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Direct determination of the Boltzmann constant by an optical method
C Daussy1, M Guinet, A Amy-Klein
1Laboratoire de Physique des Lasers, UMR CNRS 7538, Institut Galilée, Université Paris 13, 99, avenue J.-B. Clément, 93430 Villetaneuse, France.
Physical Review Letters
|August 7, 2007
Summary
Scientists measured the Doppler profile of ammonia gas to determine the Boltzmann constant. This laser spectroscopy method yielded a precise measurement, paving the way for a new kelvin definition.
Area of Science:
- Molecular Spectroscopy
- Thermodynamics
- Metrology
Background:
- Accurate determination of fundamental physical constants is crucial for scientific advancement and redefinitions of SI units.
- Laser spectroscopy offers high precision for measuring molecular properties.
- The Boltzmann constant (k B) relates temperature to energy at the molecular level.
Purpose of the Study:
- To measure the Boltzmann constant (k B) using laser spectroscopy of ammonia.
- To establish a novel method for determining k B by analyzing Doppler profiles.
- To contribute to the redefinition of the kelvin based on fundamental constants.
Main Methods:
- Recording the Doppler profile of a rovibrational line in the nu(2) band of ammonia-14 (NH3).
- Utilizing an absorption cell with ammonia gas thermalized by a water-ice bath.
- Extrapolating the Doppler width to zero pressure for accurate k B determination.
Main Results:
- First measurement of the Boltzmann constant (k B) via laser spectroscopy.
- Achieved a relative uncertainty of 2 x 10(-4) in the k B determination.
- Demonstrated the potential for improved accuracy in future measurements.
Conclusions:
- The study presents a new spectroscopic method for measuring the Boltzmann constant.
- The obtained uncertainty is competitive and suggests significant potential for future improvements.
- This work is expected to contribute to a new definition of the kelvin unit of temperature.
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