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First direct determination of the Boltzmann constant by an optical method

Christophe Daussy, Mickael Guinet, Anne Amy-Klein, Khelifa Djerroud, Yves Hermier, Stephan Briaudeau, Christian J. Bordé, Christian Chardonnet

quant-pharXiv:quant-ph/0701176

Abstract

We have recorded the Doppler profile of a well-isolated rovibrational line in the 2 band of 14NH3. 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, kB, by laser spectroscopy. A relative uncertainty of 2x10-4 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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