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

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

2009-11-13

arxiv.org/abs/0911.2507v2

Int J Thermophys (2010) 31:1347-1359

Physics

Atomic Physics

Scientific paper

10.1007/s10765-010-0755-3

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.

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