profile. We are currently developing DBT in the temperature range 300-430K, in order to demonstrate its potential and study its limitations beyond the temperature of the TPW. We will present our progress towards temprature measurements with uncertainties at the 25ppm level. The existing set-up (previously used for the determination of kB) has been upgraded. We have placed the spectroscopic cell in a variable thermostat, the temperature stability and gradient of which has been characterized. We have also improved our mid-infrared spectrometer to investigate, in particular the influence of the line-mixing on the temperature measurement accuracy.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Permalink

http://hdl.handle.net/2142/100607

DOI

10.15278/isms.2018.FD03

Copyright and License Information

Copyright 2018 Benoit Darquie

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