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# Direct determination of the Boltzmann constant by an optical method.

Laboratoire de Physique des Lasers, UMR CNRS 7538, Institut Galilée, Université Paris 13, 99, avenue J.-B. Clément, 93430 Villetaneuse, France.
Physical Review Letters (Impact Factor: 7.94). 07/2007; 98(25):250801. DOI:10.1103/PhysRevLett.98.250801
Source: PubMed

ABSTRACT We have recorded the Doppler profile of a well-isolated rovibrational line in the nu(2) band of (14)NH(3). Ammonia gas was placed in an absorption cell thermalized by a water-ice bath. By extrapolating to zero pressure, we have deduced the Doppler width which gives a first measurement of the Boltzmann constant k(B) by laser spectroscopy. A relative uncertainty of 2 x 10(-4) has been obtained. The present determination should be significantly improved in the near future and contribute to a new definition of the kelvin.

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